Injection mould for stepped precision parts, e.g. gear clusters - has stacked disc inserts of equal outside dia. each comprising one dia. of cavity for improved accuracy with spark erosion

摘要

Injection mould for precision parts having several co-axial diameters, in which the mould inserts (17,18) are composed of a number of discs (19 to 22,24,25), each of thickness corresp. to a single step or dia. of the moulding (3' to 8'), and with equal outside diameters (15,16) mating with a corresponding bore in the mould plate(s) (9,10). Tangential alignment is maintained by a radial key fitting closely in corresponding locating slots in the mould plate (9) and insert discs (19 to 22). The parts of the cavity and locating slots are spark-eroded. USE/ADVANTAGE - Moulding precision parts e.g. gears and gear clusters, for wristwatches and similar mechanisms. Normally the mould parting line occurs at the largest part diameter, so that in a one-piece insert, the smallest diameters are furthest from the insert face. Even when the cavity is closed by a separate plate, the span of the electrode wire between guides must be greater than the total insert thickness, with loss of accuracy due to deflection of the wire. This span is reduced to slightly greater than the length of the corresp. part of the moulding, giving increased accuracy. The common outside diameter and tangential key ensure accurate alignment of the parts of the cavity. The arrangement permits several cavities in a single composite insert. The disc inserts are simpler, cheaper and more accurately manufactured than the usual one-piece ("potshaped") inserts.