Sunday, September 14, 2008

High performance machining, current sense

Today the HPM (High Performance Machining) term is much more general referring to all kinds of cutting technology, substantially improving two aspects of the process:

- Productivity measured as material removal rate, i.e. the amount of material eliminated in a time unit. One should also ensure machining is done under conditions which do not lead to excessive tool wear and tear.

- Quality with regard to greater dimensional precision and less surface roughness. Figure 2 shows a precision map for a test part machined at high speed, which served to detect a non-admissible error in machining.In the last 10 years there has been a minor revolution regarding improvement in processes and an increase in knowledge thereof.

The reasons may be several:

- Materials constituting manufactured components have higher mechanical features, leading almost always to lower machinability. A good example is the growing use of titanium, nickel and cobalt alloys (heat resistant), Csi infiltrated composites, etc.

- Cutting tools have greatly improved in the last 10 years, with the appearance of new hard metal grades (sintered carbide), extrahard materials have been perfected (PCBN, and PCD). Tools tend to become ever more specialised in one application, abandoning their purpose of being applicable to many material groups.

- Tool performance improvement has contributed decisively to new coating developments, ever harder and more resistant to high temperatures. TiAIN coating applied by PVD technology ( Physical Vapour Deposition) has been extremely important.

- Detailed knowledge of processes and their modelisation has been proven to contribute to earning money, i.e. value is obtained from knowledge albeit it still limited. An example is preduction of milling stability conditions ( chatter study); after 30 years and numerous articles on chatter prediction, today there are companies and consultancies earning money with it.

- In Europe,Asia, USA and of course Spain, the machine tool and manufacture by machining sector are very important, thus research resources have been assigned by companies and administrations. Furthermore, improvement in machinery and its process concerns both machine tool builders and suppliers likewise users thereof. Western industry tends to produce components with greater added value more and more; the term high performance refers to everything which contributes to increasing this value, either because it reduces production times and costs increases manufactured quality.

Thus, today High Performance Machining is understood as everything which incorporates notable improvement with respect to traditional machining, increasing process added value both in productivity and quality. The machining term includes chipping process with defined cutting tool (milling, turning, drilling, sawing) with non-defined edge or abrasives (grinding), and even non-conventional processes (electrodischarge, ultrasounics, etc).

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