A mold surface processing technique

Abstract

The present application relates to the technical field of metal surface strengthening, and particularly relates to a mold surface processing technology, which comprises the following steps: step 1: differential pretreatment based on curvature recognition; step 2: gradient component dynamic plasma spraying, synchronous conveying of metal binder phase powder and ceramic reinforcing phase powder, in the near-matrix interval, the metal phase powder feeding rate is increased from zero, and in the far-matrix interval, the metal phase powder feeding rate is decreased while the ceramic phase is increased; step 3: energy self-adaptive functional layer strengthening, adjusting the spray gun motion parameters for the curvature mutation area, after each spraying single pass, dynamic remelting is carried out by using an energy beam, and the remelting energy is adjusted based on real-time temperature feedback; step 4: stress synergistic post-processing, according to the coating thickness distribution, a staged impact energy is applied, and aging treatment is carried out based on phase change characteristics. Through the precise curvature recognition, differential sand blasting, gradient spraying technology, energy self-adaptive remelting and stress synergistic post-processing, the overall performance of the mold surface is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of metal surface strengthening technology, and in particular to a mold surface processing technology. Background Technology

[0002] In the field of automotive body panel stamping die manufacturing, the working surface of the die is subjected to continuous impact loads of up to 800-1000 times per minute for a long time. Due to the complex curved surface design of the body panels (deep cavities, sharp angles, and steep slope structures account for ≥60%), traditional plasma spraying wear-resistant coatings face the following inherent defects: 1. Mechanism and hazards of insufficient bonding strength between curved surfaces: Due to the metal mold matrix (coefficient of thermal expansion) ) and ceramic coating ( The difference in thermal expansion coefficients exceeds 100%, generating interfacial shear stress during the spraying and cooling process. Especially in ridge areas with a curvature radius ≤3mm (such as door reinforcement grooves), the bonding strength between the coating and the substrate is less than 200MPa, only 40%-50% of that in planar areas. This defect can cause interlayer delamination under high-temperature operating conditions (mold surface temperature >300℃), resulting in loss of dimensional tolerances in stamped parts, with downtime losses for a single repair reaching up to 200,000 yuan.

[0003] 2. Causes and effects of uncontrolled porosity: In existing processes for spraying coatings on irregularly shaped surfaces, the trajectory of powder particles is affected by the turbulence of the curved surface, resulting in an angular dispersion of molten particles colliding with the substrate exceeding 30°, forming a large number of insufficiently spread, multilayered pores. Statistics show that in concave corner regions (depth-to-width ratio ≥ 5), the porosity reaches as high as 5%-8%, becoming a crack initiation point under alternating loads. When the pores connect to form a network structure (pore spacing < 50 μm), the wear resistance life of the coating drops sharply to 1 / 3 of the normal value, causing the mold to require rework every 100,000 pieces processed, far below the industry benchmark requirement of 250,000 pieces.

[0004] Therefore, there is an urgent need for a mold surface processing technology to solve the above problems. Summary of the Invention

[0005] To achieve the above objectives, the present invention provides a mold surface processing technology, comprising the following steps: Step 1: Based on curvature recognition, differential preprocessing is performed to scan the working surface of the mold and identify curvature change areas. According to the curvature distribution, the first sandblasting strategy is applied to the change areas, and the second sandblasting strategy is applied to the non-change areas. An anchor-shaped structure with increased depth is generated in the curvature change areas. Step 2: Gradient component dynamic plasma spraying, synchronously delivering metal binder powder and ceramic reinforcing powder. In the near matrix region, the metal phase powder delivery rate increases while the ceramic phase delivery rate increases from zero. In the region far from the matrix, the metal phase powder delivery rate decreases while the ceramic phase delivery rate increases. Step 3: Enhance the energy adaptive functional layer by adjusting the spray gun motion parameters for areas with abrupt curvature changes. After each single coat, an energy beam is used for dynamic remelting, and the remelting energy is adjusted based on real-time temperature feedback. Step 4: Stress-coordinated post-treatment, applying graded impact energy according to the coating thickness distribution, and implementing aging treatment based on phase transformation characteristics.

[0006] Preferably, the method for implementing the first sandblasting strategy in step 1 includes: The curvature radius of each region is calculated by analyzing 3D point cloud data, and regions with curvature radii less than a predetermined threshold are defined as curvature abrupt change regions. The air pressure value of the first sandblasting strategy is determined by the ratio of the hardness of the matrix material to the hardness of the abrasive: when the ratio is in the first range, 60%-70% of the standard air pressure is used, and when it is in the second range, 70%-80% is used. The selection criteria for abrasive grain size are as follows: for groove areas with a depth-to-width ratio greater than the predetermined value, abrasive grains with a grain size of 50%-60% of the standard value for planar areas should be selected. The dynamic adjustment method for the sandblasting incident angle is as follows: the angle deviation is compensated in real time according to the angle between the surface normal vector and the spray gun axis, so that the effective impact angle is kept within the range of 85°-95°.

