Using an SK40 Plan hydraulic expansion chuck from tool holder manufacturer
Gewefa, a Wunschmann trochoidal milling cutter was able to demonstrate its full capability on an AXA machining centre at Gewefa’s factory in Burladingen.
All the equipment equipment suppliers involved in the project were German. However, the sole sales agent for Gewefa products in the UK and Ireland, is Wiltshire-based
Nydaloxe Precision.
The machining tests produced optimal results in terms of tool life, dimensional accuracy and surface quality.
In this application, a slot measuring 1,160mm in length, 20mm in width and 6.5mm in depth had to be milled into a workpiece made of nitriding steel (34CrAlNi7), a difficult material to machine.
Alloyed nitriding steel is characterised by high surface hardness and wear resistance. Typical uses for it include high-speed spindles, shafts, gauges, precision measuring equipment and cams.
Stephan Wunschmann, managing director of the cutting tool manufacturer said: "With our solid carbide 175 ER trochoidal mill, which has a corner radius, we have the ideal cutting tool for slotting in such a demanding material.”
Norbert Schmid, head of sales for Gewefa GmbH added: "In machining, to achieve the best possible result you should consider all of the elements involved - tool, tool holder, spindle and machine - which we did in this application."
The 175 ER trochoidal mill is available in cutting lengths from 18 to 70mm and features a corner radius of between 0.25 and 0.5mm. Its proprietary HE-S high-performance PVD (physical vapour deposition) coating, formulated for hard machining, is resistant to high temperatures and oxidation. The tool features five generously dimensioned, polished chip flutes and a robust core. Thanks to its variable helix angle, vibration is minimised and so tool life is extended.
Pic: The 5-axis AXA universal machining centre at Gewefa in GermanyAt Gewefa’s factory, the trochoidal mill is used on a large
AXA five-axis, travelling-column, universal machining centre, an impressive production platform featuring an X-axis travel of 4m and a powerful swivelling spindle rated at 40kW / 191Nm. The cutter is mounted in a tool holder having face-and-taper contact in the machine spindle to prevent axial movement under heavy radial loads.
In the initial test, a 16mm diameter cutter was clamped into a collet chuck with face-and-taper contact. The cutting speed (Vc) was 80 m/min, with a feed rate of 0.16 mm/min. The machinists were satisfied with the dimensional accuracy and surface quality, but the noise level when milling the slot was rather high, so the decision was taken to swap the collet for a Gewefa SK40 hydraulic expansion tool holder, also with a dual-contact spindle interface, which rectified the noise issue. The holder transmits torque and cutting forces without slipping through both friction and positive locking.
The reason for the better cutting performance is that hydraulic expansion dual-contact tool holders provide more rigidity, leading to less vibration. Runout accuracy of typically less than 3µm is normal. Additionally, hydraulic technology results in an average 75% reduction in setup time compared to a shrink-fit chuck. Moreover, when using the former to enhance cutter rigidity, no heat-shrink units are required so setup can be carried out anywhere on the factory floor.
The hydraulic system ensures an exact, concentric, play-free connection for the milling tool. Hydraulic oil is contained within chambers in the tool holder. When pressure in the system is increased via an adjustment screw, the interior side walls are pressed firmly around the tool shank. Pressure distribution is identical at every point around the circumference; it is impossible to clamp a tool more evenly.
In the version with dual contact, the hydraulic expansion chuck becomes even more rigid and reliable. An added advantage is that the light, and hence dynamic and more productive, SK40 swivelling spindle head has lower mass inertia than a more expensive SK50 head, which might otherwise have been needed to achieve equivalent, albeit slower, machining results with standard tool holding.
Gewefa will be exhibiting at the AMB 2026 international exhibition for metalworking in Stuttgart, 15 – 19 September, on stand 1B84 in hall 1.