August 2022 Volume 4

MATERIALS

“There is a generalized advancement of digital modeling.” Having established the extraordinary impact of computer simulations on the advanced processes used by the commercial forging industry, we talked at length with Jim Miller of Scientific Forming Technology Corp. (SFTC) concerning the use of this technology to enhance die life. “There are two sides to simulation,” Miller said. “People think about the deformation of a workpiece, but not always about the mechanical and thermal fatigue involved with tooling.” Die stress simulation is a part of SFTC’s DEFORM software platform, but the first step in improving die life is optimizing the geometry and the amount of material used in the part preform that goes in the die. It has been proven that optimizing die and process design can reduce die failure, wear and fatigue performance. “For example,” Miller continues, “developing preforms that take less force to forge will reduce die wear and thus maintenance costs. It’s ultimately a fatigue issue, and fatigue analysis can be quite complex. The variability of fatigue will give you a prediction of die wear patterns and die life, but only within a statistical confidence range of outcomes – not an exact answer.” Of course, there is a cost associated with software licenses and the time and effort to run simulations. Jim Miller says one of the quickest paths to recovering the investment in simulation software is through savings on tooling. “Tooling costs are significant, often running 10 percent or more of the total job cost. Anticipated tool cost savings can quickly add up for a company that has never applied simulation technology. Reducing die failure or maintenance expenses on even a few jobs per year can offset or pay back the cost of simulation software.” On a broader scale, Miller is very sanguine about the prospects of computer simulation and the advancement of the commercial forging process. He is enthusiastic about the Design of Experiments optimization module of the DEFORM software platform (see sidebar). “There is a generalized advancement of digital modeling,” he said. “Further, the potential opportunities presented by industry megatrends such as Industry 4.0, and newer fields such as digital analytics and digital twin technologies, dovetail nicely with computerized simulations.” A two-hit gear forging (see Figure 1) was studied with the goal of reducing tool stress in the final operation. The nominal process chain was set up in the MO environment of DEFORM-3D. The workpiece was converted to an 18-degree section to take advantage of the 1/20th symmetry of the gear. Using this symmetry allowed more resolution and a faster run time. A die stress operation was included to determine the stress state of the top die at the end of the second operation.

A coupled analysis one in which the dies are volume meshed in the forging operation concurrently with the actual part. It is more difficult and complicated to run. Stresses and temperature evolution and any other results are calculated and any impact that die deformation may have on the forging of the part is directly taken into consideration. In simulating die behavior, engineers and designers look for areas in the die that may develop high tensile stresses in use, since cracks can nucleate and propagate from these sites. Areas in compression do not crack. The Archard simulation model (see sidebar) is used for die wear analysis. The model quantifies die wear by predicting the amount of material removed after each forging cycle. Transvalor’s Z-Set routine is designed to analyze dies and parts for areas of crack propagation. This is very important in determining the potential for die failure within a certain period of time, or after a certain number of production cycles. Z-Set is heavily used in analyzing forged mission-critical components, such as aircraft engine parts. “Simulation in and of itself,” said Poulain, “doesn’t improve die life, but it can tell you what to expect. Die stress simulations are available in most of our packages, and this knowledge can be helpful in factoring in die costs for component pricing. Die life prediction is complicated and requires more time investment and higher process understanding. It’s not a plug and play routine, but our team with decades of experience is here to help,” he concluded.

Typical die stress simulation graphic

Design of Experiments and Reducing Tool Stress for Gear Forging The Design of Experiments (DOE)/Optimization module of the DEFORM software from Scientific Forming Technologies Corp. (SFTC) offers a systematic toolset for automating investigations on a process. It is tightly integrated with the Multiple Operations (MO) process chaining environment in DEFORM. Its DOE methods help users characterize existing processes, determine optimum designs/processes, and understand expected process variation.

FIA MAGAZINE | AUGUST 2022 27