Method for measuring work-affected layer of workpiece, method for processing workpiece, device for measuring work-affected layer, and machine tool

Abstract

This 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 the 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.

Description

Method for measuring workpiece processing-affected layer, workpiece processing method, processing-affected layer measuring device, and machine tool

[0001] The present invention relates to a method for measuring a workpiece's work-damaged layer, a workpiece processing method, a workpiece-damaged layer measuring device, and a machine tool.

[0002] Workpieces (workpieces) are created through several processes, including rolling, drawing, extrusion, forging, and surface treatment, resulting in the formation of a surface-affected layer. These workpieces are then machined to achieve the desired shape and dimensions. Rough machining is performed in the initial stages, resulting in a surface-affected layer. This surface-affected layer is prone to residual stress due to residual strain, which can lead to stress corrosion cracking, fatigue fracture, creep fracture, and other problems. Therefore, at the product stage, finishing processes are used to remove the surface-affected layer. In recent years, for example, difficult-to-cut materials such as nickel-based superalloys have become increasingly popular to achieve lightweight and high-rigidity aircraft parts and to achieve both high performance and fuel efficiency in jet engines. Therefore, managing the surface-affected layer in these materials has become increasingly important.

[0003] Conventionally known methods for evaluating process-affected layers include, for example, observation using an optical microscope or an 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 the processing site.

[0004] Therefore, for example, Patent Document 1 discloses a three-dimensional hardness distribution measurement method and system that utilizes an indentation test method. The indentation test method is a quasi-nondestructive testing 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. Figure 11 shows a schematic longitudinal cross-sectional view of a sample surface indented with a pyramidal indenter. Also, Figure 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), which is a coefficient when this quadratic function is used as the approximation, can be calculated. ２ ) decreases as the indentation depth h increases because shallower regions are affected by the hardened or softened work-affected layer. Furthermore, it is known that when the pyramidal indenter is indented deeply, the influence of the work-affected layer decreases beyond a certain depth, and the indentation load coefficient becomes approximately constant. Therefore, the depth of the work-affected layer can be determined from the change in the indentation load coefficient.

[0005] However, in general indentation testing methods, such as the Instrumented Indentation Technique (IIT) disclosed in Non-Patent Documents 1 and 2, a load is applied to the workpiece until a preset indentation depth or indentation load value is reached, which can leave an indentation deeper than necessary on the workpiece surface. For example, as shown in FIG. 11 , this occurs when the pyramidal indenter is indented to an indentation depth D that exceeds the thickness M of the workpiece damage layer WL. Therefore, even if an indentation test method is used to evaluate the depth of the workpiece damage layer after the rough machining process and determine whether or not to perform finish machining based on the indentation depth, if an indentation deeper than the amount of removal required in the finish machining process exists, the workpiece may not be able to be finished and may be deemed a defective product. Furthermore, in general indentation testing methods (or IIT), it is difficult to adjust the position and phase of the indenter used for indentation, making it difficult to perform indentation testing during the machining process of machined parts.

[0006] Japanese Patent Application Laid-Open No. 2021-85804

[0007] Shuhei Hikawa, Shigetake Okano, Masato Mochizuki, Masashi Hashimoto, and Ryo Tezuka, "Evaluation of the Depth of Process-Affected Layers by Indentation Method and Its Applicability to Curved Surfaces," Abstracts of the National Conference of the Japan Welding Society, Vol. 112, Japan Welding Society, April 2023, pp. 166-167; Shigetake Okano and Masato Mochizuki, "Proposal of a Quasi-Nondestructive Measurement Method for Non-Equiaxial Residual Stress Fields Using an Indentation Method Independent of the Reference Hardness Under Stress Free Condition," Transactions of the Japan Society of Mechanical Engineers, Vol. 80, No. 820, Japan Society of Mechanical Engineers, 2014, pp. 1-11

