Die repairing method for adjusting diameter of laser beam

Abstract

The invention relates to the technical field of laser cladding, and discloses a mold repairing method for adjusting the diameter of a laser beam. The method comprises the following steps: moving a laser cladding head according to a preset scanning path, and cladding a repairing material on a to-be-repaired surface of a mold so as to accumulate repairing layers layer by layer; wherein each repairing layer is of a space interlocking structure formed by a plurality of heterogeneous units which are periodically arranged; each heterogeneous unit is divided into a hard area and a soft area arranged on the periphery of the hard area; the laser cladding head is located in the same preset laser energy density interval when the hard area and the soft area are formed, and the diameter of a laser beam when the hard area is formed is smaller than that of a laser beam when the soft area is formed. According to the method, the combination of strength and ductility can be realized when the special stress part of the mold is repaired. The interaction between the cladding layers is enhanced through the interlocking structure, and the overall strength of the repairing coating is improved.

Description

Technical Field

[0001] The invention relates to the technical field of laser cladding, in particular to a mold repair method for adjusting the diameter of a laser beam. Background Art

[0002] Molds are important processing tools in modern industry. According to the manufacturing materials, processing technology and applicable fields, molds can be divided into hot working molds and cold working molds. Molds are used in high temperature and high load conditions for a long time. For example, in the die-casting process, when the mold surface contacts the molten metal, it will expand due to heat. When the mold cools down, tensile stress will be generated on the mold surface. Therefore, mold steel is very prone to failure during use, resulting in unstable product quality or completely unqualified products. It may also cause safety hazards to equipment and personnel. Therefore, the performance requirements of molds are very high.

[0003] Traditional mold repair methods (such as argon arc welding, surfacing, etc.) have the following disadvantages: a large amount of energy is input during the processing, forming a heat-affected zone with coarse structure and low hardness, resulting in the hardness and other surface properties of the repaired part being inferior to the original mold, and the mold is prone to secondary failure during subsequent use; and traditional welding methods require a lot of manual intervention and are inefficient. Laser cladding, as a new surface modification technology, uses high-energy laser as a heat source and metal powder as a process raw material. The laser and metal powder act simultaneously on the surface of the part to quickly melt and form, forming a dense, uniform and thickness-controlled metallurgical bonding layer. How to use the advantages of laser cladding technology, combined with the use conditions of the mold, to improve the comprehensive mechanical properties of the mold after repair, needs to be solved urgently. Summary of the invention

[0004] In order to solve the technical problem in the prior art that the comprehensive mechanical properties of the mold after repair are poor, the present invention provides a mold repair method for adjusting the diameter of a laser beam.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention discloses a mold repair method for adjusting the diameter of a laser beam, comprising:

[0007] The laser cladding head moves along a preset scanning path to clad the repair material on the surface to be repaired of the mold to accumulate repair layers layer by layer;

[0008] Among them, each repair layer is composed of a number of periodically arranged heterogeneous units forming a spatial interlocking structure; each heterogeneous unit is divided into a hard zone and a soft zone arranged outside the hard zone; the laser cladding head is in the same preset laser energy density range when forming the hard zone and the soft zone, and the laser beam diameter when forming the hard zone is smaller than the laser beam diameter when forming the soft zone.

[0009] As a further improvement of the above scheme, before stacking the repair layers layer by layer, the surface to be repaired of the mold is also subjected to the following pretreatment operations: mechanical processing to remove the oxide layer on the surface to be repaired, then sandblasting the surface to reduce the laser reflectivity, and then cleaning and drying.

[0010] As a further improvement of the above scheme, before stacking the repair layers layer by layer, the corresponding processing parameters of the hard area and the soft area are set respectively, and the processing parameters include: laser power, laser beam diameter, scanning speed, spacing between adjacent melt channels, powder feeding rate, layer thickness and laser specific energy.

[0011] As a further improvement of the above solution, when the laser cladding head clads the repair material, the overlap rate between adjacent melt tracks is set to 50%.

[0012] As a further improvement of the above solution, before stacking the repair layers layer by layer, the mold is also preheated to keep the overall temperature of the mold within a set range.

[0013] As a further improvement of the above solution, after the repair layers are stacked layer by layer, the mold is also tempered.

[0014] As a further improvement of the above solution, after the repair layers are deposited layer by layer, the surface of the mold with the repair layers is mechanically ground and polished to restore the original size and accuracy of the mold.

