Surface densified camshaft gear for high performance combustion engines 1. Background of the Development The shape of gears is very attractive to the PM manufacturing process. Spur gears as well as helical gears can be shaped by compaction. The performance of gears is influenced beneath the geometrical design mainly by the material parameters tooth root strength σ FE and pitting resistance σ Hlim . The comparison of these values from PM gears to wrought steel gears shows clearly, that PM gears can only be used in low loaded applications (Fig. 1). Dynamic Material properties (acc. DIN 3990) 0 200 400 600 800 1000 1200 1400 1600 Steel 16MnCr5 ESint Fe+1,5%Cu+0,4%C Sress [MPa] Tooth root strength sFE Pitting resistance sHlim Fig. 1. Tooth root strength and pitting resistance /1/ The main influence to the differences in mechanical properties has the residual porosity, which is caused by the PM manufacturing process. The porosity is distributed in the whole volume of the part. But the stress analysis of torque loaded gears shows, that the hot spots always appear near the surface of the tooth (Fig. 2). This leads to the approach to reduce the porosity in the area near the surface. Effective stress levels [Mpa] l ow high Fig.2: Stress distribution of torque loaded gears In extensive investigations it was able to show, that the surface-near areas of PM gears can be densified by a rolling process after sintering (Fig. 3). Fig. 3: Rolling process and cross section of a rolled PM tooth The influence of the densified surface layer to the performance of the gear was investigated at the FZG in Munich. The results are added in the following diagram (Fig. 4). Dynamic properties (acc. DIN 3990) 0 200 400 600 800 1000 1200 1400 1600 Steel 16MnCr5 ESint Fe+1,5%Cu+0,4%C Sint DENSGRAD Stress [MPa] Tooth root strength sFE Pitting resistance sHlim Fig. 4. Tooth root strength and pitting resistance including DENSGRAD TM values. Based on this extraordinary improvement, the PM DENSGRAD TM technology is in the position to substitute wrought steel gears keeping the existing space. 2. Gear Design by DENSGRAD TM technology In the course of technical modification of an existing diesel engine (Fig. 5) we were asked if the two steel gears, which are running the cam shafts can be substituted by sintered gears. The necessary performance data were well known. A geometrical change of the gears was due to the already existing engine not possible. Fig. 5. Diesel Engine with camshaft to camshaft gears By the use of the Standard Gear Calculation DIN 3990 and based on the determined material data of the DENDGRAD TM process it was possible to show, that DENSGRAD TM gears can fulfil the requirements with sufficient safety factors. This fact and also economical advantages convinced the customer to test these gears (Fig. 6). All tests were passed without any failure. Fig. 6: Cam shaft gears made by the DENSGRAD TM technology 3. Manufacturing of DENSGRAD TM gears High performance gears require beneath good mechanical properties especially high precision tolerances. In order to keep gear class 7 (acc. DIN 3960) we decided to finish the toothing by a honing operation. This honing process works economically up to a machining allowance of 0.04 mm. That means that the sum of all tolerances of the different manufacturing steps has to be within the honing allowance. The manufacturing steps are: • Compacting • Sintering • Sizing • Rolling • Casehardening • Hard turning • Honing • Shipping Therefore it was necessary to focus on two tasks for the development of rolling process: a proper densified layer and a near net shape toothing. The dimensional precision after rolling is mainly effected by the properties of the sintered material like density distribution and elastic behaviour. The circumferential density distribution e.g. is directly linked to run out deviations. The spring back effect after elastic deformation causes also geometrical deviations. The elastic deflection of the whole part under rolling force is mainly influenced by the design of the gear. Due to the conical web of the regarding gear it was necessary to support the gear with a specific clamping device during rolling. Deviations of tooth profile are mainly caused by elastic deflection during rolling contact. To compensate these deformations it is necessary to modify the tooth profile of the rolling tool. To do this in an efficient way, the software GEARCONTUR was developed (Fig. 7). Fig. 7: Computer aided rolling tool design – GEARCONTOUR. 4. Experience and response since serial launch Due to a perfect working project team it was possible to introduce this new technology into our existing production without big troubles. Up to now approx. 700.000 parts have been produced and delivered without complaints. Beyond that our customer noticed a clearly reduced meshing noise emission. The successful market launch of the DENSGRAD TM process opens a new and huge field for high loaded PM gear applications in the future. Literature: /1/ Niemann G., Winter H.: Maschinenelemente Band II, Springer Verlag 1989 Appendix: Main dimensions . Surface densified camshaft gear for high performance combustion engines 1. Background of the Development The shape of gears is very. DENSGRAD TM gears High performance gears require beneath good mechanical properties especially high precision tolerances. In order to keep gear class