Powder isostatic pressing method

Abstract

A powder isostatic pressing method, characterized in that it includes the following steps: a first step, loading a mixed powder or a compression-molded soft blank into a sheathing mold, wherein the mixed powder or the compression-molded soft blank is a hard alloy or metal ceramic material added with 1-4wt.% paraffin wax; placing the sheathing mold in a vacuum box and vacuum heating it, the heating temperature is 40-60°C, and the insulation time is 20-60min; on the other hand, loading resin into a metal mold, and heating the metal mold until the resin inside it is completely softened; a second step, placing the sheathing mold into the metal mold, and the sheathing mold is immersed in the resin in the metal mold; a third step, using a press to drive the punch of the metal mold, so that the punch enters the mold cavity of the metal mold to apply a pressure of 20-100MPa to the resin molten liquid, maintaining the pressure for 0-30S and then releasing the pressure, taking out the sheathing mold, and cutting the sheathing mold to obtain a formed green sheet.

Description

Technical Field

[0001] The invention relates to a method for forming a cemented carbide / metal ceramic product. The technology is applied to manufacturing the cemented carbide / metal ceramic product. Background Art

[0002] Powder pressing is a method of forming powder into a desired shape using external pressure. Powder pressing is the most commonly used forming method and is widely used in the production of powder metallurgy and fine ceramics. However, during the pressing process, the pressure loss caused by the internal and external friction between particles and between particles and the mold wall causes uneven force on various parts of the green sheet, resulting in uneven density distribution of the green sheet, which ultimately leads to uneven shrinkage of product size and uneven performance. In order to solve this problem, pressing methods such as bidirectional pressing, floating pressing, and pull-down pressing have been developed. Although these methods have improved density uniformity compared to unidirectional pressing, they cannot fundamentally solve the problem of uneven density in powder pressing because they cannot solve the cause of density differences in the forming principle.

[0003] Cold isostatic pressing technology, as an omnidirectional pressing technology, such as Figure 1 As shown, at room temperature, rubber or plastic is usually used as the sheath mold material, liquid is used as the pressure medium, and the general use pressure is 100~630MPa. The powder is formed or the density of the soft blank formed by compression molding is uniformed by omnidirectional pressure. It is mainly used for powder material molding to provide a blank for further sintering. As a molding process, compared with conventional molding technology, the density of isostatic pressing products is high, generally 5~15% higher than unidirectional and bidirectional compression molding, and the density of the pressed blank is uniform. In compression molding, whether it is unidirectional or bidirectional pressing, the density distribution of the pressed blank will be uneven. This density change can often reach more than 10% when pressing complex-shaped products. As an omnidirectional pressure molding technology, although the cold isostatic pressing technology has improved the uniformity of the density of the formed blank, this method has the disadvantages of large equipment investment (special equipment is required), low efficiency, and easy contamination of the blank. Summary of the invention

[0004] The invention aims at the problem that powder compaction easily leads to uneven density, cold isostatic pressing has the problems of large equipment investment, low efficiency and easy contamination of green body, and develops a powder isostatic pressing method.

[0005] In order to achieve the above object, the structural technical solution adopted by the present invention is: a powder isostatic pressing method, characterized in that it comprises the following steps:

[0006] The first step is to load a mixed powder or a compression-molded soft blank into a rubber encapsulation mold, wherein the mixed powder is a hard alloy or a metal ceramic material with 1-4wt.% paraffin wax added thereto, and the material of the compression-molded soft blank is also a hard alloy or a metal ceramic material with 1-4wt.% paraffin wax added thereto; the assembled encapsulation mold is placed in a vacuum box and vacuum-heated at a temperature of 40-60°C for 20-60 minutes; on the other hand, a resin with a softening point of <70°C is loaded into the metal mold, and the metal mold is heated until the resin inside is completely softened;

[0007] The second step is to place the heated encapsulation mold in the first step into the metal mold so that the encapsulation mold is immersed in the resin;

[0008] The third step is to use a press to drive the punch of the metal mold so that the punch enters the mold cavity of the metal mold to apply a pressure of 20-100MPa to the molten resin liquid, maintain the pressure for 0-30S and then release the pressure, take out the sleeve mold, and cut the sleeve mold to obtain the molded blank.

[0009] In the above solution, the outer ring of the metal mold is equipped with an electric heating ring to heat the metal mold. In practice, other existing heating methods can also be used.

