Assisting plug

Mechanical assist Plug Plug, billow, vacuum box... 

A mechanical pre-forming has to be done using an assisting plug. 

Synthetic foam is an almost universally used assisting plug material and is mostly used in roller machines. 

Resins (e.g., polyurethane resin), talc-filled with the better sliding capabilities, are used especially in vacuum machines, when the appearance of the assisting plug is very complicated. 

Metal, mostly aluminum, as an assisting plug material is used for the following... 

Polytetrafluoroethylene (PTFE) (e.g.. Teflon) can be used in special cases as an assisting plug material when the material at transforming temperature is very sticky on the surface. 

FIGURE 1.167 Fiber orientation when manufacturing an assisting plug out of wood (a) motion direction of the plug (b) fiber orientation (solid wood) ... 

There are no easy mathematic formulas for calculating the assisting plug contours. The first step can be calculated as follows ... 

The contour of the assisting plug can be determined from the contour of the mold. 

The distance a between the contour of assisting plug and the contour of the mold is calculated. 

Assisting plug radii R in the bottom area, see table below. 

Determination of the assisting plug contour for positive molds... 

In positive molds, assisting plugs are mainly used ... 

In vacuum forming, for example, the heat-plasticized sheet (either directly from an extruder or preheated in an oven) is drawn against the mold surface by the application of a vacuum from beneath the surface. Similarly, a positive pressure may be used to force the sheet against the mold surface, and where very deep draws are required, mechanical assists, plug forming, are used. In drape forming, the plasticized sheet is draped over a male mold, perhaps with a vacuum assist. 

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