Powder pressing die

Abstract

The invention relates to the technical field of powder metallurgy, and provides a powder pressing die which comprises an outer die body and a plurality of split type inner die bodies, and the outer die body is provided with an outer edge part used for being matched with a pressing equipment installation position and an outer die cavity used for containing the inner die bodies; a plurality of split type inner dies are detachably arranged in the outer die cavity, the split type inner dies are combined to form an inner die cavity used for containing metal powder, a wear-resistant coating is deposited on the surface of the inner wall of the inner die cavity, the split type inner dies are arranged, a high-aspect-ratio inner hole in the inner die is changed into a small-aspect-ratio inner hole, and therefore the wear-resistant coating is formed. Therefore, deep hole coating is equivalent to plane coating, the wear resistance of the mold is improved, and the service life is prolonged.

Description

Technical Field

[0001] The present application relates to the technical field of powder metallurgy equipment, and in particular to a powder pressing die. Background Art

[0002] Powder compacting, a widely used material forming method, is increasingly being applied in fields such as cermets, cemented carbides, and nanocomposites. In particular, in the field of metal powder metallurgy, this technology has become an important preparation method. By filling a mold cavity with powder particles and applying high pressure, a near-net-shape with high density and low porosity can be achieved, effectively avoiding the grain growth problems caused by high temperatures in traditional melt-casting processes.

[0003] At present, the molds used in powder metallurgy are mainly integral. However, this integral mold is prone to cold welding during powder pressing. When cold welds continue to accumulate or the degree of cold welding is severe, the pressing punch cannot be pulled out of the mold. If it is forcibly pulled out, the surface material of the mold will also peel off. This requires stopping the machine for polishing or repairing the mold every 15-20 pressings, greatly reducing work efficiency. Summary of the Invention

[0004] The present application aims to improve at least one technical problem in the background technology.

[0005] The present application provides a powder pressing die, which includes an outer die having an outer edge portion for matching with a mounting position of a pressing device and an outer die cavity for accommodating an inner die; A plurality of split inner molds are detachably arranged in the outer mold cavity. The plurality of split inner molds are combined to form an inner mold cavity for placing metal powder. The inner mold cavity has a structure with a high aspect ratio, and a wear-resistant coating is deposited on the inner wall surface of the inner mold cavity.

[0006] According to some technical solutions of the present application, the split inner mold is a long strip mold, each of the long strip molds has a semicircular groove, the wear-resistant coating is arranged on the inner wall of the semicircular groove, and the inner mold cavity is formed by splicing the semicircular grooves.

[0007] According to some technical solutions of the present application, the semicircular groove is arranged along the length direction of the long strip mold.

[0008] According to some technical solutions of the present application, the high aspect ratio structure has an aspect ratio ranging from 3:1 to 15:1.

[0009] According to some technical solutions of the present application, the split inner mold is a cylindrical mold, and multiple cylindrical molds are arranged in sequence along the length direction of the outer mold. A circular hole is provided through the middle of each cylindrical mold. The inner mold cavity is formed by stacking multiple cylindrical molds, and the wear-resistant coating is provided on the inner wall of the circular hole.

[0010] According to some technical solutions of the present application, the high aspect ratio structure has an aspect ratio ranging from 10:1 to 30:1.

[0011] According to some technical solutions of the present application, the wear-resistant coating is deposited by a PVD process or a PECVD process.

[0012] According to some technical solutions of the present application, the wear-resistant coating is a diamond-like coating or a ceramic-based composite coating.

[0013] According to some technical solutions of the present application, the material of the outer mold is tool steel, and / or the material of the split inner mold is cemented carbide.

[0014] According to some technical solutions of the present application, a limiting step is provided at the bottom of the split inner mold, and the limiting step is used to limit the extension length of the lower punch.

[0015] The powder pressing mold provided in the present application has at least the following beneficial effects: by providing a split inner mold, the high aspect ratio inner mold cavity on the inner mold is converted into a small aspect ratio inner hole, thereby converting the deep hole coating into a shallow surface coating, solving the problem of uneven coating thickness during deep hole coating, improving the wear resistance of the mold, and extending its service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A three-dimensional structural diagram of a powder pressing mold provided in an embodiment of the present application; Figure 2 A bottom structural diagram of a powder pressing mold provided in an embodiment of the present application; Figure 3 for Figure 2 Schematic diagram of the cross section along the AA direction; Figure 4 A schematic structural diagram of a long strip mold provided in an embodiment of the present application; Figure 5 Another schematic diagram of the structure of the powder pressing die provided in an embodiment of the present application; Figure 6 A schematic cross-sectional view of a powder pressing die according to an embodiment of the present invention; Figure 7 A schematic diagram of the explosion structure of a powder pressing die provided in an embodiment of the present application; Figure 8 Schematic diagram of the working principle of punch pressing provided in an embodiment of the present application.

