Control Distortion in Your Body in White Assemblies

Shorten your time to market and minimize manufacturing planning, tryouts, and fabrication validation costs with welding & assembly simulation

by Dr. Saurabh Aggarwal
unibody car chassis istock final

When optimizing a product, it’s easy to forget how the manufacturing process can impact the design’s performance. Therefore, to properly optimize a product’s design, engineers need to understand how that product will be manufactured and assembled and how these processes might create unexpected distortions in the final product.

“Virtual Prototyping enables design and process engineers to virtually manufacture and assemble components long before their physical prototypes are built and tested,” said Yannick Vincent, Solution Manager at ESI Group. “It facilitates the creation of countermeasures to control distortions and residual stresses in Body in White (BIW) welded assemblies. It also shortens time to market and minimizes the cost of manufacturing planning, tryouts, and pre-production validation.”

ESI Group’s Virtual Welding & Assembly Solution is a computer-aided engineering (CAE) platform that studies the effects of stamping, welding, and assembly processes on BIW assemblies distortions during product development. The solution helps engineers to simulate and mitigate the residual stresses, distortions, and defects by modeling the chained manufacturing process.

“The goal is to ensure the dimension accuracy of BIW assemblies throughout the product development journey. You can identify the critical joints, perform virtual try-out of different clamp locations, weld and clamp sequences optimization while minimizing the cost and time for manufacturing planning and pre-production validation” explained Saurabh Aggarwal, Manager of Market Strategy and Business Development at ESI Group.

How Manufacturing Effects Add Dimensional Inaccuracies in BIW Assemblies

It can be a long, hard and expensive journey designing a product and its production chain. Engineers will need to tweak the product and its production process multiple times before residual stresses and distortions are controlled.

“During the stamping process, plastification leads to material hardening and thinning. Unloading also creates springback. These all lead to residual stresses and distortions” explained Saurabh. “In the case of hot forming of steel alloys, phase transformation takes place. All these effects have a significant influence on the assembly behavior of parts during cold and hot joining processes in welding and assembly body shops.”

“In other words, mechanical load and heat effects of the welded assembly process modify material characteristics and introduce residual stresses, which leads to dimensional inaccuracies in the welded assemblies,” clarified Saurabh.

Typical body shop issues during validation of assemblies

Traditionally, these structural influences on the product were mitigated with manufacturing and engineering ‘gut-feeling’ modifications to the production processes. However, this level of trial and error isn’t efficient or accurate.

“The optimization of the clamping tools without simulation is a very difficult task— more clamps mean that more stresses are conserved in the structure, which is completely contrary to the goal,” said Yannick. “The fewer clamps, the more distortion develops, but the tolerances need to be kept. ESI’s Welding & Assembly Solution helps process engineers find quickly the best compromise.”

CAE tools, like Welding & Assembly Solution, can iterate through fixes to the production issues faster and without costly physical trials. This helps engineers better predict and correct the deformations. Simulation makes it much easier to sequence welds and pre-bend a clamped part so that the part will fit within specification once the welding is completed.

How to Virtually Model a Production Process with ESI Group’s CAE Technology

First, engineers can use ESI PAM-STAMP to simulate the stamping of parts from thin metal sheets. The output from the simulation tool is the plastic strain, stresses, and variable thickness, along with the deformed mesh. This information and the post-stamping deformation mesh are then imported into the ESI’s Welding & Assembly Solution.

“If you are in the pre-production stages when you already have the stamped parts and doing the physical try-outs for assembly processes to control distortions,” said Saurabh. “In such cases, you can also use the scanned geometry of stamp parts to start the welding & assembly simulation.”

“Sometimes the distortions cannot be reduced as expected and parts have to be compensated. In this case, design engineers must compensate for the deformed shape on the welded assembly side because doing so on the stamping side would be either very costly or highly impractical,” explained Saurabh.

ESI SYSWELD simulates the entire assembly and welding process chain in the body shop

ESI SYSWELD imports the deformed mesh after stamping,” said Vincent. “Stamped key data results, such as plastic strain, stresses, and variable thickness, are mapped. Then, subsequent simulations for prepositioning, holding and joining are performed. To chain simulations, key data and results must be transferred and mapped from stamping to prepositioning to clamping and finally to the welding simulation model. In order to reduce the time needed to perform such operations, CAT (Control Adapt Transport) is available.”

ESI SYSWELD provides dedicated workflows to include every design feature of a welding assembly process (pre-positioning, holding, and joining chained manufacturing).

The prepositioning advisor helps engineers to define a reference point system (RPS) by creating guides, locators, and fixtures/clamps. The advisor defines how the clamps will close the gaps between the components before they are joined. Engineers have access to various parameters that define the type, shape, number position, offset and sequence of clamps. Engineers can tweak these parameters until they are optimized to limit product stress and deformities.

“Finally, the user can export the deformed mesh, residual stresses and plastic strain from stamping, prepositioning and holding processes to simulate the welding operation with the defined weld properties,” said Vincent. “Depending upon the case, seam (laser and arc welding) and spot-welding effects can be taken into account.” This simulation determines the final distortions and residual stresses from the chained stamping and welding & assembly processes.

After assessing the manufacturing of the product, the user can employ further simulations to explore the product’s durability and performance in the field.

“In a nutshell, structural distortion, residual stress, plasticity behavior and phase transformation of hot and cold joined assemblies are predicted during chained manufacturing processes,” clarified Saurabh.

“The change of thermal, metallurgical and mechanical properties in a structure during chained manufacturing is thoroughly analyzed and countermeasures are taken to control the distortions and residual stresses,” he added. “The benefits include reduced costs in both design and manufacturing as physical prototyping and testing is dramatically reduced.”

Original article written by Shawn Wasserman for

For more information visit ESI's Virtual Welding & Assembly Solution

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