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For small-batch production of supports, frames and kinematics used in its high-precision optic and optoelectronic systems, Carl Zeiss uses Roder’s RXP 500DS 5-axis vertical-machining centre for HSC.

Alfred Langer is head of the business that manufactures special products at Carl Zeiss, based in Oberkochen, Germany.

In addition to producing intricate mechanical parts, his division is responsible for high-end solutions in the field of optical components and complex assemblies.

In collaboration with in-house RandD departments, customers are offered support right from the early stages of product design.

The department currently operates about 25 machine tools, mostly CNC lathes and 3/5-axis machining centres.

A wide range of materials is processed, from aluminium to carbon and tool steels, as well as numerous more exotic alloys that are difficult to machine.

Richard Kaak, a project manager at Oberkochen, said: ‘Many of the structural parts we manufacture are thin-walled, meaning that the force exerted by the cutting tool can lead to distortion of the structure, which results in reduced accuracy of the part.

‘The problem could be alleviated by reducing the cutting feed rates, but this would not only lead to higher machining costs, but would also result in unacceptable project delays.’ Further disadvantages Mr Kaak wanted to avoid were machining-induced vibrations matching the resonant frequencies of the structures and heating of the parts, causing dimensional deviations.

Noticeable improvements were expected by switching from conventional milling to high-speed cutting (HSC) machining characterised by fast chip formation and removal, lower cutting forces and higher vibration frequency induced by the increased rotational speed of the spindle.

A further important aspect of the decision was economic efficiency.

Costs are an important factor and final decisions are seldom taken by technicians alone.

‘Before reaching our final purchasing decision, we conducted a thorough assessment’, added Mr Langer.

‘The final decision in favour of the 5-axis Roders RXP 500 DS, with its 800 x 500 x 300mm axis travels in X, Y and Z and rotary/tilting table, was taken on the basis of the fast and accurate linear drives, together with the rigidity of the machine base.’ The system is equipped with frictionless and dynamic linear drives in combination with roller guideways.

Accuracy is maintained through a number of features, such as high-resolution linear scales and an advanced temperature-management system.

The latter has a total of ten different adjustment circuits including a cooling sleeve around the spindle as well as an additional control circuit detecting and compensating for spindle growth.

The 42,000rpm spindle is equipped with an HSK 40 taper and has a power rating of 14kW.

Further highlights are cleaning devices for the tool and the workpiece, a temperature-control circuit for the coolant and a laser-based tool-length measurement.

A particular ability of the machine is a correction feature for the rotary/ tilting table based on measuring the position of more than 400 reference points distributed over the working volume.

The control system computes correction values using the data, resulting in high speed and accuracy even during unattended production of components requiring multi-sided machining or simultaneous 5-axis interpolation.

One example of this is a spacer ring with cone-shaped surfaces, which has axes of a relative 5.3deg inclination angle.

The position tolerance for the intersection point of these axes, located far outside the part itself, is just 0.02mm.

The part is intended for the NIRSpec (Near-Infrared Spectrograph), the ‘super-eye’ of the satellite replacing the Hubble telescope.

In such cases, the inclined table, sophisticated internal deviation measuring and compensating feature makes is possible to achieve accuracies that in certain cases surpass by a full order of magnitude those attained with the technologies formerly used.

Roders’ automation equipment, incorporating an 18-station workpiece pallet changer and a chain magazine accommodating 100 tools, enables unattended production during overnight ghost shifts.

Roders manufactures both the machine and the control system, a holistic approach that Carl Zeiss appreciated.

The control can easily be updated, facilitating the installation and use of upgrades and special functions Roders partly tailor-made for Carl Zeiss.

Immediately upon their completion, they were simply installed from a CD.

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