Measuring method for work-affected layer of work-piece, processing method for work-piece, work-affected layer measuring apparatus and machine tool

Abstract

To provide: a measuring method for a work-affected layer of a work-piece capable of easily estimating a state of a work-affected layer of a processing surface of the work-piece on a machine tool; a processing method for work-piece; a work-affected layer measuring apparatus; and a machine tool.SOLUTION: A method includes: attaching an indenter 42 for pressing into a workpiece W to a main shaft 20; pressing the indenter 42 into the workpiece W using feed devices 22, 26, 34 of a machine tool 10; measuring an indentation load L and an indentation depth h from moment to moment; calculating an indentation load coefficient C, which is a coefficient when the indentation load L is functionally approximated with respect to the indentation depth h, from moment to moment; stopping the pressing of the indenter 42 into the workpiece W when a rate of change of the indentation load coefficient C with respect to the indentation depth h reaches a value sufficiently close to 0 from a negative; and calculating a work-affected layer depth Z by multiplying the indentation depth h when the pressing is stopped by a depth conversion constant.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for measuring a machine-damaged layer of a workpiece, a method for machining a workpiece, a machine-damaged layer measuring device, and a machine tool. [Background technology]

[0002] The material of the workpiece is made through several processes such as rolling, drawing, extrusion, forging, and surface treatment, and a process-affected layer is generated on the surface. The workpiece material is also machined to obtain the desired shape and dimensions. In this initial stage, rough processing is performed, and a process-affected layer is generated on the surface of the workpiece. In such a process-affected layer, residual stress is likely to occur due to residual strain, which can cause stress corrosion cracking, fatigue failure, creep failure, and the like. For this reason, in the product stage, the process-affected layer is managed to be removed by finishing processing. In recent years, for example, difficult-to-cut materials such as nickel-based superalloys are often used to make aircraft parts lighter and more rigid, and to achieve both performance and fuel efficiency in jet engines, and management of the process-affected layer of such materials is becoming increasingly important.

[0003] Conventional methods for evaluating processing-induced layers include, for example, observation with an optical microscope or electron microscope, X-ray diffraction (XRD), electron backscatter diffraction (EBSD), micro-Vickers testing, etc. However, these evaluation methods require cutting the workpiece and observing the cross section, as well as dedicated measuring equipment, management qualifications for handling, and measurement know-how, making them difficult to implement on a regular basis at processing sites.

[0004] Therefore, for example, Patent Document 1 discloses a three-dimensional hardness distribution measuring method and system utilizing an indentation test method. The indentation test method is a quasi-nondestructive inspection method that evaluates the residual stress distribution in the depth direction of a sample from the load-displacement curve when a pyramidal or spherical indenter is indented into the surface of the sample. FIG. 11 shows a schematic longitudinal section of a sample surface into which a pyramidal indenter has been indented. FIG. 12 shows the relationship between the indentation load L (vertical axis) and the indentation depth h (horizontal axis) from the start of loading to the unloading of the load in an indentation test. It can be seen that the indentation load L can be approximated by a quadratic function of the indentation depth h. For example, as described in Non-Patent Document 1, the indentation load coefficient (i.e., L / h 2 ) decreases as the indentation depth h increases, because in shallow regions the indentation depth is affected by the hardened or softened process-affected layer. Furthermore, it is known that when the pyramidal indenter is indented deeply, the effect of the process-affected layer decreases beyond a certain depth, and the indentation load coefficient becomes roughly constant. For this reason, the depth of the process-affected layer can be determined from the change in the indentation load coefficient.

[0005] However, in a general indentation test method such as the Instrumented Indentation Technique (IIT) disclosed in Non-Patent Document 1 and Non-Patent Document 2, a load is applied to the workpiece until a preset indentation depth or indentation load value is reached, so that an indentation deeper than necessary may be left on the surface of the workpiece. For example, as shown in FIG. 11, the pyramidal indenter is indented to an indentation depth D that exceeds the thickness M of the work-affected layer WL. For this reason, even if the depth of the work-affected layer is evaluated by the indentation test method after the rough machining process and whether or not finishing processing is required is determined according to the depth, if an indentation deeper than the amount of removal in the finish machining process exists, finishing processing cannot be performed and the workpiece may be treated as a defective product. In addition, in a general indentation test method (or IIT), it is difficult to adjust the position and phase of the indenter for indentation, so that it is difficult to perform an indentation test during the machining process of a machined part. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-85804 [Non-patent literature]

[0007] [Non-Patent Document 1] Shuhei Hikawa, Shigetake Okano, Masato Mochizuki, Masashi Hashimoto, Ryo Tezuka, "Evaluation of the Depth of Process-Affected Layer by Indentation Method and Its Applicability to Curved Surface Shapes", Abstracts of Lectures at the National Conference of the Japan Welding Society, Vol. 112, Japan Welding Society, April 2023, pp. 166-167 [Non-Patent Document 2] Shigetake Okano, Masato Mochizuki, "Proposal of a quasi-nondestructive measurement method of non-equibiaxial residual stress field by indentation method independent of stress-free reference hardness", Transactions of the Japan Society of Mechanical Engineers, Vol. 80, No. 820, Japan Society of Mechanical Engineers, 2014, pp. 1-11 Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above circumstances, the present invention aims to provide a method for measuring a workpiece's processed-damaged layer, a workpiece processing method, a processed-damaged layer measuring device, and a machine tool, which can easily evaluate the state of the processed-damaged layer on the machined surface of a workpiece on a machine tool. [Means for solving the problem]

[0009] According to one aspect of the present invention, there is provided a method for measuring a machining-damaged layer on the surface of a workpiece on a machine tool that processes a workpiece attached to a table with a tool attached to the spindle, the method including: attaching an indenter to the spindle for pressing into the workpiece instead of the tool; pressing the indenter into the workpiece using the feed device of the machine tool; measuring the indentation load for pressing the indenter and the indentation depth of the indenter into the workpiece from moment to moment; calculating an indentation load coefficient, which is a coefficient obtained by functionally approximating the indentation load with the indentation depth, from moment to moment; stopping the indentation of the indenter into the workpiece when the rate of change of the indentation load coefficient with respect to the indentation depth becomes a value that is sufficiently close to zero from negative; and multiplying the indentation depth of the indenter when indentation is stopped by a depth conversion constant to calculate the depth of the machining-damaged layer.

