Material For Injection Molding: Everything You Should Know

Tooling Metals for Injection Molding

The selection of metal for tooling is a critical decision that can affect the quality and efficiency of the injection molding process. The following factors should be considered when choosing the metal for tooling:

1. Material properties: The metal must have good strength, toughness, and wear resistance to withstand the stress and strain of the injection molding process. The material should also have good thermal conductivity to dissipate heat and prevent warping.
2. Production volume: The expected production volume of the injection molded parts will determine the type of metal to use. For low volume production, softer metals like aluminum are more suitable, while high volume production requires harder metals like tool steel.
3. Part complexity: The complexity of the injection molded part will affect the selection of metal for tooling. More complex parts require harder metals to withstand the higher stress and pressure involved in the molding process.
4. Cost: The cost of the metal used for tooling must be considered, as harder metals like tool steel are more expensive than softer metals like aluminum.

Tool Steel

Based on these factors, the best metal for injection molding tooling is generally tool steel. Tool steel is a high-grade, hardened steel that offers excellent strength, durability, and wear resistance, making it ideal for high-volume production runs and complex part geometries. Tool steel is also highly resistant to corrosion, making it a good choice for molding corrosive materials. However, for lower production volumes and less complex parts, aluminum may be a more cost-effective option, as it is less expensive and easier to machine than tool steel.

On the other hand, aluminum can also be used as a tooling metal for injection molding, especially for low to medium production volumes and less complex part geometries. Aluminum has several advantages for tooling, including:

1. Lightweight: Aluminum is a lighter metal compared to tool steel, making it easier to handle and transport.
2. Good thermal conductivity: Aluminum has excellent thermal conductivity, which means it can dissipate heat quickly, resulting in faster cycle times and better part quality.
3. Easy to machine: Aluminum is easier to machine than tool steel, which can reduce tooling costs and lead times.
4. Corrosion resistance: Aluminum is resistant to corrosion, making it a good choice for molding corrosive materials.

Aluminum

However, aluminum is not as strong or wear-resistant as tool steel, so it may not be suitable for high-volume production runs or more complex part geometries. Aluminum tooling may also require more frequent maintenance and replacement compared to tool steel tooling. Therefore, the choice of aluminum as a tooling metal for injection molding should be based on the specific production requirements and part geometries.

Important Properties for Injection Molding Materials

The applications of the final parts should be considered when choosing materials for injection molding. The material properties of the final part are critical to ensure that it will perform as intended in its application. The following factors should be considered when selecting materials for injection molding:

PROPERTY	MATERIALS
Strength	POM, Nylon, PEEK,
Rigidity	POM, PMMA, PET, HIPS
Flexibility	ABS, LDPE, PVC
Heat resistance	PET, PEI, PP, PPS
Fatigue resistance	POM, Nylon
Chemical resistance	LDPE, HDPE, PP
Affordability	LDPE, HDPE, PP, PVC

Injection Molding Materials

There are three types of suitable injection molding materials: thermoplastics, thermosets and elastomers.

1. Thermoplastics: These are materials that can be melted and re-molded multiple times without losing their properties. They are heated to a molten state and then injected into a mold where they solidify into the desired shape. Thermoplastics include materials such as polypropylene (PP), polyethylene (PE), polystyrene (PS), and polyvinyl chloride (PVC). They are widely used in injection molding due to their ease of processing, wide range of properties, and cost-effectiveness.
2. Thermosets: These are materials that, once they are molded and cured, cannot be re-melted or re-molded. They are heated and chemically cross-linked during the molding process, creating a strong, durable material that can withstand high temperatures and harsh environments. Thermosets include materials such as epoxy, phenolic, and melamine. They are used in injection molding for applications requiring high strength and durability, such as automotive parts, electrical components, and aerospace components.
3. Elastomers: These are materials that exhibit elastic properties, such as stretch and compressibility, and return to their original shape after deformation. They are often referred to as rubber materials and include materials such as silicone, natural rubber, and synthetic rubbers such as styrene-butadiene rubber (SBR) and nitrile-butadiene rubber (NBR). Elastomers are used in injection molding for applications requiring flexibility and elasticity, such as seals, gaskets, and other rubber components.

Each type of material has its own unique properties and advantages, and the choice of material will depend on the specific requirements of the application. The selection of the right material is critical to ensure that the final product performs as intended and meets the necessary performance and durability requirements.

Parts Coloring

Part coloring in injection molding is the process of adding colorants to the plastic material used to produce injection molded parts. The colorants can be in the form of pigments or dyes that are added to the plastic resin before it is melted and injected into the mold.

The purpose of part coloring is to give the injection molded parts the desired color and appearance for their intended use. Color can be used to enhance the aesthetics of the part, improve its visibility, or help identify it in a particular application. Part coloring can also be used to differentiate between parts with similar shapes or functions.

There are several methods for coloring injection molded parts, including:

1. Masterbatch: This is a concentrated form of pigments or dyes that is added to the plastic resin before it is melted and injected into the mold. The masterbatch is pre-mixed with the plastic resin to ensure an even distribution of color throughout the part.
2. Dry colorants: These are pigments or dyes in powder or granule form that are mixed with the plastic resin before it is melted and injected into the mold. The dry colorants can be added manually or using an automatic dosing system.
3. Liquid colorants: These are pigments or dyes in liquid form that are injected into the molten plastic stream as it enters the mold. The liquid colorants are often used for intricate or small parts where an even distribution of color is critical.

The selection of the appropriate coloring method and colorant will depend on the specific requirements of the application, such as the desired color, opacity, and durability of the part. The colorant must be compatible with the plastic resin used for the injection molding process and must be able to withstand the processing conditions without degrading or altering the properties of the plastic material.