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Process

How it works

Robomold employs three different thermoforming processes. We do this so that we can accommodate a variety of needs for precise plastic part construction. We will spec which process is best for your application. A basic description of the differences is as follows:

Vacuum Forming:

  • Plastic sheet is pulled over a male mold using vacuum from mold side only.
  • Appropriate for low profile parts.


Snap-back Billow Forming:

  • After heating, plastic sheet is pre-stretched into a billow box, away from the mold, using vacuum. Vacuum then switches to the mold side, at which the material is drawn tight against the mold. Without this step, deeper draw parts would have thin corners or even holes when pulled over the mold.
  • Creates uniform thickness in deep draw parts or parts with a severe draft ratio.


Pressure Forming:

  • Plastic is pulled into a female cavity mold with vacuum from the mold side and use of a plug assist or helper from the male side.
  • Detail can be similar to injection molding, with precise detail being achieved from the plastic being formed from both sides.

Tolerances

Tolerances

Typical tolerances for a thermoformed part, from tool side, are listed below. Note, tolerances will be affected by your specific part, tool construction, and material. Please let us know what you need from your part, and we will discuss options for achieving:

Tolerances of a molded part: +/- .020” + .001 in/in

Molds

Mold Construction

Thermoformed production molds are typically made from machined aluminum. If the part is large, the mold may be cast aluminum. Good rule of thumb is a minimum of 3 degrees of draft on all surfaces perpendicular to base plate on the mold. Less draft can be achieved, but it is based upon a number of factors, including part geometry, mold construction, and material. For example, Robomold’s experience has allowed us to dial in on producing negative draft features for HDPE because of the forming windows and memory of the material. Tooling can also be made with actuating features to form negative draft.

Male vs. Female Molds – The major difference between a male or female mold is which side of the part is controlled during forming. During forming, the plastic thins at predictable yet variable rates, meaning that the wall thickness of the final part will be different depending upon where you measure it. Tolerances are affected accordingly – only one side of the part will consistently hit dimensions, as the opposite side will vary based upon how much the part thins.

A male or female mold, then, will be specified based upon which side of the part is more important for tolerance control and appearance. If it is a cover that fits over something, the inside dimensions are important. If the same cover must fit up into a mating component, female might be selected for consistently controlled fit.

Materials

Material Selection

Robomold is a heavy gauge thermoformer, where starting gauge thickness ranges from .093” to .275”. The material will thin during the forming process. Based upon your desired final wall thickness and the geometry of your specific part, we will specify an appropriate starting thickness to achieve your part specifications.

Available materials:

  • HDPE
  • ABS
  • Polycarbonate
  • HIPS
  • PETG
  • CAB
  • Specialty properties:
    • UL rated flame retardant
    • Conductive
    • Custom colors
    • Variety of textures
    • RoHS and REACH compliant

Logos and Labels

Logo and Labeling Options

Thermoforming allows for permanent 3D logos and lettering to be formed directly into the plastic, either debossed or embossed. This is achieved by cutting into the tooling and adding appropriate additional vacuum to form the plastic over the letters. Note, the exact dimensions of the lettering are contingent on the starting gauge of the plastic as well as the specific font or style of the letters. A logo may need to be scaled differently or the appearance somewhat altered in order to achieve a formable and readable final product.