© 2012 Rolls-Royce plcThe information in this document is the property of Rolls-Royce plc and may not be copied or communicated to a third party, or used for any purpose other than that for which it is supplied without the express written consent of Rolls-Royce plc.This information is given in good faith based upon the latest information available to Rolls-Royce plc, no warranty or representation is given concerning such information, which must not be taken as establishing any contractual or other commitment binding upon Rolls-Royce plc or any of its subsidiary or associated companies.
EU Project MERLINNeeds and Demands for the Manufacture of Next
Generation Jet Engine Components
Jeff Allen
AKL – International Laser Technology Congress
9th May 2012
© 2012 Rolls-Royce plc
MERLIN – Project Summary The concept of the MERLIN project is to:
Reduce the environmental impact of air transport using Additive Manufacturing (AM) techniques in the manufacture of civil aero engines
Develop AM techniques, at the level 1 stage, to allow environmental benefits including:
- near 100% material utilisation- no toxic chemical usage- no tooling costs- impact the manufacture of future aero engine components (current buy to fly
ratios result in massive amounts of waste) These factors will drastically reduce emissions across the life-cycle of
the parts Also be added in-service benefits because of the design freedom in AM Light-weighting and the performance improvement of parts will result in
reduced fuel consumption and reduced emissions MERLIN will seek to develop the state-of-the-art by producing higher
performance additive manufactured parts in a more productive, consistent, measurable, environmentally friendly and cost effective way
2
© 2012 Rolls-Royce plc
MERLIN – Areas for Progression
The MERLIN consortia have identified the following areas where a progression of the state-of-the art is needed to take advantage of AM:
Productivity increase Design or Topology optimisation Powder recycling validation In-process NDT development In-process geometrical validation High specification materials process development
3
© 2012 Rolls-Royce plc
MERLIN - Beneficiaries Rolls-Royce WSK "PZL - Rzeszow" S.A. Industria de Turbo Propulsores MTU LPW Technologies Ltd Turbomeca Volvo Aero Corporation TWI Limited Fraunhofer - Gesellschaft zur Forderung der angewandten Forschung e.V. ILT Association pour la Recherche et le Developpement des Methodes et Processus
Industries (ARMINES) ASOCIACION CENTRO DE INVESTIGACION EN TECNOLOGÍAS DE UNION LORTEK BCT University West Frederick Research Centre
Total Budget - €7.1m Project Launch – Jan 2011 Project End – Dec 2014
4
© 2012 Rolls-Royce plc
MERLIN – Work Packages WP1 - Project Definition and Specification WP2 - Shape - Topology optimisation, modelling and validation WP3 - Process Development - Process development, process
monitoring and control, and thermal management WP4 - In-Process NDT development and integration, geometrical
measurement and control WP5 - Post Processing - Mechanical testing, analysis, recycling
validation and heat treatment WP6 - Technology Demonstration - Environmental and through
lifecycle evaluation WP7 - Management WP8 - Dissemination and Exploitation
5
© 2012 Rolls-Royce plc
6
Material Form
Heat Source
Powder Stream
(Various types)
Powder Bed Wire
Laser(Various types)
Electron Beam x
Electric Arc x x SMD
Heat Source/Material Form Combinations Very good surface finish & precision Slow build rate Small parts only Low build rate
Potential for high build rates Material utilisation varies Options for Repair, Hybrid & OEM Potential for component tailoring Electron Beam systems emerging Requirement for vacuum system with EB
Low cost (100% wire utilisation & medium process speed) Good for titanium parts with low/medium complexity Full fusion Good surface finish Large working envelope Cell installed at AMRC (Sheffield)
A wide range of processes exist, with varying attributes in terms of precision, cost, integrity, etc.
As with subtractive manufacture, there is no single “best process”; selection needs to consider application, including material, size, shape type and complexity, access, inspection and validation.
