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Power transmission components for automotive applications require high static and dynamic mechanical properties to insure long term system reliability. Historically, high quality wrought steel alloys have been the only materials used in the series manufacturing of high torque transmitting components such as one-way clutch races, transmission gears, sprockets and bearing races. Although powder metal technology offers lower cost components, limitations in static and fatigue properties of sintered materials preclude utilization of conventional powder metallurgy in these applications. To address these shortcomings we have developed DensiForm®, a surface densification technology. Specifically, a densification process is utilized with the net result of a full density layer on critical areas up to 1 mm deep into the part and an overall component density above 92% of the theoretical density.

During the past five years the use of assembled camshafts in the North American automotive market has grown steadily. For valve-trains that operate with roller followers at relatively high contact stress, assembled camshafts are a cost-effective solution, as compared to camshafts machined from forged bar stock. Forged bearing steels, and, to a lesser extent, powder forged steels, have been the materials of choice for the manufacture of cam lobes for assembled camshafts. Sintered alloys offer an attractive alternative to forged steel because very accurate cam lobes can be manufactured via pressing and sintering. However, the use of sintered alloys has been limited by their relatively low rolling contact fatigue properties. This paper presents the application of sintered lobes in mechanically assembled camshafts that operate in roller follower valve-trains at relatively high contact stress.

Forged bearing steels and powder forged steels (e.g. AISI 52100, SAE 5160 and MPIF FL-4680) have been used to make cam lobes for assembled camshafts operating with roller followers. Application of powder metal (pressed and sintered) alloys to this and other components that operate under high rolling contact stress has been limited by relatively poor rolling contact fatigue (RCF) properties. This paper introduces developmental sintered steel alloys with high RCF strength. The density of these alloys is 7.4-7.6 Mg/m3 and the macrohardness is 500-800 HV. Endurance limits are in the range 1,700-2,280 MPa. The RCF endurance limit at 200 million stress cycles was determined using a testing rig. Camshafts for a 4.6 L V8 engine and a 4.0 L V6 engine have been assembled. These engines have a single overhead camshaft with end pivot rocker with roller follower (type 2 valve-train).