[0007] Preferably, the method for controlling the powder feeding rate in step 2 specifically includes: The thickness of the near-matrix region is determined by calculating the difference in thermal expansion coefficients between the matrix material and the metal binder phase, and increasing the region thickness when the difference exceeds a predetermined percentage. The increasing gradient of the metal phase powder feeding rate is determined based on the temperature distribution of the plasma flow: a steep increasing gradient is used in the high-temperature region at the center of the flow, and a gentle increasing gradient is used in the low-temperature region at the edge. The initial activation point of the ceramic phase powder delivery rate is located at a predetermined distance from the substrate surface. This distance is calculated by the residence time of the powder in the plasma jet, ensuring that the powder reaches a molten state when it reaches the substrate.

[0008] Preferably, the dynamic remelting operation method in step 3 includes: The real-time temperature data acquisition location is set 2-3 mm downstream of the remelting point, and the sampling frequency is not less than 1 kHz. The remelting energy adjustment rule is as follows: when the measured temperature is lower than the target range, the energy input value per unit area is increased by one degree Celsius; when it is higher than the target range, the energy beam scanning speed is increased proportionally. The target temperature range is calculated based on the solidus temperature of the coating material: the lower limit is solidus temperature × 0.85, and the upper limit is solidus temperature × 0.92. The diameter of the focused energy beam spot is adaptively adjusted according to the coating thickness: for every 50μm increase in thickness, the spot diameter increases by a predetermined percentage.

[0009] Preferably, adjusting the spray gun motion parameters in step 3 includes: The reduction rate of scanning speed is determined by the ratio of the radius of curvature to the critical radius: when the radius of curvature is less than the critical radius, the speed is reduced to 70%-80% in the planar region; The rules for adjusting the spray gun distance are as follows: in concave areas, shorten it to 80%-90% of the standard distance; in convex areas, increase it to 110%-120%. The critical radius is determined based on the working load of the mold: for every increase of a predetermined value in the impact load, the critical radius decreases proportionally.

[0010] Preferably, the method for implementing graded impact energy in step 4 includes: The coating thickness distribution map is obtained by using an eddy current thickness gauge. Areas with a thickness greater than the first threshold are classified as high-energy impact zones, and areas with a thickness less than the second threshold are classified as low-energy impact zones. The energy value of the high-energy impact zone is 120%-130% of the reference energy. The reference energy is calculated by the nano-indentation hardness value of the coating: for every increase in hardness by a predetermined value, the reference energy increases proportionally. The selection rule for the radius of curvature of the impact needle is as follows: use a needle with a radius ≤0.2mm in areas of abrupt curvature change, and use a needle with a radius ≥0.5mm in planar areas.

[0011] Preferably, step 2, which involves simultaneously conveying the metal binder powder and the ceramic reinforcing phase powder, further includes: The metallic binder phase powder is a nickel-based alloy, and its particle size distribution is determined by Hall flow rate testing: the particle size combination with the flow rate in the optimal range is selected. The ceramic reinforcing phase powder is an alumina-zirconia composite powder, wherein the zirconia content is set according to the coating's thermal shock resistance requirements: when the mold's working temperature fluctuates beyond a predetermined range, the zirconia content is increased to a predetermined ratio.

[0012] Preferably, the control method for the time-sensitive processing in step 4 includes: After determining the phase transition point of the coating using differential scanning calorimetry, the aging temperature is taken as 40%-50% of the phase transition point temperature. The calculation logic for heat preservation time is as follows: based on the thickest part of the mold cross section, 1 hour is corresponding to every 10mm of thickness. When the change rate of cross section thickness exceeds the predetermined value, the time is calculated as 120% of the maximum thickness value. The cooling rate is controlled as follows: a slow cooling rate of ≤30℃ / min is used in the temperature range below the phase transition point.

[0013] Preferably, the method for calculating the residence time specifically includes: The trajectory of powder in a plasma jet is recorded by high-speed photography. The residence time is calculated based on the distance between the spray gun and the substrate and the average speed of the powder movement. When the residence time is less than the time required for the powder to completely melt, the plasma power is increased and the powder feeding rate is reduced simultaneously.

[0014] Preferably, the logic for determining the energy input value per unit area includes: Establish the mapping relationship between remelting depth and energy density: measure the remelting depth at different energy densities using metallographic sections; The required energy density is calculated by working backward from the target remelting depth, and the target remelting depth is set to 10%-15% of the current coating thickness; When the coating porosity exceeds the standard, the target remelting depth is increased year-on-year.

[0015] The beneficial effects of this invention are: 1. By scanning the working surface of the mold, areas of abrupt curvature changes are accurately identified, and different sandblasting strategies are employed. For sharp corners and edges with relatively small curvature, a sandblasting method using higher air pressure and smaller abrasive particles is used to create a deeper anchor-like structure, thereby enhancing the mechanical adhesion between the coating and the substrate. This strategy effectively compensates for the insufficient coating adhesion in traditional spraying processes.

