Manufacturers of forging dies are often forced to compromise between hard and tough materials. However, scientists from the Fraunhofer Institute for Production Technology (IPT) in Aachen, Germany have discovered a way to combine both characteristics and expand the useful life of forging dies.
They will introduce the new process at the Euromold trade show in Frankfurt, Germany, November 27-30.
Forging dies must withstand a lot. They must be hard so that their surface does not get too worn out and is able to last through great changes in temperature and handle the impactful blows of the forge.
However, the harder a material is, the more brittle it becomes and forging dies are less able to handle the stress from the impact. For this reason, the manufacturers had to find a compromise between hardness and strength.
One of the possibilities is to surround a semi-hard, strong material with a hard layer. The problem is that the layer rests on the softer material and can be indented by blows, like the shell of an egg.
“The forging dies we have been working on have a useful life that is up to twice as long,“ explains Kristian Arntz, head of department at the IPT.
“We are using a working material that is less hard and able to handle the impact stress well. We melt the uppermost layer of the material with a laser and introduce a powder into the melt material that is used to chemically alter the characteristics of the material. We have therefore achieved a large degree of hardness in the upper millimeter.“
The advantage is that since the characteristics of the outer layer do not change abruptly (as is the case in a deposited layer), but increases in hardness gradually (this is also called a hardness gradient) – the “egg shell effect“ can be avoided.
In addition, the particles act like sand paper and prevent the material from wearing off the die. Since the wear only occurs in certain spots of the die, the scientists are altering only these targeted surface areas. Therefore they minimize the effect the layer has on the impact resistance.
Simulations help to calculate the areas that are particularly stressed. To be able to work on the forging dies, the scientists at Alzmetall have developed a machine with which they are able to work on the free-form die inserts and forging dies.
Also, software called ModuleWorks ensures the laser travels across the surface at a constant speed and the gaps between the laser paths remain even – otherwise tears develop in the surface.
“This isn‘t a problem if the surfaces are straight; however, we had to develop special algorithms for free-formed tools that keep the path distance and the speed constant – even with complex geometries,“ said Arntz.
Plans to reduce expensive raw materials such as chromium, molybdenum and vanadium are also being worked on.