[0017] In the accompanying drawings: 100 - outer mold; 200 - split inner mold; 300 - upper punch; 400 - lower punch; 110 - outer mold cavity; 120 - outer edge; 210 - inner mold cavity; 220 - long strip mold; 221 - semicircular groove; 230 - cylindrical mold; 231 - circular hole; 240 - limiting step. DETAILED DESCRIPTION

[0018] The following describes in detail embodiments of the present application. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application and are not to be construed as limiting the present application.

[0019] In the description of this application, it should be understood that the terms "first", "second", etc. are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Involving orientation descriptions, the orientations or positional relationships indicated, such as up, down, front, back, left, right, etc., are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application. In the description of this application, unless otherwise expressly defined, terms such as setting, installing, and connecting should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in this application in combination with the specific content of the technical solution.

[0020] For the convenience of presentation, before we begin the description, we will explain the terms that will be used in the following description as follows: High aspect ratio (HAR): A structure whose height is much greater than its width. In this context, "aspect ratio" refers to the ratio of the hole depth to the hole diameter. A high aspect ratio hole refers to a hole that can have a height that is several times its width, for example, a hole structure with an aspect ratio greater than 3:1.

[0021] Cemented carbide: An alloy material made from a hard compound of a refractory metal and a binder metal through a powder metallurgy process. It exhibits a range of excellent properties, including high hardness, strong wear resistance, excellent strength and toughness, and heat and corrosion resistance. Its hardness and wear resistance are particularly outstanding. Its hardness remains largely stable even at temperatures of 500°C, and it maintains a high hardness even at temperatures of 1000°C. Due to these properties, cemented carbide is widely used in applications such as sealing components and cutting tools. The cemented carbide used in this application is primarily based on WC (tungsten carbide).

[0022] CVD: Chemical Vapor Deposition, a process that uses gaseous precursors to undergo chemical reactions on solid surfaces to generate and deposit solid thin films or coatings.

[0023] PVD (Physical Vapor Deposition) is a process in which a target material (a target material) is physically evaporated into vapor or gaseous atoms or molecules under vacuum conditions, which then condenses to form a thin film on a substrate surface. PVD is widely used in the tool and mold manufacturing industry. By depositing hard films such as titanium nitride (TiN) and titanium carbide (TiC) on the surfaces of cutting tools, drills, and molds, it significantly improves the hardness, wear resistance, and corrosion resistance of the tools, extending their service life.

[0024] PECVD (Plasma Enhanced Chemical Vapor Deposition) involves generating a glow discharge at the cathode (sample tray) in a process chamber using a low-temperature plasma under low pressure. This discharge (or with the aid of a heating device) heats the sample to a preset temperature. An appropriate amount of process gas is then introduced, where complex chemical and plasma reactions occur under the influence of a radio frequency electric field, ultimately depositing a solid thin film on the sample surface.

[0025] The following combination Figures 1 to 8 The embodiments of the present application are described.

[0026] Currently, the powder metallurgy field generally adopts an integrated mold design. To ensure the surface quality of pressed parts, the inner surface of the mold cavity is often machined to a high cleanliness level (0.025μm). However, under high pressure environments of 400MPa or higher, the lubricating oil film and the oxide layer on the mold or metal powder surface are destroyed by the high pressure, exposing a fresh, active metal surface. When the high pressure exceeds the yield strength limit of the metal (such as aluminum), it triggers plastic flow of the metal atoms. In addition, during the pressing process, the high-speed sliding friction between the metal powder and the mold generates high temperatures, further activating atomic diffusion. The combination of these two factors ultimately leads to cold welding between the metal powder and the inner surface of the mold.

[0027] If the cold welding is mild, it can directly cause scratches, burrs, or even tears on the surface of the pressed part, deteriorating the surface roughness. However, if cold welds accumulate or become severe, the punch can become difficult to remove from the die. Forced removal can cause material to peel off the die surface, requiring the machine to be stopped for polishing or repair every 15-20 presses, significantly reducing production efficiency.

