CNC Machining Productivity

Given the current state of the market, rarely has it been more important for manufacturers to focus on maximising the productivity and efficiency of every CNC machining process. This of course applies to all industry sectors, but coupled with the trend for aircraft OEMs to seek greater value than ever from their suppliers in the race to achieve increased market share, the issue becomes even more pertinent to aerospace CNC machining. With the priorities for airframes having to be primarily weight and safety, another growing trend is for aerospace designers to produce plans that combine as many different parts as is possible within single components.The only downside here is the inherent part complexity this creates, which in turn leads to a reliance on multiple machining operations. To combat this difficulty, the initial thrust of machining optimisation at many manufacturers in the aerospace supply chain centres on the machine tool itself. Here, machine tool manufacturers have made great strides in recent years, bringing to market a number of machines that offer the integration of multiple functions, including sub-processes (such as probing and balancing), allowing the workpiece to be completed on a single machine with as few set-ups and tool changes as possible.Cost savings in aerospace CNC machining.Further research into aerospace components has shown that the application of high pressure coolant offers significant benefits. Applying coolant at just 70 bar, for instance, gives an average 20% increase in speed and 50% increase in tool life, using only components and features that are standard on many machines. Ultra high pressures (up to 1,000 bar) are even more effective but additional fixturing is required. Correct nozzle positioning and sighting have considerable effects on productivity, chip handling and the elimination of the peening process to provide clear cost savings, particularly when machining critical aerospace materials such as Ti6Al4V. With hard materials, heat tends to exit via the insert rather than the workpiece. With certain inserts this has limited effect when they are new, but creates an enormous problem as they wear. Hence the need to accurately predict tool life has never been more vital.Uncontrolled tool life can lead to large increases in surface tensile stresses, compressive sub-surface layer size, depth of plastic deformation and strain hardening, particularly at higher cutting speeds. Intermediate stage machining (ISM), which as the source of the greatest production costs offers maximum scope for productivity improvements – during ISM up to 80% of metal is removed when turning heat resistant superalloys (HRSAs).

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