Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D23/00—Casting processes not provided for in groups B22D1/00 - B22D21/00
  • B22D23/06—Melting-down metal, e.g. metal particles, in the mould
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/06—Permanent moulds for shaped castings
  • B22C9/061—Materials which make up the mould
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D18/00—Pressure casting; Vacuum casting
  • B22D18/06—Vacuum casting, i.e. making use of vacuum to fill the mould
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
  • B22D27/04—Influencing the temperature of the metal, e.g. by heating or cooling the mould
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
  • B22D27/04—Influencing the temperature of the metal, e.g. by heating or cooling the mould
  • B22D27/045—Directionally solidified castings
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
  • B22D27/15—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting by using vacuum
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D30/00—Cooling castings, not restricted to casting processes covered by a single main group
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D11/00—Arrangement of elements for electric heating in or on furnaces
  • F27D11/06—Induction heating, i.e. in which the material being heated, or its container or elements embodied therein, form the secondary of a transformer
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D7/00—Forming, maintaining or circulating atmospheres in heating chambers
  • F27D7/06—Forming or maintaining special atmospheres or vacuum within heating chambers
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D7/00—Forming, maintaining or circulating atmospheres in heating chambers
  • F27D7/06—Forming or maintaining special atmospheres or vacuum within heating chambers
  • F27D2007/066—Vacuum

Definitions

• the present invention relates to a method of forming a metal component from a particulate feed material.
• the present invention also relates to an apparatus for forming a metal component from a particulate feed material.
• Powder metallurgy is a known method for forming a metal component, from a powdered feed material.
• HIP hot isostatic pressing
• powder is shaped in a mould to which both pressure and temperature are applied.
• argon gas is used to provide the isostatic pressure which may range from 50 megapascal to 300 megapascal.
• the temperature of the material is raised so as to sinter the powder and cause the particles to fuse together.
• known powder metallurgy is limited in terms of the size of products that can be produced and also in terms of the complexity of their shape. Furthermore, it is a costly and time consuming process. It is difficult to scale and often impossible to produce products having the required size and complexity when competing against products produced by a more conventional casting process.
• a method of forming a metal component in which a feed material is initially in a powdered state and a solid component is formed by the application of heat, is disclosed in the present applicant's co-pending patent application (App No. GB 13 20 168.6), the whole content of which is included herein by way of reference.
• a sacrificial positive model is created of a component and a negative mould is built around the positive model from a material having a melting point higher than the melting point (liquidus point) of the metal from which the component is to be formed.
• the sacrificial positive model is removed from the negative mould and the feed material of metal powder is deployed into the mould.
• the metal powder is heated to a temperature higher than the liquidus point (melting point) of the metal powder so as to cause the metal powder to melt within the mould.
• a method of forming a metal component from a particulate feed material comprising the steps of: placing a mould containing a feed material of metal particles in a vessel; increasing the temperature inside said vessel to within a first temperature range above a liquidus temperature of said metal during a temperature-rising interval; reducing the temperature of the vessel to a second temperature within a freezing range that is greater than the solidus temperature and less than the liquidus temperature of the metal; and maintaining the temperature of the vessel within said freezing range during a temperature maintaining interval.
• Figure 1 shows a method of forming a metal component
• Figure 2 shows procedures for the creation of a positive model
• Figure 3 shows the addition of layers of slurry to produce a mould
• Figure 4 shows a deployment of feed material into the mould
• Figure 5 shows an apparatus for forming a metal component
• Figure 6 shows a method of operating the apparatus of Figure 5 to form a metal component
• Figure 7 shows a control process performed by the controller identified in
• Figure 8 illustrates changes in temperature and pressure for a first embodiment of the invention
• Figure 9 illustrates changes in temperature and pressure for a second embodiment of the invention.
• Figure 10 illustrates changes in temperature and pressure for a third embodiment of the invention
• Figure 11 shows an alternative control process performed by the controller of Figure 5;
• Figure 12 illustrates changes in temperature and pressure of a fourth embodiment in accordance with the control process performed as shown in Figure 1 .
• a method of forming a metal component from a powdered feed material is illustrated in Figure 1.
