Method for Measuring Worked Heat-Affected Layer of Workpiece, Workpiece Machining Method, Worked Heat-Affected Layer Measuring Device, 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 machined affected layer of a workpiece, a method for machining a workpiece, a machined affected layer measuring device, and a machine tool.

Background Art

[0002] The material of a workpiece is produced through several processes such as rolling, drawing, extrusion, forging, and surface treatment, and a machined affected layer is formed on the surface. Further, the workpiece material is machined to have a desired shape and dimensions. Since rough machining is performed at this initial stage, a machined affected layer is formed on the surface of the workpiece. In such a machined affected layer, residual stress is likely to be generated due to residual strain, which can be a cause of stress corrosion cracking, fatigue failure, creep failure, etc. Therefore, at the product stage, it is managed to remove the machined affected layer by finish machining. In recent years, for example, difficult-to-machine materials such as nickel-based superalloys are frequently used for weight reduction and high rigidity of aircraft parts and for achieving both performance and fuel efficiency of jet engines, and the management of the machined affected layer of such materials has become increasingly important.

[0003] As methods for evaluating a machined affected layer, for example, observation by an optical microscope or an electron microscope, X-ray diffraction method (XRD), electron backscatter diffraction analysis method (EBSD), micro-Vickers test, etc. have been conventionally known. However, these evaluation methods require cutting the workpiece to observe the cross section, a dedicated measuring device, management qualifications for handling, and measurement know-how, so it is difficult to always perform them at the machining site.

[0004] Therefore, for example, Patent Document 1 discloses a three-dimensional hardness distribution measurement method and system utilizing an indentation test method. The indentation test method is a semi-nondestructive inspection method for evaluating the residual stress distribution in the sample depth direction from the load-displacement curve when a pyramidal indenter or a spherical indenter is pressed into the sample surface. FIG. 11 schematically shows a longitudinal sectional view of the sample surface into which the pyramidal indenter is pressed. Further, FIG. 12 shows the relationship between the indentation load L (vertical axis) and the indentation depth h (horizontal axis) from the start of the load application to the unloading in the 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 (that is, L / h 2 ) is affected by the hardened or softened machined affected layer in the region where the indentation depth is shallow, and thus decreases as the indentation depth h increases. Furthermore, it is known that when the pyramidal indenter is pressed deeply, the influence of the machined affected layer becomes small from a certain depth and the indentation load coefficient becomes approximately a constant value. Therefore, the depth of the machined affected layer can be grasped from the change in the indentation load coefficient.

[0005] However, for example, in a general indentation test method such as the Instrumented Indentation Technique (IIT) disclosed in Non-Patent Document 1 and Non-Patent Document 2, since a load is applied to the workpiece until a preset indentation depth or indentation load value is reached, an indentation deeper than necessary may be left on the surface of the workpiece. For example, as shown in FIG. 11, this is the case where the pyramidal indenter is pressed to an indentation depth D exceeding the thickness M of the machined affected layer WL. Therefore, even if the depth of the machined affected layer is evaluated by the indentation test method after the rough machining process and the necessity of performing the finish machining is judged according to the depth, if there is an indentation with a depth exceeding the removal amount in the finish machining process, the finish machining cannot be performed and the workpiece may be treated as a defective product. Also, in a general indentation test method (or IIT), since it is difficult to adjust the position and phase of the indenter for pressing, it is difficult to perform the indentation test during the machining process of the machined parts.

Prior Art Documents

Patent Document

[0006]

Patent Document 1

Non-Patent Document

[0007]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] In view of the above circumstances, an object of the present invention is to provide a method for measuring a machined affected layer of a workpiece, a machining method of the workpiece, a machined affected layer measuring device, and a machine tool, which can easily evaluate the state of the machined affected layer of the machining surface of the workpiece on the machine tool.

Means for Solving the Problems

[0009] According to one aspect of the present invention, there is provided a method for measuring a machined affected layer on the surface of a workpiece on a machine tool that machines a workpiece attached to a table with a tool mounted on a spindle. The method includes mounting a indenter for pressing into the workpiece on the spindle instead of the tool, pressing the indenter into the workpiece using a feed device of the machine tool, continuously measuring a pressing load for pressing the indenter and a depth of penetration of the indenter into the workpiece, continuously calculating a pressing load coefficient that is a coefficient when the pressing load is approximated as a function of the depth of penetration, stopping the pressing of the indenter into the workpiece when a rate of change of the pressing load coefficient with respect to the depth of penetration reaches a value sufficiently close to 0 from a negative value, and calculating a machined affected layer depth by multiplying the depth of penetration of the indenter when the pressing is stopped by a depth conversion constant.

