Tooling by Design


 

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Die-Design Validation

By: Peter Ulintz

Monday, August 1, 2016
 

It makes little difference how much individual experience we acquire or the number of experienced toolmakers and engineers that we collectively involve in our die-design processes; sooner or later we find ourselves uttering these dreaded words:

 Fig. 1
“If we only knew then what we know now, we would have designed this die differently.”

To a great extent, metal-stamping processes succeed or fail based on the suitability of the die design. If the tooling is not designed properly, there’s not much that can be done in the press shop to develop a process that runs reliably and profitably.

Unfortunately, many dies are thought to be designed properly if they can repeatedly produce parts within part-print specification at a predetermined production rate during die tryout. However, two problems arise with this approach. First, validating a design after the product already has been produced does not represent sound engineering or business practice. Shouldn’t a metalformer test and validate the design before investing time and money in die construction? Secondly, after production begins the stamper often finds that small and seemingly insignificant changes in process inputs —material properties, die lubrication, die temperature or tool geometry, for example—can send the process out of control.

During most die-design and engineering evaluations, engineers have substantial freedom early in the design phase. This design freedom degrades quickly as build and tryout phases approach. When design freedom is at its highest, the engineer often has very little part-specific manufacturing knowledge (Fig. 1). Without knowledge of the influences of variables such as friction, material properties and workpiece geometry on process mechanics, it is impossible to adequately design dies much less predict and prevent the occurrence of defects.

 Fig. 2
To address this deficiency, metalformers can turn to process simulations, which make science-based manufacturing knowledge readily available early in the die-design phase (Fig. 2). Now, the die engineer or designer can submit a design concept and try it out on the computer before developing the final design. This provides an opportunity to make process improvements while evaluating process-sensitive variables. The designer can accept simulation results, or he can repeat the simulation process with new input parameters until establishing an acceptable process.

Perhaps the greatest advantage of metal-stamping simulations is the ability to see the blank deform in small, incremental steps in a “see-through” die. How often have you encountered a problem with a tool in the press shop and tried to watch what happens as the press slide inches down? Eventually, you lose sight of what’s happening as the die closes.

Wouldn’t you have a better opportunity to solve problems and evaluate the robustness of a design if you could see what was happening inside of the die? Stamping simulations allow us to do just that. If necessary, the designer can select and evaluate an entirely different design path because the impact on project cost and timing is minimal in the absence of a hard die design.

In contrast, the designer all too often submits a die design—without the benefit of stamping simulation—to the tool shop for build. The die reaches the tryout press and for the first time results are available for a stamping process that was developed four to six months earlier. If the results fail to meet expectations, we surely will hear those dreaded words once again, “If we only knew…” MF

 

Related Enterprise Zones: Tool & Die


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