Patent Application
20060251536
This invention relates generally to sintered metallic components and more particularly to components sintered by microwave heating.
Metal Injection Molding (“MIM”) is a known process in which a fine metallic powder is mixed with a plastic binder and extruded to a desired shape using plastic molding equipment. The resulting preform is washed to remove a large portion of the plastic from the powder. Subsequent sintering consolidates the preform to form a finished component.
Prior art methods of sintering for MIM preforms require furnace heat treatment at temperatures capable of causing the metal powders to sinter together to make the preform mechanically strong enough for further processing. This is a time consuming process that results in a non uniform product due to the heating process being “from the outside in”, meaning the outer portion of the preform gets more time at high temperature and can sinter earlier causing voids to be trapped inside the preforms. This can also result in non-uniform mechanical properties.
Accordingly, there is a need for a method of sintering a metallic preform to provide a uniformly dense finished component.
The above-mentioned need is met by the present invention, which according to one aspect provides a method of producing a metallic component including: providing a mixture of a metallic powder and a binder; melting the binder and forming the mixture into a preform in the shape of the component; remove a majority of the binder from the preform; and heating the preform with microwave energy to remove the remainder of the binder and to sinter the metal powder together to form the component.
According to another aspect of the invention, a method of producing a metallic component includes providing a mixture of a metallic powder and a binder; melting the binder and forming the mixture into a continuous preform in the shape of a desired component; removing a majority of the binder from the preform; and heating the preform with microwave energy to remove the remainder of the binder and to sinter the metallic powder together to form the component.
The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:
Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,
The metallic powder may be a single alloy or it may be a mechanical mixture of more than one alloy. For optimum performance in the injection molding process and also for compatibility with the microwave heating step described below, the particle size of the metallic powder should be about 100 micrometers or less. Examples of known alloys suitable for constructing compressor blades include titanium alloys such as Ti-6Al-4V, nickel-based alloys such as INCO 718 or UDIMENT 720, and iron-based alloys such as A286.
The binder may be any material which is chemically compatible with the metallic powder and which allows the required processing (e.g. mixing, injection, solidification, and leaching). Examples of known suitable binders include waxes and polymer resins. The binder may be provided in a powder form.
The binder and the metallic powder are thoroughly mixed together, as shown in block 30. The mixture is then heated to melt the binder and create a fluid with the metallic powder coated by the binder (block 32). Next, the mixture is formed into a predetermined shape at block 34. One way of forming the mixture is to use a known injection-molding apparatus. A schematic view of an injection molding apparatus 36 including a hopper 38 and an extruder 40 with rotating screw 42 is shown in
The preform 48 comprises metal particles suspended in the solidified binder. The preform 48 is not suitable for use as a finished component, but merely has sufficient mechanical strength to undergo further processing. At block 52 of
Next, at block 54, the preform 48 is microwave sintered. As shown in
The microwave source 60 is activated to irradiate the preform 48. In the illustrated example the microwave source 60 is depicted as having a direct line-of-sight to the entire preform 48. However, it is also possible to configure the chamber 56, which would typically be metallic, so that the preform is heated by a combination of direct and reflected microwaves. Because of the small metallic particle size in the preform 48, the microwaves 62 couple with the particles and heat them. The preform 48 is heated to a temperature below the liquidus temperature of the metallic powder and high enough to cause the metallic powder particles to fuse together and consolidate. The high temperature also melts and drives out any remaining binder. The preform 48 is held at the desired temperature for a selected time period long enough to result in a consolidated compressor blade 10. The heating rate (i.e. the output wattage of the microwave source) is selected depending on variables such as the mass of the preform 48, the shape of the chamber 48 and the and the desired cycle time of the sintering process. When compared to prior art methods, the combination of the MIM-formed preform 48 with the microwave sintering step gives the compressor blade 10 a significantly greater density, that is, freedom from voids, in less time.
When the sintering cycle is complete, the compressor blade 10 is removed from the chamber 56 and allowed to cool. When required, the compressor blade 10 may be subjected to further consolidation using a known hot isostatic pressing (“HIP”) process to result in a substantially 100% dense component, as noted in block 63 of
The binder may be any material which is chemically compatible with the metallic powder and which allows the required processing (e.g. mixing, injection, solidification, and leaching). Examples of known suitable binders include waxes and polymer resins. The binder may be provided in a powder form.
The binder and the metallic powder are thoroughly mixed together. The mixture is then heated to melt the binder and create a fluid with the metallic powder coated by the binder. Next, the mixture is extruded using known injection-molding apparatus. A schematic view of an injection molding apparatus 136 including a hopper 138 and an extruder 140 with rotating screw 142 is shown in
The conveyor belt 150 carries the preform 148 through a solvent bath 152 which leaches the majority of the binder out of the preform 148. This may be done with a suitable solvent which dissolves the binder but does not attack the metallic powder.
The preform 148 then passes into a sintering chamber 156 where it is microwave sintered. As shown in
When the sintering cycle is complete, the component 162 passes out of the chamber 156 and allowed to cool. If desired, the product 162 may be subjected to additional processes such as coating, inspection, etc. in a known manner.
When required, the welding filler wire 162 may be subjected to further consolidation using a known hot isostatic pressing (“HIP”) process to result in a substantially 100% dense component. As shown in
The continuous process described above may be used to produce any other type of component with a constant cross-section. For example, the process may be used to produce sheet materials. As shown schematically in
When required, the metallic sheet 262 may be subjected to further consolidation using a HIP process to result in a substantially 100% dense component. As shown in
The foregoing has described a manufacturing process for microwave sintered components. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation, the invention being defined by the claims.