[0010] Furthermore, according to one aspect of the present invention, there is provided a method for machining a workpiece, in which a workpiece attached to a table of a machine tool is roughly machined with a tool attached to a spindle, and then a machine-damaged layer on the surface of the workpiece is measured on the machine tool, and finish machining is performed after the machine-damaged layer measurement, the method comprising the steps of: after rough machining, mounting an indenter to the spindle for pressing into the workpiece in place of the tool; pressing the indenter into the workpiece using a feed device of the machine tool; measuring the indentation load for pressing the indenter and the indentation depth of the indenter into the workpiece from moment to moment; calculating an indentation load coefficient which is a coefficient obtained by functionally approximating the indentation load with the indentation depth from moment to moment; stopping the indenter pressing into the workpiece when the rate of change of the indentation load coefficient with respect to the indentation depth becomes a value sufficiently close to 0 from negative; multiplying the indentation depth of the indenter when the indentation was stopped by a depth conversion coefficient to calculate the machine-damaged layer depth; and performing finish machining when the calculated machine-damaged layer depth is smaller than the finishing allowance of the workpiece.

[0011] According to one aspect of the present invention, there is provided a machine tool for measuring a machining-affected layer on the surface of a workpiece on a machine tool which processes a workpiece attached to a table with a tool attached to a spindle, the machine tool comprising: an indenter which can be attached to the spindle in place of the tool and which forms an indentation by being pressed into the workpiece using the machine tool's feed device; an indentation load detector which measures the indentation load applied to the workpiece at every moment; an indentation depth detector which measures the indentation depth of the indenter into the workpiece at every moment; an indenter indentation stop control means which momentarily calculates an indentation load coefficient which is a coefficient obtained when the indentation load is functionally approximated by the indentation depth, and which stops the indentation of the indenter into the workpiece when the rate of change of the indentation load coefficient with respect to the indentation depth becomes a value sufficiently close to zero from negative; and a indentation-affected layer depth calculation means which calculates the depth of the machining-affected layer by multiplying the indentation depth at which the indentation of the indenter was stopped by a depth conversion constant.

[0012] Furthermore, according to one aspect of the present invention, there is provided a processing-damaged layer measuring device that is attached to a machine tool that processes a workpiece attached to a table with a tool attached to a spindle, and that measures the processing-damaged layer on the surface of the workpiece on the machine tool, the processing-damaged layer measuring device comprising: an indenter that can be attached to the spindle in place of the tool and that forms an indentation by being pressed into the workpiece using the machine tool's feed device; an indenter holder to which the indenter is detachably attached and that has a sensor that detects the indentation load of the indenter on the workpiece; and a calculation device that can be connected to the machine tool's control device, the calculation device momentarily calculates an indentation load coefficient, which is a coefficient obtained by functionally approximating the indentation load with respect to the indentation depth, stops indenting the indenter into the workpiece when the rate of change of the indentation load coefficient with respect to the indentation depth becomes a value that is sufficiently close to zero from negative, and calculates the processing-damaged layer depth by multiplying the indentation depth at which the indentation of the indenter was stopped by a depth conversion constant. Effect of the Invention

[0013] According to the method for measuring the workpiece damage layer according to one aspect of the present invention, the indenter attached to the spindle instead of the tool is pressed into the workpiece using the feed device of the machine tool, and the indentation load for pressing the indenter and the indentation depth of the indenter into the workpiece can be measured every moment. Therefore, the position and phase of the indenter relative to the workpiece can be adjusted on the machine tool, and the workpiece damage layer on the surface of the workpiece can be measured, and the state of the workpiece damage layer can be easily evaluated. Furthermore, when the rate of change of the indentation load coefficient, which is the coefficient when the measured indentation load is functionally approximated by the indentation depth, becomes a value sufficiently close to 0 from negative, that is, when the effect of the workpiece damage layer on the indentation load becomes small, the indentation of the indenter into the workpiece is stopped, and the indentation depth of the indenter when the indentation is stopped is multiplied by a depth conversion constant to calculate the depth of the workpiece damage layer. In this way, the workpiece damage layer can be easily and quickly measured and evaluated by using the mechanical configuration that the machine tool originally has, without using a dedicated indentation measurement device and without removing the workpiece from the machine tool.

[0014] According to a method for machining a workpiece according to one aspect of the present invention, after rough machining, an indenter attached to a spindle in place of a tool is pressed into the workpiece using a feeder of a machine tool, and the indentation load for pressing the indenter and the indentation depth of the indenter into the workpiece can be measured every moment. Therefore, on the machine tool, the position and phase of the indenter relative to the workpiece can be adjusted and then the machining-affected layer on the surface of the workpiece can be measured, and the state of the machining-affected layer can be easily evaluated. Furthermore, when the rate of change of the indentation load coefficient, which is a coefficient when the measured indentation load is functionally approximated by the indentation depth, becomes a value sufficiently close to 0 from negative, that is, when the effect of the machining-affected layer on the indentation load becomes small, the indentation of the indenter into the workpiece is stopped, and the indentation depth of the indenter when the indentation is stopped is multiplied by a depth conversion constant to calculate the machining-affected layer depth. Therefore, the machining-affected layer depth can be calculated without applying a load to the workpiece until the preset indentation depth or indentation load value is reached, and the calculated machining-affected layer depth can be prevented or suppressed from becoming larger than the finishing allowance of the workpiece. This reduces the probability of the workpiece being deemed defective, and also avoids unnecessary finishing, since finishing is performed only when the calculated depth of the workpiece's machining-affected layer is smaller than the finishing allowance of the workpiece.