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

[0009] According to one aspect of the present invention, there is provided a method for measuring a work-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 instead of the tool for pressing into the workpiece; pressing the indenter into the workpiece using the machine tool's feed device; constantly measuring the indentation load for pressing the indenter and the indentation depth of the indenter into the workpiece; constantly calculating an indentation load coefficient, which is a coefficient obtained by functionally approximating the indentation load with 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 that is sufficiently close to zero from negative; and multiplying the indentation depth of the indenter when indentation was stopped by a depth conversion constant to calculate the depth of the work-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 rough-machined with a tool attached to a spindle, and then a machining-damaged layer on the surface of the workpiece is measured on the machine tool, and finish-machining is performed after measuring the machining-damaged layer, the method comprising the steps of: after rough-machining, attaching an indenter to the spindle to press into the workpiece in place of the tool; pressing the indenter into the workpiece using the machine tool's feed device; constantly measuring the indentation load for pressing the indenter and the indentation depth of the indenter into the workpiece; constantly calculating an indentation load coefficient, which is a coefficient obtained by functionally approximating the indentation load with the indentation depth; stopping the indenter from pressing 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; multiplying the indenter indentation depth at the time indentation was stopped by a depth conversion coefficient to calculate the depth of the machining-damaged layer; and performing finish-machining if the calculated depth of the machining-damaged layer 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 workpiece surface damage layer on a machine tool that processes a workpiece attached to a table with a tool attached to a spindle, 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 the machine tool's feed device; an indentation load detector that measures the indentation load applied to the workpiece at every instant; an indentation depth detector that measures the indentation depth of the indenter applied to the workpiece at every instant; indenter indentation stop control means that constantly calculates an indentation load coefficient, which is a coefficient obtained when the indentation load is functionally approximated by the indentation depth, and 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 that is sufficiently close to zero from negative; and indentation-damaged layer depth calculation means that calculates the depth of the workpiece damage layer by multiplying the indentation depth at which 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 that detachably mounts the indenter and has a sensor that detects the indentation load of the indenter on the workpiece; and a computing device that can be connected to the machine tool's control device, that constantly calculates an indentation load coefficient, which is a coefficient when the indentation load is functionally approximated by the indentation depth, and that 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 goes from negative to sufficiently close to zero, and that calculates the processing-damaged layer depth by multiplying the indentation depth at which indentation of the indenter was stopped by a depth conversion constant.

[0013] According to one aspect of the present invention, a method for measuring a workpiece damage layer can be implemented. An indenter attached to a spindle, instead of a tool, is indented into the workpiece using a machine tool's feed mechanism, and the indentation load and indentation depth of the indenter into the workpiece can be measured continuously. This allows the indenter's position and phase relative to the workpiece to be adjusted on the machine tool, allowing the workpiece damage layer on the workpiece to be measured and the condition of the workpiece damage layer to be easily evaluated. Furthermore, when the rate of change of the indentation load coefficient, which is a coefficient obtained by functionally approximating the measured indentation load with the indentation depth, becomes sufficiently close to zero from a negative value, i.e., when the effect of the workpiece damage layer on the indentation load becomes small, the indenter's indentation into the workpiece can be stopped, and the indentation depth of the indenter at the time of indentation stop can be multiplied by a depth conversion constant to calculate the workpiece damage layer depth. In this way, the indentation depth of the workpiece can be easily and quickly measured and evaluated using the machine tool's built-in mechanical configuration, without using a dedicated indentation measurement device or removing the workpiece from the machine tool.

