A method for preparing a pre-positioned laser cladding coating on a conical screw

Abstract

This invention relates to a method for preparing a pre-placed laser cladding coating on a conical screw, comprising the following steps: The conical screw is considered as a frustum of a cone; after unfolding the frustum, a fan-shaped ring is obtained, and the helix of the screw ridge is a curve wound around the side of the frustum; the three-dimensional helix wound around the side of the frustum is unfolded and calculated to be converted into a two-dimensional planar curve; based on the width of the screw ridge, regions are divided on a base film, and multiple coating strips are planned; a paste-like powder is uniformly coated onto the base film, dried to a plastic soft solid state, and then cut and segmented according to the region division to obtain coating strips; each coating strip is individually attached to the surface of the screw ridge of the conical screw, placed in a vacuum furnace for heat preservation, and then the base film is peeled off to obtain the pre-placed cladding layer. This invention not only solves the problem that traditional pre-placed laser cladding is difficult to apply to complex structural parts such as conical or variable pitch screws, but also has the advantages of simple process, strong adaptability, good repeatability, and high engineering application value, and has high application and promotion value.

Description

Technical Field

[0001] This invention relates to the field of laser cladding surface strengthening and component remanufacturing technology, and in particular to a method for preparing a pre-positioned laser cladding coating on a conical screw. Background Technology

[0002] Conical twin-screw extruders are essential molding equipment widely used in the processing of polyvinyl chloride (PVC), wood-plastic composites, thermosetting plastics, and other high-viscosity polymers. Compared to parallel twin-screw extruders, conical twin-screw extruders offer advantages such as higher compression ratios, stronger plasticizing capabilities, higher torque transmission, shorter material residence time, lower energy consumption, and a wider range of adaptable materials. They can meet the continuous and stable processing requirements of highly filled and high-viscosity materials, and are therefore widely used in the plastics, rubber, and chemical industries.

[0003] In the extrusion process, the screw, as the core component for material conveying, compression, plasticizing, and mixing, operates under complex conditions of high temperature, high pressure, high shear, and high filler particle content. The screw thread surface is continuously subjected to erosion and abrasion from material particles, fillers, and fiber reinforcement materials, making it highly susceptible to wear, dimensional reduction, and profile failure. This not only affects the plasticizing quality and extrusion efficiency but also reduces equipment lifespan and increases maintenance costs. Therefore, improving the wear resistance and service life of the screw thread surface has become an important research direction in the manufacturing and remanufacturing of conical twin-screw extruders.

[0004] Currently, common methods for improving the wear resistance of screw surfaces include thermal spraying, welding, plasma cladding, and laser cladding. Among these, laser cladding technology utilizes a high-energy laser beam as a heat source to simultaneously melt the cladding material and the substrate surface, forming a metallurgical bonding layer. It offers advantages such as a small heat-affected zone, minimal substrate deformation, refined microstructure, high bonding strength, low dilution rate, and a wide range of selectable cladding materials. It can significantly improve the surface hardness, wear resistance, and corrosion resistance of parts while ensuring the performance of the substrate, thus showing broad application prospects in screw repair and surface strengthening.

[0005] Depending on the method of supplying the cladding material, laser cladding technology mainly includes pre-positioned laser cladding, powder-feeding laser cladding (including coaxial and off-axis powder feeding), and wire-feeding laser cladding. While powder-feeding laser cladding has a high degree of automation, it places high demands on powder particle size distribution, powder feeding stability, and cladding posture, and is prone to problems such as uneven powder feeding and low powder utilization in complex curved surface processing. Wire-feeding laser cladding, on the other hand, is limited by the specifications and forming characteristics of the wire material, and its adaptability to high-hardness and high-wear-resistant alloy materials is relatively limited. In contrast, pre-positioned laser cladding, by pre-laying the cladding material on the substrate surface, not only effectively reduces the dependence of the powder feeding process on material particle size and conveying stability, but also has advantages such as flexible material selection, high freedom in composition design, and suitability for preparing high-hardness wear-resistant layers. Therefore, it has high application value in the surface strengthening of wear-resistant parts such as screws.

