GB2292750A - Metal injection-moulding - Google Patents
Metal injection-moulding Download PDFInfo
- Publication number
- GB2292750A GB2292750A GB9521380A GB9521380A GB2292750A GB 2292750 A GB2292750 A GB 2292750A GB 9521380 A GB9521380 A GB 9521380A GB 9521380 A GB9521380 A GB 9521380A GB 2292750 A GB2292750 A GB 2292750A
- Authority
- GB
- United Kingdom
- Prior art keywords
- injection
- wax
- moulded
- temperature
- moulded body
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 229910052751 metal Inorganic materials 0.000 title claims abstract description 42
- 239000002184 metal Substances 0.000 title claims abstract description 42
- 238000001746 injection moulding Methods 0.000 title claims abstract description 10
- 239000011230 binding agent Substances 0.000 claims abstract description 34
- 239000000843 powder Substances 0.000 claims abstract description 31
- 239000000314 lubricant Substances 0.000 claims abstract description 29
- 238000000034 method Methods 0.000 claims abstract description 26
- 238000002844 melting Methods 0.000 claims abstract description 22
- 230000008018 melting Effects 0.000 claims abstract description 22
- 229920000620 organic polymer Polymers 0.000 claims abstract description 14
- 238000010408 sweeping Methods 0.000 claims abstract description 5
- 239000001993 wax Substances 0.000 claims description 38
- -1 polyethylene Polymers 0.000 claims description 19
- 239000004698 Polyethylene Substances 0.000 claims description 18
- 229920000573 polyethylene Polymers 0.000 claims description 18
- 239000004200 microcrystalline wax Substances 0.000 claims description 12
- 235000019808 microcrystalline wax Nutrition 0.000 claims description 12
- 239000012188 paraffin wax Substances 0.000 claims description 11
- 238000005245 sintering Methods 0.000 claims description 10
- 238000010438 heat treatment Methods 0.000 claims description 9
- 238000011068 loading method Methods 0.000 claims description 9
- 239000012159 carrier gas Substances 0.000 abstract description 8
- 239000007789 gas Substances 0.000 abstract description 8
- 238000002347 injection Methods 0.000 abstract description 3
- 239000007924 injection Substances 0.000 abstract description 3
- 239000000203 mixture Substances 0.000 description 8
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- 235000021355 Stearic acid Nutrition 0.000 description 5
- QIQXTHQIDYTFRH-UHFFFAOYSA-N octadecanoic acid Chemical compound CCCCCCCCCCCCCCCCCC(O)=O QIQXTHQIDYTFRH-UHFFFAOYSA-N 0.000 description 5
- OQCDKBAXFALNLD-UHFFFAOYSA-N octadecanoic acid Natural products CCCCCCCC(C)CCCCCCCCC(O)=O OQCDKBAXFALNLD-UHFFFAOYSA-N 0.000 description 5
- 239000008117 stearic acid Substances 0.000 description 5
- PNEYBMLMFCGWSK-UHFFFAOYSA-N Alumina Chemical compound [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 230000008020 evaporation Effects 0.000 description 2
- 238000001704 evaporation Methods 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 229920000642 polymer Polymers 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 108010063955 thrombin receptor peptide (42-47) Proteins 0.000 description 2
- 238000005303 weighing Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- 229910001080 W alloy Inorganic materials 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 239000004203 carnauba wax Substances 0.000 description 1
- 235000013869 carnauba wax Nutrition 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 230000001066 destructive effect Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 229940087654 iron carbonyl Drugs 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 230000002028 premature Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000004094 surface-active agent Substances 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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
- B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
- B22F3/225—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip by injection molding
-
- 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
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
-
- 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
- B22F3/1017—Multiple heating or additional steps
- B22F3/1021—Removal of binder or filler
-
- 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
- B22F3/1017—Multiple heating or additional steps
- B22F3/1021—Removal of binder or filler
- B22F3/1025—Removal of binder or filler not by heating only
-
- 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
- B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
-
- 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
Abstract
