Tube Hydroforming using Marc from MSC.Software

Hydroforming is a metal forming process in which pressurized fluids are used to form the workpiece into desired shape. In a tube hydroforming process, a straight or a pre-bent tubular blank is used as the workpiece to be formed into desired shapes. While hydroforming has been used in aerospace industry for over three decades, it has been gaining popularity in the automotive and other higher volume production applications like exhaust manifolds, aluminum axles, chassis and body components, bellows, T-junction tubes etc. due to several advantages it provides, including

Ability to form complex shapes and contours, Fewer components to join for the final product leading to

reduced finishing costs, Lighter products while maintaining structural strength, and Reduced spring back compared to other forming

processes.

Hydroforming process

During a tube hydroforming process, a blank (tube) is introduced into the die and the die is closed prior to introducing the fluid. As the fluid pressure is increased, cross section of the tube expands and takes the shape of the die. In order to enable the material flow more freely, ends of the tube may be pushed in by applying additional load. The applied fluid pressure varies depending on the size and shape of the final form and also thickness of the blank and ranges from 10000 psi in low pressure hydroforming applications to 80000 psi in ultra high pressure applications.

Simulation for Hydroforming

While hydroforming offers several compelling advantages, it also involves use of relatively expensive equipment and multiple trials. Due to high pressures involved, hydroforming does not lend to trials using soft tooling. As modifications to the tools can be costly, it is important to get the design right the first time. There is also a lack of field knowledge for the process due to its relative recency in industry. Virtual manufacturing solutions like Marc offer the advantages of simulation of the process without expensive tooling costs.

Tube hydroforming

Final shape of the die

Marc, the leading nonlinear FEA solution offered by MSC.Software, is well suited for hydroforming simulation because of its ability to model nonlinear materials that undergo large deformations and strains and also due to its ease and simplicity of contact set up. The implicit technology used for the solution also helps with improved springback calculations, which are crucial in any forming process.

In addition to superior solver technology, Marc offers the advantage of automatic remeshing of the work piece to help achieve an accurate solution with fewer iterations. As the work piece experiences large deformation during forming, the elements used to model it tend to get distorted excessively, leading to failure of simulation. In order to overcome this limitation inherent to several nonlinear FEA codes, Marc offers an automatic remeshing and rezoning capability whereby the distorted mesh is replaced by a better quality mesh and the results are mapped onto the new mesh and the analysis is continued.

Here are two examples to demonstrate the use of simulation to help you design better products.

Bellows Hydroforming

Bellows are thin-walled flexible tubes often used to operate as piping expansion joint helping absorb expansions due to thermal gradients and also to absorb vibration in the piping systems. Some of the applications include HVAC and other piping systems.

Since the bellows are axisymmetric in shape, a 3D analysis is not required here. Axisymmetric shell elements are used and a pressure is applied on the shell elements to expand the work piece to conform to shape of the die. Simulation enables users to identify the required pressure, thickness distribution and also the axial force that needs to be applied for appropriate feeding of the material. With Marc’s superior capabilities, users can also estimate the spring back and adjust the process parameters.

Bellows tube – Final shape with plastic strain fringe plot

T-section Tube

Tube hydroforming is very efficient at shaping a round tube into any desired cross-section that could vary across the length of the tube. A T-tube that can be formed using this process eliminates joining processes like welding required by other processes and can also lead to a lighter structure.

In this example, the work piece is a tube, but the desired shape is non-axisymmetric. Hence a 3D analysis is required to simulate this process. However, as the tube deforms, the elements get stretched and undergo large distortions. In order to overcome this problem, a very fine mesh needs to be used in regions of high distortion, which is unknown at the start of the analysis. To overcome this difficulty, Marc offers automatic remeshing functionality, whereby the poor mesh is replaced by a better mesh enabling the analysis to run further and with improved accuracy.

T-junction – Final shape with plastic strain fringe plot

Summary

Marc offers several advantages in simulation of hydroforming, including:

Accurate springback calculations, Automatic remeshing for improved accuracy and

productivity, Ease of contact setup for improved productivity, and Ability to account for the prestresses created during the

forming process for structural analysis of the component.

Aided by the superior quality results of Marc, users can optimize the process parameters and the die and blank geometry, to realize material savings and improved designs.