User-oriented solution for hard turning and grinding
Höchste Präzision entsteht im perfekten Zusammenspiel von Maschine, Werkzeug und Bearbeitungsverfahren. Das japanisch-schweizerische Unternehmen BIG KAISER vertraut daher bei der Fertigung seiner hochgenauen Werkzeuge unter anderem auf die Kombination von Hartdrehen und Schleifen auf einer Super Precision Maschine T51 SP MSY.
Hard turning has long since established itself as a leading manufacturing process in industries such as the bearing and automotive industry, tool and mold making and tool manufacturing. In many machining cases, e.g. in ball bearing production or in tool technology, hard turning can save time and therefore money compared to grinding. When manufacturing complex workpieces in a single clamping operation, the combination of hard turning and grinding operations in a single machine results in dimensional accuracy in the lower µ range and high process reliability.
For precisely these reasons, the precision tool manufacturer BIG KAISER has seen hard turning as a suitable addition to grinding for several years in order to meet the high demands on the quality of the products for which the name KAISER has stood since its foundation in 1948 and which the merger with the Japanese company BIG Daishowa in 2015 has not changed.
On 135,000 square meters of production space, around 900 employees in four countries now ensure that the modular tool systems – 20,000 standard products and 12,000 special parts – are manufactured with consistently high precision. The machinery at BIG KAISER’s founding site in Rümlang near Zurich has long included a hard turning and grinding machine from a Swiss grinding machine manufacturer, although the main focus is on grinding.
With the necessary replacement investment for an ageing lathe in 2014, the focus shifted towards hard turning. An expansion of the machining options was also on the wish list. “When purchasing a new machine, we always put the existing production processes to the test,” says BIG KAISER Production Manager Marcel Stettler, explaining the approach to the machine search. “We are innovative with our products and this is also reflected in our machining requirements.”
The list of machine manufacturers that produce high-precision hard turning machines is not very long. One of the leading companies in this field was the machine manufacturer Hardinge, which developed the Super Precision series. This series is now part of the portfolio of the Swiss grinding group Kellenberger Switzerland AG. During a visit by Marcel Stettler and Marco Kotz, Head of Production at BIG KAISER, to an in-house exhibition of the then Swiss Hardinge representative PerfecBore, Managing Director Pierre Moser made contact with Product Manager Markus Günschmann. His presentation on hard turning on a Super Precision machine caught the attention of the BIG Kaiser managers.
After weighing up the different machine concepts from all the suppliers, it became clear that the Super Precision machines – and the T51 SP in particular – were better suited to BIG KAISER’s special requirements, especially in terms of repeat accuracy, than the machines from the competition. One of the selling points was the integration of the required circular milling into the machine. The additional challenge: the batch sizes at BIG KAISER vary from one to several hundred parts. An accuracy of 1 µm in diameter was also required. The German Hardinge subsidiary was happy to take on the challenge of developing this process-oriented solution, focusing on the customer’s requirements. This was another reason why BIG KAISER opted for the Super Precision T51SP in 2015.
BIG Kaiser production manager Marcel Stettler and production manager Marco Kotz are equally
satisfied with their choice of machine, the T51 SP MSY…
…as Pierre Moser, Managing Director of the Swiss representative PerfecBore
Stability and accuracy
Thanks to their rigidity and stability, the CNC high-precision lathes in the Super Precision series are ideal for hard turning as well as for combined hard turning and grinding operations for the production of complex workpieces in a single set-up. Measurement reports certify that the T series has a continuous machine accuracy of 3 µm, workpiece roundness of 0.25 µm (T42) and 0.70 µm (T65), a repeat accuracy (on all axes) of 0.76 µm and an achievable surface finish of better than Ra 0.15 µm or Rz1.
A 45° fully cast machine bed with Harcrete polymer concrete filling offers maximum vibration damping for higher surface qualities, longer tool life and reliable process sequences. The Collet Ready spindle concept allows the workpiece to be securely clamped directly in the spindle. The collet systems supported by the T-series are not designed as adapter systems, as is usually the case. This results in a significantly shorter projection length and machining of the workpiece as close as possible to the spindle bearings. The resulting maximum rigidity of the spindle is the prerequisite for achieving maximum precision.
The use of an independent Y-axis improves accuracy during milling and enables high-precision adjustment of the tool center for hard turning. Powerful main spindles with speeds of 6,000/5,000/4000 rpm and drive powers of 11/15/26 kW form the basis for high-precision turning.
A BMT 55 tool turret with 12 stations allows up to 24 stationary or 12 driven tools thanks to ½ indexing. The latter can be operated with a drive power of 5.5 kW, a torque of 42 Nm and speeds of up to 8,000 revolutions per minute.
Process reliability and surface quality
“Confidence in the hard turning process was the most important thing for us at the beginning. That had to come first,” says Production Manager Marco Kotz. With the commissioning of the T51 SP, previously proven machining processes were redefined and streamlined with the pleasing result of a reduction in throughput time. Within a short space of time, a large proportion of the parts suitable for this machining process were already running on the new machine. “There are still parts and processes that are better suited to a grinding machine,” says Marco Kotz. “However, the results of Super Precision hard turning are of such high quality that a grinding process is not always necessary.” As a result, the T51 SP increasingly reached the limits of its capacity.
The expertise they had gained in hard turning and the resulting stability of the production process led Marcel Stettler and Marco Kotz to consider purchasing a second hard turning machine. This time, an integrated grinding unit, which had already been considered for the first machine, was to expand the machining options. Once again, all possible manufacturers were initially considered for this requirement. “Of all the machine manufacturers we approached, however, only Hardinge guaranteed us process reliability,” says Marcel Stettler. “That was courageous and ultimately convinced us.” The new T51 SP MSY was ordered in December 2018 and delivered in summer 2019. A robot handling system for fully automated production was subsequently installed in October 2020.
View into the machine room of the T51 SP MSY Main and counter spindle, tool turret with grinding unit
For the combined turning/milling and grinding operations required for the complete machining of HSK tool holders, the new T51 SP MSY machine has been equipped with a grinding unit with driven tools developed for BIG KAISER, which has an inclined position. This inclined position is of decisive importance for the finish grinding of taper and shoulder. The T51 SP MSY is ideally suited to the high precision requirements of the workpiece in terms of roundness and diameter tolerance on the taper as well as concentricity between the HSK taper and inner bore.
Dressing the grinding wheel for shoulder grinding
Hard turning of the outer and inner contours of the workpiece
“We are very satisfied with the overall performance of the T51 SP MSY,” concludes Marco Kotz. “Although the machine can only process a limited spectrum, it does so all the more effectively.” And Marcel Stettler adds: “We expect further innovative solutions for the integration of grinding processes in the future, e.g. for dressing cycles.”
Die T51 SP MSY ist mit einer Roboterautomatisierung ausgestattet
Der große Arbeitsraum ist leicht zugänglich