The purpose of this paper is to re-design a lift truck frame (Chassis) with the optimum mass while maintaining stress constraints. The paper also demonstrate how Optimization techniques can be applied mainly when product is already launched in market and optimized design is to be implemented without altering any existing assembly fitment parameters /functional requirement.

1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 10, October (2014), pp. 45-56 © IAEME
45
STRUCTURAL OPTIMIZATION OF A POWERED
INDUSTRIAL LIFT TRUCK FRAME
Harshal D. Shirodkar1
, Dr. S.B.Rane2
1
Post Graduate Student, Sardar Patel College of Engineering, Mumbai-400058, India
2
Associate Professor, Sardar Patel College of Engineering, Mumbai -400058, India
ABSTRACT
Purpose: The purpose of this paper is to re-design a lift truck frame (Chassis) with the optimum
mass while maintaining stress constraints. The paper also demonstrate how Optimization techniques
can be applied mainly when product is already launched in market and optimized design is to be
implemented without altering any existing assembly fitment parameters/functional requirement.
Methodology: This paper describes the use of topology and size optimization technique using CAE
software OptiStruct of Altair Engineering to redesign Frame of a lift Truck and comparison of result
using alternate solver Radioss.
Findings: Up to 15% weight reduction in frame is achieved without altering any existing assembly
fitment parameters or compromising any functional requirements. Also considerable cost saving of
Rs.10000 per vehicle is achieved through this process.
Practical Implications: It is completely feasible to implement the optimized design in actual
practice/production & other organization can also benefit by implementation of similar process.
Limitation: This paper has limitation in terms of further optimization using all the features since the
design is already ready and the frame production is continued. Therefore the optimization cannot be
achieved through major change in the shape which may affect the existing production activities.
Originality/Value: This paper can help derive common methodology for optimization techniques
specific to Industrial Equipment and other Off-highway equipment like Earthmoving and
Construction equipments.
Type of Paper: Applied Research.
Keywords: Hyper Works, Lift Truck, Structural Optimization, Size, Topology.
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
AND TECHNOLOGY (IJMET)
ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 5, Issue 10, October (2014), pp. 45-56
© IAEME: www.iaeme.com/IJMET.asp
Journal Impact Factor (2014): 7.5377 (Calculated by GISI)
www.jifactor.com
IJMET
© I A E M E

2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 10, October (2014), pp. 45-56 © IAEME
46
I. INTRODUCTION
Optimization [3] is a mathematical technique that deals with computing minima or maxima
of functions subjected to design variables or constrains. There are essentially two stages of the
design process in which structural optimization [2] can be applied. In the early stage of concept
generation, topology optimization [1] should be used to develop an efficient structure from the
beginning. At this level, an automatize variation of optimization parameters is proven useful to find
the best feasible design possible. In the later stage, shape and size optimization [6] should be used to
fine-tune the structure realized from the topology optimization. Using optimization in this manner
gives great possibilities to save time; mass as well as it may produce innovative designs. As first
design step topology optimization is used for finding out proper material distribution followed by
size optimization for computing optimal thickness of structural members of Frame.
The whole challenging task, starting with pre -processing, solving and post processing is
completed using Altair’s HyperMesh, OptiStruct [4] and Hyper View FE package. Results are
compared using alternate solver of Altair Radioss [4] which are discussed in the concluding part.
II. PROCESS METHODOLOGY
Here is a simplified overview of the traditional design process and where the different types
of structural optimizations can be applied. There are basically two different areas where structural
optimization should be performed; in the early design phase where topology optimization is used to
generate a good concept and in the detailed design phase where size- and shape-optimization [7] is
used to further improve the structure.
1. Concept Generation
A flow chart for the concept generation is presented followed by a description of each step.
Choice of parameters and other details are discussed in the respective sections. The process of
concept generation should be seen as an iterative process where the problem formulation and design
domain is incrementally improved until the best possible solution is found. Refer Fig 1.
Figure 1: Flowchart – Concept Generation [4]

