TABLE OF CONTENTS Many failures in mould tools are due to metal fatigue. An injection mould tool is a highly stressed heat exchanger and has to undergo at least thousands and sometimes millions of cycles. Additionally, during production the tool is subject not only to cyclic mechanical stresses but also to cyclic thermal stresses.
On each cycle, the tool is clamped, heated by incoming material, cooled and then undamped. These cyclical loading conditions are classically those that can lead to components failing from fatigue.
Metal fatigue is understood well by metallurgists and engineers designing cars, aircraft, trains and so on. Indeed, such people would be considered negligent if fatigue studies were not undertaken, as fatal failures due to fatigue could occur.
Unfortunately, the moulding industry does not in general, carry out any fatigue checks at all on mould tools at the design (or any other) stage. Serious accidents to personnel are unlikely to occur if fatigue-induced failures happen on a mould tool during moulding, and perhaps it is for this reason that performance of fatigue analyses on mould tools does not carry the same importance as other in industries. However, serious accidents cannot be ruled out entirely.
Nevertheless, it is a fact that, traditionally, fatigue-induced mechanical failures of the mould tool cost the injection moulding industry millions of pounds annually. For this reason there is an increasing realisation that fatigue analysis is necessary as competition forces manufacturing costs down, with potentially more breakages occurring as mould tools are increasingly run nearer...
