Claims:1. A method (10) for development of feedstock for metal injection molding comprising:
mixing an alloy powder with a group of binders in a predefined ratio to prepare compound feedstock, wherein the predefined ratio ranges between 70:30 to 65:35 respectively; (20)
preparing one or more pellets of a predefined amount of the compound feedstock by extruding the compound feedstock using split feeding method in twin screw extruder; (30)
producing a predetermined complex shape specimen from the one or more pellets using a metal injection molding technique; (40) and
developing a homogenous specimen of the predetermined complex shape by eliminating the group of binders and one or more pores from the predetermined complex shape specimen using one or more de-binding techniques and a sintering technique, respectively (50).
2. The method (10) as claimed in claim 1, wherein the alloy powder comprises a metal alloy comprising at least one of steel, Inconel, aluminium, copper and a combination thereof.
3. The method (10) as claimed in claim 1, wherein the alloy powder comprises a ceramic alloy comprising at least one of alumina, zirconia and a combination thereof.
4. The method (10) as claimed in claim 1, wherein the group of binders consist of a primary binder and a second binder, wherein the primary binder and the secondary binder are mixed in a ratio of 2:1 respectively.
5. The method (10) as claimed in claim 4, wherein the primary binder comprises acetal, polyacetal or polyformaldehyde.
6. The method (10) as claimed in claim 4, wherein the secondary binder comprises low chain thermoplastic polymer.
7. The method (10) as claimed in claim 1, wherein the compound feedstock comprises a mixture of the alloy, the at least two binders and an additive, wherein the additive comprises phenolic compounds.
8. The method (10) as claimed in claim 1, wherein the additive is mixed with the mixture of the alloy and the at least two binders in 0.1 percent to 0.5 percent.
9. The method (10) as claimed in claim 1, wherein the one or more de-binding technique comprises a catalytic de-binding technique, a solvent de-binding technique and a thermal de-binding technique.
10. The method (10) as claimed in claim 1, wherein producing a predetermined complex shape specimen from the one or more pallets using a metal injection molding technique comprises producing a predetermined complex shape specimen from the one or more pallets by molding the one or more pellets horizontally.

Dated this 1st day of October 2019

Signature

Vidya Bhaskar Singh Nandiyal
Patent Agent (IN/PA-2912)
Agent for the Applicant
, Description:BACKGROUND
[0001] Embodiments of a present disclosure relate to metal injection molding and more to a method for development of feedstock for metal injection molding.
[0002] Metal injection molding (MIM) and its counterpart for ceramic injection molding (CIM) are structural part fabrication technologies which are near net shape processes that require little or no post processing. These two technologies are sometimes referred to as powder injection molding (PIM). The powder injection molding has the ability to manufacture products from any solid materials, ranging from natural minerals, pure oxides, carbides, metals and ending with multicomponent composite synthetic materials and their combinations that combine the design flexibility and high volume.
[0003] The powder injection molding process includes formation of feedstock by using a mixture of alloy and polymeric binders. However, it is difficult to identify compatible polymeric binders
[0004] One aspect of the process that poses particular problems and hazards is the de-binding step. Sufficient binder must be retained to provide a brown part that is stable and sufficiently strong to be handled and transported between the de-binding and sintering steps, but the brown preform should not contain either a type of binder or an amount of binder that would hinder or impair the sintering step. In current debinding processes, the binder is softened by heating or solvent action which further allowing the part to become too soft results in distortion or "slumping". Generally, the closer the part is to the slumping point, the faster the debinding rate. Hence, there is a compromise between debinding rate and dimensional stability. This also means that the uniformity and control of the temperature within the debinding process becomes very critical.
[0005] Hence there is a need for an improved method for development of feedstock for metal injection molding to address the aforementioned issue(s).

BRIEF DESCRIPTION
[0006] In accordance with an embodiment of the present disclosure, a method for development of feedstock for metal injection molding is provided. The method includes mixing an alloy powder with a group of binders in a predefined ratio to prepare compound feedstock, wherein the predefined ratio ranges between 70:30 to 65:35 respectively. The method also includes preparing one or more pellets of a predefined amount of the compound feedstock by extruding the compound feedstock using split feeding method in twin screw extruder. The method further includes producing a predetermined complex shape specimen from the one or more pellets using a metal injection molding technique. The method further includes developing a homogenous specimen of the predetermined complex shape by eliminating the group of binders and one or more pores from the predetermined complex shape specimen using one or more de-binding techniques and a sintering technique, respectively.