[0014] According to one aspect of the present invention, after rough machining, an indenter attached to a spindle, replacing a tool, is pressed into the workpiece using a machine tool feeder. The indenter load and the indenter depth into the workpiece can be continuously measured. This allows the position and phase of the indenter relative to the workpiece to be adjusted on the machine tool, allowing the workpiece surface to be measured and the condition of the workpiece to be easily evaluated. Furthermore, when the rate of change of the indentation load coefficient, which is a coefficient obtained by functionally approximating the measured indentation load with the indentation depth, approaches zero from a negative value, i.e., when the effect of the workpiece on the indentation load becomes small, the indenter can be stopped from pressing into the workpiece. The indenter depth at the time of stopping the indentation can be multiplied by a depth conversion constant to calculate the workpiece depth. This allows the workpiece depth to be calculated without applying a load to the workpiece until a predetermined indentation depth or indentation load value is reached, preventing or suppressing the calculated workpiece depth from exceeding the workpiece finishing allowance. This reduces the probability of the workpiece being deemed defective, and also eliminates unnecessary finishing, since finishing is performed only when the calculated depth of the workpiece's damaged layer is smaller than the finishing allowance.

[0015] According to one aspect of the present invention, a machine tool can be configured to indent an indenter attached to a spindle instead of a tool into a workpiece using the machine tool's feeder, and the indenter load and indenter depth into the workpiece can be continuously measured using an indentation load detector and an indentation depth detector. This allows the machine tool to adjust the position and phase of the indenter relative to the workpiece and measure the work-affected layer on the workpiece surface, thereby easily evaluating the state of the work-affected layer. Furthermore, the indenter indentation stop control means can stop the indenter from indenting the workpiece when the rate of change of the indentation load coefficient, which is a coefficient obtained by functionally approximating the measured indentation load with the indentation depth, becomes sufficiently close to zero from negative, i.e., when the effect of the work-affected layer on the indentation load becomes small. Furthermore, the indenter indentation depth calculation means can calculate the work-affected layer depth by multiplying the indenter indentation depth at the time indentation is stopped by a depth conversion constant. This allows the work-affected layer depth to be calculated without applying a load to the workpiece until a preset 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 measurement 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 the machine tool's feed mechanism, and a tool holder that is detachably attached to the indenter and has a sensor that detects the indenter's indentation load on the workpiece. This allows the machine tool to adjust the position and phase of the indenter relative to the workpiece and measure the work-damaged layer on the workpiece, thereby easily evaluating the condition of the work-damaged layer. The device also includes a computing device that can be connected to the machine tool's control device. This device continuously calculates an indentation load coefficient, which is a coefficient obtained by functionally approximating the indentation load with the indentation depth. When the rate of change of the indentation load coefficient with respect to the indentation depth approaches zero from negative, the indenter is stopped from indenting the workpiece. The indentation depth at the time the indenter was stopped is multiplied by a depth conversion constant to calculate the work-damaged layer depth. This allows a function that enables easy measurement of the workpiece's work-damaged layer on the machine tool to be retrofitted to a conventional machine tool other than the machine tool described above that implements the method for measuring a workpiece's work-damaged layer of the present invention.

[0017] FIG. 1 shows a side view of a machine tool according to this embodiment. FIG. 2 shows a side view of a machine tool that presses an indenter into a workpiece. FIG. 3 shows an enlarged view of the workpiece and indenter in FIG. 2. FIG. 4 shows an enlarged view of the indenter being inclined and pressed into the workpiece. FIG. 5 shows a cross-sectional view of a workpiece surface affected by the indenter. FIG. 6 shows a graph representing the relationship between the indentation load, the indentation load coefficient, and the rate of change of the indentation load coefficient and the indentation depth. FIG. 7 shows a time series representing the change in indentation load over time. FIG. 8 shows the surface of a workpiece after being pressed with a Vickers pyramidal indenter and a Knoop pyramidal indenter. FIG. 9 shows an explanatory diagram of the workpiece machining process, including an indentation test. FIG. 10 shows a flowchart of the workpiece machining process, including an indentation test. FIG. 11 shows a cross-sectional view of a sample surface pressed with a pyramidal indenter in a conventional indentation test method. FIG. 12 shows a graph representing the relationship between the indentation load and the indentation depth from the start of loading to the release of the load in an indentation test method.

