When considering plastic injection molding for a project, product designers and engineers must consider not only which thermoformable or thermoplastic resin to use, but also the choice of metal for the injection mold tooling.
The choice of tooling raw material influences production lead times, cycle times, finished part quality and cost, among other things. At Gestión de Compras we have the experience and technical and industrial knowledge to help you decide which is best for your next project, here are the most common types of tooling material and the pros and cons of each.
MATERIALS FOR PLASTIC INJECTION MOLDS
Al-7075
Aluminum 7075 is a high strength aluminum alloy with a relatively large percentage of zinc.
Pros
Aluminum has the best heat transfer properties of the common tool metals. Why is this important? It means that the tool can be heated and cooled quickly and efficiently. This has two advantages. First, the tool will require the least elaborate (and expensive) engineering for cooling channels. Second, the machining cycle is faster than that of the steel tool, which can save a lot of time in large production runs.
Cons
It is the least durable tooling material. It is not suitable for injecting corrosive resins such as POM or PVC, or those to which glass fibers are added, as glass fibers erode mold surfaces. This is less important in low-volume or bridge fabrication, where durability is not the primary concern. In addition, 7075 is not good at withstanding repeated high clamping pressures, such as would be used for large parts or parts with many complex features.
The best for
Low volumes of general purpose resins such as ABS, PP, PE and nylon.
P20
P20 is a reliable, semi-hard tool steel and the type we use most often.
Pros
It is less expensive than Al-7075 and even with abrasive resins can last up to 50K cycles or more depending on part geometry and tolerances. It also machines well and can be easily welded to repair the mold if necessary. It can be polished as well as Al-7075, but is more scratch resistant than aluminum. It is also harder, so it can withstand higher injection and clamping pressures. P20 also performs much better than Al against glass-filled materials.
Cons
Some plastic resins such as PVC are chemically corrosive. P20 steel is not very resistant to them, which can affect tool life. In some cases, aluminum may be slightly superior.
The best for
General purpose resins, abrasive resins with glass fibers, larger parts, higher injection and clamping pressures. Volumes up to 50K.
NAK80
NAK80 is another semi-hard tool steel for more demanding applications.
Pros
It is harder than P20, while machining much faster. It holds close tolerances and does not need stress relief, even after 250,000 cycles. It is also more resistant to corrosion.
Cons
A possible disadvantage is that it has worse thermal transfer, so it must be cooled more carefully, and its cost is higher than that of the AL-7075 or P20.
The best for
Engineering grade plastics such as Delrin or acetal (POM), corrosive resins, high volume production with high clamping pressures, resins with glass fibers.
H13
Another excellent option for high-volume production orders or where aggressive plastics are used is H13 air-hardened tool steel.
Pros
It is considered a “hot work” steel, which means it has excellent tensile strength from continuous heating and cooling cycles, while maintaining close dimensional tolerances. H13 is easy to machine prior to heat treatment when the metal is relatively soft. Once heat treated, the molds are further processed and finished using EDM and hard machining techniques. H13 can be used a million times or more per mold. It can also be polished to a mirror finish for transparent or optical parts.
Cons
Its disadvantage is that it has only average heat transfer capability and will be more expensive than the Al-7075 or P20.
The best for
Aggressive resins, transparent plastic optical parts such as acrylic or polycarbonate, large volumes.
S136
S136 is a high purity stainless steel that comes in various grades of hardness.
Pros
It is the most corrosion resistant when injecting PVC or POM plastics that can corrode other metals. In addition, it can be highly polished, which is ideal for producing optically clear surfaces on transparent plastics such as polycarbonates and acrylics.
Cons
These advantages will be offset by the higher cost of our available tooling materials and lower thermal efficiency.
The best for
PMMA, PVC, PP, PC and other optical grade transparent resins. We recommend this steel when surface finish is the primary consideration.
Not sure which one is right for you?
Gestión de Compras has more than 20 years of experience in the design, development and manufacture of plastic injection molds specialized in key sectors.
Contact us to get the best results in your next project.