[0016] 2. By simultaneously feeding metallic binder powder and ceramic reinforcing powder, an increasing metallic powder feeding rate and a decreasing ceramic powder feeding rate are used in areas close to the substrate, while the opposite is true in areas farther from the substrate. This precise control of powder feeding rate ensures the uniformity and density of the coating. Simultaneously, dynamic remelting is employed during the spraying process, with real-time monitoring of the coating temperature and energy adjustments, effectively eliminating porosity and reducing the porosity within the coating.

[0017] 3. Through graded impact energy treatment, appropriate impact energy is applied according to the coating thickness distribution, combined with aging treatment, to optimize the coating's microstructure and reduce internal stress. This treatment is precisely controlled using an eddy current thickness gauge to ensure that the coating is sufficiently strengthened in high-stress areas.

[0018] 4. Through dynamic control of metal and ceramic powders, the coating composition and performance of different regions are designed differently, and the hardness, wear resistance and high temperature resistance of the coating are significantly improved. In particular, the strengthening effect of ceramic phase powder improves the wear resistance of the coating. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of the steps of the method of the present invention; Figure 2 This is a flowchart illustrating the steps of implementing the graded impact energy in step 4 of the method of the present invention. Figure 3 This is a flowchart illustrating the steps involved in determining the energy input value per unit area in the method of this invention. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should also be noted that, to make the embodiments more comprehensive, the following embodiments are the best and preferred embodiments, and those skilled in the art can use other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0022] Please see Figures 1-3 This invention provides a mold surface processing technology. In step 1, a high-precision 3D scanner is first used to perform a full-area measurement of the working surface of the mold and calculate the rate of curvature change to identify areas of abrupt curvature changes (such as edges and grooves with a radius of less than 3 mm). In these areas, a first sandblasting strategy is selected, which uses corundum particles with a particle size of 80-100 mesh and a spraying pressure of 0.6-0.8 MPa to form an anchor-shaped roughening structure with a depth of 20-40 μm, thereby significantly improving the mechanical interlocking force between the ceramic coating and the substrate. For areas with gentle curvature, a second sandblasting strategy is used with abrasive particles of 100-120 mesh and a lower air pressure (0.4 MPa) to avoid the impact of excessive roughening on flatness.

[0023] In step 2, a gradient component plasma spraying process is implemented. During the spraying process, a dual-channel powder feeding system is used to simultaneously transport metals (such as NiCr) and ceramics (such as... The powder is predominantly metallic in the near-substrate region (first 10-20 μm of thickness), with a powder feed rate set at 30 g / min for metallic phase and 5 g / min for ceramic phase, gradually increasing the ceramic proportion. When spraying into areas far from the substrate, the feed rate is adjusted to 10 g / min for metallic phase and 30 g / min for ceramic phase, constructing a functional layer structure with a gradient transition, thereby enhancing wear resistance and thermal stability while ensuring adhesion.

[0024] Step 3 employs an energy-adaptive functional layer strengthening treatment. An infrared thermometer is used to monitor the coating surface temperature in real time, and the energy density of the laser or plasma remelting beam (range 1.5-3.5 J / mm²) is dynamically adjusted based on the residual heat distribution after each spray coat. In areas of abrupt curvature change, the spray gun scanning speed is appropriately reduced and the remelting energy is increased to ensure the coating is dense, crack-free, and pore-free, thereby enhancing material consistency and crack resistance.

[0025] In step 4, graded impact energy treatment is implemented based on the online coating thickness measurement results. The thick coating area uses an impact frequency of 20Hz and an energy intensity of 4J, while the thin coating area uses an impact parameter of 3J. Simultaneously, a two-hour aging treatment is performed at a controlled heating temperature within the range of 550-600℃ to promote residual stress release and induce microstructural phase transformations within the metallic phase (such as the transformation from metastable to stable phases), thereby improving the overall thermal shock resistance and structural stability of the coating.

[0026] This invention significantly enhances the bonding strength, density, and thermomechanical stability of coatings on complex curved surfaces of molds, solving the problems of easy peeling, cracking, high porosity, and short service life of traditional plasma spraying in irregularly shaped areas, ultimately achieving a significant improvement in mold reliability and lifespan.

[0027] In one possible implementation, this embodiment addresses the non-uniform response problem of complex curved surfaces in sandblasting treatment of molds by proposing a curvature-driven differentiated sandblasting strategy and designing an implementation method for the first sandblasting strategy to significantly improve the adhesion and structural uniformity of subsequent coatings.

[0028] Specifically, firstly, point cloud data of the mold surface is acquired using a high-precision 3D scanner, and then a discrete curvature calculation algorithm is used to numerically analyze the principal curvature of each sampling point. Based on a set curvature radius threshold (e.g., 1.5 mm), areas smaller than this value are defined as curvature abrupt change regions, mainly concentrated in the corners, edges, and narrow grooves of the mold. These areas, due to drastic curvature changes, are typically high-risk areas for stress concentration and coating peeling.

