A powder metallurgy sintering process

Abstract

The application discloses a powder metallurgy sintering process, comprising the following steps: step a) support preparation, step b) spacer selection, step c) assembly and synchronous sintering, step d) post-processing. The application sets up synchronous adaptive sintering with matched materials to integrate profiled support, synchronous shrinkage and easy-to-separate interface, wherein the support powder with the same material or matched thermal expansion coefficient as the workpiece realizes synchronous shrinkage in the sintering process to offset internal stress, and the design of the buffer contact surface and the application of the easy-to-peel release layer ensure the clean separation of the interface while providing stable support, significantly improving the dimensional accuracy of the special-shaped workpiece and suppressing deformation. Meanwhile, the reusability of the support and the closed-loop circulation of the homogenous material significantly reduce material consumption and comprehensive cost, so that the process can meet multiple requirements such as high-precision forming, high-furnace loading efficiency and economic sustainability.

Description

Technical Field

[0001] This invention relates to the field of metallurgical sintering technology, specifically to a powder metallurgy sintering process. Background Technology

[0002] Powder metallurgy is a processing technology that involves processing metal powder into a shape and then sintering it at high temperature to form a dense metal structure. It is widely used in the mass production of structural parts, functional parts, and irregularly shaped parts.

[0003] During the sintering process of irregularly shaped products (such as those with suspended, hollow, curved bases, or irregular edges), the following problems often occur due to structural instability:

[0004] The product is prone to deformation: the irregular structure cannot obtain sufficient support during the sintering process, resulting in deformation such as bending and collapse during thermal shrinkage;

[0005] Low furnace loading efficiency: Traditional methods can only load one type of product with a similar structure per furnace, otherwise the sintering compatibility is poor;

[0006] It requires the use of gaskets and post-processing: Usually, a special ceramic gasket (non-shrinkable) needs to be placed at the bottom of the product to form a support structure. However, the thermal shrinkage behavior of ceramic gaskets and metal parts is inconsistent, which can easily lead to the accumulation of local internal stress in the product.

[0007] High post-processing costs: Ceramic support points can cause indentations or bumps, which need to be removed by reshaping or machining, increasing labor, equipment, and time costs;

[0008] Unable to achieve simultaneous structural consistency and sintering efficiency: poor dimensional stability of the product after sintering, and large batch-to-batch consistency deviation.

[0009] Therefore, the powder metallurgy sintering process needs to be redesigned and modified. Summary of the Invention

[0010] To address the problems mentioned in the background art, the present invention aims to provide a powder metallurgy sintering process that improves the formability, disassembly, and sintering behavior matching of the support material, and enables multiple parts to be sintered in the same furnace without deformation. This solves the problems of insufficient support, inconsistent shrinkage, and structural deformation in irregularly shaped products during the sintering process.

[0011] To achieve the above objectives, the present invention provides the following technical solution: a metal injection molding sintering process, comprising the following steps: step a) support preparation, step b) separator selection, step c) assembly and simultaneous sintering, and step d) post-processing.

[0012] Step a) Support preparation: The support green body is prepared by metal injection molding process. The support raw material powder is selected to be the same material as the irregular MIM product being supported or the MIM feed material with the same coefficient of thermal expansion. The feed material is injected into the support mold through the injection molding machine to form a support green body that matches the shape of the product, so as to ensure that the subsequent sintering shrinkage behavior is consistent.

[0013] Step b) Selection of isolation film:

[0014] Choose a suitable material for the isolation sheet. The isolation sheet needs to remain stable or decompose in a controllable manner during the high temperature of the entire process of debinding and sintering of the MIM product. Its main function is to provide physical isolation during the sintering process to prevent the product and the support from diffusing and bonding at high temperature.

[0015] Step c) Assembly and simultaneous sintering: The irregularly shaped MIM product green blank, the selected and treated isolation sheet, and the support green blank prepared by the MIM process are stacked and assembled according to the design position. Ensure that there are matching supports under the suspended and hollow parts of the green blank product that need support and that they are supported by the isolation sheet. Then, the entire assembly is placed stably on the sintering plate of the sintering furnace and pushed into the atmosphere sintering furnace together to execute the standard MIM sintering process curve. This curve includes a slow debinding stage to completely remove the binder in the product and support green blank, and a subsequent high-temperature sintering densification stage.