[0010] In the above scheme, the metal mold is composed of a female mold, an upper punch and a perforated receiving plate, and the perforated receiving plate is placed in the lower part of the mold cavity of the metal mold; in the second step, the sleeve mold is placed in the center position of the perforated receiving plate.

[0011] In the above scheme, the "resin" can be terpene resin, petroleum resin, phenolic resin and other resins with a softening point <70°C.

[0012] The densification mechanism of the method of the present invention is basically the same as the cold isostatic pressing process. The difference between the two is that the method of the present invention heats the mixture with the forming agent so that the powder particles are rearranged and plastically deformed more fully. Therefore, the method of the present invention can obtain a higher and more uniform green compact density at a lower pressure. The contribution of the low-temperature and low-pressure densification of the present invention is mainly achieved through two ways: first, the lubrication effect produced by the softening of paraffin at low temperature can effectively reduce the internal friction between the particles, making it easy to rearrange the particles and obtain a densely packed structure; second, the paraffin lubricant can greatly reduce the friction between the powder particles and the mold wall, reducing the loss of the applied external pressure. The reduction of the internal friction between the particles and the mold wall friction during the low-temperature isostatic pressing process relatively increases the effective pressing pressure acting on the powder body, which is beneficial to the improvement of the green compact density.

[0013] The method of the present invention has the following advantages:

[0014] (1) Low production cost: no special equipment is required and equipment investment is low.

[0015] (2) High density of pressed green sheets: Under the same pressing pressure, the density of pressed green sheets pressed by the patented process of the present invention is 0.10~0.30g / cm higher than that of the traditional method. 3 .

[0016] (3) High green compact strength: Compared with the traditional molding process, the green compact strength manufactured by the patented process of the present invention can be increased by 10% to 40%, and the surface finish is good.

[0017] (4) Low pressing pressure: To obtain parts with the same density, the pressing pressure of the patented invention is reduced by at least 40 MPa, which is beneficial to improving the life of the equipment and producing products with complex shapes and large areas.

[0018] (5) The density distribution of the pressed green sheet is uniform and the sintering performance is good: The green sheet produced by the patented process of the present invention has a better density uniformity than the parts produced by the traditional method. After sintering, the sintering shrinkage rate is small, and the strength and toughness are higher than those of the traditional process. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the existing cold isostatic pressing technology;

[0020] Figure 2 It is a schematic diagram of the pressing state of the metal mold in Example 1 and Example 2 of the present invention.

[0021] In the figure: 1. upper punch; 2. female die; 3. receiving plate with holes; 4. encapsulating die; 5. resin; 6. mixed powder or compression molded soft blank. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0023] Embodiment 1:

[0024] A powder isostatic pressing method comprises the following steps:

[0025] The first step is to load the mixed powder into the encapsulation mold according to the designed weight. The mixed powder is a cemented carbide or metal ceramic material with 1-4 wt.% paraffin wax added. Specifically, in this embodiment, a WC-Co cemented carbide mixture containing 2wt.% of No. 56 paraffin wax is used, that is, the content of No. 56 paraffin wax is 2wt.%, and the content of the WC-Co cemented carbide mixture is 98 wt.%. The specific ratio of the WC-Co cemented carbide mixture is that the WC particle size is 0.8μm and the content is 90wt.%; the Co particle size is 0.8μm and the content is 10wt.%; after vibrating and compacting evenly, the encapsulation mold filled with the mixture is placed in a vacuum drying oven for vacuum heating. The heating temperature is 40-60°C and the insulation time is 20-60min. The optimal heating temperature is 60°C and the insulation time is 30min.

[0026] On the other hand, a resin with a softening point of less than 70°C is loaded into a metal mold. The resin can be specifically terpene resin. The amount of resin loaded must ensure that the height of the molten resin liquid after melting is not less than the height of the encapsulating mold. The metal mold is heated until the resin inside is completely softened. Specifically, Figure 2 As shown, the outer ring of the metal mold is equipped with an electric heating ring to heat the metal mold.

[0027] The metal mold is composed of a female mold 2, an upper punch 1 and a perforated receiving plate 3, and the perforated receiving plate 3 is placed in the lower part of the mold cavity of the metal mold. Figure 2 shown.

[0028] The second step is to place the cover mold into the metal mold, and immerse the cover mold in the resin in the metal mold. Figure 2 As shown, the encapsulating mold 4 is placed at the center of the perforated material receiving plate 3 in the metal mold, and the encapsulating mold 4 is surrounded by resin 5.

