Near-net forming mold insert with built-in conformal cooling pipeline and preparation method

Abstract

The invention discloses a near-net forming mold insert with a built-in conformal cooling pipeline and a preparation method, and belongs to the technical field of heterogeneous metal near-net forming. The preparation method comprises the following steps that firstly, a water-cooling pipeline is placed in a sheath to be positioned, the sheath is filled with hot work mold steel powder, vibration, heating vacuumizing and degassing are conducted, and the water-cooling pipeline is cooled to the room temperature; the step is repeated until the powder does not collapse any more, and an assembly is obtained; wherein the overall distance between the assembly and the water-cooling pipeline in the assembly is enlarged by 10%-18% according to the size of a designed drawing; secondly, the assembly is placed in a hot isostatic pressing furnace to be subjected to hot isostatic pressing; and removing the sheath of the assembly after hot isostatic pressing to obtain the near-net formed mold insert with the built-in conformal cooling pipeline. The conformal cooling channel made of stainless steel is embedded in advance before powder filling, and integrated production of the mold insert with the conformal cooling channel is achieved through hot isostatic pressing.

Description

Technical Field

[0001] The invention belongs to the technical field of near-net-shape forming of heterogeneous metals, and in particular relates to a near-net-shape mold insert with a built-in conformal cooling pipeline and a preparation method thereof. Background Art

[0002] With the industry's demand for increasing the service life of die-casting molds and rapidly improving production efficiency, large die-casting molds are gradually being made into parts. The gate sleeves, diverter cones and barrels in the molds that are used in the worst environment are selectively designed as inserts with longer service life and easier replacement. How to increase their service life is the pain point of the industry. In order to increase the service life of the inserts, the temperature of the inserts during service must be effectively controlled, so in the subsequent machining process, cooling channels must be machined on the mold. The cooling channel can be passed through the coolant during service to reduce the service temperature, thereby increasing the service life. Although the above method can play a role in reducing the service temperature, the machined straight water channel is usually connected vertically, and it is difficult to meet the cooling and heat dissipation requirements of different parts in the same insert. To improve cooling and heat dissipation, it is necessary to machine a part of the cooling channel again, and too many cooling channels in the same part will greatly reduce its strength. It is necessary to achieve the best balance between cooling and heat dissipation capacity and strength, and one aspect of performance must be sacrificed.

[0003] With the continuous updating of domestic 3D printing equipment technology, the method of using powder metallurgy to produce metal powder and using 3D printing to produce mold inserts has gradually become the mainstream of the industry. Relying on the characteristics of layer-by-layer powder laying of 3D printing technology, the printed mold inserts can realize the transformation of complex water channels from design to production of physical objects, and the cooling and heat dissipation effect of the inserts has been greatly improved, and the strength has also been improved. However, due to the excessive weight of the inserts compared to other 3D printed parts, the printing cycle is usually 3 to 4 weeks, and the delivery time is too long, which is difficult to meet the needs of today's die-casting industry; at the same time, the surface roughness of 3D printed parts is large and the cooling channels are prone to corrosion. Although the inserts have been effectively surface treated before use, such as surface nitriding, PVD coating, etc., their lifespan is still lower than the ideal lifespan; the most serious thing is that 3D printing can only print a single material, and the type and quality of powder seriously restrict its performance, and high-quality hot die steel powder still relies on a large amount of imports, such as the metal powder produced by Hegnac, and domestic substitution has not yet been completed. Similarly, due to the characteristics of 3D printing, which involves layer-by-layer powder printing, 3D printed parts also face the problem of anisotropy. Due to the different physical and chemical properties in different directions, extra attention must be paid to the direction of the workpiece during machining and service, which reduces the application scenarios of the workpiece by nearly half. In addition, due to the different heat dissipation coefficients in different directions, the thermal field of each part must be considered during design or machining for additional design and processing to avoid problems during service.

