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Hurco Europe is now offering a three-axis, high-speed-cutting (HSC) machining centre for producing large, high-precious moulds and dies.

Workpieces weighing up to three tonnes can be machined within a 1,200 x 1,000 x 500mm working envelope.

Designated the RXP 1200, the 26-tonne machine from Roeders has linear drives in all axes and a choice of spindles from 30,000rev/min (HSK F63), suitable for deep-hole drilling in hardened steel, to 60,000rev/min (HSK E32) for high-speed profiling.

According to Jurgen Roeders, chief executive officer of Roeders, the fine-tuning of the machining centres is performed at the company’s Soltau factory.

He claims that there is a large difference between a machining centre fitted with a standard control that has numerous interfaces and subroutines for a variety of applications and a machine that has a dedicated control specifically matched to its type, purpose and characteristics.

‘This will not show when you work along a straight path but, when it comes to machining complex 3D contours, our control system is able to reduce cycle times by percentages in the double-digit range,’ said Roeders.

At the same time, the Roeders control smoothes surfaces using advanced, patented mathematical algorithms that achieve smooth tangential transitions.

This is said to be evident from the absence of steps when machining with finishing cutters of a small diameter.

Another advantage is that circles, which often are not optimally converted and executed by post processors generating NC code from computer-aided-design data, are automatically rounded.

The Roeders control system incorporates optimised spline interpolation, command line execution times below 0.1ms and a look-ahead of more than 10,000 command lines.

This made it possible, together with an internal positioning resolution of less than 1nm, to achieve small increments of between 0.1 and 0.05 micron.

The results are smooth surfaces as well as high feeds of up to 60m/min and often more than 10m/min when a tool is cutting.

According to Roeders, within the finishing phase, tool makers can economise on, or waste, considerable amounts of machining time, depending on their choice of machine tool and cutting strategy.

Cycle time reductions and quality improvements ranging between 10 per cent and 20 per cent can be achieved by selecting a suitable programming strategy.

The Roeders control is said to be simple to update and upgrade.

Replacing printed circuit boards in a 10-year-old system will boost computing capacity and processing speed to such a level that the overall performance will increase by 20 per cent.

‘We have switched from industry-standard glass scales with 20-micron accuracy to the ultra-high-precision 4-micron version from Heidenhain, making it possible to move machine axes in 50nm increments,’ said Roeders.

While this limits maximum speeds to 60m/min, it has only minimal impact on machining times if one takes into account the typical job mix in tool and mould shops, characterised by short idle times of around 10 per cent and speed limitations imposed by high levels of material hardness.

The RXP is equipped with cleaning nozzles to ensure that there is no layer of lubricant to interfere with its laser-based tool dimension measuring system.

The patented cleaning system starts by spraying a solvent onto the tool at low rotational speed; otherwise, air turbulence around the tool would prevent the solvent from reaching it.

Afterwards, the tool is dried at high rotational speed, the whole cycle taking just half a minute.

The best machining results are achieved using flood coolant delivery, which helps to achieve a uniform workpiece temperature.

In addition, it is said to clean cavities and flush away chips more efficiently than in the case of minimum-quantity lubrication or dry machining.

The RXP 1200, aimed at achieving a high level of precision, features up to 10 cooling circuits, which allow the temperature of the structure to be controlled to an accuracy of 0.1C.

Temperature stability is particularly important when machining large tools or dies requiring long machining times to avoid mismatches when finish machining.

The temperature control system incorporates a cooling sleeve to prevent heat variation in the spindle.

The second cooling circuit thermally separates the spindle from the cast base of the Z axis.

As a result, there is no need for spindle growth compensation in the control, even when tackling jobs such as large plastic injection moulds taking 10, 15 or even 20 hours using modern cemented carbide tool technology.

Roeders continued: ‘These high-quality carbide tools have cutting edges with small radii and you can achieve excellent results.

‘Customers still tend to be too cautious with the in-feed, however, scratching away the metal rather than actually chipping.

‘The feed-per-tooth parameter must be sufficient.

‘While steel was initially machined at 2m/min cutting feed, current state of the art is 4m/min to 5m/min.

‘Provided you use suitable tools, our machines are fit for performing 7m/min to 8m/min at robust in-feed rates, while aluminium may be cut at 40m/min.

‘With a minimum of time spent setting, our machining centres achieve accuracies of +/-5 microns for smaller workpieces and +/-10 microns for larger parts,’ he said.

The RXP 1200 counterbalances the weight of the Z axis using two flexible, bellowed vacuum hoses at the top of the machine.

This system works without any friction and thus generates no heat within the Z-axis assembly, no matter how frequently it has to move, avoiding thermal expansion and related inaccuracies.

Looking at the machine structure, a mass of 26 tonnes can be a limiting factor if a large part of it has to be moved around; this is also the case with a gantry system.

However, with the column-type RXP 1200, the weight is mainly concentrated in the machine base and column, where it helps to dampen vibrations.

All Roeders machining centres are equipped with a patented function that determines the optimal spindle revolutions per minute by performing a test run to establish the speed that causes the lowest vibration level.

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