Die Face Design Solution Cuts Tooling Development Time

Image shows the part geometry (green), addendum geometry (yellow), and binder (blue) that needs to be optimized in the die by an engineer to ensure a part is stamped properly. (Image courtesy of ESI Group.)

Designing a die face for your stamped or drawn part isn’t as easy as creating a negative of the part.

To ensure that the metal stays in place and that thickness tolerances are met, engineers will have to create addendum features to the stamping tool.

These additions to the die and stamping equipment will hold and guide the stretching and forming of the sheet metal into the appropriate shape. Then, all the excess that was clamped and guided by these die additions is trimmed from the final part.

For instance, if an automotive engineer were designing a die for a door frame, he or she would have to fill in all the holes and extend the sheet far enough so that the binder could hold the metal down. These excess parts of metal would then be cut out to create the shape of the door frame and to add room for the window and door mechanisms.

Blank geometry after the first trimming operation (blue lines show cut off areas while yellow lines show what will be trimmed during the second operation; and the pink line is the drawbead line. (Image courtesy of ESI Group.)

Adding these addendums to the part can be tricky without computer-aided engineering (CAE) software. “To assist the user in quickly creating and modifying parametric die face models, ESI has developed two dedicated modules for die face design: one integrated in the CATIA V5 platform (ESI PAM-DIEMAKER for CATIA V5) and one integrated in ESI Group’s own VISUAL platform (VISUAL-DIEMAKER),” said Mark Vrolijk, product marketing manager, Sheet Metal Forming Solutions at ESI Group

These modules include the Die Starter tool which helps users to digitally draft a quick die face and to check the feasibility of the stamping process early in the development phase.

ESI’s Workflow for Die Face Design Optimization

Geometry is imported directly into the die face module (Image courtesy of ESI Group.)

Die Starter is a democratized tool to create die face geometry automatically. It uses a built-in, fast and advanced direct solver to create a good starting point for the die. The tool also can perform contour, thickness and thinning feasibility studies.

The engineers can then assess the die using the simulation tool ESI PAM-STAMP. This CAE tool allows design engineers to perform optimizations early in the development cycle.

This workflow can help keep development time under control, as the user will start off with a nearly optimized part before moving on to the simulation phase for fine-tuning.

“Our die face design solution, including the automated die face design functionality, enables non-experts — including people with no knowledge of die face design, such as part designers at automotive OEMs — to come up with a reasonable initial die face design quickly,” said Vrolijk. “[The software] gives a die face geometry that goes in the right feasibility direction, which the user can then fine-tune with the integrated die face design functionalities, according to the results of the feasibility analysis.”

Geometry is smoothed out without an undercut and the holes are filled in for the die face design. (Image courtesy of ESI Group.)

Engineers first need to import the part geometry and prepare it for the Die Starter feature.

As previously mentioned in the car door example, this involves smoothing out the geometry and filling in all the holes that will be cut out of the part after it is stamped.

Engineers also define if there is any symmetry in the part and position the part in a virtual press.

Once the geometry is prepared, the user can then use the Die Starter to create the die face geometry. ESI reports that within a few minutes, a good starting point for a feasible die face is created.

Then, if the die face geometry seems reasonable, the engineer can use Die Starter again to run an optimization loop to improve the geometry even further. The software will perform a series of iterations to modify the geometry of the die.

For example, the tool can modify the binder geometry and depth, as well as the addendum shape and drawbead restraining forces, in order to achieve the best feasible process with the smallest possible blank size. As a significant portion of the part cost goes into the material, using software such as Die Starter to optimize design can save a company a substantial amount of money.

Finally, after the user puts some finishing touches on the die face, the software can then be used to create an ideal distribution for the drawbead restraining forces.

Much of the setup for the simulation is done under the hood in order to make it possible for users without process and Finite Element Analysis (FEA) knowledge to get a realistic feasibility result in the very early stages of the development process.

For more control on the simulation process—for example, to take into account the requirements for following operations—Vrolijk suggested that users employ a simulation tool that specializes in stamping processes, such as ESI PAM-STAMP.

Vrolijk also suggested that ESI PAM-STAMP is an ideal option to verify the results of the Die Starter accurately, as the die face design tool and the PAM-STAMP simulation environment are very closely connected. This helps reduce set-up times further.

How the Die Face Design Solution Works

Results from the automated die face design typically takes about four to eight minutes to create using Die Starter. (Image courtesy of ESI Group.)

“Die Starter has an optimization algorithm which is able to automatically adjust binder shape, addendum geometry and drawbead restraining force in order to achieve the best feasible process with minimal material consumption,” explained Vrolijk.

The software can optimize the design of a die face to avoid cracks and thinning values that are out of specification, as well as reduce non-stretched areas. The CAE tool will also limit material waste by optimizing the stamping process so that it uses as small a blank as possible, while maintaining the feasibility of the final product.

Integrated functionality to fix the geometry for the die face design tool. (Image courtesy of ESI Group.)

The die face design solution operates with an advanced inverse solver, which attempts to find the parameters that will create results that are compatible with the part’s specifications. During this automated process, the simulation predicts where the part may experience critical thinning and thickening.

Some of the parameters for Die Starter include:

Binder type
- Inner and outer binder
- Developable and wrapable binder
- Part on binder
Material type
Thickness
Drawbead restraining force
Flanges automatically integrate into addendum geometry

The simulations also tell the engineer about the overall quality of the part. Information about safety (wrinkling, cracks, high thinning and non-stretched areas) are all recorded. “We integrated a close link to the PAM-STAMP explicit simulation environment, so the results from the Die Starter can quickly and easily also be validated with the accurate explicit code,” clarified Vrolijk.

Benefits of Simulating Part-Stamping Dies Early in the Design Cycle

Feasibility study on the results from the automated die face design tool. (Image courtesy of ESI Group.)

Traditionally, when an engineer creates a die face, he or she does so from scratch. This will take quite a lot of iteration with implicit or explicit simulation codes.

The engineer will create a die face, run simulations to check if it has to be altered anywhere, make the alterations and repeat the process. This takes a lot of manual work and a considerable amount of computational time.

According to Vrolijk, Die Starter can make an initial die face in less than five minutes and can then optimize that run in a few hours or less, depending on the number of variables set for the optimization (for example, binder-only or binder plus addendum and drawbead forces). The result is a die face that is optimized for thickness and global part quality.

“As Die Starter is fully automatic, the user can already work on the next part geometry while the tool is running to create the first die face and feasibility results,” said Vrolijk. “By using the optimization possibility of Die Starter, the user can save a lot of manual iterations, saving time and cost. The starting point to finalize the die face design is much more advanced than when the user has to do the modeling all from scratch with long calculation and set-up times.”

Engineers will also know that stamping processes can become costly. It is best if engineers optimize the stamping process during the design phase to waste the least amount of material, which will place them well ahead financially once the production process is operating in the real world.

“Die Starter can optimize the size and shape of the addendum and binder which is required to form the part correctly with minimal material usage,” said Vrolijk. “Die Starter can also deliver directly this minimal flat blank outline required to form the part, which can then be used in a nesting program, like ESI’s to obtain the best nesting of the blank in a coil. This optimal nesting will result in the least amount of scrap and thus the cheapest part to produce.”

To find out more about ESI Group’s stamping simulation abilities, read: PAM-STAMP- : From Design/Concept to Virtual Stamping RealityTry-Out.

ESI Group has sponsored ENGINEERING.com to write this article. It has provided no editorial input. All opinions are mine. —Shawn Wasserman