Method for measuring machined determination layer of workpiece, method for machining workpiece,

Abstract

The method comprises the following steps: a pressing head (42) for pressing a workpiece (W) is assembled on a main shaft (20); pressing the ram (42) into the workpiece (W) by using feeding devices (22, 26, 34) of the machine tool (10); the press-in load (L) and the press-in depth (h) are measured in real time; a press-in load coefficient (C) that is a coefficient when functionally approximating the press-in load (L) by the press-in depth (h) is calculated in real time; when the rate of change of the press-in load coefficient (C) with respect to the press-in depth (h) becomes a value sufficiently close to 0 from a negative value, press-in of the indenter (42) into the workpiece (W) is stopped. And multiplying the press-in depth (h) at the time when press-in is stopped by a depth conversion constant to calculate the depth (Z) of the work-deteriorated layer.

Description

Technical Field

[0001] This invention relates to a method for measuring the modified layer of a workpiece, a method for machining a workpiece, an apparatus for measuring the modified layer of a workpiece, and a machine tool. Background Technology

[0002] The raw materials of the workpiece are manufactured through several processes such as rolling, drawing, extrusion, forging, and surface treatment, resulting in a work-modified layer on the surface. Furthermore, the raw material is machined to achieve the desired shape and size. Rough machining is performed in this initial stage, thus creating a work-modified layer on the workpiece surface. Residual stress is easily generated in this work-modified layer due to residual strain, which can become a major cause of stress corrosion cracking, fatigue failure, creep failure, etc. Therefore, in the product stage, the work-modified layer is managed by removing it through finishing. In recent years, for example, to balance the lightweight and high rigidity of aircraft components with the performance and fuel efficiency of jet engines, many difficult-to-machine materials such as nickel-based superalloys are used, making the management of the work-modified layer of such materials increasingly important.

[0003] Methods for evaluating altered layers in processing include observation using optical microscopes, electron microscopes, X-ray diffraction (XRD), electron backscattering analysis (EBSD), and micro-Vickers hardness testing. However, these evaluation methods require cutting the workpiece to observe the cross-section, specialized measuring equipment, qualified management personnel for the process, and specific measuring skills, making them difficult to implement on-site at any time.

[0004] Therefore, for example, Patent Document 1 discloses a method and system for determining three-dimensional hardness distribution that fully utilizes the indentation test method. The indentation test method refers to a quasi-non-destructive testing method that evaluates the residual stress distribution in the depth direction of a specimen based on the load-displacement curve when a pyramidal indenter or a ball indenter is pressed into the specimen surface. Figure 11 The image schematically shows a longitudinal sectional view of the sample surface with the pyramidal indenter pressed in. Additionally, in... Figure 12 The figure shows the relationship between the indentation load L (vertical axis) and the indentation depth h (horizontal axis) from the start of the indentation test to the unloading. 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 coefficient in the case of approximating this quadratic function is the indentation load coefficient (i.e., L / h). 2 In areas with shallow indentation depth, the influence of the processed altered layer, whether hardened or softened, decreases as the indentation depth h increases. Furthermore, it is known that if the pyramidal indenter is pressed deeply, the influence of the processed altered layer diminishes from a certain depth onwards, and the indentation load coefficient becomes approximately constant. Therefore, the depth of the processed altered layer can be determined based on the change in the indentation load coefficient.

[0005] However, for example, in a general indentation test method such as the Instrumented Indentation Technique (ITT) 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, sometimes deep indentations exceeding a required level remain on the surface of the workpiece. For example, as Figure 11 shown, it is a case where a pyramidal indenter is pressed in 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 it is determined whether finishing is required based on the depth, if there are indentations deeper than the removal amount in the finishing process, it may be impossible to perform finishing and the workpiece may be treated as a defective product. In addition, in a general indentation test method (or IIT), it is difficult to adjust the position and phase of the indenter used for indentation, so it is difficult to perform an indentation test during the machining process of a machined component.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-858{04}

[0009] Non-Patent Documents

[0010] Non-Patent Document 1: Shuhei Hikawa, Naruki Okano, Masato Mochizuki, Kyoichi Hashimoto, Ryo Tezuka, "Evaluation of Machined Affected Layer Depth by Indentation Method and Examination of Its Applicability to Curved Surface Shape", Abstracts of Presentations at the Welding Society of Japan National Convention, Vol. 112, The Welding Society of Japan, April 2023, P. 166-167

[0011] Non-Patent Document 2: Naruki Okano, Masato Mochizuki, "Proposal of a Quasi-Nondestructive Measurement Method for Non-Equibiaxial Residual Stress Field by Indentation Method Independent of Reference Hardness under Zero Stress", Transactions of the Japan Society of Mechanical Engineers, Vol. 80, No. 820, The Japan Society of Mechanical Engineers, 2014, P. 1-11 Summary of the Invention

[0012] Problems to be Solved by the Invention

[0013] In view of the above circumstances, an object of the present invention is to provide a method for measuring the machined affected layer of a workpiece, a method for machining a workpiece, a machined affected layer measuring device, and a machine tool that can easily evaluate the state of the machined affected layer of the machined surface of the workpiece on a machine tool.