In a method of forming a metal injection-moulded article by injection-moulding a feedstock comprising metal powder and binder to form an injection moulded body, the binder having a wax lubricant with a range of melting temperatures and an organic polymer, the wax lubricant is progressively removed from the injection-moulded body by raising the temperature through the range of melting temperatures and sweeping liquified wax away from the injection-moulded body by a gas stream while the injection-moulded body is supported on a member which does not exert a wicking action on the liquified wax. The organic polymer is thermally removed from the injection-moulded body and the injection-moulded body is subsequently sintered to fuse the metal powder and form the metal article. Injection moulded bodies 2 are placed on a stack of trays 5 which exert to wicking action and a gas inlet pipe 1 is apertured so as to direct a carrier gas in alternate directions over successive trays. <IMAGE>
Description
INJECTION-MOULDABLE METAL FRED STOCK AND
METHOD OF FORMING METAL INJBCTION-MOUIDED ARTICLE
BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to metal injectionmoulding (MIM) and in particular relates to a method of forming a metal injection-moulded article. Metal injection-moulding involves mixing one or more metal or alloy powders with a fugitive binder to form a homogeneous injection-mouldable feedstock, which is then injectionmoulded to form a shaped body which is commonly referred to as a "green body". The binder is then removed from the green body and the body is then sintered to fuse the metal powder to a solid which retains the original injectionmoulded shape.
2. Description of the Related Art
Various binders are known in the prior art and typically consist of plain paraffin wax or carnauba wax and one or more polymers. The wax components act as a lubricant during injection-moulding and have conventionally been removed by placing the injection-moulded green body on a bed of finely divided alumina-ceramic powder and melting the wax binder. The molten wax is sucked out of the green body into the alumina powder bed by capillary action.
However, such a process tends to roughen the surface of the product and the cost of the required grade of alumina powder represents a significant expense.
Other techniques used in the prior art include the use of various solvents to remove the binder but such techniques lead to additional complications and disadvantages.
Summarv of the Invention
According to this invention there is provided a method of forming a metal injection-moulded article comprising:
i) injection-moulding a feedstock comprising metal powder and binder to form an injection-moulded body, said binder comprising a wax lubricant having a range of melting temperatures and an organic polymer;
ii) progressively removing said wax lubricant from
said injection-moulded body by raising the
temperature of said body through said range of
melting temperatures and sweeping liquified wax
away from said injection-moulded body by means of
a gas stream whilst said injection-moulded body
is supported on a support member which does not
exert a wicking action on the liquified wax
lubricant;;
iii) thermally removing said organic polymer from said
injection-moulded body, and
iv) subsequently sintering said injection-moulded
body to fuse said metal powder and form said
metal article.
Conveniently a plurality of such injection-moulded bodies are supported on one or more trays in an oven and a gas stream flows across the upper surface of each tray and sweeps liquified wax away from said injection-moulded bodies in a predetermined direction towards an edge of each tray. Preferably, in such an arrangement, said trays are arranged in a stack and said gas stream flows in alternate directions over successive trays in the stack.
Advantageously said wax lubricant is composed of two or more waxes. Preferably said wax lubricant is removed in two or more stages, each stage comprising raising the temperature of said injection-moulded body at a predetermined rate and then holding said temperature for a predetermined period.
Preferably, the wax lubricant comprises 15 - 25 parts by volume of paraffin wax and 20 - 30 parts by volume of microcrystalline wax and the temperature of the injectionmoulded body is raised at a rate not greater than 3000C/hour to a holding temperature of 800C to 1200C and is then raised at a rate of not greater than 1000hour to a holding temperature of 2000C to 2800C.
Preferably said organic polymer is polyethylene and is partially removed by endothermic depolymerisation during a controlled heating stage, the remaining polyethylene being removed by exothermic depolymerisation at a subsequent heating stage.