[0015] According to a machine tool according to one aspect of the present invention, an indenter attached to a spindle in place of a tool is pressed into a workpiece using a feeder of the machine tool, and the indentation load for pressing the indenter and the indentation depth of the indenter into the workpiece can be measured moment by moment using a pressing load detector and a pressing depth detector. Therefore, the position and phase of the indenter relative to the workpiece can be adjusted on the machine tool, and the work-affected layer on the surface of the workpiece can be measured, and the state of the work-affected layer can be easily evaluated. In addition, the indenter pressing stop control means can stop the pressing of the indenter into the workpiece when the rate of change of the indentation load coefficient, which is a coefficient when the measured indentation load is functionally approximated by the indentation depth, becomes a value sufficiently close to 0 from negative, that is, when the effect of the work-affected layer on the indentation load becomes small. Furthermore, the work-affected layer depth calculation means can calculate the work-affected layer depth by multiplying the indentation depth of the indenter when pressing is stopped by a depth conversion constant. Therefore, the work-affected layer depth can be calculated without applying a load to the workpiece until the indentation depth or indentation load value is reached. This reduces the probability of the work being rejected.

[0016] According to one aspect of the present invention, the machine-damaged layer measuring device includes an indenter that can be attached to a spindle instead of a tool and that forms an indentation by being pressed into a workpiece using a feed device of the machine tool, and a tool holder that is detachably attached to the indenter and has a sensor that detects the indentation load of the indenter on the workpiece. Therefore, the machine-damaged layer on the surface of the workpiece can be measured after adjusting the position and phase of the indenter with respect to the workpiece on the machine tool, and the state of the machine-damaged layer can be easily evaluated. In addition, since the machine tool includes a calculation device that can be connected to the control device of the machine tool, the machine-damaged layer measuring device calculates the indentation load coefficient, which is a coefficient when the indentation load is functionally approximated by the indentation depth, from time to time, and when the rate of change of the indentation load coefficient with respect to the indentation depth becomes a value sufficiently close to 0 from negative, the indentation of the indenter into the workpiece is stopped, and the indentation depth at the time when the indentation of the indenter is stopped is multiplied by a depth conversion constant to calculate the depth of the machine-damaged layer. This allows a function that allows the easy measurement of the machine-damaged layer of the workpiece on the machine tool to be added to an ordinary machine tool other than the above-mentioned machine tool that implements the method for measuring the machine-damaged layer of the workpiece of the present invention. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 shows a side view of a machine tool according to this embodiment. [Diagram 2] FIG. 2 shows a side view of a machine tool that presses an indenter into a workpiece. [Diagram 3] FIG. 3 shows an enlarged view of the workpiece and indenter of FIG. [Figure 4] FIG. 4 shows an enlarged view of the indenter being inclined and pressed into the workpiece. [Diagram 5] FIG. 5 shows a cross-sectional view of the work-affected layer on the surface of the workpiece where the indenter has been pressed. [Figure 6] FIG. 6 shows a graph illustrating the relationship between the indentation load, the indentation load coefficient, and the rate of change of the indentation load coefficient, and the indentation depth. [Figure 7] FIG. 7 shows a time series representing the amount of change in the indentation load over time. [Figure 8]FIG. 8 shows the surface of the workpiece after the Vickers pyramidal indenter and the Knoop pyramidal indenter have been pressed into it. [Figure 9] FIG. 9 shows an explanatory diagram of the workpiece processing process including the indentation test. [Figure 10] FIG. 10 shows a flow chart of the workpiece machining process including the indentation test. [Figure 11] FIG. 11 shows a cross-sectional view of a sample surface into which a pyramidal indenter has been pressed in a conventional indentation test method. [Figure 12] FIG. 12 is a graph showing the relationship between the indentation load and the indentation depth from the start of loading to the removal of the load in the indentation test method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, a machine tool according to an embodiment will be described with reference to the accompanying drawings. Similar or corresponding elements are given the same reference numerals, and duplicated explanations will be omitted. For ease of understanding, the scale of the drawings may be changed.

[0019] FIG. 1 shows a side view of a machine tool 10 according to the present embodiment. The machine tool 10 includes a bed 12 serving as a base and a column 14 erected on the upper surface of the bed 12. A table 30 is arranged on the upper surface of the bed 12 for fixing a workpiece W, which is a workpiece, with a fixture 50 (see FIG. 9). The table 30 can move on the bed 12 via a guide surface. Furthermore, a machine coordinate system is set in advance in the machine tool 10 with a predetermined position as the origin, and includes an X-axis, a Y-axis, and a Z-axis as linear axes perpendicular to each other. The machine tool 10 according to the present embodiment is vertical, and the Z-axis extends along the vertical direction. Moreover, the X-axis and the Y-axis are set on a plane perpendicular to the Z-axis, here, on a horizontal plane. In the machine tool 10, the table 30 is configured to move along the Y-axis direction (left and right direction). Moreover, a saddle 16 arranged in front of the column 14 is configured to be movable along the X-axis direction (perpendicular to the paper surface).

[0020] A spindle head 18 is disposed on the front surface of the saddle 16 so as to be movable up and down along the Z-axis direction (the machine vertical direction). A spindle 20 configured to be rotatable around an axis parallel to the Z-axis with respect to the spindle head 18 is attached to the tip side, here the lower side, of the spindle head 18. An indenter 42 or a tool 62, 64 (see FIG. 9) for machining a workpiece W while rotating together with the spindle 20 is detachably attached to the spindle 20 via an indenter holder 40 or a tool holder 60. As a result, the machine tool 10 is configured so that the spindle 20 for mounting the indenter 42 or the tool 62, 64 and the table 30 on which the workpiece W is placed can be moved relatively along the X-axis, Y-axis, and Z-axis.

