Short-process preparation method of superspeed laser cladding coating on surface of shaft part and obtained coating

Abstract

The invention discloses a short-process preparation method of an ultra-high-speed laser cladding coating on the surface of a shaft part and the obtained coating, and the method comprises the following steps: firstly, based on energy conservation and momentum balance, calculating and determining a stable process window of ultra-high-speed laser cladding; based on a geometrical optical model, the horizontal offset distance of the laser head relative to the central axis of the workpiece is calculated and controlled. Based on molten pool stress analysis under a rotating coordinate system, the relation between the rotating direction of a workpiece for restraining flowing of a molten pool and the offset direction of a laser head relative to the central axis of the workpiece is determined, under the determined conditions, ultra-high-speed laser cladding is conducted on the outer circle surface of the shaft part, and single-pass precision grinding is directly conducted after cladding. According to the method, the thin-layer coating with the smooth surface and the uniform thickness is obtained through physical stability control, the machining route of cladding-turning-grinding is simplified into cladding-single-pass precision grinding, and the machining allowance and the production cost are remarkably reduced.

Description

Technical Field

[0001] This invention relates to the fields of laser additive manufacturing and surface engineering technology, specifically to a short-process manufacturing method for ultra-high-speed laser cladding of shaft parts based on physical stability criteria. It is applicable to rotary components requiring high precision, wear resistance, corrosion resistance, and long service life, including hydraulic cylinder piston rods, rolling mill rolls, high-speed spindles, aerospace actuator rods, and shaft parts for engineering equipment. Background Technology

[0002] Ultra-High-Speed ​​Laser Cladding (UHLC) is a highly efficient, low-dilution, and small heat-affected zone method for large-area surface strengthening, offering significant advantages over traditional processes such as electroplating and thermal spraying. However, as shaft parts operate under increasingly higher temperatures, higher speeds, and heavier loads, higher demands are placed on the wear resistance, corrosion resistance, and dimensional accuracy of the coating surface. Current technologies still face the following challenges that urgently need to be addressed: Existing research largely focuses on optimizing coating material systems, such as using transition layer designs in high-entropy alloy coatings to mitigate cracking (CN117721455A); improving alumina wettability through the addition of Si in cermet composite coatings (CN120174371A); and achieving equiaxed grain structures through semi-solid solidification of bimodal particle size powders (CN116791077A). These technologies can improve coating hardness, wear resistance, or corrosion resistance, but they do not pay enough attention to the process stability issues during ultra-high-speed cladding.

[0003] In terms of processes and equipment, some patents propose multi-energy field composite processing or integrated equipment. For example, the integrated additive and subtractive manufacturing system of molten droplet arc-laser-mechanical extrusion integrates additive and subtractive manufacturing on the same equipment (CN120680136A); the laser energy directional deposition and electrical discharge machining device integrates laser deposition and electrical discharge removal, improving the processing flexibility of complex structural parts (CN120533114A); the ultra-high-speed laser cladding method for ultra-large hydraulic cylinder piston rods improves the uniformity and corrosion resistance of the surface coating of ultra-long components through the use of an integrated turning and grinding machine, segmented cladding, and power gradient overlap (CN120115949A).

[0004] However, the aforementioned existing technologies generally have the following shortcomings: (1) Lack of physical and chemical criteria for process stability

[0005] Existing ultra-high-speed cladding process parameters mostly rely on empirical selection, only providing numerical ranges for laser power, linear velocity, powder feed rate, etc., without establishing the energy closure condition for powder to be heated from solid to complete melting, or the momentum balance condition for whether the metal vapor plume is effectively constrained by the protective gas. Under high power and high powder feed conditions, molten pool instability and nozzle blockage are prone to occur.

[0006] (2) Lack of a geometric bias model for the return of reflected light.

[0007] Existing technologies for offset cladding and anti-clogging powder treatment mostly rely on empirical methods to adjust the distance and angle of the nozzle relative to the workpiece, without using geometric optics analysis to determine the laser reflection trajectory and its safe zone range. This fails to provide a universal offset calculation method for shaft parts of different diameters. For example, patent CN120115949A uses an empirical value for the offset angle without providing a calculation model.