• a feed material is initially in a powdered state (detailed in Figure 4) and a solid component is formed by the application of heat (detailed in Figure 5).
• a sacrificial positive model 102 of a component is created.
• a negative mould 104 is built around the positive model from a material having a melting point higher than the liquidus temperature (melting point) of the material from which the component is to be formed (as detailed in Figure 3).
• the sacrificial positive model is removed so as to leave a void 106 within the negative mould.
• feed material of metal powder 108 is deployed into the mould.
• heat 110 is applied to the mould to a temperature higher than the liquidus temperature (melting point) of the metal powder so as to cause the metal powder to melt within the mould, thereby establishing molten metal 111 within the mould 104.
• metal powder 108 used herein to form a metal component is, in a first embodiment, a powder consisting particles of pure metal.
• metal powder 108 is a powder comprising particles of an alloy. It should be appreciated therefore, that metal components formed from the said metal powder may be comprised either of a pure metal or an alloy compound.
• the method described herein is relatively insensitive to the size range of the powder particles.
• the only requirement is that the metal powder flows readily into the ceramic moulds.
• the mould defines sections having diameters as a little as 0.5 millimetres, spherical powders produced by gas atomisation, for example, would be more appropriate. With larger mould sections, even angular powders produced by crushing and milling would enable the mould to be filled, especially when the flow of powder is aided by vibration, as will be described further with reference to Figure 4.
• Procedures for the creation of the positive sacrificial model are illustrated in Figure 2. Operations are performed upon a source material 201 in order to produce the positive model 102. It is possible to perform a machining operation 202 upon an appropriate material in order to define the shape of the positive model. However, it should be appreciated that the material used must be of a type such that it is possible to remove the sacrificial material in order to define the negative mould.
• the positive mould by a process of additive manufacturing 204, with an appropriate rapid prototyping material for example.
• the material may be removed by the application of heat and/or the application of an appropriate solvent.
• the negative mould having a melting point higher than the melting point of the metal from which the component is to be formed, may be a ceramic shell that is relatively porous to air.
• the ceramic mould is produced by adding a plurality of layers, as illustrated in Figure 3. The layers are added as an alternating wet slurry layer followed by a substantially dry stucco layer.
• Slurry 301 is applied to the model 102.
• Dry stucco 302 is then applied that attaches itself to the wet slurry in order to build a layer.
• Ceramic mould 104 should ideally have relatively thin wall sections so as to allow the conduction of radiant heat from a radiant heating system therein, to enable to the metal powder to be melted.
• the wall sections must be sufficiently thick to prevent cracks or fracturing during processing, and therefore a compromise must be reached in creating a mould that has a high thermal conductivity, but is sufficiently strong.
• a primary refractory slurry is applied that is inert to the metal being used.
• a dry sand of similar or different material is then applied and further slurries are applied, followed by sand, stucco and so on.
• a number of suitable ceramic materials for forming the ceramic shell are known, such as silica and alumina. It has been found during testing that a silica shell does not have a sufficiently high thermal conductivity to allow the powder metal charge to be melted in a suitable time-period using a radiant heating system, as opposed to an induction heating system that heats the powdered metal directly. Therefore, in a preferred embodiment, a negative mould comprised of an alumina material having a high thermal conductivity may be used. Other types of shell material having a high thermal conductivity may be used, however they must not be susceptible to dissolution in the molten metal, as can be experienced by graphite based moulds when using certain metals.
• Step 107 for the deployment of feed material is detailed in Figure 4.
• the positive sacrificial model 102 has been removed as illustrated by step 105.
• the negative mould 104 is placed upon a vibrating table 401, itself supported by a stable base 402.
• a degree of vibration is introduced, as illustrated by arrows 403 and 404, to facilitate the dispersal and densification of the feed material within the mould.
• High frequency vibration e.g. 40-60 hertz
• with low amplitude displacement of, say 0.10-0.15 millimetres enables moulds for large and complex metal components to be filled easily.
• the feed material is deployed within the mould and then heated, as illustrated by step 109.
• the heat may be applied without pressure and the mould is heated to a temperature that causes the feed material to melt. In this way, it is possible to obtain close to 100 percent density using a process that has less overall complexity compared to known systems.