[0021] An X-axis feed device 22 is disposed on the front side of the column 14 as a feed device for displacing the saddle 16 along the X-axis direction and relatively moving the indenter 42 or the tools 62, 64 and the workpiece W along the X-axis direction. Also disposed on the column 14 is an X-axis position detector 24 for detecting the position in the X-axis direction of the indenter 42 or the tools 62, 64 attached to the spindle 20.

[0022] A Y-axis feed device 32 is disposed on the bed 12 as a feed device for displacing the table 30 along the Y-axis direction and relatively moving the indenter 42 or the tools 62, 64 and the workpiece W along the Y-axis direction. Also disposed on the bed 12 is a Y-axis position detection device 34 for detecting the position in the Y-axis direction of the table 30 on which the workpiece W is placed.

[0023] A Z-axis feed device 26 is disposed on the saddle 16 as a feed device for displacing the spindle head 18 along the Z-axis direction and relatively moving the indenter 42 or the tools 62, 64 and the workpiece W along the Z-axis direction. Also disposed on the saddle 16 is a Z-axis position detector 28 for detecting the position in the Z-axis direction of the indenter 42 or the tools 62, 64 attached to the spindle 20.

[0024] Fig. 2 is a schematic side view of the machine tool 10. Fig. 3 shows an enlarged view of the workpiece W and the indenter 42 pressed into it. The table 30 of the machine tool 10 in this figure is configured to be rotatable with respect to the bed 12. Therefore, the inclination of the workpiece W can be adjusted so that the normal direction of the surface of the workpiece W coincides with the axial direction of the indenter 42, and the indenter 42 can be pressed perpendicularly into the workpiece W. As a result, even if the surface of the workpiece W is curved or inclined, the indenter 42 can be pressed perpendicularly into the workpiece W.

[0025] In this embodiment, the indenter 42 is pressed vertically into the workpiece W by rotating the table 30. However, this is not limited to the above. As shown in FIG. 4, the main shaft may be configured to be tiltable with respect to the workpiece W, and the indenter 42 may be pressed vertically into the workpiece W by tilting the indenter 42 with respect to the workpiece W.

[0026] 1, the machine tool 10 includes an NC control unit 36 ​​as a control device for operating each of the axis feed devices 22, 32, 26, i.e., the X-axis feed device 22, the Y-axis feed device 32, and the Z-axis feed device 26, and moving the indenter 42 or the table 30 to a desired position by executing an NC program stored in an NC program storage unit 36a. This allows the indenter 42 attached to the spindle 20 to be pressed into a predetermined position in the workpiece W. The NC control unit 36 ​​is also configured to operate the spindle 20 and rotate the spindle 20 and the tools 62, 64 so that the workpiece W can be machined by the tools 62, 64 attached to the spindle 20. Furthermore, the machine tool 10 has a tool magazine 44 that stores the indenter 42 and the tools 62, 64, and is configured so that the indenter 42 or the tools 62, 64 taken out from the tool magazine 44 can be attached to and detached from the spindle 20 depending on the content of the work to be performed by operating the spindle 20, i.e., measurement or machining of the work-affected layer WL.

[0027] The machine tool 10 also includes a calculation device 38 serving as a machine-degraded layer measuring device for measuring and evaluating the machine-degraded layer WL of the workpiece W. The calculation device 38 is electrically connected to the X-axis position detector 24, the Y-axis position detector 34, and the Z-axis position detector 28, and is configured to be able to acquire position information detected by these. The X-axis and Y-axis position information represent coordinate values ​​for pressing the indenter 42 into the workpiece W, and the Z-axis position information represents a coordinate value corresponding to the pressing depth h of the indenter 42.

[0028] A load sensor 46 is disposed in the spindle head 18 as a pressing load detector for detecting a pressing load L (see FIG. 6) which is a load acting on the indenter 42 by pressing the indenter 42 into the workpiece W. The load sensor 46 is electrically connected to the computing device 38, which is configured to record the pressing load L detected by the load sensor 46. Note that in the following description, the load sensor 46 is described as being disposed in the spindle head 18, but this is not limiting, and the load sensor may be disposed in a tool holder or on a table.

[0029] FIG. 5 is a schematic cross-sectional view of the workpiece W in which the indenter 42 has been pressed into the machine-degraded layer WL. FIG. 6 is a graph showing an example of the changes in the indentation load L, indentation load coefficient C, and the rate of change (dC / dh) of the indentation load coefficient C versus the indentation depth h. When the indenter 42 is pressed into the machine-degraded layer WL, the indentation depth h and the indentation load L are detected from moment to moment by the indentation depth detection unit 38a and the load sensor 46, and these are recorded in the calculation device 38. The calculation device 38 has a stop control unit 38b as an indenter pressing stop control means, which approximates the indentation load L measured up to that point with a quadratic function of the indentation depth h, and calculates the indentation load coefficient C (=L / h 2 ) is calculated every moment. In addition, the rate of change (dC / dh) of the indentation load coefficient C with respect to the indentation depth h is calculated every moment.

[0030] The indentation load coefficient C decreases immediately after the indenter 42 is indented due to the effect of the damaged layer WL, and when the indenter 42 is indented to a certain depth, the effect of the damaged layer WL becomes small and the coefficient becomes constant. s When the indenter 42 is pressed to the indentation depth h, the indentation load coefficient C for the indentation depth h becomes a constant value C S That is, the rate of change (dC / dh) of the indentation load coefficient C goes from negative to a value sufficiently close to 0. At this time, the stop control unit 38b is configured to stop the spindle 20 via the NC control unit 36, and stop the indentation of the indenter 42. In reality, the rate of change of the indentation load coefficient C may not strictly converge to 0, and the indentation of the indenter 42 may be stopped when the rate of change of the indentation load coefficient C reaches a predetermined value sufficiently close to 0.

