Sheet Metal Forming Simulation Solidworks

[Taj Barnett]

The3DEXPERIENCE WORKS Simulation portfolio includes the ability to simulate the metal-forming process. The products can be leveraged on SOLIDWORKS models when connected to the 3DEXPERIENCE platform.

Forming processes may include stamping, punch stretching, forging, drawing, and more. Truth be told, simulating forming processes can be a difficult task. Usually because they involve geometric, material, and contact nonlinearities.

However, simulation of forming processes offer advantages that outweigh the difficulties. Forming simulations can reduce both the cost and length of a product development cycle by identifying potential problems prior to tooling or fabrication.

Simulation can also improve the quality of the part being manufactured through testing to ensure that the manufacturing processes appropriately account for spring back, stretching of the parts, and thickness reduction.

Forming simulation tools on the 3DEXPERIENCE platform recreate manufacturing processes virtually to check for potential problems such as thinning, wrinkling, or cracking. This enables you to adapt on the fly during development, which often eliminates the need for multiple physical prototypes. Plus, you can experiment with different kinds of materials to see how they will behave in the real world (virtually) and then decide which material works best for your application based on actual performance. Also, you can test process parameters such as manufacturing speeds or temperature levels.

Metal forming simulations are numerically challenging because you will often see large deformations, plasticity, or complex contact situations (with large sliding interactions and friction) which makes for highly nonlinear simulation studies.

The 3DEXPERIENCE WORKS portfolio of simulation solutions provides additional tools for your FEA tool belt. When you encounter simulations in SOLIDWORKS that demand a deeper level of nonlinear studies, you can simply reach for another tool, in this case, the explicit solver within 3DEXPERIENCE to validate forming processes that will increase the efficiency and speed of your product development process.

Click here to watch the forming simulation technical webinar that will walk you through the part development process and demonstrate how forming simulation recreates the manufacturing process virtually. If you would like more information about simulation for metal forming processes, please contact your local reseller.

The use of sheet metal bodies in SOLIDWORKS Simulation provides a streamlined study setup workflow. The nature of sheet metal geometry leads to the utilization of shell elements to represent their shape in a simulation study.

The use of solid elements is prohibitive due to the large aspect ratio difference between the span and thickness of sheet metal bodies. Their usage would lead to very large mesh size and corresponding computational effort. Shell elements allow for the creation of a mesh with high surface fidelity while limiting the required system resources needed for the calculation. This document will cover how sheet metal bodies can be used to simplify the creation of linear static analysis.

A planar surface is selected in the convert to sheet feature to represent the fixed surface for the flat pattern. Model edges can be selected to specify where the bends will take place. The software will automatically rip appropriate edges so that the body can be flattened properly. A sketch can also be used to create a rip across a solid surface so that it can be unfolded.

During the creation of a linear static analysis, sheet metal bodies are automatically converted into shell entities. A surface body is created at the mid-plane of each sheet metal body for utilization in the shell definition and the offset condition is set to middle surface. The shell thickness is tied to the thickness defined for the sheet metal body and cannot be manually changed. Changing the thickness of the sheet metal body at the part modeling level will update the shell definition. This process ensures that the resulting shell mesh will always match the underlying solid geometry during the calculation.

The global no-penetration contact condition does not apply to contact regions involving sheet metal bodies meshed with shell elements. Local no penetration contact sets need to be created and will work for the following scenarios:

Using sheet metal bodies simplifies the workflow of setting up boundary conditions since fixtures and loads can be applied to any edge or surface on a sheet metal body. A fixture or load that is applied to the exterior surface of a sheet metal body is projected onto the mid-surface of the shell mesh created for the sheet metal body. A boundary condition applied to the thickness surface of a sheet metal body is projected onto the edge of the mid-surface shell mesh.

Meshing sheet metal bodies with shell elements greatly reduces the overall size of the mesh. Shell elements only mesh the exterior surfaces of sheet metal geometry and take into account the thickness during the calculation. The number of elements and nodes in the mathematical model is dramatically reduced by not having to mesh the volume of a sheet metal body. This limits the number of degrees of freedom in the calculation resulting in greater computational efficiency.

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There are several Sheet Metal Forming tools available in the Design Library that can be easily dragged onto a Sheet Metal part to add features. Just be aware that SolidWorks Sheet Metal does not account for material deformation during the forming process. The part will have a uniform thickness through the formed feature even if the process would cause the material to thin or stretch. By default, these features will remain visible when the sheet metal part is flattened but there are additional options to show the blank without the features.

You also have the option to generate a forming tool from scratch with your own shapes and settings. A single forming tool can have multiple configurations for various sizes. Watch the video below showing the steps to generate your own tool.

Currently we can't model these products in the same way tooling shapes sheetmetal, therefore we can't make a properly realistic digital prototype. Without a proper digital prototype, all sort of downstream capabilities are shot as well. Example: I can't begin to run simulation on a soda can that doesn't correctly reflect the thickness of the material, or the progression of thick areas to thin ones.

For many years I believed this pipe-dream was never going to happen because of the complex maths involved. However now that Nastran is a piece of Inventor, I actually think this door is opened. It would probably require the Nastran solver to correctly model the material based on the geometry of a tool applied to it. Essentially we would be using Nastran to complete the feature, promoting the deformed shape of the simulation back to the parametric model.

1. Most of people designing with Inventor understand the limitation of the software and do understand the real world of sheet metal bending and deep drawning. The model you get is a good approximation of the final object.

2. If you do not use FEA, like the embedded Nastran In-CAD, you will need a powerful calculator that will consider material properties, including hardness, that will affect actual part geometry. Without doing FEA you will not be able to understand if your material will break or not given extreme conditions.

4. Say you now have your "realistic" part. Now comes another hurdle: as you know, material properties of a deep drawn part change with the deformation of the walls, so you will not have uniform material properties. This is needed if you want to do further analysis on you deformed part.

5. Conclusion: I am not denying the need for such analysis on given cases, but to have this capability in the main Inventor will involve serious computation and take a long time. To have a simplified geometric representation with thinned walls, without good correlation with material properties and shape deformation, will be just useless.

All due respect, On point #1 I have to disagree. The "Good approximation" that can be created by sheetmetal tools already in Inventor is not good enough for our needs, though I admit it might be for some. If I model a soda can with as good of an approximation as is possible in today's sheetmetal capability, then place it into the same tooling that actually makes said can, nothing lines up. Because in the real world, drawing/punching a cylinder from a disk of flat metal requires material changes in thickness, stretching and even work hardening. All things we can fake in AutoCAD, but not prototype in Inventor.

On your 4th point; If I don't have a "good enough approximation", then no further simulation can be used. The entire point of this request is to improve the digital prototype such that the physical model geometry much closer matches real-world, and to enable a mathematically accurate model that incorporates things like thickness changes and material deforms when simulations are performed.

Put another way; I don't want to have to trial/error engineer tooling in 2d AutoCAD anymore. I want to model my final product exactly as it is in real world, and use the applied tooling to generate that output. The tooling generates the solid model in its final form, not the existing features that only approximate it. In other words, once I refine my tooling enough to generate a solid I know is correct, I know my tooling is also designed. I'm solving both sides of the engineering task (product and tooling) in the same workflow.

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