[0016] Step d) Post-processing: After the sintering process is completed, the furnace is cooled to room temperature. The furnace door is opened and the sintered body is taken out. Due to the role of the isolation layer, the product and the support are easily separated. For the isolation sheet residue that was not completely decomposed during the degreasing / sintering process, it is necessary to remove it mechanically or dissolve it chemically. After the MIM workpiece is separated, it is inspected to obtain the desired product.

[0017] As a preferred embodiment of the present invention, step a) preparation of the support: the particle size distribution of the metal powder in the support feed is matched with that of the product feed, typically D50 is 5~20μm, to ensure similar sintering activity and shrinkage rate.

[0018] As a preferred embodiment of the present invention, step a) preparation of the support body: the binder system of the MIM support body blank is compatible with or the same as that of the product blank, and can be removed synchronously and uniformly during the degreasing stage to avoid deformation or cracking due to differences in degreasing rate. To facilitate demolding, a release agent can be sprayed on the surface of the mold cavity before injection.

[0019] As a preferred embodiment of the present invention, step a) preparation of the support body: After the support body is injection molded, an easy-to-peel release agent is sprayed onto the support surface area in direct contact by spraying. Then, the support body sprayed with the release agent is placed in an oven or heated by other means and kept at a temperature range of 80°C-150°C for 10-30 minutes for curing. After baking, the support body is taken out and allowed to cool naturally to room temperature in a dry environment.

[0020] As a preferred embodiment of the present invention, step a) preparation of the support body: the support body is designed according to the geometry of the suspended and hollowed-out parts of the product, and its top contact surface is designed as a buffer curved surface or a slight honeycomb / dot matrix structure that fits completely with the bottom of the product in order to optimize support and reduce contact area. This complex structure is realized by MIM injection molding process.

[0021] As a preferred embodiment of the present invention, step b) selection of the separator: There are three options for the separator:

[0022] (1) Select ultra-thin, high-flatness ceramic sheets with a thickness controlled in the range of 0.1~0.3mm, which maintain physical and chemical stability in the entire temperature range of MIM debinding and sintering;

[0023] (2) Select high temperature resistant composite films, such as flexible ceramic films reinforced with alumina fibers, which have both high temperature resistance and certain flexibility to adapt to complex curved surfaces;

[0024] (3) Select high-temperature sacrificial spacers that can be thermally decomposed or carbonized in the middle and late stages of degreasing, or composite membranes based on water-soluble polymers.

[0025] When the goal is to sinter products with the highest quality, zero risk, and high added value, ultra-thin, high-flatness ceramic sheets should be selected. When the goal is to process small to medium-sized batches or complex-shaped products that take into account performance, flexibility, and a certain degree of reusability, high-temperature resistant composite films should be selected. When the goal is to achieve large-scale production with high efficiency, low cost, and easy handling, and the product structure allows for it and there are effective post-treatment methods for the residue of the spacers, sacrificial spacers or water-soluble polymer-based composite films can be selected.

[0026] As a preferred embodiment of the present invention, step c) assembly and simultaneous sintering: taking the product green body and support made of 316L stainless steel as an example, a typical MIM sintering curve is executed: first, degreasing is performed slowly under a protective atmosphere, and the temperature is increased at a rate of 0.5-2°C / min in the range of room temperature to 600°C, and the temperature is held at key temperature points such as 200-400°C to thoroughly and gently remove the binder. Then, the temperature is increased at a controllable rate to the sintering temperature of 1360±10°C, and held at this temperature for 1-2 hours. Finally, the product is cooled under high vacuum or high-purity argon.

[0027] As a preferred embodiment of the present invention, step b) selection of the release liner: a fluorine-based non-stick coating or a high-temperature resistant silicone resin barrier layer is coated on at least one side of the release liner to further reduce the risk of adhesion. The selected coating must be able to withstand the organic atmosphere and decomposition products generated during the degreasing stage of the MIM process, and must not react with the sintered material at high temperatures. For Teflon coatings on ceramic sheets: a sintering process is usually adopted, in which a suspension containing Teflon is sprayed or dipped onto the ceramic sheet, and then sintered at a temperature much higher than the melting point of PTFE. During this process, PTFE particles melt, level and solidify to form a chemically stable and firmly adhered non-stick coating. For composite films, PTFE dispersion is impregnated and coated, and then subjected to high-temperature heat treatment to form a continuous film of PTFE on the fiber surface and in the gaps. For high-temperature resistant silicone resin coatings: liquid silicone resin is coated onto the substrate through a thermosetting process and heated at an appropriate temperature to cause a cross-linking reaction and solidify into a tough elastic film.

