Patent Application
20250083228
The application relates generally to methods of manufacturing a part made using powder injection molding and, more particularly, to green part(s) obtained by metal injection molding.
Green machining involves the machining of metal bodies in the green state prior to sintering. Metal injection molded (MIM) parts in the green state are fragile. During green machining operation, the green body has to be held in place with enough load to handle the machining operation. However, because of its fragile state, there may be a risk of breaking or damaging the green body upon applying such load.
A standard process when machining a metallic part is to use a retaining fixture to hold the part in place. However, in some circumstances, the retaining fixture may slip on the part and therefore may not hold firmly the part in place which may result in either a scrap part or an out of tolerance part.
Accordingly, improvements in manufacturing methods for MIM parts are needed.
In one aspect, there is provided a method of manufacturing a part, comprising: receiving a green body made of powder injection molding material, the powder injection molding material including a binder and a metallic powder material mixed with the binder, the green body having a first surface hardness; engaging the green body to a clamp pad engaged to a fixture member of a retaining fixture of a machine tool, the clamp pad having a second surface hardness smaller than the first surface hardness; while supporting the green body through the engagement of the clamp pad, machining the green body using the machine tool to obtain a machined green part; and debinding and sintering the machined green part.
In another aspect, there is provided an assembly comprising: a green body made of powder injection molding material, the powder injection molding material including a binder and a metallic powder material mixed with the binder, the green body having a first surface hardness; a retaining fixture of a machine tool, the retaining fixture including a fixture member having a second surface hardness greater than the first surface hardness; and a clamp pad having a fixture-engaging surface engaged to the fixture member and a green-body-engaging surface engaged to the green body, the fixture-engaging surface having a third surface hardness smaller than the second surface hardness, and the green-body-engaging surface having a fourth surface hardness smaller than the first surface hardness and the second surface hardness.
Reference is now made to the accompanying figures in which:
In this description and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.
The present application discusses a method of manufacturing a part made using metal injection molding (hereinafter “MIM”) techniques. It is an object of the present technology to provide for a method of manufacturing a MIM part by which the MIM part is machined in green state after being molded and before the debinding and sintering steps are performed. The part in the green state is held in place during the machining operation(s) using a retaining fixture, and a clamp pad having a surface hardness that is different than that of the MIM part. Since the machining is carried out for the MIM part in the green state, which is softer as compared with the finally obtained sintered part, it is possible to carry out the machining while the part is in green state, thereby enabling improvement in dimensional precision and enabling the machining of complex and intricate shapes.
As is typical in MIM, a suitable feedstock is injected into a mold cavity to obtain a green part, also referred to herein as “green body”. Such a feedstock can include high temperature resistant powder metal alloys, such as a nickel superalloy. Other high temperature resistant material powders which may include one material or a mix of materials could be used as well. The feedstock is a mixture of the material powder and of a binder which may include one or more binding material(s). In a particular implementation, the binder includes an organic material which is molten above room temperature (20° C.) but solid or substantially solid at room temperature. The binder may include various components such as surfactants which are known to assist the injection of the feedstock into the mold for production of the green body. In a particular implementation, the binder includes a mixture of binding materials, for example including a lower melting temperature polymer, such as a polymer having a melting temperature below 100° C. (e.g. paraffin wax, polyethylene glycol, microcrystalline wax) and a higher melting temperature polymer or polymers, such as a polymer or polymers having a melting temperature above 100° C. (e.g. polypropylene, polyethylene, polystyrene, polyvinyl chloride). Different combinations are also possible. In a particular implementation, the material powder is mixed with the molten binder and the suspension of injection powder and binder is injected into the mold cavity and cooled to a temperature below that of the melting point of the binder. “Green state”, “green part” or “green body” as discussed herein refers to a molded part produced by the solidified binder that holds the injection powder together.