[0031] The computing device 38 has a depth computing section 38c as a processing-affected layer depth computing means, and the depth computing section 38c converts a depth conversion constant stored in advance into the indentation depth h at the time when the indentation of the indenter 42 is stopped. s The depth Z of the work-affected layer is calculated by multiplying the indentation load L by 100%. It is said that the indentation load L is affected by up to about 7 times the indentation depth h, and the indentation load coefficient C can be considered as a representative value at a position half the indentation depth h (Non-Patent Document 1). For this reason, here, the indentation depth h at the time of stopping is used as the indentation load coefficient. s The depth conversion constant multiplied by is set to 3.5. Note that although the depth conversion constant is set to 3.5 here, since the depth conversion constant varies mainly depending on the shape of the indenter, a different value of the depth conversion constant may be used.

[0032] The machine tool 10 is equipped with a display device 52 connected to the arithmetic device 38 for displaying the calculated machine-damaged layer depth Z. This allows the user to visually confirm that the calculated machine-damaged layer depth Z is smaller than the finishing allowance of the workpiece W and that finish machining can be performed. The arithmetic device 38 is also configured to operate the machine tool 10 and proceed to finish machining if the calculated machine-damaged layer depth Z is smaller than the finishing allowance of the workpiece W, and to stop machining of the workpiece W if the calculated machine-damaged layer depth Z is larger than the finishing allowance of the workpiece W.

[0033] FIG. 7 shows a time series representing the time change dL of the indentation load L. As mentioned above, the indentation load coefficient C (= L / h 2 ) is calculated by approximating the indentation load L with a quadratic function of the indentation depth h. For this reason, in order to stabilize and improve the measurement accuracy of the indentation load L and the indentation depth h, it is preferable to set the time point when the indenter 42 is pressed into the surface of the workpiece W and the indentation depth h actually occurs as the application start point of the indentation load L. Therefore, the calculation device 38 is configured to calculate a moving average value of the recorded time change amount dL of the indentation load L from moment to moment, and to set the time point SP when the time change amount dL exceeds a predetermined threshold value TV at which it can be determined that the indentation depth h has significantly occurred as the application start point of the indentation load L and the position of the indentation depth h = 0.

[0034] Further, the machine tool 10 equipped with the computing device 38 can measure non-equibiaxial stress using an indentation method that does not depend on the reference hardness under stress-free conditions, in addition to measuring the work-affected layer WL. Specifically, the indenter can measure the indentation load L and indentation depth h using a Vickers pyramidal indenter VI having a predetermined apex angle and a square base and a Knoop pyramidal indenter NI having a predetermined apex angle and a diamond-shaped base with a major axis LA and a minor axis SA. First, prior to machining the workpiece W, the Vickers pyramidal indenter VI and the Knoop pyramidal indenter NI attached to the spindle 20 of the machine tool 10 are indented into a stress-free reference test piece (not shown) made of the same material as the workpiece W, thereby measuring the indentation load L and indentation depth h, respectively. From the measured indentation load L and indentation depth h, the indentation load ratio η of the indentation load L of the Knoop indenter NI to the indentation load L of the Vickers indenter VI at the same indentation depth h is calculated.

[0035] Next, as shown in Fig. 8, the axial feed devices 22, 32, and 26 of the machine tool 10 are used to press the Knoop pyramid indenter NI, with the major axis LA of the bottom surface oriented in the X-axis direction, which is a first direction, into the workpiece W, thereby measuring the indentation depth h of the Knoop pyramid indenter NI into the workpiece W and the first indentation load L1. Furthermore, the axial feed devices 22, 32, and 26 of the machine tool 10 are used to press the Knoop pyramid indenter NI, with the major axis LA of the bottom surface oriented in the Y-axis direction, which is a second direction perpendicular to the X-axis direction, into the workpiece W, thereby measuring the indentation depth h of the Knoop pyramid indenter NI into the workpiece W and the second indentation load L2. Furthermore, the axial feed devices 22, 26, and 32 of the machine tool 10 are used to press the Vickers pyramid indenter VI into the workpiece W, thereby measuring the indentation depth h of the Vickers pyramid indenter VI into the workpiece W and the third indentation load L3 for indenting the Vickers pyramid indenter VI. Here, the phase of the Knoop pyramidal indenter NI is changed by 90 degrees using the indexing and positioning function of the spindle 20 or the indexing and positioning function of the table 30.

[0036] The calculation device 38 calculates an X-axis stress σ 1 , which is a first residual stress in the X-axis direction at each indentation depth h, from the indentation load ratio η, the first indentation load L1, the second indentation load L2, and the third indentation load L3 measured in this manner. x and the second residual stress in the Y-axis direction, the Y-axis stress σ Y can be calculated using the following formula: F1 = (L2 - η × L3) F2 = (L1 - η × L3) F3 = (α2 - η × α3) F4 = (α1 - η × α3) σ x =(F1×F3-F2×F4) / (F4×F4-F3×F3) σ y =(F2×F3-F1×F4) / (F4×F4-F3×F3) Here, α1 is the conversion coefficient between the stress value and the load change amount when the long axis LA direction of the Knoop indenter NI is indented parallel to the stress direction, α2 is the conversion coefficient between the stress value and the load change amount when the long axis LA direction of the Knoop indenter NI is indented perpendicular to the stress direction, and α3 is the conversion coefficient between the stress value and the load change amount when the Vickers indenter VI is indented, and these are constants determined by the material of the workpiece W. The residual stress σ calculated in this way is x , σ Y If is a positive value, a compressive force is acting on the measurement point, the risk of the workpiece material breaking is small, and the workpiece W is deemed a non-defective product. On the other hand, if is a negative value, a tensile force is acting on the measurement point, and there is a risk of the workpiece material breaking due to some defect, and the workpiece is deemed a defective product. Note that, although the Vickers pyramidal indenter VI and the Knoop pyramidal indenter NI having a predetermined apex angle have been described here, this is not limiting, and pyramidal indenters with a square base and pyramidal indenters with a diamond-shaped base that do not have a predetermined apex angle may also be used. In that case, the various coefficients in the above calculation formula will change.

