elevons - ncairncair.in/newsletters/newsletterv3.2.pdf · aerospace certifications like nadcap and...

Aug 2013 . Newsletter . Volume 3 . Issue 2

MAGNESIUM ALLOYS IN AEROSPACE APPLICATIONS

Efficient Methods for Numerical Control Programming

Robotic advances in aerospace manufacturing

34

18

7 FEATURED ARTICLE

Elevons

CONTENTS List of completed and ongoing projects, Introduction to new Colleagues 5

Conference Updates, Conferences and workshops attended 6

FEATURED ARTICLE

Magnesium Alloys in Aerospace Applications 7

R&D UPDATES

High temperature properties of Ti-6Al-4V measured by Impulse Excitation Technique 10

Efficient methods for NC programming 18

Microstructure evolution in Ti-6Al-4V during high strain rate deformation 24

TECHNOLOGY UPDATES

Shaped Metal Deposition (SMD): An overview 30

Robotic advances in aerospace manufacturing 34

BUSINESS UPDATES

Aircraft maintenance, repair and overhaul industry calls for proper policy 37

Aerospace Industries are closer to Standardizing Materials Reporting 37

Fuel produced from discarded plastics 37

Acknowledgement

We extend our sincere gratitude to the faculty members of IIT-Bombay for their support. We are also thankful to the students and staff of NCAIRTM, for their valuable articles and other support.

Editors : Prof. Suhas Joshi and Prof. Asim Tewari Asst. Editors : Dr. Sarbani Banerjee Belur Ms. Vani K. Sreedhara Contact details : [email protected] Articles that fall under the purview of NCAIRTM Newsletter are always welcome.

EDITORIAL

Since the last edition of this newsletter, there have come about many new developments in NCAIRTM . We welcome you to Volume 3, Issue 2 of the NCAIRTM newsletter.

The NCAIR newsletter has a new name. From now on this newsletter will be called as NCAIR 'Elevons'. We are happy to announce that the NCAIRTM team has moved into the new office premises within IIT Bombay. The aim of this newsletter is to keep the readers informed of the ongoing developments, and innovations in research being a part of NCAIRTM. This newsletter is a collection of various review articles from different sources by NCAIRTM Ph.D./M.Tech. students and staff.

In this issue of the newsletter, we present some interesting contributions related to aerospace applications and manufacturing processes. The featured article of this issue focuses on ‘Magnesium alloys in aerospace applications’. Magnesium is an excellent choice for engineering applications when weight is a critical design parameter as it is the lightest of all metal alloys. This article gives a brief overview of the present scenario of magnesium applications in aerospace industry and how magnesium would fit in the ‘non-metallic’ future of aerospace industry. Research and development is an important aspect of NCAIRTM. This is reflected in the R&D updates, which has articles on high temperature properties of Ti-6Al-4V measured by Impulse Excitation Technique, efficient methods for numerical control programming and microstructure evolution in Ti-6Al-4V during high strain rate deformation. The technology updates section focuses on recent technological advancement in the arena of aerospace manufacturing globally. This newsletter focuses on two recent technologies i.e. shaped metal deposition (SMD) and robotic technology in aerospace manufacturing. Apart from these, the newsletter also carries important business updates and conference updates in the aerospace domain.

Hope you will find this newsletter interesting. Please feel free to provide us your feedback. You can also let us know the topics and areas which you would like to see being featured in the forthcoming editions. Email: [email protected]

This newsletter is also available online in www.ncair.in. Wishing everyone happy reading!!!

Kind Regards,Suhas Joshi & Asim TewariEditor

IDENTITY FOR NCAIRTM

Visual identity for NCAIRTM emerged from the concept of setting up an unique national centre

based on aerospace innovation and research in India. The ‘National Centre for Aerospace

Innovation and Research’ (NCAIRTM) is a collaboration between the government, industry and

the academia. It was envisaged that NCAIRTM will act as a guiding force, for building a vibrant

aerospace ecosystem in the country. This idea was brainstormed to explore and deduce that

the visual keywords should be bold, sharp, precise and extremely simple yet innovative in its

expression. The logotype, thus intelligently incorporates the visual play of the ‘arrow’ which

semantically expresses guidance and is seamlessly integrated with the uppercase letterform

‘A’. The logo of NCAIR is designed to act as a key branding element that lends uniqueness to

the identity. The Signature/Seal for NCAIRTM, uses the logotype against the backdrop of the

abstraction which is a frontal view of the propeller of an airplane. The color blue symbolizes

the endless representation of the sky.

1.

QUICK NEWS UPDATESInauguration of the new office-cum-laboratory complex of NCAIR on June 6, 2013. The chief guest for the inauguration function was Mr. Shailesh Prabhune, President, Sandvik Coromant, Pune. The present complex is a fully furnished, aesthetically designed modular office of NCAIRTM at IIT Bombay.

The office premise covers a total area of 3335 sq.ft. The office has a reception with a waiting lounge, a conference room, six small sized cabins, a confidential room, 26 seating space for the staff of NCAIRTM, a laboratory area and a pantry.

Inauguration of NCAIR brand identity and logo.

1.1, 1.2 - Inauguration of the new office-cum-laboratory complex of NCAIR on June 6, 2013.

2.1, 2.2, 2.3 - Inauguration of NCAIR brand identity and logo.

2.

1.1

2.1

2.2

1.2

2.3

A one-day training session through webinar on COMSOL Multiphysics held on 16th May, 2013 at NCAIR, IIT Bombay. Comsol Multiphysics is a simulation software, which bridges the gap between solving various physics and engineering applications. The webinar highlighted on geometry building, defining material, selection of physics and simulation.

A two-day program on 'Essentials of NADCAP Certification for Aerospace Manufacturing Processes' was conducted during April 4 - 5, 2013 at NCAIR, IIT-Bombay. This program was held in collaboration with the Performance Review Institute PRI (headquartered in Pennsylvania, USA). This certification program was intended to help in clearing the roadblock to many of the emerging aerospace manufacturing industries in India. It outlined the formalities and requirements of aerospace certifications like NADCAP and AS 9100 for aerospace manufacturing processes.

A one-day workshop on ‘Aircraft Building and Manufacturing’ for school students was held at VMCC, IIT Bombay on the April 20, 2013. The first part of the workshop focused on materials used in aircraft building, while the second part of the workshop focused on aero modelling. A total of 100 students from Std. 6, 7 and 8, of Kendriya Vidyalaya, IIT Powai participated in this workshop. This workshop was primarily a hands-on-exercise for children wherein, they built two models of aeroplanes from ready-to-assemble kits. The two models that they built were foam chuck glider and a rubber powered glider. After building the models, the students then flew their model aeroplanes in the KV grounds. They were later accompanied by some professional aero modellers who also flew some models like the hexacopter.

4 - Workshop on 'Aircraft building and Manufacturing'

3.1, 3.2, 3.3 - 'Essentials of NADCAP Certification for Aerospace Manufacturing Processes' program

4

3.

3.1 3.3

3.2

IMPORTANT ANNOUNCEMENT

eQuaLearn Training

Programme

NCAIRTM is collaborating with Performance Review Institute (PRI), USA, in organising three eQuaLearn training programs. This will be jointly hosted by NCAIRTM at IIT-Bombay and Godrej Precision Systems, Mumbai at their respective premises.

PRI is a global provider of customer-focused solutions, designed to improve process and product quality by adding value and reducing total cost. PRI also promotes collaboration among stakeholders in industries, where safety and quality are shared goals. It not only administers the NADCAP special process and product accreditation program for aerospace industry, but also conducts special processes and quality training programmes through eQuaLearn, launched in 2008. The eQuaLearn offers Professional Development programs and managed learning resources, to improve the quality of personnel, products and processes through public and onsite classes and memberships.

NCAIRTM proposes to conduct the following three eQuaLearn courses exclusively by PRI experts for the industry participants. These include:–

Introduction to Pyrometry: This program offers a full examination and comprehensive discussion on SAE’s AMS 2750E specification. The requirements covered during the course are necessary to ensure that parts or raw materials are heat treated in accordance with the applicable specification(s).

Internal Audit: This program covers establishment and management of an Internal Audit Program and skills and techniques useful when performing audits.

Root Cause Corrective Action (RCCA): This program provides a systematic approach to cause analysis and will illustrate how to respond to audit findings so as to ensure that problems are fixed and are prevented from recurring.

The proposed program would spread over five days and will be conducted between December 2 – 6, 2013. For more details contact [email protected]

4.

List of completed industrial technology projects at NCAIR™

• Analysis of various necking criteria in sheet metal forming.

• Analysis of burr formation in drilling of Ti-6Al-4V alloy.

• Modelling of shear bands and specific cutting energy in Ti-6Al-4V alloy.

• Tool wear Investigation in Ti-6Al-4V drilling under dry and oil mist cooling conditions.

• Role of retrogression to perform annealing of age hardenable aluminium alloys.

• Analysis of stress strain and temperature distribution in orthogonal cutting of Ti-6Al-4V alloy.

New Colleagues at NCAIRTM The NCAIRTM team is growing. We have new colleagues who have joined the NCAIRTM team in the past few months.

Mr. Mohammed Taha Khot

He holds a Master of Science degree in Mechanical Engineering from the American University of Sharjah, UAE. He has joined NCAIR™ as a Junior Manager (Technical).

Mr. Yogesh Shivaji Gaikhe

He holds a Master of Technology degree in Manufacturing Engineering from Dr. Babasaheb Ambedkar Technological University, Lonere (Maharashtra, India). He has joined IITB in Mechanical Engineering department as a PhD student and will be working on NCAIR projects.

5.

Call for papers and abstracts!!!3rd International Conference on ‘Additive Manufacturing Technologies’ – AM 2013, will be held during October 7- 8, 201 3 at NIMHANS Convention Centre, Bengaluru. There is call for papers for this conference. For more information visit http://www.amsi.org.in/index.htm

COPEN-8: 2013, An international conference on precision, meso, micro and nano engineering, will be held during December 13-15, 2013 at National Institute of Technology, Calicut, Kerala. Last date for the submission of papers for review is August 16, 2013. For more information visit http://www.copen8.nitc.ac.in

Conference Updates (International)7th International Conference on Fracture of Polymers, Composites and Adhesives ESIS TC4 2014 will be held during September 14-18, 2014 at Les Diablerets, Switzerland. There is a call for papers for this conference. The last date for the submission of abstracts is October 25, 2013. For more details visit http://www.esistc4conference.com/index.html

The 3rd International Conference on Engineering and Applied Science (2013 ICEAS) will be held during November 7-9, 2013 at Osaka, Japan. There is a call for papers for this conference. The due date for a two-page abstract is August 20, 2013. For more details visit http://www.iceaas.org/

International Conference and Exhibition on Mechanical & Aerospace Engineering during September 30 - October 2, 2013 at Hilton San Antonio Airport, USA. Deadline for abstracts/proposals: 2nd September 2013. For more information please visit http://www.omicsgroup.com/conferences/mechanical-aerospace-engineering-2013

Conferences and Workshops attended by NCAIR teamProf. Suhas S. Joshi

Keynote talk on ‘Research in advanced machining technologies at IIT Bombay’, on June 17, 2013 at Georgia Tech, Atlanta, Georgia. Attended the 41st Annual North American Research Conference (NAMRC-41) held at University of Wisconsin, USA during June 10-14, 2013.