• the heat is required not only to raise the temperature of the metal, but also to melt the metal completely. Consequently, it is typically heated to around 50 degrees Celsius above the melting point of the metal, in the case of a pure metal, or above the liquidus temperature in the case of an alloy.
• metal powder as a feed material may produce products having desirable properties.
• the microstructure may be very uniform, which may improve strength and fatigue properties. Properties of this type may be provided by forging operations but, as is known, forging results in the production of significant levels of waste and therefore increases overall cost.
• a casting process yield is typically 50 percent; again increasing cost, which becomes an important factor when expensive alloys are being used.
• the heating system includes a radiant heat source for producing radiant heat from an electrical supply, along with a control circuit for controlling the electrical supply in order to control temperature.
• An embodiment further includes pressure reduction apparatus configured to reduce the pressure of a chamber or vessel to a pressure below atmospheric pressure.
• An example of this apparatus is shown in Figure 5.
• the apparatus indicated generally at 501 , has a vacuum furnace 502.
• the vacuum furnace has a vacuum-tight vessel 503, with a refractory lining 504, defining a vacuum chamber 505.
• Vessel 503 is provided with a door 506, for the purpose of providing access to the chamber 505, thereby allowing the chamber to be loaded and unloaded with moulds, such as mould 501.
• the vacuum furnace 502 has a resistance heating element 507 connected to a suitable electrical power supply 508.
• resistance heating elements are formed of molybdenum or graphite, but the full specification of the vacuum furnace will depend upon the specific types of metals and alloys that are being used in the process. Furthermore, the specification will also depend upon the requirements of the metal objects that are being formed .
• the vacuum furnace and its heating element and power supply are selected such that the temperature of the chamber may be raised to a temperature in excess of 2000 degrees Celsius. Furnaces with these capabilities are commercially available, generally for the purpose of providing heat treatment operations.
• Chamber 505 is connected to a vacuum system 509 for evacuating air from the chamber, such that pressures in the chamber may be reduced to levels substantially below atmospheric pressure.
• the chamber 505 has an inlet port 511 connected to a noble gas supply.
• a tank 512 of compressed helium may be provided in combination with a tank 513 of compressed Argon.
• the apparatus 501 also includes a fan 514, having an inlet connected to outlet port 510 of chamber 505 and an outlet connected to the inlet port 511.
• Helium gas may be supplied to chamber 505 up to a predetermined pressure and the gas may be circulated by a fan 514 to provide additional cooling.
• Temperature sensor 515 is located within the chamber and is configured to provide signals indicative of an actual temperature of the powdered or molten metal in the moulds located within the chamber.
• the apparatus also includes a vacuum pressure gauge 516 configured to provide an indication of vacuum pressure within the chamber.
• the pressure gauge 516 and the temperature sensor 515 are arranged to provide signals to a controller 517 indicative of the pressure and temperature of the chamber.
• the controller is arranged to operate the power supply 508 for the resistance heating element 507 and the vacuum system 509, in response to the signals received from gauge 516 and sensor 515.
• a method for forming a metal component is illustrated in Figure 6, in which heat is applied to a mould containing a metal in a particulate form.
• a mould containing metal powder is placed in a vessel and the vessel or pressure chamber is sealed, as illustrated at 601. Inside the vessel, the mould experiences changes in temperature and pressure under processor control 602, whereafter the mould is removed from the vessel as illustrated at 603.
• the temperature inside the vessel is increased to within a first temperature range above a liquidus temperature of the metal, during a temperature-rising interval 604.
• the temperature of the vessel is maintained, after the temperature rising interval 604, during a temperature- maintaining interval 605.
• the temperature of the vessel is then reduced, after the temperature- maintaining interval 605, during a temperature-falling interval 606.
• Different results may be obtained by subtle changes occurring within each of intervals 604 to 606, as will be described with reference to Figures 8 through 12.
• the pressure inside the chamber is reduced in order to avoid contamination from the surrounding air.
• the pressure should be reduced as far as possible, effectively creating a near vacuum.
• material metal would be lost through evaporation therefore there is a lower limit in terms of the pressure reduction.