[0028] As a preferred embodiment of the present invention, step c) assembly and synchronous sintering: during the entire degreasing and sintering process, the product and the support body are highly consistent in terms of material, powder characteristics, green density and thermal expansion coefficient, and undergo almost completely synchronous degreasing shrinkage and sintering shrinkage. The isolation sheet maintains dimensional stability or decomposes at a preset stage, thereby achieving uniform and adaptive support for the product shape and effectively suppressing defects such as deformation, warping and collapse.

[0029] As a preferred embodiment of the present invention, step d) post-processing involves mechanically removing or removing the residual isolation layer through chemical cleaning, water immersion dissolution, ultrasonic cleaning, etc. After inspection, if the removed support is undamaged, it can be reused for sintering the next batch of the same model of product to reduce costs. Since the support is also made using the MIM process, its structure can be optimized for reuse. If it is for single use or needs to be recycled, it can be remelted into powder as waste material of the same type or returned to the feeding preparation process for recycling.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] This invention combines MIM injection molding, homogeneous material design, and contoured support to construct a synchronous adaptive sintering system based on the MIM process. Specifically, a support green body with the same material or matching coefficient of thermal expansion as the irregularly shaped workpiece is produced by MIM injection molding. Synchronous shrinkage is achieved throughout the standard MIM debinding-sintering process, effectively offsetting sintering stress. Through the contoured buffer surface design and easily peelable release layer preparation achievable with MIM, a clean separation interface is constructed while providing precise support, significantly improving the dimensional accuracy of the MIM irregularly shaped workpiece and suppressing deformation. As a MIM molded part, the support body is reusable, and its homogeneous material can be returned to the feeding preparation process to achieve a closed-loop cycle. This ensures high precision of the MIM product while reducing material consumption and overall cost, making this MIM sintering solution highly reliable, efficient in furnace loading, and economically viable.

[0032] 2. This invention achieves deformation-free sintering of irregularly shaped parts through a complete MIM sintering process, including MIM support preparation, isolation interface selection, MIM synchronous sintering assembly, and post-processing. The support uses the same MIM feedstock as the product, and is injection molded to obtain a preform that precisely conforms to the suspended parts of the workpiece. An easily peelable layer can be formed on the surface through spraying and curing. The isolation sheet, depending on requirements, can be a high-flatness ceramic sheet, a high-temperature resistant composite film, etc., to prevent adhesion during high-temperature MIM sintering. During assembly, the MIM workpiece preform, isolation sheet, and MIM support preform are precisely stacked and placed in a sintering furnace to execute a unified MIM sintering curve, achieving simultaneous degreasing and densification. In post-processing, the isolation layer and release layer enable non-destructive separation of the workpiece from the MIM support. The support can be reused or recycled, achieving a balance between deformation suppression, precision maintenance, and cost reduction in MIM production.

[0033] 3. Within the framework of MIM (Metal Injection Molding) technology, this invention optimizes the particle size distribution of the metal powder fed to the support (D50 of 5-20 μm) and employs a compatible binder system to ensure that the support and the product have similar sintering activity and shrinkage rate. An easily peelable layer is formed on the surface of the MIM support green body by spraying a release agent and curing it at low temperature. The separator, acting as a physical barrier layer, remains stable or undergoes controllable decomposition during the MIM degreasing and high-temperature sintering stages, further preventing diffusion and adhesion. The buffered curved surface or lattice structure of the support, achieved through MIM injection molding, reduces the contact area with the workpiece. During MIM sintering, the support and workpiece, with their consistent material and shrinkage behavior, undergo synchronized degreasing shrinkage and sintering shrinkage, while the separator provides stable isolation, together constructing an interface that is both firmly supported and easily separable.

