A method for calculating a multi-pass overlap rate of laser cladding

Abstract

The application discloses a kind of calculation methods of laser cladding multi-pass overlap rate, belong to laser cladding process technical field.The method for determining the existing laser cladding overlap rate lacks accuracy and stability, first based on single pass cladding cross section is determined as elliptic function, establish the cladding cross section height model, width model and elliptic function model of the characterization of key influence parameter of laser cladding;Then determine the distance model of the center of any adjacent pass cladding layer, the above-mentioned model is substituted into multi-pass cladding critical overlap rate model, obtains the optimal critical overlap rate calculation value satisfying actual working condition requirement.Compared with prior art, the present application has the following beneficial effects: (1) the application range of overlap rate model is wide;(2) elliptic model has strong adaptability;(3) the calculation precision of overlap rate model is high;(4) overlap rate model has flexibility and comprehensive controllability;(5) product quality is good.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser cladding process, and particularly relates to a calculation method of multi-pass overlap rate of laser cladding. BACKGROUND

[0002] As a new remanufacturing method, laser cladding has the advantages of fast melting and solidification rate, small thermal deformation of the substrate, controllable coating thickness, stable performance, wide material selection range and the like. However, in the face of surface modification or repair production of large parts and other application requirements, the cost of upgrading high-energy large-size laser beam spot is too high due to the limitation of equipment process parameters, so the multi-pass overlap cladding technology is particularly critical.

[0003] In the laser cladding process, multi-pass overlap cladding involves overlap rate, surface flatness and organizational defects and the like. Among them, the overlap rate is the main factor affecting the cladding quality, and the degree of too large or too small overlap rate will directly determine the macroscopic inclination amplitude and forming precision of the cladding layer surface morphology. At present, the methods for determining the laser cladding overlap rate mainly include differential line scanning method, color three-dimensional morphology measurement method, image processing-based method and the like. These methods all need to process and analyze data, and have relatively high requirements for instruments and software, and need to be repeatedly tested and verified, and lack accuracy and stability. SUMMARY

[0004] In view of the problem that the existing laser cladding overlap rate determination method lacks accuracy and stability, the application provides a calculation method of multi-pass overlap rate of laser cladding. That is, by establishing a relationship model of single-pass cladding cross-sectional profile characteristic parameters and critical overlap rate of multi-pass cladding, the optimal critical overlap rate calculation value of laser cladding meeting the actual working condition requirements is obtained.

[0005] In order to achieve the above purpose, the following technical solutions are adopted in the application:

[0006] A calculation method of multi-pass overlap rate of laser cladding, the method comprises the following steps:

[0007] S1: In order to simplify the theoretical calculation and analysis process, two cladding layers are arbitrarily selected to complete the construction of a multi-pass overlap model, and the following assumptions are made:

[0008] (1) The cross-sectional profile of the single-pass cladding layer is completely accurate as part of an elliptic function;

[0009] (2) In the multi-pass cladding process with the same process parameters, the cross-sectional shape, size and area of the single-pass cladding layer remain unchanged;

[0010] (3) The molten pool has good fluidity, and the next pass cladding layer is easy to spread and fill in the remelted expansion area;

[0011] (4) Ignoring the surface tension of liquid metal cladding layer and the impact of the pressure of protective gas on the forming process;

[0012] S2: The single-channel cladding layer cross-section profile in step 1 is completely accurate as part of an elliptic function, as shown in the figure. A Cartesian coordinate system is established with the horizontal boundary line of the cladding layer and the substrate as the X-axis and the vertical symmetry axis of the cladding layer as the Y-axis. The O point is the coordinate origin, and the O' point is the first cladding layer ellipse center. The cladding layer width is W, and the cladding layer height is H. Figure 1

[0013] The elliptic function expression is:

[0014]

[0015] The width W of the single-channel cladding layer is calculated as follows:

[0016]

[0017] The height H of the single-channel cladding layer is calculated as follows:

[0018] H = b - c

[0019] Where a, b, and c are elliptic function geometric structure parameters, which are functions of single-channel cladding layer process parameters. y represents the vertical coordinate of any point on the single-channel cladding layer cross-section profile, and x represents the horizontal coordinate of any point on the single-channel cladding layer cross-section profile. The a, b, and c diagnostic graphs are shown in the figure. Figure 2

