The most important advantages of gear skiving in these applications are the significantly shorter process times compared to gear shaping, the use on optimised turning/milling centres, turning and gear cutting in a single clamping operation and the elimination of undercuts at the end of the gearing. In addition, the usually more productive and cost-effective production compared to gear shaping and broaching and the four to five times shorter cycle time compared to slot shaping are convincing. This is also reflected in the possibility of hard machining gears to the full. The gear skiving tools are designed for gear cutting medium to large batches. Each tool is individually adapted to the application and the material to be machined, whereby the different tool interfaces are based on the number of teeth and module size.
Also for larger modules
For internal gears in particular, Horn offers the advantage of a short process time for larger modules, for example. Large and rigid milling/turning centres are required for the gear skiving of larger modules, which enable the corresponding synchronisation between the workpiece spindle and tool spindle. The larger the module, the more critical the machine is in terms of rigidity. This issue can be mitigated on the tool side by splitting the cut between the left and right flanks. After gaining experience with small solid carbide skiving tools, Horn utilised the expertise gained to also cover larger modules. Each application is checked for feasibility by the technicians before implementation and the tool design and recommendations for the process are discussed with the user.
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High metal removal rate, long threads having high surface quality, deep thread profiles, short chips, multi-start threads and low tool load are important advantages of the whirling process. However, in gaining these advantages, the user also faces technical challenges. One important aspect is the choice of materials, for example for bone screws. When machining titanium, stainless steels and other superalloys, the cutting edges of the whirling inserts are exposed to very high loads. In order to counteract cutting edge wear, while maintaining the desired high cutting rate and short machining time, tool manufacturers must constantly optimise and develop the tools and processes.
Horn demonstrates its expertise in thread machining with jet whirling. In cooperation with the company W&F Werkzeugtechnik from Großbettlingen, a whirling system with an internal coolant supply was jointly developed. The system delivers long tool life thanks to direct cooling of the cutting edges. Furthermore, in conjunction with the stable whirling unit, the system achieves an enhanced surface finish on the workpiece and reduces the risk of chip jamming between the inserts. Surface quality plays a major role in the production of bone screws. Any groove or burr can be a breeding ground for germs.
Horn is also demonstrating another process: high-speed (HS) whirling. This technology was developed in cooperation with the lathe manufacturer Index-Traub. HS whirling offers a significant increase in productivity thanks to concurrent turning and whirling. The speed of the process is so high that turning can take place before whirling. The turning tool, positioned in front of the whirling tool, reduces the volume of material that would otherwise have to be removed by the whirling tool. This enables longer tool life and leads to better surface quality. The whirling heads are similar to conventional whirling heads. Only the inserts differ in their geometry. The production of single- and multi-start threads is possible with a single tool.
Horn offers other whirling technologies in addition to jet and high-speed whirling. The most universally used technology is standard whirling. The whirling head can be connected to any whirling unit. Horn has developed the modular whirling system for rapid exchange of the whirling head and inserts outside the machine. Thanks to the precision interface, the whirling head does not have to be readjusted after removal from the machine. Furthermore, the whirling tool can be adapted to different interfaces using spacer rings. Horn turbo whirling promises high productivity. Using a cut distribution of roughing, pre-finishing and finishing, the load on the profiled inserts of the whirling tool is reduced. The system therefore offers faster processing times and reduced tool costs.