An Overview of the Plastic Injection Molding Process
Plastic injection molding is a manufacturing process in which melted polymer is injected under high pressures into preformed molds. It is used to produce a wide range of solid plastic parts and products, including medical instruments, vehicle components, beverage containers, and consumer goods.
Typical plastic injection molding operations involve the following stages:
- Plastic beads and fragments flow through a hopper or cone into the heating barrel.
- The barrel heats the plastic to its melting point, while a rotating screw pushes the melted plastic toward the nozzle.
- The melted plastic flows through the nozzle into the mold until all cavities are filled.
- The plastic remains under pressure until it has cooled into the desired shape.
- Ejector pins eject the cooled plastic product from the mold.
Industries Using the Plastic Injection Molding Process
Plastic injection molded parts find application across industry. Some of the sectors that regularly employ them include:
- Medical and Dental
- Military and Defense
Material Considerations for Plastic Injection Molding
When choosing a construction material for plastic injection molded parts, it is important to consider the following:
- Aesthetic qualities: the color, texture, and transparency desired in the finished product
- Physical qualities: the strength, flexibility/rigidity, and other physical characteristics desired in the finished product
- Durability: the resistances to various operating and environmental conditions, such as extreme temperatures, corrosive materials, or UV radiation, the finished product should demonstrate
- Service life: the length the finished product is expected to last based on standard usage
- Industry standards and regulations: the industry standards and regulations to which the finished product will be subjected (e.g., FDA, RoHS, REACH, and NSF)
Some of the materials most commonly employed in plastic injection molding operations include:
- Acrylonitrile butadiene styrene (ABS)
- High-impact polystyrene (HIPS)
- Polyamide (Nylon)
Design Considerations for Plastic Injection Molded Parts
When designing a plastic injection molded part, there are several factors to consider to ensure the finished piece functions as intended. Some of the key design considerations include:
- Boss and rib dimensions
- Corner transitions
- Gate and vent placement
- Wall thickness
- Weld lines
Partnering with an experienced and knowledgeable designer can save both time and money during the development and production stages by preventing part defects and manufacturing delays.
Factors Influencing the Cost of Plastic Injection Molding Operations
The design and production of the injection mold is the biggest contributor to the total cost of an injection molding operation, as each one is custom-made to suit the part and production specifications of the project. The exact investment amount depends on several factors. For example, parts with simpler geometries require less expensive molds than parts with more complex geometries (e.g., tight tolerances, intricate elements, or multiple cavities). Additionally, more durable mold materials (e.g., steel) have a higher price point than less durable mold materials (e.g., aluminum).
Beyond the mold, some of the other factors that influence the cost of an injection molding operation include:
- Part material: Materials with special characteristics (e.g., heat resistance, chemical resistance, and UV resistance) or custom formulations are more expensive than standard materials.
- Component size: The larger the part design, the more material needed to manufacture both the mold and actual component.
- Cycle time: The total time it takes for the injection molding process to finish is the cycle time. This period changes depending on the part material and size. A shorter cycle time translates to lower production costs, while a longer cycle time results in higher production costs.
Custom Plastic Injection Molding Solutions From Darter Plastics
For more than 30 years, Darter Plastics has provided high-quality plastic products to customers in a broad range of industries, including aerospace, automotive, defense, medical, and product manufacturing. Equipped with extensive industry experience and cutting-edge injection molding technology, our team manufactures injection molded products from all types of thermoplastic material. In addition to our plastic injection molding capabilities, we offer design/engineering, mold making, pad printing, hot stamping, and assembly services.