[0004] Therefore, the industry urgently needs a production method and product that has a shorter production cycle than 3D printing, is not prone to corrosion, and can achieve the combination of heterogeneous metals. Hot isostatic pressing technology is a technology developed in powder metallurgy. It uses efficient and precise temperature and air pressure control. The pressure on each part of the workpiece in the hot isostatic pressing furnace is the same, and the overall workpiece can be deformed evenly, realizing the sintering of metal powder under high temperature and high pressure conditions, and the shape of the powder forming is controlled by the sleeves of different shapes. The above advantages make hot isostatic pressing applicable to the one-piece forming of heterogeneous materials, but because each part will shrink after hot isostatic pressing, precise positioning cannot be achieved, and it is difficult to achieve the purpose of near-net forming. Summary of the invention

[0005] The object of the present invention is to provide a near-net-shape die steel with built-in conformal cooling duct and a preparation method thereof, so as to solve the problem that it is difficult for a die-casting die to achieve near-net-shape.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for preparing a near-net-shape mold insert with a built-in conformal cooling channel comprises the following steps:

[0008] The first step is to place the water-cooling pipe in the package and position it, and then fill the package with hot-working die steel powder, vibrate, heat, evacuate, and degas. Repeat this step until the powder no longer collapses to obtain an assembly; wherein the overall spacing between the assembly and the internal water-cooling pipe is enlarged by 10%-18% according to the size of the designed drawing;

[0009] In the second step, the assembly is placed in a hot isostatic pressing furnace for hot isostatic pressing; the jacket is removed from the assembly after hot isostatic pressing to obtain a near-net-shape mold insert with a built-in conformal cooling channel.

[0010] As a further illustration of the present invention, the sheath comprises an outer sheath and an inner sheath, and the diameter of the outer sheath ranges from 280 to 550 mm.

[0011] As a further illustration of the present invention, the median particle size D50 of the hot working die steel powder is distributed in a range of 190-210 μm.

[0012] As a further illustration of the present invention, the water cooling pipe is one of 200 series stainless steel, 300 series stainless steel, 400 series stainless steel and 500 series stainless steel.

[0013] As a further illustration of the present invention, in the first step, hot working die steel powder is canned into the package and vibrated until the powder no longer collapses; the heating temperature during hot vacuuming is 640-660°C.

[0014] As a further illustration of the present invention, the water cooling pipe is designed in a corresponding shape according to the working thermal field distribution diagram of the mold insert.

[0015] As a further illustration of the present invention, the water-cooled pipe assembly after filling with powder is subjected to hot isostatic pressing, and during the hot isostatic pressing process, a three-stage heat preservation process and a staged cooling process are performed;

[0016] Three-stage insulation process: In the first stage, the pressure in the furnace is pressurized to 20-35MPa through the hot isostatic pressing system, and then the temperature is increased to 750-900℃ at a heating rate of 10℃ / min. While the temperature is increased, the pressure is continued to be increased to 120-145MPa and maintained for 3-4h;

[0017] In the second stage, the temperature and pressure are raised to 1030-1150℃, 140-170MPa, and kept at this temperature for 0.5-4h;

[0018] In the third stage, the temperature is continuously raised to 1150-1190°C, the pressure is increased to 170-188MPa, and the temperature is kept at this temperature for 0.5-4h;

[0019] The specific process of staged cooling is: cooling to 650-780℃ with the furnace and keeping it warm for 1.5-3h, then cooling to the furnace exit temperature at a cooling rate of 0.9℃ / min.

[0020] The heating and pressurizing were carried out simultaneously, with the heating rate being 10°C / min and the pressurizing rate being 22MPa / h.

[0021] As a further explanation of the present invention, the second stage: heating and pressurizing to 1040-1150°C, 145-160MPa, and keeping warm for 2-4h;

[0022] The third stage: heating and pressurizing to 1150-1175℃, 170-180MPa, keeping warm for 2-4h.

[0023] As a further explanation of the present invention, the second stage: heating and pressurizing to 1150°C, 160MPa, and keeping warm for 3h;

[0024] The third stage: heating and pressurizing to 1165℃, 180MPa, keeping warm for 3h.

[0025] As a further explanation of the present invention, a sleeve is manufactured, the sleeve comprising an outer sleeve, an inner sleeve, an upper end cover and a lower end cover, the outer sleeve of the sleeve is pre-perforated, the upper end cover is provided with a powder loading port and an air extraction port, and both the upper end cover and the lower end cover are provided with concentric holes with the same diameter as the inner sleeve; the lower end cover is vertically welded to the inner sleeve, the water inlet and the water outlet of the stainless steel waterway are respectively inserted into the corresponding openings of the outer sleeve, the outer sleeve 1 inserted into the waterway is combined with the waterway and inserted into the outer periphery of the inner sleeve, the waterway position is fixed with reference to the position of the inner sleeve, and then the connection is welded, and then the outer sleeve is respectively welded to the lower end cover and the upper end cover;

[0026] A near-net-shape mold insert with a built-in conformal cooling channel is prepared by the above preparation method.

