TABLE OF CONTENTS Very rarely do large multi-impression injection mould tools run consistently on all impressions. This can happen for a variety of reasons:
Incorrect mould tool design
Poor standard of toolmaking
Unsuitable machine
Unbalanced runner systems and incorrect gates
Too many impressions to control and fill properly
Damage to the cavity or cores
Changing the material from that originally specified
Of course there may be a variety of other reasons, but it is quite common to see a mould tool not moulding on all cavities in many mould shops. This is particularly true of large multi-impression tools operating on fairly short cycle times. Unfortunately, as discussed in Chapter 6, the greater the number of impressions, the less control there is over them. With large numbers of impressions, there will be differences in conditions on each of them.
This creates a narrow operating window for moulding, which means a small range of moulding conditions over which satisfactory moulding can be achieved. Therefore, the narrower the operating window for moulding, the greater the chance of moulding rejects.
Everyone is aware that running tools under these conditions is undesirable and uneconomic, but very rarely is the loss of profit quantified. Unfortunately, the true effect often comes as a surprise when the figures become known later.
As in other industries, production is customer-driven and losing impressions on a mould tool places an extra strain on production. As the tool is now producing fewer parts per hour, it makes it almost...
