Manufacturing process and equipment of high-performance long-service-life cold working die

Abstract

The invention discloses a manufacturing process and equipment of a high-performance long-service-life cold working die. The process comprises the following steps: quenching and tempering a cold-work die steel blank to obtain a tempered martensite structure; plasma nitrocarburizing is carried out to form a reinforced diffusion layer; the micro-pit array is machined through pulse laser, and an annular heat-affected softening zone is formed around the opening of the pit; depositing a hard coating, and forming a cantilever structure on the edge of the micro pit; wherein plasma nitrocarburizing is carried out in a low-pressure plasma atmosphere, laser processing and coating deposition are carried out in a vacuum or protective atmosphere, and transfer among the steps is not exposed to the atmosphere. The invention further provides corresponding manufacturing equipment which comprises a heat treatment cavity, a plasma nitrocarburizing cavity, a surface micro-texture machining cavity, a coating deposition cavity and a vacuum transfer cavity. According to the invention, the hardness mutation between the coating and the matrix is relieved, a hardness gradient transition structure is constructed, the fatigue stripping resistance of the coating is obviously improved, and the service life of a mold is prolonged.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cold work die manufacturing, and particularly relates to a manufacturing process and equipment of a high-performance long-life cold work die. BACKGROUND

[0002] A cold work die is a core tool in the field of metal plastic working and is widely used in processes such as blanking, cold heading, cold extrusion and deep drawing. Under actual working conditions, the working surface of the cold work die is subjected to the combined action of high contact stress, severe friction and cyclic load, and is extremely prone to wear, adhesion and fatigue failure, which leads to insufficient service life of the die, reduced product precision and further affects production efficiency and economic benefits. Therefore, how to improve the surface hardness, wear resistance and fatigue resistance of the cold work die and prolong its service life has been an important research topic in the field.

[0003] At present, the technical means for improving the surface performance of the cold work die mainly include surface diffusion strengthening and surface coating technology. Plasma nitrocarburizing is a mature surface diffusion strengthening process, which can significantly improve the surface hardness and wear resistance of the die by forming a high-hardness diffusion layer on the surface of the steel substrate. Physical vapor deposition (PVD) hard coating technology further enhances the surface hardness and anti-adhesion performance by depositing hard films such as TiN, TiAlN and CrN on the surface of the die. The composite treatment process combining diffusion strengthening and coating technology uses the diffusion layer to provide support for the hard coating, which improves the load capacity and bonding strength of the coating to a certain extent.

[0004] Surface micro-texturing technology, as a new surface modification method, can store lubricants, capture wear debris and reduce the actual contact area by processing regular geometric features such as micro-pits and micro-grooves on the surface of the friction pair, thereby effectively reducing the friction coefficient and improving the lubrication state. Laser processing has been widely used in the preparation of surface micro-texturing due to its high processing precision and good controllability.

[0005] However, the existing technology has the following problems: first, the heat-affected zone generated during laser processing of micro-pits is considered as a defect and its characteristics cannot be used to improve the mechanical matching between the coating and the substrate; second, there is a geometric discontinuity at the edge of the hard coating, and there is a lack of hardness gradient transition between the coating and the diffusion layer, which leads to easy peeling failure of the coating edge; third, the die surface is easily contaminated by oxidation in the step-by-step processing process, which affects the interface bonding quality. SUMMARY

[0006] In view of the above problems existing in the prior art, the application provides a manufacturing process and equipment of a high-performance long-service-life cold work die, aiming to build a hardness gradient bearing structure, relieve the hardness mutation between the hard coating and the substrate, effectively relieve the stress concentration phenomenon of the micro-pit edge, improve the coating bonding strength and fatigue resistance, and thus significantly prolong the service life of the cold work die.

[0007] To achieve the above-mentioned purpose, the application adopts the following technical solutions: The application provides a manufacturing process of a high-performance long-service-life cold work die, comprising the following steps: S1, quenching and tempering treatment is performed on a cold work die steel blank to obtain a tempered martensite structure, and a die is obtained.

[0008] Specifically, the tempered martensite structure has good strength and toughness matching, and can provide a high-performance substrate support for subsequent surface strengthening treatment. Quenching treatment causes martensite phase change of the die steel, and a high-hardness quenched martensite structure is obtained. Subsequent multiple tempering treatments promote the decomposition and transformation of residual austenite in the quenched martensite, and dispersedly distributed secondary carbides are precipitated, which improves the toughness and dimensional stability of the substrate while maintaining high hardness.

[0009] S2, plasma nitrocarburizing is performed on the die to form a strengthened diffusion layer.

[0010] Specifically, plasma nitrocarburizing causes nitrogen atoms and carbon atoms to combine with alloying elements in the substrate to form nitrides and carbonitrides, and the formed strengthened diffusion layer has a distribution feature of gradually decreasing hardness from the surface to the inside, which provides hardness transition support for the subsequent hard coating.

[0011] S3, a micro-pit array is processed on the working surface of the die by using pulsed laser, and an annular heat-affected softening zone is formed around the mouth of each micro-pit, and the hardness of the annular heat-affected softening zone at the depth position thereof is lower than the hardness of the strengthened diffusion layer which is not affected by laser heat along the radial direction outward at the same depth position.

[0012] Specifically, pulsed laser processing is a processing method for forming micro-pits by using high-energy-density laser pulses to act on the surface of the material to make the local material melt or vaporize instantaneously. When the laser pulses act, heat will be conducted and diffused to the material around the pit, forming an annular heat-affected zone around the pit mouth. Due to the thermal cycle process of rapid heating and cooling experienced by this area, the nitrides in the original diffusion layer partially decompose or coarsen, resulting in a decrease in the hardness of this area, forming an annular heat-affected softening zone. The hardness of the annular heat-affected softening zone is lower than that of the strengthened diffusion layer which is not affected by heat, and can provide deformation coordination ability at the root of the overhanging structure. In the application, the hardness test adopts the nanoindentation method or the micro-Vickers hardness method (HV0.05), and the sampling position is the measuring point on the radial direction of the center cross section of the pit.