[0027] Beneficial effects of the present invention:

[0028] The present invention embeds the conformal cooling channel made of stainless steel before canning the powder, and uses hot isostatic pressing to realize the integrated production of the mold insert with the conformal cooling channel. At the same time, since all parts will shrink after hot isostatic pressing, the reasonable control of the enlargement ratio of the water cooling channel can realize the precise positioning of the conformal cooling channel and achieve the purpose of near net forming.

[0029] The present invention realizes the near-net forming of the water pipe and the mold steel, and the conformal cooling water cooling pipe can perform differential distribution of cooling effect based on the working thermal field distribution of the part mold steel, so as to achieve the purpose of accurate heat dissipation, greatly reduce the working temperature of the part mold steel, and improve the life of the mold steel. At the same time, the forming change of the stainless steel water cooling pipe is controllable, the two heterogeneous materials have good metallurgical combination, the element diffusion is controllable, and the drawbacks of machining and 3D printing are avoided, and the excellent performance of powder hot working die steel and stainless steel are brought into play. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be further described below in conjunction with the accompanying drawings.

[0031] Figure 1 is a schematic diagram of the package of the present invention;

[0032] Figure 2 It is a schematic diagram of multiple groups of water inlet and outlet openings on the outer sheath of the present invention;

[0033] Figure 3 It is a schematic diagram of the structure of the water inlet and outlet openings on the outer sheath of the present invention;

[0034] Figure 4 It is a schematic diagram of the anatomical cross section of the workpiece obtained in the present invention;

[0035] Figure 5 This is a diagram of the exposed defects of the water pipeline in Comparative Example 1 of the present invention;

[0036] Figure 6 is a workpiece surface diagram in Example 5 of the present invention;

[0037] Figure 7 This is a diagram of small pores in the powder matrix in Example 6 of the present invention;

[0038] Figure 8 This is a metallographic image of the annealed state of the junction between the water cooling pipe and the matrix powder in Example 9 of the present invention;

[0039] Fig. 9This is a diagram of the joint of the workpiece of Example 9 of the present invention after hot isostatic pressing and annealing and then quenching;

[0040] Fig.10 This is a diagram of the joint of the workpiece of Example 9 of the present invention after hot isostatic pressing and annealing, followed by quenching and tempering;

[0041] Fig.11 This is a metallographic structure diagram of the powder matrix after hot isostatic pressing and annealing of the workpiece in Example 10 of the present invention;

[0042] Fig.12 This is the metallographic structure diagram of the powder matrix after hot isostatic pressing and annealing of the workpiece in Example 11 of the present invention.

[0043] Figure 1 Middle: 1. Outer sleeve; 2. Inner sleeve; 3. Upper end cover; 4. Lower end cover; 5. Powder filling port; 6. Air extraction port; 7. Water inlet; 8. Water outlet. DETAILED DESCRIPTION

[0044] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] Obviously, the following descriptions are only some examples or embodiments of the present application. For ordinary technicians in this field, the present application can also be applied to other similar scenarios without creative work. In addition, it can also be understood that although the efforts made in this development process may be complicated and lengthy, for ordinary technicians in the field related to the content disclosed in this application, some changes in design, manufacturing or production based on the technical content disclosed in this application are just conventional technical means, and should not be understood as insufficient content disclosed in this application.

[0046] However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially the same structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the following description is provided for those skilled in the art to fully understand the present application and is not intended to limit the subject matter described in the claims.

[0047] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution, and all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0048] A first aspect of an embodiment of the present application provides a method for preparing a near-net-shape mold insert with a built-in conformal cooling channel, comprising the following steps:

[0049] The first step is to design the corresponding shape of the water-cooling pipe according to the working thermal field distribution diagram of the actual application mold insert; the water-cooling pipe is placed in the sleeve for positioning, hot-working mold steel powder is canned in the sleeve, vibrated, heated and vacuumed, degassed, and this step is repeated until the powder no longer collapses to obtain an assembly; wherein the overall spacing of the assembly and the internal water-cooling pipe is proportionally enlarged by 10%-18% according to the size of the designed drawing. The overall spacing of the water-cooling pipe includes the total height of the water pipe, the diameter of each layer, and the layer spacing. The present invention realizes the near-net forming of the water pipe and the mold steel, and the conformal cooling water-cooling pipe can perform differential distribution of the cooling effect based on the working thermal field distribution of the part mold steel, so as to achieve the purpose of precise heat dissipation, greatly reduce the temperature of the part mold steel during operation, and increase the number of molds of the mold steel. The positioning of the water-cooling pipe in the sleeve is determined according to the design requirements, which is an operation well known to those skilled in the art and will not be repeated here.