[0018] Hereinafter, a machine tool according to an embodiment will be described with reference to the accompanying drawings. Similar or corresponding elements are designated by 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 this 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 disposed on the upper surface of the bed 12, and a workpiece W is fixed thereto using a fixture 50 (see FIG. 9 ). The table 30 is movable along the bed 12 via a guideway. The machine tool 10 has a preset machine coordinate system with a predetermined origin, which includes an X-axis, a Y-axis, and a Z-axis as linear axes that are orthogonal to each other. The machine tool 10 according to this embodiment is vertical, and the Z-axis extends vertically. The X-axis and Y-axis are set on a plane perpendicular to the Z-axis, i.e., a horizontal plane. In the machine tool 10, the table 30 is configured to move along the Y-axis direction (left-right). A saddle 16 disposed in front of the column 14 is configured to move along the X-axis direction (perpendicular to the plane of the drawing).

[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 (machine vertical direction). A spindle 20 is attached to the tip end side (here, the lower side) of the spindle head 18 so as to be rotatable relative to the spindle head 18 about an axis parallel to the Z-axis. 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. Thus, the machine tool 10 is configured so that the spindle 20, on which the indenter 42 or the tool 62, 64 is attached, 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 for 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 detection device 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 for relatively moving the indenter 42 or 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 and for relatively moving the indenter 42 or the tools 62, 64 and the workpiece W along the Z-axis. Also disposed on the saddle 16 is a Z-axis position detection device 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 that is pressed into it. The table 30 of the machine tool 10 in this figure is configured to be rotatable relative 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. This allows the indenter 42 to be pressed perpendicularly into the workpiece W even if the surface of the workpiece W is curved or inclined.

[0025] Here, the indenter 42 is described as being pressed perpendicularly into the workpiece W by rotating the table 30, but this is not limited to this. As shown in Figure 4, the main shaft may be configured to be tiltable relative to the workpiece W, and the indenter 42 may be tilted relative to the workpiece W, thereby pressing the indenter 42 perpendicularly into the workpiece W.

[0026] 1, the machine tool 10 is equipped with 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 on 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 with 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 tools 62, 64, and is configured so that the spindle 20 can be operated and the indenter 42 or tools 62, 64 taken out from the tool magazine 44 can be attached to and detached from the spindle 20 depending on the type of 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 process-affected layer measuring device for measuring and evaluating the process-affected 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 devices. 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 when the indenter 42 is pressed 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 assumed to be 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 work-affected layer WL. FIG. 6 is a graph showing an example of the changes in the indentation load L, the indentation load coefficient C, and the rate of change of the indentation load coefficient C (dC / dh) with respect to the indentation depth h. As the indenter 42 is pressed into the work-affected layer WL, the indentation depth h and the indentation load L are detected every moment by the indentation depth detection unit 38a and the load sensor 46, and these are recorded in the computing device 38. The computing device 38 has a stop control unit 38b as an indenter pressing stop control means. The stop control unit 38b 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), which is the coefficient of the approximated quadratic function. ２ Furthermore, 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 pressed in due to the influence of the work-affected layer WL, and becomes a constant value once the indenter 42 is pressed in to a certain depth, as the influence of the work-affected layer WL becomes smaller. 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, thereby stopping the indentation of the indenter 42. In practice, 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 pre-stored depth conversion constant 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 approximately 7 times the indentation depth h. 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, the indentation depth h at the time of stopping is used here.ｓ The depth conversion constant by which to multiply is set to 3.5. Note that although the depth conversion constant is set to 3.5 here, the depth conversion constant varies mainly depending on the shape of the indenter, and therefore 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, or to stop machining of the workpiece W if the calculated machine-damaged layer depth Z is greater 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. Therefore, 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 point at which 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, and to set the point SP at which the time change dL exceeds a predetermined threshold 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 where the indentation depth h = 0.