CONFERENCE UPDATES

6.

FEATURED ARTICLE

Magnesium Alloys in Aerospace ApplicationsProf. Sushil Mishra, Department of Mechanical Engineering, IIT Bombay

The focus of aerospace industries is to develop new technology for improved fuel economy with enhanced safety measures. For this purpose, the aerospace industries are exploring new materials and also constantly improving existing material properties. Polymer composites with different types of fiber are promising materials for aerospace applications but they also entail limitations in mass manufacturing, conductivity, etc. Aluminum alloys are mainly used in the aerospace industry and researchers are striving for improvements in their properties as well as, exploring the development of new alloys for different applications. However, different alloys are also being explored for light weighting and better mechanical properties. The obvious choice for this purpose is magnesium, since it is two-third lighter than aluminum and has a high strength-to-weight ratio. It also has good electromagnetic and radio frequency interference shielding capability which makes it all the more suitable for electronic industries. Currently, magnesium is used for different applications in aerospace industries such as helicopter gearboxes, housing, compressor filter casings, canopy, brackets and jet engine components.

Pure magnesium is not preferred for manufacturing of aerospace parts due to low corrosion resistance, poor creep or high temperature properties and poor mechanical properties. To overcome these issues, different magnesium alloys have been developed. The most commonly used alloying elements are: aluminum, zinc, cerium, silver, thorium, yttrium and zirconium. These alloys are used for a range of applications based upon the desired properties. These alloys have their own strengths and weaknesses. Two major alloys which are used in the aerospace applications are Mg- Al and Mg- Zr in both cast and wrought form [1-3]. Mg-Al alloys have light weight and moderate strength with good corrosion resistance. However, they lack high temperature properties. These alloys have inhomogeneous grain size distribution. Further, microporosity can also be easily generated in them during their casting. Mg-Zr alloys have more or less homogenous and fine grain size distribution

as compared to Mg-Al alloys because Zr acts as a grain refiner [1]. To improve the high temperature properties of Mg-Zr alloys, Zn or rare earth elements are added, which also increases their castability. The main drawback of these alloys is poor corrosion resistance [4]. The desire to improve corrosion performance and the need to operate at increasing temperatures, led to the development of new magnesium alloys by addition of different alloying elements.

Cast magnesium alloys have the potential to replace engineering plastics, composites, and aluminum alloys in many aerospace applications because they have high specific strength and thin sections castablity. The production of these alloys is also more cost effective and they are easier to recycle [1, 4-5]. Cast magnesium alloys also have specific design and manufacturing advantages. They can be cast in thinner walls than aluminum and the cooling rate is quick due to a reduced latent heat of fusion per unit volume. Due to low density, high gate pressures can be achieved using moderate pressures [5]. Magnesium alloy components can be cast using all the conventional casting methods. These methods are sand, permanent and semi-permanent mold and shell, investment and die casting [4-5]. However, magnesium alloy casting suffers from defects like inhomogeneous microstructure and poor mechanical strength. Sand castings are generally used in aerospace applications because they have a clear weight advantage over aluminum and other metals. For mass production, permanent mold or die-casting can also be typically used for Mg-Al-Zn type alloys.

To overcome some of the limitations in casting magnesium alloys like porosity, inhomogeneous microstructure, and low mechanical properties, wrought magnesium alloys have been used for aerospace applications. Although wrought Mg alloys possess sufficient specific strength necessary for lightweight aerospace applications, poor ductility and formability of Mg at room temperature has been a critical roadblock. The hexagonal crystal structure of Mg implies that there are only two and not five independent slip systems as would be necessary for

7.

Fig. 1 Extruded AZ21 alloys shows better

corrosion resistance than compressed

conditions

large plastic deformation. However, recent studies have shown that suitable modifications in the microstructure can potentially allow plastic deformation of Mg alloys to large strains [6-7]. It has been found that refining the grain size of Mg alloys improves their ductility substantially [8-10]. Since magnesium alloys deform by both twinning and slip, the enhancement in ductility of fine grained materials has been attributed to their reduced propensity for twin formation [11]. Twinning, in Mg alloys is dependent on a variety of factors such as processing temperature, initial texture, grain size, strain path and alloying content [12]. Naturally, controlling one or more of these factors would enable development of a microstructure that is amenable to achieving large scale uniform plastic deformation at room temperature.

Corrosion, flammable behavior, joining and machining are some of the major obstacles in the use of magnesium for aerospace applications. Magnesium alloys are prone to oxidation and burning during melting, casting, heat treatment and machining [13]. Efforts have been made to improve or avoid flammability of magnesium alloys by processing equipment improvement, flux coverage, gaseous protection and alloying [13]. By addition of alloying elements, not only the ignition of magnesium be avoided but also mechanical strengthening is achieved. Further, it prevents equipment modifications and reduces pollution in comparison to the other processes. Alloying elements such as Ca [14], Be [14] and rare earth (RE) [13-14] are used for ignition proofing in magnesium alloys. However, Ca and Be can cause deterioration of the mechanical properties of the alloy and the poisonous nature of Be restricts the applications of alloying with Be or Ca. On the other hand, addition of RE to magnesium alloys enhances both the ignition temperature as well as the mechanical properties of magnesium alloys [13].

The biggest challenge in the use of magnesium is that it is extremely susceptible to corrosion. However, some magnesium alloys show better corrosion resistance than others. Corrosion behavior also differs from cast alloys to wrought alloys. It has been observed that micro structural modifications such as crystallographic orientation, heat treatment and alloying elements can improve corrosion behavior [7-9]. Figure 1, shows different corrosion behavior of AZ21 Mg alloy at extruded and compressed conditions.

Magnesium alloys are susceptible to galvanic corrosion, which can be in the form of galvanic corrosion associated with impurities such as Fe, Ni and Cu [4, 15]. Galvanic

8.

FEATURED ARTICLE

corrosion can be minimized by reducing the chemical potential between the two different alloys or dissimilar materials, maximizing the circuit resistance and addition of alloying elements such as Mn. While, the alloying elements provide a significant improvement to corrosion resistance by using the above methods, coating of magnesium is also an additional method to protect the surface of magnesium [15]. Coating can improve the galvanic corrosion behavior and also protect it from oxidation. Some examples of protective coatings are fluoride anodizing, chemical treatments, electrolytic anodizing, sealing with epoxy resins, standard paint finishes, vitreous enameling, electroplating and cold spraying [4,15].

In the aerospace applications, magnesium alloys can be joined using conventional methods like aluminum alloys such as riveting, bolting, brazing and welding. However, corrosion is a major concern while joining magnesium alloys, especially by riveting and bolting. Enormous care must be taken for selection of riveting or bolting materials to avoid galvanic corrosion. Proper protection using gaskets, insulators, alkali-proof paints and coating can minimize the galvanic corrosions. Most magnesium alloys can be subjected to fusion welding due to their low heat capacity and low heat of fusion. Alloying with aluminum and rare earth elements increases the weldability of magnesium alloy by helping refine grain structures. However, excess of some alloying elements may lead to weld defects. For example, more than 1 wt% Zn increases hot shortness, which leads to weld cracks [4]. Friction stir welding technique is a very widely used method of joining different magnesium alloys as well as dissimilar materials like magnesium and aluminum alloys [15]. This will also help in reducing corrosion of dissimilar metal joining and grain refinements. Magnesium alloys can also be bonded by using aerobically curing methacrylates in combination with suitable activators, and two-component epoxy glues can be used for sufficient strength [15]. Research in bonding techniques is ongoing to provide greater strength in joining different magnesium alloys.

Machining of magnesium alloys is not as tedious as is their casting or forming. Due to the low specific cutting force required for machining, the cutting speed is high and tools have a longer operating time [15-16]. Good surface quality can be achieved with less roughness. Very little or no lubricant is required for cutting, which reduces the application cost. However, use of coolants can prevent chip ignition during machining of magnesium

alloys but this is not an environment-friendly alternative. On the other hand, the more environment friendly dry machining chips can be easily ignited and even lead to fire hazard. Machining parameters are very important to avoid ignition of chips during dry machining and it is an important area of research [16].

In conclusion, magnesium is a promising material for aerospace applications. However, an enormous amount of research is needed to adopt magnesium alloys and to understand their behavior under severe conditions. The properties of this metal can be enhanced by proper alloying elements and micro structural improvements. The cost effectiveness can also be achieved by greater use of magnesium alloys and by developing new applications in aerospace and other transportation industries.

REFERENCES

[1} P. Lyon, Magnesium Technology, (2004) Edited by Alan A. Laouj,

pp. 311.

[2] E. Aghion and B. Bronfin, Materials Science Forum Vols. 350-351,

(2000) pp. 19.

[3] http://dx.doi.org/10.5772/48273

[4] Siobhan Fleming, M.E. Thesis, Rensselaer Polytechnic Institute,

Hartford, CT, August, 2012.

[5] A. Lou and M. O. Pekguleryuz, Journal of Materials Science,

Vol. 29,(1994) pp. 5259.

[6] M. Mabuchi, H. Iwahashi, K. Yanase and K. Higashi, Scripta

Materialia, (1996) pp. 36-681.

[7] S.R. Agnew, P. Mehrotra, T.M. Lillo, G.M. Stoica GM and P.K. Liaw,

Materials Science and Engineering, Vol. 408, (2005) pp. 72.

[8] K. Matsubara, Y. Miyahara, Z. Horita and T.G. Langdon, Acta

Materialia, Vol. 51, (2003) pp. 3073.

[9] A. Mussi, J.J. Blin, L. Salvo and E.F. Rauch, Acta Materialia, Vol. 54,

(2006) pp. 3801.

[10] Z. Horita, K. Matsubara, K. Maki and T.G. Langdon, Script Materialia,

Vol. 47, (2002) pp. 255.

[11] J.A. Chapman, D.V.Wilson, J. Inst Metals, Vo. 91, (1962) pp. 39.

[12] R. Gehrmann, M.M. Frommert, G. Gottstein, Materials Science and

Engineering, Vol. 395A, (2005) pp. 338.

[13] V. Ravin, J.J. Blandin, Scripta Materialia, Vol. 49, (2003) pp. 225.

[14] ZHANG Guoying, LUO Zhicheng, ZHANG Hui, and CHU Ran,

Journal of Rare Earth, Vol. 30, (2012) pp. 573.

[15] J. Goken, J. Bohlen, N. Hort, D. Letzig and K. U. Kainer, Materials

Science Forum, Vols. 426-432, (2004) pp. 153.