[0015] As a further improvement of the above solution, the laser generator of the laser cladding head adopts a fiber laser, and argon is used as a powder feeding gas and a protective gas during the process of cladding the repair material.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The mold repair method disclosed in the present invention forms a repair layer composed of heterogeneous units on the surface of the mold to be repaired by laser cladding by setting different laser diameters, which can achieve a combination of strength and ductility for the repair of special stress-bearing parts of the mold. The interaction between the interlocking structure-enhanced cladding layers improves the overall strength of the repair coating.

[0018] 2. This repair method has a high degree of automation, high repair accuracy, and small machining volume before and after mold repair. It can effectively save repair costs and accurately guarantee the repair quality. The performance of the repaired part is greatly improved, which can effectively avoid secondary failure in subsequent use. Compared with traditional welding, it reduces labor input, facilitates industrial production, and improves economic benefits.

[0019] 3. This repair method can restore the mold to its original appearance and size, and can also achieve component strength higher than the original component, saving the company a lot of money on purchasing new parts. This technology has a concentrated heat source and can achieve high-quality repair of the part's geometric shape and mechanical properties with little impact on the matrix performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the three-dimensional structure when a single-layer repair layer is formed on the mold surface in Example 1 of the present invention.

[0021] Figure 2 for Figure 1 Schematic diagram of the perspective structure of a single heterogeneous unit.

[0022] Figure 3 Schematic diagram of the principle of adjusting the diameter of the laser beam in Example 1 of the present invention.

[0023] Figure 4 It is a schematic diagram of the process of the laser cladding head in Example 1 of the present invention moving according to a preset scanning path to clad the repair material on the surface to be repaired of the mold to accumulate the repair layer layer by layer. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Example 1

[0026] See also Figure 1 and Figure 2 This embodiment provides a mold repair method for adjusting the diameter of a laser beam, which is used to repair a hot working mold of H13 material. The repair material is 85% Ni60 (nickel-based alloy powder) and 15% WC (tungsten carbide) particles, thereby forming a repair layer on the mold. Figure 1 and Figure 2 In the figure, B represents the mold, L represents the repair layer, A represents the heterogeneous unit, a1 represents the hard area, and a2 represents the soft area. Each repair layer is composed of a number of heterogeneous units arranged periodically to form a spatial interlocking structure; each heterogeneous unit is divided into a hard area and a soft area arranged outside the hard area.

[0027] The repair method includes the following steps:

[0028] S1. Pre-treatments such as machining, cleaning, sandblasting and drying are performed on the surface to be repaired of the H13 mold. In this embodiment, the surface to be repaired of the H13 mold can be rust-removed first, and then the surface to be repaired of the H13 mold is sandblasted and roughened with 45# (mesh) corundum sand, and then the oil stains on the surface to be repaired are cleaned with anhydrous ethanol.

[0029] S2. According to the size parameters and performance requirements of the mold surface to be repaired, the area to be clad is planned on the surface to be repaired, and the distribution pattern of the hard area and the soft area is divided according to the shape of the area, and the scanning path of the laser cladding head is set accordingly. For example, a three-dimensional model of the surface to be repaired is obtained using a vernier caliper or a three-dimensional scanner. The three-dimensional model is meshed to determine the path and direction of forming.

[0030] S3. Set the processing parameters of the laser cladding head and the laser generator.

[0031] In this embodiment, the laser generator uses a fiber laser, and the laser cladding head is aimed at the starting point of the H13 mold to be repaired. During the repair process, argon gas is used as the powder feeding gas and the protective gas to prevent oxidation.

[0032] Processing parameters of the hard zone: laser power 400W, laser beam diameter 0.8mm, scanning speed 15mm / s, adjacent melt channel spacing 0.4mm, powder feeding rate 3g / min, layer thickness 0.2mm, laser specific energy 33.3J / mm^2.

[0033] Processing parameters of the soft zone: laser power 1400W, laser beam diameter 3mm, scanning speed 15mm / s, adjacent melt channel spacing 1.5mm, powder feeding rate 12g / min, layer thickness 0.8mm, laser specific energy 31.1J / mm^2.

[0034] See also Figure 3 , the divergent light from the optical fiber is collimated by the collimating lens and converged by the focusing lens. By adjusting the position of the collimating lens, the focus of the laser beam can be adjusted up and down along the focusing direction, thereby adjusting the spot diameter. In this way, large and small spots are used to clad different melts, that is, the large spot clads the melt corresponding to the soft area, and the small spot clads the melt corresponding to the hard area. In addition, the overlap rate between the melts is 50%.

