Drawing implications for CNC
Component design for CNC
It was mentioned in , that CNC will impose a certain influence on the design process. Components should be designed for ease of production when using CNC-related techniques. Thought must also be given, at the design stage, to future developments that could occur within the production environment. For example, the use of automated handling techniques using robots or automatic pallet changing (APC) facilities, for the loading and unloading of components. The introduction of Flexible Manufacturing Systems with the attendant possibility of continuous unmanned working, or the possible changeover to Computer Aided Part Programming (CAPP) techniques.
A number of simple design points may be relevant when designing components for production by CNC methods. Some examples are offered below:
- Component shapes should be designed such that they can be produced by standard production tooling. The need for form tools should be eliminated.
- The variety of hole sizes should be kept to a minimum. Each different size hole necessitates at least one tool change, more if pilot holes are required. Each tool change incurs heavy time penalties, and the need for operator intervention if automatic tool changing (ATC) facilities are not available.
- The number of small-diameter holes should be minimised if at all possible. Small drills and taps break easily!
- Common component features such as fillet radii, undercuts, grooves, counterbores, chamfers, etc., should be standardised to reduce the variety of tool stocks held, and help reduce the number of tool changes required.
- Sharp corners should be eliminated on both internal and external forms. The use of radii and fillets corresponding to standard size cutters will simplify part programming and manufacture.
- Cutter path access should be simplified by providing forms that allow tool run-in and run-out.
- Machining should be kept to as few planes as possible to avoid excessive component handling.
- The variation in height of machined surfaces should be kept to a minimum. to reduce lost time in tool movement.
- If the component is symmetrical, a salient location (and orientation) feature should be provided. This will reduce handling time during set-up and make automated handling easier.
- If the component is an awkward shape it may be beneficial to provide sacrificial clamping lugs that may be removed at a later stage. This will reduce set-up times. It may also allow the component to be machined, in one setting, without the need for programmed breaks to change clamping positions.
- kIt may be relevant to provide a feature that may be grasped for component manipulation. This will allow the easy integration of robotic devices for loading and unloading especially where unmanned machining may be required.
- The use of stock size raw material should be considered, where appropriate, to reduce the amount of necessary machining.
The above points are not meant to be exhaustive, merely to stimulate thought in the design of components for production by CNC methods. In all cases the designer should ask: “Would I like to make the component to my design?’’.