[16] J. Z. Hou, Wei Zhou and N. Zhao, Materials and Manufacturing

process, Vol. 25, (2010) pp. 1048.

9.

R & D UPDATES

Dr. AKHILESH K. SWARNAKAR

Project Research Scientist, NCAIRTM,

IIT-Bombay

Dr. BERND BAUFELD

Project Manager, Nuclear AMRC,

University of Sheffield, UK

High temperature properties of Ti-6Al-4V components measured by impulse excitation technique1

AbstractHigh temperature, Young’s (E) modulus and damping behavior of Ti-6Al-4V components have been investigated in vacuum up to 1100°C by Impulse Excitation Technique (IET). The Young’s modulus decreases linearly from 118GPa at room temperature to 72GPa at 900°C, followed by a stronger decrease up to 1000°C and during the first heating a plateau thereafter. The damping curve showed two peaks around 700°C and 900°C followed by an exponential increase during heating. However, only one peak was observed around 700°C during cooling. The change in Young’s modulus and the damping behavior is interpreted by different processes like α/β transformation, oxygen alloying and grain boundary sliding.

KeywordsImpulse excitation technique, shaped metal deposition, Titanium alloy, phase transformation

IntroductionTitanium alloys are widely used in aeronautical applications due to their excellent strength-to-weight ratio [1] and in prostheses due to their superior biocompatibility, low elastic modulus and enhanced corrosion resistance [2]. Especially for aerospace industries, the behavior at elevated temperatures is of interest. Generally, titanium alloys (Ti) are expensive materials and ‘difficult-to-machine’ due to their sensitivity towards thermal treatment which influences their final microstructure [1,2]. The process by which Ti-6Al-4V alloy components are made is through shaped metal deposition (SMD). It is observed that the SMD components show a particular microstructure due to their complex temperature fields which is related to the process itself [3]. This brings to focus how properties of SMD components are similar and/or different to the standard Ti alloys. In the present work, temperature dependant Young’s modulus and damping of Ti alloy are studied using impulse excitation technique (IET). IET is a non-destructive method to measure the dynamic Young’s modulus and damping properties of different materials [4,5]. Such measurements not only provide the material properties, but may also give some insight into energy consuming processes such as phase transformation.

Experimental methodThe details of the sample preparation and characterization are mentioned in reference [6]. The studied specimens in this article were of different orientations which were prepared from the components made by SMD process. Two specimens i.e. A and B were used in this study whose length axis is parallel and perpendicular to the deposition plate. In addition, a reference specimen was prepared from a commercial Ti-6Al-4V to compare the high temperature properties with specimens prepared by SMD process.

Impulse Excitation Technique (IET)The high temperature E-modulus and damping properties of the materials were tested by the impulse excitation technique (IET). The IET method relies on the fundamental resonant frequency of test specimens of suitable geometry by exciting them mechanically with an impulse tool. A transducer (for example a non-contacting microphone or a laser vibrometer) senses the resulting mechanical vibrations of the specimen. The transit signals are analysed and the fundamental resonant frequency is isolated and measured by a signal analyser. These resonance frequencies are characteristic of the test object, as they are related to its stiffness, mass and geometry.

According to ASTM - C1259-08 [5], in case of isotropic samples of rectangular shape, the elastic modulus of the materials can be calculated as:

where, fr represents, the resonance frequency and m the mass of the sample. L, b and t are the dimensional units (Length, width and thickness) and T1 is a correction factor.

The vibrations can also be analyzed from the internal friction (Q-1) point of view, i.e., the dissipation of vibration energy in the specimen, damping, or mechanical loss. Q-1 can be deduced from the amplitude decay of free vibrations. Damping is closely related to the integral mechanisms of scattering of the mechanical energy in the material. The exact micro structural origin of damping or mechanical loss deviates from material to material and can be calculated using the exponential decay parameter K (1/sec) given below

The Young’s modulus and the damping have been measured in Argon (Ar) atmosphere from room temperature up to 1100°C with a heating and cooling rate of 2°C/min (IMCE, Belgium). The specimens were then measured in flexural mode, which means that the Young’s modulus is measured in the length direction. It must be emphasized that IET is more sensitive to the properties at the surface than in the center of the tested bar.

This article is an abridged version of the papers (1*) and (2**) and are already

published in Materials Science and Technology (MS&T) conference proceeding

and Journal of Material Science.

*[1] B. Baufeld, A.K. Swarnakar, Omer Van der Biest, R. Gault, Shaped Metal

Deposition of Ti: Microstructure and Mechanical Properties, Materials Science and Technology (MS&T) 2009, Structural

Materials for Aerospace and Defense: Challenges and Prospects, October 25-

29, 2009, Pittsburgh, Pennsylvania

**[2] A.K. Swarnakar, O. Van der Biest, B. Baufeld, Young’s modulus and damping

in dependence on temperature of Ti-6Al-4V components fabricated by shaped metal deposition, Journal of Material Science, 46 (11) 2011, pp. 3802-3811

19465.032

TtL

bfmE r ⋅

×

××=

..….……. (1)

rfKQ .

1

π=−

..….……. (2)

IET is a non-destructive method to measure dynamic Young's

modulus and damping properties of different materials [4,5].

10.

Experimental methodThe details of the sample preparation and characterization are mentioned in reference [6]. The studied specimens in this article were of different orientations which were prepared from the components made by SMD process. Two specimens i.e. A and B were used in this study whose length axis is parallel and perpendicular to the deposition plate. In addition, a reference specimen was prepared from a commercial Ti-6Al-4V to compare the high temperature properties with specimens prepared by SMD process.

Impulse Excitation Technique (IET)The high temperature E-modulus and damping properties of the materials were tested by the impulse excitation technique (IET). The IET method relies on the fundamental resonant frequency of test specimens of suitable geometry by exciting them mechanically with an impulse tool. A transducer (for example a non-contacting microphone or a laser vibrometer) senses the resulting mechanical vibrations of the specimen. The transit signals are analysed and the fundamental resonant frequency is isolated and measured by a signal analyser. These resonance frequencies are characteristic of the test object, as they are related to its stiffness, mass and geometry.

According to ASTM - C1259-08 [5], in case of isotropic samples of rectangular shape, the elastic modulus of the materials can be calculated as:

where, fr represents, the resonance frequency and m the mass of the sample. L, b and t are the dimensional units (Length, width and thickness) and T1 is a correction factor.

The vibrations can also be analyzed from the internal friction (Q-1) point of view, i.e., the dissipation of vibration energy in the specimen, damping, or mechanical loss. Q-1 can be deduced from the amplitude decay of free vibrations. Damping is closely related to the integral mechanisms of scattering of the mechanical energy in the material. The exact micro structural origin of damping or mechanical loss deviates from material to material and can be calculated using the exponential decay parameter K (1/sec) given below

The Young’s modulus and the damping have been measured in Argon (Ar) atmosphere from room temperature up to 1100°C with a heating and cooling rate of 2°C/min (IMCE, Belgium). The specimens were then measured in flexural mode, which means that the Young’s modulus is measured in the length direction. It must be emphasized that IET is more sensitive to the properties at the surface than in the center of the tested bar.

This article is an abridged version of the papers (1*) and (2**) and are already

published in Materials Science and Technology (MS&T) conference proceeding

and Journal of Material Science.

*[1] B. Baufeld, A.K. Swarnakar, Omer Van der Biest, R. Gault, Shaped Metal

Deposition of Ti: Microstructure and Mechanical Properties, Materials Science and Technology (MS&T) 2009, Structural

Materials for Aerospace and Defense: Challenges and Prospects, October 25-

29, 2009, Pittsburgh, Pennsylvania

**[2] A.K. Swarnakar, O. Van der Biest, B. Baufeld, Young’s modulus and damping

in dependence on temperature of Ti-6Al-4V components fabricated by shaped metal deposition, Journal of Material Science, 46 (11) 2011, pp. 3802-3811

19465.032

TtL

bfmE r ⋅

×

××=

..….……. (1)

rfKQ .

1

π=−

..….……. (2)


The IET method relies on the fundamental resonant

frequency of test specimens of suitable geometry by exciting

them mechanically with an impulse tool.

11.

Results Impulse Excitation TechniqueIt was observed that the Young’s moduli (E) of both SMD specimens (A and B) and the reference specimen are very similar at room temperature. They are of the order of about 118GPa and are therefore independent of their orientation (Table 1).

The article [7] published on Ti-6Al-4V alloy, reported similar Young’s modulus values between 100 and 130GPa depending on the specific moduli of the phases, their volume fraction and texture.

Fig. 1 shows a comparison between specimens A and B as well as the reference specimen. It was observed that with increasing temperature, the Young’s moduli of all three specimens decrease linearly until about 850°C, followed by a steep decrease with an increase in temperature. At around 950°C, the E-modulus begins to increase until 1000°C followed by a moderate decrease till the maximum temperature is reached. Following this plateau, the cooling curve shows a steep slope followed by a gradual increase in E-modulus.

Table 1. Young’s modulus at room temperature

Sample

Young’s modulus

[GPa]

Specimen A (parallel)

117

Specimen B (perpendicular)

118

Specimen B - after IET, oxide removed

124

Reference base plate

115

Fig. 1 Young’s modulus of specimen A, B and of the reference material in dependence on

the temperature. Also, the room temperature value of specimen A after IET and oxide

removal is given.


12.

The tested samples before and after the IET measurements, showed, significantly large values of E-modulus. The X-ray diffraction (XRD) analysis showed formation of Ti dioxide or Rutile on the surface of the samples. This layer increases the stiffness of the specimens. Even after removal of this layer, the Young’s modulus is still higher than that before testing (see Fig. 1). This indicates that besides stiffening by the formation of an oxide layer, additional changes increase the stiffness of the specimens.

The damping for all three specimens showed an exponential increase with temperature and various damping peaks (Fig. 2 a-c). Such damping peaks correspond to energy consuming processes. Specimens A and B, exhibit, two distinctive damping peaks at about 700°C and 900°C during heating. However, during cooling only one damping peak was observed around 700°C for both the specimens. Specimen A when heated, showed slightly scattered signals in comparison to a clear trend in specimen B, which is not the same during cooling. For the reference material, a very strong peak at about 910°C is visible during heating, which possibly conceals the peak at lower temperatures. During cooling, the reference material shows a very clear peak at 740°C.

Microstructure The microstructural investigations were performed by scanning electron microscopy (SEM, FEI XL30FEG). Before IET, the microstructure of the SMD specimens consisted of a Widmanstätten structure of α laths in a Vanadium

a. b. c.

Fig. 3 Back scattered secondary electron micrographs of the as-fabricated material (a)

and of specimen B after IET testing in overview (b) and near the surface (c) [6]


Fig. 2 Damping in dependence of the temperature during heating and cooling

for specimen A (a), B (b), and the reference material (c).

Temperature a.

Temperature b.