[0037] The method for measuring the workpiece W's work-induced deterioration layer WL, the method for processing the workpiece W, and the effects of the computing device 38 and the machine tool 10 according to this embodiment will be described below through an explanation of the processing process of the workpiece W, including an indentation test, in accordance with the explanatory diagrams and flow charts shown in Figures 9 and 10.

[0038] First, the process proceeds to step S510, where the workpiece W is roughly machined using a rough machining tool 62 attached to the spindle 20 via a tool holder 60. When the rough machining is completed, the process proceeds to step S520, where an indentation test is performed to measure the machine-degraded layer WL generated on the machined surface of the workpiece W.

[0039] When the indentation test is started, the process proceeds to step S10, and the indenter 42 attached to the indenter holder 40 removed from the tool magazine 44 instead of the tool 62 is attached to the spindle 20. Here, as an example, a Knoop pyramid indenter NI is used as the indenter 42. When the indenter 42 is attached to the spindle 20, the process proceeds to step S20, and the axial feed devices 22, 32, and 26 are operated to move the indenter 42 to a position where it is pressed into the workpiece W, and the inclination of the table 30 is adjusted so that the axial direction of the indenter 42 coincides with the normal direction of the surface of the workpiece W. When these adjustments are completed, the process proceeds to step S30, and the phase of the spindle 20 is calculated and adjusted. When the first indentation load L1 is measured using the Knoop pyramid indenter NI, the phase is adjusted so that the major axis LA is aligned with the X-axis direction, i.e., parallel. When the second indentation load L2 is measured, the phase is adjusted so that the major axis LA is aligned with the Y-axis direction. When the phase adjustment is completed, the process proceeds to step S40, in which the spindle 20 to which the indenter 42 is attached is lowered toward the workpiece W at a predetermined approach speed, and the process proceeds to step S50.

[0040] In step S50, the load sensor 46 is operated to start measuring the indentation load L. The computing device 38 calculates the moving average value of the recorded time change amount dL of the indentation load L from moment to moment, and determines the time point SP at which the time exceeds a predetermined threshold value TV at which it can be determined that a significant indentation depth h has occurred as the application start point of the indentation load L and the measurement start point of the indentation depth h, and proceeds to step S60.

[0041] In step S60, when the indenter 42 is pressed into the work-affected layer WL, the indentation depth h and the indentation load L are detected from moment to moment by the indentation depth detection unit 38a and the load sensor 46. The calculation device 38 records the detected data, and the stop control unit 38b approximates the indentation load L measured up to that point with a quadratic function of the indentation depth h to obtain an indentation load coefficient C (=L / h 2 Furthermore, the stop control unit 38b momentarily calculates the rate of change (dC / dh) of the indentation load coefficient C with respect to the indentation depth h. sBy pressing the material into the workpiece, the pressing load coefficient C becomes a constant value C S When the rate of change (dC / dh) of the indentation load coefficient C becomes a predetermined value approaching 0 from a negative value, the stop control unit 38b stops the descent of the spindle 20 via the NC control unit 36, and stops the indentation of the indenter 42. The depth calculation unit 38c converts a pre-stored depth conversion constant into the indentation depth h at the time when the indentation of the indenter 42 is stopped. s After the depth Z of the processed damaged layer is calculated, the process proceeds to step S80, in which the spindle 20 is raised to pull the indenter 42 out of the workpiece W.

[0042] Once the indenter 42 is pulled out, the process proceeds to step S90. If a Knoop pyramid indenter NI is used as the indenter 42 and measurement of either the first indentation load L1 or the second indentation load L2 has not been completed, the process proceeds to step S30, where the phase of the spindle 20 is changed to measure the first indentation load L1 or the second indentation load L2 for which measurement has not been completed. If measurement of both the first indentation load L1 and the second indentation load L2 using the Knoop pyramid indenter NI has been completed or if a Vickers pyramid indenter VI is used as the indenter 42, the process proceeds to step S100.

[0043] The process proceeds to step S100, and if the measurement using the Knoop pyramidal indenter NI or the Vickers pyramidal indenter VI has not been completed, the process proceeds to step S10, where the Knoop pyramidal indenter NI or the Vickers pyramidal indenter VI to be used for measurement is removed from the tool magazine 44, and the indenter 42 attached to the spindle 20 is replaced. Once the indenter 42 has been replaced, it is used to measure the indentation load L from step S20 to step S70. Once the measurement using both the Knoop pyramidal indenter NI and the Vickers pyramidal indenter VI is completed, the process proceeds to step S110, and the calculation device 38 calculates the measured and calculated machining-affected layer depth Z, the indentation load ratio η, the first indentation load L1, the second indentation load L2, the third indentation load L3, and the X-axis stress σ which is the first residual stress in the X-axis direction at each indentation depth h. x and the second residual stress in the Y-axis direction, the Y-axis stress σ Y is output to the display device 52.

[0044] When the indentation test is completed, the process proceeds to step S530, and if the calculated machine-damaged layer depth Z is smaller than the finishing allowance of the workpiece W, the calculation device 38 proceeds to step S550, operates the machine tool 10, replaces the indenter 42 with the finishing tool 64, and performs finish processing. On the other hand, if the calculated machine-damaged layer depth Z is larger than the finishing allowance of the workpiece W, the process proceeds to step S540, and finish processing of the workpiece W is stopped.