[0028] To avoid cold welding, a wear-resistant coating usually needs to be deposited on the inner surface of the mold. Currently, the processes for preparing such wear-resistant coatings mainly include CVD, PVD or PECVD.

[0029] However, the operating temperature of the conventional CVD process needs to exceed 800°C, which will cause the cobalt phase in the cemented carbide to oxidize or volatilize, resulting in a decrease in the hardness of the mold material. Therefore, in the actual mold coating process, PVD or PECVD processes are often used.

[0030] The PVD process vaporizes target atoms through physical methods such as sputtering and evaporation. These gaseous atoms strike the substrate surface in a linear motion. This makes it difficult to form a uniform coating on the bottom and sidewalls of deep-hole structures due to line of sight limitations. When the aspect ratio is greater than 5:1, the bottom coverage is typically less than 40%.

[0031] The PECVD process relies on plasma (containing high-energy electrons and ions) to activate gas-phase reactions. However, within deep holes, the plasma rapidly decays due to sheath electric field distortion and collision energy loss. Furthermore, Knudsen diffusion dominates the diffusion of the reactant gases toward the bottom of the hole, resulting in lower reactant concentrations at the bottom than at the hole entrance, leading to lower deposition rates and thicknesses at the bottom.

[0032] Therefore, for this type of mold with small pore size and large height, the diffusion of gas molecules in the pores is restricted, so that the film deposition rate at the bottom and side walls of the deep holes is often lower than that in the opening area, which ultimately leads to uneven film thickness, affecting the coating effect and the performance of the mold.

[0033] Based on this, the present application provides a powder pressing die, which includes an outer die 100 having an outer edge portion 120 for matching with a mounting position of a pressing device and an outer die cavity 110 for accommodating an inner die; Multiple split inner molds 200 are detachably arranged in the outer mold cavity 110. The multiple split inner molds 200 are combined to form an inner mold having an inner mold cavity 210 for placing metal powder. The inner mold cavity 210 has a structure with a high aspect ratio, and a wear-resistant coating is deposited on the inner wall surface of the inner mold cavity 210.

[0034] During use, metal powder is placed in the inner die cavity. The upper punch 300 and lower punch 400 each move toward the center of the inner die cavity, then press the metal powder into shape. The upper punch 300 moves upward to exit the die cavity, and the lower punch 400 continues to move upward to push the formed metal block out of the inner die cavity, completing a workflow.

[0035] Therefore, when depositing a wear-resistant coating on the surface of the inner mold cavity, a split inner mold is provided to convert the high aspect ratio inner mold cavity on the inner mold into a small aspect ratio inner hole, thereby converting the deep hole coating into a shallow surface coating, solving the problem of uneven coating thickness during deep hole coating, improving the wear resistance of the mold, and extending its service life.

[0036] Reference Figure 1As shown in the three-dimensional schematic diagram of the pressing mold, in some embodiments, the split inner mold 200 is a long strip mold 220, each of the split inner molds 200 has a semicircular groove 221, the wear-resistant coating is arranged on the inner wall of the semicircular groove 221, and the inner mold cavity 210 is formed by splicing the semicircular grooves 221.

[0037] Furthermore, the number of the long strip molds 220 is two-petal, three-petal or other number of petals. For example, the split inner mold 200 is set to a two-petal type, that is, the split inner mold is set to two long strip molds, each long strip mold 220 is provided with a semicircular groove 221, and the two long strip molds 220 are symmetrically loaded into the outer mold 100, and the semicircular grooves 221 are spliced ​​into a circular inner mold cavity 210, thereby reducing the difficulty of coating.

[0038] In some embodiments, the semicircular grooves 221 are arranged along the length of the split inner mold 200. In other words, the original deep holes are decomposed into shallow grooves, which is equivalent to a flat coating on the grooves. The semicircular grooves 221 are aligned with the length of the elongated mold 220 to ensure uniform force on the powder during pressing, further reducing the aspect ratio to optimize the uniformity of the coating.

[0039] When the aspect ratio of the deep hole is extremely large, the long strip mold 220 may still not meet the coating requirements. The axially stacked cylindrical mold 230 can decompose the deep hole into shorter structures, further reducing the aspect ratio of a single hole. Figures 5 to 7 In some embodiments, the split inner mold 200 is a cylindrical mold 230, and multiple cylindrical molds 230 are arranged in sequence along the length direction of the outer mold 100. A circular hole 231 is provided through the middle of each cylindrical mold 230. The inner mold cavity 210 is formed by stacking multiple cylindrical molds 230, and the wear-resistant coating is provided on the inner wall of the circular hole 231.