[0006] However, pre-formed laser cladding processes require the preparation of a uniform, accurate, and stable pre-coating on the surface to be processed before laser cladding. For a conical twin-screw, the screw edges are continuously spirally distributed along the conical surface, exhibiting geometric features such as taper variation, helix angle variation, and complex spatial curvature, making it a typical complex three-dimensional curved surface structure. In existing technologies, pre-formed coatings are typically prepared manually, by brushing, or by mold pressing. This not only results in low construction efficiency but also makes it difficult to ensure coating thickness uniformity and flatness, easily leading to problems such as localized accumulation, material shortages, wrinkling, edge lifting, and dimensional deviations. This results in inconsistent cladding layer thickness and significant fluctuations in forming quality during subsequent laser cladding, failing to meet the consistency and stability requirements of industrial mass production.

[0007] Furthermore, for parts with complex spatial helical structures, such as tapered screws or variable-pitch screws, existing pre-coating preparation methods typically involve direct application or manual trimming based on the three-dimensional curved surface. This lacks precise design tailored to the spatial geometry of the helical lines. During the application process, the pre-coating is prone to bending, stretching, or folding deformation, resulting in low matching accuracy between the coated layer and the thread profile. This leads to issues such as incomplete coating, uneven thickness, edge collapse, and localized gaps, ultimately affecting the dimensional accuracy and wear resistance of the cladding layer. Therefore, achieving high-precision design and stable preparation of pre-coatings for the complex three-dimensional helical structure of tapered screws, and improving the bonding accuracy, flatness, and process consistency of the pre-coating, has become a critical technical problem to be solved in the engineering application of pre-coated laser cladding technology. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a pre-positioned laser cladding coating on a conical screw.

[0009] This invention is achieved through the following technical solution: A method for preparing a pre-positioned laser cladding coating on a tapered screw includes the following steps: S1. Consider the conical screw as a frustum of a cone. After unfolding the frustum, a fan ring is obtained. The spiral line of the screw ridge is a curve that wraps around the side of the frustum. S2. The three-dimensional thread line wound on the side of the frustum is unfolded, calculated, and transformed into a two-dimensional planar curve. Based on the width of the screw ridge of the tapered screw, the area is divided on the bottom film, and multiple coating strips are planned. S3. Coat the paste powder evenly onto the base film, dry it to a plastic soft solid state, and then cut it into sections according to the area division to obtain the coating strip; S4. Each of the coating strips is attached to the surface of the screw ridge of the conical screw one by one, and after being kept warm in a vacuum furnace, the bottom film is peeled off to obtain the pre-formed cladding layer.

[0010] According to the above technical solution, preferably, in step S2, the three-dimensional thread line wound on the side of the frustum is unfolded, calculated, and converted into a two-dimensional planar curve. , , Where R is half the lower arc length of the fan ring, r is half the upper arc length of the fan ring, h is the axial height of the frustum, l is the length of the hypotenuse of the frustum's side, P is the pitch of the conical screw, and L is the radius of the larger sector in the fan ring, all in mm; θ is the central angle of the fan ring, and t is the angle during the rotation of the helix, with a value range of... All units are °.

[0011] According to the above technical solution, preferably, in step S1, the conical screw is regarded as a frustum of a cone, and the frustum is unfolded to obtain a fan ring. l is the length of the hypotenuse of the lateral side of the frustum: , The radius L of the large sector in the unfolded sector ring: , The radius S of the small sector in the unfolded sector ring: , The central angle θ of the fan ring: .

[0012] The helix of the spiral is a curve that wraps around the side of the frustum, and the total rotation angle of the helix is ​​Φt: , Using polar coordinates, calculate the coordinates (ρ, θ) of multiple points on the spiral in the unfolded diagram.exp The angle during the rotation is denoted as t, where 0 ≤ t ≤ Φt. Current height z: , Current radius R of the frustum current The radius decreases linearly from bottom to top: , The polar radius ρ of that point on the unfolded diagram is the radius of the sector corresponding to that point. , Let z and radius R current Substituting the values, we obtain the polar radius function ρ(t), and the distance from this point to the origin of the expanded graph: , The polar angle θ of this point on the unfolded diagram exp The angle through which this point rotates on the sector: , radius R current Substituting the values, we obtain the polar angle function. (t), the angle between the line connecting this point to the origin and the initial baseline: , Based on the polar radius function ρ(t) and polar angle function in polar coordinates (t), transforming the equation into a function in rectangular coordinates. according to ,get , thereby: , .

