Canadian Plastics

Thermoforming variables identified

A recent study has produced some of the fist hard data on why sheet temperature, bubble height and mold temperature most significantly impact the quality of thermoformed parts.The study, conducted by ...

May 1, 1999   Canadian Plastics



A recent study has produced some of the fist hard data on why sheet temperature, bubble height and mold temperature most significantly impact the quality of thermoformed parts.

The study, conducted by Bayer Corporation’s Polymers Division and researchers from the Massachusetts Institute of Technology investigated the formation of a monolayer sheet of Bayer’s Lustran Guardian ABS system at a thickness of 3 millimeters using vacuum snap-back thermoforming to mold a small refrigerator liner. The tool for the part included an overall area/draw ratio of 3:2, a very narrow flange area and an undercut where multiple stretching phases occur.

The study concluded:

Pre-stretch height has a large effect on part thickness variation and must be controlled properly. Use of a photoelectric eye to control height independent of sheet temperature variation is recommended

Overall sheet temperature has only moderate effects on part thickness, which provides an opportunity to profile the temperature as needed to control localized part defects.

Mold temperature must be near the “glass transition” of the material to eliminate ripples in the corners; higher mold temperature also minimizes webs. Other areas of the mold should be kept lower in temperature to maximize part uniformity. Note: contact your materials supplier to obtain the glass transition temperature of a particular resin.

For more information on this study contact Terry Virkler, senior R&D scientist, Bayer Corp. Polymers Division at 412/777-2000 or circle 149 on the reader service card located on p. 37.


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