Temperature c.

13.

(V) rich β matrix (Fig. 3a) [3], while the reference material comprised of equiaxed α grains in a β matrix. After IET measurements, three different regions have been observed (Fig. 3b): the microstructure within the specimens, another microstructure near the surface, and an approximately 29 µm thick oxide layer at the surface. In the centre, the microstructure of the SMD specimens is still characterized by the former Widmanstätten structure, but the laths are significantly coarsened (Fig. 3c). The microstructure of the reference materials still shows equiaxed α grains in a β matrix. Next to the surface, however, for all the specimens, the microstructure has changed into equiaxed grains in the size of about 0.1 mm with no β matrix. Yet, a few V rich inclusions can be found.

Micro hardness The Vickers micro hardness tests were carried out on polished cross sections of as-fabricated, heat treated specimens and specimens tested by IET applying a Leitz/Durimet 2 micro hardness tester using a weight of 100 g (HV0.1). Similar to the microstructure, the micro hardness in tested specimens changes dramatically after the IET experiment. Before IET testing, the Vickers hardness of the SMD specimens is about 345 and of the reference material is 329. The IET testing increases the hardness for all specimens significantly (Table 2). The hardness values are very high (between 688 and 891 HV) near the surface of the tested specimens and decrease continuously towards the center reaching a constant value. It is remarkable that these values in the center are still much higher than the values measured before IET testing (Table 2). Apparently, the material has hardened throughout the specimens due to testing. Similarly, very high values near the surface

and values of about 500 HV in the center were reported for commercially available Ti-6Al-4V after heat treatment for 60 hours in air at 600°C [8].

DiscussionIn IET experiments, the specimens exhibit a complex dependence on temperature. The Young’s modulus show a shallow slope at low temperatures, while a steeper one at higher temperatures and a plateau between 950°C and 1100°C. The damping displays a peak at about 700°C during heating

Table 2. Micro-hardness at room temperature before and after IET tests in the center and near the surface

Location

Centre

Near Surface

Centre

Near Surface

Specimen A

329 ± 9

—

500 ± 27

837 ± 40

Specimen B

345 ± 37

—

503 ± 24

891 ± 45

Reference Material

371 ± 16

—

471 ± 19

688 ± 50

Before IET measurement

After IET measurement


The IET testing increases the hardness for all specimens

significantly (Table 2). The hardness values are very

high (between 688 and 891 HV) near the surface of the tested

specimens and decrease continuously towards the center

reaching a constant value

14.

and cooling, and an additional peak around 900°C only during heating. This complex behavior can be explained considering the phase diagram of Ti-6Al-4V and the existence of residual oxygen in the testing atmosphere [9]. The residual oxygen results not only into an oxide layer, but also is traceable solute in the metal near the surface.

In thermal equilibrium, Ti-6Al-4V is hcp α phase from room temperature until 600°C, α + cubic β until 980°C, and β until it liquidifies at 1668°C [10]. Depending on the cooling rate, the microstructure at room temperature, after cooling down from the liquid phase may consist of V lean α phase, after very fast cooling of martensitic V rich α , and of metastable or V rich stable β phase. Typical microstructures are after very fast cooling needle like martensitic α´ structures and after moderate cooling of weaved basket like Widmanstätten structures consisting of acicular α laths in a β matrix. Since the present SMD specimens have experienced several thermal cycles due to the sequential deposition of welded layers followed by not especial fast cooling, it is assumed that the as-deposited Widmanstätten structure consists mainly of α and β phase. The damping peak centered at 700°C ., Therefore, this can be understood as the β to α transformation during heating and with α to β transformation during cooling. The change in slope of the Young’s module around 800°C possibly can be attributed to the increase in concentration of the β phase during heating, and its decrease during cooling respectively.

Oxygen acts as a α stabilizer for Ti-6Al-4V, decreasing the volume fraction of β phase at all temperatures and raising the β transus temperature [11, 12]. Furthermore, oxygen increases the strength, the elastic modulus and the hardness by interstitial solution strengthening [11, 12]. The addition of 0.99 wt% oxygen increases the hardness of Ti-6Al-4V by about 44 %. However, oxygen also embrittles the α phase of Ti alloy [13], which is the reason for the observed cracks near the surface. The following experimental findings suggest the existence of residual oxygen in the Ar atmosphere. . It can be thus deduced that oxygen dissolved in the metal, dramatically increases the hardness, the stabilization of the α phase at room temperature near the surface leading to a phenomenon known as alpha casing [14, 15], and the existence of a Ti oxide layer.

Oxidation and oxygen solution help in explaining the other peculiarities of the IET results. Solution of oxygen during heating delays or reverses the α to β transformation near the surface. This results in an increase in hardness as well as the Young’s modulus. This might be responsible for the jump in the Young’s modulus curve. It also contributes to a part of the permanent increase of the Young’s modulus of the specimens at room temperature.

The damping peak during heating at around 900°C, which is not observed during cooling, can be attributed to oxidation during heating. The formation of this oxide layer seems to be limited within a certain temperature range and does not proceed further during cooling. Therefore, oxidation results only into a damping peak during heating and not during cooling.


The damping peak centered at 700° C, therefore can

be understood as the β to α transformation during

heating and with α to β transformation during cooling

Oxidation and oxygen solution help in explaining the other

peculiarities of the IET results. Solution of oxygen during

heating delays or reverses the α to β transformation

near the surface.

15.

The exponential increase in damping at elevated temperatures above 950℃ can be attributed to grain boundary softening (Fig 2). At relatively high temperatures, damping-temperature curve of most materials increases continuously to a larger value, arising from grain boundaries. According to Nowick et al., [16] the magnitude of the high-temperature background is highly structure sensitive. The exponential background can be caused by the mechanism of grain boundary softening and consequently results in viscous slipping of neighbouring grains with respect to each other [17].

ConclusionIn this article, temperature dependent Young´s modulus and damping behavior of Ti-6Al-4V were measured by impulse excitation technique. The Young’s modulus, decreases gradually during heating until 900°C, and increases gradually during cooling from 900°C. Thus does not reflect the α/β transformation occurring at this temperature. The steep decrease of the Young s modulus between 900° and 980°C is attributed to grain boundary softening. The plateau at higher temperatures is related to the stiffening by oxygen alloying. The damping peak around 700°C during heating and cooling is associated with α/β transformation of a composition in thermal equilibrium. The damping peak around 950°C, occurring only during the first heating sequence, is attributed to the transformation from a V poor and Al rich non-equilibrium α phase related to the fast cooling of the SMD process.

Acknowledgements The research was performed with financial assistance from the RAPOLAC STREP project on 6th Framework Programme of the European Commission, which is gratefully acknowledged

REFERENCES

[1] E.W. Collings, The Physical Metallurgy of Titanium Alloys. 1984: American Society for Metals.

[2] ASM, http://products.asminternational.org/hbk/do/highlight/content/V02/D01/A25/

S0026726.html.

[3] B.Baufeld, O. Van der Biest and R. Gault, Microstructure of Ti-6Al-V specimens produced by

Shaped Metal Deposition, International Journal of Materials Research, 2008.

[4] G. Roebben, B. Bollen, A. Brebels, J. Van Humbeeck, and O. Van der Biest, “Impulse excitation

apparatus to measure resonant frequencies, elastic moduli, and internal friction at room and

high temperature”, Rev. Sci. Instrum., v68, n12, (1997), pp. 4511-4515.

[5] ASTM C1259 – 08, Standard Test Method for Dynamic Young’s Modulus, Shear Modulus, and

Poisson’s Ratio for Advanced Ceramics by Impulse Excitation of Vibration, ASTM

International, West Conshohocken, PA, 2008, 1–17.

[6] B. Baufeld, A.K. Swarnakar, Omer van der biest, R. Gault,Shaped Metal Deposition of

Ti: Microstructure and Mechanical Properties, Materials Science and Technology (MS&T)

2009, Structural Materials for Aerospace and Defense: Challenges and Prospects, October

25-29, 2009, Pittsburgh, Pennsylvania

[7] Y.T. Lee, and G. Welsch, Youngs modulus and damping of Ti6Al-4V Alloy as a function of

heat-treatment and oxygen concentration. Materials Science and Engineering a-Structural

Materials Properties Microstructure and Processing, v128, n1, (1990), pp. 77-89.

[8] H. Guleryuz and H. Cimenoglu, Surface modification of a Ti-6Al-4V alloy by thermal


The steep decrease of the Young's modulus between

900° and 980° C is attributed to grain boundary softening.

The plateau at higher temperatures is related to the stiffening by oxygen alloying.

16.

oxidation. Surface and Coatings Technology, v192, n2-3, (2005), pp. 164-170.

[9] A.K. Swarnakar, O.Van der Biest, and B. Baufeld, Thermal expansion and lattice parameters of

shaped metal deposited Ti-6Al-4V, Journal of Alloys and Compound, v509, n6, (2011), pp.

2723-2728.

[10] Boyer, R., G. Welsch, and E.W. Collings, Materials Properties Handbook: Titanium Alloys. 1994:

The Materials Information Society.

[11] A.I. Kahveci and G.E. Welsch, Effect of oxygen on the hardness and alpha-beta-phase ratio of

TI-6A1-4V alloy. Scripta Metallurgica Et Materialia, v 20, n9, (1986), pp. 1287 -1290.

[12] A.I. Kahveci, and G. Welsch, Hardness versus strength correlation for oxygen-strengthened

TI-6AL-4V alloy. Scripta Metallurgica et Materialia, v25, n8, (1991), pp. 1957 -1962.

[13] Liu, Z. and G. Welsch, Effects of oxygen and heat-treatment on the mechanical-properties of

alpha and beta titanium-alloys. Metallurgical transactions A, Physical metallurgy and

materials science, v 19, n3, (1988), pp. 527 -542.

[14] R.W. Evans, R.J. Hull, and B. Wilshire, The effects of alpha-case formation on the creep

fracture properties of the high-temperature titanium alloy IMI834. Journal of Materials

Processing Technology, v 56, n1-4, (1996), pp. 492-501.

[15] S.N. Patankar, Y.T. Kwang, and T.M. Jen, Alpha casing and superplastic behavior of Ti-6Al-4V,

Journal of Materials Processing Technology, v 112, n1, (2001), pp. 24-28.

[16] S. Nowick and B. S. Berry, Anelastic relaxation in crystalline solids, (1972) New York,

Academic Press.

[17] A.K. Swarnakar, O. Van der Biest and B. Baufeld, Young’s modulus and damping in

dependence on temperature of Ti-6Al-4V components fabricated by shaped metal

deposition, Journal of Material Science, 46 (11) 2011, pp. 3802-3811.


17.

