Due to the rapid advancement of PVD coating technology, today’s mold builders and buyers need to know more than just the properties of the bare metal that forms the mold components. In simplistic terms, molds are used to make parts by inserting a liquid material into an internal cavity. After the material solidifies, a formed object is able to be removed from the mold cavity. For example, the plastic injection molding process requires a complex industrial machine that heats plastic granules to their melting point before injecting them through a nozzle into a mold cavity. Once the plastic has cooled, the finished part can be removed, and the next cycle started for the next identical part. In die casting applications, a similar process is used in which molten metal is injected into a mold cavity to form a cast metal object that can be removed after cooling.
The injection molding process, usually used when the parts are too complex or cost prohibitive to machine, effectively produces many parts out of the same mold body. Injection molds are typically expensive to machine, and injection molding machines can be costly to run; thus process improvements to reduce costs are wise investments.
Depending on the application, ACS can offer a variety of PVD coatings that add value to mold components and reduce total cost. First, the combination of high film hardness and low friction coefficients impart the favorable properties of:
Injection mold bodies and components can experience significantly improved lifetimes when coated with PVD thin film coatings. The Platit arc deposition systems allow for full control of deposition temperatures between 160ºC and 490ºC, temperatures well suited for many of the M2, S7, P20, NAK 55, 420SS, H13 and other metals like beryllium copper and nickel that are used by mold builders.
Since PVD can provide coating thicknesses in the 2–5 μm range (0.00008” – 0.00020”), parts can be machined to final size prior to mold coating. Since coatings do not last forever, ACS can also strip the mold coating at the end of coating life without harming the base mold material. After stripping the worn coating, a new coating layer can be applied, which allows for increased mold life by reusing many of the mold body components without re-machining or re-polishing.
One of the considerations during a plastic injection molding process is the hot gas corrosion phenomenon. This refers to the potential release of corrosive gases (e.g., chlorine and fluorine) from materials like PVC, CPVC, PE, PP, PB, POM, PEEK, PC, etc. The PVD coatings offer a barrier to protect the otherwise bare steel mold surfaces from this aggressive attack by the hot resins and gases.
Many polymers are now filled with minerals, glasses, wood fibers, metal powders, flame retardants, glass beads, carbon fibers, ceramic particles, and a plethora of other application-specific materials. Many of these polymer additives contribute to the abrasive wear of the expensive mold tooling. The inherent hardness and chemical inertness of the PVD coatings serve to extend the life of the molds by adding a layer of protection.
Our customers have also reported a reduction in cycle times due to the reduced frictional and release forces that led to easier mold filling. In addition, some customers have reported the elimination or reduction in the use of release agents and lubricants as another benefit of PVD coatings.
Multi-component molds have moving parts that slide against each other on each mold cycle. Likewise, ejector pins and guides are subjected to extended sliding cycles, as are mold cores and core pins. The low frictional properties of the PVD coatings aid in the sliding properties between the sliding components to protect against galling, seizure, and failure.
Additionally, the heat of the injection molding process causes some polymers to release the additives and/or chemical components that then build up on the mold surfaces. These deposits can cause manufacturing defects on the finished product. The lower surface energy of the PVD coating can often prevent the accumulation of the particle deposits that cause those manufacturing defects. Furthermore, as previously mentioned, the action of mold coating as a highly effective release agent decreases the chance of distorting the part as the mold opens up after the injection cycle and the finished part is ejected from the surface of the mold cavity. Not only does this result in higher yields, but the surface finish is often improved.
All of the factors mentioned above have prompted the application of PVD mold coatings to keep molds operating longer between repairs. Contact us to discuss feasibility, potential return, and to see if we are the best fit to apply PVD coatings to your injection mold and die casting applications.