The invention enables the wax lubricant to be removed in a controlled manner from the injection-moulded body and, in particular, avoids the formation of a large body of liquid in the injection-moulded body which could erode or break up the body as it flows away.
Furthermore, the invention enables very high volume loadings of metallic powder, typically 1 to 6W below the critical volume loading, to be used. The volume loading is defined as the ratio of the volume of metallic powder to the volume of the binder, expressed as a percentage. The critical volume loading can be determined by a pycnometer evaluation, as known to those skilled in the art.
By utilising a volume loading of metal powder which approaches the critical volume loading, shrinkage of the injection-moulded body during sintering is minimized and, furthermore, the binder can be removed quickly and easily even from injection-moulded green bodies having hanging or cantilevered sections, without requiring any special supports for these sections.
The invention is applicable to a wide range of metal powders such as, for example, tungsten, tungsten alloys, stainless steels, carbon steel and powders derived from iron carbonyl and nickel carbonyl.
Preferably, the particle size of the metal powder is in the range 0.4 to 15 micrometres, more preferably 0.4 to 10 micrometres or, ideally, 0.4 to 5 micrometres.
Preferably, there is a double peak in the size spectrum of the metal powder.
The invention enables sintered products to be obtained whose density is 95 - 99 of the theoretical density.
In a preferred embodiment, a feedstock containing unfilled (i.e. pure) polyethylene is utilised and the polyethylene is removed by thermal depolymerisation, initially at a temperature appropriate to endothermic depolymerisation. This enables the polyethylene to be removed via a controlled equilibrium process. The depolymerisation is continued at a temperature above the crystalline melting point at which temperature it becomes exothermic. The resulting internal heating of the injection-moulded body keeps its temperature more uniform (particularly when a large number of injection-moulded bodies are being treated in an oven) and reduces the risk of premature sintering due to the externally applied heat.
In the above embodiment, the polyethylene is not depolymerised until after all the wax has been removed during a preceding low-temperature stage of the process.
In co-pending GB Patent Application No. 9311081.5 there is disclosed an injection-mouldable metal powderbinder feedstock comprising metal powder and binder, the binder comprising a lubricant and an organic polymer, the lubricant and organic polymer being removable by melting and evaporation respectively from an injection-moulded article formed from the feedstock, the lubricant being composed of a paraffin wax and a microcrystalline wax which microcrystalline wax has two or more melting temperatures whereby the lubricant can be removed progressively in liquified form from such an injection-moulded article by raising the temperature in a controlled manner from below the lowest melting temperature to above the highest evaporation temperature of the lubricant.Also in the forementioned application there is disclosed a method of forming a metal injection-moulded article comprising:
i) injection-moulding a feedstock comprising metal powder and binder to form an injection-moulded body, said binder comprising a wax lubricant having a range of melting temperatures and an organic polymer;
ii) progressively removing said wax lubricant from
said injection-moulded body by raising the
temperature of said body through said range of
melting temperatures and sweeping liquified wax
away from said injection-moulded body by means of
a gas stream whilst said injection-moulded body
is supported on a support member which does not
exert a wicking action on the liquified wax
lubricant;;
iii) thermally removing said organic polymer from said
injection-moulded body, and
iv) subsequently sintering said injection-moulded
body to fuse said metal powder and form said
metal article, and wherein said feedstock is as claimed in any of claims 1 to 8. Furthermore there is disclosed a method of forming a metal injection-moulded article comprising::
i) injection-moulding a feedstock comprising metal powder and binder to form an injection-moulded body, said binder comprising a wax lubricant having a range of melting temperatures and an organic polymer, wherein said binder comprises
a) 15 - 25 volume W paraffin wax
b) 20 - 30 volume k microcrystalline wax
c) 45 - 60 volume W polyethylene
ii) progressively removing said wax lubricant from said injection-moulded body by raising the temperature of said body through said range of melting temperatures and sweeping liquified wax away from said injection moulded body by means of a gas stream whilst said injection-moulded body is supported on a support member which does not exert a wicking action on the liquified wax lubricant;;
iii) thermally removing said organic polymer from said injection-moulded body, and
iv) subsequently sintering said injection-moulded body to fuse said metal powder and form said metal article.