[0045] The method for measuring a machine-deformed layer WL of a workpiece W, the method for machining the workpiece W, the computing device 38, and the machine tool 10 according to the present embodiment include an indenter 42 that can be attached to the spindle 20 in place of the tools 62, 64 and that forms an indentation by being pressed into the workpiece W using the axial feed devices 22, 32, 26 equipped with the axial position detection devices of the machine tool 10, and a load sensor 46 that detects the pressing load L of the indenter 42 against the workpiece W. Therefore, the machine-deformed layer WL on the surface of the workpiece W can be measured on the machine tool 10 after adjusting the position and phase of the indenter 42 relative to the workpiece W, and the state of the machine-deformed layer WL can be easily evaluated. In addition, since the machine tool 10 is provided with a calculation device 38 connectable to the NC control unit 36, the indentation load coefficient C, which is a coefficient when the indentation load L is functionally approximated by the indentation depth h, is calculated every moment, and when the rate of change (dC / dh) of the indentation load coefficient C with respect to the indentation depth h becomes a value sufficiently close to 0 from a negative value, the indentation of the indenter 42 into the workpiece W is stopped, and the indentation depth h when the indentation of the indenter 42 is stopped is calculated. S By multiplying by a depth conversion constant, the depth Z of the work-affected layer can be calculated. This makes it possible to calculate the depth Z of the work-affected layer without applying a load to the workpiece W until a preset indentation depth or indentation load value is reached, unlike the conventional indentation test method, and therefore makes it possible to measure and evaluate the work-affected layer WL while reducing the probability of the workpiece W being deemed a defective product.

[0046] Moreover, according to the method for measuring the machine-degraded layer WL of the workpiece W, the method for machining the workpiece W, the computing device 38, and the machine tool 10 of the present embodiment, the table 30 of the machine tool 10 is configured to be rotatable with respect to the bed 12. Therefore, the inclination of the workpiece W can be adjusted so that the normal direction of the surface of the workpiece W coincides with the axial direction of the indenter 42, and the indenter 42 can be pressed perpendicularly into the workpiece W. As a result, even if the surface of the workpiece W is curved or inclined, the indenter 42 can be pressed perpendicularly into the workpiece W, and the indentation load L and indentation depth h can be measured with high accuracy.

[0047] Furthermore, in the method for measuring the machine-degraded layer WL of the workpiece W, the method for machining the workpiece W, the computing device 38, and the machine tool 10 according to the present embodiment, the computing device 38 is configured to calculate a moving average value of the time change amount dL of the recorded indentation load L from moment to moment, and to set the time point SP at which the time point exceeds a predetermined threshold value TV at which it can be determined that a significant indentation depth h has occurred as the application start point of the indentation load L. Therefore, the indenter 42 is pressed into the surface of the workpiece W, and the time point at which the indentation depth h actually occurs can be set as the application start point of the indentation load L, and the measurement accuracy of the indentation load L, and therefore the accuracy of the rate of change (dC / dh) of the indentation load coefficient C can be stabilized and improved.

[0048] Furthermore, according to the method for measuring the work-deformed layer WL of the workpiece W, the method for machining the workpiece W, the computing device 38, and the machine tool 10 of the present embodiment, in addition to measuring the work-deformed layer WL, the indentation load ratio η, the first indentation load L1, the second indentation load L2, the third indentation load L3, and the X-axis stress σ which is the first residual stress in the X-axis direction at each indentation depth h are also measured. x and the second residual stress in the Y-axis direction, the Y-axis stress σ Y This makes it possible to calculate the depth Z of the damaged layer and evaluate the stress in the damaged layer WL.

[0049] As described above, the method for measuring the workpiece W's work-damaged layer WL, the method for machining the workpiece W, the computing device 38, and the machine tool 10 according to this embodiment can easily evaluate the state of the workpiece W's work-damaged layer WL on the machining surface of the workpiece W on the machine tool 10.

[0050] A device for measuring a machine-damaged layer using a normal machine tool that does not incorporate a load sensor 46 in the spindle head 18 and does not consider the measurement of the machine-damaged layer will be described. In this case, a load sensor for measuring the indentation load L may be provided in the indenter holder 40. A general-purpose personal computer is used as the computing device, and the indentation depth detection unit 38a, the stop control unit 38b, and the depth calculation unit 38c are installed in the personal computer as application software, and the personal computer is connected to the user interface of the NC device of the machine tool. By retrofitting this machine-damaged layer measuring device to a normal machine tool, the above-mentioned method for measuring a machine-damaged layer and the method for machining a workpiece can be performed, and further, the same functions as the machine tool 10 in FIG. 1 can be achieved. In other words, this machine-damaged layer measuring device can be said to be a machine-damaged layer measuring kit that packs various indenters, an indenter holder with a built-in load sensor, a personal computer that can be connected to the control device of the machine tool, and application software.

[0051] Although the embodiment of the method for measuring the machined-deformed layer WL of the workpiece W, the method for machining the workpiece W, the computing device 38, and the machine tool 10 have been described above, the present invention is not limited to the above embodiment. For example, instead of a vertical machine tool with a vertical spindle, a horizontal machine tool with a horizontal spindle may be used. In addition to the above, it is considered that a person skilled in the art would understand that various modifications of the above embodiment are possible. [Explanation of symbols]

[0052] 10 Machine tools 20 spindle 22 X-axis feed device (feed device) 26 Z-axis feed device (feed device) 32 Y-axis feed device (feed device) 36 NC control unit (control device) 38 Calculation device (processing-affected layer measuring device) 38a Push-in depth detector 38b Stop control section (indenter pressing stop control means) 38c Depth calculation unit (processing-affected layer depth calculation means) 42 Indenter 46 Load sensor (indentation load detector) L Push-in load L1 First indentation load L2 Second indentation load L3 Third indentation load h Indentation depth NI Knoop pyramid indenter VI Vickers pyramidal indenter WL Processing-affected layer

Claims

1. A method for measuring a workpiece surface damage layer on a machine tool that processes the workpiece attached to a table with a tool attached to a spindle, comprising the steps of: Attaching an indenter to the spindle in place of the tool for pressing into the workpiece; pushing the indenter into the workpiece using a feeder of the machine tool; measuring a pressing load for pressing the indenter and a pressing depth of the indenter into the workpiece from moment to moment; Calculating an indentation load coefficient every moment, which is a coefficient when the indentation load is functionally approximated by the indentation depth; Stopping the indentation of the indenter into the workpiece when the rate of change of the indentation load coefficient with respect to the indentation depth becomes a value sufficiently close to 0 from a negative value; and A method for measuring a work-damaged layer of a workpiece, comprising: calculating a depth of the work-damaged layer by multiplying the indentation depth of the indenter by a depth conversion constant when indentation is stopped.