[0013] According to the above technical solution, preferably, in step S3, the paste powder includes: alloy powder, polyvinyl butyral accounting for 5-10% of the mass fraction of the alloy powder, 3-5% anhydrous ethanol, 1-2% triethyl borate and 2-4% ethyl silicate.

[0014] According to the above technical solution, preferably, in step S3, the composition of the alloy powder includes: Ni content of 40-55% by mass, WC content of 10-15% by mass, TiC content of 10-15% by mass, NbC content of 10-15% by mass, rare earth CeO2 content of 0.5-1% by mass, rare earth La2O3 content of 0.5-1% by mass, and rare earth Y2O3 content of 0.5-1% by mass.

[0015] According to the above technical solution, preferably, step S3 includes: The base film is a BOPET film, and the paste powder is uniformly coated on the base film with a thickness of 2.0-2.2 mm; Place in a 50℃ drying oven and dry for 15 minutes until the coating is a plastic, soft solid. The bottom film is laid flat on the vacuum adsorption stage with the bottom film facing down. Vacuum adsorption is started, and a two-dimensional contour cutting path is generated according to the area division. The blade tip penetrates a layer of paste powder without damaging the bottom film. After cutting and segmenting, the coating tape is obtained.

[0016] According to the above technical solution, preferably, in step S4, the screw edge of the tapered screw is grooved using a cyclone milling method, with a depth of 2mm and a width of 1mm on both sides.

[0017] According to the above technical solution, preferably, in step S4, each of the coating tapes is attached to the groove of the screw thread one by one, and placed in a vacuum furnace at 150°C for 2 hours to allow polyvinyl butyral to be completely decomposed and carbonized, and triethyl borate and ethyl silicate to begin to decompose. The bottom film is then torn open to obtain the pre-formed cladding layer.

[0018] The beneficial effects of this invention are: This invention proposes a flexible transfer-type pre-placed laser cladding coating preparation method for conical screws. The method involves pre-coating a paste-like alloy powder uniformly onto a flexible substrate, drying it to form a soft solid coating with a certain degree of plasticity, and then transferring it onto the surface of the conical screw's screw ridges. Compared to traditional direct brushing or manual application methods, this method eliminates the need to directly form the coating on complex helical surfaces, significantly improving the thickness uniformity and smoothness of the pre-placed coating, reducing defects such as bubbles, inclusions, localized accumulation, and voids. This ensures stable adhesion between the pre-placed cladding layer and the substrate, providing a uniform distribution of cladding material for subsequent laser cladding. This results in a dense, stable, and highly bonded wear-resistant cladding layer.

[0019] Meanwhile, to address the challenge of accurately applying the complex spatial helix of a conical screw, a mathematical model of the conical screw's frustum was established. This model precisely converts the three-dimensional helix corresponding to the screw ridge into a two-dimensional planar curve. Based on the unfolding results, the design, planning, and cutting of the pre-coated layer are performed, enabling the prepared two-dimensional coating tape to accurately reproduce the spatial geometry of the screw ridge. This achieves a high-precision match between the pre-coated layer and the screw ridge contour, effectively avoiding coating defects, uneven thickness, edge lifting, and dimensional deviations caused by surface bending, stretching, and folding in traditional processes. This improves the bonding accuracy of the pre-coated layer and the dimensional consistency of subsequent cladding repair parts.

[0020] In addition, this application utilizes the two-dimensional contour after planar unfolding to divide the pre-coated area and combines it with a vacuum adsorption platform to complete digital cutting, transforming the preparation of pre-coated areas of complex three-dimensional spiral surfaces into a two-dimensional planar processing process. This not only improves cutting accuracy but also reduces the reliance on operational experience in traditional manual trimming, improves the consistency and repeatability of pre-coated preparation, facilitates the standardized and automated production of pre-coated areas for tapered screws of different specifications, and improves process stability and production efficiency. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure in this invention, in which the conical screw is regarded as a frustum.

[0022] Figure 2 This is an unfolded diagram in which the conical screw is regarded as a frustum of a cone in this invention.

