A machining process for cemented carbide dies

Abstract

The present application relates to a kind of hard alloy die processing technology, belong to hard alloy die processing technical field, the upper die is divided into two parts of die bridge and upper die split hole outer side portion, the two parts are finely processed respectively, the groove of installation shrink ring is processed at the outer circle of upper die, and shrink ring is manufactured, shrink ring is placed in groove, then the two parts of separate processing are inlaid together using the principle of thermal expansion and cold shrink, form complete upper die, next the installation groove of pressure relief cover is processed at the upper die male head feed port, and pressure relief cover is manufactured and installed;The size and shape of pressure relief cover are matched with installation groove, the upper die and lower die of processing are assembled together, solve the problem that hard alloy die in prior art is extruded in extrusion plant, larger extrusion force is simultaneously extruded to male head direction and outer circle direction, cause upper die to be attacked by pressure from multiple aspects, produce strong shear force, thereby cause broken bridge or crack bridge.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hard alloy die machining, and particularly relates to a machining process of a hard alloy die. BACKGROUND

[0002] The main components of the aluminum alloy "7 series" include zinc elements, such as 7075 alloy, which belongs to the aviation series, is an aluminum-magnesium-zinc-copper alloy, is a super-hard aluminum alloy, has good wear resistance, and can also be strengthened by heat treatment to increase the hardness, which is close to or exceeds the hardness of steel. Due to its high strength and wear resistance, it performs well under extreme conditions, so it is often used in high-tech fields such as aviation, aerospace and military.

[0003] However, there are some problems in the extrusion process of the 7 series hard alloy die in the extrusion plant at present: the 7 series aluminum alloy is a high-strength aluminum alloy containing a high zinc content, which makes it have high strength and hardness during extrusion. Due to these characteristics, the 7 series aluminum alloy is more difficult to deform than other series of aluminum alloys during extrusion forming, so it requires several thousand tons or even larger extrusion force. When processing this hard alloy die, the larger extrusion force will extrude in the public head direction (i.e. the positive direction) and the outer circle direction at the same time, resulting in strong shear force on the upper die due to the attack of pressure from multiple aspects. The pressure at the root of the upper die bridge is the strongest, but the pressure expansion strength is weak, resulting in broken or cracked bridge. To solve this problem, a machining process of a hard alloy die is provided. SUMMARY

[0004] To solve the above problems in the prior art, the application provides a machining process of a hard alloy die, which solves the problem that in the prior art, the larger extrusion force will extrude in the public head direction and the outer circle direction at the same time during the extrusion process of the hard alloy die in the extrusion plant, resulting in strong shear force on the upper die due to the attack of pressure from multiple aspects, thereby causing broken or cracked bridge.

[0005] The object of the application can be achieved by the following technical solutions:

[0006] A machining process of a hard alloy die, comprising the following steps:

[0007] S1: initial machining, according to the design drawing, three-dimensional modeling of the die is carried out, and the die blank is rough machined by using a numerical control machine tool to form the basic shape of the die;

[0008] S2: split machining, according to the characteristics of the pressure, the upper die is divided into two parts, the die bridge connecting the public head part and the upper die split hole outer side part, and the two parts are finely machined respectively to ensure the size and shape of each part are accurate;

[0009] S3: Shrink ring design, a groove for installing the shrink ring is processed at the outer circle of the upper die, and the shrink ring is manufactured and put into the groove;

[0010] S4: Assembly and inlay, the two parts processed separately are inlaid together by using the principle of thermal expansion and cold contraction to form a complete upper die;

[0011] S5: Pressure relief cover design, a mounting groove for the pressure relief cover is processed at the male head feed inlet of the upper die, and the pressure relief cover is manufactured and installed;

[0012] S6: Process the lower die, process the overall shape of the lower die, and assemble the processed upper die and lower die together.

[0013] As a further scheme of the present application, the size and shape of the pressure relief cover in S5 match the mounting groove, and the pressure relief cover needs to be installed to ensure that the pressure acts only on the cover during extrusion.

[0014] As a further scheme of the present application, in step S2, when the upper die is divided into a die bridge connected male head part and an upper die shunt hole outer side part, the thickness of the die bridge connected male head part is increased by 10% to 15% compared to the upper die shunt hole outer side part, and the contact surface of the two parts adopts a stepped fitting structure.

[0015] As a further scheme of the present application, the shrink ring in step S3 is made of elastic material.

[0016] As a further scheme of the present application, the shrink ring is made of 65Mn spring steel, the cross section of the shrink ring body is trapezoidal structure, the radial pre-tightening force of the shrink ring is controlled within the range of 50-80MPa, and the interference fit amount between the shrink ring and the groove body is 0.15-0.25mm.