[0020] S3: Selecting an appropriate function as the suitability function of the cross-section profiles of adjacent two cladding layers;

[0021] Further, the suitability functions of the cross-section profiles of adjacent two cladding layers in step S2 are as follows:

[0022]

[0023] Where y1 represents the vertical coordinate of any point on the cross-section profile of the first cladding layer, y2 represents the vertical coordinate of any point on the cross-section profile of the next cladding layer, and d is the distance between the centers of any adjacent cladding layers, as shown in the figure. The O' point is the first cladding layer ellipse center, and the O" point is the next cladding layer ellipse center. Figure 3

[0024] S4: In order to ensure that the adjacent two cladding layers form a completely flat surface, the amount of liquid metal required to fill the remelted expansion area BEG should be equal to the amount of liquid metal coinciding with the lap area CDG. And meet the ideal state of multi-lap flatness requirements, i.e. points B, M, and E are on the same horizontal line, as shown in the figure. Figure 3

[0025] ​​​​The area of each region of the cladding layer satisfies the following relationship: S BMG = S EMG = S DNG = S CNG ;

[0026] S5: write the area relationship between the remelted expansion region BEG and the lap region CDG according to the area relationship of each region of the cladding layer;

[0027] Further, the area between the remelted expansion region BEG and the lap region CDG in step S4 is expressed as:

[0028]

[0029] S6: difference the areas of the BEG and CDG regions, define the difference value as g(d), when the ideal lap state is satisfied, S BEG = S CDG , solve the value of d;

[0030] Further, the area difference between the remelted expansion region BEG and the lap region CDG in step S5 is defined as g(d):

[0031]

[0032] When the ideal lap state is satisfied, S BEG = S CDG , that is, g(d)=0, and the solution is:

[0033]

[0034] S7: substitute the value of d into the critical lap rate calculation formula to obtain the critical lap rate of multi-pass cladding;

[0035] Further, the value of d is substituted into the critical lap rate calculation formula in step S6 , and the critical lap rate of multi-pass cladding is:

[0036]

[0037] S8: verify the multi-pass cladding quality under the optimal critical lap rate, compare and analyze the multi-pass cladding quality under different lap rates, and verify the reliability of the controllable process parameter multi-pass lap model of laser cladding; as shown in Figure 4 , 5.

[0038] Compared with the prior art, the present application has the following advantages:

[0039] (1) The lap rate model has wide application range. The calculation method of the laser cladding multi-pass lap rate proposed in the application can be applied to the collaborative optimization of the critical lap rate of laser multi-pass cladding according to actual working conditions and by arbitrarily selecting appropriate process parameters.

[0040] (2) The elliptical model has strong adaptability. The single-pass cladding cross-section profile adaptability function, the elliptical model, can automatically match the corresponding relationship of the long axis, the short axis and the X and Y axes according to the cross-section profile, and can adapt to the requirement of large cross-section profile changes caused by different parameter combinations.

[0041] (3) The lap rate model has high calculation precision. The multi-pass cladding lap rate model successfully maps the interaction relationship between the process parameters such as laser power, scanning speed, powder feeding rate and the critical lap rate, and has high calculation precision.

[0042] (4) The lap rate model has flexibility and comprehensive controllability. The calculation process is simple and has high universality, greatly improves the selection efficiency of the critical lap rate of multi-pass cladding, does not require a large amount of test data, saves pre-test time and cost, consumes less energy, and has low production cost.

[0043] (5) The product quality is good. The multi-pass cladding layer has high surface flatness, the boundary is not smooth, and the powder residue phenomenon is effectively alleviated, and the composite interface is good. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 is a schematic diagram of a cross-section profile feature model;

[0045] Figure 2 is a diagnostic diagram of the geometric structure parameters a, b and c of the elliptical model. Among them, figures (a), (c) and (e) are residual distribution diagrams of the geometric structure parameters a, b and c, respectively; figures (b), (d) and (f) are relationship diagrams of the test values and the predicted values of the geometric structure parameters a, b and c, respectively;

[0046] Figure 3 is a schematic diagram of a multi-pass cladding theoretical calculation model;

[0047] Figure 4 is a macroscopic morphology of a cladding layer with different lap rates. Among them, figure (a) is a lap rate of 16%; figure (b) is a lap rate of 26%; figure (c) is a lap rate of 36%;

[0048] Figure 5 is a three-dimensional microscopic morphology of a cladding layer with different lap rates. Among them, figure (a) is a lap rate of 16%; figure (b) is a lap rate of 26%; figure (c) is a lap rate of 36%. DETAILED DESCRIPTION

[0049] In order to better explain the process technical scheme of the present application, the present application will be described in detail through specific embodiments in combination with the accompanying drawings in the embodiments of the present application.