SUDHIR AUTI

Engineer, NCAIR TM, IIT Bombay

KISHOR KUNTE

Engineer, NCAIR TM, IIT Bombay

PROF. SUHAS. S. JOSHI

IIT Bombay


IntroductionCNC technique has precedence over low manufacturing cost and machining time as compared to other conventional techniques. However, a parametrical optimization of machining processes is necessary to achieve this. This article introduces different efficient methods to improve the machining efficiency. The methods explained are: Canned cycle, STEP-NC controller, tool part touch control system, and oscillating tool path method.

Different methods of CNC programming:1. An epitrochoidal pocket : A new Canned cycle for CNC milling machines. Canned cycles, are basically a programming method of a CNC machine and are applied to the repetitive machining operations using the G/M code language [1]. These codes are the set of pre-programmed instructions permanently stored in the machine controller which automates the repetitive tasks. By the application of the canned cycle, repetitive programming lines can be shortened, thus, reducing the programming time and simplifying the whole programming process [2]. Pocket milling is one of the main machining operations used for removing the material inside a closed boundary on the flat surface of a workpiece to a fixed depth; see schematic illustration in the Fig. 1 [1]. Rectangular and circular forms of pockets are one of the standard types of pockets which are found in the modern CNC systems. This method is characterized by its simplicity since whole machining tasks can be programmed in a single block of the part program. Previously, there was not a canned cycle for epitrochoidal pocket so the program consists of a lot of steps, for avoiding such big program a new canned cycle is developed. It is as follows:

G65 P01 xx P02 xx Po3 xx P04 xx P05 xx Po6 xx P07 xx P08 xx

where, G65 selects machining for epitrochoidal pocket and P01 to P08 are parameters and they signify the starting position, pocket depth, tool diameter, and feed rate, etc.

R & D UPDATES

This method is characterized by its simplicity since whole

machining tasks can be programmed in a single

block of the part program.

18.

ApplicationsStandard canned cycles are specifically used for machining operations like drilling, counter-boring, peck drilling, pocket or slot machining. The current cycle is particularly useful for machining chambers of rotary internal combustion engine, rotary piston pumps and generally epitrochoidal-shaped housings.

2. Tool Part Touch Control System (TPTC)This method is based on registering the moment when the cutting tool comes in contact with the workpiece during a machining operation. The cutting tool approaches the workpiece with a rapid traverse; as soon as it comes in contact with the workpiece, it switches back to the work feed. In this way, the time for ‘cutting air’ can be significantly reduced [3].

A system for generating touch signal is shown in the Fig 2 [3]; high-frequency generator (1) is connected through wires to two selected points on the machine tool body (A) and (B). The voltage in the generator creates eddy currents in the body of the machine tool. When the cutting tool (5) installed in the turret (3) touches the work piece (2), an electrical loop closes, which redistributes these current, and the tool switches back to its normal feed. A sensor (4) is fixed to the slide of the machine tool in a position where this current redistribution induces maximum voltage in it. When the cutting tool

Fig.1 Pocket milling operation [1]

Fig. 2 Principal scheme of the tool-part touch control system [3]


IntroductionCNC technique has precedence over low manufacturing cost and machining time as compared to other conventional techniques. However, a parametrical optimization of machining processes is necessary to achieve this. This article introduces different efficient methods to improve the machining efficiency. The methods explained are: Canned cycle, STEP-NC controller, tool part touch control system, and oscillating tool path method.

Different methods of CNC programming:1. An epitrochoidal pocket : A new Canned cycle for CNC milling machines. Canned cycles, are basically a programming method of a CNC machine and are applied to the repetitive machining operations using the G/M code language [1]. These codes are the set of pre-programmed instructions permanently stored in the machine controller which automates the repetitive tasks. By the application of the canned cycle, repetitive programming lines can be shortened, thus, reducing the programming time and simplifying the whole programming process [2]. Pocket milling is one of the main machining operations used for removing the material inside a closed boundary on the flat surface of a workpiece to a fixed depth; see schematic illustration in the Fig. 1 [1]. Rectangular and circular forms of pockets are one of the standard types of pockets which are found in the modern CNC systems. This method is characterized by its simplicity since whole machining tasks can be programmed in a single block of the part program. Previously, there was not a canned cycle for epitrochoidal pocket so the program consists of a lot of steps, for avoiding such big program a new canned cycle is developed. It is as follows:

G65 P01 xx P02 xx Po3 xx P04 xx P05 xx Po6 xx P07 xx P08 xx

where, G65 selects machining for epitrochoidal pocket and P01 to P08 are parameters and they signify the starting position, pocket depth, tool diameter, and feed rate, etc.

19.

Fig. 3 Exaggerated representation of a chip breaking tool path [4]

leaves the workpiece, it again travels with a rapid feed.

ApplicationsThis method is useful for machining critical profile work pieces in which cycle time are very long and the ‘cutting air’ time is also more. This method is used for machining of aerospace turbine blades, impeller, housings, etc.

3. Temperature control and machine dynamics in chip breaking using CNC tool pathsIn normal turning, the formation of long, stringy chips is undesirable because they can become tangled around the tool and dragged back through the cutting zone. This potentially damages the tool and the workpiece. In contrast, short, comma-shaped chips easily fall out of the cutting zone, away from the tool and workpiece.

In this method, an oscillating tool path is used. The use of oscillating CNC tool paths has been shown to provide a reliable chip breaking alternative to conventional methods. Keeping the interface temperature below a critical threshold reduces tool wear. In this method, tool path is oscillating and every time a phase shift is done at the intersection points (A), (B) as shown in Fig 3, the chip breaks. The desired chip length is achieved by defining and controlling the amplitude ratio, RAf, oscillation frequency, ω, and the phase shift, ε between subsequent passes of the tool [4].

ApplicationThis is particularly useful for ‘difficult-to-machine’ materials, where tool wear is an issue, and for materials which are pyrophoric. The next method is completely different from above three.

4. An advanced STEP-NC controller for intelligent machining processesCurrently, the machine tool programming standard used is ISO 6983. It was standardized at the beginning of the 1980s and is also known as G-code [5]. New STEP-NC known as ISO 14649 standard is adapted in the modern machining processes. This STEP-NC standard is based on the Standard for


20.


Exchange of Product data model (STEP) and has been developed to fill in the gaps of G-code [6, 7]. It allows the bidirectional data flow between CAD/CAM and CNC without any information loss and also provides a feature-based data model; see schematic illustration in the Fig.3 [5]. A wide range of high level information is available in the STEP-NC file such as feature geometry, cutting tool description, operation attributes and work plan.

A new generation of intelligent controller can interpret STEP-NC file information to generate, simulate and optimize machining tool-paths. With the help of STEP-NC standard, the CNC controller becomes a central element in the design/manufacturing data chain and the part of the intelligence is transferred from CAM to CNC. Hence, the tool path can be computed in the CNC controller.

4) Temperature control and machine dynamics in chip breaking using CNC tool pathsIn normal turning, the formation of long, stringy chips is undesirable because they can become tangled around the tool and dragged back through the cutting zone. This can potentially damage the tool and workpiece. In contrast, short, comma-shaped chips easily fall out of the cutting zone, away from the tool and workpiece.

In this method, the tool is given the forward and backward movement as shown in figure 5. Thus, when the tool starts to move in the forward direction (A) the chip formation begins and when the tool moves in the backward direction (B) the chip breaks due to loss in contact with the tool. The use of forward-backward turning has been shown to provide a reliable chip breaking alternative to conventional methods. Due to breaking of chip, the tool tip temperature decreases and various undesirable effects of continuous chip can be eliminated [8]. It is observed that when the interface temperature is

Fig. 4 New STEP-NC high level programming [5]

21.

kept below a critical threshold, there is a reduction in tool wear. Titanium has very low thermal conductivity; hence during the formation of long continuous chips, the tool life is short. This can be avoided by breaking the chips into small segments.

ApplicationThis method is particularly useful for difficult-to-machine materials where, tool wear is an issue, as well as for materials which are pyrophoric in nature.

Conclusions• This study presents different methods of NC programming, applicable to

the different machining processes.

• For the machining operations like drilling, counter-boring, peck drilling, pocket or slot machining the standard canned cycles are used.

• The STEP-NC is a new standard; it provides new opportunities to support high level and standardized information from design to NC controller. It also allows the bidirectional data flow between CAD/CAM and CNC.

• TPTC System significantly reduces the air cutting time which reduces the cycle time and ultimately increases machining productivity.

• The application of oscillating tool path is an effective method for ‘difficult-to-cut’ materials, as it generates broken chips irrespective of cutting conditions.

Fig. 5 Representation of a chip breaking by forward backward turning


22.


REFERENCES

[1] S. L. Omirou, C. Andreas, Nearchou, An epitrochoidal pocket-A new canned cycle for CNC

milling machines, Robotics and Computer-Integrated Manufacturing, v25, (2009), pp: 73-80.

[2] J. Stenerson, Kelly Curran, Computer numerical control- operation and programming,

Prentice Hall (2005).

[3] G.V. Nenov, T. Szecsi, (2009). Increasing CNC machine tool productivity by using tool-part

touch control, Robotics and Computer Integrated Manufacturing, v18, (2009), pp: 291–296.

[4] S. Smith, B. Woody, W. Barkman, D. Tursky, Temperature control and machine dynamics in

chip breaking using CNC tool paths, CIRP Annals - Manufacturing Technology, v58, (2009),

pp: 97–100.

[5] Chih-Ching Lo, A new approach to CNC tool path generation, Computer-Aided Design, v30,

n8, (1998), pp: 649-655.

[6] ISO_6983-1 (1982). Numerical control of machines—Program format and definition of

address words—Part 1: Data format for positioning, line motion and contouring control

systems. In: International Standard Organization.

[7] Pratt MJ (2001). Introduction to ISO 10303-the STEP standard for product data exchange,

Journal of Computing and Information Science in Engineering, v1, (2001), pp: 102-103.

[8] P.J. Arrazolaa, A. Garaya, L.M. Iriarte a, M. Armendiaa, S. Maryab and F. Le Maître (2009)

Machinability of titanium alloys (Ti-6Al-4V and Ti555.3) 2223-2230.

23.

YOGESH GAIKE

PhD student

NCAIRTM, IIT-Bombay

Micro-Structural Evolution of Ti-6Al-4V during high strain rate deformation process: a review

IntroductionTitanium alloy Ti-6Al-4V is a very popular alloy because of its high ‘strength-to-weight ratio’, corrosion resistance, high toughness and heat treatable. These alloys can be subjected to various dynamic conditions such as high strain rate and high strain (like ballistic impact, explosive forming, high speed machining, etc.) mainly during their life span as well as during their manufacturing. Machining of Ti-6Al-4V is difficult due to their superior property. The main reason of tool wear in machining of Ti-6Al-4V is its propensity to form serrated/segmental chips. The chips thus formed are the kind which does not dissipate heat from the tool cutting edge. The low thermal conductivity of Ti-6Al-4V mostly leads to increased temperatures at the tool cutting edge and results in adhesion of work piece material to the cutting edge creating rapid tool wear [1]. Ti-6Al-4V is very much susceptible to shear localization. During high strain rate deformation of Ti-6Al-4V, a thermal softening phenomenon takes place which is far greater than that of the strain hardening. These effects cause thermal-mechanical instability at the localized area, and leads to formation of shear bands. The size of these shear band are in the range of size 5 μm to 100 μm. These bands are also known as adiabatic shear bands (ASBs) [1,2]. The reason behind the formation of serrated chips during high speed machining (HSM) of Ti-6Al-4V is due to the formation of the ASBs [3,4]. The microstructure evolution in ASBs plays an important role during deformation because of the shear instability which occurs in ASBs. The occurrence of the shear instability during deformation leads to material failure resulting in low toughness and low ductility [5,6].