[0008] (3) The influence of rotational dynamics on the morphology of the molten pool was ignored.

[0009] During the cladding process of shaft parts, the molten pool is in a rotating coordinate system and is subjected to multiple forces, including gravity, centrifugal force, Coriolis force, and surface tension. Existing technologies generally only improve the surface morphology from macroscopic parameters (such as linear velocity and powder feed rate) or external cooling angles, without analyzing the influence of the rotation direction (clockwise or counterclockwise) on the molten pool flow and surface ripples from a mechanical mechanism perspective.

[0010] (4) The processing flow is still relatively long.

[0011] Existing cladding coatings are typically 0.1–0.2 mm thick. Due to surface ripples, dimensional tolerances, and bending deformation, there is insufficient machining allowance in the thickness direction, limiting ultra-high-speed laser cladding technology to components that do not require surface quality. Traditional laser cladding, with its thick coating and large height differences between weld lines, cannot be directly ground and requires a "rough turning-semi-finish turning-finish turning-polishing" process, resulting in significant material waste and long processing times. It has not yet achieved a short-process, near-net-shape forming capability through direct single-pass precision grinding after cladding. For example, patents CN120115949A and CN117721455A both require turning steps.

[0012] Therefore, it is necessary to provide an ultra-high-speed laser cladding process based on the coordinated control of energy conservation, momentum balance and rotational dynamics. By constructing a dimensionless stability criterion, a geometric bias model and a rotation direction selection principle, stable cladding under high power and high powder feeding conditions can be achieved. Furthermore, a turning-free machining route can be realized through single-pass precision grinding based on thin-layer deposition. Summary of the Invention

[0013] The purpose of this invention is to overcome the shortcomings of existing ultra-high-speed laser cladding processes, such as reliance on experience-based adjustment for stability, easy nozzle clogging, obvious surface ripples in the molten pool, and long processing steps. This invention proposes a short-process method for preparing ultra-high-speed laser cladding coatings on shaft-type parts. This method achieves calculable, reproducible, and stable design of the ultra-high-speed cladding coating, as well as near-net-shape forming in a short process of "cladding + fine grinding," eliminating the turning step required in traditional ultra-high-speed laser cladding processes.

[0014] The present invention also provides a coating prepared by the method.

[0015] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A short-process method for preparing ultra-high-speed laser cladding coatings on the surface of shaft parts is characterized by determining stable process parameters through physical model calculations, controlling the laser reflection path, and optimizing the stress state of the molten pool, ultimately achieving single-pass precision grinding without turning after cladding. The method specifically includes the following steps: Step 1: Based on the principles of energy conservation and momentum balance, calculate and determine the stable process window for ultra-high-speed laser cladding; Step 2: Based on the geometric optical model, calculate and control the horizontal offset distance of the laser head relative to the central axis of the workpiece; Step 3: Based on the force analysis of the molten pool in the rotating coordinate system, determine the relationship between the workpiece rotation direction that inhibits molten pool flow and the offset direction of the laser head relative to the workpiece central axis. Step 4: Under the conditions determined in Steps 1 to 3, perform ultra-high-speed laser cladding on the outer cylindrical surface of shaft parts to form a thin deposition layer; Step 5: Perform single-pass precision grinding directly on the deposited layer to achieve the target size and surface accuracy.

[0016] Furthermore, in step one, the process stability is determined by calculating the degree of melting M and the plume constraint ratio Π, and a combination of process parameters that satisfies M ≥ 1 and Π ≤ 1 is selected as the stable operating window.

[0017] Further: The formula for calculating the degree of sufficiency of melting M is as follows: , among them Where is the effective absorption rate of the laser, and P is the laser power. This refers to the mass flow rate of the cladding powder. For constant pressure specific heat capacity, Liquidus / nominal melting point temperature The initial temperature of the cladding powder. This represents the latent heat of fusion. When M ≥ 1, it indicates that the effective energy obtained by the powder per unit time is sufficient to completely melt it, preventing a large number of unmelted particles from entering the coating.

