hot rolling process for large module gears

Record-breaking 50-centimeter gear formed by forming technology

2024-07-03 From Fraunhofer IWU | Translated by AI 2 min Reading Time

In the Gearform project, the Fraunhofer IWU developed a hot rolling process for the manufacture of durable, large module gears together with industrial partners. With this, they produced the largest gear ever manufactured by forming technology.

For the project, the participating organizations specially made a hot rolling plant.(Image: Fraunhofer IWU.) — For the project, the participating organizations specially made a hot rolling plant.
(Image: Fraunhofer IWU.)

Repairing gear damage to offshore wind turbines is very expensive. When the systems are down due to defective gearboxes, repair is often only possible using special cranes. In the Gearform project, the Fraunhofer IWU, based in Germany, together with industrial partners, developed a warm rolling process for the production of durable and large-module gears. Compared to hobbing, warm rolling has a higher material utilization rate and shorter manufacturing times. The project partners have now manufactured a gear with a diameter of 500 millimeters and a module (tooth size) of 9.5 millimeters. It is probably the largest gear made by forming technology in the world so far.

For this purpose, the project partners built a warm rolling facility that heats the rolling blank to 1200 degrees Celsius and introduces the teeth into the component under rotational movement. This forming process does not produce any chips. And since the volume is not reduced in the machining process (volume constancy), it is possible to save approximately 20 percent of the material. The time saving is also worth noting: the rolling process takes six and a half minutes, while hobbing would take about 60 minutes, according to Fraunhofer IWU.

Particularly robust gears pay off for wind turbines.
(Image:Fraunhofer IWU.)

Warm rolling improves the durability of a gear. This is because during forming, the fiber flow of the material is not separated, but merely adapted to the geometric outer contour. This increases both the tooth root strength (lower area of the teeth) and the load-bearing capacity of the tooth flank (contact area with other gears). Additionally, forming-related hardening effects such as influencing the dislocation densification and fine grain influence come into play: the plastic deformation as a result of the warm rolling process results in a significantly higher dislocation density in the metal's crystal lattice, thereby increasing its strength and hardness. At the same time, a grain refinement leads to more toughness of the material. An subsequent heat treatment also serves to harden; by means of a machining process (grinding), surfaces of the gear finally receive their final contour.

The project "Gearform: Energy and resource-efficient forming of large module gears" was funded by the Federal Ministry for Economic Affairs and Climate Protection. Project partners are, in addition to the Fraunhofer IWU (coordination), the Germany headquartered companies: Ema-Tec, Härterei Reese Chemnitz, Dreiling Maschinenbau and Flender. (dm)

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