Gearing technologies providing flexible and highly productive options

The machining of components in a single setup offers many advantages: increased machining accuracy and productivity was well as a reduction in component handling costs. To enable customers to tap this potential, HELLER is successively integrating further technologies into its machining centres. The latest examples are power skiving and gear hobbing. With these processes, users of 5-axis milling centres will be able to perform gear-cutting operations without having to reclamp the components.

Power skiving

There are hardly any tooth shapes that cannot be produced using power skiving. Whether straight or helical, external or internal gearings – anything is possible without a problem. Even profile modifications are easy to implement. The relatively low-cost gear-cutting tools and the short machining and cycle times make the process even more attractive in comparison to specialised broaching or shaping machines. The only prerequisite: the 5-axis machine used must be equipped with the turning functions of the HELLER Mill-Turn option with the directly driven DDT rotary table.

If this is the case, the power skiving technology can be easily integrated into modern Siemens controls and programmed just as easily. Even machine operators with little experience in gear cutting will have no problems creating a reliably working program. A technology cycle with a clear structure and graphically supported input mask provides the basis for this. All that programmers are asked to do is enter all relevant gearing data in a step-by-step procedure and confirm them at the end. The cycle then automatically performs a comprehensive plausibility check. If this is successful, the production process can be started.

The machining operation itself requires a high level of accuracy of all machine axes. In the focus of it is the rotary table with the workpiece and the spindle with the tool. These two rotary axes are generically coupled, as they must rotate exactly synchronously. During this simultaneous process, the milling cutter performs a rolling motion on the workpiece. At the same time, the machine carries out a consistent feed motion along the gearing centreline, thus cutting the material. The tooth shape ultimately results from the synchronous rotation and the shape of the specific cutter used.

At this year’s in-house exhibition, HELLER used the example of a planetary carrier to demonstrate the wide range of possibilities offered by the new ‘Power Skiving’ option – implemented on the HF 5500 5-axis machining centre. The component with 85 mm diameter is turned, milled and drilled in a single setup and finally the power skiving method is used to machine an internal gearing with module 2 (41 teeth). The latter operation only takes 160 seconds to complete, achieving quality 7 to DIN 3961.

Gear hobbing

Gear hobbing also enables users to produce straight and helical tooth forms with a similarly high level of quality and only slightly longer machining times. However, it only allows to mill external gears whilst profile modifications are more difficult to implement. One advantage of this process over power skiving: the option can be implemented on standard 5-axis machining centres from the HF series without mill-turn technology.

Integration of the technology cycle into the Siemens control and the programming of the gearings work just as easily and reliably as with power skiving. However, the shape of the tools and the machining process differ significantly. In gear hobbing, the workpiece and the tool form a kind of worm gear that moves synchronously. Due to the consistent feed motion along the gearing centreline, continuous cutting takes place without return strokes. Extended tool life is ensured through so-called shifting integrated into the cycle. This refers to the tangential displacement of the tool relative to the workpiece along the tool axis.

Complete machining of a splined shaft exemplifies the possibilities offered by the gear hobbing option. The component has involute toothing with module 3 and was circular milled, drilled and hobbed to DIN 3961 in quality 7 (25 teeth) on the HF 3500 5-axis machining centre in a single setup. Machining of gearing takes approx. 200 seconds.

Whether power skiving or gear hobbing: both processes expand the range of complete machining options in a simple and reliable way. The additional investment is kept within limits, as only the respective tools, software features for the CNC and the technology cycle are required. The ESR safety option integrated in the package ensures that the tool immediately retracts from the workpiece in the event of a fault without causing any damage.