Brief DoscriDtion of the Drawing A preferred embodiment of the invention will now be described by way of example only with reference to Figures 1 and 2 of the accompanying drawings, wherein:
Figure 1 is a diagrammatic sectional elevation of an apparatus for removing a binder from a metal injectionmoulded body in accordance with the invention, and
Figure 2 shows a temperature-time profile applicable to the removal of the binder in the apparatus of Figure 1.
Description of the Preferred Embodiments The preferred binder composition for use in the invention comprises:
i) 15 - 25% by volume of paraffin wax,
containing 2k oil;
ii) 20 - 30k by volume of microcrystalline wax,
the molecular weights of these waxes being in the
range 10,000 - 50,000;
iii) 45 - 60k by volume of polyethylene having a
melt-flow index of not less than 30g/10 minutes,
and having a molecular weight in the range
150,000 - 250,000, and
iv) 2 - 5% by volume of stearic acid.
The stearic acid acts as a surfactant and etches the metal powder to ensure a better coating of the binder, and also acts as a mould-release agent.
To prepare a feedstock containing the above binder, the, or each, metal powder is dried and is blended well with the stearic acid component in a blender. The blended powder mix is then heated to a temperature of 200C below the melting temperature of the polyethylene, but not exceeding 1500C. The blended metal powder/stearic acid component is then fed into a plasticised blend of the paraffin wax, microcrystalline wax and polyethylene and mixed under low and high shear conditions in a double planetary mixer.
The feedstock density is checked and should have a density within +0.lg/cm3 of a predetermined level.
The feedstock is then granulated to a size spectrum ranging from fine to a maximum of 3mm, preferably lmm to 3mm.
The resulting granulated feedstock can then be injection-moulded using standard equipment, preferably at a temperature of 1700C to 2200C, advantageously 1500C to 2000C. The resulting moulded "green bodies" should have a weight variation of not more than i0.2% (for parts weighing ig to 10g) or not more than +0.5% (for parts weighing 10g to 30g)- Referring to Figure 1, the injection-moulded green bodies 2 are placed on trays 5 which do not exert a wicking action on the liquified wax lubricant within the temperature-controlled oven, which may be electrically heated for example. The oven is provided at either end with water or air cooled doors 3 which are insulated from the interior of the oven by heat cousions 4.A gas inlet pipe 1 enters the oven and two branches thereof encircle the heat cousions 4 and a carrier gas, typically nitrogen or a blend of 15% hydrogen and 85 nitrogen is introduced at a pressure of about 0.3 to 0.43 atmospheres (4 to 6psi) at a flow rate of 0.5 to 1 standard cubic metres per hour for each cubic metre of effective oven volume, as illustrated by arrow headed line c. The branches of the inlet pipe 1 have apertures spaced around the heat cousions 4 which are aligned with the spaces between the trays 5 and which direct the carrier gas in alternate directions over successive trays in the stack, as illustrated by arrow headed line a. The carrier gas initially exits valve outlet 8, as illustrated by arrow headed line d, carrying entrained wax vapour which is cooled in a trap 6 having an external cooling system 10 and an internal cooling system 11.When the wax components of the binder have been removed, the outlet 7 of trap 6 is closed and the temperature is raised to initiate depolymerisation of the polyethylene. During this high temperature stage, the valve of outlet 9 is opened and the carrier gas containing the depolymerisation products exits from this outlet as shown by arrow headed line b.