Yongbo et al., (2006), put forth another theory according to which dynamic recrystallization (DRX) of Ti-6Al-4V takes place during high strain rate deformation inside the shear bands [2]. But again in 2008, Rittel et al., argued that DRX is not a result of ASB, but instead is a cause of ASB. Thus, DRX not only causes the localized softening but also initiates early stage deformation of Ti-6Al-4V [7].

The process of formation of an ASB in Ti-6Al-4V is very complex. Many researchers have predicted various physical phenomena that occur in the shear bands such as: phase transformation, diffusion of material, grain fragmentation, lattice rotation and dynamic recrystallization (DRX).

In the following sections, various types of ASBs are discussed which are commonly formed in shear susceptible metals like Ti-6Al-4V when subjected to

R & D UPDATES

24.

high strain rate deformation process. The ASBs are classified according to the occurrence of phase transformations in the localized zone. The various phase transformation and recrystallization during high strain rate deformation in ASB of Ti-6Al-4V are also discussed in this article. Figure.1 shows a schematic representation of research work carried on Ti-6Al-4V under a high strain rate and causes of microstructure evolution in terms of phase transformation and recrystallization.

• Yongboetal.,(2006)[2]

• Velásquezetal.,(2007)[8]

• Wanetal.,(2012)[3]

• Martinezetal.,(2007)[9]

• Peirsetal.,(2013)[4]

• Yongboetal.,(2006)[2]

• Martinezetal.,(2007)[9]

• Ritteletal.,(2008)[7]

• Wanetal.,(2012)[3]

• Peirsetal.,(2013)[4]

Phase Transformation

Recrystallization (DRX)Phase Transformation

Phase Transformation does not occur

Phase Transformation occurs

DRX occurs

DRX does not occur

Micro-structure evolution in Ti-6Al-4V (High strain-rate deformation)

Fig. 1 Schematic review of research work on micro-structure evolution in Ti-6Al-4V during

high strain-rate deformation

Types of ASBsThe two main types of ASBs mostly identified by researchers are transformed ASBs and deformed ASBs. The transformed ASBs are mainly found in alloys where, a phase transformation occurs during deformation, due to high temperature. This temperature is greater than that of the phase transformation temperature (e.g. β trans. in Ti-6Al-4V). Sometimes, the transformed ASBs are also called as a white-etching bands because of the white layer found in the region, where the deformation takes place [1]. In

Micro-structural evolution of Ti-6Al-4V during high strain rate deformation process: a review

25.

the deformed ASBs, the transformed phase is same as the parent material phase. In general, deformed ASBs are narrower than transformed ASBs, which make their classification easier. Most of the alloy consists of either transformed ASBs or deformed ASBs. However, some alloys consist of a mixed matrix of transformed and deformed ASBs. Formation of ASBs is thus dependent on various aspect of deformation such that they can be mapped with the thermal properties of the alloy, critical strain and the deformation strain rate [4]. Phase transformation decides the types of ASBs formed in a localized zone. In the following sections, the results of various researchers about phase transformation in ASBs of Ti-6Al-4V are discussed.

Phase TransformationIn Ti-6Al-4V, β-phase transformation temperature is 882.5°C. Researchers have addressed questions as regards, whether high strain rate deformation processes (105s-1) in Ti-6Al-4V, leads to phase transformation or not. Velásquez et al., (2008) in the metallurgical study of chips obtained during high speed machining (HSM) of Ti-6Al-4V by using X-ray diffraction (XRD). They found that the phases present in the as received material and phase present in the chips after machining under all cutting speeds are similar. Hence, they concluded that no phase transformation occurs inside the shear bands and the observed ASBs in Ti-6Al-4V, are the deformed ASBs [8] (Figure 1).

Peirs et al., (2013) and Martinez et al., found similar kind of results in their ballistic impact and split Hopkinson pressures compression experiments. They found that α-Ti (Hexagonal close-packed-HCP) grains surrounded by β-Ti (body centred cubic-BCC) grains in ASB by using diffraction pattern. Hence, no systematic phase transformation was found to take place during high strain rate deformation process of Ti-6Al-4V [1,9] (Figure 1).

Yongbo et al., (2006) reviewed the shear band details like deformation, phase transformation and recrystallization by high strain rate (9x 105 s-1) loading of titanium and its alloys. From transmission electron microscopy (TEM) image of ASB, they concluded that the phase transformation from α to α2 takes place within the ASB. According to the analysis of electron diffraction and dark-field image, it was confirmed that the by-product α2 phase (Ti3Al) is transformed from α matrix of Ti-6Al-4V [2] (Figure 1).

Wan et al., (2012) conducted HSM on Ti-6Al-4V for various speed ranges from 30.2 to 281.3 m/min, and concluded that the microstructure evolution of ASB was related to the cutting speed. As cutting speed increases, ASBs form in Ti-6Al-4V are in sequential pattern given by deformed band →deformed band + transformed band→ transformed band. These sequential transformations are called as martensitic phase transformation of β-Ti (BCC) to α`` phase, which is orthorhombic in structure [3] (Figure 1).

Apart from the phase transformation, recrystallization during deformation in Ti-6Al-4V also enables a good understanding of ASBs. In the next section, recrystallization in ASB of Ti-6Al-4V during high strain rate deformation


26.

process is discussed.

RecrystallizationRecrystallized grains are characterized by an equiaxed shape and having low dislocation density. Recrystallized grains are softer than deformed grains and strain hardened grains, which cause unstable deformation leading to strain localization [7].

Meyers et al., (2001) invented Nesterenko model of DRX based on randomly distributed dislocations, by which DRX occurred as shown in Figure 2 in a sequential form [10]. It is observed from Figure 1 a homogeneous distribution of dislocations rearranged into elongated dislocation cells, called as dynamic recovery. As the deformation begins, a number of dislocations start moving and disorientation increases, these cells are now elongated subgrains. Ultimately, the elongated subgrains break up into the approximately equiaxed micro-grains [10].

Martinez et al., (2007) found that during high strain rate (ballistic impact), ASBs are composed of DRX grains. The DRX microstructure was confirmed, by TEM analysis whose average grain size is observed to be ∼0.6 µm. These DRX microstructures are also observed from EBSD-OIM and color/phase mapping of the ASBs and the adjoining matrix. The grain size varied from 50-900 nm [9].

However, Peirs et al., (2013) found results contrary to that mentioned previously in compression split Hopkinson pressure bar test. They found no evidence of recrystallization taking place before the formation of the ASBs. Ultimately, elongated and strongly deformed grains were observed within the ASBs. ASBs research also concluded that the ring pattern observed in the TEM image does not prove that DRX has occurred. The reasons can be

Fig. 1 Schematic illustration of micro-structural evolution during high-strain-rate deformation

(a) Randomly distributed dislocations; (b) Elongated dislocation cell formation

(i.e. dynamic recovery); (c) Initial break-up of elongated sub-grains; (d) formation of

sub-grains with high density dislocations; (e) Recrystallized microstructure [10]

D.

E.

DislocationsA.

C. Initial break-up of elongated sub-grains

Shear Direction

B. Elongated dislocation cell formation


27.

due to the nanocrystalline structure, which arises due to the excessive shear deformation. The formation of the ring pattern in the TEM image is due to recrystallization that takes place later in the core of the shear band and not before the strain localization [4].

Concluding RemarkVarious researchers have explained theories of phase transformation and dynamic recrystallization (DRX) during high strain rate deformation of Ti-6Al-4V in ASB. However, many contradictory results do not conclusively prove the exact microstructure evolution in ASBs of Ti-6Al-4V during high strain rate deformation. The various results are shown in Appendix A (Table 1). Hence, it is necessary to go through a detailed study of microstructure of ASB in Ti-6Al-4V at high strain rate deformation. For future scope from machining point of view, it is necessary to establish relation between machinability and formation mechanism of ASB in Ti-6Al-4V

REFERENCES

[1] A. Gente, H.W. Hoffmeister, C. J. Evans, “Chip Formation in Machining Ti6A14V at Extremely

High Cutting Speeds”, CIRP Annals - Manufacturing Technology, v50, n1 (2001) pp. 49-52.

[2] X.U.Yongbo, BaiYilong and M. A. Meyers, “Deformation, phase transformation and

recrystallization in the shear bands induced by high-strain rate loading in titanium and its

alloys”, Journal of Science Technology, v22, n6, (2006), pp. 737-746.

[3] J.Peirs, W. Tirry, B. Amin-Ahmadi, F.Coghe, P.Verleysen, L.Rabet, D.Schryvers and J. Degrieck,

“Microstructure of adiabatic shear bands in Ti-6Al-4V”, Material Characterization, v75, (2013),

pp. 79-92.

[4] Z. P. Wan, Y. E. Zhu, H.W.Liu and Y.Tang, “Microstructure evolution of adiabatic shear bands

and mechanisms of saw-tooth chip formation in machining Ti-6Al-4V”, Materials Science and

Engineering A, v531, (2012), pp. 155– 163.

[5] S. M. Walley, “Shear Localization: A Historical Overview”, Metallurgical and Materials

Transactions A, v38A (2007), pp. 2629-2654

[6] A. Molinari, C. Musquar and G. Sutter, “Adiabatic shear banding in high speed machining

of Ti–6Al–4V: experiments and modeling”, International Journal of Plasticity v18, (2002),

pp. 443–459.

[7] D. Rittel, P. Landau and A. Venkert, “Dynamic Recrystallization as a Potential Cause for

Adiabatic Shear Failure”, The American Physical Society, PRL 101 (2008), pp. 165501-166605.

[8] J.D.Puerta Velasquez, B.Bolle, P.Chevrier, G.Geandier, A.Tidu, “Metallurgical study on chips

obtained by high speed machining of a Ti–6 wt.%Al–4 wt.%V alloy”, Materials Science and

Engineering A, v452–453 (2007), pp. 469–474.

[9] F.Martinez, L.E.Murr, A.Ramirez, M.I.Lopez, S.M.Gaytan, “Dynamic deformation and adiabatic

shear microstructures associated with ballistic plug formation and fracture in Ti–6Al–4V

targets”, Materials Science and Engineering A,v 454–455 (2007), pp. 581–589.