3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 10, October (2014), pp. 45-56 © IAEME
47
2. Detailed optimization Process
In this stage a CAD-model of the structure is available that is similar and have the same
topology as the end result. The objective in this stage is to fine-tune, or refine, the structure to make
it as good as possible. There are basically two different types of detailed optimization: size
optimization and shape optimization. Refer Fig.2
Figure 2: Flowchart – Detailed Optimization [4]
III. PRE-PROCESSING
In the pre-processing part, required surface model is created using Hyper Mesh. The FE
Model with design space for initial boundary condition is shown in Fig.3. Shells (QUAD4, TRIA3),
Solids (Hex 8) and rigid elements are used accordingly to define geometry and constrain conditions.
Out of different load cases, critical laden Static load case having maximum Stress value is
considered for initial structural optimization.
Figure 3: Meshing, Load & Boundary Conditions [5]

4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 10, October (2014), pp. 45-56 © IAEME
48
3. Material Details
Hot Rolled Structural Steel Specification as per IS 2062:2011 [10].
Grade: E250 A (Old Designation: Fe 410 WA)
Tensile Strength: 410 Mpa
Yield Strength: 240 Mpa
Young’s Modulus: 210 Gpa
Poisson’s Ratio: 0.3
Factor of Safety: 3 [Considered for Dynamic load Conditions]
Allowable Bending Stress: Y.S / F.O.S = 80 Mpa.
Allowable Deflection for Simply Supported Beam according to Deflection Span
Ratio [8] = Span L/360 = 2200/360 = 6 mm.
Additional safety factor of 1.1 is considered for each of above weight which considers the
overloading factor. For example the Counterweight is Cast Iron Component hence casting during
manufacturing can come above the desired weight or operator while lifting load may not exactly lift
rated load hence safety factor takes into consideration all these uncertainty.
4. Load and Boundary Conditions
Summary of loads on Frame are shown in the Fig.4 & Table: 1
1) Reaction force due to counter weight resting on structure
Total Force on each edge = 21500 / 2 = 10750 N
2) Force due to engine, transmission etc.
at their mounting:
Load on each Engine Bracket = 1408 N and
Load on each Transmission Bracket = 1343 N
3) Reaction due to steering (rear) axle to pivot
Load on each pivot = 40000/2 = 20000 N.
4) Upright load on the front bushing brackets.
Load on each bracket = 65000 / 2 = 32500 N
5) Force due to tilt cylinder operation.
Force on each cylinder = 35500 N.

5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 10, October (2014), pp. 45-56 © IAEME
49
Table 1
Component Weight in Kgs
Rated Load 5000
Lifting Mechanism
( Mast + Carriage + Forks)
1500
Front Drive Axle 300
Transmission 300
Engine 550
Rear Axle 145
Counter Weight 2150
Figure 4: Summary of Loads on Frame
IV. STRUCTURAL OPTIMIZATION
The structural optimization is carried out in three phases. In the first phase, Frame is subjected to
topology optimization. Depending on the density plots, material distribution with cut outs has been
finalized to reduce the weight. In the second phase, the Frame designed after topology run is used for
size optimization for computing optimal thickness of all the structural members. In third phase, the
output model is run for remaining load cases.
5. Topology Optimization
This present work adopts Density approach for optimal material distribution. Available
design space is defined with proper loading and boundary conditions with objective to minimize the
global compliance of the structure, subjected to mass constraint.
The density plot by topology run is shown in Fig.5.
The below mentioned criteria's are used for topology optimization.
Design variable : Density of each element within design space.
Design Constraint: Stress with specified limit.
Design Objective: Minimize the mass.

6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 10, October (2014), pp. 45-56 © IAEME
50
Figure 5: Topology optimization plot for critical load case [5]
6. Geometry Interpretation
Although the topology results appear reasonable, the design is definitely not ready to hand
over to the machine shop for fabrication. The results of the topology studies are merely rough
geometric proposals, and some interpretation is required to create the final design
Material removal was considered such that the material removed should be scraped but
utilized to fabricate other small brackets required on the Frame. The Geometry has given appropriate
result acting as cross member between two main Frame plate and transferring weight of
counterweight through the weldment ultimately to ground.
Refer Fig.6.
Figure 6: OptiStruct Proposed Topology Design & Final Geometry Extraction

