Technology for Internal Gear Tooth Profile Grinding

Liebherr offers a new internal gear tooth profile grinding technology, based on its OPAL grinding technology, involving a belt-drive spindle, which can be fitted to the standard GH 4.0 grinding head, as well as to the new GH 5.0 and GH 6.0 grinding heads. Initially, the internal gear grinding arm is available in two different sizes, while others are to follow shortly. Custom internal gear grinding arms can be developed to match customer workpieces.

Gear grinding to Liebherr quality standards is feasible for internal gears, using a range of different grinding arms that each fit the GH 4.0, GH 5.0 and GH 6.0 grinding heads.

“Simple changeover between external and internal gears takes a maximum of half an hour,” Dr. Hansjörg Geiser, head of the gear cutting machinery development and design engineering team, explains. “You detach the external gear grinding disk or worm, hang the internal gear grinding arm on the hardened stop bars to ensure repeat accuracy and fix it in place with a handful of screws, then tension the belt-drive disk and the belt and attach the cover.

Internal gears can then be ground using a grinding disk of 100 or 125 millimeters in diameter – a Liebherr innovation. The external gear grinding head does not have to be touched, and external gear grinding quality is again the same as before once the internal gear grinding arm has been detached.

IG Opal 4.0 is the name of this innovation that functions at a maximum spindle speed of 12,000 rpm. A larger version, the IG Opal 4.1, featuring a maximum grinding disk diameter of 125 millimeters, is also already available. Both arms were successfully tested using CBN and corundum disks. Where dressable grinding disks are used, the internal gear grinding arm travels up to the grinding dresser that is also used for external gear grinding. 

All internal gear grinding arms are modelled in 3D and can be used in very confined spaces. “Collision inspections are simple and extremely reliable,” emphasizes Andreas Mehr, who is responsible for grinding and shaping technology development and consultancy at Liebherr-Verzahntechnik GmbH. “Small-diameter internal gear teeth can therefore also be machined quickly and easily.

Liebherr-Aerospace, which uses Liebherr gear cutting machinery to manufacture their own components, is one of three first buyers of this new technology. As in the case of external gears, this new internal gear teeth technology works with a multiple-rib grinding disk system that can rough- and finish-grind. That is particularly important to users, who regard speed and costs as important, for instance customers from the aerospace industry. Grinding disks made of dressable corundum or electroplated CBN can be used in conjunction with the spindle. These are also manufactured at Liebherr’s plant in Ettlingen (Germany).