[0040] Specifically, cylindrical molds 230 are stacked from top to bottom, with each circular hole 231 aligned to form a deep-hole inner mold cavity 210. After powder is filled, upper and lower punches compress the powder axially. During demolding, the lower punch 400 pushes the product out. Because the hole depth of each cylindrical mold 230 is relatively small, the inner wall of each short hole can be independently coated, creating the equivalent of "segmented planar coating." This segmented coating ensures uniform coating across the entire hole wall.

[0041] The number of cylindrical molds 230 can be determined based on the depth dimension. In some embodiments, the number is set to four, five, or another number. If the number is too small, the single-section hole depth is still relatively large; if the number is too large, higher assembly precision is required. Optionally, the number of the split inner molds 200 is five. For example, if the total hole depth is 50 mm, it can be divided into five sections, each of which is 10 mm. This decomposes the deep hole into five short holes, which can further reduce the depth-to-width ratio of each section of the hole, thereby making the coating deposition more uniform. In addition, the depth of each cylindrical mold can also be determined based on the molding size of the pressed product, ensuring that the size of the final product is smaller than the depth of a single cylindrical mold. In this way, no seams will be produced after the individual finished products are molded, which helps to improve the quality of the finished product.

[0042] Furthermore, the inner die can be divided into three zones based on wear: the upper, forming, and lower sections. The middle forming zone experiences the greatest wear; the upper section also experiences significant wear because the lower punch is used to eject the part from the inner die after forming. The lower section experiences less wear because the part never passes through this zone, resulting in contact wear between the lower punch and the inner die. Based on these wear characteristics, the number of inner dies or the depth of each die can be adjusted to suit the wear levels of different zones.

[0043] In some optional embodiments, elongated molds are suitable for structures with aspect ratios ranging from 3:1 to 12:1. This is due to their greater structural stability within this range, keeping the risk of misalignment of the split planes manageable. Furthermore, compared to solutions employing multiple small cylindrical molds, elongated molds offer lower maintenance costs. After disassembly, only the semicircular groove on one side needs polishing or replating, significantly reducing downtime. Cylindrical molds, on the other hand, are suitable for structures with aspect ratios ranging from 10:1 to 30:1. Their greater bending strength effectively avoids the thermal bending deformation that can occur with monolithic molds with extremely large aspect ratios.

[0044] In some embodiments, the wear-resistant coating is deposited using a PVD or PECVD process. For example, the split inner mold 200 is placed in a deposition apparatus, reactant gases are introduced, and the coating is formed under set temperature or plasma conditions. PVD coatings offer high density and strong wear resistance, while PECVD allows for low-temperature deposition, avoiding annealing and softening of the mold substrate. It is suitable for materials such as tool steel and can be selected based on actual coating needs.

[0045] In some embodiments, the wear-resistant coating is a diamond-like coating or a ceramic-based composite coating. During pressing, the coating withstands powder extrusion and friction. The diamond-like or ceramic coating can further improve wear resistance and extend the life of the mold.

[0046] Conventional mold steel is susceptible to wear when in direct contact with metal powder. If the entire mold is made of ordinary steel, deformation during pressing can occur, leading to larger gaps between the two separate molds after assembly, compromising the precision of the finished product. In some embodiments, since the outer mold 100 does not come into direct contact with the metal powder and is only fixedly connected to the inner and outer molds, the outer mold 100 can be made of a low-wear, high-strength material with a hardness of HRC50 or higher. Alternatively, the outer mold 100 can be made of tool steel or bearing steel, such as T10 tool steel, which has a hardness of HRC50 or higher after full quenching. The high strength of tool steel and bearing steel ensures the stability of the two-piece mold during extrusion or pressing. Combined with a wear-resistant coating, it provides sufficient strength and rigidity to prevent deformation during pressing. Since the inner mold directly contacts the powder, a cemented carbide such as YG10 can be used. This type of cemented carbide has a wear resistance over 10 times that of tool steel, effectively extending the life of the inner mold.

[0047] It is understandable that in this context, both the inner mold and the outer mold can be positioned to improve assembly accuracy by increasing the Morse taper. In addition, locking is achieved by heat installation during installation. However, since this is not an improvement of this application, it will not be described here.

