August 2022 Volume 4

MATERIALS

Improving Forging Die Life With Simulation By Dean M. Peters

Computer simulation of metal forging processes are one of the great technological innovations that have changed the nature of this industry during the last 50 years. Simulations done on optimizing preforms for the forging process are equally applicable to analyzing die behavior. Digital analyses done on forging can be very helpful in optimizing and estimating die life.

“For a die, heat, pressure and friction are the enemy” According to Tom Ellinghausen, President of Forge Technology Inc., which represents the QForm metal forming software package, “One of the most important factors that affect die life is the way the material flows within the die, so before we even look at a die simulation, we want to use simulation of material flow to look at load and material flow that could contribute to die wear.” Material flow simulations help size the billet efficiently, optimize its shape, optimize multiple impression sequences, balance material flow within the die, and determine the optimum billet temperature. “The importance of material flow within the die can’t be over emphasized,” Ellinghausen continues. “For example, by determining the optimal amount of material and shape used for the preform, we can optimize die life and improve product quality. For a die, heat, pressure and friction are the enemy.” Once the material flow inside the die has been optimized, it is time to run a simulation on the die. Such a simulation can predict cracks due to overloading, plastic deformation, abrasive wear, and thermo mechanical fatigue cracks. During the course of a production Automated Preform Design Reduces Die Wear, Improves Forging Quality Many forgings require preforming to get the material in the correct shape to flow properly in the finish die cavity. The optimal preform shape is that which ensures a defect free forging with minimal flash and reduces die wear by reducing the load and the metal flow across the die surface. The ideal metal flow in a finish die is a straight line from the surface of the preform to the closest point of the die cavity. The formation of unwanted laps would be impossible with this idealized flow since there is no possibility of a rotational velocity vector at any point of the domain. QForm Direct integrates simulation and design. It finds the optimal preform shape and creates a CAD model of the preform die cavity that achieves material flow as close as possible to these idealized conditions. QForm simulation is then used to verify and optimize the proposed preform shape.

Among industries that manufacture durable goods, few if any take a greater toll on the tooling and dies used in the production of its output thanmetal forging.The commercial forging industry, despite its roots in distant antiquity and its subsequent rise as a modern economic sector, is still challenged by the behavior, performance, and longevity of its dies. The last 50-100 years of forging history are barely noticeable on the industry’s complete historical timeline and yet, during the last half century especially, forging has become an advanced manufacturing process. In so doing, it has advanced its ability to analyze and predict die behavior through the use of software simulations. The life of a forging die set is a difficult one and, despite the development of different die materials (such as H13 steel) especially suited to their task, their job is to be cyclically stressed with each stroke of a ram or more violently so with the sudden impact of a hammer. Dies are subjected to lengthy production cycles in which the application of force to shape a workpiece also deforms the tooling, making the dies subject to mechanical fatigue. Similarly, they go through cycles of thermal fatigue as they shape workpieces and receive doses of lubricant and/or cooling agents between production cycles. Forging is not possible without wear and tear on its tooling. Each production cycle a die set dies goes through brings it closer to the time when it has to be re-sunk or replaced, resulting in a cost that must be accounted for in the pricing of finished forgings. It is incumbent on every successful and progressive forging operation to keep its tooling costs, and consequently its pricing, at a manageable and competitive level. Put simply, die life is manifested as units produced before it can no longer produce specification parts. When manifested as die cost per unit produced, it is a key component to the value-added competitiveness of forgings in the markets they serve. Arguably, one of the greatest technologies that has brought forging into the modern era is computer simulation and modeling. In this article we will consider how modern simulation software platforms can help us examine and understand die behavior under load, and even predict die life expectancy. To help us understand more about how this technology can be applied to improving die life, we contacted some experts in the field.

FIA MAGAZINE | AUGUST 2022 24