In compression molding, a preshaped charge of material, a premeasured volume of powder, or a viscous mixture of liquid resin and filler material IS placed directly into a heated mold cavity. Forming is done under pressure from a plug or from the upper half of the die (Fig. 18.12). Compression molding results in the formation of flash, which is subsequently removed by trimming or by other means.
FIGURE 18.12 Types of compression molding, a process similar to forging:
(a) positive, (b) semipositive, and (c) flash. The flash in part (c) has to be trimmed off. (d) Die design for making a compression-molded part with undercuts.