Hypoid Gear Lapping Wear Coefficient and Simulation


Authors: Claude Gosselin and Qimi Jiang, Laval University, Kevin Jenski and Jack Masseth,
American Axle and Manufacturing
Because of the large volume ofmanufactured sets, hypoid gears are usually hard finishedafter heat treatment
using the lapping process. In the lapping process, a gear set is run at varying operating positions and under a
light load in order to lap the tooth surface. An abrasive lapping compound is used as ametal removal media.
Because of the rolling and slidingmotion inherent to hypoid gears, the lapping compound abrades and refines
the tooth surface to achieve smoothness in rolling action and produce high quality gear sets. The pinions and
gears are lapped in pairs and must therefore remain as coordinated pairs for the rest of their lives.
However, heat treatment distortion can vary significantly from batch to batch, and even within one batch if the
temperature is not consistent throughout the heat treatment furnace. Thus, developing alapping sequencefor
manufacturing requires both time and experienced technicians who can establish lapping operating positions
and sequence times to produce quality gear sets both in terms of performance and cost. This development is
generally trial and error as past operator experiences factor heavily into the process.
In this paper, the lapping process is simulated using advanced modelling tools such as gear vectorial
simulation for the tooth surfaces and path of contact and reverse engineering to analyze the tooth contact
pattern of existing gear sets under load (static LTCA). Test gear sets are measured using a CMM prior to a
special lapping cycle where the position of the gear sets on the lapper does not change, and then
re--measured after lapping in order to establish how much, and where, material was removed. A wear
constant named "wear coefficient" specific to the lapping compound composition is then calculated.
Based on the obtained wear coefficient value, an algorithm for simulating the lapping process is presented.
Gear sets lapped on the production line at American Axle and Manufacturing are used for simulation case
studies. Results show that it is possible to predict how much and wherematerial will be removed on the tooth
surface, thereby opening the door to better understanding of the lapping process.
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