Modeling plug‐assist thermoforming
James L. Throne · Advances in Polymer Technology · 1989
Abstract Plugs are sometimes used to prestretch thermoplastic sheet prior to drawdown into thermoform mold cavities. The amount of force required to stretch the sheet depends upon the material constants in the stress‐strain equation, the sheet thickness, the extent of stretching, and the geometry of the plug. Two decades ago, Williams proposed simplifying the general thin membrane large strain theory to obtain a tractable force‐deflection model. In this paper, it is shown that for plug forming, the general theory reduces to a relatively simple, transcendental relationship. Experimental force‐deflection data obtained on two thicknesses of natural rubber sheet agree reasonably well with the general theory but not at all with the Williams large strain model.