Click to ExpandWhat-Is-Injection-Molding

From plastic goods to gears, almost everything is made with injection molding. It is regarded as one of the best solutions for businesses developing products. Moreover, today’s modern manufacturing industries can profit greatly from this molding technique.

With injection molding, plastic materials heated to a molten state are injected into a mold before being cooled and solidified. This process plays a significant role in plastic processing and is appropriate for mass manufacturing goods with complex shapes.

What Is Injection Molding?

Injection molding is one manufacturing technique that enables the mass production of parts. The need to repeatedly recreate the same part is typical in large production operations. An injection mold may create parts in batches of a thousand, but it can also make the same part up to a million times throughout its lifetime.

With injection molding, a wide variety of parts — even those with complex shapes — can be produced swiftly and continuously in significant quantities. As a result, various sectors use this technique to create goods and products.

How Does It Work?

Creating the mold itself is the first step in the injection molding process. The majority of molds are constructed of metal, typically steel or aluminum, and are carefully machined to fit the characteristics of the product they are to manufacture.

After mold creation, the part’s material is incorporated into the heated barrel. Heat melts the material inside the barrel as a helical screw mixes it. Next, the molten plastic is poured into the mold cavity, which cools and solidifies to take on the mold’s shape. Cooling lines that circulate water or oil from an external temperature controller help shorten the cooling process. When the material has been set, plate molds (also known as “platens”) that hold the molding tools open to allow the item to be removed using ejector pins.

For an efficient injection molding process, the shape and features of the required part must be carefully designed. Materials to be used for the part and the mold should be ideal for the part being produced too. Lastly, the molding machine should be appropriate for the molding requirements of the part.

Types of Injection Molding Processes

Depending on the materials to be processed in creating parts with an injection molding machine, it can be categorized into four processes:

Plastic Injection Molding

The plastic injection molding method involves melting plastic pellets (thermosetting/thermoplastic polymers) that once flexible enough, are injected at pressure into a mold cavity, filling it, and solidifying it to create the finished product.

Liquid Silicone Rubber Molding

Although it can be damaged by some solvents like mineral spirits or gasoline, liquid silicone rubber has outstanding thermal, electrical, and chemical resistance capabilities. For this reason, silicone injection molding can be utilized in high-temperature automotive applications but should not be used for fuel lines.

Additionally, it is perfect for elastomers due to its low compression set or little permanent deformation when a force is applied and released. Compared to conventional steel molds, this enables faster and more cost-effective tooling.

Overmolding and Insert Molding

With overmolding, the substrate pieces are manufactured using a typical injection molding procedure using an aluminum mold without any internal heating or cooling systems.

After the substrate sections have been molded, the mold tooling is put together and attached to the press. Next, the substrate components are manually inserted into a mold, and each component is overmolded with either liquid silicone rubber or a thermoplastic substance.

In a similar process called insert molding, a prepared part—often made of metal—is inserted into a mold and then covered with plastic to produce the final product. Parts are packed and delivered after the run is finished.

Injection Molding Materials

There are plenty of plastic materials ideal for injection molding. For example, various plastic resins impart end-use characteristics like tensile strength and impact resistance. Additionally, there are certain processing requirements for injection molded plastics, such as melt temperature and molding pressure — several grades of the same plastic substance, including resin varieties with additives like glass or fiberglass.

Acrylonitrile Butadiene Styrene (ABS)

Acrylonitrile butadiene styrene, also known as ABS, is a type of thermoplastic injection molding material for car body parts, keyboards, and pipes. The material is known for its high-impact resistance and for being lightweight.


Nylon — or polymer fabric — is known to be the most versatile injection molding material. It is commonly used for insulators, automotive tires, and clothing accessories. It is also known for its durability, elasticity, and abrasion resistance.

High-Density Polyethylene (HDPE)

Plastic bottles, shampoo bottles, toys, recycling bins, and flower pots are the main products made from high-density polyethylene, a thermoplastic used in injection molding. The main advantage of selecting HDPE is that it is both fairly priced and constructed of hard and extremely durable material.

High flammability and a lack of biodegradability are two HDPE disadvantages. Additionally, high-density polyethylene cannot be mixed and weathers poorly.

Low-Density Polyethylene (LDPE)

Low-density polyethylene is a much softer and more flexible polymer than HDPE. Bottles, plastic bags, wraps, and playground slides are all made with low-density polyethylene using injection molding. This material’s resistance to chemicals and moisture makes it advantageous. Additionally, it is affordable and high-quality to be used in food, making it safe.

Polycarbonate (PC)

A strong, long-lasting injection molding material used in engineering is transparent polycarbonate. PC is in bulletproof glass, safety hamlets, CDs, and other electrical and telecommunication equipment.

Polyoxymethylene (POM)

POM, commonly known as acetal, is a hard, durable substance used in plastic injection molding. Automotive parts can be made using acetal. Acetal is also used to manufacture zippers, fan wheels, door handles, lock mechanisms, and insulin pens. It features high resistance to chemicals and organic solvents.

Acrylic Poly (Methyl Methacrylate) (PMMA)

One of the materials recommended for injection molding that is also frequently used as a substitute for glass is acrylic. The excellent gloss, robust abrasion resistance, and weather resilience of acrylic are among their advantages. However, it is fragile under pressure and only possesses a modest level of heat resistance.

Thermoplastic Polyurethane (TPU)

TPU features increased durometer and rubber-like flexibility. As a result, it is a perfect substitute for hard rubber. Additionally, injection-molded TPU can carry a large amount of weight and endure ozone exposure.

TPU is more resistant to corrosive substances and high temperatures than TPE. TPUs may be too stiff for some injection-molded components. Additionally more expensive on average, and drying is necessary before processing thermoplastic polyurethanes.

Thermoplastic Rubber (TPR)

Another material used in injection molding is thermoplastic rubber, sometimes an elastomer. It combines rubber and plastic elements in home appliances and other applications, such as wire and cable insulation for automotive parts. The benefit is that it can extend and return to its original shape.

Polypropylene (PP)

The second most utilized plastic in the world is polypropylene. It has a high melting point, good chemical resistance, maintains its shape after torsion or bending, and won’t break down when exposed to dampness or water. In addition, PP, commonly known as injected molded polypro, is recyclable.

Injection Molding for Medical Manufacturing by ProMed Molded Products, Inc.

ProMed was established in 1989 to meet the demand for cleanroom manufacture of silicone components, particularly those for medical use. With more than 30 years of expertise in the field, we remain dedicated to the products we offer our customers by helping improve people’s health and well-being worldwide through our high-quality molded products.

Contact us now or call us at (763) 331-3800 to learn more about how we can help with your projects.