The Japan Powder Metallurgy Association (JPMA) has announced the winners of its annual awards, which, once again, brought the ongoing developments of Japan’s PM industry centre stage. The winners showcased innovations in component development and processing technology, demonstrating the design and commercial benefits of using Powder Metallurgy as a manufacturing technique for mass production in numerous end-user categories.
JPMA awards: New design
Parking parts in a plug-in hybrid electric vehicle’s transmission
Sumitomo Electric Industries, Ltd, recieved an award for a parking lock mechanism component (Fig. 1) used in a transmission developed for PHEVs (plug-in hybrid vehicles). The part consists of a tapered section, used to guide a locking rod mechanism activated when the transmission is shifted to the park position.
The conventionally made part required extensive machining, which accounted for 50% of the total production costs. Sumitomo worked closely with the customer to re-design the part. The near-net shape incorporatres a slope formed with a punch, bolt holes formed with the core and the void formed with the die. As a result, Sumitomo succeeded in reducing the machining costs by about 40%.
Development of Soft Magnetic Powder Cores for Axial Gap motors
Sumitomo Electric Industries, Ltd, also recieved an award for the development of stator cores for axial gap motors (Fig. 2). The cores are used in pumps, and generate the rotational force of the rotor by becoming an electromagnet when an electric current flows through the wound coil.
With a move to smaller, lighter and more efficient motors, the adoption of axial gap motors is expected to become widespread. They offer a number of advantages when compared to conventional motors, being thinner and with high torque. Soft magnetic powder cores are particulalry suitable for the three-dimensional magnetic circuit required for axial gap motors, due to their magnetic isotropic properties and high design flexibility.
Sumitomo has achieved mass production of the soft magnetic powder cores by optimising the manufacturing process in a number of ways. This included the use of insulation-coated soft magnetic powder, a heat treatment to remove distortion, machining of the bolt hole for fixing and a surface coating.
High-efficiency electric oil pump parts for HEVs clutch engagement (high pressure applications)
Sumitomo Electric Industries, Ltd, recieved a further award for these internal gear rotors and body (rotor case), used for an electric oil pump in HEV clutch engagement (high-pressure application) (Fig. 3). The parts require an extremely high dimensional accuracy to ensure high efficiency and quiet operation.
In the original part, the inner diameter of the inner rotor was machined to improve the coaxial accuracy of the inner and outer diameters. However, in addition to machining, there was also a shaft press-fitting process by the customer, which increased the unit cost. Therefore, in order to omit the inner diameter machining, and maintain the coaxial accuracy of the inner and outer diameters of the inner rotor, Sumitomo modified the compacting tools and applied uniform powder-feeding technology. As a result, they achieved inner tooth tip runout accuracy equal to, or higher, than machining. By applying uniform powder-feeding technology to the outer rotor to improve roundness, the company was also able to reduce the tolerance width of the tip clearance (a gap formed when the tooth tips of the outer/inner rotor face each other) by about 50% compared to the conventional part.
Sumitomo also addressed the casing of the oil pump. The body of a conventional electric oil pump is often made of die-cast aluminium, which can result in oil leakage at high oil temperature due to the difference in linear expansion coefficient with the iron-based sintered rotor. To prevent this, the body was changed to an iron-based sintered material. This also improved accuracy and tolerance of the machined body, where the width of axial clearance (defined by the overall length difference between the body and the rotor) has been significantly reduced to less than 50% of the conventional part, reported to be the smallest level in the industry.
Development of sprocket drive for single-motor hybrids
Fine Sinter Co Ltd received an award for a sprocket drive (Fig. 4) used in single-motor hybrid vehicles, where the inverter is closely integrated and the conventional torque converter section is replaced by a high-output flat motor and clutch. In this, the number of parts has been reduced by using an integrated two-stage gear design. The newly developed clutch mechanism also requires high response and high precision in hydraulic pressure.
The involute spur gears were required to have the precision of the former JIS Grade 4. Both sprockets and spur gears require high-frequency quenching and tempering to improve wear, and the spur gear tips were required to have a chamfered shape in order to improve productivity in the assembly process.
Fine Sinter optimised the shape of the filling adjustment groove, which controls the amount of powder filled, and improved the rigidity of the die and die adapter to achieve two-stage gearing with an integrated die step. The coil shape and quenching conditions were optimised and, by establishing high-frequency quenching conditions with one coil and one shot, Fine Sinter was able to control the decline in spur gear precision.
As a result, near-net-shape sintering became possible, and cost reduction of around 50% was achieved, when compared to a machined forging.