[0013] Specifically, the depth position is measured along the normal direction of the mold working surface before laser processing as the reference surface; the contrast measuring point not affected by laser heat is located at a position not less than 3 times the micro-pit depth H radially outward from the micro-pit edge.

[0014] Further, the present application takes full advantage of the heat-affected phenomenon inevitably accompanied by laser processing, and converts the heat-affected softened zone regarded as a defect in the traditional process into a favorable factor for constructing the hardness gradient structure. By reasonably controlling the laser energy density and pulse parameters, the size and hardness reduction degree of the annular heat-affected softened zone can be regulated to match the micro-pit geometric parameters and the coating thickness, so as to realize the optimal design of the hardness gradient.

[0015] S4, depositing a hard coating on the mold working surface to make the hard coating of the micro-pit edge extend inward to form an overhanging structure.

[0016] Specifically, the hard coating is prepared by physical vapor deposition (PVD) method, and atoms or molecules of the target material are deposited on the mold surface in a vacuum environment to form a dense hard film. Since physical vapor deposition has a certain step coverage capability, the coating material will partially enter the micro-pit edge area during the deposition process, forming an overhanging structure extending inward at the pit opening. The overhanging structure partially covers the micro-pit opening, which can protect the lubricant stored in the pit and prevent the filling of the pit by abrasive debris during the mold working process.

[0017] Among them, S2 is carried out in a low-pressure plasma atmosphere formed by introducing nitrogen source and carbon source reaction gas after vacuumizing, S3 and S4 are carried out in vacuum or inert protective atmosphere, and the transfer between steps is completed in vacuum or inert protective atmosphere, so that the mold is not exposed to the atmosphere during S2 to S4. The above environment can avoid oxidation of the mold surface during high temperature treatment, ensure the uniformity of the structure of the diffusion layer and the surface quality; at the same time, it can prevent the oxidation pollution of the high-temperature active surface just completed with nitrocarburizing, and ensure the interface cleanliness and the bonding quality of the subsequent coating.

[0018] In the present application, the root of the overhanging structure refers to the position where the overhanging structure is connected with the main body of the coating on the mold working surface. The key technical feature of the present application is that the bottom of the micro-pit is located in the strengthened diffusion layer, and the root of the overhanging structure is located in the radial range of the annular heat-affected softened zone, and the overhanging structure, the annular heat-affected softened zone and the strengthened diffusion layer not affected by laser heat jointly constitute a hardness gradient bearing structure.

[0019] Further, the working principle of the hardness gradient bearing structure is as follows: when the mold working surface bears a contact load, the load is first borne by the high-hardness hard coating, and then sequentially transmitted to the root of the overhanging structure, the annular heat-affected softened zone and the strengthened diffusion layer. Since the annular heat-affected softened zone to which the root of the overhanging structure is attached has moderate hardness, it can elastically and plastically deform to a certain extent to adapt to the slight displacement of the overhanging structure, so as to avoid excessive stress concentration at the root of the overhanging structure; at the same time, the annular heat-affected softened zone is surrounded and supported by the high-hardness strengthened diffusion layer, thereby ensuring the overall bearing capacity. The hardness gradient transition structure realizes smooth transmission of the load and reasonable distribution of the stress, and effectively improves the bonding strength and anti-fatigue spalling performance of the coating.

[0020] As a preferred solution, the layer depth of the strengthened diffusion layer is D, the depth of the micro-pit is H, and the thickness of the hard coating is t, the ratio of D to t is 30-100, and the ratio of H to t is 2-10. The above ratio relationship ensures that the diffusion layer has sufficient support depth, and at the same time, the pit has a suitable storage volume of lubricant.

[0021] In the present application, the measurement and definition of each parameter are as follows: the layer depth D of the strengthened diffusion layer is the depth value corresponding to the hardness reduction to the base hardness + 50 HV on the microhardness curve; the depth H of the micro-pit is the maximum depth of the pit measured by a profilometer after laser processing and before coating deposition; the thickness t of the hard coating is the average thickness of the coating measured by cross-section metallography on the pit-free flat area; and the micro-pit area coverage rate is the ratio of the sum of the projected areas of all micro-pit openings in a unit area to the unit area.

[0022] As a preferred solution, the width of the annular heat-affected softened zone extending radially outward from the edge of the micro-pit is 0.3-1.0 times the width H, and the size in the depth direction is 0.3-1.0 times the depth H.

[0023] The determination of the above parameter range is based on the following: the radial width and the depth direction size of the annular heat-affected softened zone are associated with the depth H of the micro-pit, so as to ensure that the size of the softened zone matches the geometric parameters of the pit, which can provide necessary deformation coordination ability to relieve stress concentration, and at the same time, the size is not too large to affect the overall bearing capacity.

[0024] As a preferred solution, the overhanging width of the overhanging structure is 0.3 times to 1.5 times the thickness t of the coating, and the included angle between the lower surface of the overhanging structure and the mold working surface is 5°-25°. The above parameter range ensures that the overhanging structure has sufficient rigidity, and the inclination angle is beneficial to the dynamic balance of the lubricant.

[0025] As a preferred solution, in S3, the pulse laser processing is performed when the mold working surface temperature is 120-300℃. This temperature range is conducive to forming a ring-shaped heat-affected softening zone with appropriate size, while reducing the process waiting time.

[0026] As a preferred solution, the diameter of the micro-dimple is 20-100μm, the depth is 5-30μm, and the area coverage is 5-20%. The above parameter range comprehensively considers the balance between lubrication effect and load capacity.

[0027] As a preferred solution, the thickness of the hard coating is 2-5μm, and the deposition temperature is 380-480℃.

[0028] The coating thickness is in the range of 2-5μm, which can provide sufficient wear resistance protection and avoid peeling due to excessive internal stress caused by too thick coating; the deposition temperature is controlled in the range of 380-480℃, which ensures that the coating has good density and bonding strength, and at the same time does not significantly affect the heat treatment structure of the substrate.