Since the feedstock is wax and/or polymer based, machining the green body can be performed with cutting feeds and speeds that are higher and cutting forces that are lower than typical feeds, speeds and forces for the machining of solid metal (for example the same metal as that found in powder form in the green body), and even when compared with “soft” metals such as aluminum. In a particular implementation, a machine tool that is designed for machining wax and plastics (e.g. small desktop CNC milling machine) is used to machine the green body. In a particular implementation, the cutting feeds and speeds are similar to that used during the machining of wax. In a particular implementation, the metal powder present in the green body provides for an increased material conductivity when compared to the binder material alone, which may help dissipate heat that may be generated during machining. When in the green state, the green body may have a surface hardness that is smaller than the surface hardness of the sintered part.
In a particular implementation, the method may be used for the rapid-prototyping of powder injection molding parts, for example to obtain a part for tests. This may allow the final part to be manufactured within a timeline in the order of days rather than months, allowing for quicker manufacture of parts available for testing. For example, shrinkage and deformations of the part until the end of the sintering process can be observed and measured, and a new green body with different dimensions can be produced by machining if the desired final dimensions are not obtained. Iterations in the green body design can thus be done by machining rather than by mold modifications, which in a particular implementation significantly reduces the development time and development cost for the part. Once the final design has been confirmed, a mold can be ordered for mass production.
In the following description, different assemblies 20, 120, 220, 320 adapted for the manufacturing of a part will be described.
Referring to
After molding, the green body 30 has a relatively low surface hardness provided by the powder material mixed with the solidified binder. In addition, the green body 30 is relatively fragile and brittle, but is rigid enough to be able to maintain its shape and handle some manipulation. In order to facilitate the machining thereof and in order to prevent damaging the green body 30 during the machining, the assembly 20 further includes a clamp pad 50 engaged to each of the retaining fixtures 40 and to the green body 30. According to some embodiments, each clamp pad 50 may have a fixture-engaging surface 52 engaged to the engagement surface 42a of the fixture member 42, and a green-body-engaging surface 54 engaged to the green body 30. The clamp pad 50 may be connected to the fixture member 42 via a fastener 56. In the present implementation, the fastener 56 is an adhesive provided on the fixture-engaging surface 52 of the clamp pad 50. Other fasteners 56, such as screws, collars or braces are contemplated to be used in other implementations for connecting the clamp pad 50 to the corresponding fixture member 42. According to some embodiments, no fastener may be used. In such cases, the clamp pad can be simply placed between the green part and the fixture and held in place by the clamping load of the fixture.
In the illustrated implementation, the green body 30 has a top surface 30a, and is held in place by the engagement of the top surface 30a with the green-body-engaging surface 54 of each clamp pad 50. The green-body-engaging surface 54 has a surface hardness that is smaller than the surface hardness of the engagement surface 42a of the fixture member 42, and smaller than the surface hardness of the top surface 30a of the green body 30. The clamp pads 50 are made of a relatively soft and compliant material, such as a rubber-based or a silicon-based material. The clamp pads 50 have a thickness ranging between 30 thousandth of an inch (about 0.76 mm) and ⅜ inch (about 9.53 mm). The thickness of the clamp pad 50 depends, among other factors, on the material forming the clamp pad 50 and on the load needed to be applied by the retaining fixture 40 for holding the green body 30 in place during machining operations.