[0050] In the second step, the assembly is placed in a hot isostatic pressing furnace for hot isostatic pressing; the jacket is removed from the assembly after hot isostatic pressing to obtain a near-net-shape mold insert with a built-in conformal cooling channel.

[0051] After hot isostatic pressing is completed, full annealing and spheroidizing annealing are performed. The full annealing and spheroidizing annealing processes are 880-900°C for 18-25h and 730-740°C for 20-25h. The insulation time is determined according to the size of the workpiece. The annealing process of the subsequent embodiments is the same and will not be repeated. The sheath is removed by machining to obtain a near-net-shaped mold insert with a built-in conformal cooling channel.

[0052] In some specific embodiments, the median particle size D50 of the hot working die steel powder is 190-210 μm. The following embodiments all use the hot working die steel powder in the alloy range shown in Table 1 below, and the composition is not repeated:

[0053] Table 1

[0054]

[0055] In some specific embodiments, the water cooling pipe is one of 200 series stainless steel, 300 series stainless steel, 400 series stainless steel and 500 series stainless steel. The mold insert produced by the present invention effectively avoids the shortcomings of the two manufacturing methods of machining and 3D printing. The cooling water channel can be designed according to the temperature distribution of the thermal field, and the cooling effect is good; the use of stainless steel material enhances the corrosion resistance of the water channel; the overall surface is smooth; the heterogeneous metal metallurgy is well combined, and the element diffusion is controllable, inheriting and giving play to the advantages of hot working die steel powder and stainless steel.

[0056] In some specific embodiments, in the first step, hot working die steel powder is canned into the package, and vibrated until the powder no longer collapses; the heating temperature during hot vacuuming is 640-660°C.

[0057] As a further illustration of the present invention, the water cooling pipe is designed in a corresponding shape according to the working thermal field distribution diagram of the mold insert.

[0058] In some specific embodiments, the water-cooled pipe assembly after filling with powder is subjected to hot isostatic pressing. During the hot isostatic pressing process, a three-stage heat preservation process and a staged cooling process are performed: in the first stage, the pressure in the furnace is pressurized to 20-35 MPa by the hot isostatic pressing pressure system, and then the temperature is increased to 750-900° C. at a heating rate of 10° C. / min, and the pressure is continued to be increased to 120-145 MPa while the temperature is increased, and maintained for 3-4 hours;

[0059] In the second stage, the temperature and pressure are raised to 1030-1150℃, 140-170MPa, and kept at this temperature for 0.5-4h;

[0060] In the third stage, the temperature continues to rise to 1150-1190°C, the pressure is increased to 170-188MPa, and the temperature is kept at this temperature for 0.5-4h.

[0061] The heating and pressurizing were carried out simultaneously, with the heating rate being 10°C / min and the pressurizing rate being 22MPa / h.

[0062] In some specific embodiments, the specific process of the staged cooling is: cooling to 650-780°C with the furnace and keeping it warm for 1.5-3h, and then cooling to the furnace outlet temperature at a cooling rate of 0.9°C / min.

[0063] In some specific embodiments, the second stage: heating and pressurizing to 1040-1150° C., 145-160 MPa, and keeping warm for 2-4 hours;

[0064] The third stage: heating and pressurizing to 1150-1175℃, 170-180MPa, keeping warm for 2-4h.

[0065] In some specific embodiments, the second stage: heating and pressurizing to 1150° C., 160 MPa, and keeping warm for 3 hours;

[0066] The third stage: heating and pressurizing to 1165℃, 180MPa, keeping warm for 3h.

