This thesis is accomplished in the transmission department, DX, on Scania, Södertälje. The purpose is to compare the method lapping, that are used today, with the method grinding. The two methods are used for hard surfacing on bevel gears, one of the components in the transmission for trucks and busses. The methods are compared with a widely perspective and constructions, production, logistic and economy are taken in to considerations.
Scania has experienced some problems with the lapping process and that’s why they want this pre-study done. In the lapping process the material removal occurs when the flanks of the wheel and pinion touches, this makes it necessary to synchronise the production flow for wheel and pinion before the machining. This cause loses in efficiency and makes it difficult to plan the production. With grinding the removal of material is carried out by a grinding wheel that separate the production and planning for the wheel and pinion. Lapping has also a very limited capacity in removal of material. With grinding it is possible to remove more materials, up to five times.
During the study even more problem with lapping occurs. The method can’t guarantee a stable quality and automatization of the hard surfacing of the gear is not possible with lapping. Grinding on the other hand guarantee constant quality and creates opportunities for automatization. Grinding solves a lot of the problems that appears today but it also has other advantages. More complex forms on the flank can be created with grinding then with lapping, making opportunities for the construction department. By using modification of the flank form the gear can evolving in both load carrying capacity and noise behaviour.
There are also risks with grinding. This report identifies several and burnings are one of them. Burning appears when the temperature between the flank and the grinding wheel get to high. This causes damage on the flank surface. Another risk has to do with the heat treatment. Because of the higher removal of material with grinding, it is necessary to leave more material on the flank in the cutting. The consequence could be that a longer time is required in the furnace to get the same depth of case.
Even more indirect effects of a change in method are observed in the report. By using grinding, potential for cutting with a higher speed appears which leads to reduction in cycle time. In the hard turning machine, where the wheels are machined, the cycle time will increase.
The conclusion of the report is, with respect to the purpose, that Scania should grind all their bevel gears. The strongest argument is the potential in separating the production system for wheel and pinion, the increased performance of the bevel gear and the constant quality that grinding achieves.