[0035] S4. The laser cladding head moves along a preset scanning path to clad the repair material on the surface to be repaired of the mold to accumulate repair layers layer by layer.

[0036] Among them, each repair layer is composed of a number of periodically arranged heterogeneous units forming a spatial interlocking structure; each heterogeneous unit is divided into a hard area and a soft area arranged outside the hard area; the laser cladding head is in the same preset laser energy density range when forming the hard area and the soft area (that is, the density is close or similar), and the laser beam when forming the hard area is smaller than the laser beam diameter when forming the soft area.

[0037] See also Figure 4 , the specific process of step S4 is:

[0038] S41, the laser cladding head clads the repair material through a large spot at the surface to be repaired closest to the mold (ie, B in the figure), i.e., the first layer, to form all the soft areas of the first layer (ie, a2).

[0039] S42. In the area surrounded by each soft area, a small light spot is used to melt and repair the material to form a hard area (i.e., a1).

[0040] Since the laser beam diameter in the hard zone is small, the melt path and layer thickness formed are also relatively small. Therefore, in an area surrounded by a soft zone, it is necessary to clad the hard zone multiple times. The number of melt paths in the hard zone each time also increases with the increase in height, until the top of the last melt path in the hard zone is flush with the top of the corresponding melt path in the soft zone, forming a heterogeneous unit in a repair layer.

[0041] It should be noted that due to the differences in the sizes of molten pools of different diameters, the height within the same repair layer must be strictly controlled and matched so that the construction process of the next repair layer starts from the same base surface.

[0042] In some embodiments, the projection of the heterogeneous unit on the horizontal plane can be in the shape of a square, a circle, a long strip, or a designed irregular shape, and accordingly, the scanning path of the laser cladding head also needs to be adjusted. For example, it can be scanned linearly from left to right, or scanned continuously along the "bow" shape, or scanned from the outer circle to the inner circle.

[0043] S43. After forming all the heterogeneous units of the first repair layer, take the first repair layer as the base surface, refer to steps S41 to S42, and stack upward to form a second repair layer. Repeat this operation to form several stacked repair layers on the surface of mold B.

[0044] It should be noted that the repair coating is filled in a layer-by-layer scanning manner. During the cladding process, the height of each layer needs to be controlled and the height ratio of the hard area and the soft area needs to be calculated.

[0045] S5. After the repair layer is formed, the mold is subjected to medium-temperature tempering treatment at a temperature of 400°C.

[0046] S6. Process the repaired mold surface to restore the original dimensional accuracy.

[0047] In summary, compared with the prior art, the mold repair method of the present invention has the following advantages:

[0048] 1. The present invention realizes the strength-plasticity synergy of heterogeneous structural materials through heterogeneous deformation-induced strengthening, and has both "hard" and "soft" characteristics. The heterogeneous structure is composed of heterogeneous regions with significantly different mechanical or physical properties, and the coupling of these heterogeneous regions produces a synergistic effect. This structure has excellent mechanical or physical properties that cannot be achieved by traditional homogeneous materials. The integration of this soft and hard alternating non-uniform structure plays a key role in effectively absorbing and dissipating the external load energy introduced during crack propagation. This geometric arrangement significantly reduces the effective stress intensity factor along the crack path, thereby improving the ability to resist external loads.

[0049] One of the reasons for the difference in strength between the hard zone and the soft zone is the grain boundary strengthening, which is caused by grain refinement. The peak temperature of the molten pool in the hard zone is higher than that in the soft zone, where the peak cooling rate of the hard zone is 4 times that of the soft zone. The molten pool formed at a smaller spot diameter solidifies at a higher cooling rate, which promotes grain refinement. Due to the faster cooling rate, the carbides, Laves, and γ′ phases in the hard zone have a shorter residence time during phase precipitation than the soft zone, resulting in insufficient growth time and smaller size. During the deformation process of the hard zone, small particles with a high volume fraction hinder the movement of dislocations and promote the propagation of dislocations, thereby increasing the accumulation of dislocations and the strain hardening rate.