[0018] Furthermore, the formula for calculating the plume constraint ratio Π is as follows: In the formula P r The back pressure for evaporating raw metal powder. P s The effective pressure provided by the protective gas; when Π ≤ 1, it indicates that the steam plume is effectively suppressed by the protective gas and will not break through the gas curtain, causing powder rebound and nozzle blockage.

[0019] Furthermore, in step two, the offset distance of the laser head (i.e., the center of the laser spot) relative to the central axis of the workpiece... L The calculation formula is: , among them R The outer radius of the workpiece; d Where is the diameter of the laser spot; α is the laser reflection angle, ranging from [x, 45°], where x is determined by the following formula: Where D is the critical outer diameter of the nozzle (or its protective cover), which is the diameter of the obstacle that the reflected light must avoid, and H is the working distance of the laser head (that is, the vertical distance from the nozzle outlet to the workpiece surface).

[0020] Furthermore, in step three, the relationship between the workpiece rotation direction and the offset direction of the laser head relative to the workpiece's central axis is as follows: when the laser spot is offset to the right of the workpiece's rotation axis, the workpiece rotates counterclockwise; when the laser spot is offset to the left of the workpiece's rotation axis, the workpiece rotates clockwise. In this way, the normal Coriolis force component of the molten pool points towards the center of the circle, opposite to the direction of the centrifugal force pointing outward, thereby reducing the normal composite driving force and making the molten pool shape more stable.

[0021] Furthermore, in step four, the process parameters for ultra-high-speed laser cladding meet the following requirements: powder feeding rate not less than 64 g / min, laser power is determined according to the amount of powder, i.e., the energy allocated per gram of powder, and its range is (90 W / g-110 W / g), and the outer diameter linear velocity of the workpiece is not less than 36 m / min.

[0022] Furthermore, in step five, the single-pass precision grinding adopts a floating grinding process.

[0023] Furthermore, the shaft-type parts mentioned are rotary seals such as hydraulic cylinder piston rods, rolling mill rolls, high-speed spindles, and aerospace actuator rods.

[0024] The thickness of the coating on shaft parts obtained by the above method is 0.45-0.65 mm, and after single-pass precision grinding, the surface roughness Ra ≤ 0.4 μm, roundness ≤ 0.01 mm, and coaxiality ≤ 0.02 mm.

[0025] Compared with the prior art, the present invention has the following beneficial effects: (1) For the first time, a dimensionless stability criterion based on the degree of melting M and the plume constraint ratio Π was proposed, which transformed the ultra-high speed laser cladding process window from empirical trial and error to calculable design.

[0026] (2) For the first time, a laser bias geometry model was established, and the reflection safety angle and the bias distance L were quantitatively correlated, providing a general design method for nozzle layout of shaft parts with different diameters.

[0027] (3) For the first time, rotational dynamics was introduced into the control of molten pool morphology, and the principle of rotational direction selection based on the balance of Coriolis force and centrifugal force was given, so as to effectively suppress molten pool ripples at high linear velocity.

[0028] (4) By controlling physical stability, a thin coating with a smooth surface and uniform thickness is obtained, which simplifies the processing route from "cladding - turning - grinding" to "cladding - single-pass precision grinding", significantly reducing the processing allowance and production cost.

[0029] (5) The method of the present invention is applicable to typical shaft parts such as hydraulic cylinder piston rod, high-speed spindle, and rolling mill, and has good engineering promotion value. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall process flow of the method of the present invention; Figure 2 Schematic diagram of the stability window for melting sufficiency M and plume constraint ratio Π; where 2(a) shows the laser-powder-molten pool reaction image of the ultra-high power laser (UHLC) powder molten pool process; 2(b) shows the thermal imaging of the molten pool and metal vapor in the ultra-high power laser powder molten pool process; 2(c) shows the light-powder-gas coupling schematic diagram of the ultra-high power laser powder molten pool process.

[0031] Figure 3 The diagram shows the relationship between the offset distance L and the reflection angle α. 3(a) shows the nozzle / beam layout; 3(b) shows the envelope of the reflected light (offset window); 3(c) shows the envelope of the 3.6 mm beam on workpieces with different R values; 3(d) shows the construction of the required lateral offset L under the condition of fixed α.