[0010] Furthermore, according to one aspect of the present invention, there is provided a workpiece machining method in which after rough machining a workpiece attached to a table of a machine tool with a tool mounted on a spindle, the machined affected layer on the surface of the workpiece is measured on the machine tool, and finish machining is performed after the measurement of the machined affected layer. The method includes mounting a indenter for pressing into the workpiece on the spindle instead of the tool after rough machining, pressing the indenter into the workpiece using a feed device of the machine tool, continuously measuring a pressing load for pressing the indenter and a depth of penetration of the indenter into the workpiece, continuously calculating a pressing load coefficient that is a coefficient when the pressing load is approximated as a function of the depth of penetration, stopping the pressing of the indenter into the workpiece when a rate of change of the pressing load coefficient with respect to the depth of penetration reaches a value sufficiently close to 0 from a negative value, calculating a machined affected layer depth by multiplying the depth of penetration of the indenter when the pressing is stopped by a depth conversion coefficient, and performing finish machining when the calculated machined affected layer depth is smaller than the finish allowance of the workpiece.

[0011] Further, according to one aspect of the present invention, there is provided a machine tool that measures a processed altered layer on the surface of a workpiece on the machine tool for machining the workpiece attached to a table with a tool mounted on a spindle, the machine tool comprising: an indenter that can be mounted on the spindle instead of the tool and forms an indentation by being pressed into the workpiece using a feed device of the machine tool; a pressing load detector that measures the pressing load of the indenter on the workpiece at each time; a pressing depth detector that measures the pressing depth of the indenter into the workpiece at each time; a pressing load coefficient calculation means that calculates at each time a pressing load coefficient that is a coefficient when the pressing load is approximated by a function of the pressing depth, and stops the pressing of the indenter into the workpiece when the change rate of the pressing load coefficient with respect to the pressing depth reaches a value sufficiently close to 0 from negative; and a processed altered layer depth calculation means that calculates the processed altered layer depth by multiplying the pressing depth when the pressing of the indenter is stopped by a depth conversion constant.

[0012] Furthermore, according to one aspect of the present invention, there is provided a processed altered layer measuring device attached to a machine tool for machining a workpiece attached to a table with a tool mounted on a spindle, the processed altered layer measuring device measuring a processed altered layer on the surface of the workpiece on the machine tool, the processed altered layer measuring device comprising: an indenter that can be mounted on the spindle instead of the tool and forms an indentation by being pressed into the workpiece using a feed device of the machine tool; an indenter holder that detachably attaches the indenter and has a sensor that detects the pressing load of the indenter on the workpiece; and an arithmetic unit that can be connected to a control device of the machine tool, the arithmetic unit calculating at each time a pressing load coefficient that is a coefficient when the pressing load is approximated by a function of the pressing depth, stopping the pressing of the indenter into the workpiece when the change rate of the pressing load coefficient with respect to the pressing depth reaches a value sufficiently close to 0 from negative, and calculating the processed altered layer depth by multiplying the pressing depth when the pressing of the indenter is stopped by a depth conversion constant.

Advantages of the Invention

[0013] According to the method for measuring the machined affected layer of a workpiece according to one aspect of the present invention, a indenter mounted on the spindle instead of a tool is pressed into the workpiece using the feed device of a machine tool, and the pressing load for pressing the indenter and the depth of penetration of the indenter into the workpiece can be measured moment by moment. Therefore, on the machine tool, the measurement of the machined affected layer on the surface of the workpiece can be performed after adjusting the position and phase of the indenter with respect to the workpiece, and the state of the machined affected layer can be easily evaluated. Further, when the change rate of the indentation load coefficient, which is the coefficient when the measured pressing load is approximated by a function with respect to the depth of penetration, reaches a value close enough to zero from negative, that is, when the influence of the machined affected layer on the pressing load becomes small, the pressing of the indenter into the workpiece is stopped, and the depth of the machined affected layer can be calculated by multiplying the depth of penetration of the indenter when the pressing is stopped by a depth conversion constant. In this way, without using a dedicated indentation measuring device and without removing the workpiece from the machine tool, the measurement and evaluation of the machined affected layer of the workpiece can be easily and quickly performed using the mechanical configuration originally possessed by the machine tool.

[0014] According to the method for machining a workpiece according to one aspect of the present invention, after rough machining, a plunger mounted on the spindle instead of the tool is pushed into the workpiece using the feed device of the machine tool, and the pushing load for pushing the plunger and the pushing depth of the plunger into the workpiece can be measured moment by moment. Therefore, on the machine tool, the measurement of the machining affected layer on the surface of the workpiece can be performed after adjusting the position and phase of the plunger with respect to the workpiece, and the state of the machining affected layer can be easily evaluated. Further, when the change rate of the pushing load coefficient, which is the coefficient when the measured pushing load is approximated by a function with respect to the pushing depth, becomes a value close enough to zero from negative, that is, when the influence of the machining affected layer on the pushing load becomes small, the pushing of the plunger into the workpiece is stopped, and the machining affected layer depth can be calculated by multiplying the pushing depth of the plunger when the pushing is stopped by a depth conversion constant. Therefore, the machining affected layer depth can be calculated without applying a load to the workpiece until a preset pushing depth or pushing load value is reached, and it is possible to prevent or suppress the calculated machining affected layer depth from becoming larger than the finishing cost of the workpiece. As a result, the probability of making the workpiece a defective product is reduced, and since the finishing process is performed only when the calculated machining affected layer depth is smaller than the finishing cost of the workpiece, unnecessary finishing processes can be avoided.

