Correlation between the chip geometry and the occurrence of chip welding in dry gear hobbing

Since the introduction of dry gear hobbing in the early 1990s, coolant-based machining has been replaced in many applications due to the economic and environmental benefits. However, the elimination of coolant has led to an increase in the occurrence of surface defects on the tooth flanks during dry gear hobbing, such as smearing, streaking or chip welding. Gears with surface defects are considered scrap. While there are methods to detect and prevent smearing and streaking, gears must be inspected on a regular basis to reliably detect chip welding. Avoiding surface defects in general, and chip welding in particular, will directly reduce manufacturing costs and increase productivity. The purpose of this paper is to identify correlations between the chip geometry and the occurrence of chip welding in dry gear hobbing. Using a manufacturing simulation based on a plane-based penetration calculation, the influence of axial feed f a2 and radial infeed Δx 2 on the chip characteristics and the working tool angles is evaluated. Fly-cutting trials are then used to evaluate the number and shape of chip welds in relation to cutting speed v c2 , axial feed f a2 and radial infeed Δx 2 . To analyze the influence on the chip geometry, the bulk volume V S and the tap volume V R are measured and used to calculate the chip volume ratio RZ. Both the median number of chip welds on the tooth flanks and the chip volume ratio RZ show comparable trends with respect to the cutting speed v c2 and the axial feed f a2 , independent of the radial infeed Δx 2 .