• a range of pressures therefore exist defined by a lower limit, below which evaporation would take place and an upper limit, above which contamination would take place. The specific range will vary depending upon the actual constitution of the metal.
• Step 703 represents the start of the temperature-rising interval 604, during which the temperature within the vessel is increased.
• a question is asked as to whether the required temperature has been reached and if answered in the negative, further heating occurs at step 703.
• the temperature- rising interval 604 is completed when the question asked at step 704 is answered in the affirmative.
• Step 705 initiates the temperature-maintaining interval 605.
• the control processor maintains the operating temperature, within specified limits, and at step 706 a question is asked as to whether the temperature has been maintained for the required duration.
• the temperature is maintained at step 605, while an answer in the affirmative represents the end of the temperature-maintaining interval 605.
• the temperature of the chamber is raised and maintained such that the temperature within the metal itself will be above the melting point (or liquidus temperature) of the metal, to ensure that the metal is in a fully liquid state.
• the temperature of the chamber may be raised to a level that is fifty degrees higher than the actual melting point of the metal. This temperature is maintained sufficiently long enough for all of the metal in the mould to be taken above the melting point (liquidus temperature), such that all of the particles in the mould will have melted.
• measures are taken to compensate for shrinkage while melting and solidification take place.
• the start of the temperature falling interval 606 is initiated with a pressure increase at step 707 followed by temperature reduction at step 708.
• a question is asked as to whether the required temperature has been reached and if answered in the negative, further temperature reduction continues at step 708.
• a further increase in pressure occurs, returning the pressure in the vessel to atmospheric pressure.
• Further temperature reduction occurs at step 711 until the temperature-falling interval 606 is complete and the mould may be removed from the vessel.
• a first graph of pressure 801 and the second graph of temperature 802 are plotted against a common time axis 803.
• the pressure in the chamber is reduced, in accordance with step 707, until the pressure drops below an upper pressure limit 805 and is maintained above a lower pressure limit 806, resulting in the question asked at step 702 being answered in the affirmative.
• the end of the temperature-raising interval 604 occurs when the temperature goes above a lower predetermined temperature 808, thereby entering the temperature- maintaining interval 605.
• the temperature is held above lower limit 808 and below an upper temperature limit 809.
• the temperature in the vessel is maintained between temperature 808 and temperature 809 for a predetermined period of time, during the temperature- maintaining interval 605, until the resistive heating elements are powered down.
• the temperature-maintaining interval 605 occurs between time 810 and power down time 811.
• a noble gas such as argon or helium
• the pressure is returned to atmospheric pressure as indicated at 814. Below temperature 813, the objects may be removed from the vessel without experiencing excessive oxidation.
• FIG. 9 A substantially similar process to that shown in Figure 8 is shown in Figure 9.
• the temperature-rising interval starts at time 901 and a temperature- maintaining interval starts at time 902, with a temperature falling interval then following at time 903.
• time 903 representing the start of the temperature- falling interval 606
• noble gas is supplied into the vessel and blown through the vessel by fan 514 in order to provide an increased rate of cooling.
• helium gas is used to improve heat transfer.
• the pressure in the vessel increases at time 903, it remains below ambient pressure, as indicated by pressure 904, whereafter the pressure is increased to ambient pressure at time 905.
• FIG. 10 A similar example is shown in Figure 10, again showing plots of pressure and temperature against a common time axis.
• the temperature-rising interval 604 is initiated at time 1001
• the temperature-maintaining interval 605 is initiated at time 1002
• the temperature-falling interval 606 is initiated at time 1003.
• helium gas is supplied into the vessel at increased pressure, indicated by pressure 1004, that may be several times atmospheric pressure and is maintained until time 1005. During this period, helium gas is supplied and blown through the vessel in order to increase the rate of cooling. This approach is taken in order to obtain crystals of reduced size within the metal component.
• the apparatus of Figure 5 is therefore configured to form a metal component in which heat is applied to a mould containing metal in particulate form.
• the apparatus includes a pressure vessel 503, a heating device 507 for heating the contents of the pressure vessel, a pressure adjustment device 509 for adjusting pressure within the pressure vessel and a control system for controlling the heating device and the pressure adjusting device over controlled intervals.
