Internal matters

5 min read

Andrew Allcock travelled to Switzerland to hear how Studer’s internal grinding activities are growing in breadth and capability, with interesting new models about to make their debut

Already claiming market and technology leadership in cylindrical grinding across the Studer, Schaudt and Mikrosa brands that are within its remit, Fritz Studer AG, part of the United Grinding Group of eight grinding brands, is aiming for a similar position for its internal grinding technology.

Studer acquired Biel-based internal grinding specialist Combitec in 2008. At that time, Combitec was producing some 20-25 machines a year; today the company, now also called Studer but still in Biel, has about doubled that to some 45, although has 90 units/year in its sights, says CEO Fred Gaegauf. That would make it the largest builder of such machines by volume, he says. That is no unrealistic ambition, as the company reported that at just over 40, unit orders were 70% up year on year as at July. Studer Biel is aiming for approaching 80 unit orders for 2015, so is a little behind the pace on that performance, however.

NEW MODELS, WIDER RANGE

This growth is being built on the availability of new models in an expanding range, while in support of increased output, machines are 70-80% completed at Studer’s Thun headquarters some 35 miles south. Already the company has announced a new family of internal grinders, kicking off earlier this year with the S141 (see Machinery, March 2015, p24) and to which the company has since added the S131 and S151 (see box, Filling out the range, p34). In August, Studer announced two more inernal machines, however, one to make its debut at EMO (Milan, October 5-14, see also p18) and another in its final development stages that is already drawing customer interest.

Getting its EMO première will be the S121, which sounds like just another extension to the above mentioned new range, but which has some key differentiators that actually mean that its capacity is larger than the S131. It is for internal, surface and external grinding of chuck components.

The second machine, the S122, is an automated production internal grinder that is geared to high volume manufacture of hydraulic, pneumatic and fuel injection parts, for example. This unit sits below the highest output production fuel injection machines that have twin spindles (which Studer does not make), so is not targeting the very highest volume area, but a level just below this.

The S121’s capacity is swing diameter over table of 400 mm and maximum workpiece length of 300 mm. This compares to the S131’s equivalent figures of 250 and 160 mm and is achieved by having a different slide arrangement – a T-type layout versus the compound cross-slide of the other three models. The grinding spindle turret is also different, a single fixed or a 180° indexing two-position unit. These key features underpin a compact footprint and attractive price, but not, it is emphasised, at the cost of sacrificing advanced technologies.

These include the StuderGuide guideway system for the X- and Z-axis, which guarantees high accuracy – dimension and geometry – through the entire speed range, alongside high load capacity and cushioning levels.

StuderGuide extends the benefits of hydrostatic systems and guideways through a patented surface structure. Its big advantage, in comparison with hydrostatic guides, is the damping component in the direction of motion. Furthermore, the combination of StuderGuide, linear motors and direct measuring systems guarantee “exceptional interpolation accuracies”. System resolution is 10 nm, in fact.

Studer’s Granitan is employed for the machine’s base, of course, supporting thermal stability.

Other machine features take in a workhead with manual cylindricity correction and a high resolution C-axis with direct measuring system that is suited to form and thread grinding. The S121 can employ seven grinding spindles – six internal and a 300 by 32 mm external grinding wheel unit.

Easy programming and efficient operation is via StuderWIN software, which can also handle and display in-process gauging and sensor technology for process monitoring, as well as contact detection and automatic balancing systems.

Moving to the S122 and the key visual feature here is that it boasts up to three gang-style grinding spindles, one of which can carry an external grinding wheel of up to 150 mm diameter. The machine is a production internal cylindrical grinding machine suited to low to high volume production volumes, says Studer.

Featuring a T-style axis arrangement like the S121 (they share a common base), this concept and the parallel spindle arrangement together deliver reduced idle times. Swing diameter is 220 mm and length capacity is 120 mm. Maximum grinding length is 110 mm for internal features and 40 mm for external diameters.

HIGH PRECISION; SHORT CYCLES

Granitan base and StuderGuide guideway system driven by linear motors feature again for the S122. Automatic workhead cylindricity correction is a capability, while all grinding spindles can be individually equipped with automatic arbor deflection compensation, allowing high precision machining even with the smallest arbor diameters. Maximum axis speed is 20 m/min for both axes. All of this supports high precision, efficient grinding in the shortest cycle times.

Up to three dressing stations can be employed, supporting ideal conditioning for each wheel throughout the grinding cycle, Studer emphasises. One dressing unit can be mounted in front and another behind the workhead, with hydraulic retraction pulling them out of the working area after use. The third dresser is set around the main workhead spindle itself.

A fully integrated loader that comes at a “favourable price” underpins short loading times. This linear system with two mandrels takes parts from a chute at the left-hand side of the machine (and deposits finished parts in another chute there), brings them into the machine envelope, removes the finished part with the other, empty mandrel then turns through 180° to load the new part to the chuck. Different loading systems are available, including complex systems having pre- and post-process stations, automatic correction, measured value recording and evaluation.

FILLING OUT THE RANGE

The S131 and S151 have now joined the S141 launched earlier in the year. These machines are capable of both internal and external grinding, as well as form, non-circular and thread grinding. They have a grinding spindle turret with integrated swivel axis (positioning accuracy <1 arc-second) that allows the use of up to four grinding spindles, including up to two external grinding wheels and a universal measuring probe. The workhead is mounted on a swivelling table, with the automatic swivelling axis having a range of -10° to + 20° (length 1,300 mm +15°).

A new arrangement of the dressing position and reversal of the grinding direction during external machining means the entire diameter range can be tackled when external grinding. And as the three machines can be equipped with up to two swivel-in dressing devices with stationary or rotating dressing tools, optimised grinding wheels are employed throughout the machining process, supporting high precision and surface quality, says Studer.

  • The S131 has a swing diameter over the table of 250 mm and maximum grinding length of 160 mm for internal and 125 mm for external diameters. It is available in one size for parts of maximum length 300 mm.
  • The three-model S141 handles maximum part lengths of 300, 700 and 1,300 mm, with swing diameter over the table of 400 mm for all models and maximum grinding length 250 mm for internal and 150 mm for external diameters.
  • The S151 has a swing diameter over the table of 550 mm and a maximum grinding length of 390 mm for internal and 150 mm for external diameters. Two models are available for 700 and 1,300 mm workpiece lengths.

For short changeover and set-up times, the Quick-Set option in the StuderWIN software and a robust, easy-to-use toggle lever steady-rest are employed. Added to this is quick and easy wheel change, underpinned by associated software, a one-key concept and ergonomic design.

Indeed, ergonomic design is highly emphasised, with this said to ensure safety during machine operation and workpiece inspection, efficient process control and, above all, long-term operator well-being.

Design features responsible for these advantages include: the axis layout of the machines and the arrangement of the spindles at the front of the spindle turret; the new dressing concept; the two-leaf sliding doors that allow good accessibility for workpiece and grinding wheel change, plus good visibility into the machine; and the 15 in touch-screen Fanuc control system 31i-B with integrated PC that is positioned to the right of the double sliding door such that the machine operator always has an unhindered view of the machine working area.

This article was first published in the September 2015 issue of Machinery magazine.