[0032] Figure 4 This diagram illustrates the forces acting on the molten pool in a rotating coordinate system with the laser spot offset to the right of the workpiece's rotation axis, including the decomposition of centrifugal force and Coriolis force. 4(a) shows the surface morphology of the coating after clockwise and counterclockwise rotation of the workpiece; 4(b) shows the spatial relationship between the laser, the molten pool, and the coating during counterclockwise rotation; 4(c) shows the mechanical analysis model of the molten metal in the molten pool region during counterclockwise rotation; 4(d) shows the spatial relationship between the laser, the molten pool, and the coating during clockwise rotation; and 4(e) shows the mechanical analysis model of the molten metal in the molten pool region during clockwise rotation.

[0033] Figure 5 This is a schematic diagram of the surface roughness and dimensional accuracy of the coating after a single pass of precision grinding; where 5(a) shows the surface roughness of the coating and 5(b) shows the dimensional accuracy of the coating.

[0034] Figure 6The following diagrams demonstrate the elemental distribution and dilution rate of the coating; where 6(a) shows the microstructure along the thickness direction, 6(b) shows the elemental composition analysis of four points including the matrix taken from top to bottom, 6(c) shows the surface scan distribution of Cr and Fe elements, and 6(d) shows the elemental distribution along the centerline.

[0035] Figure 7 This is a picture of the results of third-party testing on a workpiece with a coating after grinding.

[0036] Figure 8 These are images of coating effects prepared by the process of this invention; where 8(a) shows the effect of cladding due to the addition of powder midway, and 8(b) shows the effect of one-time cladding of long shafts with different diameters. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0038] like Figure 1 As shown, the short-process manufacturing method for ultra-high-speed laser cladding coating of shaft parts based on physical stability criteria of the present invention includes the following steps: Step 1: Based on the conservation of energy and momentum balance, calculate and determine the stable process window of ultra-high speed laser cladding, that is, calculate the degree of sufficiency of melting M and the plume constraint ratio Π.

[0039] (1) Construction of the degree of sufficiency of melting M By calculating the enthalpy required for powder to melt completely from room temperature to its melting point, the effective laser absorption power is compared with the powder melting power requirement to construct a dimensionless melting sufficiency value M. When M ≥ 1, the powder can completely melt under given process parameters, effectively preventing a large number of unmelted particles from entering the coating and causing defects.

[0040] Based on the above mechanism, the complete melting during the cladding layer melting process can be qualitatively described by the energy-mass ratio, that is: Among them Where is the effective absorption rate of the laser, and P is the laser power. This refers to the mass flow rate of the cladding powder. For constant pressure specific heat capacity, Liquidus / nominal melting point temperature The initial temperature of the cladding powder. This is the latent heat of fusion.

[0041] (2) Construction of plume constraint ratio Π The plume constraint ratio Π is defined by comparing the recoil pressure generated by the evaporation of the raw metal powder with the static and dynamic pressures provided by the protective gas. In the formula Pr The back pressure for evaporating raw metal powder. P s The effective pressure provided by the protective gas is calculated using the following formula: In the formula This refers to the mass flux of the cladding material powder. m For powder quality, Where is Boltzmann's constant, and T is the surface temperature of the metal powder. For environmental / chamber pressure, To shield the gas density, The volumetric flow rate at the nozzle outlet. This refers to the effective outlet area of ​​the nozzle.

[0042] The reason this invention constructs the plume constraint ratio Π and the degree of sufficiency of melting M is that in conventional laser cladding, both the laser and powder focus are located on the substrate surface, the entire process is in a stable region, the linear velocity is low, the energy input is sufficient, and the desired conditions are automatically met. and Conditions. And in the ultra-high-speed cladding process, such as... Figure 2 As shown in (a)-2(c), the laser focus is located above the powder and the molten pool, where the powder melts or partially melts within the beam. The recoil force of the metal vapor formed by the powder evaporation pushes the unmelted / partially melted particles towards the nozzle side. Under sufficient protective gas pressure, the recoil vapor is firmly confined below the nozzle and reaches equilibrium with the protective gas pressure, forming a fountain-like shape—pausing briefly near the apex before falling back. The high surface linear velocity induces near-surface tangential flow, causing vertical oscillations between the radiating gas flow and the vapor plume. When the oscillations remain within a limited range, pressure equilibrium is maintained, and the deposition process is stable. However, when the height of the recoil vapor plume continues to increase, an imbalance between the recoil pressure and the protective gas pressure triggers a vicious cycle: air entrainment → smoke and thermal radiation → secondary nozzle reflection → powder sintering and blockage.

