Design for Process Capable Tolerances: Serious about cost savings? Make sure your design tolerances can be met

摘要

Well, what is a design? When I've trained teams in Design for Manufacture and Assembly (DFMA),that has been my introductory question. I have an answer, of course: a design is an instruction and a contract. For each part in the design there is a drawing, and that drawing instructs the supplier what is to be produced. Then, if the part conforms to the drawing, the supplier will have fulfilled his contract - no one further up the supply chain right through to the customer will be able to say 'It doesn't work' or 'It doesn't fit'. Once this definition of the design is accepted, the rather daunting consequence is that it is down to the designer to ensure that the contract is feasible, and the instruction is capable. Much effort goes into analysing designs, even more into testing prototypes, to ensure the drawing captures every constraint necessary to ensure that the contract is met - that is a large part of most designers' working day and, hard work though it is, the task is pretty much satisfactorily achieved. But often the process capability (or otherwise) of the design tolerances emerges only after the start of full production, when problems in assembly or of dimensions out of tolerance then have to be addressed.