[0048] In some embodiments, a limiting step 240 is provided at the bottom of the split inner mold 200 to limit the insertion length of the lower punch 400. When the lower punch 400 rises, the step surface contacts the top of the punch, preventing it from further penetrating into the inner mold cavity 210, ensuring uniform delivery of the demolding force and protecting the mold from impact damage.

[0049] In summary, the traditional method will cause cold welding after 15-20 pressings, and the surface roughness Ra of the manufactured parts will deteriorate significantly with the increase in the number of pressings: the initial surface roughness Ra is 0.025-0.15μm, and exceeds Ra 0.5μm after 20 pressings; while the split-type improved mold of this application can achieve more than 100 pressings before cold welding occurs, and within 100 times, the surface roughness of the parts can be stably maintained at Ra 0.05-0.1μm.

[0050] Furthermore, certain terms in this specification have been used to describe embodiments of this specification. For example, “one embodiment,” “an embodiment,” and / or “some embodiments” mean that a particular feature, structure, or characteristic described in connection with that embodiment may be included in at least one embodiment of this specification. Therefore, it is emphasized and should be understood that two or more references to “an embodiment,” “one embodiment,” or “an alternative embodiment” in various parts of this specification do not necessarily refer to the same embodiment. Furthermore, particular features, structures, or characteristics may be appropriately combined in one or more embodiments of this specification.

[0051] It should be understood that in the foregoing descriptions of the embodiments of this specification, to facilitate understanding of a feature and to simplify this specification, various features are combined in a single embodiment, figure, or description thereof. However, this does not necessarily mean that these features are combined. When reading this specification, those skilled in the art may extract some of the features and understand them as separate embodiments. In other words, the embodiments of this specification can also be understood as the integration of multiple sub-embodiments. This also applies when each sub-embodiment contains fewer than all the features of a single previously disclosed embodiment.

[0052] Finally, it should be understood that the embodiments of the application disclosed herein are illustrative of the principles of the embodiments of this specification. Other modified embodiments are also within the scope of this specification. Therefore, the embodiments disclosed in this specification are merely examples and not limitations. Those skilled in the art can adopt alternative configurations based on the embodiments in this specification to implement the application in this specification. Therefore, the embodiments of this specification are not limited to the embodiments precisely described in the application.

Claims

1. A powder pressing die, characterized in that: include: An outer mold (100) having an outer edge portion (120) for matching with a mounting position of a pressing device and an outer mold cavity (110) for accommodating the inner mold; A plurality of split inner molds (200) are detachably arranged in the outer mold cavity (110), and the plurality of split inner molds (200) are combined to form an inner mold cavity (210) for placing metal powder. The inner mold cavity (210) has a structure with a high aspect ratio, and a wear-resistant coating is deposited on the inner wall surface of the inner mold cavity (210).

2. The powder pressing die according to claim 1, wherein: The split inner mold (200) is a long strip mold (220), each of the long strip molds (220) has a semicircular groove (221), the wear-resistant coating is provided on the inner wall of the semicircular groove (221), and the inner mold cavity (210) is formed by splicing the semicircular grooves (221).

3. The powder pressing die according to claim 2, wherein: The semicircular groove (221) is arranged along the length direction of the long strip mold (220).

4. The powder pressing die according to claim 2, wherein: The high aspect ratio structure has an aspect ratio ranging from 3:1 to 12:

1.

5. The powder pressing die according to claim 1, wherein: The split inner mold (200) is a cylindrical mold (230), and a plurality of the cylindrical molds (230) are arranged in sequence along the length direction of the outer mold (100). A circular hole (231) is provided through the middle of each cylindrical mold (230). The inner mold cavity (210) is formed by stacking a plurality of the cylindrical molds (230), and the wear-resistant coating is provided on the inner wall of the circular hole (231).

6. The powder compacting die according to claim 5, wherein: The high aspect ratio structure has an aspect ratio ranging from 10:1 to 30:

1.

7. The powder compacting die according to claim 1, wherein: The wear-resistant coating is deposited by a PVD process or a PECVD process.

8. The powder compacting die according to claim 7, wherein: The wear-resistant coating is a diamond-like coating or a ceramic-based composite material coating.

9. The powder compacting die according to claim 1, wherein: The material of the outer mold (100) is tool steel, and / or the material of the split inner mold (200) is hard alloy.

10. The powder compacting die according to claim 1, wherein: A limiting step (240) is provided at the bottom of the split inner die (200), and the limiting step (240) is used to limit the insertion length of the lower punch.

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