Toshiba • PM forElectronics and Energy
The Toshiba Corp. ranks among the giants inthe world of microelectronics with sales in itsfinancial year ending March 31. 1989, havingrisen to a staggering Yen 3,800 billion(USS28,794 million) and exports accountingfor about one third of this amount. Whilstmuch of the company's growth can beaccounted for by the brisk demand forelectronic devices, notably semiconductors·Toshiba is the world's fifth largestsemiconductor producer - them are a numberof other important industrial sectors whichmake up the corporate picture. These include:information processing and control systems;electronics and communications; electron andcathode ray tub"es; energy systems; industrialequipment; consumer products; and finallythe materials and components group whichincludes the company's metal division andnew material division. It is Ihe laller whichproduces a range of PM products mainly foruse in consumer products such as audio andvideo products, refrigerators, freezers, airconditioners, lighting, etc., but also forcomputers, printers and other businessmachines.It has long been Toshiba's philosophy toimprove its products from the ground up andhence the company places considerableemphasis on the research and de\'elopment ofnew materials and components which willserve as the building blocks of promising newproducts. Over 6.0% of sales - Yen 230.4
FIG. 1 Sintered tungsten-based heavy alloycomponents in proauction at Toshiba
FIG. 3 PM structural parts used in refrigeratorsand air conditioners
MPR June 1990
billion (USS1,745 million) was'ploughed backinto R&D in 1988, but of course much of thiswent into the development of informationtechnology and semiconductor-related areas.The materials area is not, however, beiogignored and considerable effort is being putinto advancing the properties and performanceof existing materials such as PM special alloysand sintemd magnets, and to develop newstructural engineering ceramics based onsilicon nitride which arc now findingapplications for diesel engines and ceramicroller bearings for gas turbine engines andsemiconductor manufacturing equipment.'Here Toshiba is ableto call upon its many yearsof experience with other types of powderproducts which have been in production forseveral decades notably: sintered electricalcontacts, tungsten and molybdenum lightingclements, self lubricating bearings, sinteredmagnets and structural PM parts, andcemented carbide tools, all of which have beenproduced on one site at the company's metalworks in Yokohoma since 1971, and whichwas visited five years ago by MPR. On thisoccasion, MPR held discussions on PMproduction with engineers from the Yokohamaplant at Toshiba's headquarters in Tokyo.
PM PRODUCTS
Toshiba first started producing sinteredproducts at the beginning of this century when
FIG. 2 Selection ofAg-IV and Gil-IV contactsand components
l'Jli. 4 :ielectlOn a} structural 1',\1 partsproduced for Toshiba's range ofbusinessmachines
it hecame the first company in Japan toproduce tungsten filalJlcnts hy refinin"tungsten ore to powder and reducing Ih~consolidated tungsten powder bar 10 wireusing a series of swaging and drawingprocesses. Today, the modern Yokohamafacility is capable of producing tungsten wiredown to 10 micron diameter, and additionalproducts based on tungsten have beendeveloped for heavy metals, anodes for X-raytubes. electrodes for discharge lamps, etc.(Fig.1) Products made from sinteredmolybdenum are also manufactured includingwire, plate and sheet, discs, furnace clementsand boats, elc.In the 1930s the company developedcopper-tungsten electrical contacts (1931)followed a short time later by sintemd silvertungsten contacts, and these continue to beproduced along with other Ag-W and Cu-Walloys for electrospark machining andelectrodes for resistance welding at a currentrate of 2 tonnes/month. (Fig.2)Self lubricating bronze bearings wereintroduced in 1938 followed by structural PMparts in the late 1950s - both findingapplications in the company's expandingrange of household appliances such as fans,washing machines, refrigeralors, airconditioners, and mechanical officeequipment. Despite the fact that many of thePM parts for office equipment were maderedundant through the introduction ofmicroelectronics, and that many of the gearsand bearings used in modern businessmachines are now made from plastics,in-house PM part production at Toshiba hascontinued 10 grow over the years. Figs.3 and 4show a selection of the current range of PMparts in production for business machines andrefrigerator compressors. Only a few PM partsare currently produced for automotiveapplications, but the company is planning toexpand its activities in transmission partswhem it sees good growth opportunities.PM self lubricating bearings made from Fe-S,Fe-Pb, Fe-Cu-C, and Cu-Sn-Pb-Zn-C powdersalso remain an important product group withlarge scale production for the company's rangeof audio and video