Processed surface evaluation method

Abstract

To provide a processed surface evaluation method that can quantitatively evaluate an appearance quality of a processed surface processed by a ball end mill, in a short time.SOLUTION: In a method in which a work-piece 20 and a ball end mill are mounted on a machine tool, the ball end mil is fed along a plurality of process paths 22 set in parallel with a constant pick-feed width P on a surface 21 of the work-piece 20 to process the surface and an appearance quality of the processed surface of the work-piece 20 is quantitatively evaluated using cutter marks 23 formed on the surface 21 of the work-piece 20, boundary lines 33 between the cutter marks 23 on the adjacent process paths 22 are obtained, ratios of widths W of the cutter marks 23 on the adjacent process paths 22 are calculated from positions of the obtained boundary lines 33, and an evaluation value showing deviations of the widths W of the cutter marks 23 is calculated from an average value and standard deviations of the ratios.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a machined surface evaluation method. [Background technology]

[0002] Cutting is performed using machine tools equipped with ball end mills to machine workpieces such as molds. During machining, multiple parallel machining paths are set on the surface of the workpiece with a constant pick feed, and the ball end mill is fed along these machining paths to perform the cutting. As a result of the machining, cutter marks are formed on the surface of the workpiece, aligned in the feed direction of the ball end mill. The machined surface of the machined workpiece is evaluated. Evaluation of the machined surface includes shape accuracy measured by a coordinate measuring machine, etc., and the quality of the machined surface. To determine the quality of the machined surface, an operator visually judges the irregularity of the width of the cutter marks that are lined up in the feed direction along the machining paths for multiple parallel machining paths. This type of visual judgment is only a qualitative evaluation, and there was a demand for a quantitative evaluation. In response to this, Patent Document 1 proposes an evaluation method in which the position of the cutter mark along the machining path is measured, the difference in the position of the cutter mark on adjacent machining paths in the pick direction is calculated, and the standard deviation of this difference is used to evaluate the surface quality. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-27049 Summary of the Invention [Problem to be solved by the invention]

[0004] In the quantitative evaluation method for machined surface quality described in Patent Document 1, the positions of cutter marks on the machining path are used for evaluation, and in Step 1, the profile curve is measured at the center positions of cutter marks aligned in the feed direction on the machining path of the machined surface. Such measurement of the profile curve needs to be performed over a fairly wide area on the machined mold surface. Therefore, although the evaluation method of Patent Document 1 allows quantitative evaluation, there is a problem in that it takes a long time to measure the cutter marks.

[0005] An object of the present invention is to provide a machined surface evaluation method that can quantitatively evaluate the surface quality of a surface machined by a ball end mill in a short period of time. [Means for solving the problem]

[0006] The machined surface evaluation method of the present invention involves mounting a workpiece and a ball end mill on a machine tool, machining the workpiece surface while feeding the ball end mill along multiple machining paths set parallel to the workpiece surface with a constant pick feed, and quantitatively evaluating the surface quality of the machined surface of the workpiece using cutter marks formed on the surface of the workpiece.The method obtains a boundary line between the cutter marks on adjacent machining paths, calculates the ratio of the widths of the cutter marks on the adjacent machining paths from the position of the obtained boundary line, and calculates an evaluation value indicating the variation in the width of the cutter marks from the average value and standard deviation of the ratio. In the present invention, the variation in width between adjacent cutter marks is calculated as an evaluation value. Because the width and depth of cutter marks are correlated depending on the curvature of the tip of the ball end mill, the variation in width of the cutter marks reflects the variation in depth. Therefore, the evaluation value can reflect the variation in depth between adjacent cutter marks, i.e., the variation in surface irregularities, allowing for quantitative evaluation of the surface quality of the machined workpiece.

[0007] In the machined surface evaluation method of the present invention, the evaluation value can be calculated by determining the width ratio R of the cutter marks at multiple locations, and using the average Rav of the ratios R and the standard deviation Rsd of the ratios R, as follows: evaluation value A = Rav-3 x Rsd. Specifically, the widths W1 and W2 of adjacent cutter marks are measured at multiple points within a specified range on the surface of the workpiece on which the cutter marks are formed, and the ratio R = W1 / W2 is calculated. The narrower of the adjacent cutter marks is designated as width W1, and the wider is designated as width W2, with the ratio R set to 1 or less. The average Rav and standard deviation Rsd of the ratio R calculated at multiple locations are then calculated, and an evaluation value A = Rav-3 × Rsd is calculated from these. The closer the obtained evaluation value A is to 1, the more consistent the cutter mark widths are and the higher the quality of the machined surface can be evaluated.