[0034] 4. This invention, based on the characteristics of MIM (Metal Injection Molding) technology, constructs a synchronous adaptive support structure through material matching and contour design. Homogeneous or matched MIM feedstocks ensure a high degree of consistency between the support and the workpiece in terms of thermal expansion and sintering shrinkage behavior, dynamically bonding and offsetting stress throughout the MIM sintering process. The contoured support surface and buffer structure of the MIM injection molding adaptively conform to the workpiece shape, reducing contact stress. During the MIM debinding stage, the adhesives of both are removed synchronously, strengthening the green body skeleton; during the high-temperature MIM sintering stage, both undergo synergistic densification with matched shrinkage rates, providing continuous and stable support; during cooling and post-processing stages, easy separation is achieved through the action of the isolation layer and the release layer. This solution suppresses deformation through synchronous MIM shrinkage, improves efficiency through co-furnace sintering of MIM, and reduces costs through MIM support reuse and material recycling. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Workpiece to be sintered and support:

[0037] Irregularly shaped MIM product blanks: powder injection molded bodies made of materials such as 316L stainless steel, iron-based alloys, and hard alloys.

[0038] Support material: Spherical / near-spherical powder with the same material as the supported product (e.g., 316L stainless steel powder) or a high coefficient of thermal expansion (e.g., iron-based powder with similar composition), and a D50 of 20-30μm.

[0039] Ceramic separator: Alumina (Al2O3) and boron nitride (BN) sheets, 0.1-0.3 mm thick.

[0040] High-temperature resistant composite film: ceramic fiber cloth coated with PTFE (polytetrafluoroethylene) coating material.

[0041] Water-soluble polymer membrane: a composite membrane based on polyvinyl alcohol (PVA, CAS No.: 9002-89-5).

[0042] Organic binder: polyoxymethylene (POM, CAS No.: 9002-81-7) or polypropylene wax (PP wax), 2-5% added.

[0043] Lubricant: Zinc stearate (CAS No.: 557-05-1), ethylene bis-stearamide (EBS, CAS No.: 110-30-5) or graphite powder, added at 0.2-1%.

[0044] Easy-peel release agent: polyethylene glycol (PEG, CAS No.: 25322-68-3) micro powder or borate coated powder.

[0045] Non-stick coating: Teflon (polytetrafluoroethylene PTFE dispersion).

[0046] Barrier layer: High-temperature resistant silicone resin.

[0047] Preparation Example 1: Feeding and Preparation of Support:

[0048] 96 parts (by weight) of 316L stainless steel powder with a D50 of 15μm were weighed as the main raw material. 3.5% polypropylene wax (PP wax) and 0.5% zinc stearate were added as binders and lubricants, respectively. The mixture was stirred evenly in an internal mixer at 150°C to obtain MIM feedstock, which was then granulated for use in injection molding supports.

[0049] Preparation Example 2: Preparation of an easy-to-peel release layer:

[0050] A suspension was prepared by mixing polyethylene glycol (PEG) micropowder with an average molecular weight of 6000 and anhydrous ethanol at a mass ratio of 1:9, and then ultrasonically dispersed until uniform. The suspension was then uniformly sprayed onto the contact surfaces of the injection-molded support preform at a spraying amount of approximately 8 mg / cm². The preform was then placed in a 120°C oven for 20 minutes to allow the ethanol to evaporate and the PEG to melt, forming a uniform release layer. After cooling, the preform was ready for use.

[0051] Preparation Example 3: Design of MIM Support with Buffer Structure:

[0052] For the curved, hollowed-out bottom surface of a certain irregularly shaped structural component, a contour-following support model that perfectly fits the bottom was designed using 3D software. The top contact surface of the support is a buffered curved surface consistent with the bottom of the product, and a micro-dimple array is designed on the curved surface to reduce the contact area. Using this model, a MIM injection molding die was developed, and a green blank of the support structure was injection molded.

[0053] Example 1:

[0054] This embodiment provides a synchronous adaptive sintering process for 316L stainless steel irregular structural parts, which uses intermediate values ​​of various ranges of process parameters, and specifically includes the following steps:

[0055] a) Using the 316L feedstock prepared in Preparation Example 1, a green blank of the contour support was injection molded, and a PEG release layer was sprayed according to the method of Preparation Example 2.