products, domesticappliances, business machines, etc. withseveral million bearings produced each year atYokohama.However, it is in Ihe areas of businessmachines, such as copiers, personal compulersand computer printers, where Toshiba hasexperienced the highest growth in recent yearswith resultant growth for new PM structuralparts, sintered iron soft magnets and rare earthmagnets. The company's range of Tosrex rareearth cobalt (RzCo I7) magnets (Fig.5) with theirhigh residual induction and maximum energyproduct have, for example, found applicationsin stepping molors, loudspeakers,headphones, coreless motors, voice coilmotors, optical pick-up heads, to name a few.whilst soft magnets are being used inincreasing quantities in the print head ofcomputer printers, voice coil motors in floppydisk drives, etc. Rare earth magnet productionis of the order of 6 tonnes/month.Engineering ceramics arc also playing anincreasingly important role in the product mixwith the development of aluminium titanate
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FIG. 5 Sintered rare earth-cobalt magnets
FIG. 6 Engineering ceramic components basedon silicon nitride and A/N
FIG. 7 One of the com'eyor belt sinteringfurnaces at the Yokohama PM plant
for high thermal conductivity substrates forsemiconductors. and lightweight siliconnitride containing rare earth oxide (yttria) toprovide high strength. low thermal expansioncoefficients. excellent thermal shockresistance. wear resistance. electricalinsulation characteristics. and good resistanceto corrosion. Fig.6 shows a selection ofengineering ceramic components inproduction at Toshiba using hot or coldpressing. injection moulding or slip castingmethods.The structural PM part department inYokohama employs around 160 people andconsumes 120 tonnes per month of metalpowders. which are mixed in-house usingdouble-cDne (1 tonne capacity) and V- typeblenders. The current range of compDsitionsincludes Fe-C. Fe-Cu-C. Fe-Ni-Cu-C. Fe-Co-Ni·Mo-C, Fe-Cr-C, stainless steel grades 304, 316,410. and 402. pure iron. Fe-P and Fe-Si for softmagnets. and copper- and iron-based powdersfDr bearings.Powder compacting and sizing is done on some60 mechanical presses ranging in capacityfrom 5 to 500 ton with automatic part handlingextensively used for press unloading andloading of parts into sintering furnaces. Thelatter includes conveyor belt furnacesoperating at 1100-1200C. pusher furnaces forsintering above 1200C. and a vacuum sinteringfurnace for special PM grades and high speedsteels. (Figs.7 and 8)Toshiba pays particular attention to specialalloys which are sintered to high density (95 98% of theoretical) stating that it wasimportant to monitor and control the rate oftemperature rise. temperature uniformity. andcooling rate in order to achieve optimumdimensiDnal control. Thus many of thefurnaces are of special constructiDn withpredetermined shape and positioning of heaterelements. Nitrogen, pure hydrogen and endo-
MPR June 1990
gas are used as sintering atmospheres.Special attention is also paid to the control ofthe continuous steam treatment furnaces usedto make structural PM parts pressure tight forcompressor applications. or to enhance theircorrosion resistance. (Fig.9)Toshiba reported that it was currentlyintroducing new PM parts to those already inproduction at a rate of between 50 and 60 peryear. Among these are the new range of highdensity soft magnetic parts made from pureiron and Fe-6.5%Si applications for whichinclude the print heads in computer printers.as shown in Fig.l0. .Production by PM is said to be 10-30% cheaperthan parts produced by precision casting. andsintered soft magnets have good magneticproperties, Le. small eddy current loss. One ofthe keys to the success of the highly complexprinter head is the use ofsupercompressibilitywater atomized iron powder which is mixedwith ferrosilicon powder and compacted athigher than normal pressure to achieve a highgreen density. Tool life of the tungsten carbidedies and core rods used to compact thesecompgnents in highly complex tooling is of theorder of 200.000 pieces.A number ofspecial steel alloys have also beendeveloped based on water atomized stainlesssteel and high speed steel powders. Oneapplication is for a 304L stainless steel powderused as the valve guide in air conditioners.Here the part must be sintered to 7.5 g/cm3density to make it air tight. Anotherapplication is a complex part also made from304 stainless and used as a holder for clothfilters. Toshiba joins some 100 of thesecomponents together to produce the 1 metrehigh holder. A PM tool steel made from gradeJIS SKH51 powder is sintered to 98%theoretical density and is used in high speedsteel motors used in laser printers.
FIG. 8 Vacuum furnace used for sinteringspecial PM alloys
FIG. 9 Continuous steam treatment furnace
FIG. 10 Sintered soft magnetic parts used incomputer printers
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