We could eject this part with pins, with a stripper plate or with sleeve ejectors. It is always preferable to avoid pin gating if the options of stripping or sleeve ejection exist, for three reasons:
- The ejection area of pins is smaller than in the other methods and we would achieve far greater ejection support with stripping or sleeve ejection. This eliminates the tendency of pins to hob or embed themselves in to the part.
- For an eight-impression tool we would need 32 rather slender pins for ejection, which entails more toolmaking work and alignment.
- The relatively slender pins may tend to deflect in the tool during ejection, causing premature wear and breakage.
This leaves the choice between stripper plate or sleeve ejection, so how do we choose between them? Basically the governing factor is the diameter of the part being stripped. Generally, smaller diameters should be sleeve-ejected and larger diameters stripped. In the opinion of the author, the cut-off point should be around 30 mm diameter. This is around the maximum comfortable size for toolmaking and for working with standard mould components.
Ejector sleeves are employed to eject specific features such as bosses, recessed holes, etc.
Small round components can be ejected by the use of one ejector sleeve about their periphery. Ejector sleeves are more costly to employ than pins and tend to wear faster in use due to their having both internal and external working faces.
Ejection forces are more evenly distributed over the wider projected area offered by the sleeve in comparison to the standard ejector pin with the added benefit of effectively doubling the venting efficiency over the latter.
Ejector pins provide one of the cheapest forms of ejection available although their use has limitations, One such limitation is that due to the very small projected area of the pins, high single point loading is transferred to the moulding during the ejection cycle.
Component damage or distortion may result where pins are located, especially in the case of thin-walled mouldings or when brittle materials are used.
Ejector pins are usually fitted as standard mould components due to their cheapness and ease of availability from standard mould part suppliers. Pins are manufactured to standard formats in metric and imperial sizes.