Plastic Injection Molding

Plastic injection molding companies like 3ERP can give a consistent matte finish to plastic injection molded parts — soft grip handles, for example — by carrying out techniques like sandblasting, chemical etching and EDM on the metal mold. The surface roughness of matte moldings typically ranges between 0.40 and 18.00 Ra µm.

It is possible to make high-shine molded parts with a gloss finish — electronics housings, for example — using post-processing techniques like sanding, polishing, and diamond buffing. The lowest level of surface roughness for acrylic molded parts is around 0.012 Ra µm.

In addition to simple matte and gloss finishes, it is possible to add more complex textures to moldings, such as wood grain effect, mottling, curved or straight lines, or diamonds. 3ERP can add textures and finishes adhering to Mold-Tech (MT) standards, of which there are hundreds, as well as Verein Deutscher Ingenieure (VDI) and Society of Plastics Industry (SPI) standards.

One of the biggest advantages of plastic injection molding is the ease with which parts can be colored. The most effective way to make color molded parts is to directly mix pigments with the material pellets before injection molding begins.

Surface texture and coloration are typically controlled by actions taken prior to the injection molding process, but we can also perform a range of secondary operations on the moldings once they have been manufactured. Such operations include:

• Painting: For adding color to certain sections of the moldings
• Laser engraving: For adding engraved design or text to the moldings
• Silk-screening: For adding text, logos, or other visual elements to moldings (best for large surface areas)
• Pad printing: For adding text, logos, or other visual elements to moldings (best for small or uneven surface areas)
• Heat staking: For bonding two or more components (including delicate components)
• Ultrasonic welding: For bonding two or more components

Plastic injection molding is a manufacturing process mainly used to make plastic parts in large quantities. Used by many industries for a wide variety of parts, plastic injection molding produces more thermoplastic parts per year than any other plastic manufacturing process.

The plastic injection process requires a metal mold and an injection molding machine. Plastic pellets are heated to melting point, then forced into the mold, where the material cools and solidifies, assuming the shape of the mold cavity.

The most common materials for plastic injection molding are thermoplastics such as ABS, nylon, and acrylic. However, it is also possible to mold thermosets and elastomers.

Plastic injection molding can produce parts in a range of sizes, from bottle caps to large automotive panels, but it is best suited to thin-walled parts, because thick sections of molded plastic are more likely to deform as they cool down inside the mold.

The process begins with the plastic injection molding manufacturer creating a two-part metal mold, typically by precision machining steel or aluminum. An injection mold can last from around 500 to a million injections of plastic, depending on its material and construction.

The plastic injection molding company then sets up the tooling in an injection molding machine. The chosen plastic material — in pellet form — is placed in the machine’s hopper, from which it is gradually dispensed into a heated barrel and mixed with a reciprocating screw or auger. The screw is used to force the now-molten plastic toward the nozzle of the barrel. The liquid plastic then exits the nozzle and enters the mold cavity via a sprue and a network of channels called runners. 

Once inside the mold, the liquid plastic rapidly cools down and hardens, becoming a solid plastic part shaped like the mold cavity. The mold is opened, and the finished part is taken out of the mold with the aid of ejector pins.

Regular users of plastic injection molding services include automotive, aerospace, industrial, medical, and consumer goods companies. Common plastic injection molded parts include medical devices, automotive panels, food containers, packaging, and toys.

The benefits of using plastic injection molding companies to make molded parts include:

• Economy of scale: Once the mold has been made, each plastic molding is rapid and inexpensive. Plastic injection molding manufacturers can make tens of thousands of duplicate parts at very low cost.
• Surface finish: The injection mold can be post-processed to adjust its surface finish: smooth, matt, or whatever texture is required. Each molding from the mold will then come out ready for use, without itself requiring post-processing. 
• Fine details: Because the molten material is injected at high pressure, it reaches every tight corner of the mold cavity. This allows for detailed parts with fine features, even at a very small scale.
• Strength: Plastic injection molding produces relatively strong plastic parts — stronger than comparable parts built using an FDM 3D printer, for example.
• Multi-material parts: Using specialist techniques like overmolding and insert molding, it is possible to make custom plastic injection molding parts with components made from different materials.