December 2005

Japan and Europe celebrate with glittering prizes

Powder metallurgy associations in Europe and Asia have announced their annual awards, and once again they show the resource, thoughtfulness and just plain cleverness of the engineers who conceptualised and brought them to fruition…

The Japan Powder Metallurgy Association (JPMA) has announced its 2005 awards singling out 14 prize winners in five categories. Although many of them are parts for automobiles and consumer goods, there is a least one departure this year with the manufacture by Mitsubishi Materials Corporation of a large stainless steel pulley for a high-performance four-stroke outboard motor which, says MMC, is a new field for PM.

The first on the JPMA's list of winners in the New Design section was Sumitomo Electric Sintered Alloy's "stopper part" for a retractable auto wing mirror. Recent downsizing and an increased strength requirement meant that PM could compete with die casting using an Fe-Ni-Cu-Mo-C alloy. Since the part was very thin, there were risks of chip and crack during manufacturing, compact pick-up and the way it was held during sizing were modified. To improve reliability, an automatic resonant acoustic device to detect cracks was developed.

Sumitomo Electric’s contributions included this part for a folding automobile wing mirror that had formerly been die cast.

The sintered stainless pulley for a high-output four-stroke outboard engine was developed by Mitsubishi Materials Corporation and took a development prize. Environmental rules governing fuel consumption and emissions mean that two-stroke outboards are being replaced by four-strokes. In the early design stages, die-cast aluminium was thought to be a competitor, but the higher strength of stainless and better corrosion resistance won the day for PM. The finished part is 110.68 mm across and 39 mm thick. It weighs 560g. Problems had to be addressed along the way. The tendency of the powder to stick to tooling was overcome by adding the binder first to coat the parts, then a large quantity of lubricant, which was vacuum-extracted from the compact. And a special oil was developed to prevent surface scratching during sizing.
Consumer goods made an appearance in this category with a nakanige sintered bearing and brass housing as one unit, manufactured by Porite. The finished piece represents a coat saving of about 50 per cent with extended bearing life.

Major cost savings of more than 50 per cent achieved through near net shape sizing were also a feature of Mitsubishi Materials' sintered piston part for a swing compressor. The part was formerly manufactured by casting.
Hitachi Powdered Metals took a New Development prize for their complex synchoniser hub for auto gearboxes. Designed to engage only with reverse gear, the part has stoppers at the end of the locating slots on one side of the part to prevent keys, shaft and sleeve disengaging. The parts were compacted using stepped dies with inserts in a CNC press to give better density control.

A high-speed sintered bearing manufactured by Porite and used for the DLP colour wheel found in home theatre, projector and television projection systems was the second of the consumer goods to take a prize in this category. It operates under harsh conditions at speeds of up to 10 800 rpm and temperatures of around 85°C. The application required long life with exceptionally low noise. A substantial amount of development time went on selecting the right impregnating oil, with low viscosity, high flash point and little vapourisation. The clearance between the internal diameter of the bearing and the shaft was set at three micron or less to reduce the clearance noise factor. The bearings achieved the 70 000 hours required under the test programme.

A five piece assembly for the seat belt pre-crash tensioning system in automobiles took the final development prize, again for Mitsubishi Materials Corporation.

The new material has almost equal machinability with cast iron and much higher wear resistance than cast iron or brass. Used with uncoated valve stems, it has the same seizure characteristics as brass. Productivity was a problem at first in both compacting and sintering, but this was overcome by optimising the powder shape and sintering conditions.

In the new materials section a complex Fe-Cu-Sn-C-P-MgSiO3-MnS alloy developed by Hitachi Powdered Metals for sintered valve guides took a prize. Requirements for the application demanded both wear resistance against the valve stem and superior machinability in a cylinder head assembly line. Both cast iron and brass have been used in the past for valve guides and brass had again come up for consideration in this context. That meant it was necessary for the sintered material to be competitive.

This large stainless steel pulley for a high-performance four-stroke outboard motor was a Development prize winner for Mitsubishi Materials Corporation.