[0029] Regarding the setting of blasting air pressure, a material response model is used, classifying the settings based on the hardness ratio of the substrate material (such as hot work die steel) to the abrasive used (such as brown fused alumina). For example, when the ratio is in the first range of 1.0-1.5, the blasting air pressure is set to 60%-70% of the standard value (0.6MPa) to avoid microcracks or erosion of the substrate; when the ratio is in the second range of 1.5-2.0, the air pressure is increased to 70%-80% to achieve a more effective roughening effect without damaging the surface integrity.

[0030] The selection of abrasive grain size is optimized for narrow groove regions with a depth-to-width ratio greater than 2. To prevent large-diameter abrasive grains from accumulating, rebounding ineffectively, or damaging the microstructure in such regions, fine-grained abrasive grains (such as 120 mesh) with a grain size of 50%-60% of the standard value (such as 80 mesh) are selected to improve the contact coverage of the bottom surface of the groove and the quality of micro-anchor pattern formation.

[0031] In terms of sandblasting angle control, a real-time angle compensation mechanism based on the surface normal vector is introduced. By calculating the angle between the unit normal vector of the current sandblasting position and the spray gun's injection axis, the incident direction of the spray gun is dynamically adjusted to ensure that the effective impact angle is always maintained between 85° and 95°. This angle range has been experimentally verified as an ideal range that ensures effective abrasive impact to form a rough structure while minimizing the risk of surface micro-peeling or lateral damage.

[0032] This first sandblasting strategy not only improves the surface roughness consistency and microstructure stability of high curvature areas, but also effectively controls the risk of sandblasting damage to the substrate, significantly enhancing the adhesion strength and service stability of subsequent coatings, and is particularly suitable for the surface pretreatment process of highly complex molds.

[0033] In one possible implementation, this embodiment provides an innovation in powder feeding rate control for mold surface processing technology to solve the problems of good bonding and uniform coating formation between the substrate surface and the metal bonding phase and ceramic phase. In particular, it provides a more precise and efficient control method for adjusting the powder feeding rate during high-temperature plasma spraying.

[0034] Specifically, the thickness of the near-substrate region is determined by calculating the difference in thermal expansion coefficients between the substrate material and the metal binder phase. A large difference in thermal expansion coefficients indicates a significant difference in thermal stress, which can easily lead to cracks or delamination between the coating and the substrate. Therefore, when the difference in thermal expansion coefficients between the substrate material and the metal binder phase exceeds a set threshold, the thickness of the near-substrate region needs to be increased to improve the thermal expansion capacity and thermal stress dispersion performance of this area, in order to avoid stress concentration and crack formation. This approach can improve the adhesion and durability of the metal coating, ensuring its stability and uniformity.

[0035] Secondly, the powder feeding rate of the metallic phase employs a strategy of setting an increasing gradient based on the temperature distribution of the plasma flame. During plasma spraying, the temperature is highest in the central region of the flame and lower at the edges. To ensure that the metal powder can fully melt and form a strong bond with the substrate, a steeper increasing gradient is used in the high-temperature central region of the flame to ensure a rapid increase in powder feed, allowing the powder to reach a molten state more quickly. In the low-temperature edge region of the flame, a gentler increasing gradient is used to avoid excessive powder being fed in, resulting in incomplete melting and thus improving the quality and uniformity of the metal coating.

[0036] The method for controlling the powder feeding rate of the ceramic phase is based on optimization of the residence time of the powder in the plasma jet. In the initial design phase, the initial activation point of the ceramic phase powder feeding rate is determined by calculating the residence time of the ceramic powder in the plasma jet; this is the starting position where the powder begins to be fed into the plasma jet. This position ensures that the ceramic powder has reached a molten state when it reaches the substrate surface, ensuring that the ceramic coating can uniformly cover and firmly bond with the substrate, thereby improving the coating's wear resistance and corrosion resistance.

[0037] This invention solves common problems in spraying, such as poor adhesion and uneven coating, between different phases by precisely controlling the powder feeding rate and the bonding process between the powder and the substrate. By adjusting the powder feeding rate gradient and activation point of the metal and ceramic powders in a timely manner, the overall quality of the coating can be ensured, and the durability and performance of the mold can be improved, especially its stability under high temperature and high pressure environments.

[0038] In one possible implementation, the melting and curing process of the coating is further optimized by real-time temperature control and energy regulation during the remelting process, thereby ensuring good bonding and uniformity between the coating and the substrate, while improving the wear resistance and corrosion resistance of the mold surface.

[0039] Specifically, firstly, the real-time temperature data is collected at a location 2-3 mm downstream of the remelting point, with a sampling frequency of at least 1 kHz. This ensures high sensitivity and precise control over temperature changes during the remelting process. Since the coating undergoes different temperature changes during remelting, collecting temperature data 2-3 mm from the remelting point allows for timely reflection of minute temperature variations, avoiding control errors caused by measurement lag. Furthermore, a sampling frequency above 1 kHz captures the details of temperature changes, resulting in more precise temperature regulation and thus ensuring the uniformity of the remelting process and the stability of the coating.

