In case of automotive mass production is obvious in all production branches. This is true also for drivetrain, gearboxes and gearwheels. Almost all gearings have an involute profile. This is given by very effective manufacturing process. Tooth flank profile is already very precisely fine-tuned. So the way to cost reduction is no more in gearwheel geometry but in the gearwheel's material and its resistance against pitting. From this reason we tried to replace standard gearset made of case hardened steel by a new one - made by PM technology. Manufactured PM gearwheels were tested in original automotive gearbox to assure same loading conditions (shaft deflection, lubrication, housing deformation, etc.) as in the car.
In our laboratory at the university there is a special back-to-back test rig. Standardly at these back-to-back test rigs only the gearset is tested. At our test rig the gearbox is placed in the same way as in the car - fastened by screws to engine cast and this whole assembly is than placed to the test rig frame using original rubber mounts. The circuit is then completed by joint shafts. To be able to set some loading torque in the circuit differencials at both gearboxes have to be disabled. Results of these tests are presented in this contribution. The target is to produce rough gearwheel profile by pressing from the powder metal and sintering to avoid expensive milling and turning operations. Of course this operation cannot include tooth flank modifications (e.g. crowning).
Of course we are not able to make rough shape of helical gearset by pressing operation because appropriate tooling would be too expensive. From this reason we have decided to make few gear sets by gearing milling from pressed and sintered PM pucks with appropriate dimensions. The technology of "Hot Isostatic Pressure" to densify the flank surface was used. At this project we cooperate with Swedish company Höganäs AB, which is the owner of PM parts technology.
Ing. Ondřej Miláček, CTU in Prague, CZECH REPUBLIC; Prof. Gabriela Achtenová, CTU in Prague, CZECH REPUBLIC