[0043] Step 2: Based on the geometric optics model, calculate and control the horizontal offset distance of the laser head relative to the workpiece's central axis. L By deriving the laser reflection path through a geometrical optical model, the relationship between the offset distance L and the reflection angle α is obtained, thus determining the safe reflection zone outside the nozzle. The geometrical optical physical model of this invention is based on the following: In ultra-high-speed laser cladding, if the laser beam is directed vertically downwards along the workpiece's rotation axis, specular reflection occurs when the beam hits the cylindrical surface. The reflected light may directly hit the inner wall of the nozzle, or even be reflected back to the laser along the optical fiber, leading to nozzle sintering and powder blockage or damage to optical components. To avoid this problem, the laser head needs to be horizontally offset by a certain distance L relative to the workpiece's central axis. To mitigate nozzle melting and blockage caused by reflection, this invention establishes a geometrical optical model of the reflection angle and its envelope when a vertically downward incident beam (spot diameter d) irradiates a rotating surface with radius R. That is: , among them R Let be the outer radius of the workpiece, and α be the laser reflection angle, with a value ranging from [x, 45°]. d The diameter of the laser spot is denoted as .

[0044] The range of laser reflection angle values ​​should ensure that the reflected light does not re-enter the nozzle orifice or hit the laser head body. Based on this criterion, its minimum value x is determined by the following formula. In the formula, D is the critical outer diameter of the nozzle (or its protective cover); H is the working distance of the laser head (the vertical distance from the nozzle outlet to the workpiece surface).

[0045] The maximum value of the reflection angle is specified as 45°. This is because ultra-high-speed laser cladding requires sufficient energy density per unit area to ensure adequate powder melting. When the incident light ray is too oblique to the normal of the workpiece surface, the light spot undergoes geometric stretching on the surface, increasing the equivalent projected area and decreasing the energy density per unit area. For a given laser power and powder feed rate, when the reflection angle α (equivalent incident angle 90° - α) continues to increase, either M decreases to a point where it is insufficient to completely melt the powder, or P needs to be significantly increased to compensate for the energy density loss, which will further exacerbate reflection and safety issues. Therefore, while maintaining the optical safety upper limit, i.e., the maximum α ≤ 45°, it is also ensured that the laser can still maintain its performance within a given power range. The process window.

[0046] Based on the above model, the calculation formula for the required lateral offset of the laser head under different workpiece diameters is derived.

[0047] The following is combined Figure 3 and oneAn example illustrates the construction process of the laser reflection angle of this invention. The figure shows the laser-workpiece layout: the nozzle end face has an outer diameter of 21 mm, an inner angle of 40°, and the focal point is located 16 mm below the end face. Under UHLC conditions, a defocusing distance of H = 17 mm is maintained. When H is fixed, the laser is horizontally offset to the right (see...). Figure 3 (a) will cause each beam edge to produce reflected rays on the curved surface; for different horizontal offset positions, a series of incident rays and their reflection lines on the arc can be drawn. Extending each reflection line in the opposite direction yields a family of "virtual light source" trajectories; the envelope curves of these reflection lines constitute a "reflection envelope surface" (see...). Figure 3 (b)). For the nozzle geometry used here, the minimum safe offset corresponds to α = 16°. We fitted an envelope curve for the range of R = 50~200 mm (radius step 10 mm) and connected the intersections at α = 16° to form the “minimum offset control line”. The tangents at each intersection of this line and the envelope curve determine the corresponding irradiation points on the arc (see...). Figure 3 (c) The maximum permissible reflection angle is 45°, at which point the reflected ray is horizontal and tangent to the top of the envelope. Therefore, the α value should be between 16° and 45°. Through the above process, in Figure 3 (d) establishes the formula for the offset distance L and the process safety window, as shown in the shaded area.

