Machining in large-sale production

"22,500 recesses with a diameter of 0.7 mm (0.028") – this is when we need a special insert", explains Michael Diethelm. Diethelm is a machine operator at Aeschlimann AG in Lüsslingen, Switzerland. Since the process optimisation, the team – headed up by process expert Fabian Stampfli – has used HORN's S274 grooving system for the profile grooving of an electronic component. "HORN is known for its solutions for micro-component 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", says Dominik Läng, turning technology product manager at HORN's Swiss partner Dihawag.

From micro-sized watch components to parts for the medical sector and excavator hydraulics, Aeschlimann AG is a specialist in the production of high-precision, rotationally symmetrical workpieces. Originally founded as a screw factory in 1937, the company now manufactures complex CNC components and offers its customers a range of special finishing processes including honing, between-centres and centreless grinding and options for super-finishing. The 165 employees at the Swiss company primarily produce turned parts measuring up to 120 mm (4.724") in diameter. But the Aeschlimann team are also experts in machining, producing milled parts with lengths of up to 300 mm (11.811"). Its customers include companies in the watchmaking, automotive, hydraulics, machinery and electronics industries. Aeschlimann also supplies its high-precision Swiss products to the medical, measuring technology and bicycle sectors.

150,000 parts per year

Diethelm manufactures a connector in Arcap AP 1 D – a free-machining Cu-Ni-Zn alloy with lead as an additive (CuNi25Zn12Pb1) – for a turned part for the electronics sector. The component has a length of 5.8 mm (0.228") and a diameter of 0.7 mm (0.028") to 1.8 mm (0.071"). Aeschlimann produces around 150,000 of these workpieces a year. "Before switching to HORN tools, we produced the parts on our old cam-type sliding head lathes", says Diet­helm. The machines – which have been in use since the 1980s – are still commonplace in Switzerland. "These machines 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. We produce the cams for the machines ourselves", explains process expert Stampfli. However, the company encountered an issue when producing this component: the material used is comparatively soft. Copying the 0.2 mm (0.008") deep workpiece profile resulted in small burrs forming on the edges and caused small "slugs" to be produced when parting off. "Minor damage to the surfaces was another problem. This damage was caused by the guide bush during the sliding-head turning process", says Diethelm. An absence of burrs, a high surface quality and a good finish after parting off are key criteria for the turned part.

To solve the problem, Stampfli and Diethelm switched the machining process over to a Tornos SwissNano CNC sliding-head lathe – which was specifically designed to machine micro-components with a high degree of precision. The workpiece profile would now be produced with a plunge cut instead of being copied. "There was another tool manufacturer in the running for supplying the tool concept alongside HORN. It was a tight race, but we didn't give the other company the contract due to chipping problems and limited tool life", explains Diet­helm. Turning technology specialist Dominik Läng from Dihawag worked with tool engineers from Tübingen to develop a solution using the HORN S274 grooving system.

45,000 recesses per insert

"The quality of the tool edge is the crucial factor," says Läng. The microgeometry of the cutting edge is extremely sharp. With the help of the ground chipbreaker, it was possible to achieve reliable chip control. Diethelm was also able to use  the tool system with higher cutting values. The service life of the double-edged insert was boosted to 45,000 recesses. The shape of the indexable insert is precision ground, and the profile depth is 0.2 mm (0.008"). The defined inner radii of 0.05 mm (0.002") are ground to chamfer the workpiece edges. "HORN really knows what it’s doing when it comes to grinding inner radii. 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 (0.001") with tolerances of just a few microns", explains Läng.

The machining process for the turned part is as follows: First, the workpiece is machined to an initial diameter of 0.7 mm (0.028") in a sliding-head turning process. The surface is then pre-turned for subsequent form plunge cutting to a diameter of 1.46 mm (0.057"). "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 (0.002") allowance", says Diethelm. Different feed rates are programmed for grooving with the wide insert; movement is faster during rapid travel and slows down during the grooving operation to prevent workpiece deflection. At the maximum grooving depth for diameters of 1.4 mm (0.055") and 1.2 mm (0.047"), Diethelm programmed a dwell time of half a second. "Grooving across a small diameter with a wide cutting edge creates high cutting pressure. This can cause the workpiece to be pushed away slightly. We 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", says Diethelm. The workpiece is also parted off using a type S274 insert.

Fast tool solution

After submission of the initial enquiry, it took around six weeks for a finished 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", says Diethelm. In addition to the tools mentioned in this article, Aeschlimann also uses a number of other HORN tool systems, including type S100 parting-off tools and Supermini inserts for internal profiling. The company also uses HORN µ-Finish tools for micro-machining of watch screws.

The µ-Finish tool system is primarily aimed at micro-machining users. Based on the S274 system, it features inserts that have been ground with outstanding precision. Every tool undergoes a comprehensive round of inspections during the production process to ensure that its cutting edges deliver excellent standards of quality. Together with the central clamping screw and the precision-ground profile  of the indexable insert, the tool holder insert seat helps the system to achieve indexability to within 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. In addition to its extensive range of standard profiles, HORN offers custom-made inserts with special designs.