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INSTITUTE OF TECHNOLOGY, NIRMA UNIVERSITY, AHMEDABAD – 382 481, 08-10 DECEMBER, 2011
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Optimisation: Need of today’s competitive age
A case study on simulation using AutoCAST
A. Harshwardhan Pandit, B. Uday Dabade
A. P.G. student, Department of Mechanical Engineering, Walchand College of Engineering, Sangli.
B. Asst. Professor, Department of Mechanical Engineering, Walchand College of Engineering, Sangli.
Abstract-- In today’s competitive age foundries are required
to be more active, efficient. They need to respond fast. More
and more competition calls for the fast response to buyer. In
this quest maintaining quality is also a key issue. In
particular, one is interested in quantifying the performance
of a system under study for various values of its input
parameters. Such quantified measures of performance can be
very useful in the managerial decision process. The cost
concerns of the metal casting company focus on the extra
time and energy spent in changing the setup configurations in
the manufacturing system. The methods layout of a casting is
an important activity in tooling development. It involves
critical decisions regarding part orientation in mold, parting
line, cores, cavity layout, feeders, feedaids and gating system.
An improper layout leads to either poor quality or low yield,
affecting manufacturing costs and productivity. The objective
is to design the methoding system and optimize it.
Optimisation can be achieved with various techniques. In this
paper optimisation of methoding parameters with the help of
simulation is discussed and it is tried to minimize efforts and
avoid conventional trial and error practice. The simulation
model is built to assess the methoding parameters.
Index words—Casting, simulation, optmisation,
I. INTRODUCTION
n a business and manufacturing environment, most of
the organisations optimize their production schedules
and flow lines in order to meet the customer demands. The
main objective is to satisfy customer demands with
minimum production cost. In the competitive business
environment today, many industries focus attention
especially on rapidity for responding to their customers’
needs. For this reason, continuous improvements are
needed to increase response times to customer changes.
Methods design is usually carried out manually on the part
to be cast. The tooling is then fabricated; trial castings are
produced in the foundry in small batches, and inspected. If
these castings contain defects, then the methoding is
modified and the process is repeated. Each such iteration
can take up several days which delays delivery schedule,
lead time and hence the customer is dissatisfied. After a
few iterations, the foundry may find the best alternative for
the methoding which may help to solve the problems
stated earlier. It may also help to increase yield, reduce the
rejection rates. This is especially true in the case of large
castings, where the cost of a trial or repair can be too
excessive. Casting simulation can take care of the above
problems as the virtual trials do not involve wastage of
material, energy and labor, and do not hold up regular
production.
In this process of simulation we first create the solid model
of casting and then a suitable methoding is generated by
iterations using software. However, most of the simulation
programs available today are not easy to use. They may
take longer times depending upon the user expertise
available and their accuracy is affected by material
properties and boundary conditions specified by users. The
problem is the preparation of 3D model of the casting
along with mold, cores, feeders, gating, etc., which
requires CAD skills and takes considerable time for even
simple parts. Methoding is an important task in casting
production, directly affecting casting quality and yield. It
involves several decisions, such as the size of mold box
and number of cavities, orientation of casting in the mold,
location of the parting line, design of core prints, and the
location, shape and size of feeders and gating elements.
The methoding is validated and improved through several
iterations of design, pattern modification, trial production
and inspection. The goal is to consistently produce castings
with zero internal defects (such as shrinkage porosity,
inclusions, blowholes, cold shuts and inadequate
mechanical properties), while ensuring the maximum
possible yield.
I
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Fig.1. Optmisation in foundry at various stages [1]
For achieving an end, some means is required. If casting is
an end, gating can be considered as a means. An efficient
and effective means is a prerequisite to achieve a
satisfactory and desired level of end in good manner.
Gating:
Various parts of gating system like sprue, runner etc., have
some specific purpose. Sprue is required for facilitating the
pouring operation. Metal has to be transferred from ladle
to casting at sufficient pressure without causing it to
freeze. Sprue serves as a means to create the pressure in
the system. Without sprue head, travel to casting shall not
be at required pressure. Runner helps in transferring the
pressure from sprue through the mould up to the casting
like a conductor in electrical system. Finally, ingates are
required to pass on the metal to the casting which act as a
connectors. Choke in gating system acts like a current
limiter. Gating should ensure that metal reaches the
remotest portion of the casting. For this, it shall be
necessary to have large enough sizes of runner bars
carrying the metal to the inaccessible portion of the
casting. At times, some special method shall be required to
reach the casting. It is very much required that all the
portions of the casting be filled nearly simultaneously.