[0015] According to the machine tool according to one aspect of the present invention, a plunger mounted on the spindle instead of a tool is pushed into the workpiece using the feed device of the machine tool, and the pushing load for pushing the plunger and the pushing depth of the plunger into the workpiece are continuously measured using a pushing load detector and a pushing depth detector. Therefore, on the machine tool, the measurement of the processed and altered layer on the surface of the workpiece can be performed after adjusting the position and phase of the plunger with respect to the workpiece, and the state of the processed and altered layer can be easily evaluated. Further, when the change rate of the pushing load coefficient, which is the coefficient when the measured pushing load is approximated by a function of the pushing depth, becomes a value sufficiently close to 0 from negative by the plunger pushing stop control means, that is, when the influence of the processed and altered layer on the pushing load becomes small, the pushing of the plunger into the workpiece can be stopped. Furthermore, the depth of the processed and altered layer can be calculated by multiplying the pushing depth of the plunger when the pushing is stopped by a depth conversion constant by the processed and altered layer depth calculation means. Therefore, the depth of the processed and altered layer can be calculated without applying a load to the workpiece until a preset pushing depth or pushing load value is reached. As a result, the probability of making the workpiece a defective product can be reduced.

[0016] According to the processed layer measurement device according to one aspect of the present invention, it can be attached to the spindle instead of the tool, and includes an indenter that forms an indentation by being pushed into the workpiece using the feed device of the machine tool, and a tool holder that is detachably attached to the indenter and has a sensor for detecting the pushing load of the indenter against the workpiece. Therefore, on the machine tool, after adjusting the position and phase of the indenter with respect to the workpiece, the measurement of the processed layer on the surface of the workpiece can be performed, and the state of the processed layer can be easily evaluated. Further, since it is provided with an arithmetic unit that can be connected to the control device of the machine tool, the indentation load coefficient, which is the coefficient when the indentation load is approximated as a function of the indentation depth, is calculated moment by moment, and when the change rate of the indentation load coefficient with respect to the indentation depth reaches a value close enough to zero from negative, the pushing of the indenter into the workpiece is stopped, and the depth conversion constant is multiplied by the indentation depth when the pushing of the indenter is stopped to calculate the processed layer depth. As a result, it is possible to add, as an after - attachment, a function that enables easy measurement of the processed layer of the workpiece on a normal machine tool that is not the above - mentioned machine tool for implementing the workpiece processed layer measurement method of the present invention.

Brief Description of the Drawings

[0017]

Figure 1

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Figure 12

DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, a machine tool according to an embodiment will be described with reference to the accompanying drawings. The same or corresponding elements are denoted by the same reference numerals, and redundant descriptions are omitted. For ease of understanding, the scale of the drawings may be changed for the description.

[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. On the upper surface of the bed 12, a table 30 for fixing a workpiece W, which is a workpiece to be machined, by a fixture 50 (see FIG. 9) is arranged. The table 30 can move on the bed 12 via a guide surface. In addition, machine coordinates with a predetermined position as the origin are preset in the machine tool 10, and include an X-axis, a Y-axis, and a Z-axis as linear motion axes orthogonal to each other. The machine tool 10 according to the present embodiment is an upright type, and the Z-axis extends along the vertical direction. Further, 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-right direction). In addition, a saddle 16 arranged on the front surface of the column 14 is configured to be movable along the X-axis direction (direction perpendicular to the paper surface).

[0020] On the front surface of the saddle 16, a spindle head 18 is arranged so as to be movable up and down along the Z-axis direction (machine vertical direction). Further, on the tip side of the spindle head 18, here, on the lower side, a spindle 20 configured to be rotatable about an axis parallel to the Z-axis with respect to the spindle head 18 is attached. To the spindle 20, a pressure element 42, or tools 62, 64 (see FIG. 9) for machining the workpiece W while rotating together with the spindle 20 are detachably attached via a pressure element holder 40 or a tool holder 60. Thus, the machine tool 10 is configured such that the spindle 20 for attaching the pressure element 42 or the tools 62, 64 and the table 30 on which the workpiece W is arranged are relatively movable along the X-axis, Y-axis, and Z-axis.

[0021] On the front side of the column 14, an X-axis feed device 22 as a feed device is arranged to displace the saddle 16 along the X-axis direction and relatively move the pressure element 42 or the tools 62, 64 and the workpiece W along the X-axis direction. Further, on the column 14, an X-axis position detection device 24 for detecting the position of the pressure element 42 or the tools 62, 64 attached to the spindle 20 in the X-axis direction is arranged.