[0067] See also Figure 1As shown, in some specific embodiments, a sleeve is made, and the sleeve includes an outer sleeve 1, an inner sleeve 2, an upper end cover 3 and a lower end cover 4. The outer sleeve 1 in the sleeve is pre-opened, and the upper end cover 3 is provided with a powder loading port 5 and an air extraction port 6. The upper end cover 3 and the lower end cover 4 are both provided with concentric holes with the same diameter as the inner sleeve 2; the lower end cover 4 is vertically welded to the inner sleeve 2, and the water inlet 7 and the water outlet 8 of the stainless steel waterway (water cooling pipe) are respectively inserted into the corresponding openings of the outer sleeve 1, and the outer sleeve 1 inserted into the waterway is combined with the waterway and inserted into the outer periphery of the inner sleeve 2, and the position of the waterway is fixed with reference to the position of the inner sleeve 2, and then the connection is welded, and then the outer sleeve 1 is respectively welded to the lower end cover 4 and the upper end cover 3;

[0068] In some specific embodiments, the inner sleeve 2 is first vertically welded to the lower end cover 4, a group of holes are pre-opened in the outer sleeve 1, and the water inlet 7 and the water outlet 8 of the completed water pipe are respectively inserted into the corresponding holes of the outer sleeve 1. After forming a whole, the inner sleeve 2 and the lower end cover 4 are inserted into the outer periphery of the assembly. With the inner sleeve 2 as a reference, the water pipe is accurately fixed, and then the connection between the water pipe and the outer sleeve 1 is welded first, and after grinding, the remaining places are welded.

[0069] In some specific embodiments, the diameter of the outer sleeve 1 ranges from 280 to 550 mm; the diameter of the inner sleeve 2 is determined during the design and has sufficient processing margins. The number and size of the openings in the outer sleeve 1 are determined according to the number of water inlets 7 and water outlets 8 designed for the water cooling pipe. The water outlet 8 corresponds to the water inlet 7 one by one. Regarding the setting of the water outlet 8 and the water inlet 7, if the water inlet 7 and the water outlet 8 are at the same level, the positions of the water outlet 8 and the water inlet 7 can be swapped. If the water outlet 8 and the water inlet 7 are not at the same level, the principle of bottom-in and top-out is followed. For example, the setting of the water outlet 8 and the water inlet 7 on the sleeve can be Figure 2 or Figure 3 One of them.

[0070] In some specific embodiments, the finished product is dissected, and the cross-sectional view is as follows: Figure 4 As shown, L1 is the distance from the water pipe to the outer wall, and L2 is the distance from the water pipe to the inner wall.

[0071] The values ​​of L1 and L2 should not be too small. If the value of L1 is too small, once a collision occurs, the outer wall will be easily damaged, resulting in water leakage. Because the inner wall is in direct contact with high-temperature molten metal, if the value of L2 is too small, it will not only lead to a decrease in cooling effect, but also reduce the life of the insert.

[0072] A second aspect of the embodiments of the present application provides a near-net-shape mold insert with a built-in conformal cooling channel prepared by the above-mentioned preparation method.

[0073] The following is further described in conjunction with specific embodiments.

[0074] Example 1

[0075] This embodiment provides a near-net-shape mold insert with a built-in conformal cooling channel, which is prepared by the following steps:

[0076] The first step is to design the corresponding shape of the water cooling pipe according to the working thermal field distribution diagram of the actual mold insert; use Q235 steel to make a sleeve, where the outer sleeve diameter is 310mm and the inner sleeve diameter is 75mm, put the water cooling pipe into the sleeve and position it, fill the sleeve with hot working die steel powder (D50 is 202.55μm), vibrate for 20 minutes, heat and evacuate, degas, repeat this step until the powder no longer collapses, and obtain an assembly; wherein, the overall spacing of the assembly and the internal water cooling pipe is proportionally enlarged by 15% according to the size of the designed drawing. The overall spacing of the water cooling pipe includes the total height of the water pipe, the diameter of each layer, and the layer spacing.

[0077] In the second step, the assembly is placed in a hot isostatic pressing furnace for hot isostatic pressing; the jacket is removed from the assembly after hot isostatic pressing to obtain a near-net-shape mold insert with a built-in conformal cooling channel.

[0078] The hot isostatic pressing process:

[0079] In the first stage, the furnace pressure is first increased to 25 MPa, then the temperature is increased to 850°C at a rate of 10°C / min, and the pressure is increased to 135 MPa at the same time, and the temperature is kept for 3 hours;

[0080] In the second stage, the temperature and pressure are raised to 1030℃ and 145MPa at the same time and kept at this temperature for 2h;

[0081] In the third stage, the temperature is raised to 1150℃, pressurized to 170MPa, and kept at this temperature for 2.5h; the furnace is cooled to 700℃ and kept at this temperature for 3h, and then cooled to the furnace exit temperature at a cooling rate of 0.9℃ / min. The positioning of each layer of the water pipe is relatively accurate.