[0048] It should be noted that the above 16°-45° range is derived based on the preferred nozzle geometry of this invention (40° interior angle, 16mm below the focal point, defocus H=17mm, and 21mm outer diameter of the nozzle end face boundary). For other nozzle configurations, a new model needs to be built based on their geometric parameters, but the geometric optics modeling method provided by this invention is universal. Of course, regardless of the nozzle configuration, the maximum value of the reflection angle cannot exceed 45°.

[0049] Step 3: Based on the force analysis of the molten pool in the rotating coordinate system, determine the workpiece rotation direction to inhibit molten pool flow. The following analysis assumes the laser spot is offset to the right of the workpiece's rotation axis. A rotating coordinate system is established to analyze the forces acting on the molten pool (see...). Figure 4 ),in Figure 4 (b)- Figure 4 (c) shows the spatial relationship between the laser, the molten pool, and the coating during the counterclockwise rotation of the workpiece, as well as the mechanical analysis model of the molten metal in the molten pool region. Figure 4 (d)- Figure 4(e) The spatial relationships between the laser, the molten pool, and the coating, as well as the mechanical analysis model of the molten metal in the molten pool region, are shown during the clockwise rotation of the workpiece. As can be seen from the figure, regardless of whether the workpiece rotates clockwise or counterclockwise with an angular velocity ω, the molten pool fluid exhibits a relative velocity component in the tangential direction, and the Coriolis force has a component pointing towards the center in the normal direction. However, when the workpiece rotates counterclockwise, the Coriolis force is opposite in direction to the centrifugal force pointing outwards. (See figure...) Figure 4 (b)- Figure 4 (c) This reduces the normal composite driving force, resulting in smaller surface ripples and a more uniform coating thickness under the same linear velocity conditions. Therefore, in actual processing, when the laser spot deviates to the right side of the rotation axis, the workpiece is set to rotate counterclockwise. Figure 4 (a) shows the surface morphology of the coating obtained after the workpiece is rotated clockwise and counterclockwise. Figure 4 (a) The coating diagram on the left is the coating obtained in the offset + clockwise mode on the right. It can be seen that there are many wrinkles and bulges on the coating surface, and the peaks and valleys between the surface melt channels are obvious. Figure 4 (a) The coating schematic diagram on the right shows the coating obtained in the right-side offset + counterclockwise mode. It can be seen that the coating is flat and uniform with low roughness. This illustrates the importance of further controlling the workpiece rotation direction and the laser spot offset direction while controlling the horizontal offset distance of the workpiece's central axis.

[0050] Step 4: Under the conditions determined above, perform ultra-high-speed laser cladding on the outer cylindrical surface of the shaft-type parts. Process parameters for ultra-high-speed laser cladding: powder feed rate is 78 g / min, laser power is 100 W / g (7800 W), and workpiece outer diameter linear velocity is not less than 36 m / min.

[0051] Step 5: Perform single-pass precision floating grinding directly on the deposited layer. Floating grinding is preferred to avoid workpiece deformation caused by the force generated by a rigid grinding wheel. The surface roughness Ra of the ground coating is ≤ 0.4 μm, the roundness is not greater than 0.01 mm, and the coaxiality is not greater than 0.02 mm.

[0052] It should be noted that the floating mill process is a mature precision machining technology that has existed and been applied for many years. Its specific operation process is well known in the field and will not be described in detail again.

[0053] The following example illustrates the manufacturing of a wear-resistant and corrosion-resistant coating for a 30CrMnSiA steel shaft used in engineering machinery. The outer diameter of the steel shaft is 160 mm, and its length is 2.0 m. The requirement is to form a stainless steel wear-resistant and corrosion-resistant coating with a thickness of approximately 0.55 mm, meeting assembly-level precision requirements of Ra ≤ 0.4 μm and roundness ≤ 0.01 mm.

