Slot milling performance Hydraulic tool holder reduces vibration in trochoidal milling on Axa machine

A hydraulic expansion tool holder with dual-contact technology helped improve stability, reduce vibration and shorten setup times during trochoidal milling tests in demanding nitriding steel, demonstrating the impact of optimised tool holding on machining performance.

Using an SK40 Plan hydraulic expansion chuck from tool holder manufacturer Gewefa, a Wunschmann trochoidal milling cutter was able to demonstrate its capability on an Axa machining centre at their factory in Burladingen.

In this particular application, a slot measuring 1,160 mm in length, 20 mm in width and 6.5 mm 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 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 70 mm and features a corner radius of between 0.25 and 0.5 mm. 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.

At Gewefa’s factory, the trochoidal mill is used on a large Axa 5-axis, travelling-column, universal machining centre, an impressive production platform featuring an X-axis travel of four metres and a powerful swivelling spindle rated at 40 kW / 191 Nm. 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.

Toolholding

Seco expands collet chuck range for high-speed milling

In the initial test, a 16 mm 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 (fz) 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 improved cutting performance is attributed to the increased rigidity provided by hydraulic expansion dual-contact tool holders, which minimise vibration. According to Gewefa, typical runout accuracy is better than 3 µm. The company also reports that hydraulic tool holders reduce setup times by an average of 75 percent compared with shrink-fit chucks. As no heat-shrink equipment is required, tools can be assembled and exchanged anywhere on the shop floor, providing greater flexibility and reducing setup effort.

Gewefa explains that the hydraulic system creates an exact, concentric and backlash-free connection between the tool holder and the milling cutter. Hydraulic oil is enclosed in chambers within the holder. Tightening an adjustment screw increases the hydraulic pressure, causing the inner walls of the holder to clamp uniformly around the tool shank. This delivers even pressure distribution across the entire circumference, ensuring highly consistent clamping performance.

The dual-contact version further increases the rigidity and reliability of the hydraulic expansion chuck. According to Gewefa, it also allows the use of a lighter SK40 swivelling spindle head, whose lower mass inertia improves machine dynamics and productivity. This can eliminate the need for a larger and more expensive SK50 spindle head to achieve comparable machining performance with conventional tool holders.

Gewefa will be exhibiting at the AMB 2026 international exhibition for metalworking in Stuttgart, 15th – 19th September, on stand 1B84 in hall 1.

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