The advantages of the process combination hard turning + grinding lie in process stream consolidation, improved component quality and greater flexibility. But process combinations can also be used to great effect for the shortening of cycle times. Where all the hard fine-machining operations can be carried out on a single machine, throughput, transport times and storage periods can be drastically reduced. There are also benefits to be had in the reduction of time and effort spent on setting up the machine.

An important requirement for combination machines is the unhindered fall of the turning and grinding chips. The VLC 250 DS with its vertical work spindle and its tools positioned below the workpiece offers the best possible chip flow conditions. All machine modules are mechanically sturdy and particularly vibration resistant. This is augmented by the machine base in MINERALIT polymer concrete, with its great vibration damping properties, and by the design of the work spindle, which forms an integral part of a sturdy quill that carries out its Z-axis movement in a high-precision, hydrostatic guideway – also a design particularity that has a highly effective vibration damping effect.

The tooling systems are firmly anchored in the machine base and provide a stable basis for demanding turning and grinding operations – an important precondition for time-saving hard pre-turning work and for achieving the best surface finish with a hard finish-turning or grinding operation. Number and design of the stationary tooling systems can be chosen to suit the individual machining requirement. Continuous monitoring of the machine temperature ensures a high degree of thermal stability. The operating temperature is quickly reached and maintained within tight limits of the ambient temperature by a powerful cooling unit. The pick-up technique employed on the VLC 250 DS Turning and Grinding Center ensures that the machine loads itself. Gantry loaders – or other cost-intensive, space-devouring loading devices that involve time-consuming resetting work – are a thing of the past.

The VLC 250 DS can handle complex manufacturing processes. Whether there is a call for turning work at high chip removal rates or for the somewhat gentler grinding operation – the machine covers a wide range of applications. The advantage is obvious: complete-machining in a single setup, and thus the elimination of reclamping errors. Measuring operations too can be included. This would ensure optimal integration of a quality control function into the overall process. The measuring probe is located between machining area and pick-up station, where it is safe from the ingress of chips and coolant. As the workpiece remains clamped during the gauging process, intermediate measurements can also be taken.

A typical example of successful combination machining is the manufacture of gearwheels. The end face is hard finish-turned, whilst bore and cone are pre-turned and then finish-ground to ensure that the high quality requirements are met. For this purpose the machine is equipped with two grinding spindles, whereby one spindle machines the bores and the other carries out the external grinding work. As the amount to be ground is only a few hundredth of a millimetre the grinding wheels need only be designed for finishing operations.

The advantages offered by the VLC 250 DS:
•Vertical hard turning and finish-grinding on a single machine and in one setup
•All sectors of the workpiece that can be turned with process integrity are hard finish-turned, and only those are ground (after hard pre-turning) where quality requirements and process integrity demand it.
•Improved workpiece quality and higher productivity rates, as the workpiece is complete-machined in a single setup, whereby the hard pre-turning process leaves an allowance of just a few microns for the subsequent grinding process.
•The grinding process needs to remove only very little material. The wear and tear on the grinding wheel is therefore minimal and it needs to be dressed only infrequently, and only by a fraction. This is of considerable advantage where cycle times are a concern.
•The grinding wheel specification can be fixed as “finishing quality”, as only a very small allowance needs to be removed. This produces process-capable surface finishes in the Rz < 1.2 µm range.
•Unlike hard turning processes the grinding operation will, on the same machine, generate absolutely scroll-free surfaces.
•Rear end faces are difficult to reach with a grinding wheel – a problem that is easily solved with hard turning.
The cross-operational machine design provides exceptionally easy access.