[0007] To further clarify the advantages and features of the present invention, a more particular description of the invention will follow by reference to specific embodiments thereof, which are illustrated in the appended figures. It is to be appreciated that these figures depict only typical embodiments of the invention and are therefore not to be considered limiting in scope. The invention will be described and explained with additional specificity and detail with the appended figures.
BRIEF DESCRIPTION OF DRAWINGS
The disclosure will be described and explained with additional specificity and detail with the accompanying figures in which:
[0008] FIG. 1 is a flow chart representing the steps involved in a method for development of feedstock for metal injection molding in accordance with an embodiment of the present disclosure;
[0009] FIG. 2 is a schematic representation of specimen prepared in metal injection molding using the developed feedstock in the method of FIG. 1 in accordance with an embodiment of the present disclosure; and
[0010] FIG. 3 is a schematic representation of scanning electron microscopic images of the homogeneous specimen of the feedstock of FIG. 1 in accordance with an embodiment of the present disclosure.
[0011] Further, those skilled in the art will appreciate that elements in the figures are illustrated for simplicity and may not have necessarily been drawn to scale. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the figures by conventional symbols, and the figures may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the figures with details that will be readily apparent to those skilled in the art having the benefit of the description herein.
DETAILED DESCRIPTION OF THE INVENTION
[0012] For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the figures and specific language will be used to describe them. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as would normally occur to those skilled in the art are to be construed as being within the scope of the present invention. It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
[0013] The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such a process or method. Similarly, one or more devices or sub-systems or elements or structures or components preceded by "comprises... a" does not, without more constraints, preclude the existence of other devices, sub-systems, elements, structures, components, additional devices, additional sub-systems, additional elements, additional structures or additional components. Appearances of the phrase "in an embodiment", "in another embodiment" and similar language throughout this specification may, but not necessarily do, all refer to the same embodiment.
[0014] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs. The system, methods, and examples provided herein are only illustrative and not intended to be limiting.
[0015] Embodiments of the present disclosure relate to a method for development of feedstock for metal injection molding. The method includes mixing an alloy powder with a group of binders in a predefined ratio to prepare compound feedstock, wherein the predefined ratio ranges between 70:30 to 65:35 respectively. The method also includes preparing one or more pellets of a predefined amount of the compound feedstock by extruding the compound feedstock using split feeding method in twin screw extruder. The method further includes producing a predetermined complex shape specimen from the one or more pellets using a metal injection molding technique. The method further includes developing a homogenous specimen of the predetermined complex shape by eliminating the group of binders and one or more pores from the predetermined complex shape specimen using one or more de-binding techniques and a sintering technique, respectively.
[0016] FIG. 1 is a flow chart representing the steps involved in a method (10) for development of feedstock for metal injection molding in accordance with an embodiment of the present disclosure. The method (10) includes mixing an alloy powder with a group of binders in a predefined ratio to prepare compound feedstock. The predefined ration ranges between 70:30 to 65:35 respectively in step 20. In one embodiment, the alloy powder may include a metal alloy such as at least one of steel, Inconel, aluminium, copper or the like and the combination thereof. In another embodiment, the alloy powder may include a ceramic alloy such as at least one of alumina, zirconia or the like and the combination thereof.
[0017] In some embodiments, the group of binders consist of a primary binder and a secondary binder, wherein the primary binder and the secondary binder may be mixed in the ratio of 2:1 respectively. In such embodiment, the primary binder may include acetal, polyacetal, polyformaldehyde or the like. In another such embodiment, the secondary binder may include low chain thermoplastic polymer.
