Injection molding is a popular manufacturing process for producing large quantities of plastic parts from materials called thermoplastics. It's the process of melting plastic, injecting it into a mold then repeating the process to make thousands or even millions of the same part.
What is a Injection Moulding?
Injection moulding is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals (for which the process is called die-casting), glasses, elastomers, confections, and most commonly thermoplastic and thermosetting polymers. Material for the part is fed into a heated barrel, mixed, and injected into a mould cavity, where it cools and hardens to the configuration of the cavity. Injection moulding is widely used for manufacturing a variety of parts, from the smallest components to entire body panels of cars. Advances in 3D printing technology, using photopolymers that do not melt during injection molding of some low temperature thermoplastics, can be used for some simple plastic injection molds.
What Materials are Used in Injection Molding?
There are many plastic or resin materials available in the manufacturing industry. Selecting the right match for your custom injection molding project is essential to producing a high-quality injection mould parts. Each material will have its own set of unique characteristics and chemical makeup. When selecting the best material for your plastic mould injection molding project, consider the durability, performance, texture, flexibility, density and color.
Here are some of the materials for injection molding manufacturing:
Polycarbonate is a commercially available thermoplastic that can withstand strong impacts, is transparent and amorphous. It can be pliable at room temperature and may be reformed without the application of heat. Polycarbonate can be liquified at its melting point, making it easy to use for injection molding applications. Some common applications of polycarbonate include windshields, phone cases, pens, vehicle headlights and more.
Polypropylene (PP) is the second most widely-produced plastic globally, after polyethylene (PE). Its behavioral characteristics are similar to PE, but it is slightly harder and more heat-resistant. It is a commodity–grade polymer popular in the packaging and labeling industries. PP is tough, fatigue- and chemical-resistant, but vulnerable to UV radiation and is flammable. It is a versatile plastic, as it is easily customized with additives. It is naturally white. Due to the elasticity of PP, it makes a good material for living hinges. It is also used in many common products such as buckets, packaging, bottle caps, toys and many other items.
Polyvinyl Chloride (PVC) is a popular polymer that is naturally white and brittle. It is available in two forms, flexible and rigid. The first form is a rigid or unplasticized polymer (RPVC or uPVC) commonly used for construction products such as vinyl siding or pipes. The second form, flexible, plasticized PVC, is made bendable by the addition of phthalates. It is used for flooring, insulation, electrical wires and more.
Acrylic (polymethyl methacrylate PMMA), sometimes called plexiglass, is a thermoplastic homopolymer that is often used as an impact–resistant replacement for glass. The light transmittance of acrylic is 92%, which is similar to optical quality glass. Acrylic is UV and light resistant and will not fade. It is ten times more impact resistant than glass. There are numerous benefits to using acrylic for injection molding manufacturing. Common acrylic applications include lenses, medical devices, screens, furniture, paint, beauty products and more.
Injection molding resins (or thermoplastic resins) are plastics that are easy to manipulate or mold once heated to a certain temperature and become solid once they are cooled. Resins are ideal for the injection molding process because they can be liquified, injected into a mold using pressure and then cooled to form a custom product. Some common resins used for injection molding include crystalline plastics, amorphous plastics, imidized plastics, polyethylene, polypropylene, acrylonitrile butadiene styrene, polyoxymethylene, polystyrene and more.
Nylon (PA) or Nylon Polyamide is a common synthetic thermoplastic polymer that is popular due to its high melting temperature, tensile strength, low friction and resistance to chemicals. It is both durable and flexible. Nylon can be combined with other thermoplastics to achieve increased strength. Nylon can be combined with many additives to create different variants and material properties. Its overall versatility is just one of its many advantages.
Acrylonitrile Butadiene Styrene or ABS is a thermoplastic polymer widely used for injection molding. It is durable and can stand up to scratching, is budget-friendly and is easy to machine and fabricate. ABS can be used in conjunction with a metal coating as many metals can adhere strongly to ABS plastic. ABS is perfect for projects that demand strength, stiffness and impact resistance. It can be painted, glued and is easy to recycle. ABS plastic properties are not highly sensitive to temperature or humidity. Molding ABS at a high temperature produces resistance to heat and a nice gloss, while molding it at a low temperature will result in strength and impact resistance. Therefore, its final properties and strength are influenced by the conditions used during the manufacturing process.
Injection molding thermoplastic rubbers are plastics that are easy to manipulate or mold once they have been heated to a certain temperature and then become solid at room temperature or through a cooling process. Thermoplastic rubbers are ideal for injection molding manufacturing because they can be liquified, injected into a mold using pressure and then cooled to form a custom product. There are many advantages and applications of thermoplastic rubber.
Polystyrene (PS) is a transparent thermoplastic most often used to create single-use products. It is odorless and non-toxic. Polystyrene is available in either solid or foamed. As a solid, it is used to make plastic cutlery, electronics, toys and auto parts. As a foam (Styrofoam) it can be extruded to make packing peanuts, disposable drinking cups and more.
Low–Density Polyethylene (LDPE) is a form of polyethylene (PE) that is made using high pressure and high temperature. LDPE is a flexible type of polyethylene used mainly for packaging. It has superior moisture resistance but is not suitable for products that require weatherability or that must withstand high temperatures. LDPE has good impact strength and chemical resistance. LDPE can be used to make six-pack rings, toys and computer components. In recycled form, polyethylene can be used to make trash cans, tiles, paneling and furniture. Polyethylene products account for 34% of total plastics on the market.
Fiber–reinforced plastics (FRP) is a cost-effective material that results in lighter weight products with increased durability. They are a composite material consisting of a resin and select fibers such as glass or carbon. By adding fibers to resin, the material receives additional support. Fiber–reinforced plastic for injection molding lowers material and labor costs, reduces production time and creates minimal waste. The result is a product that is durable and resistant to warping and cracking.
High impact polystyrene (HIPS) is polystyrene that has rubber additives to improve its flexibility and impact strength. While polystyrene is normally transparent, HIPS is opaque and can be painted and labeled. High impact polystyrene is a cost-effective material that is easy to customize, recycle and manufacture. HIPS is ideal for smaller parts and products that require higher levels of detail and variable thickness.
Polyoxymethylene (POM, acetal, polyacetal, polyformaldehyde) is a combination of plastic material used to create parts with good dimensional stability, low friction and high rigidity. It is opaque white and is available in many colors. Similar to other thermoplastics, POM becomes a liquid at its melting point, making it an easy material to use in the injection molding process. POM is commonly used for eyeglass frames, fasteners, guns, knife handles, lock systems and other engineering and automotive parts.