[0040] Regarding remelting energy regulation, when the measured temperature is below the target range, the energy input per unit area is increased for every degree Celsius difference. This means that when the temperature is below the set target temperature range, the system will increase the energy input in a timely manner to accelerate the melting process and ensure that the coating reaches the ideal molten state. Conversely, when the temperature is above the target range, the energy input is adjusted by increasing the energy beam scanning speed to avoid overheating, excessive melting or evaporation of the coating, and to ensure that the coating remains within an ideal temperature range during the melting process, thereby improving coating quality.

[0041] The target temperature range is set based on the solidus temperature of the coating material, with a lower limit of 85% and an upper limit of 92% of the solidus temperature. The solidus temperature refers to the temperature range at which the coating material begins to change from a solid to a liquid state. Therefore, setting the target temperature range near the solidus temperature ensures that the coating material is in an ideal temperature range during the melting process, thereby avoiding over-melting or under-melting and ensuring the adhesion and strength of the coating.

[0042] The diameter of the focused energy beam spot is adaptively adjusted according to the coating thickness. For every 50 μm increase in coating thickness, the spot diameter increases by a predetermined percentage. This adjustment ensures that the energy beam can uniformly cover the surface of the coating. As the coating thickness increases, the spot diameter is appropriately increased to avoid uneven melting of the coating due to excessive concentration of the energy beam, ensuring that each layer of the coating is heated evenly.

[0043] The dynamic remelting operation method of this invention solves the problems of uneven coating quality and poor adhesion caused by temperature fluctuations in traditional processing through precise temperature monitoring and intelligent energy regulation. This method effectively improves the density, hardness, and durability of the coating on the mold surface, and has significant technical advantages for improving the service life and performance of the mold.

[0044] In one possible implementation, the reduction ratio of the scanning speed is first determined by the ratio of the radius of curvature to the critical radius. When there is a curvature change on the processed surface, if the radius of curvature is smaller than the preset critical radius, it indicates that there is a large geometric curvature change in that area, such as sharp corners or concave structures. Due to their complex morphology, such areas are prone to uneven coating accumulation and poor adhesion if sprayed at a conventional speed. Therefore, the scanning speed is reduced to 70%-80% of that in planar areas. This extends the deposition time of the coating in that area, ensuring sufficient material filling, and reduces the rate of change of the heat input gradient, thereby reducing thermal stress concentration caused by rapid movement and improving the coating bonding quality and density.

[0045] Secondly, the distance between the spray gun and the processing surface is optimized according to different geometric features: in concave corner areas, the spray gun distance is shortened to 80%-90% of the standard distance, which increases the deposition density of the coating material in the concave corner area and improves the thin coating phenomenon caused by the inability to cover dead corners in traditional processes; while in convex corner areas, in order to prevent the coating from accumulating too thickly, causing uneven surfaces or peeling, the spray gun distance is appropriately increased to 110%-120%, reducing energy density and particle kinetic energy, so as to achieve uniform coating. This differentiated distance control enhances the coating consistency and adhesion strength on uneven surfaces.

[0046] The critical radius is dynamically determined based on the load conditions of the mold during actual operation. The greater the impact load on the mold, the higher the requirements for the strength and toughness of its surface structure, especially in local microstructure areas. This invention, based on the increasing trend of impact load, rationally reduces the critical radius value, thereby identifying high-risk geometric structures in advance in high-load areas and actively slowing down and adjusting the spray gun distance to strengthen potentially weak parts. This critical radius adjustment mechanism, linked to load response, not only improves the coating consistency on complex curved surfaces but also enhances the reliability and stability of the mold under extreme working conditions.

[0047] The dynamic adjustment method of the spray gun motion parameters can effectively solve the deposition problem caused by surfaces with varying curvature, improve spraying accuracy and process adaptability, and is especially suitable for surface strengthening treatment of high-precision molds and complex structural parts, with significant engineering application value.

[0048] In one possible implementation, the method for implementing graded impact energy in the mold surface processing of the present invention is to optimize the hardness and strength distribution of the coating by precisely controlling the distribution of impact energy in different areas. Specifically, the implementation steps include using an eddy current thickness gauge to accurately measure the thickness of the coating, and dynamically adjusting the impact energy in combination with the nano-indentation hardness value of the coating, thereby achieving precise processing of different areas of the coating surface.

[0049] Specifically, firstly, an eddy current thickness gauge is used to obtain a thickness distribution map of the coating, which divides the coating surface into multiple distinct regions. Based on the thickness value, these regions are classified into two categories: high-energy impact regions and low-energy impact regions. Regions with a coating thickness greater than a first threshold are classified as high-energy impact regions, while regions with a coating thickness less than a second threshold are classified as low-energy impact regions. This classification method allows for the application of different impact energies to regions with varying coating thicknesses, thereby optimizing the uniformity and density of the coating.