[0054] (1) Process window calculation: based on the specific heat capacity C of the powder material p Melting point T m Initial temperature T0 and latent heat of fusion L f Calculate the enthalpy required for complete melting of a unit mass of powder; based on the effective absorption rate of the iron-based powder used for coating. Under the initial conditions of laser power P = 7.8 kW and powder feed rate ṁ = 78 g / min, M was calculated by substituting the values ​​into the formula for the degree of sufficiency of melting, and the result was M ≥ 1. Simultaneously, the evaporation backpressure P was estimated based on the molten pool temperature and steam flow rate. r Then, the effective pressure P of the protective gas is calculated based on the type of protective gas, flow rate, and nozzle cross-sectional area. s The plume constraint ratio Π ≤ 1 indicates that the combination of process parameters is within a stable process window.

[0055] If M and Π are not within the required range, then the laser power and powder feeding rate need to be changed, and M and Π need to be recalculated until the selected laser power and powder feeding rate t satisfy M ≥ 1 and Π ≤ 1.

[0056] (2) Laser offset geometry design: Select a reflection safety angle α = 25°. Based on the workpiece radius R = 80 mm and the laser spot diameter d = 3.5 mm, the horizontal offset distance L = 35.5 mm is calculated. The cladding nozzle is offset to the right relative to the workpiece center axis according to this distance. At the same time, since the vertical height changes after the offset, it also needs to be adjusted to the required height so that the laser reflected light will not enter the powder feeding nozzle cavity after being reflected from the workpiece surface.

[0057] (3) Rotation direction selection: According to the principles of this invention, when the laser head is offset to the right of the axis, in order to use the Coriolis force to counteract the negative impact of centrifugal force on the molten pool, the workpiece should be rotated counterclockwise (CCW). Of course, the cladding nozzle can also be offset to the left of the workpiece's central axis, in which case the workpiece rotates clockwise.

[0058] (4) Ultra-high-speed laser cladding: Ultra-high-speed laser cladding is performed under the above process window, offset distance, and rotation direction conditions. Specific parameters include: laser power of approximately 7.8 kW (calculated based on 78 g / min powder, with power taken as 100 W / g), workpiece outer diameter linear velocity of approximately 36 m / min, powder feeding rate of approximately 78 g / min, carrier gas flow rate set according to powder particle size, and protective gas flow rate based on P when criterion Π ≤ 1. s Adjustment. The thickness of the cladding coating is approximately 0.55 mm, and metallographic measurements show that the thickness fluctuation range is less than 50 μm, with a dilution rate of less than 1%.

[0059] (5) Single-pass precision grinding: After the cladding layer cools to room temperature, precision grinding is performed directly using a diamond floating grinding wheel, without turning. Based on the coating thickness distribution and roundness measurement results, the single-pass grinding allowance is set to 80–120 μm. The measured surface roughness Ra after grinding is... ≤ The diameter is 0.4 μm, the roundness is approximately 0.01 mm, and the coaxiality is approximately 0.02 mm, meeting the requirements for high-precision assembly. The coated workpiece after grinding passed third-party testing, proving that its salt spray corrosion resistance meets production standards (see...). Figure 7 ). Figure 5 This is a schematic diagram of the surface roughness and dimensional accuracy of the coating after a single pass of precision grinding.

[0060] Figure 6 This reflects the elemental distribution and dilution rate of the coating prepared in this embodiment. The figure shows a low dilution rate and uniform elemental distribution. Figure 6 b and 6c clearly show that the matrix and coating elements do not intermelt, indicating that the dilution rate is well controlled.

[0061] In addition, from Figure 8 The cladding effect shows the stability and durability of the process of the present invention. In 8(b), it was verified that long shafts of different diameters were clad in one go without segmentation or downtime. The break in the middle of the picture 8(a) is due to the addition of powder in the middle.

[0062] This embodiment demonstrates that, through the M-Π stability criterion, bias geometry model L, and rotational dynamics control proposed in this invention, a stable and smooth thin-layer cladding coating can be obtained under high power, high powder feed, and ultra-high speed conditions, and near-net-shape forming without turning can be achieved through single-pass precision floating grinding. Those skilled in the art can adjust the parameter values, powder system, and matrix material without departing from the spirit of this invention, and all such adjustments should fall within the protection scope of this invention.

