Horn skiving tools raise aerospace gear production efficiency

Machining time for the gear teeth alone is more than halved and overall production time is down by nearly two-thirds

Collins Aerospace in Figeac designs and manufactures systems and components mainly for the aerospace industry. It is one of the world’s leading producers of propeller systems for aircraft, cockpit and cabin equipment and horizontal stabiliser actuators. At its plant in the south-west of France, it also manufactures propellers for the Airbus A400M. Part of the company’s activities involves the production of families of gears, which was formerly carried out in multiple operations by conventional gear cutting techniques.

Following the purchase of new, modern machine tools with process-optimised software on which the spindle speed and axis motions can be closely controlled, including a multi-tasking turn-mill centre, Collins switched to gear skiving tools from German tooling manufacturer, HORN. The products are available in the UK and Ireland though subsidiary company Horn Cutting Tools, Ringwood.

Collins and HORN have been working together for 30 years. The former’s Pascal Janot, who is in charge of tool procurement recalled, “It all began when we started using the tooling supplier’s Mini and Supermini boring, profiling and grooving systems to machine Inconel.

“Our company relies on HORN for the majority of parts where we need to cut grooves, but we also buy milling solutions from the same source.”

Pascal Moulènes, process developer specialising in gears at Collins added, “HORN does not just offer excellent tools. Thanks to the high quality of its support and services, the company is our preferred partner for tooling.

“Many companies can sell, but it’s rare to find one that can develop manufacturing strategies and actively support their implementation.”

Mr Moulènes, together with machine operator Jean-Paul Noyes, team leader Jean Pierre Destruel and process engineer Joel Bousquet, teamed up with the tool supplier to implement the skiving process for various types of gears. They first saw the process being used by a machine tool manufacturer to mass-produce components, sparking considerable interest within Collins as to how it could be exploited in the Figeac factory. The technology also shaped the company’s selection of machining processes and the purchase of new machine tools.

Mr Moulènes witnessed the process in action on the HORN stand at an EMO machine tool show in Hannover. Technical support for the project was provided by engineer Emmanuel Gervais, who is the primary contact at HORN for applications involving the machining of critical aerospace components. Based near Toulouse, the epicentre of the European aerospace industry, he also supports the development of new tool concepts by providing valuable knowledge and experience.

With the help of the new skiving technology, Mr Moulènes was able to optimise the production processes because fewer set-ups were required and he also managed to eliminate the idle time between process steps. In addition to reducing cycle times, the technology also increased component quality.

He explained, “The gear skiving process was new to Collins, so we had to start by familiarising ourselves with it in detail. However, we were not in a position to carry out a lengthy evaluation because of the sheer volume of orders going through our factory. HORN therefore suggested performing trial runs at its test centre in Tübingen, Germany.

Mr Gervais said, “The optimum machining parameters for the gear material, a nickel-chromium-molybdenum alloyed case hardening steel (1.6657), which is tough, wear resistant and relatively difficult to machine, were determined in Tübingen following multiple series of tests. The results were reproducible across all products and the quality was consistently high.”

HORN sent the test parts back to the Collins plant so the quality could be checked. The maximum permissible profile error for the gear teeth is 0.03 mm and the deviation measured was significantly lower than this. For the application, the supplier provided gear skiving tools with a concentricity correction system. Naturally the primary aim was to achieve the appropriate component quality, but long tool life was also very important to control costs.

Introduction of gear skiving at Collins went without a hitch following the successful tests. The cutting data that had been determined for the process in Tübingen was transferred virtually unaltered for implementation in Figeac. Machining time for the gear teeth alone was more than halved compared with the previous process. Overall, gear machining time was reduced from over 20 minutes to 7 minutes due to the fewer set-ups.

The gear skiving process is divided into 14 roughing, two pre-finishing and two finishing operations, leaving a grinding allowance of 0.1 mm. After hardening, the component is ground. As an indication of the extended cutter life that may be expected, one tool manufactures many hundreds of gears in five variants having the same module.

Productive tool system

The HORN tool range includes highly productive gear skiving tools for manufacturing external and internal gears, splines and other internal profiles. The key advantages offered by gear skiving are significantly shorter process times compared to broaching, the ability to use the technique on modern turn-mill centres, turning and gear cutting in one clamping and the possibility of hard machining of gear teeth into the solid.

Gear skiving tools are designed for producing medium to large batches. Each tool is individually adapted to the application and to the material being machined, with the various tool interfaces based on the number of teeth and the module.

HORN’s gear cutting portfolio comprises a range of solid carbide tools, interchangeable head systems and toolholders with indexable inserts, for the production of gears from module 0.25 to 30. Whether this involves spur gears, shaft/hub connections, worm shafts, bevel gears, pinions or customised profiles, all can be manufactured extremely cost-effectively.