[0017] As a further scheme of the present application, the thermal expansion and cold contraction inlay process in step S4 specifically includes: heating the upper die shunt hole outer side part to 300-350℃, while cooling the die bridge connected male head part to -50--80℃, and after 30-45 minutes of heat preservation, quickly assembling.

[0018] As a further scheme of the present application, the pressure relief cover in step S5 is made of tungsten-cobalt-based hard alloy, the working surface of the pressure relief cover is provided with a 5°-15° flow guide cone angle, and the bottom of the mounting groove is provided with a 0.2-0.5mm buffer gap.

[0019] As a further scheme of the present application, the flow guide cone angle of the pressure relief cover is specifically designed to be 8°±0.5°, and the working surface is treated by PVD plating layer, the plating layer thickness is 3-5μm, and the plating layer material is TiAlN composite coating.

[0020] As a further scheme of the present application, after the steps S4 and S5 are completed, the assembly is subjected to isostatic pressing treatment, the treatment pressure is 200-250 MPa, the pressure maintaining time is 2-3 hours, and the treatment medium is silicon-based heat-conducting oil.

[0021] As a further scheme of the present application, the lower mold of the step S6 is processed with a micro-texture array on the surface of the mold cavity during the extrusion process in the extrusion plant, the texture unit is a hemispherical pit with a diameter of 50-80 μm, and the area occupancy is controlled at 15%-20%.

[0022] The present application has the following beneficial effects:

[0023] By precisely matching the size of the pressure relief cover with the mounting groove, it is ensured that only the cover body bears the frontal impact pressure after installation, the male body is physically separated from the pressure source through structural isolation, the elastic shrink ring is wrapped around the outer edge of the upper mold, the circumferential pressure fluctuation is absorbed through elastic deformation, the two parts of the upper mold are embedded together by using the thermal expansion and cold contraction principle through the thermal expansion and cold contraction inlay process, and the complete upper mold is formed. The combination of the whole solves the problem that in the prior art, during the extrusion process in the extrusion plant, the large extrusion force extrudes in the direction of the male head and outward at the same time, the upper mold is subjected to pressure attack from multiple aspects, strong shear force is generated, and the bridge is broken or cracked. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to facilitate the understanding of those skilled in the art, the present application will be further described below with reference to the accompanying drawings.

[0025] Figure 1 It is a schematic diagram of the overall structure of the upper mold of the present application.

[0026] Figure 2 It is a schematic diagram of the local structure of the upper mold of the present application.

[0027] Figure 3 It is a schematic diagram of the shrink ring installation of the present application.

[0028] Explanation of main element symbols:

[0029] In the figure: 1, upper mold; 2, male head part; 3, shunt hole; 4, shrink ring. DETAILED DESCRIPTION

[0030] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined invention purpose, the specific implementation, structure, features and effects according to the present application are described in detail as follows in combination with the drawings and preferred embodiments.

[0031] Please refer to Figure 1 - Figure 3 The present embodiment provides a processing technology of a cemented carbide mold, comprising the following steps:

[0032] S1: Initial processing, according to the design drawing, three-dimensional modeling of the mold is carried out, and the mold blank is rough machined by using numerical control machine tool to form the basic shape of the mold;

[0033] S2: Split processing, according to the characteristics of the pressure, the upper die is divided into two parts, the die bridge and the male head part, and the outer side part of the upper die split hole, the two parts are respectively processed by numerical control machine tool or other fine processing tool, to ensure the size and shape of each part is accurate; Split processing can reduce the complexity of processing, improve the processing accuracy, and facilitate the subsequent assembly, accurate control of the size and shape of each part, to ensure the performance and stability of the mold in actual use;

[0034] S3: Shrink ring design, a groove for installing the shrink ring is machined at the outer circle of the upper die, and a shrink ring is manufactured, which is placed in the groove; The shrink ring can enhance the fastening of the mold, prevent the mold from shifting or deforming due to pressure changes during use; The shrink ring is made of elastic material, which wraps the outer circle of the upper die, absorbs the circumferential pressure fluctuation through elastic deformation, and offsets a part of the circumferential tensile stress, preventing the mold from expanding and cracking, and improving the size stability of the mold in continuous extrusion;

[0035] S4: Assembly and inlay, the two parts processed separately are inlaid together to form a complete upper die, using the principle of thermal expansion and cold contraction, the two parts of the upper die are inlaid together, one part is heated to expand, and the other part is inlaid after cold contraction, and the two parts are tightly matched after cooling to form a complete upper die, the assembly method of thermal expansion and cold contraction can ensure that there is no gap between the two parts, improve the sealing and stability of the mold;

