Aeschlimann is a Switzerland-based manufacturer of high-precision, rotationally symmetrical complex components for a range of markets, including automotive, bicycle, electronics, hydraulics, measuring technology, medical and watchmaking. The company recently invested in a SwissNano CNC sliding head lathe from Switzerland-based Tornos and a S274 grooving system from Germany-based Paul Horn (Horn) to overcome quality finish issues in the manufacture of an electronic component.
Originally founded as a screw factory in 1937, Aeschlimann today primarily produces turned parts measuring up to 120 mm in diameter but also possesses expertise in machining, producing milled parts that have lengths of up to 300 mm. Furthermore, the company offers a range of special finishing processes, including honing, between centres and centreless grinding, and superfinishing options.
Aeschlimann manufactures 150,000 connectors annually for a turned part in the electronics industry. The connector is produced in Arcap AP1D, a free-machining copper-nickel-zinc alloy with lead as an additive (CuNi25Zn12Pb1). It has a length of 5.8 mm, a depth of 0.2 mm and a diameter of 0.7 to 1.8 mm. Michael Diethelm, a machine operator at Aeschlimann, put this into perspective: “That’s 22,500 recesses with a diameter of 0.7 mm.”
Aeschlimann initially copied the connector using traditional, cam-controlled CNC sliding head lathes. These machines have been in use since the late 1980s and are still commonplace in Switzerland. As Fabian Stampfli, process expert at Aeschlimann, stated: “They are essential in the large-scale series production of very small turned parts that require a high degree of precision and fast cycle times. If they’re correctly configured, they can run for days on end, without intervention.”
However, issues arose due to Arcap AP1D being a comparatively soft material, namely minor damage to the surfaces caused by the guide brush and the formation of small burrs and slugs along the edges during parting off. Given that an all-over high-quality finish is essential for the turned component, an alternative machining method needed to be found.
Aeschlimann switched to using Tornos’ SwissNano CNC sliding head lathe because it is specifically designed for machining extremely difficult, high-precision microcomponents. This lathe can be used for turning, drilling, milling, cutting/deburring and roughing/finishing operations.
According to Tornos, the SwissNano is 40 percent more productive than comparable lathes, therefore making it a suitable choice for manufacturers such as Aeschlimann that are looking to switch from traditional, cam-controlled lathes and achieve equivalent production volumes. Moreover, it is said to be the smallest sliding head lathe available, its installation requiring 1.1 x 0.65 m, thereby freeing up valuable process space and allowing the most difficult bar turning challenges to be overcome.
The SwissNano required that the connector profile be plunge cut rather than copied, necessitating the use of an appropriate cutting tool. Aeschlimann considered Horn alongside another company for supplying said tool, but the latter lost out on account of limited tool life and chipping issues.
Horn’s S274 grooving system is a tool system designed for turning, grooving, parting off and threading. It comprises a machine-specific tool holder and an indexable (interchangeable) insert. The insert is made of a different material to the tool holder and features the cutting edge. It is inserted into the tool holder insert seat and secured using a central clamping screw.
Horn’s S274 grooving system has proven an excellent choice for Aeschlimann. Dominik Läng, turning technology product manager at Horn’s Swiss partner Dihawag, and tooling engineers at Horn’s headquarters in Tübingen together developed a custom, double-edged S274 insert that has a precision-ground, 0.2 mm depth profile. Läng commented: “Horn is known for its solutions for microcomponent machining. This special insert with a precision-ground profile is yet another example of an exceptional product from our friends in Germany, and here in Switzerland. We’re very satisfied with it.”
As pointed out by Läng: “The quality of the tool’s cutting edge is the crucial factor.” Therefore, the microgeometry of the cutting edge is extremely sharp and incorporates a precision-ground chipbreaker to ensure reliable chip control. Diethelm is also able to use the insert for higher cutting values, as its service life has been increased to 45,000 recesses.
The insert’s defined inner radii of 0.05 mm are precision-ground in order to chamfer the connector edges. “Horn really knows what it’s doing when it comes to grinding inner radii,” continued Läng. “It’s important to remember that it is not only the inner radius that needs to be considered. In form grinding, the side and front relief angles of the insert also require expert knowledge. We can even grind inner radii to a defined size as low as 0.025 mm, with tolerances of just a few microns.”
The machining process for the component is as follows. First, the component is machined to an initial diameter of 0.7 mm in a sliding-head turning process. The surface is then pre-turned for subsequent form grooving to a diameter of 1.46 mm. “Due to the ratio between the length and the diameter, the soft material and the cutting pressure, we machine the diameter to leave a 0.06 mm allowance,” explained Diethelm.
Different feed rates are programmed for grooving with the insert because being doubled-edged, it is wide; movement is faster during rapid travel and slows down during the grooving operation to prevent component deflection. Diethelm programmes a dwell time of half a second at the maximum grooving depth for diameters of 1.4 and 1.2 mm. “Grooving across a small diameter with a wide cutting edge creates high cutting pressure,” he said. “This can cause the workpiece to be pushed away slightly. We have optimised the Horn tool holder so that we can use a special thread to make tiny adjustments to the angle of the tool. This enables us to counteract any tapering of the diameter with a correction angle.”
After submission of the initial enquiry, it took around six weeks for a machining process to be developed and implemented. “We are very satisfied with how our requirements were dealt with. We’re impressed with the performance and process reliability of the tools,” concluded Diethelm.
Aeschlimann possesses a number of other Horn tool systems. One of these is the μ-Finish, which it uses for the micromachining of watch screws. The μ-Finish is based on the S274 system, affording inserts that have outstanding precision-ground profiles.
Every tool undergoes a comprehensive round of inspections during the production process to ensure that its cutting edge delivers excellent standards of quality. The precision-ground profile of the insert, the toolholder insert seat and the central clamping screw all help the system to achieve indexability in microns. This, in turn, allows the insert to be indexed in the machine without the need to re-measure the centre height or any other dimensions.
From left to right: Fabian Stampfli, process expert at Aeschlimann, Michael Diethelm, a machine operator at Aeschlimann, Fabian Stampfli, process expert at Aeschlimann, Dominik Läng, turning technology product manager at Dihawag, and Dennis Engemann, application engineer at Horn.
Aeschlimann
Tornos
Paul Horn
Dihawag