[0050] 2. The present invention dynamically adjusts the laser beam diameter during the laser cladding process, thereby changing the cooling rate of the solidification process. The larger the beam diameter and the higher the energy input, the larger the size of the molten pool formed and the lower the cooling rate. Different cooling rates will cause non-equilibrium solidification of the molten pool, which will cause the component to form a special microstructure and superior mechanical properties that are completely different from traditional processes. For materials that are sensitive to changes in cooling rate, this method can achieve controllability of strength. Geometrically necessary dislocations pile up and accumulate near the boundary of the soft zone, generating back stress in the soft zone and front stress in the hard zone. Heterostructured materials have unique deformation behavior, forming dispersed microscopic strain bands, which helps to distribute plastic strain throughout the length, improve uniform elongation, and improve plasticity.

[0051] 3. The present invention arranges the laser cladding structure reasonably, and the structures with different diameters form a periodic distribution and spatial interlocking structure, with alternating characteristics of "soft" and "hard" perpendicular to the scanning direction and parallel to the scanning direction. This uneven area can be achieved by precise arrangement, placing the areas with significant strength differences in the appropriate position within a single component and achieving superior mechanical properties.

[0052] It should be noted that the mechanical interlocking effect refers to the relationship between the mechanical behavior and structural properties of a material. The mechanical interlocking effect enables the material to increase its plastic deformation capacity through internal stress transfer and interaction between grains. This ability gives the material higher ductility and toughness and higher strength. The mechanical interlocking effect limits the free deformation of the material and improves its ability to resist external loads. When the material is subjected to external loads, its internal structure changes. This interaction between dislocation movement and grain boundary movement can improve the mechanical properties of the material. Dislocations in the material can hinder the slip of grain boundaries, thereby increasing the strength of the material. In this repair method, the mechanical interlocking effect is achieved by changing the organizational structure of the material. In addition, it can also be achieved by changing the crystal orientation and grain boundary characteristics.

[0053] 4. In the heterogeneous structure of the present invention, the contribution of heterogeneous deformation-induced hardening to the overall strain hardening is higher, which is attributed to the higher density of geometrically necessary dislocations appearing at the heterogeneous grain boundaries during the deformation process, resulting in higher heterogeneous deformation-induced strain hardening, thereby exhibiting better tensile properties.

[0054] Example 2

[0055] This embodiment provides a mold repair method for adjusting the diameter of a laser beam. The difference from Embodiment 1 is that H13 powder is used as a repair material to repair a hot working mold made of H13 material. Specifically, the following steps may be included:

[0056] According to the depth and width of the crack, mechanical processing is performed around the damaged area. The damaged area and the surrounding oxide layer are removed, cleaned with acetone and dried.

[0057] The chemical composition of H13 powder repair material includes 5% Cr, 0.3% Mn, 1% Si, 0.4% C, 1.5% Mo and 0.9% V, and the remainder is Fe. The powder size is 53μm to 105μm.

[0058] Before repairing, the mold is heated to make the overall temperature of the mold uniform at 120°C.

[0059] In this embodiment, cladding is performed under the protection of an inert gas to melt powder having the same composition as that of the substrate to be repaired.

[0060] Among them, the processing parameters of the hard area are: laser power 300W, laser beam diameter 0.8mm, scanning speed 12mm / s, adjacent melt channel spacing 0.4mm, powder feeding rate 3g / min, layer thickness 0.2mm, laser specific energy 31.3J / mm^2.

[0061] Processing parameters of the soft zone: laser power 1200W, laser beam diameter 3mm, scanning speed 12mm / s, spacing between adjacent melt channels 1.5mm, powder feeding rate 12g / min, layer thickness 0.8mm, laser specific energy 33.3J / mm^2.

[0062] The scanning principle of the laser cladding head during the repair process is similar to that of Example 1 and will not be described in detail here.

[0063] After the repair layer is formed, the mold is subjected to medium-temperature tempering at a temperature of 400°C.

[0064] Finally, the repaired mold surface is processed to restore the original dimensional accuracy.

[0065] Example 3

[0066] This embodiment provides a mold repair method for adjusting the diameter of a laser beam. The difference from Embodiment 1 is that WC+Fe-based alloy powder is used as a repair material to repair a cold working mold of a G20CrMo material. Specifically, the following steps may be included:

[0067] First, use 150# silica sandpaper to polish the surface to be repaired to remove uneven surface areas and oxide scale, while preventing the surface from being too smooth, which may cause excessive laser reflectivity.

[0068] Place the sample to be repaired in an ultrasonic cleaner, add alcohol to clean it, remove surface oil, and dry it for later use.