[0029] As a preferred solution, the hard coating is any one of TiN layer, TiCN layer, TiAlN layer, CrN layer, AlCrN layer, or a multilayer composite coating composed of any two or more of them. The above coating materials can select single coating or multilayer composite coating according to the working conditions.

[0030] As a preferred solution, the cold work die steel blank includes, by mass percentage: C 0.80-1.30%, Cr 7.0-13.0%, Mo 0.50-1.50%, V 0.50-1.50%, and the balance of Fe and unavoidable impurities.

[0031] The above composition range belongs to a typical high-carbon high-chromium cold work die steel, in which: the carbon content of 0.80-1.30% ensures that the steel has sufficient quenching hardness and wear resistance; the chromium content of 7.0-13.0% is conducive to forming chromium carbide and nitride, improving wear resistance and nitrocarburizing effect; the molybdenum content of 0.50-1.50% can improve the tempering stability and softening resistance; the vanadium content of 0.50-1.50% forms fine dispersed vanadium carbide, refines the grain and improves the wear resistance.

[0032] As a preferred solution, in S1, the quenching temperature is 1000-1080℃, the tempering temperature is 500-560℃, and the tempering times is 2-3 times.

[0033] The quenching temperature is in the range of 1000-1080℃, which can make the alloy carbide fully dissolved in austenite, and obtain higher quenching hardness; the tempering temperature is in the range of 500-560℃, which is near the peak of secondary hardening, and multiple tempering can make the residual austenite fully transform, and fine secondary carbide is precipitated, so that the tempered martensite structure with high hardness and good dimensional stability is obtained.

[0034] As a preferred solution, in S2, the plasma nitrocarburizing temperature is 450-550℃, and the depth of the strengthened diffusion layer is 0.15-0.40mm.

[0035] The nitrocarburizing temperature is controlled in the range of 450-550℃, which is preferably not higher than the tempering temperature, so as to reduce the risk of over-tempering softening of the substrate structure; and the depth of 0.15-0.40mm can provide sufficient support depth for the hard coating.

[0036] As a preferred solution, a solid lubricant layer deposition step is further included between S2 and S3: a solid lubricant layer with a thickness of 0.2-2μm is deposited on the surface of the strengthened diffusion layer, the material of the solid lubricant layer is one or more of MoS2, WS2, h-BN and diamond-like carbon; in S3, the laser processing penetrates the solid lubricant layer to form micro-pits, so that the bottom and / or sidewall of the micro-pit retains the solid lubricant; and in S4, the hard coating is deposited on the solid lubricant layer to seal the solid lubricant in the micro-pit.

[0037] The preferred solution realizes the directional storage and slow-release supply of the solid lubricant by pre-depositing the solid lubricant layer and retaining the lubricant in the micro-pit in the subsequent laser processing, and finally sealing it with the hard coating. During the working process of the mold, as the hard coating is gradually worn, the solid lubricant sealed in the micro-pit is gradually released to the friction interface, continuously providing lubrication, further reducing the friction coefficient and adhesive wear.

[0038] The application also provides a cold work die manufacturing device for implementing the above manufacturing process, which comprises a heat treatment chamber, a plasma nitrocarburizing chamber, a surface micro-texturing chamber, a coating deposition chamber, a vacuum transfer chamber and a multi-parameter coordinated control device, and each process chamber is connected through the vacuum transfer chamber, so that the mold is not exposed to the atmosphere during S2 to S4.

[0039] The key technical feature of the device is that the mold is always in a vacuum or protective atmosphere environment during S2 to S4, avoiding surface oxidation and contamination during transfer between processes. By connecting each process chamber through the central vacuum transfer chamber, the transfer between different processes is carried out in a vacuum or protective atmosphere, completely avoiding the surface oxidation and contamination problem of the mold during transfer in the atmosphere in the traditional split-type device, and ensuring the cleanliness and bonding quality of each strengthened layer interface.

[0040] As a preferred solution, the multi-parameter collaborative control device comprises: a layer depth calculation module for calculating the layer depth D of the strengthened diffusion layer in real time according to the discharge power, processing time and workpiece temperature of the plasma nitrocarburizing chamber; a geometry acquisition module for measuring the depth H and area coverage of the micro-dimple; a coating calculation module for calculating the target coating thickness t according to the layer depth D and dimple depth H and outputting the coating deposition parameters; a stress prediction module for calculating the stress concentration factor according to the micro-dimple geometry parameters and sending a parameter adjustment instruction when the preset threshold is exceeded.

[0041] The multi-parameter collaborative control device realizes intelligent association and adaptive adjustment among the process parameters. The layer depth calculation module predicts the diffusion layer depth by real-time monitoring of the nitrocarburizing process parameters, providing basic data for subsequent processes; the geometry acquisition module obtains the micro-dimple size information of actual processing; the coating calculation module dynamically adjusts the target value of the coating thickness according to the actual results of the previous process, ensuring that the strengthened diffusion layer depth, micro-dimple depth and coating thickness meet the preset proportional relationship; the stress prediction module evaluates the stress concentration degree under the current geometry parameters through finite element calculation or empirical formula, and timely sends an adjustment instruction when the prediction result exceeds the safety threshold, avoiding the processing of surface structures with excessively serious stress concentration.

[0042] As a preferred solution, it further comprises a solid lubricant layer deposition chamber arranged between the plasma nitrocarburizing chamber and the surface micro-texture processing chamber and connected with the vacuum transfer chamber through a vacuum valve.

[0043] The solid lubricant layer deposition chamber is used to implement the preferred process solution of the solid lubricant layer, and the solid lubricant layer is deposited after the completion of plasma nitrocarburizing and before laser micro-dimple processing.

[0044] As a preferred solution, an online profile measuring instrument is arranged in the surface micro-texture processing chamber; the workpiece temperature monitoring device triggers laser processing when the mold surface temperature decreases to the preset temperature range; the laser energy density of the pulsed laser processing device is adjustable, which is used to form an annular heat-affected softening zone around the micro-dimple while forming the micro-dimple.

