The winners of the Japan Powder Metallurgy Association 2018 Powder Metallurgy Awards once again served to highlight the ongoing developments being made to further expand the range of PM applications. The winners included innovations in component design and processing, demonstrating the continued potential for new applications in the automotive sector, as well as other high-volume application areas.
Oil impregnated sintered bearing with 1 μm inner dimensional tolerance
A prize was awarded to Porite Corporation for the development of an oil impregnated sintered bearing. The part has a 1 μm inner dimensional tolerance, with an inner diameter of φ 2.5 mm and a length of 11 mm (four times the inner diameter). The bearing is applied to a polygon scanner motor, which requires very high operating speed levels and high precision.
In recent years, higher operating speeds have required miniaturised motors to have higher outputs. However, at these high speeds, if the clearance between the motor shaft and the inner diameter bearing is too wide, noise and vibration will occur. On the other hand, if the clearance is too narrow, the motor current value increases and it takes more time to reach specified revolutions. In order to solve these problems, the clearance between the bearing and the shaft must be optimised by reaming the bearing inner diameter after the normal sizing operation. However, in this method, management of the rotating sizing tools was reported to be expensive and not easy.
The part’s developers succeeded in reducing the inner diameter variation by one third, compared with conventional sizing, by improving the bearing material, tooling and the processes of compaction, sintering and sizing. As a result, a 1 μm inner dimensional tolerance was achieved using only the sizing process, negating the need for a reaming process.
Transmission parts for new-generation hybrid vehicles
Fine Sinter Co. Ltd received an award for the development of an important functional transmission part for the next generation of hybrid automobiles. The part supports the whole weight of a vehicle when the parking lock is on. High reliability is critical for this part, as any damage could lead to physical injury.
As the fuel efficiency of hybrid automobiles is particularly important, this part is required to be designed differently from earlier versions, requiring a reduction in part weight as well as a reduction in the number of components in the unit.
In the original design, it was difficult to compact the shape of the part. Working with the customer, Fine Sinter optimised the part geometry, including the peripheral parts inside the unit, after making a review of the design. Further improvements, for example in restructuring of the die, were also carried out.
The two-step shape, which the old product did not have, was achieved with minimal and simple machining. Through this process, Fine Sinter was able to maintain the functionality required in the customer’s initial design, and succeeded in removing two components from the original part design. The effect of this was a reduction in the cost of a unit by about 40%, and reduction in weight by about 10%, contributing to an improvement in the customer’s competitiveness.
Sintered eccentric bush used in a motorcycle ABS hydraulic control unit
Porite Corporation received a second award for its development of an eccentric bush used in a motorcycle’s anti-locking brake system’s hydraulic control unit. The unit is used for the conversion of the rotary motion of the shaft into a linear reciprocating motion of the hydraulic driving piston.
ABS is widely used in cars, but not in motorcycles. However, in recent years, motorcycle ABS has been becoming mandatory worldwide. Accordingly, production volumes for this device are expected to be increased significantly.
At the first stage of the development, the customer chose to use an integrated camshaft manufactured by a machining process. In order to reduce the cost, the design was then changed to the combination of the sintered eccentric bush and the straight shaft.
In general, ferrous material is selected when this type of machine part is designed. However, a copper-based material was selected for three reasons; corrosion resistance, an elongation level that can allow easy deformation in a sizing process to fulfil the very thin wall thickness requirement of 0.7 mm and ease of sizing to achieve a dimensional tolerance of 6 μm in the inner and outer dimensions. As a result, around 50% cost reduction was successfully achieved.