The removal of the binder using the apparatus of
Figure 1 will now be described with reference to the heating profile, as shown in Figure 2, which is applicable to a binder incorporating paraffin wax having melting regions around 450C and 630C and microcrystalline wax which registers four melting regions in the range 620C to 1440C.
As the temperature in the oven is progressively increased, the paraffin wax in the binder gradually melts and flows out, creating fine paths for the subsequent melting of the microcrystalline wax at higher temperatures.
The gradual rise in temperature within the injectionmoulded bodies 2 and the staged melting of the wax components avoids the formation of a destructive liquid mass in the vicinity of the injection-moulded bodies.
Initially, as shown in stage S1 in Figure 2, the contents of the oven are heated rapidly at a rate of 2200C - 2400C per hour to a temperature of 1100C (for parts of 0.5mm - Smm thickness) or 900C (for parts of Smm - 15mm thickness).
The temperature is then held (stage S2) for a calculated period, e.g. 1.1 minutes per litre of oven volume (0.5 hour/cubic foot).
During periods S1 and S2, most of the wax is removed from the injection-moulded bodies 2.
The temperature is then raised to 2300C - 2500C at the rate of 400C - 600C/hour (stage S3) and held for 1.1 minutes per litre of effective oven capacity (half an hour for each cubic foot of oven capacity), to enable the wax to vaporise and to be entrained in the carrier gas and purged out of the oven without congestion. This stage is shown as S4 in Figure 2.
The temperature is then raised at 200C - 300C per hour to 3750C and held for half an hour (stages S5 and S6).
Endothermic depolymerisation of the polyethylene begins at about 350"C and continues until the end of stage S6. The temperature is then raised at a rate of 800C - 1200C per hour to 5000C (stages S7 and S8) and is finally raised to 6000C at a rate of 1500C - 2000C per hour and held at 6000C for 0.54 minutes per litre of oven volume (15 minutes/cubic foot), as shown at stage S9 in Figure 2. Exothermic depolymerisation of the polyethylene occurs over the temperature range 375"C to 4500C.
During these latter stages, when the polyethylene is depolymerised, the valve on outlet 9 and the valve on outlet 8 are shut (Figure 1).
In general, the lower range of heating rates given above are applicable to bodies 2 of dimension greater than 8mm and the higher range of heating rates is applicable to bodies of dimension below 8mm.
For thick wall bodies (greater than 15mm), the low temperature polymer removal stage S4 can be assisted by closing the carrier gas inlet 8 and connecting the binder trap outlet 7 to a vacuum pump.
The final stage S9 in Figure 2 is a pre-sintering stage and the pre-sintered bodies 2 can be sintered in a standard sintering furnace under vacuum of an inert gas and/or hydrogen. Typically, the sintering temperature will be in the range 1,0000C - 1,5000C and the sintering time can be determined in a conventional manner.
The invention will now be illustrated further by a non-limiting example.
EXAMPLE
Carbonyl iron powder of average particle size 4 - 5 micrometres and having a carbon content of 0.03% and carbonyl nickel powder (123 grade) of average particle size 4 - 5 micrometres were utilised as the metallic raw materials. 10kg of a mixture of the two metal powders containing 98% carbonyl iron powder and 2k carbonyl nickel powder were blended with 0.014kg of stearic acid for one hour.
The well blended materials were heated to a temperature of 1100C and added to a mixture containing a previously plasticised binder comprising 0.376kg pure polyethylene, 0.154kg paraffin wax, and 0.225kg microcrystalline wax. The volume loading of the metal powder mixture in the binder was 62. The resulting mixture was granulated to form a granulated feedstock for injection-moulding and the granulated feedstock was injected into moulds. The weight of feedstock injected into each mould was controlled to within +0.2%.
Moulded green bodies 2 were placed on ceramic refractory plates 5, as illustrated in Figure 1, and were subjected to binder removal in accordance with the temperature-time profile, illustrated in Figure 2.
