INJECTION MOLDING

Injection Molding Process

A plastic injection machine can be divided into two units. These include the injection unit, which consists of the hopper, barrel, screw, and injector; and the clamping unit, which is responsible for opening and closing the mold and ejecting the finished product. Depending on the manufacturing material and product, a variety of clamps are available.

Injection molding machines come in a wide range of sizes, based on clamping force. To ensure the correct machine is being used for the project at hand, engineers and machine operators must take into consideration the mold dimensions and shot size, or volume, of the mold.

Plastic injection molding machines consist of four primary components: a feed hopper, reciprocating screw, heating barrel, and injector nozzle. The injection process is outlined as follows:

1. A prefabricated hollow metal mold is clamped into the injection molding machine. 
2. Plastic pellets, granules, or powder are fed into the barrel via the hopper. 
3. The plastic material is heated in the barrel using the friction generated by the turning reciprocating screw. Reciprocating screws for injection machines are manufactured with a wider diameter toward the nozzle end to increase heating friction and injection pressure. 
4. The melted material is transported along the barrel by the threads of the reciprocating screw from the hopper to the injector nozzle. In addition to friction from the reciprocating screw, heating bands around the barrel help to keep the plastic in a molten state. 
5. The injector nozzle is located between the barrel and the mold, and is manipulated to adjust the pressure and quantity of plastic injected into the mold cavity. The sprue, or nozzle opening, connects with the mold and fills it with molten plastic at a predetermined pressure and quantity, as programmed. If there are multiple molds, runners connect the cavities so that the injector will only inject one shot of resin to fill multiple molds. 
6. Once the plastic in the mold has hardened and cooled, the product is removed through the use of ejector pins. Depending on the material, parts created via plastic injection molding often require minimal finishing.

Injection Mold Materials

The injection molding process employs metal molds that are typically composed of aluminum or steel, depending on the type of plastic being molded and the intended production method. 

Aluminum is widely used for mold production due to its easy formability, lightweight nature, and quick cooling capabilities. It allows for faster and more efficient production, and is significantly less expensive to form into molds than steel. Aluminum designs are also easy to adapt, so there is less potential expense in the event that a mold design must be adjusted. However, aluminum is less durable than steel and can warp or wear when used for complex or abrasive plastic blends or in extremely high-volume production. 

Steel is the better option for molds that will be used in high-volume production, as it will retain its shape with very little wear. While it is a more expensive material, it will eventually pay for itself over the course of a large production run. Steel is less susceptible to wear and scratching that could be caused by reinforced or rough plastics that would score softer aluminum molds. 

Injectable Plastics

There are a wide range of plastics used in the production of injection molded parts and components, including:

• ABS
• Acetal
• Acrylic
• Copolymer and homopolymer polypropylene
• HTPE/LDPE
• Microcellular
• Nylon
• PEEK
• PET
• Polyaryletheretherketone
• Polycarbonate
• Polyester
• Polypropylene
• Polystyrene
• Polyurethane
• Thermoplastic
• Thermoset

Benefits of Injection Molding

Injection molding is widely used for the production of plastic parts and components, as it offers a wide range of advantages over other plastic fabrication processes. Some of these advantages include:

Detail and Precision

Plastic is injected into molds at high pressures to ensure that all mold cavities are completely filled with material. This ensures highly detailed precision and accuracy. It further allows for the creation of geometrically complex and sophisticated components that would be extremely expensive to create using other manufacturing methods, such as tooling or milling.

Eco-Friendly and Low Waste

Plastic scrap that is generated during the injection process can easily be ground and reprocessed, thereby reducing wastage for a more environmentally friendly and cost-effective process.

Enhanced Efficiency and Automation

Plastic injection molding enables the production of large quantities of parts in a short period of time, providing greater manufacturing efficiency. Automation significantly reduces the cost of labor and increases the rate of output, as well. Through the use of computer-aided design (CAD) and computer-aided manufacturing (CAM) programs, injection molded parts are more consistent and are less error-prone than other processes that require a more hands-on approach.

Improved Component Strength and Durability

Plastic injection molding is highly versatile and allows for the use of fillers and enhancers to improve the strength and durability of plastics during the molding process. Unlike machining and tooling, plastic injection allows fillers to be added throughout the production process.

Multi-Material Injection

In addition to mixing different materials together, injection molding allows manufacturers to combine multiple plastic materials into one product at the same time. For example, they can create the basic form of a plastic toothbrush and add the rubber-like grip material on the same production line. 

Production-Ready With Minimal Finishing

Injection molding allows for a smooth and detailed finish that rarely requires post-production finishing. 

Cost Benefits

The use of plastic injection molding results in multiple cost-saving benefits, including: 

• Material costs. Reduced wastage and precise computerized calibration ensures lower overall material costs.
• Production costs. Automation and large-scale production allow for economies of scale that facilitate a lower cost-per-item on high-volume runs. 
• Tooling costs. Affordable aluminum tooling reduces costs on smaller runs, while more expensive steel tooling costs are mitigated over time by larger runs.

Injection Molding With Darter Plastics

Our plastic injection molding is ISO compliant and meets high industry standards. We mold any plastic material except rigid PVC. All waste is recycled and reprocessed.

Our advanced machinery is equipped to handle thermoplastic, thermoset materials and can provide small to larger shot sizes, ranging from .07 to 40 ounces, depending on client specifications. Constructed with a (+/-) .005 inch precision tolerance and a maximum 400 ton clamping force, our premium plastic molding has successfully served the needs of a wide variety of industries.

From single prototype to OEM high volume production, Darter Plastics can manage all your plastic injection molding requirements. Please inquire about our additional services, which include engineering, mold making, product development, rapid prototyping and tooling.