Still referring to
Referring now to
The green body 130 has a top surface 130a that is curved. The green body 130 has a wedge shape best seen in
Turning now to
The green body 230 is cylindrically shaped, and has a surface 230a that is cylindrical. In order to support the green body 230 for machining operations, the retaining fixture 240 is a chuck jaw having three fixture members 242. The retaining fixture 240 is adapted to hold the green body 230 while rotating, for example, on a lathe during turning operations. The retaining fixture 240 is also configured for having a longitudinal axis 230b of the green body 230 coaxial with a central axis 240a of the retaining fixture 240. On each of the fixture members 242, a clamp pad 250 is engaged between the surface 230a of the green body 230 and the engagement surface 242a of the fixture member 242. A groove 246 is defined in the engagement surface 242a of each fixture member 242. The groove 246 extends parallel to the axes 230b, 240a. A ridge 248 projects from the fixture-engaging surface 252 of each clamp pad 250. The groove 246 and ridge 248 define locating features complementarily shaped for locating one another upon engagement to one another. In the implementation shown, the ridge 248 is a male locating feature projecting away from the clamp pad 250, and it is snuggly engaged within a corresponding female feature, e.g. the groove 246, defined in the fixture member 242. More than one pair of locating features may be used and/or the configurations of the locating features may vary, but are configured to allow for the clamp pad 250 to be engaged to the corresponding fixture member 242 with a known location. Other locating features, such as a pin and a complimentarily shaped hole, are contemplated in other implementations. It is contemplated that in implementations having locating features on the clamp pad 250 and the fixture member 242, there is not necessarily a need for connecting the clamp pad 250 to the fixture member 242 using a fastener such as an adhesive.
Still referring to
Referring now to
The green body 330 has curved top surfaces 330a. In order to support the green body 330 for machining operations, arc-shaped clamp pads 350 are engaged to the top surfaces 330a of the green body 330 and to the engagement surface 342a of two arc-shaped fixture members 342 of the retaining fixture 340, which is a clamp. Each of the fixture members 342 has the engagement surface 342a embracing a surface profile of a corresponding one of the top surfaces 330a of the green body 330. Hence, the fixture members 342 apply a downward load on the clamp pads 350, and the clamp pads 350 transmit the downward load to the green body 330. Having the fixture members 342 and the clamp pads 350 embracing the surface profile of the green body 330 on the portion thereof that is engaged by the green-body-engaging surface 354 of each clamp pad 350 may limit stress concentration and assist in spreading the load applied by the retaining fixture 340.
As is apparent from the description of the assemblies 20, 120, 220, 320, the clamp pad may take different shapes and sizes. For example, the clamp pad is therefore selectable among a set of clamp pads having, for example, different configurations of green-body-engaging surface. The clamp pads of the set may also have different configurations for use with different fixture members, retaining fixtures and/or different machine tools. The selection of the clamp pad(s) can also be made based on a surface profile of the green body that is to be engaged by the clamp pad(s).
With reference to
Although in the implementations shown the molded green body 30 is depicted as a block shape, i.e. having none of the features of the desired final shape for the part which are thus all obtained by machining, it is understood that in other implementations the green body may be molded having some of the features of the desired final shape such that only part of the green body is machined, or with an intermediate shape between the block shape and the desired final shape, for example a rough shape approximating and larger than the desired final shape. The method 400 may also be used to perform secondary machining operations on molded parts in the green state, including the removal of gates created by the molding process, testing new/modified features on already molded parts (as opposed to directly molding the modified part using a new/modified mold), and machining difficult to mold features with easier to mold features being directly obtained in the molding step.
The method 400 may be used to shape any type of part that may be obtained by a metallic powder injection molding process, including, but not limited to, gas turbine engine elements such as pieces of fuel nozzles, combustor panels, brackets, vanes, vane segments, vane rings, heat shields, combustion air swirlers, shroud segments, bosses, flanges, tube fittings, adaptors, airfoils, blades, levers, etc.
It is understood that the machined green part may be assembled to one or more other green part(s) (whether machined or directly molded to shape) prior to debinding, and these parts may be assembled in their green state, connected using any type of suitable non-detachable connections or detachable connections, and debound and sintered to fuse them together to form the final element. In a particular implementation, the parts are fused during the debinding step. Alternately, the parts are joined after the debinding step and prior to the sintering step.
The implementations described in this document provide non-limiting examples of possible implementations of the present technology. Upon review of the present disclosure, a person of ordinary skill in the art will recognize that changes may be made to the implementations described herein without departing from the scope of the present technology. Yet further modifications could be implemented by a person of ordinary skill in the art in view of the present disclosure, which modifications would be within the scope of the present technology.