[0050] In the high-energy impact zone, the energy value used is 120%-130% of the reference energy, which is determined by the nanoindentation hardness value of the coating. Specifically, the reference energy is increased accordingly for every predetermined increase in the coating's hardness value. In this way, areas with higher coating hardness receive greater impact energy to enhance their surface properties, while areas with lower hardness receive lower impact energy to avoid coating damage or over-compaction due to excessive impact.

[0051] Furthermore, the selection rules for the radius of curvature of the impact needle are also part of this technical feature. Choosing an appropriate impact needle radius is crucial when processing areas with different curvatures. In areas with significant abrupt changes in curvature (such as sharp corners or bends), needles with a radius ≤0.2mm are used to ensure that the impact energy is effectively concentrated in a small area, enhancing the surface hardness of that region. Conversely, in flat areas with gentler curvature, needles with a radius ≥0.5mm are used to distribute the impact energy more evenly, avoiding excessive concentration that could lead to surface damage or uneven coating.

[0052] Through the above method, this invention achieves precise impact energy distribution to regions with different coating thicknesses and hardnesses, ensuring the efficiency and uniformity of mold surface processing and avoiding coating defects or performance inconsistencies caused by uneven energy. This graded impact energy control not only improves the precision of mold surface treatment but also significantly enhances the wear resistance and corrosion resistance of the coating, thereby improving the service life and working performance of the mold.

[0053] In one possible implementation, the metal binder powder is first selected as a nickel-based alloy. This alloy possesses excellent high-temperature resistance and good adhesion, effectively enhancing the adhesion and stability of the coating. When determining the particle size distribution of the nickel-based alloy powder, the flow characteristics of the powder are accurately measured using Hall effect velocity testing. Hall effect velocity testing can determine the most suitable particle size range based on the size, shape, and distribution of the powder particles. Generally, a particle size combination with flow rates within the optimal range ensures the uniformity and stability of the powder during transport and deposition, thereby ensuring uniform coating thickness and stable performance.

[0054] For the ceramic reinforcing phase powder, an alumina-zirconia composite powder is used. Alumina has good hardness and wear resistance, while zirconia has high thermal shock resistance and crack resistance. Therefore, the combined use of the two can simultaneously improve the hardness and thermal stability of the coating. However, the zirconia content needs to be adjusted according to the temperature fluctuations of the mold's working environment. When the mold's working temperature fluctuations exceed the predetermined range, the zirconia content needs to be increased. By increasing the proportion of zirconia, the thermal shock resistance of the coating can be significantly improved, preventing cracks or peeling caused by rapid temperature changes, and enhancing the stability and durability of the coating under extreme temperature variations.

[0055] By simultaneously feeding metallic binder powder and ceramic reinforcing powder, this combination ensures the coating exhibits multiple properties, including high-temperature resistance, wear resistance, and thermal shock resistance. The selection of the metallic binder powder and the optimized ratio of the ceramic reinforcing powder enable the coating to demonstrate excellent adhesion, strength, and thermal stability under high temperatures and complex operating conditions. This technical feature effectively extends the service life of molds and improves their performance in harsh environments, demonstrating significant practical value and economic benefits.

[0056] In one possible implementation, the aging temperature is first selected based on the phase transformation characteristics of the coating material. The phase transformation point temperature is precisely determined using differential scanning calorimetry (DSC), which can detect the phase transformation temperature that occurs in the coating material during heating. To ensure optimal coating performance, the aging temperature is selected to be 40%-50% of the phase transformation point temperature. Within this temperature range, the material's microstructure can effectively transform into a favorable state, thereby improving the coating's hardness, wear resistance, and crack resistance.

[0057] Secondly, the holding time is calculated based on the mold's geometric dimensions, especially the thickness of the thickest part of the cross-section. Each 10mm increase in thickness corresponds to one hour of holding time. This design ensures the coating completes a uniform aging process at an appropriate temperature, guaranteeing the expected changes in the material's microstructure. When the mold's cross-sectional thickness change rate exceeds a predetermined value, the holding time is calculated based on 120% of the maximum thickness. This method avoids the impact of localized thickness unevenness, ensuring optimal aging results in all areas.

[0058] Finally, controlling the cooling rate is also a crucial aspect of aging treatment. During aging, rapid temperature changes can cause the coating to crack or lose its high-temperature resistance. Therefore, in the temperature range below the phase transition point, the cooling rate should be controlled to not exceed 30°C / min. This slow cooling process prevents stress concentration caused by rapid temperature changes, effectively avoiding coating cracking and maintaining its long-term stability.

[0059] By precisely controlling the aging temperature, holding time, and cooling rate, a uniform microstructure can be achieved in the coating during processing, improving its mechanical properties and thermal stability, extending the service life of the mold, and enhancing its reliability and durability under extreme conditions. This control method achieves comprehensive optimization of coating performance and has significant technical advantages.

