One step and Incremental Forming Simulation of Rear Axle housing

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1 One step and Incremental Forming Simulation of Rear Axle housing Gaurav Sirsaj Project Lead Dana India Technical Centre S No 279, Hinjewadi Phase II Pune India gaurav.sirsaj@dana.com Kutboddin Algur Senior Project Engineer Dana India Technical Centre S No 279, Hinjewadi Phase II Pune India algur.kutboddin@dana.com Abbreviations: FE Finite Element, CAE Computer Aided Engineering, CAD Computer Aided Design, OEM Original Equipment Manufacturer. Keywords: Hot forming, Simulation, % thinning, formability Abstract Automotive product design cycles are getting shorter by the day. In any design process, weight, tooling cost and design cycle time of the product are key factors. Time efficient optimized design solutions through CAE is the main focus area for OEM's and suppliers. In various structural design problems, decision of best feasible design considering material layout and manufacturing aspects is the most difficult task. To achieve this, it is required to integrate manufacturing processes into CAE simulations. HyperForm provides the capability to drive this to take effective product decisions in the less time and thus helps to shorten the development time. Dana India Technical Centre used Altair HyperForm tool to simulate one step and incremental forming simulations. It helped to determine percentage thinning and formability for the initial layout of the rear axle housing. This study also provided guidance for forming supplier reviews in early design phases and fine tune the forming process parameters. With this tool, Dana India could come up with final design in quick around time and helped to reduce the prototype cost. Proposed developed forming simulation using HyperForm seems very promising in terms of significant reduction in the time and effort required to achieve performance targets. The method has been validated and has shown immense savings in turnaround time and hence, will be deployed for all future development work. Introduction The objective of this research work was to develop an effective strategy for accurate finite element simulation of hot forming processes and carry out simulations for a rear axle housing geometry and compare the results with corresponding experimental/scanned data. Rear axle housing is a structural member which carries the vehicle weight whose thickness varies from 6-16 mm. This housing is formed by multistage hot forming (mostly in 2 steps). In 1 st step the blank gets housing shape whereas in 2 nd step it gets final required feature. Hot forming is the plastic deformation of metal at a temperature and strain rate such that recrystallization occurs simultaneously with deformation, thus avoiding strain hardening. For this to occur, high workpiece temperature (matching the metal's recrystallization temperature) must be attained throughout the process. Hot forming is a good technology in the automotive industry used for the manufacturing of lightweight crash resistant/fatigue resistant parts with ultra-high strength. The Finite Element (FE) simulation of hot forming should consider the combined effects of thermal, mechanical, and microstructural fields. As a result, simulation of hot forming is a complex process and requires detailed information on various factors such as material properties, process parameters and the right choice of software code. Some of the benefits of hot forming are - 1. Reduction / elimination of subsequent machining. 2. Generally high productivity. 3. Facility for integration of several functions / geometries in a single component. 4. Minimal process, logistic and transport costs. As per industry practice, the housing is formed at supplier end and the initial formability check is done by them. In case of any modification, supplier suggest those changes based on feasibility and OEM s perform the necessary design modification and send it back to the supplier for the formability check. Once the design is finalized, die and punch is setup and forming process starts. To reduce this to and fro process and overall development time, Dana India has initiated hot forming simulation inhouse. 1

2 Process Methodology PART GEOMETRY ONE STEP FORMING FOR BLANK CREATION STAGE1 INCREMENTAL HOT FORMING STAGE2 INCREMENTAL HOT FORMING (RESTIKING OPERATION) COMPARE RESULTS WITH SCAN MODEL Figure. 1: Overview of forming methodology Hyperform 14.0 Incremental hot forming module was used for formability analysis. Hot forming component Rear axle housing half Mechanical and Thermal properties used 1. Coefficient of friction 2. Convection Coefficient 3. Emissivity 4. Forming Speed 5. Blank transfer time 6. Tool approach time 7. Quenching time 8. Conductance 9. Material: Hot forming with strain rate (from material database) 10. Initial Blank Temperature 11. Tool Temperature 12. Material thickness 13. Element type: a. Blank Shell b. Tool Rigid shell 2

3 One step forming - Blank creation: Figure. 2: Forming process Housing half CAD model is imported in Hyperform 14.0 One step module. Mid-surface of CAD model is extracted and meshed with R-mesh. One step crash form setup is analyzed to obtain blank shape. Stage-I Incremental hot forming: Blank shape obtained from one-step forming is used as an input for first stage incremental forming. Die, punch and blank are meshed with R-mesh. Blank is meshed with fine elements whereas die and punch are rigid, there is no need to do fine meshing. Using hot forming crash-form module, all the parameters to the model are assigned. The model is solved by using Radioss solver. Stage-II Incremental hot forming (Restriking operation): Blank shape formed after first forming is used as an input for second stage incremental forming (*. sta file is imported). Die and punch of second stage is meshed similarly as in first stage. Using hot forming crash-form module, all the parameters to the model are assigned. The model is solved by using Radioss solver. Result comparison with scanned geometry: % thinning results were compared with actual formed physical component s scanned geometry. Dimensions at various cross sections were measured and compared the results with formed results at same locations. 3

4 Results & Discussions One step results: Figure. 3: Blank shape Figure. 4: %Thinning Figure. 5: Formability Check From one step forming, we can get good results of blank shape and formability check at initial stage of designing but % thinning results are conservative. 4

5 Incremental forming results: Figure. 6: %Thinning Results Benefits Summary Finite Element (FE) simulation of hot forming offers several advantages for the automotive industry and for organization as well. Some of them are stated below - 1. To check the feasibility in terms of formability and % thinning. 2 Reduce number of iterations at supplier end. 3 Reduce development time. 4 Achieve optimum design. 5 Developed forming Simulation capability. Challenges The key challenges faced during the setup of methodology are listed below: 1. Supplier is having reservation in sharing proprietary information. 2. Different suppliers may use different input parameters / different software, which will cause difference in results. 3. Availability of die and punch geometry is difficult. 4. Availability of strain rate material curve. 5

6 Future Plans The future scope based on the current work done are as follows - 1. To perform incremental forming with solid elements to achieve more accuracy. 2. To perform spring back analysis to achieve residual stresses. 3. Result Mapping. 4. A methodology for hot forming tool design and optimization should be developed. Conclusions 1. With the current skills, Dana India can perform simulation for newly developed components using Hyperform. 2. This has improved design capabilities. 3. This will reduce iterations at supplier end. 4. Analysis time for one iteration is around 20 minutes and easily carried on any desktop machine. 5. Set up a work flow for forming simulation process. 6. Can provide the optimal blank positioning on the forming strip, this is value addition for supplier. ACKNOWLEDGEMENTS The author would like to thank Mr. Pavan Kallurkar, Technical Manager, Altair team for valuable tips on hot forming process. Sincere thanks to Mr. Umesha Gangarudraiah, Deputy General Manager, Dana India Technical Centre for going through the draft paper and offering valuable suggestions. REFERENCES [1] Sheet Metal Forming (Processes and Applications) Edited by Taylan Altan and Erman Tekkaya [2] Altair Hyper Works manual 14. 6