[10] M. A. Meyers., F. NesterenkoVitali., C. LaSalvia Jerry, Xue Qing, “Shear localization in dynamic

deformation of materials: microstructural evolution and self-organization”, Materials Science

and Engineering A, v317 (2001), pp. 204–225.


28.

Appendix A Table 1 Summary of literature on microstructure evolution in Ti-6Al-4V during high strain rate deformation

Sr. No.

1.

2.

3.

4.

5.

6.

References

Peirs et al., (2013) [4]

Wan et al., (2012) [3]

Rittel et al., (2008) [7]

Martinez et al., (2007) [9]

Velásquezetal.,(2007)[8]

Yongbo et al., (2006) [2]

Process

Split Hopkinson pressure bar setup.

HSM of Ti-6Al-4V

Physical Review Letters (ASB)

Ballistic impact with plug formation in Ti-6Al-4V

Metallurgical study on chips by HSM of Ti-6Al-4V alloy

Review paper on shear band details

Remark

• Systematic phase transformation does not take place during high strain rate deformation process of Ti-6Al-4V.

• No evidence for recrystallization in ASB.

• As cutting speed increases, microstructure changes from transitional region to center of ASB. It is as follows: deformed band →deformed band + transformed band→ transformed band.

• This transformation is called as martensitic phase transformation of β-Ti (BCC) to α`` phase (orthorhombic).

• Serrated chips in Ti-6Al-4V during HSM is due to ASB.

• Dynamic Recrystallization as a main cause for ASB formation.

• There was no evidence for a systematic α → β phase transformation in the ASB/DRX zone.

• The DRX zone grain sizes were observed to vary from 50 to 900 nm, in contrast to the α-Ti (hcp) grains, which varied from 5 to 50 µm; with surrounding β-Ti (bcc) grain sizes in the 5µm range.

• No phase transformation was observed inside the shear bands.

• ASBs is the main reason of formation of serrated chips.

• Phase transformation from α to α2 within the ASB by observing the TEM image of the ASB of Ti-6Al-4V.

• The equiaxed and distortion-free grains observed within the bands are proposed to be the results of dynamic recrystallization.


29.

Traditionally, metal working has always involved cutting large blocks of metals into desired shapes of required dimensions by tooling. However, tooling in such cases is time consuming, expensive and incurs a substantial amount of material wastage. Metal working in the recent times have advanced in all phases i.e. forming, cutting, casting and joining. The need for cost reduction and time to flight of components without compromising safety and performance in aeronautical parts encouraged investigation of novel manufacturing routes. Additive manufacturing is the next-generation innovation in manufacturing. This process is one of the novel manufacturing processes which has a wide application on different materials and enables creation of various products ranging from medical implants to different parts of aircrafts [1]. Among different additive layer manufacturing processes, shaped metal deposition (SMD) is an innovative time compression technology, patented by Rolls-Royce. SMD is similar to multi-pass welding. It is a preferred process in comparison to other processes because it allows the possibility of employing standard welding equipment without the need for extensive new investment [2]. This technology of manufacturing creates near net shaped components layer by layer with the help of weld deposition [3]. Thus, due to fabrication of the components in successive layers, there is a drastic reduction in the wastage of materials. Additionally, the expensive tooling requirement during forging can also be considerably eliminated by the SMD process. The only inventory held in the SMD process is wire. Large-scale aerospace parts can thus be built directly from the design model (CAD) with no need for a prototype stage and the 'parts' can be stored as programs and produced to order, thereby reducing inventory costs. This is the major advantage of SMD process as it reduces the inventory costs substantially [4].

Shaped Metal Deposition was patented by Prinz and Weiss [5, 6] as a combined weld material build-up with CNC milling, called shaped deposition manufacturing (SDM), in the year 1994. In 1994-99, Cranfield University developed shaped metal deposition (SMD) for Rolls Royce to make engine casings, various processes and materials. In 2005, RAPOLAC project (Rapid Production of Large Aerospace Components) started with the aim to investigate and further refine the SMD process for use in the production of large components and for adding new metal features to the existing parts [7]. The project was funded between 2007 and 2010 by the EU's 6th Framework

Dr. AKHILESH K. SWARNAKAR

Project Research Scientist,

NCAIRTM, IIT-Bombay, India

Dr. BERND BAUFELD

Project Manager, Nuclear AMRC,

University of Sheffield, UK

TECHNOLOGY UPDATES

Shaped Metal Deposition (SMD): An Overview

Among different additive layer manufacturing processes,

shaped metal deposition (SMD) is an innovative time

compression technology, patented by Rolls-Royce. SMD is

similar to multi-pass welding.

30.

Aeronautics and Space Programme. It was coordinated by the Advanced Manufacturing Research Centre (AMRC) at the University of Sheffield, in collaboration with partners in Belgium, Italy and Argentina who provided complementary expertise.

Titanium alloys, which are widely used in aeronautical applications, have been previously difficult to shape by traditional methods such as casting, forging and machining [2]. However, additive layer manufacturing by SMD has made it easy to machine titanium into different shapes without significant material loss during the shaping process. Thus, SMD has created new opportunities with promising advantages. Aerospace manufacturers are using SMD as a process to manufacture large components such as engine casings thereby reducing fabrication time duration from months to a few weeks.

A set up for SMD process in general is enclosed in an airtight chamber filled with an inert gas ensuring high purity and control of moisture inside the chamber. Maintaining the inert environment allows the manufacturers to obtain a final product with low oxygen and nitrogen contamination. In particular, the SMD plant is equipped with a pyrometer and a thermal camera, for analyzing both the temperature distribution, and heating and cooling rates over the time during the deposition process. A combination of a welding camera and intra red (IR) sensors has been used as a monitoring system for the process [8].

Figure 1 shows a schematic representation of the SMD deposition process described by Bonaccorso et al. [8].The SMD rig consists of a robot with a TIG (Tungsten Inert Gas) welding process in conjunction with ‘cold’ wire to give a layer-wise build-up. The working variables such as current (heat source), injected material mass rate (WF), torch speed (TS) and the thickness imposed for each layer (SH) needs to be controlled. Wall thickness is controlled by the current, travel speed and wire feed rate and also to some extent by the wire thickness. The material is deposited layer by layer using a CAD/CAM interface that generates an offline programme using a specifically developed software, to provide the robot with the necessary weld path information.

Baufeld et al. have discussed mathematical formulae to calculate the thickness of each layer during the SMD process [3]. As SMD is a layer by layer deposition process, the thickness of each layer depends on the amount of materials supplied within a certain time. The volume of materials deposited within a certain time ‘t’ using a wire with a radius ‘r’ is:

V=π∙r2∙WFS∙t

where, WFS is wire feed rate. Depending on the table speed ‘v’, this volume is distributed within ‘t’ on a length

L=v∙t

Fig. 1 A schematic representation of the SMD deposition process.


31.

Then for a layer width w, the layer thickness is

The SMD fabricated part requires the least surface finishing, therefore reducing the scrap rates up to a minimal. The accuracy of the fabricated component depends on the thermal stresses induced during the process. Controlling the heat transfer during deposition can reduce the residual stresses and hence the distortion of the fabricated part [7]. The heat treatment sets are also required in some cases to relieve the stress as generated during fabrication of these parts.

Benefits and drawbacksRAPOLAC partners in collaboration with AMRC researchers have highlighted the commercial benefits of SMD which includes the following [2, 7]. Comparison of SMD with other traditional process reveals that the components developed through SMD process have their lead time reduced up to 60%. This eliminates reducing the need for tooling and prototyping. SMD process leads to a 40% reduction in the cost of manufacturing, while 90% reduction of inventory depending on the materials used in the process. There are significant savings in energy when components are made with SMD process thus increasing the process efficiency.

In a rapidly changing aerospace manufacturing scenario, SMD exhibits a huge potential on designing and production of various parts and repair of high performance alloy components. SMD has a value added advantage over traditional methods of forging and machining in which metals are subtracted from the work piece to get the desired shape [2]. A crucial factor during the SMD process is controlling the heat transfer during the deposition process because it can generate large amount of residual stresses, which could lead to a reduced product quality. During the SMD processes, the molten material is deposited along a well-defined path using the welding

Table 1, summarizes the main process parameters from various research studies for making SMD components by different materials.

S.No

1

2

SMD component Shape

Tubular shape with squared cross section

Ring rolled combustor outer casing

Material

Ti-6Al-4V alloy

Nickel-based superalloy (718)

Wire Diameter

ϕ1.2mm

Wire feed rate

2.4 m/min

10 m/min

Travel speed

0.3m/mm

0.6mm/min

TElectrical current (A)

150

35

Step height

1mm

20mm

Ref.

[3]

[9]


32.

equipment therefore, the optimization of pre-process parameters is required for a successful manufacturing of a component. In case of prototyping, pre-process parameters are defined by trial and error, which sometimes could makes the SMD process costly and time consuming [10]. Another possible drawback of the SMD process is that it facilitates manufacturing of large components but fabrication of very small components could be challenging.

For more details about the process please visit: http://www.amrc.co.uk/featuredstudy/shaped-metal-deposition/ http://www.rapolac.eu/smd_info.html

REFERENCES

[1] http://emps.exeter.ac.uk/engineering/research/calm/whatis/

[2] http://www.amrc.co.uk/featuredstudy/shaped-metal-deposition/

[3] Bernd Baufeld, Omer vanderbiest and Rosemary Gault, Microstructure of Ti-6Al-4V

specimens produced by shaped metal deposition, International Journal of Materials

Research, v100, n11, (2009), pp.1536.

[4] L.E. Weiss, R. Merz, F.B. Prinz, G. Neplotnik, R Padmanabhan and L. Schultz and K.

Ramaswami, Shape Deposition Manufacturing of Heterogeneous Structures, Journal of

Manufacturing Systems, v16, n4, (1997), pp.239-248.

[5] E.B. Prinz and L.E. Weiss, Method for Fabrication of Three Dimensional Articles, U. S. Patent

5,301,415, (1994).

[6] www.norsktitanium.no/en/News/~/media/NorskTitanium/Titanidum%20day%20

presentations/Paul% 20Colegrove%20Cranfield%20Additive%20manufacturing.ashx

[7] http://www.rapolac.eu/smd_info.html

[8] F. Bonaccorso, L.Cantelli and G. Muscato, Arc welding control for Shaped Metal Deposition

Process, International Federation of Automatic Control (IFAC), 18th IFAC World Congress

Milano (Italy) August 28 - September 2, 2011.

[9] D. Clark, M.R. Bache and M.T. Whittaker, Shaped metal deposition of a nickel alloy for aero

engine applications, Journal of materials processing technology 203 (2008) pp.439–448.

[10] Anca, V. Fachinotti, and A. Cardona, Finite element modelling of shape metal deposition,

MecánicaComputacionalVol XXVIII, págs. 3011-3035, Cristian García Bauza, Pablo Lotito,

Lisandro Parente, Marcelo Vénere (Eds.) Tandil, Argentina, 3-6 November 2009.