Nitrogen was used as the carrier gas. The pre-sintered products were then sintered and a dimensional tolerance of s2% and a density of 97% of the theoretical density were achieved.
Claims (15)
1. A method of forming a metal injection-moulded article comprising:
i) injection-moulding a feedstock comprising metal powder and binder to form an injection-moulded body, said binder comprising a wax lubricant having a range of melting temperatures and an organic polymer;
ii) progressively removing said wax lubricant from
said injection-moulded body by raising the
temperature of said body through said range of
melting temperatures and sweeping liquified wax
away from said injection-moulded body by means of
a gas stream whilst said injection-moulded body
is supported on a support member which does not
exert a wicking action on the liquified wax
lubricant;
iii) thermally removing said organic polymer from said
injection-moulded body, and
iv) subsequently sintering said injection-moulded
body to fuse said metal powder and form said
metal article.
2. A method according to claim 1, wherein a plurality of such injection-moulded bodies are supported on one or more trays in an oven and a gas stream flows across the upper surface of each tray and sweeps liquified wad away from said injection-moulded bodies in a predetermined direction towards an edge of each tray.
3. A method according to claim 2 wherein said trays are arranged in a stack and said gas stream flows in alternate directions over successive trays in the stack.
4. A method according to any preceding claim wherein said wax lubricant is composed of two or more waxes.
5. A method according to any preceding claim wherein said wax lubricant is removed in two or more stages, each stage comprising raising the temperature of said injectionmoulded body at a predetermined rate and then holding said temperature for a predetermined period.
6. A method as claimed in any preceding claim wherein said wax lubricant comprises 15 to 25 parts by volume of paraffin wax and 20 to 30 parts by volume microcrystalline wax and the temperature of said injection-moulded body is raised at a rate not greater than 3000C/hour to a holding temperature of 800C to 1200C and is then raised at a rate of not greater than 1000hour to a holding temperature of 2000C to 280cm.
7. A method as claimed in any preceding claim wherein said organic polymer is polyethylene and is partially removed by endothermic depolymerisation during a controlled heating stage, the remaining polyethylene being removed by exothermic depolymerisation at a subsequent heating stage.
8. A method as claimed in claim 1, wherein said binder also comprises 45 - 60 volume % polyethylene.
9. A method as claimed in claim 1, where said wax lubricant comprises a multiple melting point microcrystalline wax and a paraffin wax.
10. A method as claimed in claim 1, wherein the volume loading of said metal powder is from 1 to 68 below a critical volume loading.
11. A method as claimed in claim 1, wherein said metal powder has a size distribution within the range 0.4 to 15'ism.
12. A method as claimed in claim 9, wherein said microcrystalline wax registers 4 melting regions in the range 620C to 1440C.
13. A method according to claim 1 utilising apparatus substantially as described hereinabove with reference to
Figure 1 of the accompanying drawings.
14. A method according to claim 1 utilising a heating profile substantially as described hereinabove with reference to Figure 2 of the accompanying drawings.