[0036] S5: Due to the direct impact of the male head root stress concentration during extrusion, it is easy to cause fracture, for this, a pressure relief cover is designed, an installation groove for the pressure relief cover is machined at the upper die male head inlet, and the pressure relief cover is manufactured and installed; The size and shape of the pressure relief cover match the installation groove, and the pressure relief cover needs to ensure that the pressure only acts on the cover after installation, through the precise matching of the size of the pressure relief cover and the installation groove, only the cover body bears the front impact pressure after installation, through structural isolation, the male body is physically separated from the pressure source, the pressure is limited on the replaceable pressure relief cover, avoiding damage to the male body. Reduce the impact load borne by the die bridge root, prolong the service life of the mold, the pressure impacting the "split hole bridge" and the pressure impacting the "male head" has been separated in advance during the extrusion process, so there is no shear force generated by mutual pulling, and the bridge breakage or crack is also prevented;

[0037] S6: Process the lower die, process the overall shape of the lower die, and assemble the processed upper die and lower die together.

[0038] Aluminum alloy "7 series" main components have zinc elements, such as 7075 alloy, belongs to the aviation series, is aluminum magnesium zinc copper alloy, is super hard aluminum alloy, has good wear resistance, because of its excellent performance in extreme conditions, so often used in aviation, aerospace, military and other high-tech fields, but the current use of 7 series hard alloy die in the extrusion plant extrusion process there are some problems: 7 series aluminum alloy is a high strength aluminum alloy, contains a high zinc content, which makes it has high strength and hardness in the extrusion process, due to these characteristics, 7 series aluminum alloy is more difficult to deform than other series of aluminum alloy in extrusion forming, so it needs thousands of tons or even greater extrusion force, and in the processing of this hard alloy die, the larger extrusion force will be extruded to the public head direction and the outer circle direction, resulting in the upper die being attacked by pressure from multiple directions, generating strong shear force, while the upper die bridge root bears the strongest pressure but the expansion strength is weak, resulting in broken bridge or cracked bridge.

[0039] In order to solve the above problems, in the embodiment, by the characteristics of the pressure, the upper die is divided into two parts, the die bridge connecting the public head part and the upper die shunt hole outside part, the two parts are finely processed respectively to ensure the size and shape of each part is accurate, a slot for installing the contraction ring is processed at the outer circle of the upper die, and the contraction ring is manufactured, the contraction ring is put into the slot, then the two parts processed separately are embedded together by using the principle of thermal expansion and cold contraction to form a complete upper die, next, the installation slot of the pressure relief cover is processed at the public head inlet of the upper die, the pressure relief cover is manufactured and installed; the size and shape of the pressure relief cover match the installation slot, and the pressure relief cover needs to ensure that the pressure only acts on the cover during extrusion after installation, the overall shape of the lower die is processed, the processed upper die and lower die are assembled together, solving the problem that in the prior art, the larger extrusion force will be extruded to the public head direction and the outer circle direction during the extrusion process of the hard alloy die in the extrusion plant, resulting in the upper die being attacked by pressure from multiple directions, generating strong shear force, thereby causing broken bridge or cracked bridge.

[0040] Because the thickness of the die bridge area in the current integral upper die is insufficient, fatigue fracture is easy to occur under the action of shear force, in order to solve this problem, in an embodiment, when the upper die is divided into the die bridge connecting the public head part and the upper die shunt hole outside part in step S2, the thickness of the die bridge connecting the public head part is increased by 10% to 15% than that of the upper die shunt hole outside part, the bending section modulus is enhanced, and the contact surface of the two parts adopts a stepped embedded structure to increase the contact area and the shear resistance, the shear resistance of the die bridge is improved, avoiding tearing caused by multi-directional pressure, and the stepped embedded structure increases the bonding strength of the split assembly.

[0041] It should be noted that the elastic ring is used as a shrink ring, which needs to bear a large force, so the ordinary reinforcing ring is not elastic enough, and the interference fit is easy to fail, leading to the ring body falling off or stress concentration. In order to avoid this problem, in an embodiment, the shrink ring is made of 65Mn spring steel, the cross section of the shrink ring body is trapezoidal structure, the radial pre-tightening force of the shrink ring is controlled in the range of 50-80MPa, the interference fit amount between the shrink ring and the groove body is 0.15-0.25mm, the material is selected from 65Mn spring steel, the yield strength is ≥785MPa, the elastic modulus is adapted to the hard alloy base, the trapezoidal cross section design makes the contact stress of the ring body and the groove wall uniformly distributed, the interference amount of 0.15-0.25mm ensures that the pre-tightening force is controllable, the radial pre-tightening force of 50-80MPa effectively compensates for the thermal expansion difference, avoids the ring body loosening under high temperature working condition, and the trapezoidal cross section reduces the stress concentration coefficient to below 1.2 (the traditional rectangular cross section is 1.8).