[0045] The online profile measuring instrument can measure the geometry size of the processed micro-dimple in real time, providing data for the geometry acquisition module and feedback basis for the adjustment of the processing parameters of the subsequent dimple; the workpiece temperature monitoring device ensures that the laser processing is carried out at a suitable substrate temperature to obtain a suitable annular heat-affected softening zone; the adjustable laser energy density enables the operator to adjust the range and degree of the heat-affected softening zone according to specific needs.

[0046] Compared with the prior art, the present application has the following beneficial effects: 1、The present application creatively transforms the heat-affected softening phenomenon inevitably accompanied by laser processing from a defect in traditional processes into a functional feature: by controlling the temperature and energy parameters of laser processing, an annular heat-affected softening zone with moderate hardness is formed around the mouth of the micro-pit, and the root of the overhanging structure of the hard coating is located within the radial range of the softening zone, thereby constructing a hardness gradient bearing structure composed of a hard coating, an annular heat-affected softening zone, and a strengthened diffusion layer. This structure effectively relieves the stress concentration at the edge of the micro-pit, significantly improves the bonding strength and fatigue spalling resistance of the coating, and greatly prolongs the service life of the mold.

[0047] 2、The present application completes the three key processes of plasma nitrocarburizing, laser micro-pit processing, and coating deposition in a continuous vacuum or inert protective atmosphere environment, and transfers between processes through a vacuum transfer chamber. The mold surface is not exposed to the atmosphere during the period from nitrocarburizing to coating deposition, completely avoiding the problem of oxidation of the high-temperature active surface in contact with the atmosphere in traditional step-by-step processes, and significantly improving the cleanliness and bonding quality of the interfaces of each strengthened layer.

[0048] 3、The present application sets a quantitative proportional relationship between the depth of the strengthened diffusion layer, the depth of the micro-pit, and the thickness of the hard coating, and cooperates with the geometric matching design of the annular heat-affected softening zone and the overhanging structure to achieve controllable preparation of the hardness gradient bearing structure, ensuring process stability and product performance consistency.

[0049] 4、The manufacturing equipment provided by the present application adopts an integrated layout with a central vacuum transfer chamber connecting each process chamber, and cooperates with a multi-parameter collaborative control device to realize intelligent association and self-adaptive adjustment of diffusion layer depth prediction, pit geometry collection, coating thickness calculation, and stress concentration evaluation, improving production efficiency and process controllability.

[0050] 5、In the preferred scheme, a solid lubricant layer deposition step is added between plasma nitrocarburizing and laser processing, so that the lubricant is retained inside the micro-pit and sealed with the hard coating, realizing directional storage and slow-release supply of the solid lubricant, further reducing the friction coefficient, reducing adhesive wear, and prolonging the service life of the mold. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 Figure 1 is a schematic diagram of the manufacturing process of the present application; Figure 2 Figure 2 is a schematic diagram of the hardness gradient bearing structure of the present application; Figure 3 Figure 3 is a schematic diagram of the manufacturing equipment of the present application.

[0052] Figure 4 is a schematic diagram of the manufacturing equipment of the present application. DETAILED DESCRIPTION

[0053] The application will be further described in conjunction with the specific embodiments, but not used to limit the application to these embodiments. Those skilled in the art should recognize that the application covers all possible alternatives, improvements and equivalents within the scope of the claims.

[0054] The application will be further described in conjunction with the specific embodiments, but not used to limit the application to these embodiments. Those skilled in the art should recognize that the application covers all possible alternatives, improvements and equivalents within the scope of the claims. Figure 1 , the hardness gradient bearing structure is shown in Figure 2 , and the manufacturing equipment structure is shown in Figure 3 . Embodiment 1

[0055] The embodiment provides a manufacturing process of a high-performance long-life cold work die. S1, quenching and tempering treatment

[0056] The cold work die steel is selected as the die material, and the chemical composition of the cold work die steel is as follows in terms of mass percentage: C 1.00%, Cr 8.5%, Mo 1.00%, V 0.80%, and the balance of Fe and inevitable impurities.

[0057] The die steel blank is placed in a heat treatment cavity for quenching treatment: heated to 850 ℃ at a heating rate of 10 ℃ / min for preheating, and the internal temperature gradient of the workpiece is eliminated; then heated to 1040 ℃ for 40 min, so that the carbide is fully dissolved in austenite to obtain a high-temperature austenite structure with uniform composition; then high-purity nitrogen gas is used for gas quenching cooling, the gas pressure is 0.4 MPa, and the cooling is performed to room temperature to obtain a quenched martensite structure.

[0058] After quenching, three times of tempering treatment is performed: the first tempering temperature is 530 ℃, the holding time is 2 h, and the air cooling is performed to room temperature; the second tempering temperature is 520 ℃, the holding time is 2 h, and the air cooling is performed to room temperature; the third tempering temperature is 510 ℃, the holding time is 2 h, and the air cooling is performed to room temperature. After multiple tempering treatment, a tempered martensite structure is obtained, and the die is obtained, and the matrix hardness reaches 60-62 HRC. S2, plasma nitrocarburizing

[0059] The die after the heat treatment is transferred into a plasma nitrocarburizing cavity through a vacuum transfer cavity, and after vacuumizing, process gas is introduced, and plasma nitrocarburizing treatment is performed in a low-pressure plasma atmosphere.

[0060] Firstly, the chamber is vacuumed to below 5 Pa to remove the residual air and moisture in the chamber. Then, the process gas is introduced, and in this embodiment, a mixed gas of ammonia and carbon dioxide is used, with a flow ratio of NH3 to CO2 being 95:5, and the working gas pressure is maintained at 400 Pa. The glow discharge is started, the workpiece is connected to a negative high voltage as the cathode, and the chamber wall is connected to the ground as the anode, with a discharge voltage of 700 V to form a stable glow discharge.

[0061] The co-diffusion temperature is controlled at 500°C, which is lower than the tempering temperature to avoid over-tempering softening of the matrix, while ensuring sufficient diffusion rate. The treatment time is 8 h.