[0022] On the bed 12, a Y-axis feed device 32 as a feed device is arranged to displace the table 30 along the Y-axis direction and relatively move the pressure element 42 or the tools 62, 64 and the workpiece W along the Y-axis direction. Further, on the bed 12, a Y-axis position detection device 34 for detecting the position of the table 30 on which the workpiece W is arranged in the Y-axis direction is arranged.

[0023] On the saddle 16, a Z-axis feed device 26 as a feed device is arranged to displace the spindle head 18 along the Z-axis direction and relatively move the pressure element 42 or the tools 62, 64 and the workpiece W along the Z-axis direction. Further, on the saddle 16, a Z-axis position detection device 28 for detecting the position of the pressure element 42 or the tools 62, 64 attached to the spindle 20 in the Z-axis direction is arranged.

[0024] FIG. 2 schematically shows a side view of the machine tool 10. Further, FIG. 3 shows an enlarged view of the workpiece W and the plunger 42 that presses 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 plunger 42, and the plunger 42 can be pressed perpendicular to the workpiece W. Thereby, even if the surface of the workpiece W is a curved surface or an inclined surface, the plunger 42 can be pressed perpendicular to the workpiece W.

[0025] Here, it is described that the plunger 42 is pressed perpendicular to the workpiece W by rotating the table 30, but it is not limited to this. As shown in FIG. 4, the main shaft is configured to be tiltable with respect to the workpiece W, and the plunger 42 may be pressed perpendicular to the workpiece W by tilting the plunger 42 with respect to the workpiece W.

[0026] As shown in FIG. 1, the machine tool 10 includes an NC control unit 36 as a control device that operates each axis feed device 22, 32, 26, that is, the X-axis feed device 22, the Y-axis feed device 32, and the Z-axis feed device 26, by executing the NC program stored in the NC program storage unit 36a, to move the plunger 42 or the table 30 to a desired position. Therefore, the plunger 42 attached to the main shaft 20 can be pressed into a predetermined position of the workpiece W. Further, the NC control unit 36 is configured to operate the main shaft 20 to rotate the main shaft 20 and the tools 62, 64 so that the workpiece W can be machined with the tools 62, 64 attached to the main shaft 20. Furthermore, the machine tool 10 has a tool magazine 44 that stores the plunger 42 and the tools 62, 64, and is configured to operate the main shaft 20 and detach and attach the plunger 42 or the tools 62, 64 taken out from the tool magazine 44 to the main shaft 20 according to the content of the work performed by operating the main shaft 20, that is, the measurement of the machined affected layer WL or the machining.

[0027] Further, the machine tool 10 includes an arithmetic unit 38 as a processed layer measurement device for measuring and evaluating the processed altered layer WL of the workpiece W. The arithmetic unit 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 acquire the position information detected by these devices. The position information of the X-axis and Y-axis represents the coordinate values for pushing the indenter 42 against the workpiece W, and the position information of the Z-axis represents the coordinate values corresponding to the pushing depth h of the indenter 42.

[0028] A load sensor 46 as a pushing load detector for detecting the pushing load L (see FIG. 6), which is the load acting on the indenter 42 by pushing the indenter 42 against the workpiece W, is disposed on the spindle head 18. The load sensor 46 is electrically connected to the arithmetic unit 38, and the arithmetic unit 38 is configured to record the pushing load L detected by the load sensor 46. In the following description, the load sensor 46 is described as being disposed on the spindle head 18, but the present invention is not limited to this, and the load sensor may be provided in the tool holder or on the table.

[0029] FIG. 5 schematically shows a cross-sectional view of the workpiece W with the indenter 42 pushed into the processed altered layer WL. FIG. 6 graphically shows an example of the changes in the pushing load L, the pushing load coefficient C, and the change rate (dC / dh) of the pushing load coefficient C with respect to the pushing depth h. When the indenter 42 is pushed into the processed altered layer WL, the pushing depth h and the pushing load L are detected moment by moment by the pushing depth detector 38a and the load sensor 46, and these are recorded in the arithmetic unit 38. The arithmetic unit 38 has a stop control unit 38b as indenter push stop control means. The stop control unit 38b approximates the pushing load L measured up to that point as a quadratic function of the pushing depth h, and calculates the pushing load coefficient C (=L / h 2 ) which is the coefficient of the approximated quadratic function moment by moment. Further, the change rate (dC / dh) of the pushing load coefficient C with respect to the pushing depth h is calculated moment by moment.

[0030] The indentation load coefficient C decreases immediately after the indenter 42 is pressed in because it is affected by the work-affected layer WL. When the indenter 42 is pressed in to a certain depth, the influence of the work-affected layer WL becomes small and it becomes a constant value. The indentation depth h at which the influence of the work-affected layer WL becomes small s When the indenter 42 is pressed in until, the indentation load coefficient C with respect to the indentation depth h becomes a constant value C S That is, the change rate (dC / dh) of the indentation load coefficient C becomes a value that approaches zero sufficiently from negative. At this time, the stop control unit 38b is configured to stop the main shaft 20 via the NC control unit 36 and stop the pressing of the indenter 42. In practice, the change rate of the indentation load coefficient C may not converge exactly to zero, and the pressing of the indenter 42 may be stopped when it reaches a predetermined value that is sufficiently close to zero.

