Choosing the right injection molding material means understanding your application requirements, which may vary between prototyping and production.

Fortunately, you don't need a PhD to make the right material choice. 

Of course, there are many factors to consider, but everything starts with the basics: the names and abbreviations of the main materials, their pros and cons, typical applications, and common brands and grades.

There are ten common injection molding materials:

• Acrylic (PMMA)

• Acrylonitrile Butadiene Styrene (ABS)
• Nylon Polyamide (PA)

• Polycarbonate (PC)

• Polyethylene (PE)
• Polyoxymethylene (POM)
• Polypropylene (PP)
• Polystyrene (PS)
• Thermoplastic Elastomer (TPE)

• Thermoplastic Polyurethane (TPU)

For each injection molding plastic, this chapter introduces three.

1. PMMA, or acrylic acid, is a durable, transparent thermoplastic material, a lightweight, shatter-resistant alternative to glass. 

Because PMMA is transparent and has excellent optical clarity, it allows a high percentage of light to pass through.

Advantages and disadvantages of PMMA 

Acrylic resin has high tensile strength, can withstand loads, does not absorb odors, and can maintain strict tolerances during injection molding. 

The material can also resist sunlight and weather, making it suitable for outdoor use. 

Because it does not degrade when in contact with water, PMMA does not release bisphenol A (BPA), a chemical found in many plastics that can adversely affect human health.

Acrylic resin has some important limitations. 

It is more expensive and easier to scratch than glass. It is also susceptible to grease and oil stains. 

Additionally, for certain industrial applications, PMMA has a low usage temperature. 

Injection-molded acrylic resin lacks strong solvent resistance and is prone to stress cracking under particularly heavy loads.

2. ABS is an engineering-grade thermoplastic material with a relatively low melting point, making it easy to mold. 

This opaque polymer supports the use of colorants and offers different textures and surface finishes. ABS is renowned for its strength and impact resistance.

Advantages and disadvantages of ABS 

ABS is tough, relatively inexpensive, and has good resistance to heat, oil, acids, and alkalis. 

Its styrene content gives injection-molded parts a glossy, aesthetic appearance, while its butadiene content provides excellent toughness even at low temperatures.

Because ABS does not resist sunlight or weather well, it is not a good choice for outdoor applications. 

ABS also produces a significant amount of smoke when burned, has poor resistance to high friction, and lacks resistance to solvents like water.

Applications and grades of ABS 

Injection-molded ABS is used for electronic components and keyboard keys, protective headgear, plastic wall panels for power sockets, and automotive parts such as dashboards, wheel covers, and car body parts. Other applications include consumer goods, sports equipment, and industrial fittings.

ABS can also be combined with glass fillers to increase strength or with polycarbonate to improve resistance to low-temperature impact. Some suppliers produce filled and unfilled ABS plastics.

3. PA is a broad class of materials that can be either natural or synthetic. However, nylon, a type of polyamide, is always synthetic. 

Injection molding nylon can be challenging because this polyamide tends to shrink and may suffer from inadequate filling.

Advantages and disadvantages of PA 

PA's advantages include toughness and high heat resistance. 

They also have high abrasion resistance, good fatigue resistance, and noise-damping properties. 

Injection-molded nylon, with its low friction coefficient, is suitable for high-friction and wear applications. 

Although nylon does not provide inherent flame retardancy and can burn rapidly, flame-retardant versions can be used. 

Similarly, while nylon is susceptible to degradation by sunlight, adding UV stabilizers can enhance performance. 

Additionally, the material has poor resistance to strong acids and bases.

Applications and grades of PA

PA is commonly used in robust mechanical parts such as bearings, bushings, gears, and slide rails.

It is also an ideal choice for housings and snap closures, threaded inserts, power slide plates, jigs, and fixtures. Other applications range from toothbrushes and wheels to medical implants and electrical connectors.

Although PA is a specific type of polyamide developed by DuPont, this polyamide can also be obtained from other companies. 

Today, PA has four main grades: PA 66, 11, 12, and 46. Each grade has slightly different mechanical properties. 

PA 66 has a higher melting point and better acid resistance, suitable for chemical processing applications. 

PA 11 has higher resistance to dimensional change due to its higher moisture resistance, making it suitable for outdoor applications. 

PA 12 has the lowest melting point and relatively good water resistance. Nylon 46 has a higher working temperature than other grades of nylon.