[0034] Furthermore, in addition to measuring the work-affected layer WL, the machine tool 10 equipped with the computing device 38 can measure non-equibiaxial stress using an indentation method that does not depend on a reference hardness under stress-free conditions. Specifically, the indenter can measure the indentation load L and indentation depth h using a Vickers pyramidal indenter VI with a predetermined apex angle and a square base and a Knoop pyramidal indenter NI with a predetermined apex angle and a rhomboidal base having 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 to measure 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] 8 , the axial feed devices 22, 32, and 26 of the machine tool 10 are used to press the Knoop pyramidal 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 and the first indentation load L1 of the Knoop pyramidal indenter NI into the workpiece W. Furthermore, the axial feed devices 22, 32, and 26 of the machine tool 10 are used to press the Knoop pyramidal 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 and the second indentation load L2 of the Knoop pyramidal indenter NI into the workpiece W. Furthermore, the axial feed devices 22, 26, and 32 of the machine tool 10 are used to press the Vickers pyramidal indenter VI into the workpiece W, thereby measuring the indentation depth h of the Vickers pyramidal indenter VI into the workpiece W and the third indentation load L3 for pressing the Vickers pyramidal indenter VI into the workpiece W. Here, the method of changing the phase of the Knoop pyramidal indenter NI by 90 degrees is performed using the indexing positioning function of the spindle 20 or the indexing positioning function of the table 30.

[0036] The calculation device 38 calculates the X-axis stress σ , which is the 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 way. ｘand 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 x L3) F2 = (L1 - η x L3) F3 = (α2 - η x α3) F4 = (α1 - η x α3) σ ｘ =(F1×F3-F2×F4) / (F4×F4-F3×F3) σ ｙ = (F2 x F3 - F1 x F4) / (F4 x F4 - F3 x F3) where α1 is the conversion coefficient between the stress value and the load change amount when the Knoop indenter NI is pressed with the major axis LA direction parallel to the stress direction, α2 is the conversion coefficient between the stress value and the load change amount when the Knoop indenter NI is pressed with the major axis LA direction 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 pressed, and these are constants determined by the material of the workpiece W. The residual stress σ calculated in this way ｘ , σ Ｙ If the value is positive, a compressive force is acting at 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 the value is negative, a tensile force is acting at 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 while the Vickers pyramidal indenter VI and Knoop pyramidal indenter NI, which have a predetermined apex angle, have been described here, this is not limiting; pyramidal indenters with a square base and a diamond-shaped base that do not have a predetermined apex angle may also be used. In such cases, the various coefficients in the above calculation formula will change.

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

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

[0039] When the indentation test is started, the process proceeds to step S10, where the indenter 42 attached to the indenter holder 40 removed from the tool magazine 44 is attached to the spindle 20 instead of the tool 62. Here, as an example, a Knoop pyramidal indenter NI is used as the indenter 42. Once the indenter 42 is attached to the spindle 20, the process proceeds to step S20, where the axial feed devices 22, 32, and 26 are operated to move the indenter 42 to a position where it will be pressed into the workpiece W, and the tilt of the table 30 is adjusted so that the axial direction of the indenter 42 is aligned with the normal direction to the surface of the workpiece W. Once these adjustments are complete, the process proceeds to step S30, where the phase of the spindle 20 is calculated and adjusted. When measuring the first indentation load L1 using the Knoop pyramidal indenter NI, the phase is adjusted so that the major axis LA is aligned with the X-axis direction, i.e., parallel to the X-axis direction. When measuring the second indentation load L2, 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, where 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 activated 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, and determines the time SP at which the time exceeds a predetermined threshold 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 detection unit 38a and the load sensor 46 detect the indentation depth h and the indentation load L from time to time. The calculation device 38 records these 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 constantly calculates the rate of change (dC / dh) of the indentation load coefficient C with respect to the indentation depth h. ｓ By pressing it down to the point where the pressing load coefficient C reaches a constant value CＳ When the rate of change (dC / dh) of the indentation load coefficient C goes from negative to a predetermined value sufficiently approaching 0, 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 the pre-stored depth conversion constant into the indentation depth h at the time when the indentation of the indenter 42 is stopped. ｓ After calculating the depth Z of the work-affected layer, the process proceeds to step S80, in which the spindle 20 is raised and the indenter 42 is pulled out of the workpiece W.