[0031] The arithmetic unit 38 has a depth calculation unit 38c as a work-affected layer depth calculation means. The depth calculation unit 38c multiplies the indentation depth h at the time when the pressing of the indenter 42 is stopped by a depth conversion constant pre-recorded therein s to calculate the work-affected layer depth Z. The indentation load L is said to be affected up to about 7 times the indentation depth h, and the indentation load coefficient C can be considered as a representative value at the position half of the indentation depth h (Non-Patent Document 1). Therefore, here, the depth conversion constant multiplied by the indentation depth h s at the time of stopping is set to 3.5. Here, although the depth conversion constant is set to 3.5, since the depth conversion constant mainly varies depending on the shape of the indenter, different values of the depth conversion constant may be used.

[0032] The machine tool 10 includes a display device 52 connected to the arithmetic unit 38 for displaying the calculated work-affected layer depth Z. Thereby, the user can visually confirm that the calculated work-affected layer depth Z is smaller than the finishing cost of the workpiece W and that finishing can be performed. Further, the arithmetic unit 38 is configured to operate the machine tool 10 and proceed to the finishing process when the calculated work-affected layer depth Z is smaller than the finishing cost of the workpiece W, and to stop the processing of the workpiece W when it is larger than the finishing cost of the workpiece W.

[0033] FIG. 7 shows a time series representing the amount of change dL in the pushing load L over time. As described above, the pushing load coefficient C (= L / h 2 ) is calculated by approximating the pushing load L as a quadratic function of the pushing depth h. Therefore, in order to stably improve the measurement accuracy of the pushing load L and the pushing depth h, it is preferable that the indenter 42 is pushed into the surface of the workpiece W, and the start point of the load application of the pushing load L is set at the time when the pushing depth h actually occurs. Therefore, the arithmetic unit 38 calculates the moving average value of the amount of change dL in the pushing load L at each recorded time, and sets the time point SP when it exceeds a predetermined threshold value TV at which it can be determined that the pushing depth h has significantly occurred as the start point of the load application of the pushing load L, and the position where the pushing depth h = 0.

[0034] In addition, the machine tool 10 including the arithmetic unit 38 can measure non-uniaxial stress by using an indentation method that does not depend on the reference hardness under no stress in addition to measuring the processed and altered layer WL. Specifically, the indenter can measure the pushing load L and the pushing depth h by using a Vickers pyramid indenter VI having a predetermined apex angle and a square bottom surface and a Knoop pyramid indenter NI having a predetermined apex angle and a rhombus bottom surface having a major axis LA and a minor axis SA. First, before machining the workpiece W, the Vickers pyramid indenter VI and the Knoop pyramid indenter NI attached to the spindle 20 of the machine tool 10 are pushed into a reference test piece (not shown) in a stress-free state made of the same material as the workpiece W to measure the pushing load L and the pushing depth h, respectively. From the measured pushing load L and pushing depth h, the pushing load ratio η of the pushing load L of the Knoop indenter NI to the pushing load L of the Vickers indenter VI at the same pushing depth h is calculated.

[0035] Next, as shown in FIG. 8, by using the axial feed devices 22, 32, 26 of the machine tool 10 to push the Vickers pyramid indenter NI with the major axis LA of the bottom surface directed in the X-axis direction, which is the first direction, into the workpiece W, the penetration depth h of the Vickers pyramid indenter NI into the workpiece W and the first penetration load L1 are measured. Further, by using the axial feed devices 22, 32, 26 of the machine tool 10 to push the Vickers pyramid indenter NI with the major axis LA of the bottom surface directed in the Y-axis direction, which is the second direction perpendicular to the X-axis direction, into the workpiece W, the penetration depth h of the Vickers pyramid indenter NI into the workpiece W and the second penetration load L2 are measured. Also, by using the axial feed devices 22, 26, 32 of the machine tool 10 to push the Vickers pyramid indenter VI into the workpiece W, the penetration depth h of the Vickers pyramid indenter VI into the workpiece W and the third penetration load L3 for pushing the Vickers pyramid indenter VI are measured. Here, the method of changing the phase of the Vickers pyramid 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 arithmetic unit 38 calculates, from the penetration load ratios η, the first penetration load L1, the second penetration load L2, and the third penetration load L3 measured in this way, the X-axis stress σ, which is the first residual stress in the X-axis direction at each penetration depth h x and the Y-axis stress σ, which is the second residual stress in the Y-axis direction Y using the following calculation formulas. 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 represents the conversion coefficient between the stress value and the load change amount when the long axis LA of the Vickers indenter NI is pushed in parallel to the stress direction, α2 represents the conversion coefficient between the stress value and the load change amount when the long axis LA of the Vickers indenter NI is pushed in perpendicular to the stress direction, and α3 represents the conversion coefficient between the stress value and the load change amount when the Vickers indenter VI is pushed in. These are constants determined by the material of the work W. The residual stress σ x , σ Y If it is a positive value, a compressive force acts on the measurement point, and the risk of the work material breaking is small, and this work W is regarded as a good product. On the other hand, if it is a negative value, a tensile force acts on the measurement point, and there is a risk that the work material breaks starting from some defect, and this work is regarded as a defective product. Here, the Vickers pyramid indenter VI and the Knoop pyramid indenter NI having a predetermined apex angle have been described, but it is not limited to this, and a pyramid indenter having a square bottom surface or a pyramid indenter having a rhombus bottom surface without a predetermined apex angle may also be used. In that case, the various coefficients in the above calculation formula will change.