[0082] Example 2

[0083] Compared with Example 1, the difference between this embodiment is that the enlargement ratio is adjusted to 13%, and the other raw materials and preparation process remain the same as those of Example 1. Compared with Example 1, the positioning of the waterway pipeline is more accurate.

[0084] Example 3

[0085] Compared with Example 1, the difference between this embodiment is that the enlargement ratio is adjusted to 10%, and the other raw materials and preparation process remain the same as those of Example 1. After machining to the finished product size, dissection found that the distance L2 from the water channel to the inner wall was small.

[0086] Example 4

[0087] Compared with Example 1, the difference between this embodiment is that the enlargement ratio is adjusted to 18%, and the other raw materials and preparation process remain the same as those of Example 1. After machining to the finished product size, dissection found that the distance L1 from the water channel to the outer wall was small.

[0088] Comparative Example 1

[0089] The difference between this comparative example and Example 1 is that the enlargement ratio is adjusted to 25%, and the other raw materials and preparation process remain the same as those of Example 1. Figure 5 shown.

[0090] Comparative Example 2

[0091] The difference between this comparative example and Example 1 is that the enlargement ratio is adjusted to 20%, and the other raw materials and preparation process remain the same as those of Example 1. The water channel is exposed from the base.

[0092] Comparative Example 3

[0093] The difference between this comparative example and Example 1 is that the enlargement ratio is adjusted to 7%, and the other raw materials and preparation process remain the same as those of Example 1. The water channel is exposed from the base.

[0094] Example 5

[0095] The difference between this embodiment and embodiment 1 is that the hot isostatic pressing process conditions are controlled differently, and the other raw materials and preparation process remain the same as those in embodiment 1.

[0096] Specific conditions during hot isostatic pressing:

[0097] The first section is the same as in Example 1;

[0098] In the second stage, the temperature and pressure are raised to 1040℃ and 145MPa at the same time and kept at this temperature for 2h;

[0099] In the third stage, the temperature is raised to 1150℃, the pressure is increased to 150MPa, and the temperature is kept for 2.5h. The furnace is cooled to 700℃ and kept for 3h. Then, the furnace is cooled to the outlet temperature at a cooling rate of 0.9℃ / min. Figure 6 shown.

[0100] Example 6

[0101] The difference between this embodiment and embodiment 1 is that the hot isostatic pressing process conditions are controlled differently, and the other raw materials and preparation process remain the same as those in embodiment 1.

[0102] Specific conditions during hot isostatic pressing:

[0103] In the first stage, the furnace pressure is first increased to 25 MPa, then the temperature is increased to 850°C at a rate of 10°C / min, and the pressure is increased to 135 MPa at the same time, and the temperature is kept for 4 hours;

[0104] In the second stage, the temperature and pressure are raised to 1140℃ and 145MPa at the same time and kept at this temperature for 4h;

[0105] In the third stage, the temperature is raised to 1150℃, the pressure is increased to 150MPa, and the temperature is kept for 3h; the powder is cooled to 700℃ and kept for 3h, and then cooled to the furnace exit temperature at a cooling rate of 0.9℃ / min. Sampling revealed that there were a small number of small pores in some areas of the matrix, and the density distribution was uneven. The powder matrix small pores are shown in the figure. Figure 7 .

[0106] Example 7

[0107] The difference between this embodiment and embodiment 1 is that the hot isostatic pressing process conditions are controlled differently, and the other raw materials and preparation process remain the same as those in embodiment 1.

[0108] Specific conditions during hot isostatic pressing:

[0109] In the first stage, the furnace pressure is first increased to 25 MPa, then the temperature is increased to 850°C at a rate of 10°C / min, and the pressure is increased to 135 MPa at the same time, and the temperature is kept for 4 hours;

[0110] In the second stage, the temperature and pressure are raised to 1140℃ and 145MPa at the same time and kept at this temperature for 4h;

[0111] In the third stage, the temperature was raised to 1175℃, the pressure was increased to 180MPa, and the temperature was kept for 4h; the furnace was cooled to 700℃ and kept for 3h, and then cooled to the furnace exit temperature at a cooling rate of 0.9℃ / min. Sampling revealed that there were a small number of small pores in some areas of the matrix, and the density distribution was uneven.

