An Overview of Injection Molding

An Overview of Injection Molding

Injection molding is a manufacturing process for producing items in large volumes. It is typically used in mass-production processes, where the same part is created thousands or even millions of times in succession. Injection molding works by introducing molten material into a mold, then allowing the material to solidify and removing the completed, molded shape.

Advantages of Injection Molding

The main advantage to injection molding is the ability to scale production en masse, with extremely low price per unit costs as more and more units are produced. In high volume production, injection molding creates virtually identical parts. The first part will be virtually indistinguishable from the ten thousandth, which is a wonderful characteristic for brand consistency. Low scrap rates relative to traditional manufacturing processes like machining make injection molding an attractive option for manufacturers in a wide variety of industries.

History of Injection Molding

Originally invented in 1868 by billiard ball manufacturer Phelan and Collander to create celluloid balls, injection molding was patented in 1872. In the first injection molding machines, a plunger injected the molten plastic into molds through heated cylinders.

In the 1940s, World War II created a huge consumer demand for inexpensive, mass produced products, and injection molding exploded in popularity, resulting in many advances for the technique. In 1946, the first screw injection molding machine was built, revolutionizing the process with an auger design and allowing for much faster and more efficient injection molding on a mass scale.

Advances in Injection Molding

The auger design represented a tremendous advance for the process of injection molding, as the auger is placed inside a cylinder containing the raw material, mixing the material before it is injected into the molds. This allowed for many more materials options to be introduced to the virgin material. Today, screw injection molding is the favored process, accounting for 95 percent of all injection molding being done around the world.

Applications of Injection Molding

Injection molding is used in a variety of industries including automotive, equipment, electronics, furniture, machinery, aerospace, and medical equipment manufacturing. It is ideal for mass production of the same object.

Injection molding is the preferred process for manufacturing plastic parts. Today, injection molding produces packaging, toys, musical instruments and parts, automotive and mechanical parts, single piece plastic furniture such as chairs and tables, storage containers, and most of the typical plastic products you use every day, from toothbrushes to handles. That’s because injection molding is the most common manufacturing method for plastics globally.

Injection molding is a flexible process that can be used to produce parts made of a wide variety of material. Tens of thousands of different materials are used in injection molding. Thermoplastic or thermosetting polymers are commonly used in injection molding, with dozens of new materials being introduced every year.  

Materials Used in Injection Molding

The two main types of plastics used in injection molding are thermoset materials and thermoplastic materials. Thermoset material cures or hardens and would burn after curing if another attempt is made to melt it. Thermoplastic material, on the other hand, can be melted, cooled, solidified, and then melted again without risk of burning. This makes thermoplastic materials preferable in some instances, because there is very little waste when used for injection molding.

Pros and Cons of Injection Molding

The advantages of injection molding are high tolerances, repeatability, low labor costs, wide material selections, low materials losses, and creation of parts that require little finishing after molding. The injection molding process does have a few downsides. Injection molding requires expensive investments in molds, tooling, and the need for prototypes to work out problems that can occur, such as warp. Injection molding also requires a lot of time to initiate. Typically, 3D printing produces the first prototypes of the desired parts so molds can be created for volume production. Only after extensive testing is the injection molding process ready to begin.

Another potential disadvantage to injection molding is the difficulty in making design changes once the process has begun. Injection molding also requires uniform thicknesses to prevent inconsistencies in the cooling process which can result in defects. So, in this way, injection molding also affects design. Products should be designed from the start with the potential limitations of injection molding in mind to avoid any issues inherent to the process.

Injection molding is a great technology for finished production on a massive scale. If you need more information about injection molding, contact the European Subcontractor Network. We can connect you with a wide variety of subcontractors who can assist you with your injection molding questions.