[0037] Through the description of the processing steps of the work W including the indentation test along the explanatory diagrams and flowcharts shown in FIGS. 9 and 10, the measurement method of the processed altered layer WL of the work W according to the present embodiment, the processing method of the work W, and the functions and effects of the arithmetic unit 38 and the machine tool 10 will be described below.

[0038] First, it proceeds to step S510, and rough machining of the work W is performed using the rough machining tool 62 attached to the spindle 20 via the tool holder 60. When the rough machining is completed, it proceeds to step S520, and an indentation test is performed to measure the processed altered layer WL generated on the machining surface of the work W.

[0039] When the indentation test is started, the process proceeds to step S10, and the indenter 42 attached to the indenter holder 40 taken out from the tool magazine 44 is attached to the spindle 20 instead of the tool 62. Here, as an example, the Vickers 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 pushed 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 to determine and adjust the phase of the spindle 20. When measuring the first indentation load L1 using the Vickers pyramid indenter NI, the phase is adjusted so that the major axis LA is along the X-axis direction, that is, parallel. Also, when measuring the second indentation load L2, the phase is adjusted so that the major axis LA is along the Y-axis direction. When the phase adjustment is completed, the process proceeds to step S40, and 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 arithmetic unit 38 calculates the moving average value of the time change amount dL of the indentation load L recorded at each moment, and sets the time point SP when it exceeds a predetermined threshold value TV at which it can be determined that a significant indentation depth h has occurred as the load 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 pushed into the work-affected layer WL, the indentation depth h and the indentation load L are detected at each moment by the indentation depth detection unit 38a and the load sensor 46. The arithmetic unit 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 and calculates the indentation load coefficient C (=L / h 2 ) at each moment. Further, the stop control unit 38b calculates the rate of change (dC / dh) of the indentation load coefficient C with respect to the indentation depth h at each moment. When the indenter 42 reaches an indentation depth h at which the influence of the work-affected layer WL becomes small sBy being pushed in until, the pushing load coefficient C becomes a constant value C S When it becomes, and the change rate (dC / dh) of the pushing load coefficient C approaches a predetermined value sufficiently close to 0 from negative, the stop control unit 38b stops the descent of the main shaft 20 via the NC control unit 36 and stops the pushing of the indenter 42. The depth calculation unit 38c multiplies the pushing depth h at the time when the pushing of the indenter 42 is stopped by a depth conversion constant recorded in advance to calculate the depth Z of the machined affected layer. When the depth Z of the machined affected layer is calculated, the process proceeds to step S80, and the main shaft 20 is raised to pull out the indenter 42 from the workpiece W. s When the indenter 42 is pulled out, the process proceeds to step S90. When using the Vickers pyramid indenter NI as the indenter 42 and the measurement of either the first pushing load L1 or the second pushing load L2 has not been completed, the process proceeds to step S30, the phase of the main shaft 20 is changed, and the first pushing load L1 or the second pushing load L2 for which the measurement has not been completed is measured. When the measurements of both the first pushing load L1 and the second pushing load L2 using the Vickers pyramid indenter NI have been completed or when using the Vickers pyramid indenter VI as the indenter 42, the process proceeds to step S100.

[0042] When the process proceeds to step S100 and the measurement using the Vickers pyramid indenter NI or the Vickers pyramid indenter VI has not been completed, the process proceeds to step S10, the Vickers pyramid indenter NI or the Vickers pyramid indenter VI used for the measurement is taken out from the tool magazine 44, and the indenter 42 attached to the main shaft 20 is exchanged. When the indenter 42 is exchanged, the pushing load L is measured from step S20 to step S70 using this. When the measurements using both the Vickers pyramid indenter NI and the Vickers pyramid indenter VI have been completed, the process proceeds to step S110, and the arithmetic unit 38 outputs the measured and calculated depth Z of the machined affected layer, pushing load ratio η, first pushing load L1, second pushing load L2, third pushing load L3, and the X-axis stress σ which is the first residual stress in the X-axis direction at each pushing depth h

[0043] and the Y-axis stress σ which is the second residual stress in the Y-axis direction x to the display device 52. Y

[0044] When the indentation test is completed, the process proceeds to step 530. If the calculated depth Z of the heat-affected layer is smaller than the finishing allowance of the workpiece W, the process proceeds to step S550, and the machine tool 10 is operated to replace the indenter 42 with a finishing tool 64 for finishing. On the other hand, if the calculated depth Z of the heat-affected layer is larger than the finishing allowance of the workpiece W, the process proceeds to step S540, and the finishing of the workpiece W is aborted.