• a control system is configured to increase the temperature inside the vessel to within a first temperature range above the liquidus temperature of the metal during the temperature-rising interval.
• control system also controls the pressure adjustment device; thereby reducing pressure inside the vessel during a pressure reduction interval, prior to the temperature-rising interval.
• the temperature is maintained at step 1101 and at step 1 02 a question is asked as to whether the temperature has been maintained for the required duration.
• This duration may be substantially similar in duration to the entire temperature-maintaining interval 605 in Figure 7.
• step 1103 representing the start of the second portion 1110, the temperature is reduced while the reduced pressure is maintained and a question is asked at step 1104 as to whether the required temperature has been reached. When answered in the negative, further temperature reduction occurs at step 1103, again while maintaining reduced pressure.
• the end of the second portion 1110 and the start of the third portion 1111 is identified by the question asked at question 1104 being answered in the affirmative, in that the required temperature has been reached; this being a second specified temperature within the temperature maintaining interval 605.
• a question is then asked at step 1106 as to whether the temperature has been maintained for the required duration, during portion 1111 and when answered in the negative the temperature is maintained at step 1 05.
• step 1107 representing the start of the temperature-falling interval 606.
• step 1108 a question is asked as to whether a required temperature has been reached and when answered in the negative further temperature reduction occurs at step 1107, while still at reduced pressure.
• the question asked at step 1108 will be answered in the affirmative, resulting in a pressure increase at step 710 and further temperature reduction at step 711.
• the temperature-rising interval 604 starts at time 1206 and the interface between the temperature-rising interval 604 and the temperature-maintaining interval 605 occurs at time 1207.
• the solidus temperature 1208 is shown, above which there is the liquidus temperature 1209; the interval between these being dependent upon the particular material being used to form the component. Above this there is a lower predetermined temperature 210 and an upper predetermined temperature 1211.
• the temperature is held between the lower predetermined level 1210 and the upper predetermined level 1211, both above the liquidus temperature 1209.
• the temperature is reduced at time 1212 until, at time 1213, it is has fallen below the liquidus temperature 1209 but above the solidus temperature 1208.
• the temperature is maintained at temperature 1214 to encourage the formation of large crystals.
• crystallisation occurs during the third portion of the temperature-maintaining interval 605, with complete solidification occurring after time 1215.
• the vessel is returned to atmospheric pressure 1217.
• the temperature-falling interval 606 has been divided into a fourth portion 218 and a fifth portion 1219. During the fourth portion, the metal is cooled below the solidus temperature at reduced pressure and during the fifth portion, further cooling is achieved at increased pressure, possibly with forced cooling.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Powder Metallurgy (AREA)
• Mold Materials And Core Materials (AREA)
• Molds, Cores, And Manufacturing Methods Thereof (AREA)
• Crystallography & Structural Chemistry (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)

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• 2013
  • 2013-08-02 GB GBGB1313849.0A patent/GB201313849D0/en not_active Ceased
  • 2013-11-12 GB GB1320170.2A patent/GB2516991A/en not_active Withdrawn
  • 2013-11-15 GB GB1320171.0A patent/GB2516992A/en not_active Withdrawn
  • 2013-11-15 GB GB1320168.6A patent/GB2516990A/en not_active Withdrawn
• 2014
  • 2014-08-01 KR KR1020167005189A patent/KR20160038004A/ko not_active Withdrawn
  • 2014-08-01 WO PCT/GB2014/000301 patent/WO2015015142A1/en not_active Ceased
  • 2014-08-01 WO PCT/GB2014/000303 patent/WO2015015144A1/en not_active Ceased
  • 2014-08-01 EP EP14749941.2A patent/EP3027342B1/en not_active Not-in-force
  • 2014-08-01 JP JP2016530593A patent/JP6412128B2/ja not_active Expired - Fee Related
  • 2014-08-01 US US14/909,520 patent/US20160193653A1/en not_active Abandoned
  • 2014-08-01 WO PCT/GB2014/000302 patent/WO2015015143A1/en not_active Ceased
  • 2014-08-01 CN CN201480042531.5A patent/CN105492142A/zh active Pending

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