15. A method of forming an injection-moulded article according to claim 1 substantially as described hereinabove with reference to the Example.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9521380A GB2292750B (en) | 1992-06-02 | 1993-05-28 | Method of forming metal injection-moulded article |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB929211586A GB9211586D0 (en) | 1992-06-02 | 1992-06-02 | Injection-multiple metal feedstick and method of forming metal injection-moulded article |
| GB929224632A GB9224632D0 (en) | 1992-11-24 | 1992-11-24 | Injection-mouldable metal feedstock and method of forming metal injection-moulded article |
| GB9311081A GB2267455B (en) | 1992-06-02 | 1993-05-28 | Injection-mouldable metal feedstock and method of forming metal injection-moulded article |
| GB9521380A GB2292750B (en) | 1992-06-02 | 1993-05-28 | Method of forming metal injection-moulded article |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9521380D0 GB9521380D0 (en) | 1995-12-20 |
| GB2292750A true GB2292750A (en) | 1996-03-06 |
| GB2292750B GB2292750B (en) | 1996-12-04 |
Family
ID=27266217
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9521380A Expired - Lifetime GB2292750B (en) | 1992-06-02 | 1993-05-28 | Method of forming metal injection-moulded article |
| GB9311081A Expired - Lifetime GB2267455B (en) | 1992-06-02 | 1993-05-28 | Injection-mouldable metal feedstock and method of forming metal injection-moulded article |
Family Applications After (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9311081A Expired - Lifetime GB2267455B (en) | 1992-06-02 | 1993-05-28 | Injection-mouldable metal feedstock and method of forming metal injection-moulded article |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB2292750B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0978337A2 (en) * | 1998-08-07 | 2000-02-09 | Air Products And Chemicals, Inc. | Method for de-lubricating powder metal compacts |
| CN106270522A (en) * | 2016-09-23 | 2017-01-04 | 江西悦安超细金属有限公司 | A kind of for metal injection molded feeding and preparation method thereof |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ES2140300B1 (en) * | 1997-05-09 | 2000-10-16 | Bostlan Sa | ADDITIVE FOR THE INTRODUCTION OF ONE OR MORE METALS IN ALUMINUM ALLOYS. |
| KR100366773B1 (en) * | 2000-03-29 | 2003-01-09 | 이재성 | Manufacturing method of nano-metal feedstock for metal injection molding |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1370274A (en) * | 1972-05-05 | 1974-10-16 | Leybold Heraeus Verwaltung | Method and apparatus for sintering compacts of powder materials |
| US4404166A (en) * | 1981-01-22 | 1983-09-13 | Witec Cayman Patents, Limited | Method for removing binder from a green body |
| EP0379777A1 (en) * | 1989-01-20 | 1990-08-01 | Kawasaki Steel Corporation | Method of debinding for injection molded objects |
| US5048801A (en) * | 1989-07-12 | 1991-09-17 | Risi Industries | Sintering furnace |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0686608B2 (en) * | 1987-12-14 | 1994-11-02 | 川崎製鉄株式会社 | Method for producing iron sintered body by metal powder injection molding |
| JP2751966B2 (en) * | 1989-07-20 | 1998-05-18 | 住友金属鉱山株式会社 | Injection molding composition |
-
1993
- 1993-05-28 GB GB9521380A patent/GB2292750B/en not_active Expired - Lifetime
- 1993-05-28 GB GB9311081A patent/GB2267455B/en not_active Expired - Lifetime
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1370274A (en) * | 1972-05-05 | 1974-10-16 | Leybold Heraeus Verwaltung | Method and apparatus for sintering compacts of powder materials |
| US4404166A (en) * | 1981-01-22 | 1983-09-13 | Witec Cayman Patents, Limited | Method for removing binder from a green body |
| EP0379777A1 (en) * | 1989-01-20 | 1990-08-01 | Kawasaki Steel Corporation | Method of debinding for injection molded objects |
| US5048801A (en) * | 1989-07-12 | 1991-09-17 | Risi Industries | Sintering furnace |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0978337A2 (en) * | 1998-08-07 | 2000-02-09 | Air Products And Chemicals, Inc. | Method for de-lubricating powder metal compacts |
| EP0978337A3 (en) * | 1998-08-07 | 2001-05-02 | Air Products And Chemicals, Inc. | Method for de-lubricating powder metal compacts |
| CN106270522A (en) * | 2016-09-23 | 2017-01-04 | 江西悦安超细金属有限公司 | A kind of for metal injection molded feeding and preparation method thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2292750B (en) | 1996-12-04 |
| GB9311081D0 (en) | 1993-07-14 |
| GB2267455A (en) | 1993-12-08 |
| GB9521380D0 (en) | 1995-12-20 |
| GB2267455B (en) | 1996-12-18 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PE20 | Patent expired after termination of 20 years |
Expiry date: 20130527 |