[0050] A calculation method of a laser cladding multi-pass overlap ratio, the base material is 27SiMn steel, the cladding layer material is GS-Fe01 alloy powder, comprising the following steps:

[0051] S1: In order to simplify the theoretical calculation and analysis process, two cladding layers are arbitrarily selected to complete the construction of the multi-pass overlap model, and the following assumptions are made:

[0052] (1) The cross-sectional profile of a single cladding layer is exactly a part of an elliptic function;

[0053] (2) In the process of multi-pass cladding with the same process parameters, the cross-sectional shape, size and area of a single cladding layer remain unchanged;

[0054] (3) The molten pool has good fluidity, and the next pass cladding layer is easy to spread and fill in the remelted expansion area;

[0055] (4) The influence of liquid metal cladding layer surface tension and protective gas impact pressure on the forming process is ignored.

[0056] S2: The cross-sectional profile of a single cladding layer is exactly a part of an elliptic function, as shown in Figure 1 , the elliptic function expression is: The calculation formula of the width W of a single cladding layer is: The calculation formula of the height H of a single cladding layer is: H = b-c.

[0057] Wherein: a, b, c are applicability function geometric structure parameters, which are functions of single cladding layer process parameters.

[0058] The calculation method of the applicability function geometric structure parameters a, b and c is introduced as follows:

[0059] (1) Taking laser power (p), scanning speed (v) and powder feeding rate (v f ) as the key input variables, 16 groups of single cladding orthogonal test schemes are constructed, as shown in Table 1.

[0060] Table 1 16 groups of single cladding orthogonal test

[0061]

[0062] (2) Selecting exponential regression model, combining polynomial function and trigonometric function model to carry out multivariate nonlinear fitting on 16 groups of data, and introducing standard simplex hill climbing method and general global optimization method to determine the optimal parameters of the model, and using MATLAB software to realize one-step optimization of the model multi-parameters, and obtaining the target function of the geometric structure parameters-process parameters of the applicability function.

[0063] a = 0.39261 (p 0.27230 v 0.00369 v f -0.40507 + 2.31260 sin (v f + 0.12452) - 3.35727

[0064] b = 6.12358 x 10 3 (p -0.72213 v -0.61507 v f 0.18576 - 0.46651 cos (p + 1.99589) - 0.95726

[0065] c = -9.26016 x 10 -5 (p -0.15465 v 2.34145 v f 0.02714 - 0.24563 cos (v + 0.11984) - 0.28974 cos (2p - 963.25493) - 7.69138 x 10 -7 v 3 + 3.82432 x 10 -4 pv f 2 - 6.91820 x 10 -8 p 2 + 1.73812

[0066] In the formula, p, v, vf are laser cladding process parameters laser power, scanning speed and powder feeding rate respectively, and a, b, c are elliptic function geometric structure parameters respectively.

[0067] (3) The fitting accuracy of the above model on 16 groups of data can be checked by the diagnostic graph of geometric structure parameters a, b, c, which mainly includes residual distribution graph and test value and predicted value relationship graph.

[0068] As Figure 2 shown, the residual data points are all randomly falling in the horizontal strip area within the range of (-0.1, 0.1), without any systematic distribution trend and predictability information, fully meeting the normality property, indicating that the fitting effect of the model on the data is good. In addition, the determination coefficient R2 All are much greater than 0.9, which proves that the error of test value and prediction value is small and the correlation is good.

[0069] S3: The cross-section profile applicability function of adjacent two cladding layers is respectively:

[0070]

[0071] Wherein: d is the distance of the center of any adjacent cladding layer, as shown in Figure 3 .

[0072] S4: In order to ensure that the adjacent two cladding layers form a completely flat surface, the amount of liquid metal required to fill the remelting expansion area BEG should be equal to the amount of liquid metal overlapped in the area CDG, and the area of each area of the cladding layer satisfies the following relationship: BMG = S EMG = S DNG = S CNG , and meet the ideal state of multi-layer overlapping to flatness, that is, points B, M, E are on the same horizontal line. As shown in Figure 3 .