Development of plug parts for shale gas drilling tool
Porite Corporation receievd an award for this downhole plug component (Fig. 5) used in the shale gas drilling process. To collect shale gas, engineers need to first excavate the well and then create extensive artificial fractures around well bores by hydraulic fracturing (fracking).
In the hydraulic fracking process, plugs can be used to divide the well into smaller sections, alowing the sections to be fractured sequentually. After fracturing, the plugs are drilled through and the well is depressurised. This creates a pressure gradient so that gas flows out of the shale into the well.
The plug therefore needs to be strong enough to withstand ultra-high water pressure, yet easily destroyed after use. Porite used a Fe-Cu-Mn-Mo-C material which can obtain the necessary strength with high-temperature sintering. It underwent an optimised heat-treatment process that limited the depth of cure, but ensured surface hardness, resulting in a high strength and good destructivity.
Sintered bearing for suction motor of robot vacuum cleaner
Porite Corporation also received an award for this sintered oil-impregnated bearing (Fig. 6) used in the suction motor of a robotic vacuum cleaner. In recent years, there has been an increase in demand for devices that reduce the burden of housework, and the convenience of automatic robot vacuum cleaners has been widely accepted by the market and is gaining popularity.
Until now, the majority of bearings used in the suction motors for robot vacuum cleaners have been expensive ball bearings. In order to enter this market, Porite worked to develop a sintered oil-impregnated bearing that meets the required characteristics (quietness, long life, low friction, and high-speed rotation).
The shape of the bearing was designed to have a centre relief bore, and the load was evenly distributed by lengthening the sliding surface with high load and shortening the sliding surface with low load. Porite used a copper-coated iron powder, optimised the sintering conditions and product density, and added zinc. A polyalphaolefin-based impregnation oil with low evaporation rate to extend the service life, was also developed.
As a result, the bearings have been adopted for a number of vacuum cleaners. The cost ratio to ball bearings is less than half, contributing to the overall cost reduction of the suction motors.
JPMA awards: New materials
Development of copper-base sintered alloy slider with low trolley wire wear
Fine Sinter Co Ltd received an award for this copper-based sintered alloy, used for manufacture of a railway component (Fig. 7). The slider part is attached to the top of a pantograph installed on the top of a railway vehicle, and connects with the electified trolley wire. The slider is required to have high conductivity, high mechanical strength, high wear resistance, and high self-lubrication that does not attack the trolley wire.
The copper-based sintered alloy material has the characteristic of being highly conductive.
The base material of both the copper-based sintered alloy’s slider and the trolley wire are copper. This can result in a large amount of abrasion and loss of the trolley wire, which is a problem for copper-based sliders.
In the conventional material, FeMo was added as a hard particle and (Cu,Fe)S was added as a lubricating component. In the development of the material, Fine Sinter partially replaced FeMo with FeTiNx which has a lower hardness than FeMo to reduce the aggressiveness to the trolley wire. To improve the lubricating performance, the solid lubricant was changed from (Cu, Fe) S to MoS2 and the amount of sulfur component was increased accordingly.
The above changes caused a decrease in the mechanical strength however, so to raise the mechanical strength of base materials, pure Fe powder was added so that the mechanical strength of the entire slider could be maintained. As a result, the wear resistance was higher than that of the conventional material, and the trolley wire abbration was reduced to 1/5. Although the material cost of the slider increased slightly, the reduced maintenance costs involoved with replacing the sliders and the trolley wire far outweighted this.
JPMA awards: Effort Prize
Adoption of sintered parts in EPB units for medium-heavy duty vehicles
Fine Sinter Co Ltd also received an Effort Award for this gear used in the electric parking brake unit (EPB) of medium-heavy duty vehicles (Fig. 8). EPB units for these vehicles are equipped with speed control and stop-and-hold functions for low-speed automatic operation. In the future, it is expected to become a standard feature in all automobiles, improving the performance of these safety devices.
In this example, each EPB unit consists of six types of gears, with twelve units required in total. Sintered parts have the great advantage of low cost and high strength. Also, this unit has many rotating parts that require lubrication, suited to the oil-bearing properties inherent in PM.
In the produciton of the components, Fine Sinter made use of warm compaction. A coining stage was used to create a chamfered edge, and a high-purity anti-rust oil was selected. The company devised ways to place the products during quenching and tempering, and automated the visual inspection process. As a result, the six parts have been adopted, and Fine Sinter expects a significant increase in volume is possible as the global use of this part expands.