How do you determine needed thickness of sheet for thermoforming?

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How do you determine needed thickness of sheet for thermoforming?

This is a very simple and straightforward question that can have a very long and complicated answer. I will keep my answer short and stick to the basics. You can call the Technical Center at (207) 490-4230 if you would like to discuss the question in further detail.

Each design and application has to be evaluated independently to determine the required sheet thickness. Some considerations that are taken into account include:

  • What is the part's function?
  • What is expected from this part?

Once these are known, you then must determine how the material properties match up to the expectations of the part. Some considerations are:

  • Loads: What type of loads and at what temperature?
  • Pressure: How much pressure and from what direction?
  • Impact: Will the part be subjected to impacts and to what direction and magnitude?
  • Rigidity: What is the maximum deflection allowed?

Once the mechanical properties of the material are evaluated then you must look at the type of thermoforming that is going to be used and the mold design. For instance, when vacuum forming, material distribution (thinning of parts) depends on the following:

  • How evenly the sheet is heated
  • The mold temperature
  • Hot strength of the material
  • Rate of air evacuation

In general, the hotter the mold and the faster the air evacuation, the better the material distribution (less thinning).

It is also important to realize that high draw ratios will cause excessive thinning of parts unless techniques of "prestretching" or "snap back" forming are employed. (The draw ratio for a female mold is the surface area of the mold cavity divided by the area of the sheeting available for forming. In the case of a cylindrical cavity, the draw ratio is 1+(4H/D) where H is the cavity depth and D is the cavity diameter.)

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