[0008] In the machined surface evaluation method of the present invention, the width Q of the cutter mark in actual machining is calculated using the evaluation value A, the tool diameter D of the ball end mill, and the ideal pick feed width P for machining, and the difference E in unevenness between adjacent cutter marks can be calculated. Specifically, if the tool diameter of the ball end mill is D, the ideal pick feed width during machining without fluctuations is P (ideal cutter mark width), and the actual cutter mark width due to fluctuations along the cutter mark path is Q, the difference E between the heights of the bottom surfaces of adjacent cutter marks (height in the direction perpendicular to the workpiece surface) can be expressed by the following equation.

[0009]

number

[0010] Here, if the ratio of the widths of adjacent cutter marks is R (R≦1), then R=(2P-Q) / Q, and therefore Q=2P / (R+1). Then, by using the average Rav and standard deviation Rsd of the ratio R mentioned above to calculate the fluctuating width Q as R=Rav(1+3×Rsd), the difference in unevenness E between adjacent cutter marks can be specifically evaluated as the value of the difference in height of the machined surface between adjacent passes.

[0011] In the machining surface evaluation method of the present invention, the surface of the workpiece is photographed, and multiple parallel reference lines are set on the obtained photographed image in a direction intersecting the machining path, and boundary points are set at the intersections of the boundary portions of the cutter marks on adjacent machining paths and the reference lines, and the boundary points are connected sequentially along the machining path to obtain the boundary line. In this invention, the boundary portion can be defined as a ridge line that is continuous or discontinuous in the feed direction and formed during machining between cutter marks along adjacent machining paths. The position of the ridge line of the boundary portion also fluctuates in the pick direction during machining, but by selecting boundary points at the intersections with the boundary using multiple parallel reference lines set in a direction intersecting the machining path and then sequentially connecting these along the machining path, a polygonal boundary line can be obtained. The distance between the boundary points on the same reference line on both sides of the machining path can then be defined as the width of the boundary line.

[0012] In the machined surface evaluation method of the present invention, an extracted image is created in which the boundary line is set for a photographed image of the surface of the workpiece, and a convolutional neural network model is created from a data set in which points on the boundary line extracted as the extracted image are linked to points in the photographed image.The photographed image of the workpiece to be evaluated is input into the convolutional neural network model, and the boundary line can be set for the photographed image of the object to be evaluated. In this way, the present invention can significantly improve the efficiency of the operation of setting a boundary line on the surface of a machined workpiece to be evaluated. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a machined surface evaluation method that can quantitatively evaluate the surface quality of a machined surface machined by a ball end mill in a short period of time. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a perspective view showing a main part of a machine tool and a workpiece according to an embodiment of the present invention; [Figure 2] 3 is a flowchart showing a machined surface evaluation method in the embodiment. [Figure 3] 10 is a flowchart showing a procedure for obtaining a boundary line in the embodiment. [Figure 4] FIG. 4 is a diagram showing a reference line in the embodiment. [Figure 5] FIG. 4 is a diagram showing boundary points in the embodiment. [Figure 6] FIG. 4 is a diagram showing a boundary line in the embodiment. [Figure 7] 5A to 5C are schematic diagrams showing a procedure for measuring the width of a boundary point in the embodiment. [Figure 8] 5A to 5C are schematic diagrams showing variations in width of a boundary line in the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Specific embodiments of the machined surface evaluation method of the present invention will be described below. 1, a machine tool 10 has a table 11 and a spindle 12. A ball end mill 13 is attached to the spindle 12, and a workpiece 20 is fixed to the table 11. The machine tool 10 operates under the control of a control device not shown, and cuts the surface 21 of the workpiece 20 by rotating the spindle 12 while moving the spindle 12 relative to the table 11 and feeding the tip of the ball end mill 13 in a predetermined direction (feed direction Dc, described later) while contacting the surface 21 of the workpiece 20 along the surface 21.