Gas-fuelled engines that offer low environmental damage collateral have been much in the news. However, they have their problems. Mitsubishi Materials Corporation has developed powder forged valve sheets for gas engine application composed of Fe-C-Cr-Mo-Co-Ni-Nb-CaF2. Parts in gas engines are exposed to a very dry environment and higher adhesive wear resistance was required. In this development, high density, high cohesive strength of matrix, and hard particles were achieved by optimising both processes and adding hard particles, and high adhesive wear resistance was achieved by using of CaF2 instead of Pb.

This brake lining for a high-speed train is capable of operation at speeds of up to 320kph and won a prize for Fine Sinter in the New Materials section.

Two types of valve sheets are available: one has higher adhesive wear resistance with Fe-Mo hard particles, and another has lower valve attack property with partially replacing Fe-Mo with Co-Mo hard particles.
With high strength and high adhesive wear resistance, powder forged valve sheets can be applied to cast iron cylinder head gas engines as well as aluminum cylinder head gas engines.

Although automobile makers make up the largest collective customer for the PM industry, powder metallurgy products find application in other transport systems too. Aerospace is probably the one that attracts the most attention, but the claims of the train should not be forgotten. In this case, the new material that caught the judges' eye was a Cu-Fe+Ni+Cr-ZrO2+MgO-Gr-Mo-Sn alloy product developed by Fine Sinter Co and applied as a brake liner on a high-speed train. With current top speeds in the region of 300 kph and ambitions to achieve 350 kph more than a glint in the train builders' eyes, railroad vehicles need to be lighter, from the wheels and brake linings up.
Under hard braking the linings get hot because the energy they need to absorb rises in proportion to the square of the speed. This material has dramatically changed the matrix by changing from a conventional Cu-Sn base to Cu-Sn-Ni-Cr-Fe. The aims were to improve wear resistance in high-temperature areas and to stabilize the friction coefficient by adding ceramics and graphite to reduce the heating load on the lining. This material has a current speed limitation of 320 kph, say the makers, but a material with stable performance at 350 kph could be developed.

New ways were used to fabricate this magnetic detecting gear for a spindle motor winning a Process Development prize for Suruga Seiki.

A new fabricating technique of a magnetic detecting gear for a spindle motor of a machine tool has been developed by Suruga Seiki Co reduced costs by 70 per cent and won an award in the process development section of the competition.

The technique is composed of two processes, a powder metallurgy process and a shaving process and it makes two parts into one part to get effective cost reduction. The detecting gear has a plural-teeth-gear and a one-tooth-gear in each half thickness. It was conventionally fabricated by machining wrought alloys almost same to mechanical properties of S45C steels for requiring high dimensional accuracy because of superior magnetic detecting. The plural-teeth-gear and the one-tooth-gear are machined respectively and then they are assembled into one part.

Key points in the powder metallurgy and the shaving are as follows. In the compacting process, powder motion within the feeding box and powder filling into the die were improved to fulfill high dimensional accuracy. In the shaving process, the most available blade shape and material were selected for improving the accuracy after shaving the sintered gear.

Fine Sinter’s manual gearbox part took a prize in the Effort category.

A free-machining agent, a fine powder that contains complex calcium oxide and could replace the MnS powder typically used for sintered parts, has been developed by Kobe Steel. It won an award in the New Powders section of the competition. Machinability is improved even with a small addition. Since it doesn't react with a sintering atmosphere, harmful gas and sooting of sintered parts is not generated.

Turning and drilling tests were performed using two types of materials. One was a Fe-Cu-C composition at the density of 6.9mg/m3, the other a Fe-Ni-Cu-Mo-C composition at the density of 7.1mg/m3. It displayed superior tool life and less tool wear compared with MnS powder at increased cutting speeds.
This developed agent especially contributes to the reduction of machining costs of high speed machining and high hardness materials. Further applications are expected in the future with the expansion of high-strength sintered parts.

Fine Sinter scooped both prizes in the Effort section with a sintered exhaust part with a complicated sloped shape that required corrosion resistance at high temperatures and a complex part used for automotive manual transmission. The transmission part has six projections that act as guides for other parts of the assembly. The shapes had to be optimised and the part was designed for near net shape finishing. Because of the fine dimensions, production engineers also had to optimise handling equipment for mass production.