Laser heat source
Argon chamber / vacuum for EB
Mirrors (focussing /deflection coils for EB
Powder bed
Filters
Focussing Lens
Lens series
Overview of Technologies & Selection
© 2012 Rolls-Royce plc
7Overview Powder Bed
Small Parts
Blown Powder Repair Hybrids
Advantages V.good precision of deposition Good surface finish Good material properties Good utilisation of powder Uses established basic technology Automatic operation Better at overhung surfaces Can make shapes which were
previously impossible
Limitations Relatively low build rates Not straightforward to
achieve sub 10ppm oxygen levels
Need to build on a flat base
Relatively low build volume
Limited range of materials at present
Advantages System development Easy Inert atmosphere operation High Deposition rate capability Usable for additive manufacture Usable for repair Relatively wide process window Low heat input to substrate
Limitations Low Powder usage efficiency No so good at overhung
surfaces Tend to have rough surface
finish Need complex manipulation
systems for 3D parts Can get scatter on material
properties
© 2012 Rolls-Royce plc
8Business Opportunities
Reduced time to marketSimple/minimal tooling,
Reduced material costReduced waste material (high buy-to-fly ratio)
Reduced ‘removal’ operationsNo roughing, Minimal finishing, Less WIP
Repair capabilities to support aftermarket opportunitiesLower total life cycle cost
Enhanced product opportunitiesDesign for NNS
Additive Bosses
Built up Leading / Trailing EdgeAdditive Flanges
© 2012 Rolls-Royce plc
9
Graded & Tailored Materials Can change the alloy composition throughout the shape of the component, avoiding abrupt
changes in material properties Add desired properties to a part only in the areas they are needed without abrupt changes in
alloy compositioneg: Hard facing for integral bearing tracks on shafts
Organic Shapes Can be used to produce components previously not capable of being manufactured, minimum
weight and maximum strength structures akin to ‘natural’ shapes such as: butterfly wings (eg: isogrids) graded spheroidal void structures such as wood and bone
Geodesic structures Skeletal or polygon faceted structures with high specific stiffness, such as the Beijing National
Stadium. Material efficient designs
Design Opportunities
Image courtesy of Optomec Inc.
© 2012 Rolls-Royce plc
10Powder Bed - Modes
Rapid Prototyping ModeDevelopment partsShort Lead timeAbility to change design until the last minuteExpect to pay a premium on price
Powder Bed - Modes
Rapid Prototyping ModeDevelopment partsSmall numbersShort Lead timeAbility to change design until the last minuteExpect to pay a premium on price
Powder Bed - Modes
Rapid Prototyping Mode Development parts Short Lead time Ability to change design
until the last minute Expect to pay a
premium on price
OEM* Parts Manufacture Mode Have to compete with
established processes High cost of
Qualification Need Powder Supply
Chain Need Parts Supply
Chain
* Original Equipment Manufacture
© 2012 Rolls-Royce plc
11Issues – Specific Cost of Deposited Material
Assumes a self checking, self controlling, serialised, productionsystem
Specific cost of deposited material is primarily a function ofbuild rate and powder cost
- Raw Material Cost- Material Usage Efficiency- Technical support time (programming and development)- Process Labour Cost- Capital Cost - depreciation- Machine Utilisation- Power Cost and usage- Power Conversion Efficiency (wall:delivery)- Build Rate (incorporating feature and surface control)- Consumable form- Set-up time- Planned maintenance & consumables- Associated costs of ancillary processing,
- e.g. machining, heat treatment, inspection
© 2012 Rolls-Royce plc
Issues – Multiple Spots In very simple terms – to a first approximation!
Material Props = fn Crystal Structure Crystal Structure = fn Cooling rate Cooling Rate = fn Molten Pool Size Molten Pool size = fn Spot size
Specific Cost of deposited material = fn deposition rate Deposition rate = fn Spot size
Surface Finish = fn Spot Size (larger spots give coarser surface finish)
Ie: Practical systems reach a limit on max spot size This limits the deposition rate & surface finish and defines the material
properties
Points towards the use of Multiple Spots
12
© 2012 Rolls-Royce plc
13
Issues – Material Properties UTS
Between Cast and Forged Fatigue
Dependent on level of micro cracking Creep
Fine grain structure tends to lower creep performance Anisotropy
Deposition Parameters can be optimised to minimise anisotropy Fracture Toughness (Hot Creep Rupture)
Can be problematic if the resulting grain structure exhibits epitaxial grain growth
Surface Finish External Surfaces Internal Surfaces Effect on fatigue life
© 2012 Rolls-Royce plc
14
Issues – Maximum Component Size
Limited by the tank size of the powder bed system This is presently typically 250 x 250 x 250 Development systems are planned for 400 x 400 x 400 Then 600 x 600 x 600
© 2012 Rolls-Royce plc
15Issues – Powder Source
Limited number of sources approved for powder supply into Aerospace
Expensive and long term to Approve new suppliers Development usage is small cf Production Difficult to predict future requirements Ti 6-4 supply particularly difficult Gas Atomised
Plasma Rotating Electrode Powder (PREP) Specialist Nickel Superalloys difficult to supply to
specification Particle size distribution Chemistry Morphology Trace elements eg Lanthanum & Yttrium are difficult to
control at low ppm levels
© 2012 Rolls-Royce plc
16
Issues – Residual Stress/Distortion
Material structure is defined when the deposit is hot Thermal contraction must take place during cooling to ambient Results in a combination of:
residual stress distortion in the part Cracking
Aim to accommodate thermal contraction effects in the form of residual stresses which are below the material UTS
Can stress relieve in some cases May result in enforced overbuild to allow the finished shape to be machined
from the distorted geometry EB processes preheat the powder bed – results in reduced residual stress Dev work to use auxiliary lasers to preheat laser powder bed processes at
ILT Can use Preheated base plates to minimise distortion & cracking on cooling
Need 900° - 1000°C for high performance Ni superalloys
© 2012 Rolls-Royce plc
17Issues - Process Window Note that for superalloys there are definite practical limits to rate:
The effect of distortion and cracking – though these are not insurmountable Fine melt pool size allows development of optimised parameters for reduced
segregation Rate is limited by consumable feed process control and thermal management
DilutionPorosity
No fusion
Pow
er d
ensi
ty (i
ncre
asin
g as
a
func
tion
ofin
crea
sing
spo
t rad
ius .