[0056] b) Select an alumina ceramic sheet with a thickness of 0.2 mm and a sintered Teflon coating as the separator.

[0057] c) Precisely assemble the 316L workpiece green, ceramic separator, and support green, and place them in a vacuum sintering furnace. Execution curve: Degrease at 450℃ with a heating rate of 1°C / min and hold for a sufficient period, then sinter at 1360℃ with a heating rate of 5°C / min, hold for 1.5 hours, and cool with the furnace.

[0058] d) After cooling, the workpiece easily separates from the support. The support is found to be intact and reusable after inspection. The workpiece dimensions are accurate and there is no deformation.

[0059] Example 2:

[0060] This embodiment provides a synchronous adaptive sintering process for iron-based alloy structural components, which uses process parameters that are combinations of lower limits of various ranges, and specifically includes the following steps:

[0061] a) The support was injection molded using the same iron-based alloy feedstock (powder D50=5μm) as the workpiece, without applying an additional release layer.

[0062] b) A high-temperature resistant composite film (ceramic fiber cloth covered with PTFE) with a thickness of 0.1 mm was selected as the separator.

[0063] c) After assembly, sinter in a hydrogen-protected atmosphere furnace: slowly degrease to 600°C at 0.5°C / min, then raise the temperature to 1250°C and sinter for 1 hour.

[0064] d) The product did not collapse after separation, and the support body was slightly adhered and could be reused after cleaning.

[0065] Example 3:

[0066] This embodiment provides a synchronous adaptive sintering process for complex porous components, which uses process parameters that are combinations of the upper limits of various ranges, and specifically includes the following steps:

[0067] a) A high-density support body was injection molded using a cemented carbide feeder identical to the workpiece, and a release layer was sprayed according to Preparation Example 2.

[0068] b) PVA-based water-soluble polymer composite membrane was selected as the separator.

[0069] c) After assembly, sinter in a vacuum furnace: degrease at 2°C / min and promote the decomposition of PVA film, then sinter at 1450°C for 2 hours by raising the temperature at 8°C / min.

[0070] d) After cooling, the assembly is immersed in water, the PVA film dissolves, and the workpiece automatically separates from the support. The support is then recycled as raw material.

[0071] Comparative Example 1:

[0072] Compared to traditional methods, this method uses non-shrinkable alumina ceramic shaping pads to support the suspended parts of the same 316L stainless steel irregular-shaped product blank, without using synchronously shrinking metal supports. The same sintering process curve as in Example 1 was executed. After sintering, due to a severe mismatch in shrinkage rates between the product and the ceramic pads (metal shrinks by ~15-20%, ceramic shrinks almost nothing), significant internal stress concentration occurred at the contact edges, causing warping deformation of the product, and leaving indentations on the bottom of the product by the ceramic pads.

[0073] Comparative Example 2:

[0074] Compared to unsupported sintering, the same irregularly shaped green body was placed directly on a sintering plate without any bottom support (process curve same as in Example 1). During sintering, the suspended parts of the product suffered severe sagging and twisting due to gravity and shrinkage stress, resulting in product scrap.

[0075] Comparative Example 3:

[0076] Compared with a support made of a different material. A support made of ordinary low-carbon steel powder (whose shrinkage behavior differs from that of 316L) was used in conjunction with a ceramic spacer to support and sinter the 316L product (process curve same as in Example 1). After sintering, due to the incomplete synchronization of the shrinkage rates of the two materials, microcracks appeared in some parts of the product, and there were friction marks between the support and the product caused by minor misalignment, making separation slightly difficult.

[0077] Test Example 1: Sintering Deformation Control and Dimensional Accuracy Test

[0078] Test method: The sintered workpieces obtained in Examples 1-3 and Comparative Examples 1-3 were measured using a coordinate measuring machine (CMM). Key indicators such as flatness, collapse of suspended parts, and specific contour were measured and compared with the product design CAD model to calculate dimensional deviations.

[0079] Test Results and Analysis: As shown in Table 1, the key dimensional deviations and flatness errors of Examples 1-3 using the synchronous adaptive process of this invention are much smaller than those of the comparative examples. Comparative Example 1 suffers deformation and indentation due to the ceramic gasket; Comparative Example 2, lacking support, suffers severe collapse; Comparative Example 3 exhibits decreased dimensional consistency due to mismatched shrinkage of the support. The process of this invention achieves excellent deformation suppression through material matching and synchronous shrinkage.

