Closing the efficiency gap in gear machining


2022-04-28 16:19

Manufacturers of gear parts and bevel gears are constantly looking for alternatives to traditional machining processes. Maximizing flexibility has become a major consideration when selecting a machine tool, as companies are reluctant to limit themselves to a relatively small gear segment. Germany HellerMaschinenfabrik GmbH, in cooperation with Voith, has developed a process that can significantly improve production efficiency, and its pre-milling and gear milling operations can often be completed on a single machine.

It is worth noting that gear milling has recently become a hot topic for some machine tool builders. In fact, it is clear that we can use our existing capabilities in five-axis machining to explore new areas of application beyond the traditional scope of machining centers. Heller is also working on this. Heller, headquartered in Nürtingen, Germany, has gone one step further in the application of five-axis technology following the launch of the new F-Series in the fall of 2009. Gear milling offers the opportunity to tap into all the potential of the five-axis machining centres F-series and the proven MCH-C-series, and to take full advantage of the machine's capabilities and various machining possibilities. Finally, Heller has worked closely with Voith to develop new processes for specific applications. Both companies have filed patent applications for the process, hoping to make a splash in the industry.

While traditional manufacturers in the gear segment continue to focus on specialized machine tools and tools for gear machining, machining center manufacturers offer complete machining for a variety of applications and solutions for modeling gears using specialized software. This type of machining is based on mathematical methods that allow the creation of perfect geometries through CAD/CAM processes. According to the gear technology literature, there is no comprehensive mathematical model, such as bevel gear tooth system. Therefore, each CAD model used in the CAD/CAM process is an approximate model. Traditional gear cutting machines are based on a specific machine structure and have corresponding kinematics. This type of machine generates the corresponding tooth profile according to the setup parameters entered into the machine. Although similar to the gear hobbing process, Heller takes a completely different approach: The gear parameters specified on the drawing are entered directly into the machine control panel. The control panel then uses this data to generate five-axis cutting paths suitable for roughing and finishing in real time. This eliminates the need for mathematically accurate 3D geometric models. Instead, use predefined gear data from drawings. The measuring machine will report compensation data that can be entered directly into the machine control panel for processing. Another major benefit of this approach is that current tool data, such as tool wear, can be incorporated into ongoing processes in real-time. Therefore, the accuracy is correspondingly improved. In addition to interdental machining, HELLER also offers pre-milling processes for semi-finished products. This allows complete pre-cutting of the outer and inner contours in the first clamping, and milling of the teeth in the second clamping. To improve process control, specially adapted NC programs have also been developed. In this way, the entire workpiece can be machined on a single machine.

Production efficiency increased by 2 times

When programmed accordingly, there are other 5-axis machining centers claiming their machining centers are just as versatile and suitable for gear milling. For example, the use of end mills provides a high degree of flexibility. However, according to Heller's business development manager, Dr. Hannes Zipse, this approach is not particularly productive. "Our machining usually has a high chip removal rate and the aim is to achieve the same results when milling gears. Therefore, we worked closely with Sandvik Coromant to develop custom crown milling tools with indexable inserts (crown -millingcutter), such as hob-type tools. This plays an important role and increases productivity by a factor of 2 compared to conventional machining methods. This means that the wider the tooth spacing, the higher the productivity that can be achieved. "Productivity levels are inherently dependent on the static and dynamic stability of the machine. According to Reinhold Siegler, Head of Technology Development at Heller, this is the most important of them all: "A very tight clamping is a must. This means that in our solution the pallet chuck is very close to the upper edge of the pallet in order to hold it firmly. Clamping gears or bevel gears. Other benefits include our exceptionally strong spindles, highly rigid machine elements, and the use of short tools that are well suited for demanding roughing processes. That's why we can get a more vertical type for roughing operations Another reason for the higher productivity of the machining process.

Specializing in general solutions

The new process will undoubtedly provide a high-efficiency solution for workpieces of different sizes (starting module 4): the smaller five-axis machining center model FP2000 is suitable for diameters up to 720mm; the larger model FP4000 is suitable for maximum diameters. 900mm diameter; model MCH-C with HSK100 spindle taper for diameters up to 1800mm; upcoming new machine series for diameters up to 3000mm. Although tool changes are time-consuming, the use of dedicated machines is still very efficient for high-volume pinion production. Therefore, the Heller/Voith process is not directly aimed at traditional contract gear manufacturers who mass produce fewer types of workpieces. The solution is aimed at system suppliers such as vehicle manufacturers, machine tool manufacturers or machine tool parts manufacturers who also use the machine for other machining tasks. Gearbox manufacturers are also interested, and their products also include complete assemblies. This solution is particularly suitable for large gears, as Heller offers machines and technologies suitable for a wide range of machining tasks, with the added benefit of efficiently machining gears and bevel gears. Kenneth Sundberg, global business development manager for Sandvik Coromant, sees this as a very exciting market opportunity: recent years have shown that machining solutions for gear components and bevel gears are constantly being introduced on the market. Therefore, Sandvik Coromant has improved the standard tool and incorporated the newly developed product into the milling tool. So far, we are very satisfied with the machining results obtained. Next we will focus on the hard milling process. Although solid carbide end mills can be used, both we and Heller believe that the use of special crown and side milling cutters will provide greater productivity and economic efficiency. "Potential target customers are more than happy to hear that the process provides them with the spirituality and productivity they need without creating dependencies, such as relying on specific software.