Injection Molding

Serving the injection molding industry for over 30 years JW Molding, Inc. has expanded our knowledge of many types of plastics from “Easy” grades, Polypropylenes, styrenes and ABS, to tougher grades such as carbon fiber filled grades of polycarbonate, glass filled Nylons, Valox, and Acetal.

Colors are always available in most specified materials. Just provide us with a color sample and our color house will match it.

About Injection Molding

Injection molding is a manufacturing process for producing plastic injection molds from both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel, mixed, and forced into a mold cavity by a reciprocating screw or a ram injector, where the injection molded part cools and hardens to the configuration of the mold cavity. After a part is designed, usually by an industrial designer or an engineer, molds are then manufactured by an injection mold company, where it is assigned to a mold maker (or toolmaker). Injection molds are usually constructed using either steel or aluminum, and precision-machined to form the features of the desired parts. Injection molding is widely used for manufacturing a variety of parts, from the smallest component to entire body panels of cars. Injection molding is the most common method of production, with some commonly made injection molded items including computer components to outdoor furniture.

The Process and Characteristics of Injection Molded Parts:

Utilizes screw-type plunger to force molten plastic material into a mold cavity
Produces a solid or open-ended shape (typically a cavity and core shape) which conforms to the contour of the injection molded part
Injection molds require the use of thermoplastic or thermoset materials
Parting line, sprue, and gate marks are present
Ejector pin marks are usually present on injection molds

History

How did the world of injection molded parts begin? In 1868, billiard ball maker Phelan and Collander, John Wesley Hyatt invented a way to make billiard balls by injecting celluloid into a mould. Hyatt improved the celluloid so that it could be processed into a finished form. In 1872 John and his brother Isaiah patented the first injection molding machine. This machine was relatively simple compared to the machines used by today’s injection molding companies. It contained a basic plunger to inject the plastic into a mold through a heated cylinder. The industry progressed slowly over the years producing injection molded products such as plastic collar stays, buttons, and hair combs. In the 1940’s the concept of injection molds grew in popularity. This is because World War II created a huge demand for inexpensive, mass-produced products.

In 1946, James Hendry built the first screw injection molding machine, revolutionizing the plastics industry with an auger design to replace Hyatt’s plunger. The auger is placed inside the cylinder and mixes the injection molded material before pushing forward and injecting the material into the mould. This allowed colored plastic or recycled plastic to be added to the virgin material and mixed thoroughly before being injected. Today screw injection molding machines account for 95% of all injection machines companies. The industry of injection molds has evolved over the years, from producing combs and buttons to a diverse array of custom injection molded products for the following industries: medical, aerospace, consumer, toys, plumbing, packaging, automotive, and construction.

Applications of Injection Molds

Plastic injection molding is the preferred process for manufacturing plastic parts. Injection molds are used to create many things such as electronic housings, containers, bottle caps, automotive interiors, pocket combs, and most other plastic products available today. Plastic injection molds are ideal for producing high volumes of plastic parts, due to the ability of making multi-cavity injection molded parts, where multiple parts are made with one cycle. Some advantages of injection molding are high tolerances, repeatability, a wide range of material selection, low labor cost, minimal scrap losses, and little need to finish parts after molding. Some disadvantages of this process include an expensive tooling investment and the need to prototype, as some custom complex parts may encounter problems during the injection molding process such as warp or surface defects. Therefore, injection molded parts must be designed with careful molding consideration.

Examples of Polymers Best Suited for Injection Molds

Most polymers may be used for molds, including all thermoplastics, some thermosets, and some elastomers. There are tens of thousands of different materials available for injection molds and that number is increasing every year. The materials can mixed with alloys or blends of previously developed materials. This allows product designers to choose from a vast selection of materials so they can choose exactly the right properties for the injection molded part or parts they need. Mold materials are chosen based on the strength and function required for the final part and each material has different parameters for molding that must be considered. Common polymers like Epoxy and phenolic are examples of thermosetting plastics while nylon, polyethylene, and polystyrene are thermoplastic.

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