[0023] Figure 3 This is a curve graph drawn using a formula in this invention.

[0024] Figure 4 This is a schematic diagram illustrating the use of curve planning to divide multiple regions in this invention.

[0025] Figure 5 This is a schematic diagram of slotting on the screw edge of the tapered screw in this invention.

[0026] Figure 6 This is a schematic diagram illustrating the principle of cladding the screw edges of the conical screw in this invention.

[0027] Figure 7 This is a schematic diagram of the metallographic structure of the cladding layer after laser cladding in this invention. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0029] As shown in the figure, this invention provides a method for preparing a pre-placed laser cladding coating on a conical screw, comprising the following steps: Step S1. Consider the conical screw as a frustum of a cone. After unfolding the frustum, a fan ring is obtained. The spiral line of the screw edge is a curve that wraps around the side of the frustum.

[0030] The conical screw is considered as a frustum of a cone. When the frustum is unfolded, a fan ring is obtained. This fan ring is composed of a part of two concentric circles (the center of which is the vertex of the frustum).

[0031] l is the length of the hypotenuse of the lateral side of the frustum: , Using the similar triangle theorem, the radius L of the larger sector in the expanded sector ring is: , The radius S of the small sector in the unfolded sector ring: , The central angle θ of the fan ring: .

[0032] The helix of the spiral is a curve that wraps around the side of the frustum, and the total rotation angle of the helix is ​​Φt: , Using polar coordinates, calculate the coordinates (ρ, θ) of multiple points on the spiral in the unfolded diagram. exp The angle during the rotation is denoted as t, where 0 ≤ t ≤ Φt. Current height z: , Current radius R of the frustum current The radius decreases linearly from bottom to top: , The polar radius ρ of that point on the unfolded diagram is the radius of the sector corresponding to that point. , Let z and radius R current Substituting the values, we obtain the polar radius function ρ(t), and the distance from this point to the origin of the expanded graph: , The polar angle θ of this point on the unfolded diagram exp The angle through which this point rotates on the sector: , radius R current Substituting the values, we obtain the polar angle function. (t), the angle between the line connecting this point to the origin and the initial baseline: , Based on the polar radius function ρ(t) and polar angle function in polar coordinates (t), transforming the equation into a function in rectangular coordinates. according to ,get , thereby: , , Where R is half the lower arc length of the fan ring, r is half the upper arc length of the fan ring, h is the axial height of the frustum, l is the length of the hypotenuse of the frustum's side, P is the pitch of the conical screw, and L is the radius of the larger sector in the fan ring, all in mm; θ is the central angle of the fan ring, and t is the angle during the rotation of the helix, with a value range of... All units are °.

[0033] Step S2. Unfold and calculate the three-dimensional thread line wrapped around the side of the frustum and convert it into a two-dimensional planar curve. Based on the width of the screw ridge of the tapered screw, divide the area on the bottom film and plan multiple coating strips.

[0034] In this step, the conical screw is regarded as a frustum of a cone, and a mathematical model of the frustum unfolding is established. The three-dimensional spiral wound on the surface of the frustum is accurately unfolded into a two-dimensional planar curve. Based on this, the planning, cutting and preparation of the pre-coating are completed, so that the two-dimensional pre-coating can accurately correspond to the spatial contour of the conical screw's screw edge. For the first time, the geometric unfolding concept of complex three-dimensional spiral surfaces is applied to the design of screw pre-coatings, which fundamentally solves the problem that it is difficult to ensure the geometric accuracy of complex spiral surfaces in the traditional manual application process, and improves the dimensional accuracy and bonding accuracy of the pre-coating.

[0035] In this example, R is 57.94 mm, r is 53.8 mm, h is 275 mm, and P is 150 mm, resulting in the following equation: , , in, .

[0036] Use the curve function of engineering drawing software to draw curves, such as Figure 3 As shown. Subsequently, using its curve to plan the cutting and unfolding curve, as well as the thread width, the film-forming area is planned, and multiple areas are divided for convenient mass production. Specifically, in this example, based on the above curve and the thread width of 15mm, 24 coating strips are planned here (the number can be arbitrarily planned according to requirements), as shown. Figure 4 As shown.