[0014] Solutions to the Problems

[0015] According to one aspect of the present invention, a method for measuring the machining alteration layer of a workpiece is provided. The method involves measuring the machining alteration layer on the surface of the workpiece on a machine tool that uses a tool mounted on a spindle to machine a workpiece mounted on a worktable. The method includes: replacing the tool by mounting a pressure head for pressing into the workpiece onto the spindle; pressing the pressure head into the workpiece using the machine tool's feed device; measuring in real-time the pressing load and the pressing depth of the pressure head into the workpiece; calculating in real-time a pressing load coefficient, which is a coefficient used to approximate the pressing load as a function of the pressing depth; stopping the pressing of the pressure head into the workpiece when the rate of change of the pressing load coefficient relative to the pressing depth changes from a negative value to a value sufficiently close to 0; and calculating the depth of the machining alteration layer by multiplying the pressing depth of the pressure head at the point where pressing has stopped by a depth conversion constant.

[0016] Furthermore, according to one aspect of the present invention, a method for machining a workpiece is provided, which involves rough machining of a workpiece mounted on a machine tool table using a tool mounted on a spindle, measuring the surface alteration layer of the workpiece on the machine tool, and performing finish machining after measuring the alteration layer. The method includes: after rough machining, replacing the tool and mounting a pressure head for pressing into the workpiece on the spindle; pressing the pressure head into the workpiece using the machine tool's feed device; measuring in real-time the pressing load and the pressing depth of the pressure head into the workpiece; calculating in real-time a pressing load coefficient, which is a coefficient used to approximate the pressing load as a function of the pressing depth; stopping the pressing of the pressure head into the workpiece when the rate of change of the pressing load coefficient relative to the pressing depth changes from a negative value to a value sufficiently close to 0; calculating the depth of the altered layer by multiplying the pressing depth of the pressure head at the point where pressing has stopped by a depth conversion factor; and performing finish machining if the calculated depth of the altered layer is less than the finishing allowance of the workpiece.

[0017] In addition, according to one aspect of the present invention, a machine tool is provided for measuring the surface modification layer of a workpiece by using a tool mounted on a spindle to machine a workpiece mounted on a worktable. The machine tool includes: a pressure head, which can be replaced by a tool and mounted on the spindle, and forms an indentation by pressing it into the workpiece using the machine tool's feed device; a pressure load detector, which measures the real-time pressure load of the pressure head relative to the workpiece; a pressure depth detector, which measures the real-time pressure depth of the pressure head into the workpiece; a pressure head pressure stop control unit, which calculates in real-time a pressure load coefficient as a coefficient when the pressure load is approximated as a function of the pressure depth, and stops pressing the pressure head into the workpiece when the rate of change of the pressure load coefficient relative to the pressure depth changes from a negative value to a value sufficiently close to 0; and a modified layer depth calculation unit, which calculates the modified layer depth by multiplying the pressure depth at which the pressure head pressure is stopped by a depth conversion constant.

[0018] Furthermore, according to one aspect of the present invention, a processing altered layer measuring device is provided, which is attached to a machine tool that processes a workpiece mounted on a worktable using a tool mounted on a spindle, and measures the processing altered layer on the surface of the workpiece on the machine tool. The processing altered layer measuring device comprises: an indenter, which can be replaced by a tool and mounted on the spindle, and forms an indentation by pressing it into the workpiece using the machine tool's feed device; an indenter holder, which detachably holds the indenter and has a sensor for detecting the indentation load of the indenter relative to the workpiece; and a computing unit, which can be connected to the machine tool's control device to calculate in real time an indentation load coefficient, which is a coefficient used to approximate the indentation load as a function of the indentation depth; when the rate of change of the indentation load coefficient relative to the indentation depth changes from a negative value to a value sufficiently close to 0, stopping the indenter from pressing into the workpiece; and multiplying the indentation depth at which the indenter stops pressing by a depth conversion constant to calculate the processing altered layer depth.