[0042] In actual use, due to assembly and inlay, the principle of thermal expansion and cold contraction is adopted, that is, the two parts of the upper mold are inlaid together, one part is heated to expand first, and then the other part is inlaid after cold contraction, and after cooling, the two parts are tightly fitted to form a complete upper mold. However, during this process, the external environment temperature has a certain influence on the heating and cooling process of the assembly, and high or low environment temperature may affect the heating and cooling speed of the assembly, and then affect the formation of temperature difference, which is easy to cause insufficient temperature difference when the split assembly is inlaid, and the micro gap exists in the combined surface of the split assembly when inlaid, which affects the structural strength. In order to solve this problem, in an embodiment, the thermal expansion and cold contraction inlay process in step S4 specifically includes: heating the outer side part of the upper mold flow hole to 300-350℃, while cooling the male head part of the mold bridge to -50--80℃, and after 30-45 minutes of heat preservation, rapid assembly is carried out. The outer side part is heated to 300-350℃ (the linear expansion coefficient of hard alloy is 5.2x10 -6 / ℃), the male head part is deep cooled to -80℃ (contraction rate 0.12%), forming a 0.25-0.35mm assembly gap, the temperature difference recovers after rapid assembly, realizing the molecular level combination of 0.08-0.12mm interference, avoiding the problem of grain coarsening caused by high temperature brazing, and improving the fatigue life of the mold;

[0043] In addition, during mold production, the metal flow impact at the feed inlet may also cause pressure fluctuation, leading to micro-motion wear between the pressure relief cover and the groove body. To this end, in an embodiment, the pressure relief cover of step S5 is made of tungsten-cobalt hard alloy, the working surface of the pressure relief cover is provided with a 5°-15° flow guide cone angle to reduce the impact kinetic energy, and the bottom of the installation groove is provided with a 0.2-0.5mm buffer gap. The 0.2-0.5mm buffer gap allows the pressure relief cover to move slightly, absorbs the instantaneous impact, and also improves the uniformity of the metal flow.

[0044] In order to avoid the metal flow deviation caused by the taper angle deviation, and to cause the surface wear of the pressure relief cover to be intensified, in an embodiment, the flow guide taper angle of the pressure relief cover is specifically designed as 8°±0.5°, the taper angle tolerance is controlled within ±0.5°, 8° is determined as the best balance point through fluid simulation, the working surface is treated by PVD plating, the plating thickness is 3-5 μm, the plating material is TiAlN composite coating, the TiAlN plating (hardness HV3200) reduces the friction coefficient to below 0.15, the plating improves the wear resistance, and the accurate flow guide angle improves the material utilization.

[0045] Further, residual stress is introduced due to the split inlay and the assembly of the pressure relief cover, and the overall bearing capacity of the mold is reduced, in order to solve the problem, in an embodiment, after steps S4 and S5 are completed, the assembly is subjected to isostatic pressing treatment, the treatment pressure is 200-250 MPa, the 200-250 MPa isostatic pressing treatment forces the silicon-based heat-conducting oil to penetrate into the micro gap, uniformly transmits the pressure, and the pressure maintaining time is 2-3 hours, the treatment medium is silicon-based heat-conducting oil, part of the assembly stress is eliminated by pressure maintaining for 2-3 hours, and the silicon oil medium avoids the oxidation problem of the hard alloy caused by traditional water pressure.

[0046] Since the high-zinc aluminum alloy (such as 7075) has strong adhesion, it is easy to cause demolding difficulty and fast mold cavity wear, in an embodiment, the lower mold of step S6 is processed with a micro-texture array on the surface of the mold cavity during the extrusion process in the extrusion factory, the texture unit is a hemispherical pit with a diameter of 50-80 μm, the hemispherical pit with a diameter of 50-80 μm forms a micro oil storage structure, the area occupancy is controlled within 15%-20%, the friction coefficient is reduced, the demolding force is reduced, and finally the continuous production capacity of the mold is improved, and the pit can be repaired by secondary processing.

