The winners of this year’s Japan Powder Metallurgy Association (JPMA) PM component awards highlight the continuing developments being made to further expand the range of applications for our technology. The number of components recognised for their innovation suggests that there continues to be the potential for new applications in the automotive sector, particularly in the latest generation of highly efficient international combustion engines and automatic gearboxes.
Development Prizes: New Design
Development of a low-cost sintered ravigneaux planetary carrier
A Development Prize was awarded to Toyota Motor Corporation for a ravigneaux planetary carrier for a new high-efficiency automatic transmission. It consists of a PM carrier A, a PM carrier B, a steel sleeve and a steel hub (Fig. 1). The carrier design was optimised for PM to provide a significant reduction in manufacturing costs compared with forging and stamping. The stress to be applied to the ravigneaux carrier was reduced to below the fatigue limit by optimising the shape of the part at the points where stress was concentrated. The average density of this PM carrier is 7.05 g/m3. For forming of the different height of the legs, green machining was adopted to provide further cost benefits.
The two PM carriers A, B (of composition Fe-2Cu -0.9°C) and a steel sleeve, having an optimal joint design, were brazed during the sintering process. After brazing, the steel hub was welded to the sleeve.
For the purpose of cost reduction, a completely automatic production line from compaction to machining was developed and the number of operators was halved. In order to improve productivity, adjustment of compacting conditions was abolished through the introduction of a filling method to stabilise filling density, and tool changeover time was reduced to less than 160 seconds.
These developments contributed to substantial improvements in cost competitiveness. It is expected that these technologies will be applied to global production in the future.
Development of a complex shaped pulley with high-accuracy non-circular gear teeth
Sumitomo Electric Industries Ltd. received a prize for a pulley with non-circular – in this case, triangular – gear teeth, which is a part of a VTC in a 3-cylinder engine (Fig. 2). The part was developed to achieve a reduction in vibration.
To deliver the required improvements in function, a complex shape and high dimensional accuracy had to be achieved. High accuracy was required to achieve the extremely tight geometrical tolerances of the non-circular external teeth (the outer diameter, the whole circumference, profile and squareness). In relation to the shape requirements, the female screw holes and oil passing slots had to be formed, taking into account the subsequent assembly. Additionally, production of the pulley had to correspond to the requirements for future globalisation in production.
Uneven density after compaction and deformation due to sintering were identified as factors affecting external teeth accuracy. These were resolved by optimising the sizing conditions. Four oil-passing slots were formed by long and thin side cores in the tool-set; however, this led to the breakage of these side-cores after the compaction of around 500 parts. Therefore, two measures were taken; improvements were made to the side-core design to enhance rigidity, and side-core extraction during green compact ejection was delayed.
Eventually, the mass production of large parts having high accuracy non-circular gear tooth surfaces was achieved by optimising production conditions. It is expected that, in the future, demand for sintered pulleys with non-circular gear teeth for VCTs will expand greatly, particularly in Europe.
Development of a sprocket drive for a low fuel consumption automatic transmission (AT) oil pump
Diamet Corporation was awarded a prize for its development of a sprocket drive for a next-generation fuel consumption AT oil pump (Fig. 3). From a cost point of view, an Fe-Cu-C based sintered sprocket with 6.8g/cm3 density was used for this unit, instead of a fine-blanked sprocket.
Although induction hardening treatment is often used for gear tooth surface hardening, post-processing is required since dimensional accuracy deteriorates. In order to achieve both mechanical strength and low cost, Diamet has tried to improve the dimensional precision of an as-induction hardened body.
By setting the sizing conditions to minimise residual stress, it was possible to reduce the deformation during induction hardening and to achieve the required parallelism, with a dimensional accuracy of 50 μm, without post-processing.
The next-generation of AT units are expected to see an expansion of production volumes in the future thanks to their superior fuel consumption and further expansion of demand for the sintered parts can therefore be expected.