[0019] The effects of the invention

[0020] According to one aspect of the present invention, a method for measuring the machined altered layer of a workpiece involves pressing a pressure head, fitted with a replacement tool and mounted on the spindle, into the workpiece using a machine tool's feed device. The pressing load and the depth of the pressure head into the workpiece can be measured in real time. Therefore, on a machine tool, the machined altered layer on the workpiece surface can be measured based on adjustments to the position and phase of the pressure head relative to the workpiece, allowing for easy evaluation of the state of the machined altered layer. Furthermore, when the rate of change of the coefficient (i.e., the pressure load coefficient) used to approximate the measured pressure load using the pressing depth changes from a negative value to a value sufficiently close to 0—that is, when the influence of the machined altered layer on the pressing load decreases—the pressing of the pressure head into the workpiece is stopped, and the depth of the machined altered layer can be calculated by multiplying the depth of the pressure head at the point of cessation by a depth conversion constant. Thus, without using a dedicated indentation measuring device and without removing the workpiece from the machine tool, the measurement and evaluation of the machined altered layer of a workpiece can be performed easily and quickly using the existing mechanical structure of the machine tool.

[0021] According to one aspect of the workpiece machining method of the present invention, after rough machining, a pressure head, fitted with a replacement tool and mounted on the spindle, is pressed into the workpiece using the machine tool's feed device. The pressing load and the pressing depth of the pressure head into the workpiece can be measured in real time. Therefore, on the machine tool, the surface of the workpiece can be measured based on adjustments to the position and phase of the pressure head relative to the workpiece, and the state of the surface of the surface of the surface of the surface of the workpiece can be easily evaluated. Furthermore, when the rate of change of the coefficient (i.e., the pressing load coefficient) when approximating the measured pressing load by the pressing depth changes from a negative value to a value sufficiently close to 0, that is, when the influence of the surface ... This reduces the probability of a workpiece being rejected, and finishing is only performed when the calculated depth of the altered layer is less than the finishing allowance of the workpiece, thus eliminating the need for unnecessary finishing.

[0022] According to one aspect of the machine tool, a press head, which is mounted on the spindle and has a replacement tool, is pressed into a workpiece using the machine tool's feed device. The press load detector and the press depth detector can be used to measure the press load on the press head and the press depth into the workpiece in real time. Therefore, on the machine tool, the surface of the workpiece can be measured based on adjustments to the position and phase of the press head relative to the workpiece, and the state of the surface ... This reduces the probability of a workpiece being classified as a defective product.

[0023] According to one aspect of the present invention, a machining alteration layer measuring apparatus includes: an indenter, which can be replaced by a tool and mounted on a spindle, and forms an indentation by pressing it into a workpiece using a machine tool's feed device; and a tool holder, which is detachably mounted on the indenter and has a sensor for detecting the pressing load of the indenter relative to the workpiece. Therefore, on a machine tool, the machining alteration layer on the surface of the workpiece can be measured based on adjustments to the position and phase of the indenter relative to the workpiece, and the state of the machining alteration layer can be easily evaluated. Furthermore, since it includes a computing device that can be connected to the machine tool's control device, it can calculate in real time the pressing load coefficient, which is a coefficient when the pressing load is approximated as a function of the pressing depth. When the rate of change of the pressing load coefficient relative to the pressing depth changes from a negative value to a value sufficiently close to 0, the pressing of the indenter into the workpiece is stopped, and the depth of the machining alteration layer is calculated by multiplying the pressing depth at which the pressing of the indenter is stopped by a depth conversion constant. Thus, a function that allows for easy measurement of the machining alteration layer of a workpiece on a conventional machine tool, even for machine tools that do not implement the machining alteration layer measurement method of the present invention, can be added. Attached Figure Description

[0024] Figure 1 This is a side view of the machine tool according to this embodiment.

[0025] Figure 2 This is a side view of a machine tool in which the pressure head is pressed into the workpiece.

[0026] Figure 3 express Figure 2 Enlarged view of the workpiece and the pressure head.

[0027] Figure 4 This is an enlarged view showing the situation where the pressure head is tilted and pressed into the workpiece.

[0028] Figure 5 A cross-sectional view showing the processed altered layer on the surface of the workpiece being pressed into the indenter.

[0029] Figure 6 A graph showing the relationship between the indentation load, the indentation load factor, and the rate of change of the indentation load factor and the indentation depth is shown.

[0030] Figure 7 The time series representing the time variation of the indented load is shown.

[0031] Figure 8 This refers to the surface of the workpiece after it has been pressed into the Vickers pyramid indenter and the Knoop pyramid indenter.