[0080] Table 1. Test results of dimensional accuracy and deformation of sintered parts:

[0081] Group Flatness error (mm) Collapse of the suspended section (mm) Critical dimensional deviation (mm) in conclusion Example 1 0.05 0.02 ±0.08 Minimal deformation, precise dimensions Example 2 0.08 0.05 ±0.12 Good deformation control Example 3 0.04 0.01 ±0.05 Excellent deformation control Comparative Example 1 0.25 0.15 (edge ​​warping) ±0.30 Ceramic gaskets cause significant deformation Comparative Example 2 1.50 2.00 (collapse) Unable to measure Without support, it was severely deformed and rendered unusable. Comparative Example 3 0.12 0.08 ±0.20 (with micro-cracks) Mismatched shrinkage leads to decreased quality

[0082] Test Example 2: Furnace Compatibility and Post-Processing Cost Assessment

[0083] Test methods: 1) Furnace compatibility: In the same furnace, three products A, B and C with different shapes but the same material (e.g., all 316L) are loaded simultaneously, and each is equipped with a dedicated synchronous sintering support and isolation plate. After sintering, the pass rate of each product is evaluated. 2) Post-processing cost: The time and cost of post-processing (such as straightening and polishing the shim indentation) required to meet the drawing requirements after sintering in Example 1 and Comparative Example 1 are statistically analyzed.

[0084] Test Results and Analysis: As shown in Table 2, the process of this invention can achieve "co-furnace sintering" of products of different shapes made of the same material, with a high pass rate, significantly improving furnace loading efficiency and production capacity. Regarding post-processing, the product of Example 1 requires little or no processing, while Comparative Example 1 requires extensive straightening and machining due to deformation and indentation, resulting in high costs.

[0085] Table 2 Comparison of Furnace Loading Compatibility and Post-Processing Costs:

[0086] Evaluation Project Example 1 (Process of the Invention) Comparative Example 1 (Traditional Ceramic Gasket) in conclusion Firing pass rate of multiple varieties in the same furnace Product A: 99%, Product B: 98%, Product C: 97% This is not possible; typically, one furnace produces one product. This invention achieves efficient mixed packaging Post-processing time (per piece) ≤0.1 hours (simple check) ≥0.5 hours (orthopedics + polishing) This invention reduces post-processing costs by more than 80%. Support reuse rate >90% (Inspected and undamaged, reusable) 0% (Ceramic gaskets are consumables) The support structure of this invention is recyclable and has low material costs.

[0087] Test Example 3: Support Interface Separability and Product Surface Quality:

[0088] Test method: After sintering and cooling, assess the ease of separation between the product and the support (easy separation, requires slight prying with tools, difficult separation). Observe the surface quality of the contact area between the product and the support using a surface roughness meter and an optical microscope.

[0089] Separability rating: The separation process between the product and the support after sintering and cooling is rated as follows: Grade A (easy manual separation), Grade B (requires simple tools, no damage), Grade C (difficult to separate, may cause damage to the product or support).

[0090] Test Results: In Examples 1-3, due to the use of separators (ceramic sheets, composite films, water-soluble films) and / or easily peelable release layers, the products and supports could be easily separated without damage. The supported surfaces of the products were smooth, without adhesion or damage. In Comparative Example 3 (mismatched support), slight adhesion occurred, making separation slightly more difficult. Although Comparative Example 1 (ceramic gasket) was easily separated, it left indentations on the product surface.

[0091] Table 3. Assessment results of the reusability, separability, and resource utilization of the support structure:

[0092] Group Average number of reuses Difficulty of separation rating Waste recycling performance (when mixed with 20%) Overall support costs (compared to traditional methods) Example 1 8-10 A Green strength retention rate >85%, sintering performance not significantly decreased Reduced by approximately 70% Example 2 5-7 A Green body strength retention rate >80% Reduced by approximately 60% Example 3 3-5 (Long lifespan due to high-pressure molding) A (Water-soluble membrane separation) It can be recycled as a high-quality raw material. Reduced by approximately 65% Comparative Example 1 0 A (but with indentation) Ceramic materials cannot be recycled as metal raw materials Benchmark (100%) Comparative Example 3 1-2 (required repair due to deformation) B The recycled powder has a complex composition and low utilization rate. Reduced by approximately 30%, but the product carries risks.

