Plastic is so prolific in the modern era that most of us don’t give it a second thought. It is just a normal part of how we live our lives. But have you ever considered how plastic parts are made? Manufacturers usually choose one of three processes. Each one has its strengths and weaknesses.
For the record, manufacturers need to source raw materials before they can manufacture parts. Those raw materials can be virgin plastic pellets, recycled plastic pellets, or a combination of both.
Seraphim Plastics, a Tennessee company that produces plastic regrind from recycled industrial plastics, says a lot of manufacturers are willing to combine regrind with virgin plastic if it helps the bottom line.
1. Plastic Extrusion
Moving on to how plastic parts are made, the first process is known as extrusion. It is a process that forces hot, liquid plastic through a steel die to create a particular shape. Extrusion can be continuous or set up to produce one part at a time. Its main benefit is repeatability.
Let us say you want to produce small plastic tubes for ballpoint pens. With a die and extrusion, you can produce tens of thousands of identical pieces with very little labor. Repeatability guarantees consistency across an entire run.
Extrusion does have two big downsides. First is the fact that you are limited to very simple shapes. Extrusion doesn’t allow you to do anything complex for the simple fact that a die can only create one fixed shape. The other downside is the complexities of manufacturing the die. You are working with steel, and that is difficult and time-consuming.
2. Injection Molding
Injection molding also uses steel forms. But rather than single-shaped dies through which liquid plastic is forced, these are forms machined into the shape of the parts being manufactured. The steel form becomes a closed mold into which liquid plastic is injected. The liquid quickly cools just before a blast of air or a spring-loaded cam pushes the part out.
Again, repeatability is the big benefit here. Manufacturers can mass-produce tens of thousands of parts and know for sure that each one is identical. Quality is consistent as long as the plastic formulation remains consistent. As an added bonus – and it’s a big one – injection molding allows for an unlimited number of shapes and designs.
On the downside, manufacturing steel molds is even more difficult than making the dies for extrusion. With different shapes comes the need for a lot more work in the mold department.
3. 3D Printing
Last on the list is 3D printing. This particular process relies on high-tech printers that translate computer code into three-dimensional objects using a printer remarkably similar in design to an inkjet printer. But rather than the printhead working with ink, it works with molten plastic.
3D printing’s biggest advantage is fast setup and turnaround time. Where it could take weeks to create a die or mold for one of the other two processes, a 3D printer can be set up in a matter of hours. That makes it ideal for prototyping purposes. Manufacturers can print one or two pieces, check them against specs, make modifications, and then try again. They can do it all much more quickly than they could with extrusion and injection molding.
On the downside, the actual printing process is much slower. That makes it unsuitable for mass production. It is also more expensive per part. But designers and engineers are working on changing that. Someday, 3D printing may replace both extrusion and injection molding for mass producing cheap plastic parts. And now you know.