[0032] Figure 9 An explanatory diagram showing the machining process of a workpiece that includes an indentation test.

[0033] Figure 10A flowchart showing the processing steps of a workpiece that includes an indentation test.

[0034] Figure 11 This is a cross-sectional view of the sample surface in a conventional indentation test where a pyramidal indenter is pressed in.

[0035] Figure 12 A graph showing the relationship between the indentation load and the indentation depth from the start of load application to the unloading in the indentation test method is presented. Detailed Implementation

[0036] Hereinafter, the machine tool according to the embodiments will be described with reference to the accompanying drawings. The same or corresponding elements will be labeled with the same reference numerals, and repeated descriptions will be omitted. For ease of understanding, the scale of the drawings may sometimes be changed for illustration.

[0037] exist Figure 1 The image shows a side view of the machine tool 10 according to this embodiment. The machine tool 10 includes a bed 12 that serves as a base and a column 14 erected on the upper surface of the bed 12. A fastener 50 (see reference 50) is disposed on the upper surface of the bed 12. Figure 9 A worktable 30, which serves as the workpiece W, is fixed in place. The worktable 30 can move on the bed 12 via a guide surface. Furthermore, a mechanical coordinate system, with a predetermined position as the origin, is pre-set in the machine tool 10, consisting of mutually orthogonal linear axes including the X-axis, Y-axis, and Z-axis. In this embodiment, the machine tool 10 is vertical, with the Z-axis extending vertically. The X-axis and Y-axis are set on a plane perpendicular to the Z-axis, which is horizontal in this case. In the machine tool 10, the worktable 30 is configured to move along the Y-axis direction (left-right direction). Additionally, the saddle 16, disposed on the front surface of the column 14, is configured to move along the X-axis direction (the direction perpendicular to the paper plane).

[0038] A spindle head 18 is arranged on the front surface of the saddle 16 in a manner that allows it to move up and down along the Z-axis (mechanical vertical direction). Furthermore, a spindle 20, configured to rotate relative to the spindle head 18 about an axis parallel to the Z-axis, is mounted on the front end side, specifically the lower side. A pressure head 42 or tools 62 and 64 (see reference) are used to process the workpiece W while rotating together with the spindle 20. Figure 9 The pressure head 42 or tool 62, 64 are mounted on the spindle 20 in a detachable manner via the pressure head holder 40 or tool holder 60. Thus, the machine tool 10 is configured such that the spindle 20, which is used to mount the pressure head 42 or tool 62, 64, and the worktable 30, which is used to hold the workpiece W, can move relative to each other along the X-axis, Y-axis, and Z-axis.

[0039] To enable the saddle 16 to move along the X-axis and the pressure head 42 or tools 62, 64 to move relative to the workpiece W along the X-axis, an X-axis feed device 22, serving as a feed device, is provided on the front surface of the column 14. Additionally, an X-axis position detection device 24 is provided on the column 14 to detect the position of the pressure head 42 or tools 62, 64 mounted on the spindle 20 in the X-axis direction.

[0040] To enable the worktable 30 to move along the Y-axis and the pressure head 42 or tools 62, 64 to move relative to the workpiece W along the Y-axis, a Y-axis feed device 32 is provided on the bed 12 as a feed device. Additionally, a Y-axis position detection device 34 is provided on the bed 12 for detecting the position of the worktable 30 with the workpiece W positioned thereon in the Y-axis direction.

[0041] To enable the spindle head 18 to move along the Z-axis and the pressure head 42 or tools 62, 64 to move relative to the workpiece W along the Z-axis, a Z-axis feed device 26 is provided on the saddle 16 as a feed device. Additionally, a Z-axis position detection device 28 is provided on the saddle 16 to detect the Z-axis position of the pressure head 42 or tools 62, 64 mounted on the spindle 20.

[0042] exist Figure 2 The diagram schematically shows a side view of the machine tool 10. Additionally, in... Figure 3 The figure shows an enlarged view of the workpiece W and the pressing head 42 pressed into it. The worktable 30 of the machine tool 10 in this figure is configured to rotate relative to the bed 12. Therefore, the tilt of the workpiece W can be adjusted so that the normal direction of the surface of the workpiece W is aligned with the axial direction of the pressing head 42, allowing the pressing head 42 to be pressed in perpendicularly relative to the workpiece W. Thus, even if the surface of the workpiece W is curved or inclined, the pressing head 42 can be pressed in perpendicularly relative to the workpiece W.

