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Wear in Injection Molds: To Float or Not to Float
One of the most difficult and challenging mold design issues is how to reduce or eliminate wear in injection molds. After all, the more wear that occurs, the higher the mold repair costs and/or the shorter the life of the mold. It’s a given that both the mold designer and the mold builder are committed to designing and building molds with the least wear, but it often seems to be an elusive target, especially with mold designs that have various actions taking place during the molding cycle.
The Wear Challenge
Mold designers and builders try to use the typical methods of minimizing wear—such as using differential metals; using low-wear coatings; specifying high metal hardness thus equating high hardness with low wear; designing shutoffs with high angles thus avoiding locking shutoff angles; and, many more concepts that their experience leads them to believe works best in specific applications. However, one design principle that is not well understood by mold designers and mold builders is wear caused by mold components that are under some load or stress during the molding cycle.

Mold designers and builders see the mold as it is built and especially during the mold assembly phase. Every attempt is made by them to assemble the mold components such that all inserts are fitted so the mold can be assembled by hand. In the better mold building shops, the use of hammers, pry bars and clamps is either strictly forbidden or the use is severely limited. Most molds then are assembled by hand with many of the mold components fitted with close tolerances but, by design, are not under a stress. On the bench then, the mold is in a Static condition.

The molder then sees the mold in a Dynamic condition. Components may be moved out of position due to a variety of molding conditions—such as being clamped up under tonnage; cams moving back and forth with the opening and closing of the mold; thermodynamic changes in the mold due to differential heating and cooling; and, stresses caused by injection pressures trying to move mold components out of position. Therefore, to the perceptive molder, a mold is alive or a dynamic device, not a static device during the molding process.

For years there has been a small group of molders and mold builders that recognize that molds are dynamic devices. They have recognized that this dynamic condition often has caused mold components to be forced out of a designed position. As forces are exerted on mold components, they move out of their desired position and may be forced against their mating components such that very high loads or stresses between these components occur. One of the more serious results of these stresses is high rates of mold wear. It is almost inevitable that increasing loads will increase the wear between these mold components.

Mold Alignment Approach
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