Consumable feed rate(hypothesised)Superalloy Process Window
Bead profile aspect ratio
Energy per unit length –related to velocity
(After Steen)
General (laser powder) deposition processing windowFor high temperature alloys, solidification effects and the thermo-mechanical effects of deposition and heat treatment / post processing must be considered. This is due to crack sensitivity / strain aging and end microstructure requirements.
Pow
er d
ensi
ty (i
ncre
asin
g as
a
func
tion
ofin
crea
sing
spo
t rad
ius.
Lin
ked
to
cons
umab
le fe
ed ra
te a
nd lo
cal
dyna
mic
hea
t sin
k.
Travel speed, linked to location
Liquation
Excess segregationSolidification
cracking
Lack of inter-run fusion
Adapted (After Reed)
© 2012 Rolls-Royce plc
18
Process Capability
Need a process suitable for routine use on the shop floor Stable Repeatable Predictable
Eg: Powder Bed Intra bed variance Inter-build variance Inter machine variance Inter Operator variance
Depends on the maturity of the system
Measurement and control of Key Process Variables
© 2012 Rolls-Royce plc
19Issues - Integrity of Deposited MaterialThere are many claims with regard to density and forged properties,What do they mean?Usually that the porosity is usually fine…
BossBoss
PadPad
The maximum flaw-size is significant for component life
Flaws of various sizes will randomly intersect test bars.
Scatter in performance and tight acceptance thresholds show the importance of control
But aero-applications can experience arduous loading regimes, including:• Stress rupture• Fatigue• Dynamic loading
Schematic (not to scale) of flaws dispersed through a mechanical test block .
…does that always mean that the material is homogeneous?
Interface encompassing fusion zone and HAZ
© 2012 Rolls-Royce plc
20Properties of Thin Walls
Outer surfaces of parts are subjected to abrasive blast
Removes adhered powder particles Normalises surface finish
Abrasive blast results in a 100µ thick surface layer
contains cracks (fatigue initiation sites) Material properties would not be expected to be
the same as the bulk material Particular problem when performing stress
analyses of components with thin (c.0.5mm) walls
Unknown material properties for FE Model FE modellers tend to err on the cautious
resulting in designs which are perceived to be overweight
Erodes the business case for WXB Noise attenuators
Need to establish the properties of thin walls for input in to FE Stress models
20
100µ 100µ
500µ
300µ
100µ thick layer from abrasive blast
- Contains cracks
- Unknown material Properties
Usable thickness of base material reduced to 300µ
Unknown effect on base material from defects in the surface layer
© 2012 Rolls-Royce plc
21Surface finish External Surface Finish Surface finish is generally a
function of: Orientation of surface in build tank Deposition Rate Powder Size distribution
Laser Processes Smoother Surface Finish Lower Deposition rate
Electron Beam processes Rough surface Finish Higher deposition rates
General approach is to have different sets of parameters for ‘skin’ and ‘fill’ sections of the build
Need to optimise this approach to maximise surface finish quality whilst maximising the overall deposition rate
Need to look further at improving surface finish on overhung & low angle surfaces
21
Internal Surface Finish Need a method of post processing
internal surfaces to achieve an acceptable surface finish
Chemical? Electro Polish? Abrasive media?
Need to use designs which are optimised to give best internal surface quality
© 2012 Rolls-Royce plc
22Summary
Need to Develop: Systems with economically competitive
deposition rates and capacities Deposition Parameters and Techniques for High
Temperature Nickel Superalloys Powder sources with suitable Quality and Cost Capable NDE techniques Methods of Topological Optimisation Post processing methods to give acceptable
Surface Finish & Materials Properties