Plug Material vs. Plug Geometry: A Thermofoming Test

It’s one of our favorite thermoforming questions: “Which is more important – the plug material or the plug geometry?” It’s really a trick question, though, because the answer is usually, “It depends!” So let’s take a look at a recent test we did with 2 types of HYTAC plug assist where multiple variables were involved.

Motivation for the test:

The cups in question have a plug mark at 20mm from the bottom of the cup. After changing the plug geometry and plug material (from XTL to FLX) there was a better result. It was not clear if that was because of the different type of material or because of the different shape of the plug.

General details:

      Machine: tilt-mold, cut-in-place

      Part:  Ø70,5mm (2.77″)

      Material: White PP 1,05mm (0.041″)

      Machine oven temperature: 408°C / (766°F) (top and bottom)

      Sheet temperature: ± 150°C (302°F)

Test procedure:

The test was run with 4 different types of plugs in the same row of the tool.

  1.     Hytac XTL: Small Radius (R 4.0) Angle 4.0° (Cavity  5)
  2.     Hytac FLX: Small Radius (R 4.0) Angle 4.0° (Cavity  3)
  3.     Hytac XTL: Large Radius (R 8.0) Angle 5.0° (Cavity  2)
  4.     Hytac FLX: Large Radius (R 8.0) Angle 5.0° (Cavity  4)

Results:

The machine was cycled for about 3 minutes with cups measured from the same shot.

  1.     Hytac XTL: Small Radius (R 4.0) Angle 4.0° (Cavity 5)

  •          There is a plug mark at 20mm from the bottom of the cup.

  •          Enough material in the bottom; bottom thickness is good.

  1.     Hytac FLX: Small Radius (R 4.0) Angle 4.0° (Cavity 3)

  •          There is a plug mark at 20mm from the bottom of the cup.

  •          Less material in the bottom; bottom thickness is acceptable.

  1.     Hytac XTL: Large Radius (R 8.0) Angle 5.0° (Cavity 2)

  •          There is no line at the bottom of the product.

  •          Enough material in the bottom; bottom thickness is good.

  1.     Hytac FLX: Large Radius (R 8.0) Angle 5.0° (Cavity 4)

  •          There is no line at the bottom of the product.

  •          Less material in the bottom; bottom thickness is acceptable.

Conclusion & Discussion:

  • The plug with the small radius (R 4.0) creates a plug mark at ±20mm from the bottom of the product.
  • Hytac XTL carries more material to the bottom compared to Hytac FLX.
  • Plug No. 3, Hytac XTL with Radius= R 8.0, gives the best result in this test.
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