2. The method for measuring a machine-affected layer of a workpiece according to claim 1 , wherein the indenter is pressed in along a normal direction to the surface of the workpiece.

3. 2. The method for measuring a processing-affected layer of a workpiece as described in claim 1, wherein the indentation load measured by pressing the indenter is set to a point at which the moving average value of the change in the indentation load from moment to moment exceeds a predetermined threshold value, which is the start point of the application of the indentation load.

4. The indenter is a pyramidal indenter having a square base or a rhombic pyramidal indenter having a rhombic base having a major axis and a minor axis, Prior to machining the workpiece, a feed device of the machine tool is used to indent the square-base pyramidal indenter and the diamond-base pyramidal indenter into a stress-free reference test piece made of the same material as the workpiece, thereby measuring the indentation load and indentation depth, and calculating an indentation load ratio of the indentation load of the diamond-base pyramidal indenter to the indentation load of the square-base pyramidal indenter at the same indentation depth; using a feed device of the machine tool to press the pyramidal indenter having a diamond-shaped bottom surface, with the major axis of the bottom surface oriented in a first direction, into the workpiece, thereby measuring the indentation depth of the pyramidal indenter having a diamond-shaped bottom surface into the workpiece and a first indentation load for indenting the pyramidal indenter having a diamond-shaped bottom surface; using a feed device of the machine tool to press the pyramidal indenter having a rhombic bottom surface, with the major axis of the bottom surface oriented in a second direction perpendicular to the first direction, into the workpiece, thereby measuring the indentation depth of the pyramidal indenter having a rhombic bottom surface into the workpiece and a second indentation load for indenting the pyramidal indenter having a rhombic bottom surface; measuring an indentation depth of the square-bottom pyramidal indenter into the workpiece and a third indentation load for indenting the square-bottom pyramidal indenter into the workpiece using a feed device of the machine tool; and 4. A method for measuring a workpiece's machining-induced damage layer as described in any one of claims 1 to 3, comprising calculating a first residual stress in the first direction and a second residual stress in the second direction at each indentation depth from the indentation load ratio, the first indentation load, the second indentation load, and the third indentation load.

5. A method for machining a workpiece, comprising the steps of: rough machining a workpiece attached to a table of a machine tool with a tool attached to a spindle; measuring a machine-deformed layer on a surface of the workpiece on the machine tool; and performing finish machining after measuring the machine-deformed layer, comprising: After the rough machining, an indenter is attached to the spindle in place of the tool for pressing into the workpiece; pushing the indenter into the workpiece using a feeder of the machine tool; measuring a pressing load for pressing the indenter and a pressing depth of the indenter into the workpiece from moment to moment; Calculating an indentation load coefficient every moment, which is a coefficient when the indentation load is functionally approximated by the indentation depth; stopping the indentation of the indenter into the workpiece when a rate of change of the indentation load coefficient with respect to the indentation depth becomes a value sufficiently close to 0 from a negative value; Calculating the depth of the work-affected layer by multiplying the indentation depth of the indenter by a depth conversion coefficient when the indentation is stopped; and A method for machining a workpiece, comprising the steps of: performing finish machining when the calculated depth of the machining-affected layer is smaller than a finishing allowance of the workpiece.

6. A machine tool that processes a workpiece attached to a table with a tool attached to a spindle, and measures a work-deteriorated layer on a surface of the workpiece on the machine, comprising: an indenter that can be attached to the spindle in place of the tool and that forms an indentation by being pressed into the workpiece using a feed device of the machine tool; an indentation load detector that measures the indentation load of the indenter against the workpiece at every moment; a pressing depth detector for measuring the pressing depth of the indenter into the workpiece at every instant; an indenter indentation stop control means for constantly calculating an indentation load coefficient, which is a coefficient when the indentation load is functionally approximated by the indentation depth, and for stopping the indentation of the indenter into the workpiece when the rate of change of the indentation load coefficient with respect to the indentation depth becomes a value sufficiently close to 0 from a negative value; a work-affected layer depth calculation means for calculating a work-affected layer depth by multiplying the indentation depth at the time when the indentation of the indenter is stopped by a depth conversion constant; A machine tool comprising:

7. A machine-deformed layer measuring device that is attached to a machine tool that processes a workpiece attached to a table with a tool attached to a spindle and measures a machine-deformed layer on a surface of the workpiece on the machine tool, comprising: an indenter that can be attached to the spindle in place of the tool and that forms an indentation by being pressed into the workpiece using a feed device of the machine tool; an indenter holder for removably mounting the indenter and having a sensor for detecting a pressing load of the indenter against the workpiece; a calculation device connectable to a control device of the machine tool, which momentarily calculates an indentation load coefficient which is a coefficient obtained by functionally approximating the indentation load with the indentation depth, stops indenting the indenter into the workpiece when a rate of change of the indentation load coefficient with respect to the indentation depth becomes a value sufficiently close to 0 from a negative value, and calculates a depth of a work-affected layer by multiplying the indentation depth at the time when the indentation of the indenter was stopped by a depth conversion constant; A processing-affected layer measuring device comprising:

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