7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 10, October (2014), pp. 45-56 © IAEME
51
7. Size Optimization
OptiStruct has the capability of performing size optimization. Size optimization can be
performed simultaneously with the other types of optimization. In size optimization, the properties of
structural elements such as shell thickness, beam cross-sectional properties, spring stiffness, and
mass are modified to solve the optimization problem.
The output design by topology optimization with introducing cutouts is set for size
optimization to get the optimized thickness of all structural members. The following criteria are
defined for size optimization.
The output thickness result are seen in Fig.7
Design Variable : Thickness of the components
Design Objective: Minimize mass
Design Constraint: Stress with specified limit
Design by size optimization is considered for remaining load cases followed by adjustment of
cut outs for maintaining C. G. location of Frame
Figure 7: Thickness values by size optimization [5]
7.1 Interpretation of results
The output *.out file contains a summary of the size optimization process. From the
information in the *.out file, one can see how the objectives, constraints, and design variables are
changing from one iteration to the next. Below Table 2 & 3 show excerpt from *.out file showing
Lower and Upper Bound Design variables converged to desired thickness. OptiStruct used six design
iterations to reach optimum shell thickness for given conditions.

8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 10, October (2014), pp. 45-56 © IAEME
52
Table 2: Result of Size Optimization
DESIGN
VARIABLE
I.D
DESIGN
VARIABLE
LABEL
LOWER
BOUND
DESIGN
VARIABLE
UPPER
BOUND
06 Inside P 8.000E+00 1.159E+01 2.000E+01
07 Inside P 8.000E+00 9.189E+00 2.000E+01
08 Outer si 4.000E+00 4.000E+00 1.200E+01
09 fender 6.000E+00 1.351E+01 1.600E+01
10 counter 1.200E+01 2.025E+01 2.400E+01
Table 3: Result of Size Optimization
DVPREL1/2 USER ID PROP-TYPE PROP-ID ITEM-CODE PROP-VALUE
DVPREL1 10 PSHELL 14 T 4.000E+00
DVPREL1 09 PSHELL 12 T 8.770E+00
DVPREL1 08 PSHELL 11 T 1.181E+01
DVPREL1 07 PSHELL 13 T 2.020E+01
DVPREL1 06 PSHELL 15 T 1.344E+01
V. FINAL RESULT AND CONCLUSION
8. Result Obtained After Topology And Size Optimization In OptiStruct.
After the size optimization, the stress value should be reviewed to make sure that the stress
constraints are not violated. Displacement and stresses results of optimized design are shown in Fig:
8 & 9 respectively.
Figure 8: Displacement plot with OptiStruct Solver [5]

9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 10, October (2014), pp. 45-56 © IAEME
53
Figure 9: Stress plot with OptiStruct Solver [5]
The work has shown how topology and size optimization tools can be used for the design of
Frame. Through optimization techniques weight of Frame is reduced by around 15% with no
significant increase in stress and deflection value. Comparative results for existing and optimized
design of Frame are tabulated in Table 4.
Table 4: Summary of Results
Weight(kg) Deflection(mm) Stress (Mpa)
Existing design 910 0.6 70.8
Optimized design 780 0.65 79.7
9. Result Compared Using Alternate Solver – Radioss
The analysis is carried in Radioss Solver & comparative results for stress and displacement
are shown in Table 5.
The Stress has increased marginally with no significant rise in deflection.
Figure 10: Displacement plot with Radioss Solver

10. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 10, October (2014), pp. 45-56 © IAEME
54
Figure 11: Stress plot with Radioss Solver
Table 5: Summary of Results
Solver Deflection(mm) Stress (Mpa)
OptiStruct 0.65 80
Radioss 0.68 86
9. Justification of Optimized Design
The stability of Lift truck is very important criteria which limits the value for reducing the
weight of the Frame. The Lift truck has to pass the various stability tests as per the guidelines in
Indian Standard IS 4357: 2004. [9].The location of C.G of entire Lift Truck is calculated with
reference to front drive axle as pivot point for calculating moment. Next, front & Rear laden as well
as un laden reactions are found.
Then Stability Ratio of the Lift Truck is calculated as below as per Industrial Norms of Lift
Truck Manufacturer:
Stability Ratio =
ோ௘௔௥ ௅௔ௗ௘௡ ோ௘௔௖௧௜௢௡
ோ௘௔௥ ௎௡௟௔ௗ௘௡ ோ௘௔௖௧௜௢௡
Stability Ratio Range between 25 to 28% is considered as Average Range.
Stability Ratio Range between 28 to 30% is considered as Desired or Optimum Range.
Mentioned range may vary depending upon the Tonnage of Lift Truck.
As calculated the values are as below;
Stability Ratio before optimization = 30.1%
Stability Ratio after optimization = 28.9%

11. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 10, October (2014), pp. 45-56 © IAEME
55
The significance of Stability ratio can be explained as below:
When the Lift Truck is un laden the front & rear reactions are approximately same since
weight is equally distributed. But when the rated capacity is lifted in front the entire C.G is shifted &
the rear reaction reduces.
Stability ratio of 28% means even after lifting rated load of 5000 kgs the reactions on the rear
wheels are not allowed to reduce to zero instead a buffer is maintained to compensate the dynamic
change in Laden C.G which take place when the load is lifted at various height and also tilted in
front by max 6° for stacking the load at maximum height of 3.5m.
10. Benefits Summary
1. With this approach, the design cycle time is reduced by 25%; the optimum configuration is
achieved directly through the use of OptiStruct optimization tool.
2. Cost reduction of Rs.10000/- per vehicle is achieved as a befit of this research activity.
3. The research has demonstrated a methodology of how to use optimization techniques when the
product is already in market & challenge is to implement optimized new design with far higher
strength to weight ratio to that of original design prepared without altering any existing
assembly fitment parameters/functional requirement.
11. Future Scope
1. Future scope would be towards implementation of Shape Optimization along with Topology
optimization to limit the design domain and shape in early phase of development.
2. Also Dynamic load conditions would be simulated so as to have optimum design which would
ensure excessive safety factor is not considered.
12. Acknowledgement
We would like to express our gratitude to Mr.Pinaki Ghosh, GM - Engineering R&D for
giving us an opportunity to work on this project in Voltas Material Handling Pvt Ltd, Pune and
providing the necessary approval for publishing this paper. Special thanks to Mr.Khusal Kesrod,
Design tech for his support and encouragement throughout this project. And last but not the least
senior Professors and colleagues from Sardar Patel College of Engineering, Mumbai for their
valuable guidance and constant encouragement towards completion of this research.
VI. REFERENCES
Thesis:
1. Martin Fagerstrom and Magnus Jansson, 2002, “Topology optimization in the design
process”, Master's thesis, Chalmers University of Technology.
Books:
2. Martin Philip Bendsoe, 1995, “Optimization of Structural Topology, Shape and Material”,
Springer-Verlag Berlin Heidelberg.
3. Singiresu S. Rao, 1996, “Engineering Optimization | Theory and Practice”, John Wiley &
Sons, third edition.
4. Altair Engineering Inc, 2009, “OptiStruct 10.0 help files”.

12. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 10, October (2014), pp. 45-56 © IAEME
56
Proceedings Papers:
5. Dr S.B.Rane, Harshal Shirodkar, P.Sridhar Reddy, 2013, “Finite Element Analysis and
Optimization of Forklift Chassis”, India Altair Technology Conference.
6. Gerald Kress and David Keller, 2007, “Structural Optimization”, Swiss Federal Institute of
Technology Zurich.
7. Marco Cavazzuti and Luca Splendi, “Structural optimization of automotive Chassis: Theory,
set up, design”, Mille Chili Lab, Dipartimento di Ingegneria Meccanica Civile, Modena, Italy.
Journal Papers:
8. Hirak Patel, Khushbu C. Panchal, Chetan S. Jadav, April 2013, “Structural Analysis of Truck
Chassis Frame and Design Optimization for Weight Reduction”, International Journal of
Engineering and Advanced Technology (IJEAT), ISSN: 2249 – 8958, Volume-2, Issue-4.
Standards:
9. IS 4357:2004,Methods for Stability Testing of Forklift Truck, The Bureau of Indian
Standards (BIS)
10. IS 2062:2011, Hot Rolled Medium and High Tensile Structural Steel, The Bureau of Indian
Standards (BIS).