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Available through Hurco Europe, the RXP range of machining centres from German manufacturer Roeders provides high-speed cutting (HSC) in tool- and mould-making applications.

The machining centres are suitable for processing a range of materials from graphite and copper electrodes to hardened tool steel.

The ability to process a variety of materials efficiently in one RXP machine means that a second machining centre or mill is not needed, so capital investment is reduced and less space is taken up on the shop floor.

One user, Peter Buchler, production manager at Ermet in Bad Windsheim, Germany, said: ‘In typical tool-making operations, EDM [electric discharge machining] is the dominant technology as many geometries are so intricate and filigree that they simply cannot be achieved by milling alone.

‘Even a cursory glance at the tools we make for the electronics sector shows that moving from EDM to milling is difficult,’ he added.

The intricate tools that Buchler manufactures are characterised by many tightly intertwined features with narrow contours, small radii, high aspect ratios and sharp edges.

Stringent requirements with respect to the dimensional accuracy of the plastic parts they are designed to produce demand high-precision tool components – down to +/-5um and sometimes lower.

However, EDM is a time-consuming process; it requires the milling of copper or graphite electrodes as a preliminary process step and then die sinking is a comparatively slow process (as is wire erosion), resulting in limited productivity per machine.

The consequence is a significant handicap in terms of throughput time, capital investment and floor-space utilisation.

At Ermet, an analysis of its products showed that there was a significant range of jobs that could be performed by milling instead of EDM.

What was needed was a machine suitable for both production paths.

After a thorough assessment of different systems, the company decided to buy a Roeders RXP 500 three-axis machining centre.

During the ramp-up period, copper electrodes accounted for about 80 per cent of the jobs.

The machining of hardened steel was introduced in small steps, but recently the proportion of hard machining has trebled to 60 per cent of throughput.

Even thin deep grooves, say 1mm in width and 9mm in depth, are now reliably machined into hardened material.

Not only is production faster and less costly than EDM, but the accuracy of the parts is also improved.

Precision fits can often be milled directly instead of having to finish the parts by grinding in a further process step.

Additional benefits are better surface quality and the easier de-moulding of plastic parts during production.

Most of the steels machined at Ermet are hardened to 52-54 HRC.

Tool diameters usually range from 2mm to 3mm but sometimes rise to 8mm.

The smallest tool diameters are 0.5mm for steel and 0.2mm for copper.

Buchler continued: ‘The HSC machining of hardened steel will not completely replace EDM operations, as some geometries can still only be tackled using that process.

‘However, the extended use of HSC for producing appropriate features has significantly eased critical bottlenecks that we used to encounter with our EDM capacity.

‘High tool-path accuracy afforded by the RXP control system, even at elevated speeds, ensures that tight dimensional tolerances as well as high productivity are achieved by milling,’ he said.

With suitable tools, RXP machining centres can achieve a 8m/min cutting feed in steel at robust infeed rates, while aluminium may be machined at 40m/min, thanks to linear motor drives in combination with roller guideways.

Accuracy is maintained by various measures including 10 cooling circuits, spindle growth compensation, high-resolution linear glass scales and tool measuring by laser.

The control software is said to be adept at machining complex 3D contours, smoothing the cutter paths using patented algorithms that are particularly effective at tangential transitions.

RXP three-axis machining centres have axis travels from 300mm to 1,200mm.

The machines are also available in five-axis versions.

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