[0018] Furthermore, the method (10) includes preparing one or more pellets of a predefined amount of the compound feedstock by extruding the compound feedstock using split feeding method in twin screw extruder in step 30. As used herein, the term “pellet” is defined as the small particles typically created by compressing an original material. Similarly, as used herein, “twin screw extruder” is used to mix fillers and additives with the polymer in a continuous manner, so that the compound may perform as required and achieve the desired properties. The twin-screw extruder consists of two intermeshing, co-rotating screws mounted on splined shafts in a closed barrel. Due to a wide range of screw and barrel designs, various screw profiles and process functions may be set up according to process requirements. Hence, a twin-screw extruder is able to ensure transporting, compressing, mixing, cooking, shearing, heating, cooling, pumping, shaping with high level of flexibility.
[0019] In one embodiment, the compound feedstock may include a mixture of the alloy, the at least two binders and an additive. In such embodiment, the additive may be phenolic compounds. The method (10) further includes producing a predetermined complex shape specimen from the one or more pellets using a metal injection molding technique in step 40. In a specific embodiment, the predetermine complex shape specimen may include a I-shape specimen. As used herein, the “metal injection molding technique” is defined as a metalworking process in which finely powdered metal is mixed with binder material to create a feedstock that is then shaped and solidified using injection molding. The molding process allows high volume, complex parts to be shaped in a single step.
[0020] Moreover, the method (10) further includes developing a homogenous specimen of the predetermined complex shape by eliminating the group of binders and one or more pores from the predetermined complex shape specimen using one or more de-binding techniques and a sintering technique, respectively in step 50. In one embodiment, the one or more de-binding technique may include a catalytic de-binding technique, a solvent de-binding technique and a thermal de-binding technique or the like. In some embodiments, producing a predetermined complex shape specimen from the one or more pallets using a metal injection molding technique may include producing a predetermined complex shape specimen from the one or more pallets by molding the one or more pellets horizontally.
[0021] In operation, master alloys are used along with the specialized primary binder and optimized with the suitable secondary binder to prepare feedstock. The feedstock is compounded in the customized twin screw extruder to develop a plurality of uniform sized pellets. The compounded feedstock used to develop the product under low injection pressure. The customized formulation is especially for catalytic debinding. The compounded feedstock was subjected to Metal injection molding to develop the I-shaped more particularly, a dog bone shaped specimen (FIG. 2) to characterize the mechanical property indirectly the formulations. The processing steps such as green, brown and final that is after compounding, molding, de-binding and sintering respectively are undergone and the specimens are tested for density, microstructure and surface morphology using densitometer, microscope and scanning electron microscopy respectively. The microstructure study reveals that there are no voids or gaps and the polymer homogeneity at these processing conditions is suited well. The density of the final specimen is around 7.0 to 7.4 gram per millimetre.
[0022] FIG. 3 is a schematic representation of scanning electron microscopic images (100) of the homogeneous specimen of the feedstock of FIG. 1 in accordance with an embodiment of the present disclosure. The scanning electron microscopic (SEM) images (100) depicts suitable dispersion of the group of binders. The SEM images (100) also shows the proper homogeneity of the metal powder, wherein the metal powder used may be steel alloy-4340 and steel alloy-4605. The grains boundaries are clear with well-defined boundaries. Furthermore, the needle shaped appearance in the SEM image indicates the phase transformation of the alloy after treatment. In addition, there are no visible pores appeared in the medium which intend to create the fractures under stress. The SEM image shows the spherical shaped metal alloy powder not more than 22 micron. The SEM image also shows the melted primary and secondary binders.
[0023] Various embodiments of the method for development of feedstock for metal injection molding described above enables the production of the component at low molding pressure in the metal injection molding thereby increased the shelf life of the die. The method provides Customizable solution as it is possible to develop in-house. The method also provides Complete control of the process and hence, considered as cost effective.
[0024] Furthermore, the method declares that the unique combination of primary and secondary binder with master alloy powder suited well and it can be horizontally implemented to the other master alloys to develop in-house customized feedstock. Moreover, the mold life of the injection mold will improve as this formulation able to develop the component at lower injection pressure.
[0025] The present method may be applicable in field of automotive, defence and medical devices. The metal injection molding process is most effective model in the production process where the volume of the production is very high, and cost of the component will come down.
[0026] It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the disclosure and are not intended to be restrictive thereof.
[0027] While specific language has been used to describe the disclosure, any limitations arising on account of the same are not intended. As would be apparent to a person skilled in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein.
[0028] The figures and the foregoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, the order of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts need to be necessarily performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples.