When Should I Use Plastic Injection Molding?

If you’re planning to manufacture plastic parts or components, you’ve more than likely begun to consider using plastic injection molding. It’s an incredibly efficient way to produce plastic parts. But how can you determine whether it makes sense for you to use plastic injection molding, as opposed to another method, such as plastic machining?

First, let’s take a look at the process of plastic injection molding, how it works, and where it’s commonly used. As the name suggests, this is the process of injecting heated material into a mold. (By the way, this is commonly spelled as “mould” in the U.K. and elsewhere, so you may also see the expression “plastic injection moulding”.) This is most often done using thermoplastic and thermosetting polymers, though the process can also be used with metals and glass.

Injection molding is widely used for making an extraordinary number of different products. If you’re not using one or more of them right now, there are likely to be dozens within arm’s reach as you’re reading this. It’s probably the most widely used manufacturing process at this point in time, and the spectrum of products made in this way include pocket combs, bottle caps, musical instruments, single-piece furniture, handheld gaming devices, and storage containers, to name a few.

Based on a design by an engineer or other designer, metal molds are fabricated. The heated material is forced into the cavity of the mold, and as it cools, it hardens in the configuration of the mold.

Because there is considerable effort and expense involved in designing and fabricating the molds, the process is well suited to high-volume production. If you’re only producing limited runs of a part, it may not be worth the expense of the preliminary work of creating a mold. But for larger runs, plastic injection molding is an excellent solution. It can be astonishingly fast. Though production rates will vary based on the specifics of the part you’re making, it can run as rapidly as 15 to 30 seconds per cycle, producing amazing numbers of parts per hour. If you’re producing smaller quantities, you may want to consider other methods of production, such as plastic machining.

Again because of the initial upfront investment of creating the mold, you’ll find that plastic injection molding is preferably when you’re working with designs that you won’t need to change or adjust. In many cases, making the mold can be as much as 90% of the job. If you need to change the design frequently, 3D printing with its new advances technology, for example, may be a better solution, and may also make sense for lower volume production as well.

Another situation for which plastic injection molding is particularly useful would be the cases in which you are using more than one type of plastic in the same part, or if you need two colors of material in the same part. A variation known as two shot plastic injection molding is ideal for these situations. Overmolding, a process by which an additional layer of material is added to an existing part, has already been shown to produce dramatic results in the production of consumer products and also high tech items like medical devices.

Consider carefully the parts you need to produce, their complexity, the quantity you need, and other factors including your budget. As we’ve mentioned, though there are some situations in which may not make the most sense, In many cases, you’ll find plastic injection molding to be an ideal solution.

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