Claims

1. A short-process method for preparing an ultra-high-speed laser cladding coating on the surface of shaft-type parts, characterized in that, It uses physical models to calculate and determine stable process parameters, control the laser reflection path, and optimize the stress state of the molten pool, ultimately achieving single-pass precision grinding without turning after cladding. Specifically, it includes the following steps: Step 1: Based on the principles of energy conservation and momentum balance, calculate and determine the stable process window for ultra-high-speed laser cladding; Step 2: Based on the geometric optics model, calculate and control the horizontal offset distance of the laser head relative to the workpiece's central axis; Step 3: Based on the force analysis of the molten pool in the rotating coordinate system, determine the relationship between the workpiece rotation direction that inhibits molten pool flow and the offset direction of the laser head relative to the workpiece central axis. Step 4: Under the conditions determined in Steps 1 to 3, perform ultra-high-speed laser cladding on the outer cylindrical surface of shaft parts to form a thin deposition layer; Step 5: Perform single-pass precision grinding directly on the deposited layer to achieve the target size and surface accuracy.

2. The short-process preparation method for ultra-high-speed laser cladding coating on the surface of shaft parts as described in claim 1, characterized in that, In step one, the process stability is determined by calculating the degree of melting M and the plume constraint ratio Π, and a combination of process parameters that satisfies M ≥ 1 and Π ≤ 1 is selected as the stable operating window.

3. The short-process preparation method for ultra-high-speed laser cladding coating on the surface of shaft parts as described in claim 2, characterized in that, The formula for calculating the degree of sufficiency of melting M is as follows: , among them For the effective absorption rate of laser, P For laser power, This refers to the mass flow rate of the cladding powder. For constant pressure specific heat capacity, Liquidus / nominal melting point temperature The initial temperature of the cladding powder. This is the latent heat of fusion.

4. The short-process preparation method for ultra-high-speed laser cladding coating on the surface of shaft parts as described in claim 2, characterized in that, The formula for calculating the plume constraint ratio Π is as follows: In the formula P r The back pressure for evaporating raw metal powder. P s Effective pressure provided for protective gas.

5. The short-process preparation method for ultra-high-speed laser cladding coating on the surface of shaft parts as described in claim 1, characterized in that, In step two, the offset distance of the laser head relative to the central axis of the workpiece L The calculation formula is: , Among them R The outer radius of the workpiece; d Where is the diameter of the laser spot; α is the laser reflection angle, ranging from [x, 45°], where x is determined by the following formula: Where D is the critical outer diameter of the nozzle or its protective cover, and H is the working distance of the laser head.

6. The short-process preparation method for ultra-high-speed laser cladding coating on the surface of shaft parts as described in claim 1, characterized in that, In step three, the relationship between the workpiece rotation direction and the offset direction of the laser head relative to the workpiece's central axis is as follows: when the laser spot is offset to the right of the workpiece's rotation axis, the workpiece rotates counterclockwise; when the laser spot is offset to the left of the workpiece's rotation axis, the workpiece rotates clockwise.

7. The short-process preparation method for ultra-high-speed laser cladding coating on the surface of shaft parts as described in claim 1, characterized in that, In step four, the process parameters for ultra-high-speed laser cladding are as follows: powder feeding rate is not less than 64 g / min, laser power is determined according to the amount of powder, i.e., the energy allocated per gram of powder, and its range is 90 W / g-110 W / g, and the outer diameter linear velocity of the workpiece is not less than 36 m / min.

8. The short-process preparation method for ultra-high-speed laser cladding coating on the surface of shaft parts as described in claim 1, characterized in that, In step five, the single-pass precision grinding adopts a floating grinding process.

9. The short-process preparation method for ultra-high-speed laser cladding coating on the surface of shaft parts as described in claim 1, characterized in that, The shaft-type parts include at least hydraulic cylinder piston rods, high-speed spindles, and roller rotation seals.

10. A coating for shaft parts prepared by any one of claims 1-9, characterized in that, The thickness of the coating on the shaft parts is 0.45 to 0.65 mm, and after a single pass of precision grinding, the surface roughness Ra ≤ 0.4 μm, roundness ≤ 0.01 mm, and coaxiality ≤ 0.02 mm.

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