[0093] Test Example 3 shows that the process of the present invention not only has advantages in product molding quality, but also performs outstandingly in terms of economy and sustainability. The synchronous sintering support can be reused multiple times, and the closed-loop circulation of homogeneous materials significantly reduces material consumption and overall production costs. At the same time, the efficient separation method avoids damage in subsequent processing, making the entire process chain more efficient and environmentally friendly.

[0094] In summary: By using powders with the same or matching coefficients of thermal expansion as the product, injection molding of contour supports, optimizing powder gradation, adding binders / lubricants, spraying an easy-peel layer (such as PEG) on the surface, and designing buffer contact surfaces, the support's good formability, strength, demolding properties, and support fit are ensured.

[0095] Based on product value, batch size, and shape complexity, three options are offered: high-flatness ceramic sheets (zero risk, high quality), high-temperature resistant composite films (flexible and reusable), and water-soluble polymer films (low cost and easy to handle), which can prevent high-temperature diffusion adhesion and ensure easy separation after sintering.

[0096] This invention successfully solves the three major problems of deformation, inefficiency, and high cost in the sintering of irregularly shaped MIM parts. It is an advanced powder metallurgy sintering solution that combines high precision, high efficiency, high economy, and good sustainability.

[0097] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0098] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A metal injection molding sintering process, comprising the following steps: Step a) Support preparation, Step b) Selection of spacer, Step c) Assembly and simultaneous sintering, Step d) Post-processing: Step a) Support preparation: The support green body is prepared by metal injection molding process. The support raw material powder is selected to be the same material as the irregular MIM product being supported or the MIM feed material with the same coefficient of thermal expansion. The feed material is injected into the support mold through the injection molding machine to form a support green body that matches the shape of the product, so as to ensure that the subsequent sintering shrinkage behavior is consistent. Step b) Selection of isolation film: Choose a suitable material for the isolation sheet. The isolation sheet needs to remain stable or decompose in a controllable manner during the high temperature of the entire process of debinding and sintering of the MIM product. Its main function is to provide physical isolation during the sintering process to prevent the product and the support from diffusing and bonding at high temperature. Step c) Assembly and simultaneous sintering: The irregularly shaped MIM product green blank, the selected and treated isolation sheet, and the support green blank prepared by the MIM process are stacked and assembled according to the design position. Ensure that there are matching supports under the suspended and hollow parts of the green blank product that need support and that they are supported by the isolation sheet. Then, the entire assembly is placed stably on the sintering plate of the sintering furnace and pushed into the atmosphere sintering furnace together to execute the standard MIM sintering process curve. This curve includes a slow debinding stage to completely remove the binder in the product and support green blank, and a subsequent high-temperature sintering densification stage. Step d) Post-processing: After the sintering process is completed, the furnace is cooled to room temperature. The furnace door is opened and the sintered body is taken out. Due to the role of the isolation layer, the product and the support are easily separated. For the isolation sheet residue that was not completely decomposed during the degreasing / sintering process, it is necessary to remove it mechanically or dissolve it chemically. After the MIM workpiece is separated, it is inspected to obtain the desired product.

2. The metal injection molding sintering process according to claim 1, characterized in that: Step a) Support preparation: The particle size distribution of the metal powder in the support feed is matched with that of the product feed, usually D50 is 5~20μm, to ensure similar sintering activity and shrinkage rate.

3. The metal injection molding sintering process according to claim 1, characterized in that: Step a) Support preparation: The binder system of the MIM support green body is compatible with or the same as that of the product green body. It can be removed synchronously and uniformly during the degreasing stage to avoid deformation or cracking due to differences in degreasing rate. To facilitate demolding, a release agent can be sprayed on the surface of the mold cavity before injection.

4. The metal injection molding sintering process according to claim 1, characterized in that: Step a) Support preparation: After the support is injection molded, an easy-to-peel release agent can be sprayed onto the support surface area in direct contact by spraying. Then, the support sprayed with the release agent is placed in an oven or heated by other means and kept at a temperature of 80°C-150°C for 10-30 minutes to cure. After baking, the support is taken out and allowed to cool naturally to room temperature in a dry environment.