[0042] Once the indenter 42 is withdrawn, the process proceeds to step S90. If a Knoop pyramidal 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 and the first indentation load L1 or the second indentation load L2 for which measurement has not been completed is measured. If measurement of both the first indentation load L1 and the second indentation load L2 using the Knoop pyramidal indenter NI has been completed or if a Vickers pyramidal 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 work-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 depth Z of the work-affected layer 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 finishing. On the other hand, if the calculated depth Z of the work-affected layer 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 the machine-damaged 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-damaged 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-damaged layer WL can be easily evaluated. Furthermore, since the machine tool 10 is provided with a calculation device 38 connectable to the NC control unit 36, an 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 is multiplied by a depth conversion constant to calculate the depth Z of the work-affected layer. 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 conventional indentation testing methods, and it is possible to measure and evaluate the work-affected layer WL while reducing the probability of the workpiece W being deemed a defective product.

[0046] Furthermore, according to the method for measuring the work-degraded layer WL of the workpiece W, the method for machining the workpiece W, the computing device 38, and the machine tool 10 of this embodiment, the table 30 of the machine tool 10 is configured to be rotatable relative 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 work-affected layer WL of the workpiece W, the method for machining the workpiece W, the arithmetic device 38, and the machine tool 10 according to this embodiment, the arithmetic 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 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 time point at which the indenter 42 is pressed into the surface of the workpiece W and the indentation depth h actually occurs can be set as the application start point of the indentation load L, thereby stably improving the measurement accuracy of the indentation load L, and ultimately the accuracy of the rate of change (dC / dh) of the indentation load coefficient C.

[0048] Furthermore, according to the method for measuring the work-damaged layer WL of the workpiece W, the method for machining the workpiece W, the computing device 38, and the machine tool 10 of this embodiment, in addition to measuring the work-damaged 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, can be calculated. ｘ and the second residual stress in the Y-axis direction, the Y-axis stress σ Ｙ This allows the stress in the damaged layer WL to be evaluated in addition to the calculation of the damaged layer depth Z.

[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 machine tool 10.

[0050] This section describes a device for measuring work-damaged layers on a conventional machine tool that does not incorporate a load sensor 46 in the spindle head 18 and is not designed to measure work-damaged layers. In this case, a load sensor for measuring the indentation load L is provided inside the indenter holder 40. A general-purpose PC is used as the computing device, and the indentation depth detector 38a, stop controller 38b, and depth calculator 38c are installed as application software on the PC, which is then connected to the user interface of the machine tool's NC device. Retrofitting this work-damaged layer measuring device to a conventional machine tool allows the above-described work-damaged layer measurement method and workpiece machining method to be implemented, and furthermore, allows the device to perform functions equivalent to those of the machine tool 10 shown in FIG. 1 . In other words, this work-damaged layer measuring device can be considered a work-damaged layer measurement kit that combines various indenters, an indenter holder with a built-in load sensor, a PC connectable to the machine tool's control device, and application software.

[0051] The above describes embodiments of 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, but the present invention is not limited to the above embodiments. 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, those skilled in the art will understand that various modifications of the above embodiments are possible.