[0047] The working principle and use process of the application are as follows:

[0048] By the characteristics of pressure, the upper die is divided into two parts, the die bridge male head part and the upper die split hole outside part, and the two parts are finely processed respectively to ensure the size and shape of each part accurate, the groove for installing the shrink ring is processed at the outer circle of the upper die, and the shrink ring is manufactured and put into the groove, then the two parts processed separately are embedded together by using the principle of thermal expansion and cold shrinkage to form a complete upper die, then the installation groove of the pressure relief cover is processed at the male head inlet of the upper die, and the pressure relief cover is manufactured and installed; the size and shape of the pressure relief cover match the installation groove, and the pressure only acts on the cover during extrusion after the pressure relief cover is installed; the overall shape of the lower die is processed, the upper die and the lower die are assembled together, the size of the pressure relief cover and the installation groove are accurately matched to ensure that only the cover body bears the front impact pressure after installation, the male head body is physically separated from the pressure source through structural isolation, at the same time, the upper die outer edge is wrapped by the elastic shrink ring, the circumferential pressure fluctuation is absorbed through elastic deformation, and the two parts of the upper die processed separately are embedded together by using the principle of thermal expansion and cold shrinkage to form a complete upper die, so that the combination of the whole solves the problem that in the prior art, the large extrusion force will extrude in the male head direction and the outer circle direction at the same time during the extrusion process in the extrusion plant, which causes the upper die to be attacked by pressure from multiple aspects and generates strong shear force, resulting in the problem of broken bridge or cracked bridge.

[0049] The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, without departing from the technical solution of the present application. Any modification, change and modification of the above embodiments according to the technical essence of the present application, as long as it does not deviate from the technical solution of the present application, is still within the scope of the present application.

Claims

1. A process for machining a cemented carbide die, characterized in that, It comprises the following steps: S1: initial processing, according to the design drawing, the three-dimensional modeling of the mold is carried out, and the mold blank is rough machined by numerical control machine tool to form the basic shape of the mold; S2: split processing, according to the characteristics of the pressure, the upper die is divided into two parts, the die bridge connecting the male head part and the upper die shunt hole outside part, and the two parts are respectively finely processed to ensure the size and shape of each part is accurate, the thickness of the die bridge connecting the male head part is increased by 10%-15% than the upper die shunt hole outside part when the upper die is divided into the die bridge connecting the male head part and the upper die shunt hole outside part, and the contact surface of the two parts adopts stepped fitting structure; S3: shrink ring design, a groove for installing the shrink ring is processed at the outer circle of the upper die, and the shrink ring is manufactured, the shrink ring is put into the groove, the shrink ring in the step S3 is made of elastic material, the shrink ring is made of 65Mn spring steel, the cross section of the shrink ring body is trapezoidal structure, the radial pre-tightening force of the shrink ring is controlled within 50-80MPa, and the interference fit amount between the shrink ring and the groove body is 0.15-0.25mm; S4: assembly and inlay, the two parts processed separately are inlaid together by using the principle of thermal expansion and cold shrinkage to form a complete upper die; S5: pressure relief cover design, an installation groove for the pressure relief cover is processed at the male head inlet of the upper die, and the pressure relief cover is manufactured and installed; S6: processing the lower die, the overall shape of the lower die is processed, and the processed upper die and lower die are assembled together; The size and shape of the pressure relief cover in the step S5 match the installation groove, and the pressure acting on the cover during extrusion needs to be ensured after the pressure relief cover is installed; the pressure relief cover in the step S5 is made of tungsten-cobalt hard alloy, the working surface of the pressure relief cover is provided with a 5°-15° flow guide cone angle, and the bottom of the installation groove is provided with a 0.2-0.5mm buffer gap.

2. A process for machining a cemented carbide die according to claim 1, characterized in that The thermal expansion and cold shrinkage inlay process in the step S4 specifically comprises: heating the upper die shunt hole outside part to 300-350℃, while cooling the die bridge connecting the male head part to-50--80℃, and after 30-45 minutes of heat preservation, rapid assembly is carried out.

3. A process for machining a cemented carbide die according to claim 2, characterized in that The flow guide cone angle of the pressure relief cover is specifically designed as 8°±0.5°, the working surface of the pressure relief cover is treated by PVD plating layer, the plating layer thickness is 3-5μm, and the plating layer material is TiAlN composite coating.

4. A process for machining cemented carbide dies according to claim 1, characterized in that After the steps S4 and S5 are completed, the assembly is subjected to isostatic pressing treatment, the treatment pressure is 200-250MPa, the pressure holding time is 2-3 hours, and the treatment medium is silicon-based heat conducting oil.

5. A process for machining cemented carbide dies according to claim 1, characterized in that The lower die in the step S6 processes a micro-texture array on the surface of the die cavity during the extrusion process in the extrusion plant, the texture unit is a hemispherical pit with a diameter of 50-80μm, and the area occupancy rate is controlled within 15%-20%.

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