Common materials used in the manufacturing of plastic injection molds include:
- Steel:
- P20: A pre-hardened mold steel with good polishability and photoetching properties, making it suitable for molds where an excellent visual finish is required. It is less wear-resistant than hardened tool steels but is used where the high cost of hardened steels is not justified.
- H13: A hot-work steel with high toughness and heat resistance, ideal for high-production molds designed for high temperatures. It resists thermal fatigue cracking, which is important for molds that will undergo many heating and cooling cycles.
- S7: A shock-resistant steel used for molds that must withstand sudden impacts. This tool steel is beneficial for durable molds that require high impact resistance.
- 420 Stainless Steel: A corrosion-resistant steel, often used for medical or food-processing applications. It provides excellent cleanliness and maintains its properties even at high temperatures, making it ideal for molds used in harsh environments.
- Aluminum:
- Al7075: A strong aluminum alloy with good mechanical properties, thermal conductivity, and machinability. It is appropriate for prototype molds that produce limited runs of parts due to its reduced wear resistance compared to steel. However, the faster heat dissipation can lead to shorter cycle times.
- Al6061: A versatile alloy that is easier to machine and is less expensive than other grades, making it suitable for low-volume production or prototype tools. The trade-off for its lower cost is a reduced lifespan compared to other materials.
- Beryllium Copper:
- This alloy stands out for its superior thermal conductivity, which allows for rapid cooling of the mold, thereby increasing the speed of the injection molding process. It often finds use in the cooling systems of molds or in areas with intricate geometric features that require rapid heat removal. However, its higher cost and potential health hazards during machining (requiring specific safety protocols) limit its use to specialized applications.
- Pre-hardened Steels:
- These are less wear-resistant than hardened tool steels but are often selected for larger molds where the higher cost of hardened steel may not be justified.
These materials are selected based on factors such as the expected production volume, the plastic material to be injected, and the desired lifespan of the mold.
Each material has its advantages and limitations that make it better suited for particular applications:
- Steel, such as P20 and H13, is typically favored for high-volume production molds because of its durability and resistance to wear and tear. H13, in particular, is excellent for advanced high-temperature applications, outperforming other materials but comes with a higher cost.
- Aluminum molds, particularly those made from Al7075 and Al6061, are faster to manufacture and can achieve faster cycle times due to better thermal conductivity. However, they are less durable than steel molds and are often designated for prototypes or low-volume production.
- Beryllium copper is exceptional for cooling effectiveness but is a niche material primarily utilized in areas where its specific properties are necessary, and safety measures can be strictly adhered to.