[0043] It should be noted that this description focuses on the case where the pressure head 42 is pressed perpendicularly to the workpiece W by rotating the worktable 30, but it is not limited to this. Figure 4 As shown, it can also be configured such that the main shaft can be tilted relative to the workpiece W, and the pressure head 42 is pressed perpendicularly into the workpiece W by tilting the pressure head 42 relative to the workpiece W.

[0044] like Figure 1As shown, the machine tool 10 includes an NC control unit 36 ​​as a control device. This NC control unit 36 ​​executes an NC program stored in the NC program storage unit 36a to operate the feed devices 22, 32, and 26 of each axis—namely, the X-axis feed device 22, the Y-axis feed device 32, and the Z-axis feed device 26—to move the pressure head 42 or the worktable 30 to a desired position. Therefore, the pressure head 42 mounted on the spindle 20 can be pressed into a predetermined position on the workpiece W. Furthermore, the NC control unit 36 ​​is configured to rotate the spindle 20 and tools 62 and 64 to operate the spindle 20, enabling the workpiece W to be machined using the tools 62 and 64 mounted on the spindle 20. Furthermore, the machine tool 10 has a tool magazine 44 for storing pressure heads 42 and tools 62, 64, configured such that, depending on the content of the operation performed to make the spindle 20 work, namely the determination of the modified layer WL or machining, the pressure head 42 or tools 62, 64 taken out from the tool magazine 44 can be attached to or detached from the spindle 20.

[0045] Additionally, the machine tool 10 includes a computing unit 38, which serves as a processing altered layer measuring device. This computing unit 38 is used to measure and evaluate the processing altered layer WL of the workpiece W. The computing unit 38 is configured to be electrically connected to the X-axis position detection device 24, the Y-axis position detection device 34, and the Z-axis position detection device 28, and is capable of acquiring the position information detected by them. The X-axis and Y-axis position information represent the coordinate values ​​of pressing the pressure head 42 relative to the workpiece W, and the Z-axis position information represents the coordinate values ​​corresponding to the pressing depth h of the pressure head 42.

[0046] A load sensor 46, serving as a press-in load detector, is configured on the spindle head 18. This load sensor 46 is used to detect the load, i.e., the press-in load L, applied to the press head 42 by pressing it into the workpiece W (see reference). Figure 6 The load sensor 46 is electrically connected to the arithmetic unit 38, which is configured to record the indented load L detected by the load sensor 46. It should be noted that the following description focuses on the case where the load sensor 46 is located on the spindle head 18, but it is not limited to this configuration; the load sensor can be located either within the tool holder or on the worktable.

[0047] exist Figure 5 The diagram schematically shows a cross-sectional view of the workpiece W being pressed into the modified layer WL by the pressure head 42. Additionally, in Figure 6The diagram illustrates an example of how the indentation load L, the indentation load coefficient C, and the rate of change of the indentation load coefficient C (dC / dh) are represented relative to the indentation depth h. When the indenter 42 is pressed into the modified layer WL, the indentation depth h and the indentation load L are detected in real time using the indentation depth detection unit 38a and the load sensor 46, and these are recorded in the calculation unit 38. The calculation unit 38 includes a stop control unit 38b, which acts as a stop control component for the indenter indentation. The stop control unit 38b approximates the indentation load L measured up to that point in time using a quadratic function of the indentation depth h, and calculates in real time the coefficient of the approximate quadratic function, i.e., the indentation load coefficient C (= L / h). 2 Furthermore, the rate of change (dC / dh) of the indentation load coefficient C relative to the indentation depth h is calculated in real time.

[0048] The indentation load coefficient C decreases immediately after the indenter 42 is pressed in due to the influence of the processed altered layer WL. As the indenter 42 is pressed to a certain depth, the influence of the processed altered layer WL diminishes, thus becoming a constant value. The indentation depth h to which the influence of the processed altered layer WL diminishes further decreases... s At this time, the indentation load coefficient C relative to the indentation depth h becomes a constant value C. S Therefore, the rate of change of the pressing load coefficient C (dC / dh) changes from a negative value 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 pressing of the pressing head 42. In reality, the rate of change of the pressing load coefficient C sometimes does not strictly converge to 0, and the pressing of the pressing head 42 can be stopped when it becomes a predetermined value sufficiently close to 0.

[0049] The arithmetic unit 38 includes a depth calculation unit 38c, which serves as a depth calculation component for processing the modified layer. The depth calculation unit 38c multiplies a pre-recorded depth conversion constant by the indentation depth h at the indentation time of the stop indenter 42. s The depth Z of the processed metamorphic layer is calculated. It can be assumed that the indentation load L is affected by approximately 7 times the indentation depth h, and the indentation load coefficient C is a representative value at half the indentation depth h (Non-Patent Document 1). Therefore, here, the indentation depth h at the stopping time point... s The depth conversion constant for multiplication is set to 3.5. It should be noted that while the depth conversion constant is set to 3.5 here, it varies depending on the shape of the indenter, and therefore different values ​​can be used.

[0050] The machine tool 10 includes a display device 52 connected to the arithmetic unit 38 for displaying the calculated machining altered layer depth Z. This allows the user to visually confirm that the calculated machining altered layer depth Z is smaller than the finishing allowance of the workpiece W, enabling finishing. Furthermore, the arithmetic unit 38 is configured to operate the machine tool 10 such that if the calculated machining altered layer depth Z is less than the finishing allowance of the workpiece W, finishing is initiated; and if the calculated machining altered layer depth Z is greater than the finishing allowance of the workpiece W, machining of the workpiece W is stopped.

[0051] exist Figure 7 The figure shows a time series representing the time variation of the indentation load L, dL. As mentioned earlier, the indentation load coefficient C (=L / h) 2 The pressing load L is calculated by approximating it using a quadratic function of the pressing depth h. Therefore, based on stabilizing and improving the measurement accuracy of the pressing load L and the pressing depth h, it is preferable to press the indenter 42 into the surface of the workpiece W and take the actual time point at which the pressing depth h is generated as the loading start point of the pressing load L. Therefore, the calculation device 38 is configured to calculate the moving average of the recorded real-time time change dL of the pressing load L, and set the time point SP that exceeds a predetermined threshold TV that can be judged as having generated a meaningful pressing depth h as the loading start point of the pressing load L and the position where the pressing depth h = 0.

[0052] In addition to measuring the modified layer WL, the machine tool 10 equipped with the computing device 38 can also measure non-uniform biaxial stress using an indentation method that does not rely on the reference hardness under stress-free conditions. Specifically, the indenter can use a Vickers pyramid indenter VI with a predetermined apex and a square base, and a Knoop pyramid indenter NI with a predetermined apex and a rhomboid base having a major axis LA and a minor axis SA, to measure the indentation load L and indentation depth h. First, before machining the workpiece W, the Vickers pyramid indenter VI and the Knoop pyramid indenter NI, mounted on the spindle 20 of the machine tool 10, are pressed into a stress-free reference test piece (not shown) made of the same material as the workpiece W, thereby measuring the indentation load L and indentation depth h respectively. Based on the measured indentation load L and indentation depth h, the indentation load ratio η of the Knoop indenter NI at the same indentation depth h relative to the indentation load L of the Vickers indenter VI is calculated.

[0053] Next, as Figure 8As shown, using the axis feed devices 22, 32, 26 of the machine tool 10, the Knoop pyramid indenter NI with the long axis LA of the bottom surface facing the first direction, i.e., the X-axis direction, is pressed into the workpiece W, thereby measuring the indentation depth h of the Knoop pyramid indenter NI into the workpiece W and the first indentation load L1. Further, using the axis feed devices 22, 32, 26 of the machine tool 10, the Knoop pyramid indenter NI with the long axis LA of the bottom surface facing the Y-axis direction, which is the second direction orthogonal to the X-axis direction, is pressed into the workpiece W, thereby measuring the indentation depth h of the Knoop pyramid indenter NI into the workpiece W and the second indentation load L2. In addition, using the axis feed devices 22, 26, 32 of the machine tool 10, the Vickers pyramid indenter VI is pressed into the workpiece W, thereby measuring the indentation depth h of the Vickers pyramid indenter VI into the workpiece W and the third indentation load L3 for pressing the Vickers pyramid indenter VI. Here, the method of changing the phase of the Knoop pyramid indenter NI by 90 degrees is performed using the indexing positioning function of the spindle 20 or the indexing positioning function of the worktable 30.

[0054] The arithmetic unit 38 can calculate the first residual stress in the X-axis direction, i.e., the X-axis stress σ, at each indentation depth h through the following calculation formula based on 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. x and the second residual stress in the Y-axis direction, i.e., the Y-axis stress σ Y .