[0073] S5: The area of BEG and CDG area can be expressed as:

[0074]

[0075] S6: The difference between the area of BEG and CDG area is defined as g(d):

[0076]

[0077] When the ideal overlapping state is met, S BEG = S CDG , that is, g(d) = 0, and the solution is:

[0078]

[0079] S7: Substitute the above formula into the critical overlapping rate calculation formula , and the critical overlapping rate of multi-layer cladding is:

[0080]

[0081] In summary, the multi-layer overlapping model of controllable process parameters of laser cladding is:

[0082] H = b-c

[0083]

[0084] a = 0.39261(p 0.27230 v 0.00369 vf -0.40507 + 2.31260sin(v f + 0.12452) - 3.35727

[0085] b = 6.12358 x 10 3 (p -0.72213 v -0.61507 v f 0.18576 ) - 0.46651cos(p + 1.99589) - 0.95726

[0086] C = -9.26016 x 10 -5 (p- 0.15465 v 2.34145 v f 0.02714 ) - 0.24563cos(v + 0.11984) - 0.28974cos(2p - 963.25493) - 7.69138 x 10 -7 v 3 + 3.82432 x 10 -4 pv f 2 - 6.91820 x 10 -8 p 2 + 1.73812

[0087]

[0088]

[0089] Based on a laser single-channel cladding process parameter combination, that is, laser power is 744 W, scanning speed is 233 mm / min, powder feeding rate is 1.2 r / min, and spot diameter is 2.5 mm, a multivariate nonlinear mathematical model is constructed by taking the elliptic function coefficients a, b and c as target response indexes, and the geometric structure parameters of the single-channel cladding cross-section profile applicability function are effectively predicted. On this basis, the accurate information of the cross-section profile width (W) and height (H) is further obtained, and the above parameters are substituted into the multi-channel overlapping model of the laser cladding controllable process parameters, and the optimal critical overlapping rate of the single-channel cladding suitable for this working condition is obtained as 26%.

[0090] S8: Multi-channel cladding quality verification under the optimal critical overlapping rate:

[0091] The multi-channel cladding quality under three conditions of the overlapping rates of 16%, 26% and 36% is compared, and it is found that Figure 4 , Figure 5The average height difference between the bottom of the concave area and the top of the cladding layer is about 270 μm, which does not meet the requirements of multi-pass cladding forming and belongs to under-lapping state. At the same time, the surface of the boundary area of each pass cladding layer is not smooth, and a large amount of un-melted metal powder particles are mixed.

[0092] When the overlap rate increases to 26%, which is the critical overlap rate calculated by the multi-pass cladding model, the metal material in the cladding area of the cladding layer basically fills the concave part of the remelted expansion area, the overall forming height of the cladding layer is basically consistent, there is no obvious groove between each pass, the surface is smooth and flat, and meets the requirements of multi-pass cladding forming, and only a small amount of powder residue exists between each pass.

[0093] When the overlap rate increases to 36%, the boundary climbing area and the climbing amplitude increase significantly, the maximum height difference is more than 3000 μm, the groove between each pass has completely disappeared, and a large number of black burning areas appear on the surface of the cladding layer.

[0094] In summary, when the overlap rate is 26%, the multi-pass cladding forming can obtain a cladding layer flatness close to the expected result, which proves the reliability of the multi-pass cladding model of the controllable process parameters of laser cladding.

[0095] The contents not described in detail in the specification of the present application belong to the prior art known to those skilled in the art. Although the above describes the specific embodiments of the present application for the purpose of facilitating the understanding of the present application by those skilled in the art, it should be clear that the present application is not limited to the scope of the specific embodiments, and for those skilled in the art, it is obvious that various changes are within the spirit and scope of the present application defined and limited by the appended claims, and all the inventions utilizing the concept of the present application are within the scope of protection.

