AIM Processing Small Plastic Parts Blog

Historically, small plastic part injection molding has been performed primarily with steel molds. There are many advantages to steel, including:

Nylon is a synthetic thermoplastic first produced in 1935 and introduced as a fabric during the 1939 New York World's Fair. You will also see Nylon referred to by its chemical designation “PA.” It is commonly available in black, white, and off-white or beige, which is its natural color. Nylon can be produced as fibers, filaments, sheet stock, and films, and also as the raw material for injection molding.

Acetal is the common name for polyoxymethylene (POM), a white semi-crystalline thermoplastic. It is strong, abrasion and impact resistant, and tolerates many organic chemical compounds. It has a low coefficient of friction and durable stiffness, so it is often used in moving parts. Because it is widely available in sheet and block form, many machined prototypes are made of acetal. Examples of items made from acetal include a variety of large and small plastic parts:

Polycarbonates (PC) are a group of strong, impact-resistant, heat-resistant, thermoplastics. They are naturally transparent, with the raw material capable of transmitting light as well as glass—and they are much lighter than glass. While they are clear by default, PC plastics are commercially available in many colors.

 ABS is an acronym for acrylonitrile butadiene styrene. (Now you understand why it goes by its initials!) It is an opaque thermoplastic polymer. The term “thermoplastic” refers to a class of plastics that can be reprocessed after an initial heat cycle; as opposed to "thermoset" plastics that undergo an irreversible chemical change during its first heat cycle. ABS is a common engineering grade plastic and it is used in many products around you, particularly electronic enclosures.

It’s not uncommon for a small plastic injection molded part to be expected to hold up under a large load. One of the ways to strengthen a part is by adding one or more “ribs” to the design. Ribs are thin protrusions that extend perpendicular from a wall or plane to provide added stiffness and strength.

If you have a new plastic project in mind, one of the first things you’re likely to wonder is, “What will it cost to create this small plastic part?” In order to answer your question, an injection molder will need to know a little more. Though you may not have precise answers, even educated guesses can help shape an accurate quote so you can explore your options.

Insert molding is a technique in which an item such as a threaded fastener, tube or stud, electrical component, or label is present in the mold. As the viscous plastic fills in around it and hardens, the item becomes a component of the finished part. When performing insert molding, it’s obviously critical that the insert does not move as the mold closes or as plastic is injected under pressure into the cavity — no small feat as hot resin can enter at 20k-30k psi.

Light pipes are rigid, transparent plastic shapes that transfer the light from a light-emitting diode (LED) within an electronic enclosure to the outside. They serve many purposes, including letting  the user of a device know whether it is on or off, whether its battery is in need of charging, etc. Light pipes can transmit as much as 80 percent of the light emitted by an LED mounted on a printed circuit board, making them a great way to share the status provided by an internal component while keeping that component safely enclosed. They can also be used for decorative purposes like illuminating a product logo.

When it comes to the angles used in the plastic part design of injection molded parts, you’d be surprised to learn what a big difference as little as half a degree can make. In particular, the draft of a part can play a major role in everything from how easy it is to eject the part from the mold to how smooth the surface of the finished part is.