33.


SARBANI BANERJEE BELUR

SUMIT KATEKAR

NCAIRTM, IIT-Bombay

Robotic technology has advanced tremendously in the recent years across various industries and regions of the world. Evolution of robotic technology has moved ahead from being simple machines of the early 60s to the more automated ones, programmed for complex tasks that are being used today. Industrial robots were first used in the automotive industry installed at General Motors plant in New Jersey in the year 1961. In comparison to the automotive industry where robotic advances have been well established and technologically matured, the same is not true in the case of aerospace manufacturing. Unlike the automotive industry, which mass produces automobiles, aerospace manufacturers face unique challenges such as low production volumes, innovations in materials used and large components with complex shapes. Also, due to the scale of the structures involved, it is more difficult to achieve full interchangeability of parts. The delay caused in adoption of robotic technology in aerospace manufacturing has been largely due to this insufficient accuracy. However, the industrial robots that are being used today in the aerospace manufacturing sector can have as many as six degrees of freedom of movement and can be programmed for many complex tasks. Nowadays, robots play an important role in fabrication of aircraft engines, drilling, fastening, painting as well as providing assistance in the assembly of aircraft components and work hand in hand with humans on the production floor. The primary reason the robots are favored in aerospace manufacturing are because they reduce manpower, increase throughput and increase quality. Unlike gantry systems and fixed automation machines that are heavy, robots can be quickly deployed and can be of help in various arena of aerospace manufacturing. Thus, use of robots can reduce the number and cost of hard tools used for manufacturing. As more and more robots are being employed in aerospace manufacturing and other manufacturing industries, a new robot safety standard that has been developed by Robotics Industries Association (RIA). The ANSI/RIA R15.06-2012 standard is a global standard which has been updated for the first time in 2013 since 1999 and is now harmonized with the International ISO 10218:2011 standard for robot manufacturers and integrators.

There are several advantages of the use of robotics in aerospace manufacturing. Some of them are listed below:

Flexibility: Use of robots in aerospace manufacturing has enabled a single machine to manufacture multiple parts and work on multiple parts.

Lower cost: Robots are priced for mass manufacturing. The changes made in the manufacturing process can be easily monitored and executed, thereby reducing start-up costs. Thus, new product or adjustment in specifications

TECHNOLOGY UPDATES

34.


can be added without purchasing new equipment. In this way, precision can be achieved without expensive machining cost.

Shorter lead times: Robots in aerospace manufacturing allow for reduced lead times when ordering as compared to a custom equipment. The reduced lead times on equipment allows for more process engineering to be complete before equipment ordering. This can effectively reduce the scope of changes required that are typically identified between equipment order and production build.

Work safety improvements: Robots are preferred over human workforce because they can work in environments deemed unsuitable for humans e.g. Painting, de-painting, composite laminating, forging of cast parts for engine components, assembly and inspection in tight locations such as underneath the component or in places which are unreachable in person.

Reduced design limitations: Robots can reach and process parts of complex geometries that are not easily accessed by gantry based machinery or human beings allowing for more creativity in the design of the end product.

Increased quality: The inherent repeatability of robotic processes allows for better predictability and control of process parameters. Thus making it easier to identify and refine process parameters that affect the quality of the component.

Higher throughput: Robots can execute complex or repetitive processes at very high speeds. Intelligence based processes like accuracy tools have enabled robots the ability to adapt their processes to the changing environment allowing for much shorter setup times with less tooling and fixture requirements between parts.

Examples of robots used in various aerospace manufacturing processesSnake-arm robot is made up of segments linked together. A number of segments in the arm as well as the length of the segments can be varied depending on the payload and curvature required. This allows the robot to be used for a wide variety of functions. The snake-arm can be changed with the help of a quick release mechanism. No active elements are present in the arm and the arm is controlled by a driver unit. The entire robot is controlled by a computer and a joystick. Tools can be attached at the tip of the snake-arm via a wrist and interface. The tip can be manoeuvred in different directions once it reached open space. Snake-arm robot can be attached as an extension to an industrial robot. Snake-arm robots have many applications in the aerospace sector. They may be used in an environment where minimum contact with the work-piece is required. Tasks such as inspection, laser welding, NDT and thermal imaging can be carried out with the help of interchangeable tools. Snake-arm can also be used for processes that require contact with the environment, like deburring, painting, riveting and drilling.

35.

Wheeled robot is powered by motorized wheels. The number of wheels may vary according to the requirements. As the centre of gravity of these robots is closer to the ground due to which they are always balanced. Wheeled robots can be used to transport heavy tools from a workstation to another to carry out processes. Technologies like optical tracking, mechanical guide elements and positioning aids are used to position the tools accurately.

Crawler robots are robots have legs, and in the aerospace industry, they can be used for inspection. These robots have suction caps on their legs which help them crawl on the surface of the aircraft. They may be equipped with eddy current sensors and/ or optic imagers to scan the skin of the aircraft.

Six axis robots are robots that have six degrees of freedom. They can perform a wide variety of the tasks because of greater flexibility. They can be used for inspection, testing, welding, assembly, etc.

ConclusionAerospace manufacturing in the present times is facing many challenges. The industry has become largely competitive, catering to large demands requiring higher production at shorter notices. New developments in the materials used and design of aircrafts will have greater consequences in the near future. Hence, in order to steer through the changing scenario, production needs to be strategically managed. Robotic advances have come about as a welcome change in aerospace manufacturing. Stationary single robotic systems have given way to multiple robots with specialisation roles thus becoming a crucial part of aerospace production.

REFERENCES

• http://www.referenceforbusiness.com/management/Pr-Sa/Robotics.html

• http://www.fanucrobotics.com/robotics-articles/Robotic_Accuracy_Improves_Aerospace_

Manufacturing.aspx

• http://www.ocrobotics.com/downloads/Aerofast03.pdf

• http://www.robotee.com/index.php/types-of-robots/

• http://www.kuka-robotics.com/en/solutions/solutions_search/L_Premium_AEROTEC_

Placing_of_extreme_loads.htm

• M. Siegel, P. Gunatikale and G. Pondar, G. Robotic Assistant for Aircraft Inspectors. IEEE

Instrumentation and Measurement Magazine 1(1):16–30

• (http://www-2.cs.cmu.edu/afs/cs/project/sensor-9/ftp/papers/imm97.pdf).

• http://www.kuka-robotics.com/en/solutions/solutions_search/L_R198_Robot_guides_

probe_in_wind_tunnel.htm

• http://www.robots.com/faq/show/what-are-six-axis-robots


36.

Aircraft maintenance, repair and overhaul industry calls for proper policy

India aims to become the third largest aviation market of the world by the year 2020. Aircraft maintenance, repair and overhaul (MRO) forms an important business activity of the aviation industry. Currently, India constitutes 1 percent of the global MRO market worth USD 45 billion. MRO spending in India has been USD 800 million for 2011 and is expected to grow to over USD 1.5 billion by the year 2020. India has a huge potential to become a major hub due to low cost benefits and favourable geographical location. As per estimates, servicing of an aircraft at a local MRO helps an airline to save 30% to 40 % in plane’s maintenance costs despite high service taxes and import of spare parts. The airlines in India spend about 13% - 15% of their revenues towards maintenance which is the second highest cost item for airlines after their expenditure on fuel.

India needs to take an aggressive step ahead to establish a perfect stance in the aerospace MRO sector. Setting up an MRO is a highly capital intensive with a long break-even time. It also requires continuous investment in tooling, certification from safety regulators and to stay relevant in the competitive global environment.

Thus, there is an urgent need to take proper steps not only by the government but also by the airport operators which can enable Indian companies to compete with MRO companies in the neighbouring countries like Sri Lanka, Singapore and Indonesia.

Ref:http://economictimes.indiatimes.com/news/news-by-industry/

transportation/airlines-/-aviation/aircraft-maintenance-repair-and-

overhaul-industry-calls-for-proper-policy/articleshow/19764435.cms

Aerospace industries are closer to standardizing materials reporting

Standards play an integral role throughout the aerospace industry in design, manufacture and support of aerospace products. The industry being global in nature uses hundreds and thousands of standards from organisations worldwide. However, there is very less emphasis on reporting these standards to prevent unwarranted proliferation, reducing redundant standards and consolidating the standards ‘supply chain’. Standards not only have an inherent role of maintaining quality but they

BUSINESS UPDATES

also enable efficiency by cutting down on environmental hazards.

In the recent times, around the world, regulations are increasing to demarcate the use/non-use of certain materials in aerospace products. These are primarily because of environmental pollution, release of harmful gases into the atmosphere and issues related to global warming. In this regard, various materials and substances that are relevant for reporting throughout the supply chain has been identified. This will enable greater efficiency in manufacturing products, reductions in duplications, cost savings in the areas of certifications and tests. Reporting of the standardised materials is significant as it will enable the supply chain to share the information about the chemicals and materials used to manufacture parts for aerospace products. Many suppliers support several companies globally. Hence, sharing this knowledge can enhance efficiency, thereby lowering costs, and ultimately improving health and the environment.

Ref: http://www.prweb.com/releases/2013/4/prweb10593785.htm

Fuel produced from discarded plasticsPlastic was always a redundant material until the 1950s, its properties like durability, low cost and light weight were being focused on. Engineers began recognising its usefulness for various industries which also included the aerospace. Recent technological advances have moved ahead from recycling plastics to distilling plastics into fuel, using processes that do not pollute the air. As plastics are mostly petroleum based, converting them into fuel sidelines plastics known as a popular pollutant causing environmental hazards. The best part of this technological advancement is that it uses plastic trash, which is discarded and non-recyclable.

The fuel produced from discarded plastic is developed through a process called pyrolysis, where the plastic is thermo-chemically decomposed at high temperatures in the absence of oxygen. Thus, about 1 tonne of petroleum based plastic can be converted into 900 litres of diesel. This fuel will be used to fly small planes. From plastic pollution, it is now a move towards solution of the problem.

Ref: http://www.aerospace-technology.com/news/newsfuel-produced-

from-discarded-plastics-to-be-used-cessna-172-jet

37.

ELEVONS are aircraft control surfaces that combine the functions of the elevator (used for pitch control) and the aileron (used for roll control), hence the name.

National Centre for Aerospace Innovation and Research (NCAIR), 2nd Floor, Pre-engineered building, Opp. Power house, IIT-Bombay, Powai, Mumbai-400076

All postal/courier correspondences to NCAIRTM should be made on the adjacent postal address:

Disclaimer: The views and opinions expressed in this newsletter are those of the respective authors. The content of this newsletter is solely for the purpose of dissemination of knowledge and not for any commercial purposes. The articles in this newsletter should not be utilized in real-world analytic products, as they are based only on very limited and open source information, without the prior consent of the authors.

elevons - ncairncair.in/newsletters/newsletterv3.2.pdf · aerospace certifications like nadcap and...

Documents