[0016] In the machine tool 10, a machining path 22 indicating the movement path of the ball end mill 13 during machining is set in the operation program of the control device. A plurality of machining paths 22 are set parallel to the surface 21 of the workpiece 20. The machining paths 22 extend along the feed direction Dc of the ball end mill 13. The direction in which the plurality of machining paths 22 are lined up (a direction intersecting with the feed direction Dc) is set to be the pick direction Dp. The arrangement pitch of the plurality of machining paths 22 in the pick direction Dp is set to a predetermined pick feed width P.

[0017] The machine tool 10 sequentially cuts the surface 21 of the workpiece 20 by feeding the ball end mill 13 in the feed direction Dc along multiple machining paths 22. Through this machining, cutter marks 23 are formed on the surface 21 of the workpiece 20, extending in the feed direction Dc of the ball end mill 13 along each machining path 22. Each of the multiple cutter marks 23 has a minute uneven shape aligned in the feed direction Dc, and a continuous or discontinuous ridge line 24 is formed in the feed direction Dc at the boundary between adjacent cutter marks 23 in the pick direction Dp.

[0018] In the machined workpiece 20, these cutter marks 23 and ridge lines 24 affect the evaluation of the surface quality of the machined surface of the workpiece 20 (the machined portion of the surface 21). In this embodiment, the machined surface of the workpiece 20 is evaluated using a machined surface evaluation method based on the present invention.

[0019] In Figure 2, the machined surface evaluation method according to the present invention quantitatively evaluates the surface quality of the machined surface of the workpiece 20 using the cutter marks 23 formed on the surface 21 of the workpiece 20 by obtaining a boundary line 33 (see Figure 6) from the ridge line 24 between the cutter marks 23 on adjacent machining paths 22 (process S11), determining the ratio of the widths of the cutter marks 23 on the adjacent machining paths 22 from the position of the obtained boundary line 33 (process S12), and determining an evaluation value from the average value and standard deviation of the ratio (process S13). The steps S11 to S13 will be described in detail below.

[0020] In the first step S11, the boundary line 33 between adjacent cutter marks 23 is obtained. In FIG. 3, to obtain the boundary line 33, first, the surface 21 of the machined workpiece 20 is photographed with a camera (step S21), and a photographed image 30 (see FIG. 4) is obtained. 4, the photographed image 30 shows multiple rows of cutter marks 23 formed on the surface 21 of the workpiece 20, and ridge lines 24 at the boundaries between the rows of cutter marks 23. The cutter marks 23 and ridge lines 24 are formed along the multiple machining paths 22 described above, and extend in the feed direction Dc of the ball end mill 13.

[0021] Following step S21, a reference line 31 (see FIG. 4) that intersects with the machining path 22 is set on the photographed image 30 (step S22). The reference lines 31 are defined as a plurality of parallel straight lines that intersect with the plurality of machining paths 22 in the photographed image 30 obtained in process S21. The intersecting angle between the reference line 31 and the machining path 22 is not limited to a right angle, and may be simplified as being the horizontal direction of the photographed image 30.

[0022] Once the reference lines 31 have been set in step S22, boundary points 32 (see FIG. 5) are set at the intersections of the reference lines 31 and the ridge lines 24 of the boundary portions of the cutter marks 23 (step S23). In FIG. 5, boundary points 32 are set at the intersections of each of the reference lines 31 and the plurality of edge lines 24, respectively.

[0023] Once the boundary points 32 have been set in step S23, for each machining path 22, the boundary points 32 between adjacent machining paths 22 are sequentially connected along the machining path 22 to obtain a boundary line 33 (see Figure 6) (step S24). 6, the boundary line 33 is a broken line with boundary points 32 aligned in the feed direction Dc as nodes, and indicates the boundary between the cutter marks 23 formed on adjacent machining paths 22. The boundary line 33 is formed by sequentially connecting the ridge lines 24 that form the boundary points 32, and indicates the arrangement of the ridge lines 24 that are the boundary portions of the cutter marks 23. The machining paths 22 have a constant arrangement pitch in the pick direction Dp, which is the pick feed width P, and the width of the machining paths 22 is constant even if the reference line 31 is inclined with respect to the pick direction Dp. However, the width W of the cutter marks 23 varies with machining.

[0024] By the above-described processes S21 to S24, the boundary lines 33 between the cutter marks 23 between adjacent machining paths 22 can be acquired for all machining paths 22 on the surface 21 of the machined workpiece 20. This completes the first process S11 (see FIG. 2).

