Where some secondary operations have to be performed on the mouldings, such as drilling，tapping, dressing-off, flash-removal, polishing, etc., these may be very adversely affected, increased in duration and complexity, or even rendered impracticable, as a result of failures to maintain the mould in proper working condition.
Here again, the moulding manufacturer will find himself confronted with additional worry, increased costs which were not foreseen or provided for in his original estimates covering the job.
Only one or two illustrative instances can be given now, but they will serve to indicate ways in which trouble can arise at subsequent machining operations because of a very minor fault in the mould mechanism.
Many plastic mouldings are made with plain cored holes which have to be tapped at a subsequent operation. If these holes are moulded blind and there occurs an inadvertent displacement of the core member forming such blind holes，considerable troubles may arise in threading, resulting in substantial breakage of threading taps. Similarly, a poorly worn core piece may lead to excessive reduction in tapped hole size which again will cause increased load on the taps and as a result more frequent breaking.
Alternatively, another very common feature in plastic moulded articles is to have opposed sides cored out for suitable holes so that a single spindle may eventually be located freely therein. This means that both core members must lie in the same axial plane and coaxial with each other so that the two holes will be in proper alignments Wear of the cores themselves or their housings may lead to excessive misalignment, entailing a subsequent reaming operation on the mouldings to restore alignments
These are some ways in which additional work and cost are involved when very minor mould faults and errors are allowed to continue uncorrected and where there is no proper maintenance procedure which is calculated and intended to afford the requisite oversight for observing such faults as they arise in the first place.
Expensive Corrections Often Involved to Retrieve Mouldings
Costly and protracted corrective measures may also be necessary in order to restore original accuracy of the produced article which has become lost because of unremedied mould wear and error. In this respect it is worthy of note by production managers that very much time and expense can be absorbed in such subsequent operations，since it is not usually possible to scrap a batch of faulty parts，even though that would be the least expensive way out.
Delivery time is often the determining factor to satisfy a customer’s urgent requirements. It may be essential to take steps to retrieve the faulty mouldings，disregarding the extra costs incurred.In addition，such measures sometimes seriously upset the rest of the moulding shop production program since machines engaged on other work have to be broken down and reset for the correction operation.
Repetitive Mould Settings Usually Incurred
Another recurring disadvantage, many times overlooked, relates to the loss of time involved in the frequently repeated setting¬up and removal of a mould from the press or injection machine in order to effect running repairs.
One may draw a mould from the storage department after lying there for weeks; it is be set-up on the machine only to find on commencing production that some simple adjustment needs.It had it been observed and reported when completing the last production run, could have been carried out very well during the time the mould was out of use.
From his own practical experience the moulding maker had known cases where a mould had been out of service for months, lying in the store-room, ail the while possessing some deleterious error or fault.Moreover, those points some person had overlooked when the mould was last used, and which resulted in a complete wastage of the setting-up time.Since the tool could not be operated satisfactorily, and the adjustment or repair was one which could be performed satisfactorily only with the mould back on the tool-room bench.
.This kind of thing occurs more often than one would imagine in these days when most moulding firms are finding their tool-making and production departments subjected to very heavy pressure.
This again is yet another compelling reason why maintenance should be comprehensively and carefully planned so that such occurrences can be avoided, and a greater conservation of the activities of the hard- pressed tool-making sections affected.
Unbalancing of Load on Tool room
Still, another crucial disadvantage arising from such an absence of planned maintenance is that the organization and allocation of the workload upon the tool-room staff and machines maybe thrown very considerably out of balance.
A number of moulds may be withdrawn from the stores to be put into production at round about the same time. Before production commences on a proper scale from some of these tools it is found that a whole crop of items of repair, fixture, setting, adjustment and the like according attention have not been dealt with during their period of idleness.
This means their return to the tool-room and a great pressure of work in that department upon urgent repairs- Thus to effect these and allow production to proceed the tool-room foreman is often compelled to shut-down on compelling new work，and draft skilled toolmakers to these repairs, thereby causing delays and failure to meet scheduled delivery dates on the new work.
Also, such activities are very fruitful of errors and mistakes on the part of the tool-maker who is thus transferred backward and forwards from one job to another before he has had the chance to complete one task. Most mould-making operations involve a considerable degree of skill, training, and concentration, and frequent change-over to another entirely different task in the middle of, say, an involved die-sinking operation may cause serious errors to arise, due to no other reason than the break in the concentrated attention the job demands.
In this connection, it is not always sufficiently realized and appreciated that such machining operations as die-sinking, engraving, hobbing, milling, etc” required in most plastic mould manufacture are in reality very highly skilled tasks and demand concentration and uninterrupted attention if they are to be successfully performed.
In fact, it is safe to assert that every tool-maker will be able to recall instances of serious mistakes made because of the disorganization caused by the need for effecting some urgently required repair when a little organization and foresight could have ensured a more convenient arrangement.
Inaccurate Tool Costing May Result
In the matter of tool depreciation allotment also，the work’s accountant may find his reckonings very wide of the mark indeed if he makes the customary nominal assessment, because a mould may rapidly deteriorate if not given adequate maintenance service. Thus a completely false monetary valuation of the moulds may be created due to the lack of organization on the maintenance side of the firm’s activities, resulting in these assets figuring on the firm’s balance sheet or stock-book with an inflated value.
The foregoing by no means includes all the practical disadvantages arising from failure to plan moulds maintenance in an orderly fashion, but certainly enough has been enumerated to convince even the most skeptical that the reduction or elimination of the above-mentioned substantial drawbacks to smooth-running and successful production from plastic moulds is a well worth-while activity.