Injection Molding — Guide to Buying Manufacturing in China

What is my role as a buyer?

Material selection, and why it is important

  • Acrylonitrile butadiene styrene (ABS): It solidifies quickly, has good impact resistance, is tough and sturdy, has a glossy appearance and doesn’t shrink easily when molded. ABS is used to make light and rigid parts such as pipes, toys and golf stick heads. However, it melts or warps at temperatures above 93 degrees Celsius, making it unsuitable for parts that are subject to sustained and intense heat.
  • Polycarbonates (PC): These are a group of hard, stiff, and tough thermoplastics that are also known for their thermal stability. Being naturally transparent, polycarbonates are used to make safety goggles, riot shields, compact discs, and baby bottles among others. However, they are not ideal for products that require a certain degree of flexibility or color aesthetics.
  • Polypropylene (PP): This highly pliable thermoplastic is used for products that are flexible, lightweight, heat-resistant, and water-resistant. Food packaging, pipes, cables, bottle caps, washing machine drums and toys, for example. It can also be spun into fiber to make upholstery, carpets and rope. Polypropylene is often called the “steel of plastics” due to its versatility. However, it is difficult to dye or paint, is prone to UV degradation and is flammable.
  • Nylons: A class of plastics with high heat, chemical and wear resistance, nylons are also flexible, durable and flow easily around complex inserts. Toothbrushes, fasteners, and food packaging are some examples of nylon molded parts. However, nylons are prone to shrinkage. They also have poor dimensional stability, water absorption and heat resistance.
  • Acetal: This stiff and strong thermoplastic has high dimensional stability, is easy to machine and has good wear resistance. It also offers great friction resistance, can be dyed easily and is pocket-friendly. Garden hose heads, zippers and valves are some products molded from Acetal. This plastic is unsuitable for products that will be used in environments where they are exposed to acids, UV rays and high temperatures.
  • Polyethylene (PE): Polyethylene is moisture-resistant and perfect for waterproof molded parts. Think plastic shopping bags. It is also lightweight, flexible, soft, and affordable. It comes in a high-density and low-density version. Low-density polyethylene (LDPE) is used to make six-pack rings, containers, and computer parts. It is not suitable for use in high temperatures or harsh weather. High-density polyethylene (HDPE) is highly versatile with both common (lotion bottles, pipes) and uncommon applications (used in facial reconstruction procedures).
A plastic injection molded spoon among wooden beads

Common design mistakes and how to avoid them

The plastic and pollution debate

  • Recycled plastic plays a big role in plastic injection molding. While its performance might not be as good as new plastic, using it is a planet-friendly decision that can also lower production costs.
  • Similarly, plastic products can be re-purposed and re-used after being recycled. For example, recycled LDPE shopping bags are often put to use a second time as trash cans, floor tiles, furniture and paneling.
  • Plastic injection molding machines run on power. But, with technological advances, today’s devices are said to consume 20% to 50% less energy than machines from a decade ago. Also, if given a choice, you can pick an electric machine over a hydraulic machine as it is more energy-efficient.




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