Plastic Injection Molding or Plastic Extrusion—What Do I Want?

Posted on: May 12, 2021

Of the two most prevalent methods for producing plastic products, when shopping for a vendor how do you know which process is best for your project?

You have a project requiring a plastic part, but you’re not sure how to get it made. You can find vendors, but they all offer various methods for producing plastic parts, with many handling different processes at their one facility. There are so many possibilities, and you don’t understand the differences between, for example, a blow mold and a roto mold. 

The vast majority of plastic parts production still requires either plastic injection molding or extrusion. How do you know which application is right for your part?

Plastic Injection Molding

From disposable razors to automobile dashboards, computer housings and knife handles to the ubiquitous Lego blocks—about 80% of all the durable plastic items you’ll find out in the world are made using the plastic injection molding method.

The process itself is pretty straightforward. Using a steel or aluminum mold, a plastic injection molding machine heats plastic until it’s liquified. It then injects it under intense pressure into the mold. The finished part is removed from the mold, and the process repeats, creating the next part.

Most commonly, plastic injection molding uses high-density polyethylene (HDPE) and low-density polyethylene (LDPE) plastics. This method is particularly useful for detailed pieces that need to be produced in large quantities—hundreds of thousands or even millions—at a low cost (like that Lego brick mentioned above). Injection molding also requires careful design of the mold, to ensure both quality and production speed.

Plastic Extrusion

In the plastic extrusion process, molten plastic is pushed, usually using a rotating screw, through a die that shapes the plastic (picture a more complicated version of the toy press in the Play Doh Fun Factory you played with as a kid). The extruded forms can be cut to various lengths with basic machining (such as notching or punching) as the material is formed. Depending on the piece being produced, the extruded part may then be placed in a former to cool.

There’s also the option to produce a piece using coextrusion, where two different plastics are driven through the die at the same time to create a layered effect in the final piece.

Pieces created using the plastic extrusion process are usually longer, including tubes, pipes, curtain rods, railing, wire insulation, plastic sheeting, and adhesive tape. The plastics used for extrusion typically include polyethylene (PE), Polypropylene (PP), and PVC (Polyvinylchloride).

Plastic extrusion is a good choice for parts that require great length, high-volume production, and low cost per part.

Which Process is Best For Your Part?

Because of the tooling required, the pressurized injection equipment, and the hydraulic clamps to close and release the molds, plastic injection molding is definitely more expensive—especially at the beginning when the metal molds must be made. But it becomes cost effective when used to create pieces in very high volumes.

Plastic extrusion is generally less expensive, especially in terms of initial costs.

But here’s the interesting part: In some cases, the same piece can be produced using either method. Depending on the finished piece’s profile, a simple piece that’s been produced through injection molding could be produced at a lower cost using the plastic extrusion process.

The way to find out: ask. Talk to your supplier and see which process they each recommend for producing your piece. Send us your part and specifications and our engineers will take a look at your part and application requirements to determine if there are more cost effective ways to achieve the same or superior quality to what you are currently achieving.

What Should You Look for in a Vendor?

The good news is that both of these processes are so widely adopted, there are plenty of options and partners you can work with. How do you select the right one?

First, adaptability is key. Does the vendor have access to a range of materials and resins? Are they accustomed to a consultative sales and design conversation? What does their history look like in the industry? 

While some vendors specialize (medical, consumer goods, aerospace, etc.), consider consulting with a company that has a broad footprint across a range of consumer and commercial goods. The longer the history in working across different verticals, the more likely that company is not only to recommend the right process, but to help you innovate creative and cost-effective solutions. 

Need Help? Consult with a CPRO Expert

With our expertise and industry knowledge, the professionals at Custom Profiles can help you decide if your piece should be manufactured using plastic extrusion, saving you both time and money. We work with a wide range of high-quality engineering resins and general-purpose plastic materials. We’re happy to answer any questions about plastic extrusion and discuss solutions to produce the exact part you need in the best and least-costly way.

For custom plastic extrusion products for your unique part, call us at 229-423-2929 or contact us online.

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