[0025] In the next step S12, the ratio of the widths of adjacent cutter marks 23 is calculated. The width W of the cutter mark 23 is measured by calculating the distance between the boundary points 32 on the reference line 31 set previously. In Figure 7, an X axis is set parallel to the multiple reference lines 31 and a Y axis is set perpendicular to them, and the distance between boundary points 32 on each reference line 31 (Y = Ya) from the reference line 31 at one end (Y = Y1) to the reference line 31 at the opposite end (Y = Y2) is measured. On the reference line 31 at the Y=Y1 position, the intervals W11, W12, . . . between the points X11, X12, X13, . On the reference line 31 at the Y=Ya position, the intervals Wa1, Wa2, . . . between the points Xa1, Xa2, Xa3, . On the reference line 31 at the Y=Y2 position, intervals W21, W22, . . . between points X21, X22, X23, . As a result, the distance between the boundary line 33 passing through point X11 and the boundary line 33 passing through point X12 is W11 at the Y=Y1 position, Wa1 at the Y=Ya position, and W21 at the Y=Y2 position. The distance between the boundary line 33 passing through point X12 and the boundary line 33 passing through point X13 is W12 at the Y=Y1 position, Wa2 at the Y=Ya position, and W22 at the Y=Y2 position. By measuring in the same way, the distance between adjacent boundary lines 33 at the reference line 31 can be measured, and this can be used as the width W of the cutter mark 23.

[0026] The ratio R of the widths of adjacent cutter marks 23 is calculated from the width W of the cutter marks 23 measured previously. For example, the width W11 of the cutter mark 23 between the points X11 and X12 and the width W12 of the cutter mark 23 between the points X12 and X13 are calculated as a ratio R1=W11 / W12. In this case, the divisor and dividend are selected so that the ratio R is 1 or less in the calculation. For example, the width W21 of the cutter mark 23 between points X21 and X22 and the width W22 of the cutter mark 23 between points X22 and X23 are calculated as a ratio R2=W22 / W21, since W21>W22.

[0027] In this way, the ratio R of the widths W of adjacent cutter marks 23 at the position of the reference line 31 can be measured. This completes the process S12 (see FIG. 2).

[0028] In the next step S13, the average Rav of the ratio R, the standard deviation Rsd, and the evaluation value A are calculated. In the above-mentioned process S12, the ratio R of the width W at the position of the reference line 31 between adjacent cutter marks 23 was calculated. The number of ratios R is m = (number of reference lines 31 - 1) in the feed direction Dc, and n = (number of machining paths 22 - 1) = (number of boundary lines 33 - 2) in the pick direction Dp. In step S13, the average Rav and the standard deviation Rsd of the ratios R are calculated for these m×n ratios R, and an evaluation value A=Rav−3×Rsd is calculated from these. The closer the obtained evaluation value A is to 1, the more uniform the width of the machining path is and the higher the quality of the machined surface can be evaluated.

[0029] In this embodiment, the previously calculated evaluation value A, the tool diameter D of the ball end mill 13, and the ideal pick feed width P for machining are used to calculate the width Q of the cutter mark 23 in actual machining, and the difference E in unevenness between adjacent cutter marks 23 is calculated. In FIG. 8A, the cutter marks 23 processed with the ideal pick feed width P each have a width P in the pick direction Dp. In Figure 8(B), if the ball end mill 13 is fed along the machining path 22 and fluctuates in the direction perpendicular to the machining surface during machining, the width of the cutter mark 23 may expand (or narrow) as shown by Q. If the width of the fluctuated cutter mark 23 is Q, the width of adjacent cutter marks 23 is (2P-Q). If the ratio of the widths of adjacent cutter marks is R (R<1), then R=(2P-Q) / Q, and therefore the width Q=2P / (R+1). Using these widths P and Q, the difference E in height (height in the direction perpendicular to the work surface) between the bottom surfaces of adjacent cutter marks 23 can be calculated.

[0030]

number

[0031] In the difference E, the width P is the ideal pick feed width, and the width Q = 2P / (R + 1). Therefore, by using the average Rav and standard deviation Rsd of the ratio R calculated in step S12 to calculate the fluctuating width Q as R = Rav(1 + 3 × Rsd), the unevenness difference E between adjacent cutter marks 23 can be specifically evaluated as the value of the difference in height of the machined surface between adjacent passes.

