Mouldmaking In General
In mouldmaking not only is there the necessity of being skillful in fashioning steel, but there is also the need to be able to estimate accurately how long it will take and how much it will cost to produce a mould suitable for a given component.Much could be said about the philosophical aspects of estimating, quoting and competing in the mouldmaking market place.
The Need for Communication
There is a great deal to be said, however, in favour of encouraging a more intense dialogue between the customer (the person who needs the moulding), his designer, the mould maker，and, very often these days， the contract moulder who will produce the mouldings in quantity. Seldom is there the fullest understanding between all these people at the same time, and therefore it is not unusual to find a conflict of requirements at some stage during the contract. Also, more frequently there is the necessity to change the design at a later stage because some initial point has been forgotten by the designer or because the design was not entirely complete at the outset.Whatever the reason, time，money and patience can all be saved if plenty of time is taken at the outset to discuss the project in the fullest possible terms with all of those concerned.
The Essence of Data Storage
Slowly, those toolmakers having the most experience are realizing the need to store data, and to keep a library of components，from dies and moulds, that have been produced during the past. From this fund of knowledge, they can predict fairly accurately what kind of problems they will face in making future dies and moulds. In addition, of course, this is the jumping off place for the application of computer aided design/computer aided manufacture (CAD/CAM) techniques and the use of graphics. Within this framework is included the widespread use of additional technology such as heat transfer and material flow properties, which are dealt with in other parts of this book.
Range of Mould Sizes
Many factors influence the size of a particular moulding tool. Not only is the overall size based on the geometry of the component, but the actual quantities of components required play a significant part in the economic equation. Relatively small components are seldom produced in a single impression mould,depending on the size of the component, the quantity produced in a single shot can be as many as 128. At the other end of the scale，single-impression moulds can weigh several tonnes，e.g. the mould used to produce cab components，and those required to produce certain types of car bumpers can also be quite large.
Handling of Moulds
Not only do large components present the mouldmaker with difficult problems as far as machining is concerned，very often it is necessary to put together a matrix of large pieces of steel, but also there is a handling problem when the intricate business of fitting the various components is reached To overcome some of the problems in this area, tool positioning presses have been developed. Fitting the shut-off faces of a mould can be a time-consuming operation, particularly for a large die.
Clearly, the factor that influences the maximum size of mould is the machine that will provide the volume of plastic required. Thus, there is a compromise between relatively thin-sectioned large-area components and relatively heavy-sectioned components. The largest injection mould that has been produced recently was for an International size sailing dinghy for which a single impression mould produced one-half of the complete hull
As will be seen later, many other factors such as heat treatment, hand finishing, etc., tend to make large moulding tools extremely expensive and therefore the moulding of large components needs to be a well thought-out and carefully planned project.