In simulation, there is ongoing effort to prove who can claim to be the best at “virtual tryout.” Product brochures and websites promote software solutions that “bypass soft tooling” and “minimize die tryout.” While these are certainly desirable goals, perhaps they do not go far enough. Soft tooling has been driven to near extinction by metal forming simulation software already. The idea of building and trying out tools that have not been engineered using simulation is currently unthinkable. This makes promoting particular simulation software as a means to eliminate soft tools or to proclaim tryout reduction compared to conditions without simulation a little disingenuous. Just how proud should one be of the “virtual tryout” title?
Soft tool (also proof tool) development is the practice of discovering, through trial-and-error on a short-run tool, to achieve a desired sheet metal part. In the past, this took weeks or months. It required die makers to attempt numerous tooling changes, process modifications, and part concessions to resolve splitting, wrinkling, or springback issues— literally trying out anything and everything to make the tool work. It involved grinding and welding of the tool, manual feeding of blanks into dies, shims, plastic bags, soap, sandpaper, other die maker secrets, and countless iterations of tooling adjustments and production settings.
Proof tool development: build a soft tool, stamp parts, adjust physical tool, modify design, repeat
Once a feasible combination was found in the soft tool, hard tools were created to bring to production the lessons learned in the soft tool development. Unfortunately, material often behaved very differently in the soft tool than the hard tool; soft tools were made of Kirksite and hard tools of cast iron. The entire trial and error cycle would repeat. The application of metal forming simulation to eliminate the soft tool was a very welcome innovation in the mid ‘90s.
As simulation developed, it reduced the unknowns of soft tooling and tryout. Analysis could show if the process was “feasible,” allowing engineers to build feasibility into the design. With simulation into engineering process tool development and build timeline, iteration and modification of the stamping process now happens up front during engineering.
Early virtual tryout: build CAD tools, simulate on supercomputers, evaluate results, repeat
Further innovations in modeling allowed for a nearly seamless integration of the engineering and design of the tooling process with the evaluation and validation of the stamping process. At first, it was limited to draw die design, but it is now commonly applied to line die processes and progressive dies.
Tryout: build physical tool, stamp parts, if safe OK, if failing adjust tooling, repeat
Early draw simulations could take a day for analysis; more recently complete processes from draw to final forming can be completed in as little as an hour. Early simulation models required many hours of prep in CAD along with meshing and editing prior to simulation; advances in modeling and meshing now streamline the tooling development. This speedup of the simulation preparation and computation time leads many to the conclusion that their virtual tryout solution has fully optimized their tooling engineering process.
However, speeding up the time to analyze a tool design concept and process is still no different than what was done in tryout or soft tool development. The tryout press and proof tool have been replaced with a virtual press and virtual die tryout. Is this really as good as it gets? Faster design and computation of stamping process is little more than guessing faster—well- informed, educated guessing based on know-how and experience, but still trial and error, still guessing. Commit to CAD your best guess, then wait and see. It still happens that after numerous design and process changes the analysis may still show failure, process engineers must return to the drawing board and attempt a completely new process proposal.
What is needed to reach further efficiency in manufacturing is a better process engineering methodology—a methodology where the simulation results not only indicate success or failure but indicate what to change in the design to make it safer. It should enable the user to evaluate the impact of her decisions without a several-hour wait to see how that decision impacts the design. It should provide metrics that inform the designer on the “opportunity cost” that accompanies any proposed resolution to observed issues. Don’t just guess faster and more often, but truly evaluate the possible methods to stamp a part and evaluate them in a systematic and comprehensive manner.
Robustness can only be achieved if we consider the potential for variation in the inputs
We achieve Systematic Process Improvement by front-loading multiple process engineering design variations, and map the response to the adjustments and variations. Rather than making a change to the tool based on individual interpretation of simulation results, it is possible to quantify relationships between key forming performance indicators, like thinning and springback, to the variables that influence them. Equipped with a method to review those relationships, engineers today can proactively define stamping processes that produce a safe result under likely ranges of forming conditions.
Under such an engineering process, very little that happens in the tryout or production environments will be a surprise. Material variation, production line fluctuations, and the like will have already been analyzed and designed for. It’s not virtual tryout anymore; it is engineering, design, and verification. That seems the better application of technology and computational power.
Soft tool development, virtual tryout, and Systematic Process Improvement