Reliable knurling of small diameters

Precision down to the smallest detail

Häni chooses custom-made zeus knurling tools

It is a feature of their industry that manufacturers of medical and dental technology impose exacting requirements on their products, and these requirements are passed on to their suppliers. Consequently, only high-quality materials such as stainless steel are used, while high-precision work is an absolute must, particularly for small parts. Häni + Co. AG is a Swiss manufacturer of precision turned parts for the medical technology and automotive industries. Their demands on the tools used in the production process are correspondingly rigorous. For a profile on a small turned part with a diameter of 1 mm (part of a dental instrument), the company found the right solution in the form of a zeus knurling tool specially configured for the application.

Häni + Co. AG, based in Arch, Switzerland, has made a name for itself as a manufacturer of high-quality precision turned tools thanks to its uncompromising quality standards in fields such as medical and dental technology, the automotive industry and electrical engineering. The company specialises in turned parts made from steel, non-ferrous metals, aluminium, titanium and plastic, with diameters ranging from 1 mm to 42 mm.

For the manufacture of a turned part made from stainless steel (INOX 1.4104) in small-scale series production of 1,000 to 5,000 units per year, Häni sought a partner for a small but important detail – the turned part is used in an instrument for dental hygiene. A knurl was to be applied to the upper end of the turned part, with a small grinding wheel attached to it. The knurling profile was to act as an additional anchor point alongside the adhesive to attach the grinding wheel firmly and securely to the turned part. This represented something of a first for Häni. The company normally works with knurls on minimum diameters of 1.5 mm. On this occasion, however, the knurl had to be applied to a diameter of just 1 mm.

Philipp Grosjean, project manager at Häni + Co. AG: "As a commercial partner to Hommel+Keller Präzisionswerkzeuge GmbH, we consider Vargus to be the knurling expert in Switzerland, and so they were our first port of call on the search for a suitable tool for this job." Vargus Werkzeugtechnik snel AG, based in Cham in Switzerland, has operated for more than 50 years as a manufacturer of high-quality thread-turning and thread-milling tools, as well as cutting, grooving and deburring tools for the metal and plastics industries. In addition, the Swiss company is a sales partner to prominent tool manufacturers, including Hommel+Keller Präzisionswerkzeuge GmbH.

Careful machining with zeus 391 knurling tool
Applying a knurling profile to a small diameter calls for specialist expertise. As a global market leader in knurling technology, Hommel+Keller Präzisionswerkzeuge GmbH is a highly skilled point of contact in this field. This, coupled with the company's collaboration with Vargus and its years of experience in micromachining, was the perfect starting point for Häni. "When we were addressing the issue of knurling the small diameter of the turned part precisely and reliably, it quickly became clear that a standard tool was out of the question", agree Philippe Bachmann, product manager at Vargus, and Reinhold Dreher, application expert and technical sales representative at Hommel+Keller Präzisionswerkzeuge GmbH.

With the zeus 391 special tool for form knurling, they found just the right solution for the application, because the special tool design facilitates extremely careful machining of small and pressure-sensitive workpieces. This is because the three knurling wheels mean that only minor lateral pressure is generated, resulting in minimal stress on the workpiece.

The knurling tool can be used on a diverse array of machinery including conventional and CNC lathes, automatic long- and short-turning lathes, turning/milling centres, multi-spindle machines, rotary transfer machines, indexing table machines and transfer machines. Another benefit is that the tool is extremely easy to use because the knurling wheels can be replaced quickly in just a few steps.

Knurling wheels tailor-made for the workpiece
Ensuring that the knurling wheels are perfectly suited to the workpiece to be machined is crucial to achieving outstanding results. The turned part from Häni has a knurling profile of RGE 30°. Two knurling wheels at BL 30° and one knurling wheel at BR 30°, each with a diameter of 5 mm, are used for the application. The experts from Hommel+Keller Präzisionswerkzeuge GmbH adjusted the number of teeth precisely to the circumference of the workpiece. Reinhold Dreher: "The less favourable the spacing, the more the knurling result deteriorates and the shorter the tool life of the knurling wheels becomes. In extreme cases, this can lead to profile deformation or even double-track knurling."
To improve the forming process at the corners and to prevent tooth tips from breaking out, the form knurling wheels have a 45° chamfer. Moreover, special surface hardening increases wear resistance.

Successful partnership
"We are using zeus knurling tools for the first time on this project and are very satisfied. The tool performs outstandingly, boasts a long tool life and ensures first-class results. Not only that, but our partnership with Vargus and Hommel+Keller Präzisionswerkzeuge GmbH was superb. We will certainly call upon their support again for future projects", adds Philipp Grosjean.