[0045] According to the method for measuring the heat-affected layer WL of the workpiece W, the method for machining the workpiece W, the arithmetic unit 38, and the machine tool 10 according to the present embodiment, instead of the tools 62 and 64, an indenter 42 that can be attached to the main shaft 20 and forms an indentation by pressing into the workpiece W using the axial feed devices 22, 32, and 26 provided 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 are provided. For this reason, on the machine tool 10, after adjusting the position and phase of the indenter 42 with respect to the workpiece W, the heat-affected layer WL on the surface of the workpiece W can be measured, and the state of the heat-affected layer WL can be easily evaluated. Further, since the arithmetic unit 38 that can be connected to the NC control unit 36 of the machine tool 10 is provided, the indentation load coefficient C, which is the coefficient when the indentation load L is approximated as a function of the indentation depth h, is calculated moment by 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 negative, the pressing of the indenter 42 into the workpiece W is stopped, and the indentation depth h when the pressing of the indenter 42 is stopped S is multiplied by a depth conversion constant to calculate the depth Z of the heat-affected layer. As a result, different from the conventional indentation test method, the depth Z of the heat-affected layer can be calculated without applying a load to the workpiece W until a preset indentation depth or indentation load value is reached, and the probability of considering the workpiece W as a defective product can be reduced, and the measurement and evaluation of the heat-affected layer WL can be performed.

[0046] Also, according to the method for measuring the machined affected layer WL of the workpiece W, the machining method of the workpiece W, the arithmetic unit 38, and the machine tool 10 according to 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 pushed into the workpiece W perpendicularly. As a result, even if the surface of the workpiece W is a curved surface or an inclined surface, the indenter 42 can be pushed into the workpiece W perpendicularly, and the pushing load L and the pushing depth h can be accurately measured.

[0047] Furthermore, according to the method for measuring the machined affected layer WL of the workpiece W, the machining method of the workpiece W, the arithmetic unit 38, and the machine tool 10 according to the present embodiment, the arithmetic unit 38 calculates the moving average value of the time change amount dL of the pushing load L at each recorded moment, and is configured such that the starting point SP of the load application of the pushing load L is set at the time when the pushing depth h significantly occurs and exceeds a predetermined threshold value TV that can be determined. Therefore, the time when the indenter 42 is pushed into the surface of the workpiece W and the pushing depth h actually occurs can be set as the starting point of the load application of the pushing load L, and the measurement accuracy of the pushing load L, and thus the accuracy of the change rate (dC / dh) of the pushing load coefficient C can be stably improved.

[0048] Also, according to the method for measuring the machined affected layer WL of the workpiece W, the machining method of the workpiece W, the arithmetic unit 38, and the machine tool 10 according to the present embodiment, in addition to the measurement of the machined affected layer WL, the pushing load ratio η, the first pushing load L1, the second pushing load L2, the third pushing load L3, and the X-axis stress σ which is the first residual stress in the X-axis direction at each pushing depth h x and the Y-axis stress σ which is the second residual stress in the Y-axis direction Y can be calculated. As a result, in combination with the calculation of the depth Z of the machined affected layer, the stress in the machined affected layer WL can be evaluated.

[0049] As described above, the method for measuring the machined affected layer WL of the workpiece W, the machining method of the workpiece W, the arithmetic unit 38, and the machine tool 10 according to the present embodiment can easily evaluate the state of the machined affected layer WL on the machining surface of the workpiece W on the machine tool 10.

[0050] A device for measuring a machined affected layer in a normal machine tool that does not incorporate the load sensor 46 in the spindle head 18 and does not consider the measurement of the machined affected layer will be described. In this case, a load sensor for measuring the pushing load L may be provided in the indenter holder 40. Further, a general-purpose personal computer is used as the arithmetic unit, and the push depth detection unit 38a, the stop control unit 38b, and the depth arithmetic unit 38c are installed in this personal computer as application software, and the personal computer is connected to the user interface of the NC device of this machine tool. By retrofitting this machined affected layer measuring device to a normal machine tool, the above-described method for measuring the machined affected layer and the method for machining the workpiece can be implemented, and furthermore, a function equivalent to that of the machine tool 10 in FIG. 1 can be exhibited. That is, this machined affected layer measuring device can be said to be a machined affected layer measuring kit that packs various indenters, an indenter holder incorporating a load sensor, a personal computer connectable to the control device of the machine tool, and application software.