[0112] Example 8

[0113] The difference between this embodiment and embodiment 1 is that the hot isostatic pressing process conditions are controlled differently, and the other raw materials and preparation process remain the same as those in embodiment 1.

[0114] Specific conditions during hot isostatic pressing:

[0115] In the first stage, the furnace pressure is first increased to 25 MPa, then the temperature is increased to 850°C at a rate of 10°C / min, and the pressure is increased to 135 MPa at the same time, and the temperature is kept for 3 hours;

[0116] In the second stage, the temperature and pressure are raised to 1150℃ and 160MPa at the same time and kept at this temperature for 3h;

[0117] In the third stage, the temperature was raised to 1175℃, the pressure was increased to 180MPa, and the temperature was kept for 4h; the furnace was cooled to 700℃ and kept for 3h, and then cooled to the furnace outlet temperature at a cooling rate of 0.9℃ / min. Sampling revealed overburning.

[0118] Example 9

[0119] The difference between this embodiment and embodiment 1 is that the hot isostatic pressing process conditions are controlled differently, and the other raw materials and preparation process remain the same as those in embodiment 1.

[0120] Specific conditions during hot isostatic pressing:

[0121] In the first stage, the furnace pressure is first increased to 25 MPa, then the temperature is increased to 850°C at a rate of 10°C / min, and the pressure is increased to 135 MPa at the same time, and the temperature is kept for 4 hours;

[0122] In the second stage, the temperature and pressure are raised to 1150℃ and 160MPa at the same time and kept at this temperature for 3h;

[0123] In the third stage, the temperature is raised to 1165℃, pressurized to 180MPa, and kept at this temperature for 4h; the furnace is cooled to 700℃ and kept at this temperature for 3h, and then cooled to the furnace exit temperature at a cooling rate of 0.9℃ / min. Sampling revealed that there were no pores in all parts, the powder density reached 99.99%, and the welding rate of the interface between the water cooling pipe and the matrix powder was >99.9%. The annealed metallographic image of the junction between the water cooling pipe and the matrix powder is shown in the figure below: Figure 8 As shown in the figure, the left part is powder and the right part is stainless steel water pipe. The workpiece is hot isostatically pressed and annealed before quenching. Fig. 9 As shown, the metallographic structure of the powder matrix after hot isostatic pressing and annealing is as follows Fig.10 shown.

[0124] Example 10

[0125] The difference between this embodiment and embodiment 9 is that the outer sleeve diameter is 467mm and the inner sleeve diameter is 90mm. The other raw materials and preparation process remain the same as those of embodiment 9. There are no pores in each part. The powder density reaches 99.99%. For the annealed state of the matrix powder, the welding rate of the interface between the water cooling pipe and the matrix powder is greater than 99.9%. The metallographic structure of the powder matrix after hot isostatic pressing and annealing of the workpiece is as follows: Fig.11 shown.

[0126] Embodiment 11

[0127] The difference between this embodiment and embodiment 9 is that the outer sleeve diameter is 515mm and the inner sleeve diameter is 90mm. The other raw materials and preparation process are the same as those of embodiment 9. Sampling found that the powder density reached 99.99%, and the welding rate of the interface between the water cooling pipe and the matrix powder was greater than 99.9%. The metallographic structure of the powder matrix after hot isostatic pressing and annealing of the workpiece is shown in the figure below. Fig.12 shown.

[0128] The unnotched impact energy test was carried out in accordance with GB / T229-2020 "Metallic Materials Charpy Pendulum Impact Test Method". To avoid the influence of the decarburized layer on the results of the sample, the sample was sampled with a size of 13*11*55mm, and after heat treatment (quenching and oil cooling at 1035℃, tempering at 590℃ twice), it was flat-ground to a size of 10*7*55mm. The average unnotched impact energy of the workpieces in the above Examples 6 to 10 and the modulus improvement multiples under the same service conditions are shown in Table 2;

[0129] Table 2

[0130] Sample Organizational morphology Average unnotched impact energy (J) Life expectancy improvement Example 5 good 365 33％ Example 6 good 364 35％ Example 7 good 362 32％ Example 8 good 366 32％ Example 9 good 361 35％ Example 10 good 362 34％ Embodiment 11 good 366 32％

[0131] In accordance with GB / T231.1-2018 "Brinell Hardness Test for Metallic Materials", in order to prove that the water pipe has no effect on the macroscopic properties of the powder matrix, the samples after hot pressing annealing in Examples 6 to 10 above were cut into appropriate sizes and heat treated (the quenching temperature was 1035°C, oil cooling was performed, and tempering was performed twice at 590°C). The hardness distribution of the powder matrix, water pipe and powder matrix at different distances is shown in Table 3.