[0069] In the repair material, the chemical composition of the Fe-based alloy powder is: 15.3% Cr, 1.2% B, 0.55% Mn, 1.45% Mo, 0.24% C, 1.9% Ni, 1.23% Si, and the balance is Fe.

[0070] Then 90% of Fe-based alloy powder and 10% of WC particles were mixed and ball milled in a glove box to avoid oxidation in the air. The specific ball milling parameters were as follows: the diameter of the ZrO2 ceramic ball was 3 mm, the ball-to-material ratio was 10:1, the ball mill running speed was 120 r / min, and the ball milling time was 3 h.

[0071] Place the prepared powder in a drying oven and dry at 100°C to 110°C for 2 hours.

[0072] In this embodiment, before the formal repair, the mold is preheated as a whole (480° C. to 520° C.), and then laser cladding repair is performed.

[0073] The scanning principle of the laser cladding head during the repair process is similar to that of Example 1 and will not be described in detail here.

[0074] After the repair is completed, the mold is placed in a tempering furnace 50°C higher than the preheating temperature for insulation. After being placed in the furnace for the insulation time, it is cooled to room temperature with the furnace.

[0075] Finally, the mold is mechanically ground and polished to restore its original size and accuracy.

[0076] In this embodiment, WC particles have the characteristics of high melting point, high corrosion resistance, good ductility, low thermal expansion coefficient, high fracture toughness, etc. In addition, the wetting angle between WC particles and iron-based alloy is very small, indicating that the two have excellent wettability. The moderate dissolution of WC reinforcing particles can avoid excessive reduction in their volume in the composite coating, while enhancing the strengthening effect on the substrate and the bonding strength of the bonding, which is conducive to improving the overall performance of the composite coating.

[0077] In addition, the wear mechanism of Fe-based coating is mainly severe adhesive wear, abrasive wear and excessive oxidation wear. The wear mechanism of Fe-based / WC coating is mainly abrasive wear accompanied by slight fatigue peeling. The wear surface of the coating with WC added is mainly shallow and fine furrows, without adhesive layer and peeling pits. The wear surface is relatively smooth and has the best surface wear resistance.

[0078] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A mold repair method for adjusting the diameter of a laser beam, characterized in that: include: The laser cladding head moves along a preset scanning path to clad the repair material on the surface to be repaired of the mold to accumulate repair layers layer by layer; Among them, each repair layer is composed of a number of periodically arranged heterogeneous units forming a spatial interlocking structure; each heterogeneous unit is divided into a hard area and a soft area arranged outside the hard area; the laser cladding head is in the same preset laser energy density range when forming the hard area and the soft area, and the laser beam diameter when forming the hard area is smaller than the laser beam diameter when forming the soft area.

2. A mold repair method for adjusting the diameter of a laser beam according to claim 1, characterized in that: Before stacking the repair layers layer by layer, the surface of the mold to be repaired is subjected to the following pretreatment operations: mechanical processing to remove the oxide layer on the surface to be repaired, sandblasting to roughen the surface to reduce the laser reflectivity, and then cleaning and drying.

3. The mold repair method for adjusting the laser beam diameter according to claim 1, characterized in that: Before stacking the repair layers layer by layer, processing parameters corresponding to the hard area and the soft area are set respectively, and the processing parameters include: laser power, laser beam diameter, scanning speed, adjacent melt channel spacing, powder feeding rate, layer thickness and laser specific energy.

4. The mold repair method for adjusting the laser beam diameter according to claim 3, characterized in that: When the laser cladding head clads the repair material, the overlap rate between adjacent melt paths is set to 50%.

5. The mold repair method for adjusting the laser beam diameter according to claim 1, characterized in that: Before stacking the repair layers layer by layer, the mold is preheated to keep the overall temperature of the mold within a set range.

6. A mold repair method for adjusting the laser beam diameter according to claim 5, characterized in that: After the repair layers are deposited layer by layer, the mold is further subjected to a tempering treatment.

7. The mold repair method for adjusting the laser beam diameter according to claim 1, characterized in that: After the repairing layers are deposited layer by layer, the surface of the mold with the repairing layers is mechanically ground and polished to restore the original size and precision of the mold.

8. The mold repair method for adjusting the laser beam diameter according to claim 1, characterized in that: The laser generator of the laser cladding head adopts a fiber laser, and argon is used as the powder feeding gas and the shielding gas during the cladding repair material process.

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