Claims

1. A method for calculating the overlap rate of multiple laser cladding passes, characterized in that, The method includes the following steps: S1: Arbitrarily select two cladding layers to complete the construction of the multi-layer overlap model, and make the following assumptions: (1) The cross-sectional profile of a single cladding layer is perfectly and precisely a part of an elliptic function; (2) During the multi-pass cladding process using the same process parameters, the cross-sectional shape, size and area of ​​the single cladding layer remain unchanged; (3) The molten pool has good fluidity, and the subsequent cladding layer is easy to spread and fill into the remelting expansion area; (4) The effects of the surface tension of the liquid metal cladding layer and the impact pressure of the protective gas on the forming process are ignored; S2: The cross-sectional profile of the single cladding layer is precisely defined as a part of an elliptic function. A Cartesian coordinate system is established with the horizontal boundary between the cladding layer and the substrate as the X-axis and the vertical axis of symmetry of the cladding layer as the Y-axis. Point O is the origin, point O′ is the center of the ellipse of the first cladding layer, the width of the cladding layer is W, and the height of the cladding layer is H. Then: The expression for the elliptic function is: , Formula for calculating the width W of a single cladding layer: , Formula for calculating the height H of a single cladding layer: H = bc Where a, b, and c are elliptic function geometric structure parameters, all of which are functions of the single-pass cladding process parameters; y represents the ordinate of any point on the cross-sectional profile of the single-pass cladding layer; and x represents the abscissa of any point on the cross-sectional profile of the single-pass cladding layer. Furthermore, the objective function for the geometric structure parameters of the elliptic function and the process parameters of the single-pass cladding layer is: a=0.39261(p 0.27230 v 0.00369 v f -0.40507 )+2.31260sin(v f +0.12452)-3.35727 b=6.12358×10 3 (p -0.72213 v -0.61507 v f 0.18576 )-0.46651cos(p+1.99589)-0.95726 c=-9.26016×10 -5 (p -0.15465 in 2.34145 in f 0.02714 )-0.24563cos(v+0.11984)-0.28974cos(2p-963.25493)-7.69138×10 -7 in 3 +3.82432×10 -4 pv f 2 -6.91820×10 -8 p 2 +1.73812 In the formula, p, v, v f These are the laser cladding process parameters: laser power, scanning speed, and powder feeding rate. S3: Select the elliptic function from step S2 as the applicability function of the cross-sectional profile of two adjacent cladding layers; S4: Ensure that the amount of liquid metal to be filled in the remelted expansion zone BEG is equal to the amount of liquid metal overlapping the overlapping zone CDG; and meet the flatness requirements of ideal multi-layer overlap. S5: Based on the area relationships of each region in the cladding layer, write the area relationship between the remelting expansion region BEG and the overlapping region CDG, where the area between the remelting expansion region BEG and the overlapping region CDG is expressed as: ； S6: Subtract the areas of the BEG and CDG regions, and define the difference as g(d). When the ideal overlap condition is met, S BEG =S CDG Solve for the value of d, where the expression for the area difference g(d) is as follows: , When the ideal overlap condition is met, S BEG =S CDG That is, g(d) = 0, solving for g(d) gives: ； S7: Substitute the value of d into the critical overlap ratio calculation formula In the process, there are multiple critical overlap rates for cladding, as shown below: ； S8: Verify the quality of multi-layer cladding under the optimal critical overlap rate.

2. The method for calculating the overlap rate of multiple laser cladding passes according to claim 1, characterized in that, In step S3, the applicability functions for the cross-sectional profiles of two adjacent cladding layers are as follows: , Where y1 represents the ordinate of any point on the cross-sectional profile of the first cladding layer, y2 represents the ordinate of any point on the cross-sectional profile of the next cladding layer, and d is the distance between the centers of any adjacent cladding layers.

3. The method for calculating the overlap rate of multiple laser cladding passes according to claim 1, characterized in that, In step S4, the amount of liquid metal required to fill the remelted expansion region BEG is equal to the amount of liquid metal that overlaps with the overlapping region CDG; and the flatness requirement for multi-layer overlap in an ideal state is met, i.e., points B, M, and E are on the same horizontal line; the area of ​​each region of the cladding layer satisfies the following relationship: S BMG =S EMG =S DNG =S CNG .

4. The method for calculating the overlap rate of multiple laser cladding passes according to claim 1, characterized in that, The specific operation of step S8 is as follows: compare and analyze the quality of multi-pass cladding under different overlap rates to verify the reliability of the multi-pass overlap model of controllable laser cladding process parameters.

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