[0060] In one possible implementation, the trajectory of the powder in the plasma jet is first recorded using high-speed photography. This step employs high-speed photography technology to capture the specific movement path and time information of the powder in the plasma jet at an extremely high frame rate. Through this precise real-time recording, key data such as the powder's trajectory and velocity changes from the spray gun to the substrate surface in the plasma jet can be obtained, thus providing an accurate basis for subsequent residence time calculations.

[0061] Next, the residence time of the powder is calculated based on the distance between the spray gun and the substrate and the average velocity of the powder. The distance between the spray gun and the substrate directly affects the time it takes for the powder to reach the substrate, while the average velocity of the powder determines its residence time in the plasma jet. By combining the spray gun distance and the powder velocity, the actual residence time of the powder in the plasma jet can be accurately calculated, that is, the time required for the powder to travel from the spray gun until it reaches the surface of the substrate.

[0062] When the calculated residence time is less than the time required for complete powder melting, process parameters need to be adjusted. In this case, to ensure complete powder melting and achieve the desired coating quality, it is necessary to simultaneously increase the plasma power and decrease the powder feed rate. Increasing the plasma power increases the heat input, thereby extending the melting time of the powder in the plasma jet, ensuring that the powder can fully melt and form a uniform coating. Reducing the powder feed rate helps to decrease the powder flow rate, resulting in a longer residence time for each powder particle in the plasma jet, further ensuring the sufficiency of the melting process.

[0063] By precisely controlling the residence time and adjusting the combination of plasma power and powder feeding rate, it is possible to ensure that the powder coating reaches a completely molten state during processing, thereby obtaining a uniform and dense coating and improving the wear resistance and corrosion resistance of the mold surface. This technique effectively avoids the unstable coating quality caused by incomplete powder melting, thus improving the service life and performance stability of the mold.

[0064] In one possible implementation, a mapping relationship between remelting depth and energy density was first established. Remelting depth refers to the depth to which the substrate surface melts during plasma spraying, while energy density refers to the thermal energy applied per unit area. To obtain this mapping relationship, metallographic sectioning techniques were used to measure the remelting depth under different energy densities through experiments. These experimental results provided fundamental data for further determining processing parameters.

[0065] Next, the required energy density is calculated by working backward from the target remelting depth. In actual processing, the target remelting depth is set to 10%-15% of the current coating thickness. This range is set to ensure good adhesion between the coating and the substrate, while avoiding excessive melting that could lead to overheating of the substrate or an excessively thin coating. In this way, the corresponding energy density can be calculated based on the target remelting depth, thus providing guidance for power adjustments during actual operation.

[0066] When the coating porosity exceeds the standard, the target remelting depth needs to be adjusted. High porosity indicates incomplete melting or weak bonding, affecting the coating's density and durability. Therefore, in this case, the target remelting depth needs to be increased proportionally to improve melting and reduce porosity. Appropriately increasing the target remelting depth enhances melting, reduces porosity, and ensures the coating quality meets requirements.

[0067] Precise energy density control enables stable and controllable coating quality, especially in preventing over-melting or under-melting, ensuring the uniformity, density, and durability of the coating on the mold surface. Simultaneously, timely adjustment of the target remelting depth helps optimize coating porosity, improve mold surface performance, and extend service life.

[0068] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0069] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A mold surface processing technology, characterized in that, Includes the following steps: Step 1: Based on curvature recognition, differential preprocessing is performed to scan the working surface of the mold and identify curvature change areas. According to the curvature distribution, the first sandblasting strategy is applied to the change areas, and the second sandblasting strategy is applied to the non-change areas. An anchor-shaped structure with increased depth is generated in the curvature change areas. The implementation method of the first sandblasting strategy in step 1 includes: The curvature radius of each region is calculated by analyzing 3D point cloud data, and regions with curvature radii less than a predetermined threshold are defined as curvature abrupt change regions. The air pressure value of the first sandblasting strategy is determined by the ratio of the hardness of the matrix material to the hardness of the abrasive: when the ratio is in the range of 1.0-1.5, 60%-70% of the standard air pressure is used; when it is in the range of 1.5-2.0, 70%-80% is used. The selection criteria for abrasive particle size are as follows: for groove areas with a depth-to-width ratio greater than 2, use fine abrasive with a particle size of 50%-60% of the standard value; The dynamic adjustment method for the sandblasting incident angle is as follows: the angle deviation is compensated in real time according to the angle between the surface normal vector and the spray gun axis, so that the effective impact angle is kept within the range of 85°-95°. Step 2: Gradient component dynamic plasma spraying, synchronously delivering metal binder powder and ceramic reinforcing powder. In the near matrix region, the metal phase powder delivery rate increases while the ceramic phase delivery rate increases from zero. In the region far from the matrix, the metal phase powder delivery rate decreases while the ceramic phase delivery rate increases. Step 3: Enhance the energy adaptive functional layer by adjusting the spray gun motion parameters for areas with abrupt curvature changes. After each single coat, an energy beam is used for dynamic remelting, and the remelting energy is adjusted based on real-time temperature feedback. Step 3, adjusting the spray gun motion parameters, includes: The reduction rate of scanning speed is determined by the ratio of the radius of curvature to the critical radius: when the radius of curvature is less than the critical radius, the speed is reduced to 70%-80% in the planar region; The rules for adjusting the spray gun distance are as follows: in concave areas, shorten it to 80%-90% of the standard distance; in convex areas, increase it to 110%-120%. The value of the critical radius is determined based on the working load of the mold: for every increase of a predetermined value in the impact load, the critical radius decreases proportionally. Step 4: Stress-coordinated post-treatment, applying graded impact energy according to the coating thickness distribution, and implementing aging treatment based on phase transformation characteristics.

