Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/10—Sintering only
  • B22F3/1003—Use of special medium during sintering, e.g. sintering aid
  • B22F3/1007—Atmosphere
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/12—Both compacting and sintering
  • B22F3/16—Both compacting and sintering in successive or repeated steps
  • B22F3/164—Partial deformation or calibration
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/17—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces by forging
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps

Definitions

• the invention relates to a method for the manufacturing of sintered metal parts. Specifically the invention concerns a method for the manufacturing of sintered metal parts having a densified surface.
• a gear wheel is formed from a pressed and sintered powder metal blank, the surface of which is hardened by rolling. It is taught that the sintering is performed at high sintering temperatures up to 1350°C, i.e. at high sintering temperatures. No specific example concerning the exact temperatures used for the sintering are disclosed but normally the term "high sintering temperatures" means that the sintering is performed at about 1250°C. In addition to the high energy consumption the high sintering temperatures will nega- tively affect dimension tolerances of the sintered parts, which may lead to tolerance problems of the rolled part.
• the US 6 171 546 discloses a method for obtaining a densified surface.
• the surface densification is obtained by rolling or, preferably, by shot peening of a green body of an iron-based powder. From this patent it can be concluded that the most interesting results are obtained if a pre-sintering step is performed before the final densification and sintering operations. According to this patent the sintering can be performed at 1120°C, i.e. at conventional sintering temperatures, but as two sintering steps are recommended the energy consumption will be quite considerable.
• a simple and cost effective method requiring minimal dimensional change between the green and sintered compact for the preparation of gear wheels and similar products would thus be attractive and the main object for the pre- sent invention is to provide such a method.
• Another aspect of the invention is that lower energy consumption and accordingly lower energy costs may be achieved.
• Suitable metal powders which can be used as starting materials for the compaction process are powders prepared from metals such as iron. Alloying elements such as car- bon, chromium, manganese, molybdenum, copper, nickel, phosphorous, sulphur etc can be added as particles, pre- alloyed or diffusion alloyed in order to modify the properties of the final sintering product.
• the iron-based powders can be selected from the group consisting of sub- stantially pure iron powders, pre-alloyed iron-based particles, diffusion alloyed iron-based iron particles and mixture of iron particles or iron-based particles and alloying elements. Most preferable powders are prealloyed iron-based powders due to their high hardenability.
• high velocity compaction is used in order to obtain the products having the desired high density and narrow dimensional toler- ances .
• An example of an equipment for HVC-compaction is the computer controlled percussion machine disclosed in US patent 6,207,757 which is referred to above and which is hereby incorporated by reference.
• the impact ram of such a percussion machine may be used for impacting the upper punch of a die including the powder in a cavity having a shape corresponding to the desired shape of the final compacted component .
• a system for holding a die e.g.
• this percussion machine permits an industrially useful method for production of high-density compacts.
• a ram speed above 2 m/s is used in order to reach densities above 7.2 g/cm 3 .
• the sintering according to the present invention is performed as low temperature sintering, i.e. below 1200°C, preferably below 1160°C and most preferably between 1120°C and 1160°C. Any conventional sintering furnace may be used and the sintering times may vary between about 15 and 60 minutes.
• the atmosphere of the sintering furnace may be an endogas atmosphere, a mixture between hydrogen and nitrogen or in vaccuum.
• the density of the compacted part is at least about 7.2 g/cm 3 and that the sintering can be performed at low temperatures .
• the possibility of utilizing low sintering temperatures will reduce the energy consumption compared with that required for high temperature sintering. Additionally, the dimensional scatter of the part after low temperature sintering, e.g. within the temperature range of 1120°C to 1160°C, is significantly smaller compared with the dimensional scatter after high temperature sintering. Narrow dimensional tolerances on the sintered blank are essen- tial in order to reach a high quality of the surface densified part.
• the method according to the present in- vention has the advantage that one pressing step and one sintering step are eliminated.
• the surface densification may be perfomed by radial or axial rolling, shoot peening, sizing etc.
• a preferred method is radial rolling as this method provides short cycle times in combination with great densification depth.
• a preferred densi- fication depth of up to 1.5 mm, 2 mm and 3 mm or even higher can be obtained on cylindrical parts.
• the achieved densification depth is at least 0.3 mm, preferably at least 0.5 mm.
• the powder metal parts will obtain better mechanical properties with increasing densifying depth.
• Fig 1 is a diagram showing the relationship between sintered density and the surface densifying depth.
• Fig 2a is a photomicrograph of a conventional compacted and surface densified sample.
• Fig 2b is a photomicrograph of a high velocity compacted and surface densified sample.
• Fig 3 is a diagram showing the standard deviation for the dimensional change between green and sintered components.
• Cylinders were compacted from a powder metallurgical com- position consisting of the pre-alloyed powder Astaloy Mo with a graphite addition of 0,3 % and amide wax lubricant. For obtaining green densities above 7.2 g/cm 3 high velocity compaction were used and for densities up to 7.2 g/cm 3 conventional uniaxial compaction were used.
• the cylinders were sintered at 1120°C, 30 minutes in an atmosphere of 90 % nitrogen and 10 % hydrogen. Surface den- sification were performed by radial rolling and the diameter reduction during rolling was 0.3 mm. Densification depths were evaluated using image analysis, and is defined as the shortest distance from the surface to the point where the density has decreased to 98 % of theo- retical density.
• FIG 2 photomicrographs of compacted, sintered and surface densified cylinders are shown.
• the cylinder in fig 2a was conventionally compacted to a density of 7.0 g/cm 3 and the achieved densified depth is 1 mm, while the cylinder shown in fig 2b was high velocity compacted to a density of 7.5 g/cm 3 and the achieved densified depth is 2 mm.
• Example 3 High velocity compacted cylinders, sintered at 1120°C for
• the diameter reduction during rolling was 0.3 mm.
• Polished cross sections of the rolled cylinders were investigated in light optical microscope and the densification depths were evaluated using image analysis.
• the gears manufactured by route 1 reached a sintered density of 7.27 and the gears manufactured by route 2 reached a sintered density of 7.36.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Mechanical Engineering (AREA)
• Powder Metallurgy (AREA)

Applications Claiming Priority (2)

Publications (1)

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• 2003
  • 2003-10-17 SE SE0302763A patent/SE0302763D0/xx unknown
• 2004
  • 2004-10-15 WO PCT/SE2004/001493 patent/WO2005037466A1/en active Application Filing
  • 2004-10-15 RU RU2006116882/02A patent/RU2311263C1/ru not_active IP Right Cessation
  • 2004-10-15 CA CA002541855A patent/CA2541855A1/en not_active Abandoned
  • 2004-10-15 EP EP04775563A patent/EP1680250A1/en not_active Withdrawn
  • 2004-10-15 CN CNA2004800272212A patent/CN1856379A/zh active Pending
  • 2004-10-15 JP JP2006535314A patent/JP2007508460A/ja active Pending
  • 2004-10-15 KR KR1020067009534A patent/KR20060109914A/ko not_active Application Discontinuation
  • 2004-10-18 TW TW093131551A patent/TW200534942A/zh unknown

Non-Patent Citations (1)

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