Tale of a worn gate
Injection mold components experience remarkable wear and tear as high temperature polymers, often with abrasive and corrosive additives, are injected into the mold.
A challenge for many injection mold makers and plastic injection production teams is how to ensure that the mold components will not only last through several million cycles, but also maintain the efficiency witnessed in the first 10,000 cycles.
A Common Wear Story
One of the nation’s largest mold makers called on us after experiencing yield loss and downtime from a worn valve gate. Forced through a tiny 0.8mm gate hole, an abrasive elastomer caused, excessive wear widening the gate and causing an unacceptable gate vestige.
Gate inserts wouldn’t work due to the valve gate system and the mold maker needed a solution that would withstand the abrasive nature of the elastomer without altering the tight tolerances of the mold.
We use a technique called Physical Vapor Deposition, or PVD coating, to make tooling materials harder, corrosion resistant, and present a lower surface energy to help with the ejection and release of molded parts.
In Physical Vapor Deposition, the source material is ionized creating a high energy material used to impregnate the mold substrate. Different combinations of alloys can be used with this process, such as titanium, nitrides, carbides, and oxides.
For most injection mold coatings, a zirconium nitride is used, which provides the hardness to withstand millions of shots of abrasive material and the lubricity required for effective release of the part.
A standard, uncoated mold may have a hardness of around 45 Rockwell C. A titanium nitride or zirconium nitride coating will have a hardness of around 80 Rockwell C. And tolerances are maintained.
A coating can be anywhere from four hundred nanometers to five microns thick and because of the high energy process, the material is an integral part of the mold substrate, not a layered veneer, which can chip or crack.
The Physical Vapor Deposition process can be performed on a variety of materials, including stainless steel, hardened steels, aluminum, 3D printed polymers, even metal or plastic parts that are injection molded or CNC machined.
The Happy Ending
For this particular mold maker the gates were failing within the first 100,000 shots. After impregnating the 32-cavity mold and mold components with a zirconium nitride injection mold coating, the tool was able to run for well over two million cycles.
Plastic injection mold tools have yield issues in other components beyond the gate. Other components of the mold, such as screws, bushings, barrels, slides, lifters, check rings and the cavities are susceptible to wear and tear. These can all be PVD coated to extend the life of the mold, protect your investment and decrease downtime.
Are you experiencing wear issues, trying to improve release, or increase efficiency? Let’s schedule a time to chat to see if we can help.