[0032] In this embodiment, the above-mentioned process S11, that is, obtaining the boundary line 33 between the cutter marks 23 between adjacent machining paths 22, can be automated using a convolutional neural network model. For example, as explained in the process S11, a reference line 31 (see FIG. 4) and a boundary point 32 (see FIG. 5) are set for a captured image 30 of the surface 21 of the workpiece 20, and a boundary line 33 (see FIG. 6) is obtained from these to create an extracted image, and a convolutional neural network model is created from a data set that links the points on the boundary line 33 extracted as the extracted image with the points on the captured image 30. Then, by inputting a photographed image 30 of the workpiece 20 to be evaluated into a convolutional neural network model, it is possible to obtain a boundary line 33 in the photographed image 30 to be evaluated. In this case, it is preferable that the extracted image to be modeled and the obtained boundary line 33 are black and white binary data, and it is preferable to automate this process using an autoencoder. This significantly improves the efficiency of the operation of setting the boundary line 33 on the surface 21 of the machined workpiece 20 to be evaluated.

[0033] According to the present embodiment described above, the variation in width W of adjacent cutter marks 23 can be calculated as evaluation value A. Since the width W and depth of the cutter marks 23 correlate with each other depending on the curvature of the tip of the ball end mill 13, the variation in width W of the cutter marks 23 reflects the variation in depth. Therefore, the variation in depth of adjacent cutter marks 23, that is, the variation in surface irregularities, can be reflected in evaluation value A, and the surface quality of the machined workpiece can be quantitatively evaluated. In particular, in this embodiment, the difference E in unevenness between adjacent cutter marks 23 can be specifically evaluated as the difference in height of the machined surface between adjacent passes. [Industrial Applicability]

[0034] The present invention can be used in a machined surface evaluation method. [Explanation of symbols]

[0035] 10...machine tool, 11...table, 12...spindle, 13...ball end mill, 20...workpiece, 21...surface, 22...machining path, 23...cutter mark, 24...ridge line, 30...captured image, 31...reference line, 32...boundary point, 33...boundary line, A...evaluation value, D...tool diameter, Dc...feed direction, Dp...pick direction, E...difference in bottom height, P...pick feed width, Q...actual cutter mark width, R,R1,R2...ratio, Rav...average, Rsd...standard deviation, S11,S12,S13,S21,S22,S23,S24...processing, W,W1,W2...width.

Claims

1. A method for quantitatively evaluating the surface quality of a machined surface of a workpiece by mounting a workpiece and a ball end mill on a machine tool, feeding the ball end mill along a plurality of machining paths set in parallel with a constant pick feed on the surface of the workpiece, and using cutter marks formed on the surface of the workpiece, comprising: A machining surface evaluation method that obtains a boundary line between the cutter marks on adjacent machining paths, calculates a ratio of the widths of the cutter marks on the adjacent machining paths from the position of the obtained boundary line, and calculates an evaluation value indicating the variation in the width of the cutter marks from the average value and standard deviation of the ratio.

2. 2. The machined surface evaluation method according to claim 1, The evaluation value is calculated by calculating the ratio R of the width of the cutter mark at multiple locations, and using the average Rav of the ratio R and the standard deviation Rsd of the ratio R, as follows: evaluation value A = Rav - 3 x Rsd.

3. 3. The machined surface evaluation method according to claim 2, wherein the width Q of the cutter mark in actual machining is calculated using the evaluation value A, the tool diameter D of the ball end mill, and the ideal pick feed width P in machining, and the difference E in unevenness between adjacent cutter marks is calculated.

4. In the machined surface evaluation method of the present invention described in any one of claims 1 to 3, A machining surface evaluation method in which the surface of the workpiece is photographed, a plurality of mutually parallel reference lines are set on the obtained photographed image in a direction intersecting the machining path, boundary points are set at the intersections of the reference lines and boundary portions of the cutter marks on adjacent machining paths, and the boundary points are connected sequentially along the machining path to obtain the boundary line.

5. 5. The machined surface evaluation method according to claim 4, wherein an extracted image in which the boundary line is set is created for a photographed image of the surface of the workpiece, a convolutional neural network model is created from a data set in which points on the boundary line extracted as the extracted image are linked to points in the photographed image, the photographed image of the workpiece to be evaluated is input to the convolutional neural network model, and the boundary line is set for the photographed image of the object to be evaluated.

Images