[0062] After the co-diffusion is completed, the obtained reinforced diffusion layer has the following characteristics: the layer depth D is 0.25 mm (250 μm); the surface hardness is 1000 HV; the hardness decreases along the depth direction, and at a depth of about 0.20 mm, the hardness decreases to 800 HV, and at a depth of about 0.25 mm, the hardness decreases to about 750 HV (the matrix hardness + 50 HV), and thereafter, it continues to smoothly transition to the matrix hardness. S3, laser micro-pit processing

[0063] The mold is transferred to the surface micro-texture processing chamber while maintaining the vacuum environment continuously with S2. A workpiece temperature monitoring device is used to monitor the mold surface temperature in real time, and when the temperature naturally decreases to 200°C, the pulsed laser processing is started.

[0064] The pulsed laser processing device is used for micro-pit processing, and the laser parameters are as follows: wavelength 1064 nm, pulse width 100 ns, repetition frequency 20 kHz, single pulse energy 50 μJ, focused spot diameter 30 μm, and laser energy density about 7 J / cm 2 A two-dimensional galvanometer scanning system is used to control the laser spot to perform fixed-point processing on the working surface of the mold according to the preset pattern, and the micro-pit array adopts a square arrangement, with a center-to-center distance of 180 μm. Five laser pulses are applied to each pit position, and the micro-pit is formed by rapid melting and partial vaporization of the material.

[0065] After processing, an online profile measuring instrument is used to measure the geometric parameters of the micro-pit: the pit diameter is about 50 μm, the depth H is about 15 μm, and the area coverage rate is about 6%. The pit edge shape is regular, showing a smooth circular arc transition, and there is no obvious splash and recast layer accumulation.

[0066] During laser processing, the heat from the pulsed laser is conducted and diffused to the material surrounding the pit, forming a ring-shaped heat-affected diffusion zone around the pit opening. The hardness distribution of the softened zone was measured radially using a nanoindenter: the width of the softened zone extending radially outward from the pit edge is approximately 7 μm, which is 0.47 times the pit depth H; the dimension along the depth direction is approximately 6 μm, which is 0.40 times the pit depth H; the average hardness of the softened zone is approximately 780 HV, lower than the hardness of the unaffected diffusion layer (1000 HV), providing the necessary deformation compatibility to alleviate stress concentration. S4, Hard Coating Deposition

[0067] Maintaining a continuous vacuum environment, the mold is transferred to the coating deposition chamber through a vacuum transfer chamber, and a TiAlN hard coating is deposited using a physical vapor deposition device with multi-arc ion plating technology.

[0068] First, the mold surface is cleaned by argon ion etching: high-purity argon gas is introduced at a pressure of 0.5 Pa, a -800V pulse bias voltage is applied to the workpiece, and the cleaning time is 15 min.

[0069] Then, a TiAlN coating deposition was performed: using Ti... 50 Al 50 (Atomic ratio) alloy target material, target diameter 100mm, arc current 100A; high-purity nitrogen gas is introduced as the reactant gas, nitrogen partial pressure 0.8Pa; -100V pulse bias voltage is applied to the workpiece to promote ion bombardment and improve coating density; deposition temperature 420℃; deposition time 90min. To improve the bonding strength between the coating and the substrate, a gradient transition design is adopted: first deposit a pure Ti metal transition layer of about 0.3μm, then gradually introduce nitrogen gas to deposit a TiN transition layer, and finally deposit a TiAlN functional layer.

[0070] Observation of the cross-sectional morphology revealed that the total coating thickness was approximately 3.0 μm, of which the TiAlN functional layer thickness was approximately 2.5 μm and the surface hardness was approximately 2600 HV; the cantilever width of the cantilever structure was approximately 1.2 μm, which is 0.4 times the coating thickness t; and the angle between the lower surface of the cantilever structure and the working surface of the mold was approximately 12°.

[0071] In this embodiment, the depth D of the enhanced diffusion layer is 250 μm, the depth H of the micro-pits is 15 μm, and the thickness t of the hard coating is 3.0 μm.

[0072] In this embodiment, D / t≈83, H / t=5. Example 2

[0073] The selected material is cold work die steel with the following chemical composition by mass percentage: C 0.85%, Cr 7.5%, Mo 0.60%, V 0.55%, with the balance being Fe and unavoidable impurities.

[0074] S1. Quenching and tempering treatment: Quenching temperature 1010℃, holding temperature 35min; tempering temperature 550℃, tempering twice, matrix hardness 58-60HRC.

[0075] S2. Plasma nitrocarburizing: This process is carried out in a plasma nitrocarburizing chamber with a mixed gas flow ratio of NH3 to CH4 of 92:8, a working pressure of 350 Pa, a discharge voltage of 680 V, a co-diffusion temperature of 480 °C, and a treatment time of 4 h. The resulting reinforced diffusion layer has a depth D of 0.15 mm (150 μm) and a surface hardness of 920 HV.

[0076] S3. Laser Micro-Dimple Machining: After transferring to the surface micro-texturing cavity, machining begins when the mold surface temperature drops to 150℃. Laser parameters: pulse width 80ns, single pulse energy 35μJ, focused spot diameter 25μm. Micro-dimple diameter approximately 40μm, depth H approximately 10μm, area coverage 8%. Annular heat-affected softening zone radial width approximately 3μm (0.30H), depth dimension approximately 3μm (0.30H), hardness approximately 760HV.

[0077] S4. Hard Coating Deposition: The coating is transferred to the coating deposition chamber via a vacuum transfer chamber and deposited using multi-arc ion plating at a deposition temperature of 400℃. The coating thickness t is 5.0μm, and the surface hardness is 2350HV. The cantilever structure has a cantilever width of approximately 1.5μm (0.30 times the coating thickness t) and a cantilever angle of approximately 5°.

[0078] In this embodiment, D / t=30, H / t=2. Example 3

[0079] The selected cold work die steel has the following chemical composition by mass percentage: C 1.25%, Cr 12.0%, Mo 1.40%, V 1.35%, with the balance being Fe and unavoidable impurities.

[0080] S1. Quenching and tempering treatment: Quenching temperature 1070℃, holding temperature 45min; tempering temperature 505℃, three temperings, matrix hardness 62-64HRC.