[0037] Step S3. Coat the paste powder evenly onto the base film, dry it to a plastic soft solid state, and then cut it into sections according to the area division to obtain the coating tape.

[0038] The alloy powder composition includes: Ni content 40-55% by mass, WC content 10-15% by mass, TiC content 10-15% by mass, NbC content 10-15% by mass, rare earth CeO2 content 0.5-1% by mass, rare earth La2O3 content 0.5-1% by mass, and rare earth Y2O3 content 0.5-1% by mass. The particle size range is 50-106 μm. It is subjected to planetary mechanical stirring for 4 hours at 50-60 rpm.

[0039] The paste powder includes: alloy powder, polyvinyl butyral (PVB) at a mass fraction of 5-10% of the alloy powder, anhydrous ethanol at 3-5%, triethyl borate at 1-2%, and ethyl silicate at 2-4%. The stirred alloy powder is mixed with PVB, anhydrous ethanol, triethyl borate, and ethyl silicate until a uniform paste is formed.

[0040] The material has high strength, which is due to the synergistic superposition of multiple strengthening mechanisms. Specifically: (1) Solid solution strengthening: The Ni matrix generates lattice distortion through solid solution of W, Ti, Nb and other atoms, which significantly improves the yield strength of the matrix itself, so that it can effectively support the hard phase without plastic collapse; (2) Second phase strengthening: WC, TiC and NbC, three high hardness carbides, are dispersed in the Ni matrix in a ratio of 10-15%, forming a multi-scale hard support network, which directly bears the contact load and hinders the movement of dislocations; (3) Grain refinement strengthening: Rare earth oxides (CeO2 / La2O3 / Y2O3) provide heterogeneous nucleation sites in the molten pool and pin grain boundaries, which significantly refines the dendrites and carbide clusters of the Ni matrix. Size, according to Hall-Petch relationship, the finer the grains, the higher the material strength; (4) Dispersion strengthening: Rare earth oxide particles themselves are distributed in the matrix and interface as non-deformable dispersed phases, hindering dislocation climb and high temperature creep, while purifying the melt and eliminating weak inclusions along the grain; (5) In-situ composite carbide strengthening: After WC is partially dissolved, W atoms diffuse into the FCC lattice of TiC / NbC, forming (Ti,Nb,W)C composite solid solution carbide in situ. Its multi-component lattice distortion and chemical continuity interface further enhance the inherent strength of the hard phase and the bonding force with the matrix, making the overall strength exceed the linear superposition of simple mixing.

[0041] This step employs a bonding system composed of polyvinyl butyral, anhydrous ethanol, triethyl borate, and ethyl silicate. This system enables the alloy powder to exhibit excellent film-forming properties, flexibility, and cutability during the prefabrication stage. It ensures that the coating tape remains intact during handling and application, and allows the bonding components to gradually decompose during vacuum insulation. This ensures that the pre-formed cladding layer is stably attached to the screw surface, reducing material detachment or positional displacement during subsequent laser cladding. This improves the forming quality and process reliability of the pre-formed layer.

[0042] In this example, the base film is a BOPET film. A paste-like powder is evenly coated onto the base film using a doctor blade to a thickness of 2.0-2.2 mm. After coating, it is placed in a 50°C drying oven for 15 minutes until the coating reaches a pliable, soft solid state. The base film is then laid flat on a vacuum adsorption stage with the base film facing down. Vacuum adsorption is initiated, and a two-dimensional contour cutting path is generated according to the area division. The blade tip penetrates a layer of paste-like powder without damaging the base film. After cutting and segmenting, the coated tape is obtained.

[0043] Preferably, this step uses a CNC engraving machine or a small precision engraving machine with three-axis linkage capability as the motion platform. The X / Y axis repeatability is required to be better than ±0.02mm, and the Z axis uses ball screw drive to ensure stable pressing depth. A specially made tungsten steel needle tip shank is installed at the spindle end. The needle tip material is YG6 or YG8, and the tip is ground into a 90° cone angle and rounded to a spherical surface with an radius of R0.15-0.25mm to avoid puncturing the PET base film. The worktable is equipped with a vacuum adsorption system, which firmly adsorbs and fixes the BOPET film along with the pre-coated green film above it through a porous aluminum plate.

