Why a management control?
It is often quoted that CNC is not a machine control, but a management control. CNC is primarily an automatic machine, or process, control discipline. However, its intelligent adoption also greatly increases the potential control that management has over the production process. Management is concerned with the planning, organising and efficient usage of all factors and resources that are available. Most manufacturing organisations that fail do so, not because of an inability to manufacture, but because of ineffective management. Indeed, the responsibility for success or failure rests fairly and squarely with management.
In the context of considering CNC as a management control, it is useful to examine all the areas of manufacture on which CNC imposes an influence.
CNC and Design
Traditionally, the way in which a part is designed is subject to the individual preferences of the designer. The adoption of CNC will immediately impose a certain influence on the design process. This, in turn, will influence the training of design personnel.
Designs will be originated for ease of production. In many instances an exercise known as value analysis can be carried out with the purpose of making production easier or cheaper. In the majority of cases, however, value analysis is usually carried out retrospectively on components that have already been designed and manufactured.
The effect of the above is clear. Designers will be allowed to spend more time on the design process, rather than on the mere “housekeeping” tasks of updating drawings, etc.
The second consideration must be that the utilisation of computer power at the machine tool (via CNC) inevitably leads to the utilisation of computer power in other facets of the production process. Thus, the design process itself is being influenced by the application of computers, notably in computer graphics. The designers only function now is purely to design. Dimensioning, drawing production, filing, etc. can be carried out automatically by the system.
CNC techniques and process planning
CNC and production planning
The greatest application of CNC is in the small to medium batch product runs. Advantages are reaped in the very short changeover times that can be accomplished between jobs. Thus, lead times and production times are optimised, they become reliably predictable, and downtime is reduced to a minimum. This means that more accurate cost estimates can be generated, production runs can be planned more accurately, work in progress can be kept to a minimum, and customer service can be increased by specifying shorter delivery times and quicker response to modification requirements.
The need for extensive jigging and tooling can be considerably reduced, thus reducing their respective lead times. Finally, since the part programs can be produced, and proven, remote from the machine tool, more production time is available to allow the production areas to concentrate on producing.
CNC and quality control
Since the machining process is now automatic, better quality in terms of dimensional and geometrical accuracy is attained. Repeatability is increased, and this may enable inspection techniques to be re-designed. Because of the uniformity of the products, the processes of fitting and assembly can possibly be streamlined. Scrappage and re-work costs should be almost eliminated.
Inspection and measurement processes are themselves becoming subject to CNC control by the inception of specialist CNC measuring equipment.
The above points are valid and important. The decision to invest in CNC machine tools must not be taken on the basis of machining technology alone.