Injection Molding

What is Injection Molding?

Injection molding is a manufacturing process that forms plastic (both thermoplastic and thermosetting) into usable shaped parts, such as a toothbrush.

How does injection molding work?

Before any melting of plastic can occur, a mold must first be manufactured. Molds are typically composed of steel or aluminum and comes in two parts, the injection mold and the ejector mold. The design of the product is precision machined between the two pieces of the mold.

After the mold is complete, it is installed into an injection molding machine. Plastic resin is poured into the hopper for heating and mixing at high temperatures. The molten plastic is then forced or “injected” into the mold cavity. As the mold remains cool, the injected plastic quickly solidifies and is formed into the shape of the cavity.

What is the injection molding process?

• Step 1
  Plastic resin is stored and feed into the injection molding machine via the hopper. Plastic resin can be in the form of beads, granules, or flakes.
• Step 2
  For most injection molding machines, the hopper feeds into the injection barrel via gravity. There are also vacuum loading systems available in the market. The injection barrel melts the plastic and prepares it for injection into the mold cavity. Any coloring is typically added at this stage.
• Step 3
  The molten plastic is driven through the injection barrel through one of two different methods. Either a reciprocating screw drives the plastic forward, or a hydraulic ram is used. The reciprocating screw is more precise and is therefore more commonly used.
• Step 4
  Once the molten plastic is injected into the empty mold cavity, it is allowed to cool and solidify. As the mold contains two parts, they separate to allow the part to fall out.
• Step 5
  Some components do not simply fall out, instead an additional ejector pin is added to knock the part out of the mold once it solidifies.

What types of products can injection molding produce?

Injection molding is the most common method of plastic part manufacturing. It’s quick, accurate, involves low labor cost and scrap loss, and can be used with many polymer types. The issue with injection molding is its high initial cost for producing the mold, which can range from hundreds to thousands of dollars (depending on size, sophistication, surface finishes, etc.).

Some examples of injection molded parts include: small plastic components, bottle caps, pocket combs, model kits (model plane, model cars, etc), CD & DVD cases, automotive dashboards, Lego pieces, etc.

The injection molding process video: