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Knowhow: what is plastic injection molding?

plastic injection molding

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This guide outlines how plastic injection molding works, including its history, processes and what it can be used for.

Injection molding refers to a manufacturing procedure involving parts by injecting a molten substance into the mold. You can perform injection molding using host materials such as elastomers, metals, confections, glasses, thermosetting and thermoplastic polymers. Injection molding is similar to the jello-making procedure.

What is plastic injection molding?

Plastic injection molding is a process that involves the production of plastic parts by introducing molten plastic into metal molds. John Wesley Hyatt, an American inventor, was the first to perform the first plastic injection molding. He created the plastic injection molding machine while substituting ivory billiard balls with plastic balls.

Although the resulting product did not meet his requirements, the machine did. Following the launching of the molding machine, the industry has dramatically soared and advanced from producing tiny ingenious plastic parts such as buttons to making complex medical equipment. The device makes it possible to manufacture intricate products while ensuring 100% similarity.

What products can you make from an injection molding process?

Injection molding is the most common manufacturing process for the mass production of different types of goods. You can produce several products using plastic injection molding service, ranging from large objects such as garbage cans to tiny mobile phone cases.

Manufacturers prefer the process to create non-consumer parts, whose visual appeal is not of concern because the procedure leaves behind a coating of impurities on the parts, which ruins their physical appearance. They may use this process to make products such as mechanical parts.

What does the injection molding process include?

The process involves four distinct steps, including:

  • Melting the material

The first step of the injection molding process is subjecting materials under high temperatures to melt. There are many materials that manufacturers may use, including glasses, metals, elastomers, and confections. However, thermoplastics and thermosetting polymers are often used for this process.

  • Introducing the molten material into a mold

After the material melts, the molten plastic or metal enters the mold, and the air gets out through vents. The heated material needs to fill the mold to attain the right shape appropriately.

  • Allowing the molten material to cool and solidify under low temperatures

Once the mold is filled, the molten is allowed to cool to harden. Cooling time is relative, and it depends on the type of material used. For example, steel may take longer to set than glass.

  • Withdrawing the hardened substance from the cavity of the mold

After cooling, the mold opens, and the part falls in a bin.

The injection machine comprises four parts that play a vital role in injection molding. These parts include:

  • Injection unit
  • Control
  • Clamping unit
  • Base

How does a plastic injection machine function?

plastic injection molding

The first step of the process involves feeding plastic pellets from a hopper into a barrel, which comprises an internal auger. An auger refers to a spiral-shaped tool that provides material into the barrel by rotating. The heat bands heat the screw and barrel, changing the plastic into molten material.

The initiation of the machine cycle closes the mold and triggers the auger to lurch forward due to the high pressure. In no time, the internal auger introduces the molten plastic into the mold cavity. A coolant then flows through the channels to hasten the cooling process of the molten plastic. In less than a minute, the molten plastic solidifies, taking the shape of the cavity. Afterward, the mold opens, releasing the plastic part. Once the machine disgorges the part, the process begins again.

What type of plastic is suitable for injection molding?

Plastic part manufacturers assert that thermoplastics are elite in the plastic injection molding process. Thermoplastics are preferable because they melt under high temperatures and solidify under low temperatures.

Additionally, you can heat and cool thermoplastics multiple times before they are completely degraded, unlike thermoset plastic material, which flares when heated multiple times. Thermoplastics are used to make the plastic pellets for the molding process. You can combine the plastic pellets with recycled material, colorants, or glitters to improve the physical appearance of your desired product. Some of the thermoplastics suitable for the process include:

  • Polycarbonates
  • Acrylonitrile Butadiene Styrene (ABS)
  • Polypropylene
  • Nylon
  • Polyethylene

What are the advantages of injection molding?

The manufacturing industry accounts for about 1.5% of employment per annum on average in the entire manufacturing industry. Manufacturers prefer plastic products because of the following reasons:

·         High efficiency

Plastic injection molding is a fast process with shorter periods between cycles. Speed varies depending on the complexity of the product design, but there are approximately 15-120 seconds between each cycle. As such, it allows cost-effective, high production output. Using a single mold, manufacturers can produce several parts, making the process effective and efficient.

·         Enhanced strength

Strength is an essential factor that manufacturers consider since it determines the efficacy of a product. The process allows the use of fillers in injection molds which help reduce the density of plastic and strengthen a particular part. Other molding processes may not achieve this, making the process suitable for producing solid and durable products.

·         Complex part design

Injection molding is famous for producing complex parts while maintaining uniformity. Today, most medical and automotive industries use the process to make most of their products. However, to optimize the precision of end products, the design needs to be top-tier. Any errors in the plan may result in processing mistakes which translates to high production costs.

·         Color flexibility

The benefit of having the right color for your plastic parts cannot be overstated. Wrong color choices can misrepresent a brand and misinform your consumers. Injection molding allows you to get custom colors for your products. The process supports several coloring techniques that include master batching, solvent coloring, dry pigment mixing, and compounded colors.

Injection molding is taking the market by storm, and over time manufacturers are inventing ways of manufacturing more complex products using the injection molding process. Join the bandwagon to enhance the chances of seeing your manufacturing business reach the next level.