[0051] As described above, the method for measuring the machined affected layer WL of the workpiece W, the method for machining the workpiece W, and the embodiments of the arithmetic unit 38 and the machine tool 10 have been described, 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, it is considered that those skilled in the art can understand that various modifications of the above embodiments are possible.

Description of Reference Numerals

[0052] 10 Machine tool 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 Arithmetic unit (machined affected layer measuring device) 38a Push depth detection unit 38b Stop control unit (indenter push stop control means) 38c Depth arithmetic unit (machined affected layer depth arithmetic means) 42 indenter 46 load sensor (pushing-in load detector) L pushing-in load L1 first pushing-in load L2 second pushing-in load L3 third pushing-in load h pushing-in depth NI Knoop indenter VI Vickers indenter WL machined affected layer

Claims

1. A method for measuring a processed and altered layer on the surface of a workpiece on a machine tool that processes a workpiece attached to a table using a tool mounted on a spindle, comprising: mounting a indenter for pressing into the workpiece on the spindle instead of the tool; pressing the indenter into the workpiece using a feed device of the machine tool; continuously measuring a pressing load for pressing the indenter and a depth of penetration of the indenter into the workpiece; continuously calculating a pressing load coefficient that is a coefficient when the pressing load is approximated by a quadratic function of the depth of penetration; stopping the pressing of the indenter into the workpiece when a rate of change of the pressing load coefficient with respect to the depth of penetration reaches a value that is sufficiently close to zero from a negative value, and calculating a depth of the processed and altered layer by multiplying the depth of penetration of the indenter when the pressing is stopped by a depth conversion constant. A method for measuring a processed and altered layer of a workpiece, characterized by including the above steps.

2. The method for measuring a processed and altered layer of a workpiece according to claim 1, wherein the indenter is pressed along a normal direction of the surface of the workpiece.

3. The method for measuring a processed and altered layer of a workpiece according to claim 1, wherein a starting point of the pressing load is a point in time when a moving average value of a change amount of the pressing load at each moment exceeds a predetermined threshold value for the pressing load measured by pressing the indenter.

4. A method for processing a workpiece, wherein after rough machining a workpiece attached to a table of a machine tool using a tool mounted on a spindle, the processed and altered layer on the surface of the workpiece is measured on the machine tool, and finish machining is performed after the measurement of the processed and altered layer, comprising: mounting an indenter for pressing into the workpiece on the spindle instead of the tool after the rough machining; pressing the indenter into the workpiece using a feed device of the machine tool; continuously measuring a pressing load for pressing the indenter and a depth of penetration of the indenter into the workpiece; Calculating the indentation load coefficient, which is the coefficient when approximating the indentation load with a quadratic function of the indentation depth, at each moment; Stopping the pressing of the indenter against the workpiece when the rate of change of the indentation load coefficient with respect to the indentation depth reaches a value close enough to zero from a negative value; Calculating the depth of the machined affected layer by multiplying the indentation depth of the indenter when the pressing is stopped by a depth conversion coefficient, and A workpiece processing method characterized by performing finishing machining when the calculated depth of the machined affected layer is smaller than the finishing allowance of the workpiece.

5. On a machine tool for machining a workpiece mounted on a spindle with a tool attached to a table, a machine tool for measuring the machined affected layer on the surface of the workpiece, An indenter that can be mounted on the spindle in place of the tool and forms an indentation by pressing against the workpiece using the feed device of the machine tool, An indentation load detector that measures the indentation load of the indenter against the workpiece at each moment, An indentation depth detector that measures the indentation depth of the indenter against the workpiece at each moment, Calculating the indentation load coefficient, which is the coefficient when approximating the indentation load with a quadratic function of the indentation depth, at each moment, and a means for controlling the stop of the indenter pressing that stops the pressing of the indenter against the workpiece when the rate of change of the indentation load coefficient with respect to the indentation depth reaches a value close enough to zero from a negative value; A means for calculating the depth of the machined affected layer that calculates the depth of the machined affected layer by multiplying the indentation depth when the pressing of the indenter is stopped by a depth conversion constant, A machine tool characterized by comprising the above.

6. An apparatus for measuring the machined affected layer attached to a machine tool for machining a workpiece mounted on a spindle with a tool attached to a table, and measuring the machined affected layer on the surface of the workpiece on the machine tool, An indenter that can be mounted on the spindle in place of the tool and forms an indentation by pressing against the workpiece using the feed device of the machine tool, A collet holder having a sensor that removably attaches the collet and detects the pushing load of the collet against the workpiece; An arithmetic unit connectable to a control device of the machine tool, which continuously calculates a pushing load coefficient that is a coefficient when approximating the pushing load with a quadratic function of the pushing depth, and stops the pushing of the collet into the workpiece when the change rate of the pushing load coefficient with respect to the pushing depth reaches a value close enough to zero from negative, and an arithmetic unit that calculates the depth of the machined heat-affected layer by multiplying the pushing depth when the pushing of the collet is stopped by a depth conversion constant; A machined heat-affected layer measuring device, characterized by comprising the above.

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