5. The metal injection molding sintering process according to claim 1, characterized in that: Step a) Support preparation: The support is designed according to the geometry of the suspended and hollowed-out parts of the product. Its top contact surface is designed as a buffer curved surface or a slight honeycomb / matrix structure that fits completely with the bottom of the product to optimize support and reduce contact area. This complex structure is realized by MIM injection molding process.

6. The metal injection molding sintering process according to claim 1, characterized in that: Step b) Selection of separator: There are three options for separators: (1) Select ultra-thin, high-flatness ceramic sheets with a thickness controlled in the range of 0.1~0.3mm, which maintain physical and chemical stability in the entire temperature range of MIM debinding and sintering; (2) Select high temperature resistant composite films, such as flexible ceramic films reinforced with alumina fibers, which have both high temperature resistance and certain flexibility to adapt to complex curved surfaces; (3) Select high-temperature sacrificial spacers that can be thermally decomposed or carbonized in the middle and late stages of degreasing, or composite membranes based on water-soluble polymers. When the goal is to sinter products with the highest quality, zero risk, and high added value, ultra-thin, high-flatness ceramic sheets should be selected. When the goal is to process small to medium-sized batches or complex-shaped products that take into account performance, flexibility, and a certain degree of reusability, high-temperature resistant composite films should be selected. When the goal is to achieve large-scale production with high efficiency, low cost, and easy handling, and the product structure allows for it and there are effective post-treatment methods for the residue of the spacers, sacrificial spacers or water-soluble polymer-based composite films can be selected.

7. The metal injection molding sintering process according to claim 1, characterized in that: Step c) Assembly and simultaneous sintering: Taking the product green body and support made of 316L stainless steel as an example, a typical MIM sintering curve is executed: First, degrease slowly under a protective atmosphere, then heat at a rate of 0.5-2°C / min in the range of room temperature to 600°C and hold at key temperature points such as 200-400°C to thoroughly and gently remove the binder, then heat at a controllable rate to the sintering temperature of 1360±10°C and hold at this temperature for 1-2 hours, and finally cool under high vacuum or high-purity argon.

8. The metal injection molding sintering process according to claim 6, characterized in that: Step b) Selection of release liner: Coat at least one side of the release liner with a fluorine-based non-stick coating or a high-temperature resistant silicone resin barrier layer to further reduce the risk of adhesion. The selected coating must be able to withstand the organic atmosphere and decomposition products generated during the degreasing stage of the MIM process and must not react with the sintered material at high temperatures. For Teflon coatings on ceramic sheets: a sintering process is usually used, in which a suspension containing Teflon is sprayed or dipped onto the ceramic sheet, and then sintered at a temperature much higher than the melting point of PTFE. During this process, PTFE particles melt, level, and solidify to form a chemically stable and firmly adhered non-stick coating. For composite films, PTFE dispersion is impregnated and coated, followed by high-temperature heat treatment, so that PTFE forms a continuous film on the fiber surface and in the gaps. For high-temperature resistant silicone resin coatings: liquid silicone resin is coated onto the substrate through a thermosetting process and heated at an appropriate temperature to cause a cross-linking reaction and solidify into a tough elastic film.

9. The metal injection molding sintering process according to claim 1, characterized in that: Step c) Assembly and synchronous sintering: During the entire degreasing and sintering process, the product and the support body are highly consistent in terms of material, powder characteristics, green density and thermal expansion coefficient, and undergo almost completely synchronous degreasing shrinkage and sintering shrinkage. The isolation sheet remains dimensionally stable or decomposes in a preset stage, thereby achieving uniform and adaptive support for the product shape and effectively suppressing defects such as deformation, warping and collapse.

10. The metal injection molding sintering process according to claim 1, characterized in that: Step d) Post-processing: Remove the isolation layer residue mechanically or through chemical cleaning, water immersion, ultrasonic cleaning, etc. After inspection, if the removed support is undamaged, it can be reused for sintering the next batch of the same model of product to reduce costs. Since the support is also made by the MIM process, its structure can be optimized for reuse. If it is for single use or needs to be recycled, it can be remelted into powder as waste material of the same type or returned to the feeding preparation process for recycling.