Breviary Technical Ceramics






7.1 The Design Sequence

The task of an engineer is the solution of a technical problem. This solution must both fulfil the technical specifications and must be economically feasible. It is absolutely necessary that both these conditions are met. This means that a compromise must be found between improved performance and the required expense. Solutions that either do not guarantee the technical function or that are too expensive are unsatisfactory.

In a good design that is appropriate for ceramics, the advantageous properties of the ceramic materials are maximised and the disadvantages (such as brittleness) are minimised or even nullified through the use of good design principles (for example, separation of functions, modular techniques, compressive loading, etc.).

During the planning phase, information concerning the exact function of the part to be designed and the properties of the ceramic materials under consideration must first be obtained. It is thus helpful if the design engineer and the manufacturer work together at the earliest possible stage of the planning phase, in order to decide on the fundamental feasibility of the construction. Not only must the technical specifications be taken into consideration, but also manufacturing costs, including planning and development, so that the possibility of wasted investment is detected as early as possible in the design process. It is particularly advantageous when, on one hand, the design engineer already possesses knowledge of designing with ceramics, and on the other hand if the component maker has an understanding of the sequence of the customer's operations.

A valuable prerequisite for reaching a decision regarding the technical feasibility and for the purposes of cost calculations is a complete and correct drawing. With reference to the first design with which the design engineer approaches the ceramic manufacturer, it is desirable for all the variable parameters (shape, dimensions, tolerances, surface quality, etc.) be clearly emphasised. The same is true for any dimensions whose maintenance is crucial to the design.

The way in which the component will function, and the stresses to which it will be subject, should be explained in the initial discussions with the ceramic manufacturer, so that the optimum ceramic material for the particular case can be chosen. As a second step, the variable parameters mentioned above should be discussed with reference to the ultimate function, so that both sides become clearly aware of any difficulties that might arise.

During the first meeting between the user and the component manufacturer, figures concerning the expected lot sizes should be available, since these are decisive for the choice of manufacturing process to be used, and therefore for the expected manufacturing costs. Small lot sizes, single parts and prototypes are often machined from a preform, while the construction of expensive tools, for example, for dry pressing, extrusion or injection moulding, are only cost-effective with large batch sizes. Parts manufactured using different processes do not necessarily possess identical properties, a fact which must also be taken into consideration when transferring experimental results to ordinary manufacturing conditions (density gradients, tolerances, wall thicknesses, taper, internal stress, taper etc. for example).

On the basis of the drawings with which he has been provided and of discussions held with the user, the component manufacturer is able to suggest changes that are necessary because of the production technology. These changes frequently do not have any effect at all on the function of the part, but are often necessary to make it at all possible to manufacture the part, or offer a reduction in costs without which economical manufacture would not be possible.

As a rule, a few sample parts are manufactured and tested after the modified design drawings have been discussed and approved. On the basis of experience that can be obtained from field tests using these parts a decision is reached as to whether the production order can begin or whether the part must be modified once again.

There can be differences between the properties of the prototype and the Mass Prod.s part. Tests prior to final approval should therefore use samples produced in a way similar to full production.

Figure 130: The development of ceramic components


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