[0055]

[0056] Here, α1 represents the conversion coefficient of the stress value and the load change amount when the long axis LA direction of the Knoop indenter NI is pressed in parallel with the stress direction, α2 represents the conversion coefficient of the stress value and the load change amount when the long axis LA direction of the Knoop indenter NI is pressed in perpendicular to the stress direction, and α3 represents the conversion coefficient of the stress value and the load change amount when the Vickers indenter VI is pressed in. They are constants determined by the material of the workpiece W. If the residual stresses σ x , σ Y calculated in this way are positive values, a compressive force acts at the measurement point, and the risk of fracture of the workpiece material is small, and the workpiece W is a qualified product. On the other hand, if it is a negative value, a tensile force acts at the measurement point, and there is a risk that the workpiece material fractures starting from a certain defect, and the workpiece is a non-qualified product. It should be noted that here, the Vickers pyramid indenter VI and the Knoop pyramid indenter NI with a predetermined apex angle are described, but it is not limited thereto, and a pyramid indenter with a square bottom surface and a pyramid indenter with a rhombus bottom surface without a predetermined apex angle can also be used. In this case, the various coefficients of the above calculation formula change.

[0057] Hereinafter, by following Figure 9 and Figure 10The explanatory diagrams and flowcharts shown illustrate the processing steps of the workpiece W, including the pressing test, and explain the method for measuring the processed altered layer WL of the workpiece W in this embodiment, the processing method of the workpiece W, the operation of the computing device 38, and the effects of the machine tool 10.

[0058] First, proceed to step S510, where the workpiece W is rough-machined using a roughing tool 62 mounted on the spindle 20 via a tool holder 60. At the end of the roughing process, proceed to step S520, where an indentation test is performed to measure the machining alteration layer WL generated on the machined surface of the workpiece W.

[0059] At the start of the pressing test, proceed to step S10, where tool 62 is replaced and the pressing head 42, which is attached to the pressing head holder 40 taken from the tool magazine 44, is installed on the spindle 20. Here, as an example, a Knoop pyramid pressing head NI is used as the pressing head 42. When the pressing head 42 is installed on the spindle 20, proceed to step S20, where the axis feed devices 22, 32, and 26 are activated to move the pressing head 42 to the position for pressing into the workpiece W, and the tilt of the worktable 30 is adjusted so that the axial direction of the pressing head 42 is aligned with the normal direction of the surface of the workpiece W. After these adjustments are completed, proceed to step S30, where the phase of the spindle 20 is derived and adjusted. When measuring the first pressing load L1 using the Knoop pyramid pressing head NI, the phase is adjusted so that the long axis LA is parallel to the X-axis direction. Furthermore, when measuring the second pressing load L2, the phase is adjusted so that the long axis LA is parallel to the Y-axis direction. When the phase adjustment is completed, proceed to step S40, so that the spindle 20 with the pressure head 42 is lowered toward the workpiece W at a predetermined approach speed, and proceed to step S50.

[0060] In step S50, the load sensor 46 is activated to begin measuring the indentation load L. The computing unit 38 calculates the moving average of the recorded real-time time change dL of the indentation load L, and takes the time point SP that exceeds a predetermined threshold TV that can be determined to have produced a meaningful indentation depth h as the loading start point of the indentation load L and the measurement start point of the indentation depth h, and proceeds to step S60.

[0061] In step S60, when the indenter 42 is pressed into the modified layer WL, the indentation depth h and the indentation load L are detected in real time using the indentation depth detection unit 38a and the load sensor 46. The calculation unit 38 records these detected data, and the stop control unit 38b approximates the indentation load L measured up to that time point using a quadratic function of the indentation depth h, and calculates the coefficient of the quadratic function, i.e., the indentation load coefficient C (= L / h), in real time. 2Furthermore, the stop control unit 38b calculates in real time the rate of change (dC / dh) of the indentation load coefficient C relative to the indentation depth h. The effect of the indenter 42 being pressed into the modified layer WL at an indentation depth h becomes smaller. s Thus, the pressure load factor C becomes a constant value C. S When the rate of change of the indentation load coefficient C (dC / dh) changes from a negative value to a predetermined value that is sufficiently close to 0, the stop control unit 38b, via the NC control unit 36, stops the descent of the spindle 20, thereby stopping the indentation of the indenter 42. The depth calculation unit 38c multiplies the pre-recorded depth conversion constant by the indentation depth h at the time point at which the indenter 42 stops indenting. s The depth of the modified layer Z is calculated. Once the depth of the modified layer Z is calculated, the process moves to step S80, where the spindle 20 is raised to pull the pressure head 42 out of the workpiece W.

[0062] When the indenter 42 is pulled out, the process proceeds to step S90. If the measurement of either the first indentation load L1 or the second indentation load L2 is not yet completed when the Knoop pyramid indenter NI is used as the indenter 42, the process proceeds to step S30, where the phase of the spindle 20 is changed, and the measurement of either the first indentation load L1 or the second indentation load L2 is measured. If the measurement of both the first indentation load L1 and the second indentation load L2 using the Knoop pyramid indenter NI is completed, and the Vickers pyramid indenter VI is used as the indenter 42, the process proceeds to step S100.