[0044] In actual operation, the coated green sheet (PET side down), baked to a malleable soft solid state, is laid flat on the vacuum adsorption stage, and vacuum adsorption is initiated. The CNC machine generates a two-dimensional contour toolpath by unfolding the contour area according to the pre-imported screw and dividing the DXF file. The Z-axis drives the needle tip to scribing along the contour line with a constant downward pressure. The needle tip only penetrates the paste / powder coating (to a depth of approximately 75-90% of the paste thickness), leaving the PET base film intact. After scribing is completed, the vacuum is turned off, the entire sheet of material is removed, and it is gently folded in the opposite direction along the scribing line. The paste layer then neatly breaks and separates along the groove, while the PET base film remains intact and can be directly transferred to the transfer process.

[0045] In this step, a vacuum adsorption platform combined with a bottom film cutting process is used to directly convert the two-dimensional unfolded model into a cutting path, realizing the digital processing of the pre-coated layer. This avoids the dimensional errors caused by traditional reliance on manual trimming and experience control, improves the processing accuracy and repeatability of the pre-coated layer on complex tapered screws, and enables the rapid preparation of pre-coated layers on tapered screws of different specifications. This facilitates standardized, batch, and automated production, and improves process stability and industrial application capabilities.

[0046] Step S4. Apply each of the coating tapes to the surface of the screw ribs of the conical screw one by one, place them in a vacuum furnace for heat preservation, and then peel off the bottom film to obtain the pre-formed cladding layer.

[0047] The tapered screw is grooved using a cyclone milling method, with a depth of 2mm and a width of 1mm on both sides. After cladding, the two sides usually have a sloping shape. After grooving, filling is performed to help make the edges at both ends full.

[0048] According to the area division, the coating is divided using a cutting machine. Each of the divided curved coating strips is then attached to the groove of the screw thread and placed in a vacuum furnace at 150°C for 2 hours to allow the polyvinyl butyral to completely decompose and carbonize, and the triethyl borate and ethyl silicate to decompose and begin to function. The base film is then peeled off to obtain the pre-formed cladding layer.

[0049] like Figure 5 As shown, offline programming using PQart was employed for cladding of the screw threads, employing a left-right oscillation method. The program was written based on the screw thread curve, using this left-right oscillation method for cladding. The process parameters used were: spot size 6mm, power 2100W, powder feed rate 15g / min, single-pass lateral movement 2mm, and protective gas flow rate 20L / min. After cladding, as shown... Figure 6 As shown in the metallographic image, the morphology is free of pores and cracks.

[0050] In summary, this application provides a method for preparing a pre-positioned laser cladding coating for conical screws. It organically combines mathematical modeling of complex three-dimensional helical surfaces, two-dimensional planar unfolding, flexible transfer preparation, and digital cutting processes, forming a complete preparation method suitable for pre-positioned laser cladding of conical screws. This method not only effectively solves the problem that traditional pre-positioned laser cladding is difficult to apply to complex curved surface parts such as conical screws and variable pitch screws, but also has advantages such as high processing accuracy, good process stability, and ease of promotion and application. It can be widely used in the manufacturing and remanufacturing of wear-resistant parts such as conical twin-screws, and has good engineering application prospects and industrialization value.

[0051] 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 method for preparing a pre-placed laser cladding coating on a conical screw, characterized in that, Includes the following steps: S1. Consider the conical screw as a frustum of a cone. After unfolding the frustum, a fan ring is obtained. The spiral line of the screw ridge is a curve that wraps around the side of the frustum. S2. The three-dimensional thread line wound on the side of the frustum is unfolded, calculated, and transformed into a two-dimensional planar curve. Based on the width of the screw ridge of the tapered screw, the area is divided on the bottom film, and multiple coating strips are planned. S3. Coat the paste powder evenly onto the base film, dry it to a plastic soft solid state, and then cut it into sections according to the area division to obtain the coating strip; S4. Each of the coating strips is attached to the surface of the screw ridge of the conical screw one by one, and after being kept warm in a vacuum furnace, the bottom film is peeled off to obtain the pre-formed cladding layer.