[0132] Table 3

[0133]

[0134] The results of the above embodiments show that in order to achieve precise control of the water channel and avoid serious deviations from the designed workpiece size, the proportional enlargement of the cooling water channel should be controlled at 13% during design. The appropriate hot isostatic pressing process can avoid the defect of pores in the matrix powder. At the same time, the water cooling pipe and the matrix powder form an effective metallurgical bond, and the deviation from the matrix hardness is less than 1 degree, and the strength is effectively guaranteed. At the same time, after the workpieces of different sizes were tested on the machine, the mold life was effectively improved, and the improvement was greater than 30%.

[0135] This invention effectively solves the pain points of short mold life, long 3D printing cycle and high roughness in harsh environments of die-casting molds, with low cost and high efficiency.

[0136] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0137] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a near-net-shape mold insert with a built-in conformal cooling channel, characterized in that: The steps include: The first step is to place the water-cooling pipe in the package and position it, and then fill the package with hot-working die steel powder, vibrate, heat, evacuate, and degas. Repeat this step until the powder no longer collapses to obtain an assembly; wherein the overall spacing between the assembly and the internal water-cooling pipe is enlarged by 10%-18% according to the size of the designed drawing; In the second step, the assembly is placed in a hot isostatic pressing furnace for hot isostatic pressing; the jacket is removed from the assembly after hot isostatic pressing to obtain a near-net-shape mold insert with a built-in conformal cooling channel.

2. The method for preparing a near-net-shape mold insert with built-in conformal cooling channels according to claim 1, characterized in that: The sheath comprises an outer sheath and an inner sheath, and the diameter of the outer sheath ranges from 280 to 550 mm.

3. The method for preparing a near-net-shape mold insert with built-in conformal cooling channels according to claim 1, characterized in that: The median particle size distribution of the hot working die steel powder is 190-210 μm.

4. The method for preparing a near-net-shape mold insert with built-in conformal cooling channels according to claim 1, characterized in that: The water cooling pipe is one of 200 series stainless steel, 300 series stainless steel, 400 series stainless steel and 500 series stainless steel.

5. The method for preparing a near-net-shape mold insert with built-in conformal cooling channels according to claim 1, characterized in that: The heating temperature during heating and vacuuming in the first step is 640-660°C.

6. The method for preparing a near-net-shape mold insert with built-in conformal cooling channels according to claim 1, characterized in that: The water cooling pipe is designed in a corresponding shape according to the working thermal field distribution diagram of the mold insert.

7. The method for preparing a near-net-shape mold insert with built-in conformal cooling channels according to claim 1, characterized in that: During the hot isostatic pressing process, a three-stage heat preservation process and a staged cooling process are performed; Three-stage insulation process: In the first stage, the pressure in the furnace is pressurized to 20-35MPa through the hot isostatic pressing system, and then the temperature is increased to 750-900℃ at a heating rate of 10℃ / min. While the temperature is increased, the pressure is continued to be increased to 120-145MPa and maintained for 3-4h; In the second stage, the temperature and pressure are raised to 1030-1150℃, 140-170MPa, and kept at this temperature for 0.5-4h; In the third stage, the temperature is continuously raised to 1150-1190°C, the pressure is increased to 170-188MPa, and the temperature is kept at this temperature for 0.5-4h; Staged cooling process: cool to 650-780℃ with the furnace and keep warm for 1.5-3h, then cool to the exit temperature at a cooling rate of 0.9℃ / min.

8. The method for preparing a near-net-shape mold insert with built-in conformal cooling channels according to claim 7, characterized in that: The second stage: heating and pressurizing to 1040-1150℃, 145-160MPa, keeping warm for 2-4h; The third stage: heating and pressurizing to 1150-1175℃, 170-180MPa, keeping warm for 2-4h.

9. The method for preparing a near-net-shape mold insert with built-in conformal cooling channels according to claim 7, characterized in that: The second stage: heating and pressurizing to 1150℃, 160MPa, keeping warm for 3h; The third stage: heating and pressurizing to 1165℃, 180MPa, keeping warm for 3h.

10. A near-net-shape mold insert with a built-in conformal cooling channel, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 9.

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