[0081] S2. Plasma nitrocarburizing: This process is carried out in a plasma nitrocarburizing chamber with a mixed gas flow ratio of NH3 to CO2 of 94:6, a working pressure of 450 Pa, a discharge voltage of 720 V, a co-diffusion temperature of 500 °C, and a treatment time of 6 h. The resulting reinforced diffusion layer has a depth D of 0.20 mm (200 μm) and a surface hardness of 1020 HV.

[0082] S3. Laser Micro-Dimple Machining: After transferring to the surface micro-texturing cavity, machining begins when the mold surface temperature drops to 280℃. Laser parameters: pulse width 150ns, single pulse energy 80μJ, focused spot diameter 45μm. Micro-dimple diameter approximately 80μm, depth H approximately 20μm, area coverage 15%. Annular heat-affected softening zone radial width approximately 16μm (0.80H), depth dimension approximately 14μm (0.70H), hardness approximately 720HV.

[0083] S4. Hard Coating Deposition: The coating is transferred to the coating deposition chamber via a vacuum transfer chamber and deposited using magnetron sputtering at a deposition temperature of 460℃. The coating thickness t is 2.0μm, and the surface hardness is 2200HV. The cantilever structure has a cantilever width of approximately 3.0μm (1.5 times the coating thickness t) and a cantilever angle of approximately 25°.

[0084] In this embodiment, D / t=100, H / t=10. Example 4

[0085] The same mold steel material and S1 and S2 processes as in Example 1 were used.

[0086] S2a. Solid Lubricant Layer Deposition: After plasma nitrocarburization, maintaining a continuous vacuum environment, the mold is transferred into the solid lubricant layer deposition chamber via a vacuum transfer chamber. A MoS2 solid lubricant layer is deposited using radio frequency magnetron sputtering technology. The target material is a MoS2 ceramic target, the sputtering power is 150W, the argon pressure is 0.4Pa, the deposition time is 25min, and the deposition temperature is 180℃. A MoS2 lubricant layer with a thickness of 1.0μm is obtained.

[0087] S3. Laser Micro-Dent Machining: After transferring to the surface micro-texturing cavity, laser processing is initiated when the mold surface temperature drops to 180°C. The laser parameters are basically the same as in Example 1, with the single-pulse energy adjusted to 55 μJ to ensure penetration of the MoS2 lubricant layer. The laser pulse first penetrates the surface MoS2 layer and then forms micro-dents in the reinforced diffusion layer. The temperature is highest in the central region of the pit, where MoS2 is vaporized and removed; the temperature is relatively lower at the pit edges and sidewalls, where some MoS2 material is retained and adheres to the inner surface of the pit.

[0088] The micro-pits are approximately 52 μm in diameter and 14 μm in depth (approximately 13 μm in depth within the enhanced diffusion layer after deducting the MoS2 layer thickness), with an area coverage of 7%.

[0089] S4. Hard Coating Deposition: The TiAlN coating is transferred to the coating deposition chamber via a vacuum transfer chamber and deposited using the same multi-arc ion plating process as in Example 1. The coating covers the MoS2 lubricant layer, forming overhanging structures at the edges of the micro-pits to seal the MoS2 lubricant retained within the pits. The coating thickness is 3.2 μm, and the surface hardness is 2580 HV.

[0090] In this embodiment, the depth H of the micro-pit is determined based on the maximum pit depth measured before coating deposition, with the surface of the co-permeation layer as the reference, H≈14μm; the coating thickness t≈3.2μm; D is still about 0.25mm, and D / t≈78, H / t≈4.4. Example 5

[0091] Using the same mold steel material and S1 to S3 processes as in Example 1, a reinforced diffusion layer with a depth of 0.25 mm and a micro-pit array with a depth of 15 μm were obtained.

[0092] S4. Hard coating deposition: The coating is transferred to the coating deposition chamber through a vacuum transfer chamber and deposited using a combination of multi-arc ion plating and magnetron sputtering technology.

[0093] First, a TiCN underlayer was deposited: a Ti target was used, and a mixture of N2 and C2H2 gas (flow ratio 3:1) was introduced. The arc current was 90A, the workpiece bias voltage was -80V, the deposition temperature was 400℃, and the deposition time was 40min, resulting in a TiCN layer thickness of approximately 1.5μm.

[0094] Then, a TiAlN top layer is deposited: using Ti... 50 Al 50 An alloy target was used, pure N2 gas was introduced, the arc current was 100A, the workpiece bias voltage was -100V, the deposition temperature was 420℃, and the deposition time was 50min to obtain a TiAlN layer with a thickness of about 2.0μm.

[0095] The total thickness of the composite coating is approximately 3.5 μm, and the surface hardness is 2750 HV. The TiCN / TiAlN composite structure combines the advantages of both coatings, with the TiCN bottom layer providing toughness support and the TiAlN top layer providing hardness and wear resistance. Comparative Example 1

[0096] A coating mold with micro-pits was prepared using a traditional step-by-step process, in comparison with Example 1.

[0097] Process flow: Quenching and tempering treatment → Plasma nitrocarburizing → Remove the mold and allow it to cool naturally to room temperature in an atmospheric environment → Perform laser micro-pit processing in an atmospheric environment → Cleaning → Load into coating equipment to deposit TiAlN coating.

[0098] The main differences from Example 1 are: (1) There is atmospheric exposure between plasma nitrocarburization and laser processing. The high-temperature active surface after co-diffusion is oxidized by contact with air, forming an oxide film about 50-100 nm thick; (2) Laser processing is carried out at room temperature (about 25°C), and the formation conditions of the heat-affected softening zone are different from those in Example 1; (3) There is atmospheric exposure between laser processing and coating deposition, and the inner surface of the micro-pits is oxidized. Comparative Example 2

[0099] The laser micro-dimple processing step is omitted, and only plasma nitrocarburization and hard coating deposition are performed.

[0100] Process flow: Quenching and tempering treatment → Plasma nitrocarburizing → (maintaining a vacuum environment) → Direct deposition of TiAlN coating.