2. The method for preparing a pre-positioned laser cladding coating on a conical screw according to claim 1, characterized in that, In step S2, the three-dimensional thread line wrapped around the side of the frustum is unfolded, calculated, and transformed into a two-dimensional planar curve. ， ， Where R is half the lower arc length of the fan ring, r is half the upper arc length of the fan ring, h is the axial height of the frustum, l is the length of the hypotenuse of the frustum's side, P is the pitch of the conical screw, and L is the radius of the larger sector in the fan ring, all in mm; θ is the central angle of the fan ring, and t is the angle during the rotation of the helix, with a value range of... All units are °.

3. The method for preparing a pre-positioned laser cladding coating on a conical screw according to claim 2, characterized in that, In step S1, the conical screw is considered as a frustum of a cone, and the frustum is unfolded to obtain a fan-shaped ring. l is the length of the hypotenuse of the lateral side of the frustum: ， The radius L of the large sector in the unfolded sector ring: ， The radius S of the small sector in the unfolded sector ring: ， The central angle θ of the fan ring: 。 4. The method for preparing a pre-positioned laser cladding coating on a conical screw according to claim 3, characterized in that, In step S1, the helix of the spiral is a curve wrapped around the side of the frustum, and the total rotation angle of the helix is ​​Φt: ， Using polar coordinates, calculate the coordinates (ρ, θ) of multiple points on the spiral in the unfolded diagram. exp The angle during the rotation is denoted as t, where 0 ≤ t ≤ Φt. Current height z: ， Current radius R of the frustum current The radius decreases linearly from bottom to top: ， The polar radius ρ of that point on the unfolded diagram is the radius of the sector corresponding to that point. ， Let z and radius R current Substituting the values, we obtain the polar radius function ρ(t), and the distance from this point to the origin of the expanded graph: ， The polar angle θ of this point on the unfolded diagram exp The angle through which this point rotates on the sector: ， radius R current Substituting the values, we obtain the polar angle function. (t), the angle between the line connecting this point to the origin and the initial baseline: ， Based on the polar radius function ρ(t) and polar angle function in polar coordinates (t), transforming the equation into a function in rectangular coordinates. according to ,get , thereby: ， 。 5. The method for preparing a pre-positioned laser cladding coating on a conical screw according to claim 1, characterized in that, In step S3, the paste-like powder comprises: The alloy powder contains 5-10% polyvinyl butyral, 3-5% anhydrous ethanol, 1-2% triethyl borate, and 2-4% ethyl silicate by mass.

6. The method for preparing a pre-positioned laser cladding coating on a conical screw according to claim 5, characterized in that, In step S3, the alloy powder comprises: The mass ratio of Ni is 40-55%, the mass ratio of WC is 10-15%, the mass ratio of TiC is 10-15%, the mass ratio of NbC is 10-15%, the mass ratio of rare earth CeO2 is 0.5-1%, the mass ratio of rare earth La2O3 is 0.5-1%, and the mass ratio of rare earth Y2O3 is 0.5-1%.

7. The method for preparing a pre-positioned laser cladding coating on a conical screw according to claim 5 or 6, characterized in that, Step S3 includes: The base film is a BOPET film, and the paste powder is uniformly coated on the base film with a thickness of 2.0-2.2 mm; Place in a 50℃ drying oven and dry for 15 minutes until the coating is a plastic, soft solid. The bottom film is laid flat on the vacuum adsorption stage with the bottom film facing down. Vacuum adsorption is started, and a two-dimensional contour cutting path is generated according to the area division. The blade tip penetrates a layer of paste powder without damaging the bottom film. After cutting and segmenting, the coating tape is obtained.

8. The method for preparing a pre-positioned laser cladding coating on a conical screw according to claim 1, characterized in that, In step S4, a vortex milling method is used to cut grooves in the screw edge of the tapered screw, with a depth of 2mm and a width of 1mm on both sides.

9. The method for preparing a pre-positioned laser cladding coating on a conical screw according to claim 8, characterized in that, In step S4, each of the coating tapes is attached to the groove of the screw thread one by one, and placed in a vacuum furnace at 150°C for 2 hours to allow polyvinyl butyral to completely decompose and carbonize, and triethyl borate and ethyl silicate to begin to decompose. The bottom film is then peeled off to obtain the pre-formed cladding layer.

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