AGMA 05FTM09-2005 pdf free download.Hypoid Gear Lapping Wear Coefficient and Simulation Claude Gosselin and Qimi Jiang, Laval University, Kevin Jenski and Jack Masseth, American Axle and Manufacturing.
Hypoid gears are widely used in vehicles. Two basic cutting processes can be used, either face milling or face hobbing [1-3]. the latter now often being preferred for its cost effectiveness. Whichever cutting process is used. tooth surface errors appear, in part because of tooling wear and machine distortion, in part because the gears are heat treated after cutting which releases internal strain and causes tooth flank distortion. Therefore. a finishing operation is necessary.
Finishing can be done by grinding the gear teeth. but it is expensive in terms of tooling and time, and is therefore usually limited to small productions such as aerospace gears. Finishing can also be done by lapping, whereby the gear set is operated for a short time, under limited speed and torque, at varying positions such that the abrasive lapping compound imporves the contact surfaces. Lapping is normally applied to hypoid gear finishing because it is economical for large production volumes. As a result, excellent smoothness and quietness of operation can be obtained.
To evaluate tooth surface errors, gears are measured with a Coordinate Measurement Machine (CMM) to obtain the actual tooth flank topography, The CMM coordinates are compared to reference coordinates obtained from a 3 dimensional modelling software where the actual machine settings and cutter dimensions allow precise calculation of the theoretical tooth flank.
The CMM coordinates may be used to reverse engineer the actual tooth flank as developed by Gosselin [4]. Reverse engineering provides the machine settings of a theoretical reference matching the actual tooth such that the kinematics of an actual gear set may be calculated the same way the theoretical gear set is calculated.
In practice, lapping is an abrasive wear process. The pinions and gears are lapped in pairs and must therefore remain as coordinated pairs in operation. Because of the vanability in tooth surface errors caused by different machine production lines, varying tool wear, and different positions in the heat treatment furnace, tooth surface errors vary significantly from batch to batch, piece to piece, and even tooth to tooth. As a result, the contact pattern is different from gear set to gear set, while the lapping cycle must be same.
There are many factors affecting the lapping wear rate (weight removal per unit of time), including grain size, shape. material and hardness of the lapping grit, applied torque, pinion RPM. hardness of the gear set, etc. Thus, developing a lapping cycle for production requires both time and experienced technicians to establish lapping operating positions and cycle time to produce quality gear sets.
So far, theoretical knowledge on the relationship between material removal, lapping time and applied torque is limited. To help address this problem. one key parameter dubbed wear coefficienr can be determined.
Since the wear coefficient can be affected by factors such as grain size, shape, material and hardness of the lapping grit, this work is based on lapping tests made using the same lapping compound and conditions such that the above factors can be neglected. In other words, this work focuses on presenting an algorithm working with data measured from hypoid gear sets lapped under the same conditions (same production lines).AGMA 05FTM09 pdf download.