[0101] The main difference from Example 1 is that the mold surface has no micro-pit structure, no overhang structure and no annular heat-affected softening zone, and cannot form a hardness gradient load-bearing structure. Performance Testing and Evaluation

[0102] The performance of each embodiment and comparative example of the present invention was evaluated using the following test methods: (1) Tribological and wear performance test The friction coefficient and wear rate were tested using a ball-disc friction and wear tester (ASTM G99 standard, GCr15 steel balls, load 10N, dry friction at room temperature).

[0103] (2) Coating bonding strength test The coating bond strength was tested using the Rockwell indentation method (VDI 3198 standard).

[0104] (3) Contact fatigue performance test Contact fatigue life (Hertz stress 1.5 GPa, oil lubrication) was tested using a rolling contact fatigue testing machine. Test Results

[0105] Table 1. Performance test results of the examples and comparative examples: .

[0106] Note: The relative life is calculated based on the contact fatigue life of Comparative Example 2 (without micro-dimples) (100%). Results Analysis

[0107] As shown in Table 1, the friction coefficients and wear rates of Examples 1-5 are significantly better than those of the comparative examples, with Example 4 showing the best performance due to the slow-release effect of the solid lubricant. The coating adhesion of Examples 1-5 all reached HF1-HF2 level, while the adhesion of Comparative Example 1 decreased to HF3 level due to interfacial oxidation caused by atmospheric exposure between processes. The contact fatigue life of Examples 1-5 is 2.0-2.8 times that of Comparative Example 2, verifying the fatigue resistance effect of the hardness gradient load-bearing structure. These results demonstrate that the present invention, by constructing a hardness gradient load-bearing structure and maintaining a continuous vacuum environment, effectively improves the coating's adhesion strength, wear resistance, and fatigue spalling resistance. Detailed structure of the equipment

[0108] The various chambers of the manufacturing equipment of the present invention will be described in detail below.

[0109] The heat treatment chamber is used for quenching and tempering the molds. The heating device uses resistance heating elements and is equipped with a temperature control system. The quenching and cooling device uses a high-pressure gas quenching system with high-purity nitrogen as the cooling medium. The heat treatment chamber is equipped with an independent vacuum system and a protective gas refill system, enabling heat treatment in a vacuum or protective atmosphere environment.

[0110] The plasma nitriding and carburizing chamber is used for plasma nitriding and carburizing treatment of molds. The plasma discharge device uses a pulsed DC power supply, with the workpiece as the cathode and the chamber wall as the anode, forming a glow discharge. The gas supply system is equipped with independent mass flow controllers for various process gases, allowing for precise adjustment of the composition and flow ratio of the mixed gases. The chamber is equipped with auxiliary heating devices and temperature measuring devices.

[0111] The surface micro-texturing cavity is used to process an array of micro-dimples on the working surface of the mold. The pulsed laser processing device uses a nanosecond pulsed laser. The laser beam is deflected by a galvanometer scanning system and focused onto the workpiece surface. The pulse width, repetition frequency, single pulse energy, and focused spot diameter are all adjustable. The workpiece temperature monitoring device uses an infrared thermal imager to monitor the temperature distribution on the mold surface in real time. When the temperature drops to the set range, the laser processing program is automatically triggered. An online contour measuring instrument is used to measure the geometric parameters of the micro-dimples, such as diameter and depth. A precision motion platform is installed inside the cavity to support and position the mold workpiece.

[0112] The coating deposition chamber is used to deposit hard coatings on the mold surface. The physical vapor deposition apparatus employs a multi-arc ion plating and magnetron sputtering hybrid system, allowing selection of the deposition method based on the coating material and performance requirements. The coating deposition chamber is equipped with a workpiece bias power supply, a process gas supply system, a heating system, and a workpiece rotating frame. The workpiece bias power supply is used for argon ion etching and cleaning, as well as ion bombardment during the coating deposition process; the workpiece rotating frame uses a planetary rotating frame system to ensure the uniformity of coating thickness on all surfaces of complex-shaped molds.

[0113] The vacuum transfer chamber is located in the center of the equipment and is connected to the heat treatment chamber, plasma nitriding and carbonization chamber, surface micro-texturing chamber, and coating deposition chamber via vacuum valves. The transfer mechanism adopts a vacuum manipulator structure, including a telescopic arm, a rotary table, a lifting mechanism, and an end effector, for transferring mold workpieces between the chambers. The vacuum transfer chamber is equipped with an independent high-vacuum system to ensure that the mold surface is not oxidized during the transfer between chambers.

[0114] The multi-parameter collaborative control device uses an industrial computer as its hardware platform, which is electrically connected to the control elements and sensors in each process chamber to achieve centralized monitoring of the entire equipment and collaborative optimization of process parameters. The software system includes the following functional modules: Layer depth calculation module: Receives real-time data on discharge power, gas composition, gas pressure, processing time, and workpiece temperature from the plasma nitrocarburizing cavity, and calculates the layer depth D of the enhanced diffusion layer online. The calculation can employ any of the following methods: a diffusion kinetic model based on Fick's diffusion law, an empirical regression formula fitted from process test data, or a trained machine learning prediction model. The parameters of the calculation model are verified and corrected by measuring the actual layer depth using the cross-sectional microhardness method.

[0115] Geometric acquisition module: Receives measurement data from the online contour measuring instrument, automatically identifies the edges of the pits, and calculates the pit diameter, depth, and area coverage.

[0116] Coating calculation module: Based on the diffusion layer depth D and the pit depth H, calculates the allowable range of the target coating thickness t according to the preset size ratio, and outputs the coating deposition parameters.

[0117] Stress prediction module: Calculates the stress concentration factor based on the geometric parameters of the micro-dimples, and sends a parameter adjustment command to the laser processing system when the stress concentration factor exceeds the preset threshold.

[0118] Central control unit: coordinates the work of various functional modules, manages the sequential execution of the process flow, has a safety interlock function, and records all process parameters and measurement data.

