Comparing the processing of high-precision parts with the requirements of general forming processing, it is necessary to pay attention to more details and the measurement technology required to reach the level of accurate measurement. This tool must ensure that the moulding temperature and cooling rate in the cavity of each moulding are the same. The most common problem in precision gear machining is how to deal with the symmetry cooling of the gear and the consistency between the cavities.
The mould of precision gear generally does not exceed 4 cavities. Since the first generation of moulds only produced one gear, there are few specific instructions, and gear tooth inserts are often used to reduce the cost of secondary cutting.
The precision gear should be injected from a gate at the center of the gear. Multiple gates are easy to form fusion lines, change pressure distribution and shrinkage, and affect gear tolerances. For glass fiber reinforced materials, since the fibers are arranged radially along the welding line, it is easy to cause eccentric “collision” in the radius when using multiple gates.
A moulding expert can control the deformation of the tooth space and obtain a product with a controllable, consistent and uniform shrinkage ability is based on good equipment, moulding design, stretchability of the material used, and processing conditions. During moulding, precise control of the temperature, injection pressure and cooling process of the moulding surface is required. Other important factors include wall thickness, gate size and location, filler type, amount and direction, flow rate and internal stress of moulding.
The most common plastic gears are spur gears, cylindrical worm gears and helical gears. Almost all gears made of metal can be made of plastic. Gears are usually formed by split mould cavities. When the helical gear is processed, the gear or the gear ring forming the teeth must be rotated during injection, so attention to its details is required.
The noise generated by the worm wheel during operation is smaller than that of a straight tooth, and it can be removed by unscrewing the cavity or using multiple sliding mechanisms after forming. If a sliding mechanism is used, it must be operated with high precision to avoid obvious seam lines on the gears.