[0029] The third step is to use an ordinary four-column hydraulic press to drive the upper punch 1 of the metal mold, so that the upper punch 1 enters the mold cavity of the metal mold to apply a pressure of 20-100MPa to the molten resin liquid, maintain the pressure for 0-30S and then release the pressure, take out the encapsulating mold 4, and cut the encapsulating mold 4 to obtain the molded blank.

[0030] In specific operation, the metal mold in the first step can be positioned and clamped on the workbench of the ordinary 40-ton four-column hydraulic press at the beginning. The subsequent heating of the metal mold and the placement of the rubber cavity sleeve mold are completed on the press workbench. In the third step, the press is directly used to apply force, which is more convenient to operate.

[0031] The density of the soft green body pressed by the method of this embodiment is 0.10g / cm higher than that of the traditional method. 3 Compared with the traditional molding process, the strength of the pressed green sheet can be increased by 30%; the dimensional accuracy of the hard green sheet after sintering is increased by 20% compared with the traditional molding process.

[0032] Embodiment 2:

[0033] A powder isostatic pressing method comprises the following steps:

[0034] The first step is to wrap a cylindrical metal ceramic compression molding soft blank containing 2.5 wt.% No. 48 paraffin wax in a sleeve mold, wherein the specific material ratio of the metal ceramic compression molding soft blank is: Ti (C, N) 40-65%, Ni powder 22-32%, Mo powder 12-18%, WC powder 5-8%; then, put it into a vacuum drying oven for vacuum heating, the heating temperature is 50°C, and the insulation time is 20 minutes;

[0035] At the same time, a cylindrical metal mold is placed on the workbench of an ordinary four-column hydraulic press on the other side. The outer ring of the metal mold is equipped with an electric heating ring. A certain amount of petroleum resin (resin softening point <60°C) is added to the mold (the height of the molten resin liquid after melting is not less than the height of the rubber soft mold). The mold is heated to 60°C until the resin is completely softened.

[0036] In the second step, the cover mold enclosing the compression molded soft blank in the first step is placed into the mold cavity of the metal mold, and the cover mold enclosing the compression molded soft blank is immersed in the molten liquid of the petroleum resin;

[0037] In the third step, the press is started, the upper punch slowly enters the mold cavity to apply a pressure of 20-100MPa to the molten liquid, the pressure is released after holding for 5S, the upper punch is reset, the encapsulation mold is taken out of the molten liquid, and the molded blank is obtained after the encapsulation mold is cut open.

[0038] The green compact density of the compact produced by the method of this embodiment is 0.20 g / cm higher than that of the conventional method. 3 Compared with the traditional molding process, the strength of the pressed green body can be increased by 40%; the dimensional accuracy of the hard green body after sintering is increased by 30% compared with the traditional molding process.

[0039] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A powder isostatic pressing method, characterized in that: The following steps are involved: The first step is to load a mixed powder or a compression-molded soft blank into a rubber encapsulation mold, wherein the mixed powder is a hard alloy or a metal ceramic material with 1-4wt.% paraffin wax added thereto, and the material of the compression-molded soft blank is also a hard alloy or a metal ceramic material with 1-4wt.% paraffin wax added thereto; the assembled encapsulation mold is placed in a vacuum box and vacuum-heated at a temperature of 40-60°C for 20-60 minutes; on the other hand, a resin with a softening point of <70°C is loaded into the metal mold, and the metal mold is heated until the resin inside is completely softened; The second step is to place the heated encapsulation mold in the first step into the metal mold so that the encapsulation mold is immersed in the resin; The third step is to use a press to drive the punch of the metal mold so that the punch enters the mold cavity of the metal mold to apply a pressure of 20-100MPa to the molten resin liquid, maintain the pressure for 0-30S and then release the pressure, take out the sleeve mold, and cut the sleeve mold to obtain the molded blank.

2. The powder isostatic pressing method according to claim 1, characterized in that: The outer ring of the metal mold is equipped with an electric heating ring to heat the metal mold.

3. The powder isostatic pressing method according to claim 1, characterized in that: The metal mold is composed of a female mold, an upper punch and a perforated receiving plate, and the perforated receiving plate is placed in the lower part of the mold cavity of the metal mold; in the second step, the sheath mold is placed at the center position of the perforated receiving plate.

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