Thermoforming may be one of the coolest plastic forming methods out there. The only thing that comes close to the level of precision is injection molding. This is when plastic is injected into a mold and removed to get a fully formed piece. But not even injection molding looks as cool as thermoforming. The plastic sheet almost liquifies right in front of you and seemingly melts over the mold. Just as quickly it’s solid again and in a whole new shape.
At the same time thermoforming is a very efficient and cost effective way to shape plastic. As mentioned, plastic injection molding is the only thing that comes close, but it doesn’t quite get the level of detail and consistency as thermoforming. Injection molding also isn’t as cost effective unless you’re making tons of units...quite literally tons.
Thermoforming is comparable to injection molding because both methods soften or liquify plastic in order to reshape it. With injection molding the plastic is literally injected into a mold. Thermoforming, on the other hand, is basically heating a sheet of plastic to soften it and then molding it into a desired shape. Both methods are good ways to mold and form plastic, but knowing when to use the right method can be a lifesaver.
Let’s take a look at the thermoforming process. You’ll usually hear vacuum thermoforming or pressure thermoforming. There is a difference, but before we get into that let’s start at the beginning.
Before any forming happens, a mold has to be created. Molds are typically made from wood or aluminum. They can be male or female, meaning generally convex or concave, although pressure molding predominantly uses female molds. They won’t have every little detail of the final product, but they are the basic shape
Once the mold is placed in the machine, a sheet of plastic called a thermoplastic is held over it. The sheet is then heated to the necessary temperature and placed over the mold. Then air pressure is used to shape the plastic. Vacuum thermoforming uses--you guessed it--a vacuum to pull the plastic down over the mold. In addition to or instead of a vacuum, some machines will have air pressure that comes from above the plastic sheet and blows the sheet over the mold. Slightly different processes, but same effect.
The finishing details are added once the newly shaped plastic has been removed from the mold and allowed to cool. The excess material is removed and any finishes, like holes and notches, are added. Presto...you’ve got your plastic part. It really is that simple.
So, we have a better understanding of what thermoforming is, but why use it? Well, thermoforming is typically used for small and mid-sized production runs. The pieces can be any size (as long as they fit in the machine). The process has low tooling costs and quick turnaround times.
Basically, all this means nine times out of ten, thermoforming is going to be the way you want to go. It’s cost effective, so you can stay under budget. It’s a fairly quick process, so you’ll meet your deadline.
Now, everything has a time and place, and there is a place for injection molding. When you have a large run (we’re talking tens of thousands of pieces) and a good lead time, injection molding is going to be the better method. The cost is generally higher than thermoforming, but when the production run hits that amount, the cost is offset and it becomes the logical choice. Unless, you’re a major bottled water manufacturer, it isn’t likely you’ll be making that many parts.
It’s no wonder thermoforming is used by almost every industry from automotive to agricultural to retail. You likely see items made by thermoforming everyday. Packaging is a big one. Use a toothbrush? The plastic package it came in was thermoformed. Batteries? Same thing. Your car? Parts inside and outside were made with thermoforming.
Knowing when to use thermoforming can save a ton in production costs and time. It’s a method that allows you to quickly form plastics. Whether it’s a single part or many pieces, it’s most likely the best way to get the job done.