Finite Element analysis and Optimization of an Forklift Chassis

Transcription

1 Finite Element analysis and Optimization of an Forklift Chassis Dr S.B.Rane Associate Professor Department of Mechanical Engg. Sardar Patel College of Engineering Harshal Shirodkar Assistant Manager- Design Voltas Material Handling Pvt. Ltd., 5/4 Chandan Nagar, Pune P.Sridhar Reddy Senior Design Engineer (CAE) Voltas Material Handling Pvt. Ltd., 5/4 Chandan Nagar, Pune Keywords: CAE-Computer aided Engineering, HW-HyperWorks, optimization, size, topology, forklift. ABSTRACT This paper describes use of optimization technique to redesign Chassis (Frame) of a Forklift Truck. Forklift trucks are all about space constraints, there are dimensional limits and must be able to reduce the overall package size and still lift the same amount of load. Different load cases with given boundary conditions & loadings are used. Study of optimum material distribution gives an idea of load flow path based on which new design with far higher strength to weight ratio to that of original design prepared without altering any assembly fitment parameters/functional requirement. This paper is part of project work undertaken in Voltas Material Handling (VMH ) Pune (Kion Group Company GmbH), The Voltas brand is one of the leading suppliers of material handling equipment in India. The product range includes diesel trucks, LPG trucks and electric forklift trucks with load capacities of 1.5 to 16 tonnes plus warehouse trucks. INTRODUCTION: This paper deals with design optimization of Forklift Chassis with the aim of reducing weight for specified loads, constrains and design space. Optimization is a mathematical technique that deals with computing minima or maxima of functions subjected to design variables or constrains. 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 Chassis. Results are discussed in the conclusion part. The whole challenging task, starting with pre processing, solving and post processing is completed using Altair s HyperMesh, OptiStruct and HyperView FE package Simulate to Innovate 1

2 Process Methodology In the pre-processing part, required surface model is created using HyperMesh. The FE Model with design space for initial boundary condition is shown in Figure 1. Shells (QUAD4, TRIA3), Solids (Hex 8) and Rigid elements are used according to define geometry and constrain conditions. Out of different load cases, critical load case having maximum Stress value is considered for initial structural optimization. Flowchart showing methodology to achieve optimization. Fig 1.Chassis FE Model_ elements shows design space Simulate to Innovate 2

3 Structural Optimization The structural optimization is carried out in three phases. In the first phase, Chassis 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 Chassis 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. Topology Optimization This present work adopts Density approach for optimal material distribution. Available design space is defined with proper loading and boundary conditions (figure 2) with objective to minimize the global compliance of the structure, subjected to mass constraint. The density plot by topology run is shown in figure. 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 Fig 2.Topology optimization plot for critical load case Simulate to Innovate 3

4 Size Optimization 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 details at front of tilt beam are shown in figure:3. Design Variable : Thickness of the components Design Objective : Minimize mass Design Constraint : Stress with specified limit Figure 3: Thickness values by size optimization Design by size optimization is considered for remaining load cases followed by adjustment of cut outs for maintaining C. G. location of Chassis. The optimized design of Chassis is shown in figure: 3. Displacement and stresses results of optimized design are shown in figure: 4 & 5 respectively Simulate to Innovate 4

5 Figure 4: Displacement plot Results and Conclusion Figure 5: Stress plot The work has shown how topology and size optimization tools can be used for the design of chassis. Through optimization techniques weight of chassis is reduced by around 14.5% with significant change in deflection value. Comparative results for existing and optimized design of chassis are tabulated below Weight(kg) Deflection(mm) Stress (Mpa) Existing design Optimized design Result Summary Simulate to Innovate 5

6 Benefits Summary With this approach, the design cycle time is considerably reduced; the optimum configuration is achieved directly through the use of OptiStruct optimization tool. The methodology developed here has helped for other structural requirements also. Future Plans Now after this success of this analysis we have planned to implement similar methodology for future projects. ACKNOWLEDGEMENTS 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 and providing the necessary approval for publishing this paper. Special thanks to Mr.Khusal Kesrod,Designtech for his support and encouragement through this project. REFERENCES 1. Altair Engineering Inc. Optistruct 11.0 help files, Gerald Kress und David Keller.Structural Optimization,Swiss Federal Institute of Technology Zurich, Singiresu S. Rao. Engineering Optimization Theory and Practice. John Wiley Sons, third edition, 1996 Simulate to Innovate 6