Here, proportioning of gating system plays a role. A long
casting may require several ingates along the length.
Streamlining of the gating components helps in ensuring
smooth flow.
Risering:
Riser acts like a reservoir or UPS. When power fails UPS
starts its function. Similarly, after pouring stops, risers
keep on feeding the liquid metal to the casting. It is very
important to have proper connections between riser and
casting. Otherwise, feeding shall not be effective.
II. NEED FOR OPTIMISATION
Optimisation is the process of finding the best way of
using your resources, at the same time not violating any of
the constraints that are imposed. By "best" we usually
mean highest profit, or lowest cost. Even after spending
significant resources i.e. man-hours, materials, machine
overheads and energy etc for casting development, one of
the following situations may arise during regular
production [2]:
(a) Under design: resulting in high percentage of defective
castings. This usually happens when the number or size of
feeders and gating elements are inadequate, or their
placement is incorrect. Sometimes the cause is an
undersized neck or a thin intermediate casting section,
which prevents feed metal flow from the feeder to the hot
spot inside the casting.
(b) Over design: leading to acceptable quality level, but
poor yield and thereby higher cost. In this case, the number
and/or size of feeders and gating elements are much higher
than their respective optimal values. This situation usually
arises because of lack of time or resources to fine-tune the
methoding solution or to try other alternative solutions.
(c) Borderline design: irregular defect levels during
regular production, although sample castings are defect-
free. This happens when the methoding solution is just
optimal (perhaps by accident), which will produce good
castings only under controlled conditions. This is difficult
to expect in practice, especially with manual molding and
pouring.
Foundries try to reduce rejections by experimenting with
process parameters (like alloy composition, mold coating,
and pouring temperature). When these measures are
ineffective, then methods design (gating and feeding) is
modified. When even this is not effective, then tooling
design (part orientation, parting line, cores and cavity
layout) is modified. The effect of any change in tooling,
methods or process parameters is ascertained by pouring
and inspecting test castings. Studies show that replacing
shop-floor trials by computer simulation saves time,
provides a better insight, and helps in reducing the
rejections [3].
III. CASE STUDY [4, 5]
1) Selected Product:
The selected product for the methoding design is Gear
Case Cover
• Material: FG 260
• Unit weight of casting: 7.20 kg
• Number of components poured in a box: 2
• Size of box:
– Cope: 4.5 inch
– Drag: 4.5 inch
• Shape of box: Rectangular
• Type of gating system used: Pressurized Gating system
For the component first of all the manual
calculations were done with the help of standard
formulae.
2) Geometric Model:
The input for the AutoCAST is the geometric model
created in the CATIA software. This model is imported in
the AutoCAST as the .stl format.
INSTITUTE OF TECHNOLOGY, NIRMA UNIVERSITY, AHMEDABAD – 382 481, 08-10 DECEMBER, 2011
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3) Procedure:
The following steps were performed on AutoCAST
software so as to get the Methoding for the casting i.e.
Gear case cover.
1. Import the solid model of the gear case cover in the
AutoCAST software. The 3-D model from CATIA is
converted in to the STL Format.
2. The model is assigned the material- FG 260.
3. The process selected as- Sand Casting.
4. The properties were calculated, which shows the surface
area, number of holes, volume, weight etc.
5. The parting line and parting plane is suitably adjusted
taking into consideration the ease of removing the pattern
from the cope and drag part.
6. The cored characters were generated.
7. For the whole assembly the mould box is selected as per
the company’s regular practice.
8. Next feeding function is carried out so as to know about
the possible areas which are prone to shrinkage. Probably
the area with the highest massive thickness is the area for
generation of shrinkage.
9. The analysis through it showed the two dominant areas
which were prone to the shrinkage and micro porosities.
10. For these areas to be taken care of the feeders were
provided as visible in the figures.
11. The number of ingates was finalized and the locations
also were finalized by us considering the cooling analysis
of the gear case cover.
12. The runner bar was designed so as to feed the molten
metal to the farthest point from point of metal pouring.
13. The sprue is designed.
14. The total model is created and the pouring is simulated.
Since the pouring time calculations showed that for gear
case cover the pouring time of around 8-12 seconds is
sufficient, the system was again designed for that much
second and simulation is carried out. This given the idea of
the sizes of ingates, runner, sprue etc.
