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How the Injection-Molding Process Helps Create Pretty Much Everything

  • Injection molding is used to create many mass-produced, inexpensive products that you use every day.
  • Although it was invented in 1872 by two brothers, demand for mass-produced items during World War II drove further innovation of this manufacturing process.
  • Software advancements and cloud computing have made it so that injection molding is accessible to more than just plastic engineers.
  • Automation of the process has cut down on labor costs, making it an efficient way to manufacture mass goods.

You may not know it, but the injection-molding process plays a key role in creating a multitude of products you use every day. Did you comb your hair or button up your clothes this morning? Or maybe you strapped your little one into a car seat or cracked open a bottle of water. Without the injection-molding process, hair combs, buttons, car seats, and bottle caps wouldn’t be the ever-present, mass-produced, inexpensive products that they are today.

It all started more than 145 years ago in 1872, when brothers John and Isaiah Hyatt patented a device for heating and injecting celluloid into molds by means of a plunger. As plastics evolved, the injection-molding process became more pervasive in manufacturing. Learn about the history of the injection-molding process and how it paved the way for inexpensive mass production of common consumer goods.

What Is Injection Molding?

Injection molding is a manufacturing process that works by injecting polymers, like molten plastic, into a premade mold. Injection molding creates parts quickly, efficiently, and at a low cost.

It was invented by John and Isaiah Hyatt in 1872 when they patented a device for heating and injecting celluloid into molds with a plunger. Back then, it was used to produce hair combs, buttons, and collar stays.

What Can Be Manufactured With It?

Modern-day injection molding is used to create everything from tables and chairs to food containers. Plastic injection molding is highly efficient and allows for the mass production of objects with complicated shapes, like toys.

What Are the 4 Stages of the Injection-Molding Process?

The injection-molding process is divided into 4 parts:

  • Clamping: The two halves of the mold are clamped shut with enough force that the mold will stay closed as the material is injected.
  • Injection: The polymer shot is injected.
  • Cooling: More polymer is injected to compensate for shrinkage as the plastic cools. The screw turns and is retracted as the next shot is prepared.
  • Ejection: Once it has cooled, the part is ejected and the process starts again.

All in all, this entire injection process can take anywhere from 2 seconds to 2 minutes.

Is Injection Molding Cost-Effective?

Very. Modern-day manufacturing has lowered labor costs through automation, and the use of cloud computing allows engineers and designers to spot problems before they become expensive.

[Video Transcript]

Narrator: What do toys, car seats, and bottle caps have in common? They’re all made with a manufacturing process called injection molding. This process works by injecting polymers—like plastic—into a premade mold. Injection molding allows parts to be produced quickly, efficiently, and at low cost.

 It all started in 1872, when John and Isaiah Hyatt patented a device for heating and injecting celluloid into molds with a plunger. This method was then used to produce items such as hair combs, buttons, and collar stays.

Then, in 1909, Leo Hendrik Baekeland discovered phenol-formaldehyde plastic, otherwise known as Bakelite. A thermosetting resin that was well suited to injection molding, Bakelite was found to be better suited for this process than celluloid. Bakelite had useful insulating properties that made it ideal for electrical applications.

The 1930s marked the beginning of the use of thermoplastic materials that are still in use today: polystyrene, PVC (polyvinyl chloride), polyolefins, and Perspex (polymethyl methacrylate). This laid the foundation of plastics use in manufacturing as we know it today. Soon, more items would be made of plastic than ever before.

Eleven years later, World War II created a huge demand for cheap, mass-produced materials—and injection molding was the perfect solution.

Then, in 1946, American inventor James Watson Hendry built the first extrusion-screw injection machine, which gave much better control over injection speed and quality. This method overcame a major shortcoming of plunger-style machines: the uneven heating of the plastic material. Now, items could be created more quickly, efficiently, and cheaply than ever before.

In 1956, another American, W. H. Willert, received a patent for a reciprocating-screw plasticator in 1956. This reciprocating-screw mechanism sat inside the plasticator machine and heated mixed plastic, allowing material to be moved to the right places. This method increased mixing efficiency by reducing cycle time.

In the 1970s, James Watson Hendry developed the first gas-assisted injection-molding process, which allowed for the production of more complex designs, like those with hollow insides. It also allowed for greater precision while reducing surface blemishes, sink marks, and internal stresses.

The improved design flexibility also meant better strength and finish, as well as reduced production time, cost, weight, and waste.

 In 1972, industrial robotics and injection molding were combined for the first time. Using robots to perform secondary operations while the injection-molding machine was working led to greater increased efficiency and output. At this time, mold design and process refinement were still expensive and required a lot of trial and error in the physical testing of new mold configurations and process settings.

In 1978, Moldflow simulation software was released. Engineers and designers were able to leverage the software to monitor injection pressure and temperature to optimize production, eliminating problems before they became expensive.

1985: Milacron introduces the first all-electric molding machine, which helped reduce energy costs and reduce the environmental concerns of hydraulically powered injection-molding machines.

By the end of the 1990s, Moldflow had released Moldflow Adviser, which opened up the technology for people who weren’t dedicated plastic engineers. This software also made the process cheaper and easier to use and opened it up to an entire nonexpert audience.

When Autodesk acquired Moldflow in 2008, the process was paired with CAD and CAD translators. The software’s focus shifted to a strong emphasis on “ease of use” and the user experience. With this booming popularity and the increased global demand for products, injection molding began to be integrated into other, more customizable applications.

By the late 2000s, improved automation capabilities helped significantly cut down on labor and costs. And, as the world became more eco-conscious, the industry saw a shift to using recycled, renewable, and reclaimed plastics.

In 2010, Moldflow created the first cloud-computing offering, providing computational power for optimization and design of experiments.

Today, injection molding is used by engineers and designers to create almost everything you see around you—from tables and chairs to food containers and mop heads. As progress continues, injection molding will tie further into the cloud, making the technology more accessible and collaborative.

With injection molding cementing its capabilities into new integrations, the opportunities to create are endless. The future of manufacturing is clearly being molded for a new era of innovation.

This article has been updated. It originally published in May 2019.

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