Thermoforming molds

Due to the low cost of thermoforming molds we can economically make short runs of specialty or niche market products, for which an injection mold would be prohibitively expensive. This is especially important for large moldings, such as whirlpool tubs and large panels for recreational vehicles, for which injection molds and presses would be astronomically expensive. 

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Consequently, their use is best confined to short run or prototype use. In normal production, the improved heat transfer capability of a metal mold will more than repay the greater cost. Aluminum is most commonly used for thermoforming molds other options include cast or sprayed low melting point alloys, porous sintered metals, and copper alloys (Chapter 17). 

The principal decision to be made when designing a thermoforming mold is to determine which of the two product faces is to be defined by the mold. As so many thermoformings are containers and are substantially cup or box-shaped, this decision determines whether the mold is to be of the male or female type. The shape of a thermoforming is sharply defined only on the surface in contact with the mold, so whichever is the primary presentation face of the product may determine the mold strategy. 

The variety of forming equipment also provides wide contrast in thermoforming mold design. Factors to be considered are as follows ... 

Aluminum is the most commonly used material for thermoforming molds. The advantages of aluminum as a mold material are its good thermal conductivity and workability. Specific alloys help meet the stiffness requirements. Modern computer-aided milling techniques allow small series of this material. Large-volume molds are made from aluminum blocks cast under vacuum. 

In thermoforming molds, water is mostly used as a cooling media. The cooling (water flow) can be calculated with the reduction of the heat volume. In sheet processing machines, part of the heat volume can be reduced using air which is blown onto the molded part with a cooling fan. The reduced heat volume using air can be 50% of the entire heat volume to be reduced. 

For all their apparent simplicity, molds for rotational molding are subjected to more rigorous demands than those used in other processes. Injection, blow, and thermoforming molds are used to shape molten or softened plastic. Rotational molding tools are used to heat the raw material from ambient conditions, shape it, and then cool it back close to ambient conditions again. This thermal cycle presents a dichotomy for the mold maker in that the mold must be thin enough to... 

The thermoforming mold is usually single-surfaced. Aluminum is the preferred material for longer production runs for both thin- and thick-gauge thermoformers. The mold serves several purposes and has several requirements. 

There are many occasions when only a few to a few dozen products are needed. Traditional vacuum forming uses low pressures and relatively low sheet temperatures. As a result, many common materials often serve as thermoforming molds. There are two general types of prototype molds. 

When a semicrystalline plastic is heated and formed above its melting temperature range, it must be recrystallized on the thermoforming mold. The rate of recrystallization is important when... 

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