2. The mold surface processing technology according to claim 1, characterized in that, The specific method for controlling the powder feeding rate in step 2 includes: The thickness of the near-matrix region is determined by calculating the difference in thermal expansion coefficients between the matrix material and the metal binder phase, and increasing the region thickness when the difference exceeds a predetermined percentage. The increasing gradient of the metal phase powder feeding rate is determined based on the temperature distribution of the plasma flow: a steep increasing gradient is used in the high-temperature region at the center of the flow, and a gentle increasing gradient is used in the low-temperature region at the edge. The initial activation point of the ceramic phase powder delivery rate is located at a predetermined distance from the substrate surface. This distance is calculated by the residence time of the powder in the plasma jet, ensuring that the powder reaches a molten state when it reaches the substrate.

3. The mold surface processing technology according to claim 1, characterized in that, The dynamic remelting operation method in step 3 includes: The real-time temperature data acquisition location is set 2-3 mm downstream of the remelting point, and the sampling frequency is not less than 1 kHz. The remelting energy adjustment rule is as follows: when the measured temperature is lower than the target range, the energy input value per unit area is increased by one degree Celsius; when it is higher than the target range, the energy beam scanning speed is increased proportionally. The target temperature range is calculated based on the solidus temperature of the coating material: the lower limit is solidus temperature × 0.85, and the upper limit is solidus temperature × 0.

92. The diameter of the focused energy beam spot is adaptively adjusted according to the coating thickness: for every 50μm increase in thickness, the spot diameter increases by a predetermined percentage.

4. The mold surface processing technology according to claim 1, characterized in that, The implementation method of graded impact energy in step 4 includes: The coating thickness distribution map is obtained by using an eddy current thickness gauge. Areas with a thickness greater than the first threshold are classified as high-energy impact zones, and areas with a thickness less than the second threshold are classified as low-energy impact zones. The energy value of the high-energy impact zone is 120%-130% of the reference energy. The reference energy is calculated by the nano-indentation hardness value of the coating: for every increase in hardness by a predetermined value, the reference energy increases proportionally. The selection rule for the radius of curvature of the impact needle is as follows: use a needle with a radius ≤0.2mm in areas of abrupt curvature change, and use a needle with a radius ≥0.5mm in planar areas.

5. The mold surface processing technology according to claim 1, characterized in that, The simultaneous conveying of the metal binder phase powder and the ceramic reinforcing phase powder in step 2 also includes: The metallic binder phase powder is a nickel-based alloy, and its particle size distribution is determined by Hall flow rate testing: the particle size combination with the flow rate in the optimal range is selected. The ceramic reinforcing phase powder is an alumina-zirconia composite powder, wherein the zirconia content is set according to the coating's thermal shock resistance requirements: when the mold's working temperature fluctuates beyond a predetermined range, the zirconia content is increased to a predetermined ratio.

6. The mold surface processing technology according to claim 1, characterized in that, The control method for time-sensitive processing in step 4 includes: After determining the phase transition point of the coating using differential scanning calorimetry, the aging temperature is taken as 40%-50% of the phase transition point temperature. The calculation logic for heat preservation time is as follows: based on the thickest part of the mold cross section, 1 hour is corresponding to every 10mm of thickness. When the change rate of cross section thickness exceeds the predetermined value, the time is calculated as 120% of the maximum thickness value. The cooling rate is controlled as follows: a slow cooling rate of ≤30℃ / min is used in the temperature range below the phase transition point.

7. The mold surface processing technology according to claim 2, characterized in that, The method for calculating the dwell time specifically includes: The trajectory of powder in a plasma jet is recorded by high-speed photography. The residence time is calculated based on the distance between the spray gun and the substrate and the average speed of the powder movement. When the residence time is less than the time required for the powder to completely melt, the plasma power is increased and the powder feeding rate is reduced simultaneously.

8. The mold surface processing technology according to claim 3, characterized in that, The logic for determining the energy input value per unit area includes: Establish the mapping relationship between remelting depth and energy density: measure the remelting depth at different energy densities using metallographic sections; The required energy density is calculated by working backward from the target remelting depth, and the target remelting depth is set to 10%-15% of the current coating thickness; When the coating porosity exceeds the standard, the target remelting depth is increased year-on-year.

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