What Are Injection Molds Made Of?

One of the most effective and popular methods of manufacturing large volumes of accurate and high-quality plastic items is injection molding. Injection mold is a tool used to create the required shape of molten plastic, and this process is an adaptation of it. So, what exactly are injection molds made of?

Injection molds are precision-engineered tools, typically made of hardened metals and alloys, that can withstand the high pressures, temperatures, and abrasions of the plastic injection molding process. The material chosen for an injection mold is a decision made on many factors, including how strong the mold needs to be, how functional it needs to be, how much it will cost to produce the mold and how good the produce the final product needs to be.

In this article, we will cover the most popular types of injection mold manufacturing materials, their features, and how GV Mold makes use of advanced technology to provide the best solutions to our clients.

The Importance of Mold Material Selection

Injection molds are utilized in the manufacturing process and therefore are exposed to pressures, cyclical usage, heat and chemicals. This means that the choice of a suitable material for a mold is important in the sense that it should be durable, dimensionally stable and affordable. Wrong material selection can result in early wear, corrosion or low performance, which, in the long run, increases the level of maintenance and replacement.

Key factors that decide the type of material include the volume of production, complexity of the part, flow of material, surface finish needed, and the cost. All of them directly affect the performance, cost and life of the mold.

All of these variables are carefully measured by the leading injection mold manufacturers, like GV Mold, when designing a mold to optimize material selection for each project. It is not just a matter of selecting a material for a metal matrix composite. It is about considering technical demands and production goals to produce the highest return on investment. 

Selecting the correct material can reduce defects, speed up the rate of production, and deliver more consistent products.

Common Materials Used in Injection Molds

Mold materials also differ in terms of their hardness, toughness, thermal conductivity, and corrosion resistance. The most widely used materials in injection mold manufacturing are:

Tool Steels

Tool steels are widely used in the manufacturing of injection molds, as they have good hardness and wear resistance. They are available in different grades based on what is required in a certain run of production.

• P20 Steel: A good machinable and polishable pre-hardened tool steel is used for cutting metal, plastics, ceramics and hard-to-machine alloys. P20 is preferred when it comes to molds that are of average use and can be machined at a relatively cheap price. Thus, it is a good combination of durability and affordability. This makes P20 a favoured material for consumer goods since it can create a surface that is good enough for cosmetic parts.

• H13 Steel: H13 is famous for its high endurance and thermal fatigue properties, it can be used in mass production of molds or in areas where temperature is high. It is highly utilized in molds of automotive and other industrial products due to its non-crazing feature when subjected to multiple thermal cycles. It also has a long life span or lifecycle, and that's why it requires minimal upkeep.

• S7 Steel: S7 steel is a material used for molds that are expected to take a knock or high stress, because of its shock resistance and toughness. It has relatively higher toughness than H13 but is used in applications that need to withstand shocks, such as when making molds for thick sections or structural parts.

• Stainless Steel (420, 440C): Stainless steels are used for molds that require the material to be corrosion resistant especially in the medical field, food processing and cosmetic industry. Also, they provide good polishing that is good for hi-gloss parts. In comparison with aluminium alloy, stainless steel can resist chemical attack and will thus have a longer mold life for molding aggressive or corrosive resins.

Aluminum Alloys

Aluminium molds are gradually gaining more acceptance because they require a shorter period of time in machining, are cheaper in the short run and, are mostly used for prototyping to moderate production.

• 7075 Aluminum: This is high strength aluminium alloy that is useful for prototype molds and finds application in electronics, aircraft industry and automobile industry. This material has a great processibility, good strength and is ideal for short-run applications, which in turn also offer short lead times. The molds from aluminum 7075 are more preferred because they allow much shorter lead time compared to conventional molding techniques.

• QC-10 Aluminum: QC-10 is used when manufacturers need the life of the mold to be made longer than standard aluminum yet not up to steel. It provides a harder and more wear resistant material than the other aluminum alloys.

However, these aluminum molds are not as strong as steel molds, they are lighter, cool faster and are relatively cheaper to machine, thus they are used in industries where cost is a concern. Specifically, they can be used in the development of consumer product prototypes, first runs of a product and testing of designs.

Beryllium-Copper Alloys

Due to its high thermal conductivity, beryllium copper can also be employed in some parts of the mold, for example, as a core or an insert. Due to this property, it can easily shed heat, and therefore, it can be useful in reducing cycle time and improving the part quality where heat concentration is an issue. Further, it also helps in preventing warping or sink marks on thick cross-sections of the molded parts.

Beryllium copper inserts can also be used to provide additional cooling in certain areas of molds with intricate shapes or geometry. The one drawback of this material is that it costs more than other types of materials, but it can provide a good return on the investment if used correctly.

Specialty Materials

Niche applications call for extreme properties like lightweight strength or thermal insulation; for instance, some molds come with specialized materials like titanium or ceramic composites. Because of their high cost, these materials are normally reserved for very technical or experimental applications.

Molding chemically aggressive plastics or applications with extreme environmental conditions may also use specialty materials. Though not common in day-to-day mold making, they are vital solutions for aerospace, defence, and high-performance applications.

Factors Influencing Material Choice

So, which material is the best for your mold? There is no one right answer to this. There are many factors to consider when choosing the right material. Let's talk about a few:

• Production Volume: For high-volume runs, harder and more durable materials like H13 steel are needed to survive the wear and tear over millions of cycles.

• Part Geometry and Finish: Materials with better machinability may be required for complex or intricate part designs. Stainless steel may be needed for high-gloss finishes to allow the best polishing.

• Thermal Requirements: Furthermore, the molded material must be able to undergo thermal loads of multiple injection cycles without warping or cracking. Lower cooling time (to enable higher cycle efficiency) can be achieved with higher thermal conductivity materials.

• Corrosion Risk: Molds that will work with corrosive resins or in a humid environment should be made from corrosion-resistant materials like stainless steel.

• Budget and Lead Time: Aluminum molds are good for short runs and a faster turnaround, while steel molds will make sense for longer production runs.

At GV Mold, we work very closely with customers to consider the pros and cons of the of each mold material and suggest the best option for each project. Using a combination of material knowledge and manufacturing expertise, GV Mold optimizes the mold selection process for any application. 

Real-World Applications of Different Mold Materials

The nature of materials used affects the functioning of molds in the different industrial uses that are available. Here are a few examples:

• Automotive Industry: Car parts, which are high volume commodities, call for H13 steel molds since they are more durable, require little or no maintenance and can handle the rigorous cycling. H13 is extensively used for the engine parts, dashboard, and other under-hood parts due to its hard and heat-resistant nature.

• Medical Devices: Stainless steel molds are compulsory for medical components due to their corrosion resistance and smooth and hygienic finish. These molds are compatible with the highest regulations, including sterility.

• Consumer Electronics: Aluminum molds are often employed in the manufacturing of electronic boxes to improve lead time and maintain the overall affordability of the process.

• Packaging Industry: In high-speed, thin-wall packaging molds, fast cycle times are made possible by using beryllium copper inserts that improve heat transfer and reduce the time taken for the parts to cool.

Understanding these needs for the applications, GV Mold offers material solutions to meet the technical requirements as well as cost requirements.

Conclusion

The injection molds are made from various materials to ensure that they are able to serve the needs of today's manufacturing industry. These materials bring unique properties to various production situations. Lifespan, accuracy, and efficiency of the mold highly depend on the material selection.