15. The quality health checks were calculated.
Fig.2. Casting in case study The solid modeling is carried out in CATIA. The model is
imported in .stl format in AutoCAST (refer fig.3). The
areas for maximum and minimum section thickness were
checked (refer fig.4).The casting properties are then
checked. It showed the massive area where the hot spot
occurrence possibility is more (refer fig.5). A feeder is
arranged near this area so as to take care of shrinkage
arising out of hot spot (refer fig.6). The property analysis
showed that hot spots are still in casting. So there is need
to increase riser size (refer fig.7). Thus riser size is
increased (refer fig.8). Then it is observed that hot spots
are absorbed inside riser. So these dimensions are finalized
(refer fig.9). The tail end portion of casting showed small
hot spot so a chill is placed (refer fig.10, 11). The cross
section showed hot spots are minimized due to riser and
chill (refer fig.12). To take care of productivity concern
two castings in a single mold box are molded (refer
fig.13). The arrangement is adjusted so that a central
gating system common to both can be made (refer fig.14).
The pouring simulation showed the mould filling
phenomenon (refer fig.15). It is then observed that in this
methoding the hotspots are avoided and also the cross
section ensured the same fact (refer fig.16, 17). The final
methoding is then suggested (refer fig.18). Fig. 19 shows a
methoding system adapted as per given suggestions.
Fig.3. Casting solid model is imported in AutoCAST
Fig.4. Areas for maximum section thickness are checked
Fig.5. Massive section shows chances of hotspots
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Fig.6. A riser is provided near hot spot.
Fig.7. Hot spots absorbed partially in side riser
Fig.8. The size of riser increased
Fig.9. For increased riser dimensions hotspots are absorbed in riser
Fig.10. Chill is added to take care of hotspot at end as in fig.8
Fig.11. Hot spots absorbed in riser
Fig.12. Cross section of casting showing no hotspots
Fig.13. For productivity two casting in single box are added
INSTITUTE OF TECHNOLOGY, NIRMA UNIVERSITY, AHMEDABAD – 382 481, 08-10 DECEMBER, 2011
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Fig.14. The casting connected by runners
Fig.15. Simulation of mould filling
Fig.16. Hot spots in riser and methoding system
Fig.17. Cross section of assembly showing hot spot in riser
Fig.18. Suggested final methoding system
Fig.19. Final methoding system and casting
In the above cases number of iterations was carried out in
order to reach to the optimum dimensions of the feeders,
sprue, runners etc. The dimensions were optimized in such
a way that the yield can be maintained to its maximum
level. The process is carried out under the limiting
conditions of mold box sizes. To take care of productivity
two components were molded in single mold box.
Optimisation of dimensions leads to material saving.
The following are the advantages gained by using
simulation software for the design of methoding for
casting:
1. The time required is very less as compared to the
conventional method of design of methoding.
2. Number of options were made available to suitably
select the same.
3. The cost was much lower as compared to the
conventional trial and error method.
4. Visualisation of mold filling phenomenon makes the
process easy to understand to the user.
5. Hot spots were easily located where probable chance of
occurrence of defect was more.
6. The key parameters of the process were identified
easily.
7. The rejection due to the defects arising out of methoding
design was reduced to some extent.
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Thus the optimisation by using aid of simulation leads to
following noticeable outcomes.
In regards of costing we can say that,
1. Faster Design + Fewer Trials + Information Retrieval
=HIGHER OUTPUT.
2. Design for casting + Economic Tooling + Improved
Partnership = LOWER COST.
3. Higher yield + Reduced Scrap + Value Addition
= HIGHER PROFIT.
IV. CONCLUSION
Optimisation plays vital role in business. It is an effort
towards making the things run smoothly with efficient
utilisation of available resources. Optimisation is the
philosophy of life. When applied to the engineering sector,
that too to foundry it saves unnecessary wastage of
resources. This leads to the noticeable savings in terms of
cost.
V. REFERENCES
1. B. Ravi, “A Holistic Approach to Zero Defect Castings,” Technical
Paper for 59th Indian Foundry Congress, Chandigarh, February
2011.
2. B. Ravi, “Digital Methoding: Child’s Play? Yes and No.”,
Technical paper for presentation at Steel and Alloy Steel Castings
(SAS-2001), April 14-15, 2001, Mumbai.
3. B. Ravi and Durgesh Joshi, “10-Year Survey of Computer
Applications in Indian Foundry Industry,” Indian Foundry Journal,
56(1), 2010.
4. Harshwardhan Pandit, Sarvesh Naik,Nitin Patil, and Laxmi Nikam,
“Design for Methoding of Casting and Rejection Analysis”,
Production Engineering Graduation Dissertation Work at K.I.T’s
College of Engineering, Kolhapur, 2008-09.
5. Harshwardhan Pandit, “Casting Simulation Case Study- Gear Case
Cover (CI, GSC),”Indian Foundry Journal, 57(4), 2011.