What is Thermoforming?
Definition: Thermoforming of plastics is the operation in which a thermoplastic sheet is heated to its softening point, stretched into a single sided mold and then it is holded in a place till it cools and solidifies into a desired shape.
Thermoforming of plastics is mainly used for manufacturing of food packing boxes, toys, trays, aircraft windshields, etc.
Well, this is just a simple overview. But further I have mentioned so many important things regarding thermoforming techniques like; Types of thermoforming polymers, Types of thermoforming operations, Examples of thermoforming products, etc.
How does thermoforming work?
Thermoforming of plastic is done in the following steps.
- In thermoforming operation, first of all the thermoplastic sheet is clamped into a holding device and then it is heated.
- This heated thermoplastic sheet is placed over a mold in a horizontal direction and then it is stretched into a mold by either vacuum pressure, air pressure or mechanical pressure.
- Because of this pressure, the heated plastic sheet occupies the shape of the mold.
- The plastic is held in this stage for some time and it is allowed to solidify.
- The excess material is trimmed away and the final thermoformed plastic is ejected from the mold.
- The excess material can be mixed with the unused polymer and it can be reused.
Types of thermoforming plastics
Different thermoforming plastics materials used for thermoforming operation are listed below.
- Polyvinyl chloride (PVC)
- Low density polyethylene
- High density polyethylene
- Cellulose acetate
- Acrylonitrile butadiene styrene (ABS)
Types of thermoforming
There are 3 types of thermoforming operations used for molding of plastics.
- Vacuum thermoforming
- Pressure thermoforming
- Mechanical thermoforming
Let’s discuss each of these plastic thermoforming types one by one.
#1) Vacuum thermoforming
In vacuum thermoforming of polymers, the preheated plastic sheet is shaped by the means of vacuum produced in the mold cavity.
Because of the vacuum pressure, the soft plastic sheet gets deformed and it occupies the shape of the mold cavity.
The cooling of plastic takes place when it comes in contact with the mold surface. And then the solidified plastic component is ejected out from the mold.
#2) Pressure thermoforming
In pressure thermoforming of plastics, the preheated plastic sheet is shaped by the means of air pressure.
The pressurized air forces the heated plastic into the mold cavity and it occupies the desired shape.
The plastic cools down in the mold and then it is ejected out of the mold.
#3) Mechanical thermoforming
In mechanical thermoforming, the preheated plastic sheet is shaped by the means of mechanical force.
As shown in the above diagram, the plug forces the heated polymer sheet in the mold.
Mechanical thermoforming gives better dimensional accuracy and good surface finish to the molded plastic.
Uses/Application/Examples of thermoforming
Thermoforming of plastics is used to manufacture different products like;
- Food packing boxes,
- Disposable cups,
- Aircraft windshields, etc.
The sheet with thin gauge is used for rigid or disposable packaging, while the thick gauge sheet is used for manufacturing of shower enclosures, electronic equipment, etc.