Hydroforming Simulation: Becoming Cost Effective
Finding out how process variables affect hydroformed products and hydroforming equipment can cost less on a computer than in a tryout press room. It can also avoid expensive design changes because of forming process problems.
By Harjinder Singh, General Manager, HydroDynamicTechnologies Inc., Auburn Hills, MI
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Computer simulation to predict thestructural performance of components, assemblies and complete vehicles is widespread in the automotive industry. Detailed Finite Element Models are created and used to predict structural performance in crash-worthiness, injury criteria, vibration, and durability. The application of Finite Element Analysis (FEA) and other computer-aided engineering techniques to product design at an early stage inthe design cycle significantly reduces the time to take a vehicle from concept to production.
Similar gains and understanding of the tubular hydroforming process can be realized by the application of computer simulation FEA techniques. Results from the analysis can be used to optimize product and hydroforming tool design and hydroforming process parameters. The objective is to producecost-effective, optimized, hydroformed-component design. This article discusses hydroforming process steps that can be successfully simulated using LSDYNA3D or similar computer programs.
Figure 1. FEA model with all controlling tool surfaces to represent the bending setup
The main advantages of tubular hydroforming over conventional manufacturing techniques are reduced weight and reducedcomponent and assembly costs. In order to achieve and maximize these advantages, component design, material choices, and the hydroforming process must be addressed early in the design process. This must be done before the tool design and prototype tryout. Otherwise, last minute changes driven by trial-and-error prototype development will compromise the design and some advantages will be lost. By theprototype stage, it is often too late to modify component design. Then premium material, lubrication, pre-forming, or expensive heat-treatment steps may have to be added to the process. Hydroforming process limitations must be predicted early in the design cycle so expensive, late decisions can be avoided. One method of achieving this is to conduct a timely computer simulation. Hydroformingprocess simulation results--displacements and stresses--can also be carried forward to be used in further FEA for product performance assessment. Hydroforming tool structural integrity can also be assessed using FEA prior to building the tool.
Hydroforming Process Steps
Before conducting an FEA-based computer simulation, it is important to understand the process steps and material parameters that mustbe represented in the simulation model. To model the hydroforming process, the simulation program should be capable of accurately representing:
• Tool geometry
• Tube material properties in the forming range
• Surface interactions between part and tool
• Internal fluid pressure
• Boundary constraints required to represent tool and part motion
Commercially availablecomputer programs, such as LSDYNA3D and PAM-STAMP, are routinely used for forming simulations. These programs also can be successfully applied to understand hydroforming processes.
To fully comprehend hydroforming, one needs to understand what is happening to the material through the following processes:
• Tube rolling (manufacture)
• Tube bending