Ways to increase the energy efficiency of cutting processes

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If not a new machine tool, then maybe something else

The potential energy savings mentioned so far can only be realised, in most cases, by the purchase of new, energy-efficiency-optimised machine tools. The investment for such a machine is generally only worthwhile if a replacement purchase is due anyway. In view of the large number of existing machine tools in countries like Germany and their long service lifetimes, however, it is necessary to examine and realise potential savings by optimisation of tools and processes with the machines currently in place.

For the optimisation of tool and process, it is sensible to structure the energy consumption of a machine tool differently . In the following, all devices in the machine are grouped together that are constantly or from time to time in operational readiness. The powers required by these loads are grouped together as the basic power of the machine. The powers required by all devices associated with the cooling lubricant system are grouped together as the CLS power. The power, additional to the basic power, required by the tool machine during machining is called the process power. Multiplied by the running times, each of these powers gives an energy total (process energy, CLS energy, energy for the processing machine).

And, finally, it is sensible, for an overall optimisation, to consider the energy for manufacturing the cutting tools. Without considering this, the energy optimum for the user could coincide with extremely short tool service lifetimes, which would lead to a high energy uptake on the tool manufacturing side.

Easy-cutting tools reduce process energy

The shares of these four energies in the total energy requirement are, of course, extremely dependent on the machine tool and the process. In most cases, the process energy is, however, less than 20% of the total energy. The CLS power can amount to a substantially larger share if a high-pressure internal coolant system is used.

An immediately obvious approach to reducing process energy is to use especially easy-cutting tools. With these, the cutting force is comparatively low, due to suitable micro and macro-geometries (small cutting edge radii, large cutting angle) and a low-friction coating. By these measures, the energy needed for chip formation, and thus the cutting force, can be reduced significantly. Benchmark drilling tests in stainless steel with a total of nine solid carbide drill bits showed differences in cutting force and energy for chip formation of up to 24% at the same productivity. Calculating from this potential saving of 24% in the process energy, however, the total energy of the cutting process is only lowered by 3 to 4 %. The basis for these figures are measurements on a typical processing centre for large-scale series production in the auto industry (Alfing 2 spindle) and a further processing centre used for series production and also for tool and mould construction (Hermle C30).

Machine up time influences total energy use

In most cases, a reduction of the cutting force at constant productivity has only a slight influence on the energy consumption. Only in cutting processes where the process energy has a large share in the total energy consumption – as in heavy roughing work – does the reduction of the cutting force at constant productivity result in a significant increase in energy efficiency.

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