One of the most important parts of the injection-molding process is cooling—it also takes the longest! In fact, more than 80 percent of the cycle time is related to cooling. You also can’t cut corners with cooling—the cooling rate must be carefully controlled to achieve tight tolerances and no defects.
However, the faster the heat transfer occurs between the part and the mold, the faster the part cools and the sooner it can be ejected from the mold. One way to enable cooling is to make the mold from specialty materials that have higher thermal conductivities compared to standard mold steel. The steel you choose depends on the properties of the selected material (engineered polymers with additives can be more challenging), production and performance expectations, and budget.
Although there are many variables at play, in general, specialty steel molds with high thermal conductivities can reduce overall production costs by about 25 percent, compared to standard steel molds.
If you are interested in speeding up the cooling process, consider making molds from specialty materials with high thermal conductivity. Three of the most popular are Mold Max®, aluminum, and tungsten carbide.
Mold Max is a family of beryllium-copper alloys that can be easily machined with standard tool-making equipment. The biggest attribute of these materials is their heat-transfer rate—molds made from Mold Max cool 3-4 times faster than standard mold steels like P20 or H13, which greatly improves cycle times. Mold Max is ideal for those parts of a mold that can’t accept cooling channels because they are too narrow or the geometry is too complex.
Mold Max can be welded, polished, and accept metallic and ceramic coatings. Welding is a big advantage because repairs can be made on the floor. Drawbacks include higher wear with glass-filled materials and the occasional development of surface corrosion, which is easily removed.
When most people think of aluminum, they think of a lightweight, soft metal. Aluminum also has a thermal conductivity similar to Mold Max. The softness of an aluminum mold can still lead to premature wear, which has created the widely-held belief that aluminum molds are only good for short runs. That, however, is starting to change. Aluminum alloys continue to get harder (for example, QC-10 and Alumold have a Brinell hardness of 150-180 and Rockwell hardness of B82-B87) and can handle bigger production runs.
Drawbacks to aluminum molds include high wear, even for harder aluminums. Aluminum is also very difficult to weld; any mold failures require the mold to be shipped out for repair, which can result in costly delays. In general, aluminum molds are much easier to damage than steel molds.
Tungsten carbide is a very hard, somewhat brittle material with a compressive strength that is greater than almost all other metals and alloys. It is much more rigid than steel, brass, and cast iron. Another key advantage is that tungsten carbide has a high thermal conductivity—about 2-3 times that of P20, and just slightly less than aluminum and Mold Max.
This great hardness, however, means it can only be machined with diamond tools. The combination of high thermal conductivity and great strength make tungsten carbide is an ideal material for core pins. This application alone can reduce molding cycle times by 25 percent or more on certain projects.
Depending on your production needs, using a specialty material with a high heat-transfer rate for your mold could be a very cost-effective move. The biggest advantage is that these specialty metals and metal alloys can reduce cycle times by as much as 30-40 percent, which speeds up production and reduces costs significantly.
Not sure if your project would benefit from molds built from specialty steel?
Give us a call at 920-686-5800 and we’ll review your project and help you decide if high-thermal-conductivity materials would be a good choice for meeting your production objectives.