Finite Element Analysis of Variable Thickness Disc Wheel Rim for Weight Optimization

The objective of this paper is to introduce light weight wheel rim by opting variable wall thickness of wheel disc without affecting its key functions and life. Wheel rim 3D model prepared in Pro-E software. Linear static structural analysis of wheel rim were performed in FEM ANSYS software to determine stress level at various loading conditions, given boundary conditions to optimize disc thickness, weight, cost of wheel rim. The results of the FEA analysis to validate with the experimental test results. Keywords— Wheel rim; Wheel rim disc; Variable thickness; Pro-E design; FEA.

INTRODUCTION A wheel rim is a highly stressed component in an automobile that is subjected to bending and torsional loads. Since it is subjected to high stresses and demand of long life, light in weight, which it becomes very important to select right material and manufacturing process in rim design. There are competitions among materials and manufacturing processes due to cost performance and weight. The main components of the wheels & tire system aggregates is the wheel rim. Performance of wheel rim directly affects the vehicle performance and safety. Wheel rim size selection is based on tire size used in vehicle, It has standard catalogue -JATMA which recommends standard wheel rim size accordingly.
Tata 1109 ILCV Vehicle recommended wheel rim size is 6.5 x 20 is as per JATMA standard for 8.25R20-14PR tire size. Wheel rim was taken for weight optimization analysis and experimental study purpose refer below three piece wheel rim figure no.1 In this perspective expecting wheel rim design with significant mass reduction without compromise in its function and performance. The above wheel rim weight can be reduced by recognizing various stress regions and corresponding changes in wheel rim design. Rim material can be removed wherever is lower stress region and has low vehicle load effect.

II. PROBLEM STATEMENT
Currently Tata 1109 ILCV vehicles recommended wheel rim size has higher weight, cost which need to be analyze and optimized under finite element analysis. Analysis of wheel rim to determine the material removal area, changes in von misses stresses and deformation for current and modified rim design within given boundary condition to gain significant advantages for lighter mass vehicle wheels.

III. METHODOLOGY
The methodology involves technology for performing the designing and analyzing of the object.
• Design and modeling of three piece wheel rim

Analysis by ANSYS
• Analysis to perform at various load condition on existing and modified rim design.

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Analysis of wheel rim under boundary condition to obtain deformation and von misses stresses of model.

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Obtained optimized wheel rim and compare with existing model.

i) Three Piece Wheel Rim Optimization Scope -Design
The following are the design changes incorporated to reduce the wheel rim weight, cost and improve its performance: • Increase in nave thickness to avoid crack initiation in the region due to fretting. • Variable disc thickness to reduce weight and cost of rim. • Increased cold working effect on the product.
• Optimized brake drum clearance thru variable thickness. • Wheel rim flow forming manufacturing process.     Optimized wheel rim design proposal made based on Finite element analysis (FEA). Wheel disc thickness increased at the region identified to have higher stress and gradual reduction of material thickness at lower stressed regions. The modification in the design is shown in the Fig. 5 and 6.
Following design changes to be incorporated to reduce rim weight and also simultaneously improve its performance: • Increase in nave thickness to avoid crack initiation in the region due to fretting • Variable disc thickness to reduce weight, cost of the product and new process of variable disc increased cold working effect on the product. • Improvement in brake drum clearances.

Meshing and Boundary Condition for Wheel rim
Meshing and boundary condition applied in ANSYS to reduced degree of freedom from infinite to finite with the help of discretization or meshing (Nodes & Elements). Wheel rim flange were fixed and cornering load applied.

Wheel Rim Stress Distribution and Analysis
The wheels were loaded due to cornering and lateral effect and same was simulated at various test conditions and accordingly results are obtained. FEA evaluated displacement at each node of wheels according to the initial boundary conditions from which the strain can be calculated and then using Hooke's law the stress at that point can be calculated using the Young's modulus of the material of the wheel. •

VIII. RESULTS
The following table no. 5 shows comparative stress analysis results of existing as well as modified three piece wheel rim design with various load cases & boundary conditions.
• Peak stress is at the vent hole region for existing wheel rim with the thickness of 11 mm, by introducing variable thickness about 10 mm at same location the stress level can be brought down to 5 %.

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Variable disc thickness achievable with an advanced manufacturing technique called the flow form / spinning process. This process facilitated the vent hole position in a single plane with adequate ventilation area and the reduction in stresses was also noticed.

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With modified wheel rim design weight is reduced from 42.4 kg to 36 kg per wheel, which is approximately 16 % without affecting functional requirement.