[0052] REFERENCE SIGNS LIST 10 Machine tool 20 Spindle 22 X-axis feeder (feeder) 26 Z-axis feeder (feeder) 32 Y-axis feeder (feeder) 36 NC control unit (control unit) 38 Calculation unit (machining-affected layer measuring device) 38a Indentation depth detection unit 38b Stop control unit (indenter indentation stop control means) 38c Depth calculation unit (machining-affected layer depth calculation means) 42 Indenter 46 Load sensor (indentation load detector) L Indentation load L1 First indentation load L2 Second indentation load L3 Third indentation load h Indentation depth NI Knoop pyramidal indenter VI Vickers pyramidal indenter WL Machine-affected layer

Claims

1. A method for measuring a machining-damaged layer on the surface of a workpiece on a machine tool which machines a workpiece attached to a table with a tool attached to a spindle, comprising: attaching an indenter to the spindle in place of the tool for pressing into the workpiece; 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 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 calculating the depth of the machining-damaged layer by multiplying the indentation depth of the indenter at the time indentation was stopped by a depth conversion constant.

2. The method for measuring a workpiece's work-induced deterioration layer as described in claim 1, wherein the indenter is pressed in along the normal direction of the workpiece surface.

3. A method for measuring a processed-deformed layer of a workpiece as described in claim 1, wherein the indentation load measured by pressing the indenter is determined to be the start point of the application of the indentation load when the moving average value of the change in the indentation load from moment to moment exceeds a predetermined threshold value.

4. The indenter is a pyramidal indenter having a square base or a rhomboidal indenter having a long axis and a short axis, and prior to machining the workpiece, a feed device of the machine tool is used to press the square-base pyramidal indenter and the rhomboidal 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 rhomboidal indenter to the indentation load of the square-base pyramidal indenter at the same indentation depth; a feed device of the machine tool is used to press the rhomboidal indenter with the long axis of its base facing in a first direction into the workpiece, thereby measuring the indentation depth of the rhomboidal indenter into the workpiece and a first indentation load for pressing the rhomboidal indenter; 4. The method for measuring a machining-affected layer of a workpiece according to claim 1, comprising: measuring a penetration depth of the pyramidal indenter having a diamond-shaped bottom surface into the workpiece and a second indentation load for indenting the pyramidal indenter having a diamond-shaped bottom surface into the workpiece using a feed device of the machine tool, the pyramidal indenter having a diamond-shaped bottom surface, with the major axis of the base surface oriented in a second direction perpendicular to the first direction, into the workpiece; measuring a penetration depth of the pyramidal indenter having a square bottom surface into the workpiece and a third indentation load for indenting the pyramidal indenter having a square bottom surface into the workpiece using the feed device of the machine tool; and 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 of machining a workpiece, comprising: after rough machining of a workpiece attached to a table of a machine tool with a tool attached to a spindle, measuring a machining-damaged layer on the surface of the workpiece on the machine tool; and performing finish machining after measuring the machining-damaged layer, comprising: after the rough machining, attaching 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 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; calculating the machining-damaged layer depth by multiplying the indentation depth of the indenter at the time indentation was stopped by a depth conversion coefficient; 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 for measuring a machining-affected layer on the surface of a workpiece on a machine tool which processes the 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 a feed device of the machine tool; an indentation load detector which measures the indentation load of the indenter on the workpiece at every moment; an indentation depth detector which measures the indentation depth of the indenter on the workpiece at every moment; an indentation load coefficient which is a coefficient obtained by functionally approximating the indentation load with the indentation depth at every moment, and an indentation load stop control means which momentarily calculates an indentation load coefficient which is a coefficient when the indentation load is functionally approximated by the indentation depth, and 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 machining-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 is stopped by a depth conversion constant.

7. A processing-damaged layer measuring device attached to a machine tool which processes a workpiece attached to a table with a tool attached to a spindle and measures a processing-damaged layer on the surface of the workpiece on 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 a feed device of the machine tool; an indenter holder to which the indenter is detachably attached and which has a sensor which detects the indentation load of the indenter on the workpiece; and a calculation device connectable to a control device of the machine tool, which calculates from moment to moment an indentation load coefficient which is a coefficient obtained when the indentation load is functionally approximated by the indentation depth, 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 which 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.

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