[0119] When a process requiring a solid lubricant layer is needed, a solid lubricant layer deposition chamber can be added between the plasma nitrocarburization chamber and the surface microtexturing chamber. This chamber is connected to the vacuum transfer chamber via a vacuum valve and is equipped with a magnetron sputtering system, capable of depositing solid lubricant layers such as MoS2, WS2, and h-BN.

[0120] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A manufacturing process of a high performance long life cold work die, characterized by, The method comprises the following steps: S1, quenching and tempering a cold work die steel blank to obtain a tempered martensite structure and a die; S2, plasma nitrocarburizing the die to form a strengthened diffusion layer; S3, using pulsed laser to process a micro-pit array on the working surface of the die and forming an annular heat-affected softened zone around the mouth of each micro-pit, the hardness of the annular heat-affected softened zone at the depth position thereof being lower than the hardness of the strengthened diffusion layer at the same depth position which is not affected by laser heat; S4, depositing a hard coating on the working surface of the die to make the hard coating of the micro-pit edge extend inward the pit to form an overhanging structure; In the step S2, the plasma nitrocarburizing is performed in a low-pressure plasma atmosphere formed by introducing a reaction gas after vacuumizing; the steps S3 and S4 are performed in a vacuum or inert protective atmosphere; and the transfer between the steps is performed in a vacuum or inert protective atmosphere, so that the die is not exposed to the atmosphere during the steps S2 to S4; the bottom of the micro-pit is located in the strengthened diffusion layer; the root of the overhanging structure is located in the radial range of the annular heat-affected softened zone; the depth of the strengthened diffusion layer is D; the depth of the micro-pit is H; and the thickness of the hard coating is t.

2. The manufacturing process of claim 1, wherein, The ratio of D to t is 30-100; and the ratio of H to t is 2-10.

3. The manufacturing process of claim 1, wherein, In the step S3, the pulsed laser processing is performed when the temperature of the working surface of the die is 120-300℃; the diameter of the micro-pit is 20-100μm; the depth of the micro-pit is 5-30μm; and the area coverage rate is 5-20%. The width of the annular heat-affected softened zone extending radially outward from the edge of the micro-pit is 0.3-1.0 times the depth H of the micro-pit; and the size in the depth direction is 0.3-1.0 times the depth H of the micro-pit.

4. The manufacturing process of claim 1, wherein, The thickness t of the hard coating is 2-5μm; and the deposition temperature is 380-480℃; the hard coating is any one of a TiN layer, a TiCN layer, a TiAlN layer, a CrN layer and an AlCrN layer, or a multilayer composite coating composed of any two or more of them; The overhanging width of the overhanging structure is 0.3-1.5 times the thickness t of the coating; and the included angle between the lower surface of the overhanging structure and the working surface of the die is 5-25°.

5. The manufacturing process of claim 1, wherein, The cold work die steel blank comprises, by mass percent, C 0.80-1.30%, Cr 7.0-13.0%, Mo 0.50-1.50%, V 0.50-1.50%, and the balance of Fe and impurities; in the step S1, the quenching temperature is 1000-1080℃; the tempering temperature is 500-560℃; and the tempering times are 2-3 times; in the step S2, the plasma nitrocarburizing temperature is 450-550℃; and the depth of the strengthened diffusion layer is 0.15-0.40mm.

6. The manufacturing process of claim 1, wherein, A solid lubricant layer deposition step is further included between the S2 and the S3: a solid lubricant layer with a thickness of 0.2-2 μm is deposited on the surface of the strengthened diffusion layer, the material of the solid lubricant layer being one or more of MoS2, WS2, h-BN, and diamond-like carbon; in the S3, laser processing penetrates the solid lubricant layer to form micro-pits, the bottom and / or sidewall of the micro-pit retaining solid lubricant; in the S4, a hard coating is coated on the solid lubricant layer, enclosing the solid lubricant inside the micro-pit.

7. A cold work die manufacturing apparatus for carrying out the manufacturing process according to any one of claims 1 to 6, characterized by, Comprise: a heat treatment cavity configured with heating devices and quenching cooling devices; a plasma nitrocarburizing cavity configured with plasma discharge devices; a surface micro-texturing cavity configured with workpiece temperature monitoring devices and pulsed laser processing devices; a coating deposition cavity configured with physical vapor deposition devices; a vacuum transfer cavity in communication with the heat treatment cavity, the plasma nitrocarburizing cavity, the surface micro-texturing cavity, and the coating deposition cavity through vacuum valves, and provided with a transfer mechanism; a multi-parameter coordinated control device electrically connected with control elements and sensors in each process cavity; wherein the mold is transferred between the plasma nitrocarburizing cavity, the surface micro-texturing cavity, and the coating deposition cavity through the vacuum transfer cavity, so that the mold is not exposed to the atmosphere between plasma nitrocarburizing, micro-texturing, and coating deposition.

8. The manufacturing apparatus according to claim 7, wherein The multi-parameter coordinated control device comprises: a layer depth calculation module that calculates the layer depth D of the strengthened diffusion layer in real time according to the discharge power, processing time, and workpiece temperature of the plasma nitrocarburizing cavity; a geometry acquisition module that measures the depth H and area coverage of the micro-pit; a coating calculation module that calculates the target coating thickness t according to the layer depth D and pit depth H, and outputs coating deposition parameters; and a stress prediction module that calculates a stress concentration factor according to the geometry parameters of the micro-pit, and sends a parameter adjustment instruction when the preset threshold is exceeded.

9. The manufacturing apparatus according to claim 7, wherein A solid lubricant layer deposition cavity is further included, which is arranged between the plasma nitrocarburizing cavity and the surface micro-texturing cavity, and is in communication with the vacuum transfer cavity through a vacuum valve.

10. The manufacturing apparatus according to claim 7, wherein An online profile measuring instrument is provided in the surface micro-texturing cavity; the workpiece temperature monitoring device triggers laser processing when the mold surface temperature decreases to a preset temperature range; the laser energy density of the pulsed laser processing device is adjustable, and is used to form the annular heat-affected softened zone around the micro-pit while forming the micro-pit.

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