[0063] Proceeding to step S100, if the measurement using the Knoop pyramid indenter NI or the Vickers pyramid indenter VI is not yet complete, proceeding to step S10, the Knoop pyramid indenter NI or the Vickers pyramid indenter VI used for measurement is retrieved from the tool magazine 44, and the indenter 42 mounted on the spindle 20 is replaced. When the indenter 42 is replaced, the indentation load L from step S20 to step S70 is measured using this indenter 42. When the measurement using both the Knoop pyramid indenter NI and the Vickers pyramid indenter VI is completed, proceeding to step S110, the calculation unit 38 calculates and assigns the measured and calculated processed modified layer depth Z, indentation load ratio η, first indentation load L1, second indentation load L2, third indentation load L3, and the first residual stress in the X-axis direction (i.e., X-axis stress σ) at each indentation depth h. x The second residual stress in the Y-axis direction, i.e., the Y-axis stress σ Y Output to display device 52.

[0064] At the end of the pressing test, the process proceeds to step 530. If the calculated depth of the modified layer Z is less than the finishing allowance of the workpiece W, the calculation device 38 proceeds to step S550, whereby the machine tool 10 is activated, and the press head 42 is replaced with a finishing tool 64 for finishing. On the other hand, if the calculated depth of the modified layer Z is greater than the finishing allowance of the workpiece W, the process proceeds to step S540, and the finishing of the workpiece W is stopped.

[0065] The method for measuring the machined altered layer WL of workpiece W, the machining method of workpiece W, the computing device 38, and the machine tool 10 according to this embodiment include: a pressure head 42, which can replace tools 62 and 64 and is mounted on the spindle 20, and forms an indentation by pressing it into the workpiece W using the axis feed devices 22, 32, and 26 of the machine tool 10 equipped with an axis position detection device; and a load sensor 46, which detects the pressing load L of the pressure head 42 relative to the workpiece W. Therefore, on the machine tool 10, the machined altered layer WL of the surface of the workpiece W can be measured based on adjusting the position and phase of the pressure head 42 relative to the workpiece W, and the state of the machined altered layer WL can be easily evaluated. Furthermore, since it is equipped with a computing device 38 that can be connected to the NC control unit 36 ​​of the machine tool 10, it can calculate in real time the pressing load coefficient C, which is a coefficient when the pressing load L is approximated by a function of the pressing depth h. When the rate of change of the pressing load coefficient C with respect to the pressing depth h (dC / dh) changes from a negative value to a value that is sufficiently close to 0, the pressing head 42 is stopped pressing into the workpiece W. S The depth Z of the processed altered layer is calculated by multiplying by a depth conversion constant. Therefore, unlike previous indentation test methods, the depth Z of the processed altered layer can be calculated without applying load to the workpiece W before reaching a predetermined indentation depth or indentation load value. This reduces the probability of the workpiece W being deemed a defective product during the determination and evaluation of the processed altered layer WL.

[0066] Furthermore, according to the method for measuring the modified layer WL of workpiece W, the processing method of workpiece W, the computing device 38, and the machine tool 10 of this embodiment, the worktable 30 of the machine tool 10 is configured to rotate relative to the bed 12. Therefore, the tilt of workpiece W can be adjusted so that the normal direction of the surface of workpiece W is aligned with the axial direction of the indenter 42, and the indenter 42 can be pressed in perpendicularly relative to workpiece W. Thus, even if the surface of workpiece W is curved or inclined, the indenter 42 can be pressed in perpendicularly relative to workpiece W, and the pressing load L and the pressing depth h can be measured with good accuracy.

[0067] Furthermore, according to the method for measuring the modified layer WL of the workpiece W, the processing method of the workpiece W, the computing device 38, and the machine tool 10 of this embodiment, the computing device 38 is configured to: calculate the moving average of the recorded real-time time change dL of the indentation load L, and take the time point SP that exceeds a predetermined threshold TV that can be judged as having generated a meaningful indentation depth h as the loading start point of the indentation load L. Therefore, when the indenter 42 is pressed into the surface of the workpiece W, the time point at which the actual indentation depth h is generated can be taken as the loading start point of the indentation load L, and the measurement accuracy of the indentation load L, and even the accuracy of the rate of change (dC / dh) of the indentation load coefficient C, can be stabilized and improved.

[0068] Furthermore, according to the method for measuring the modified 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 modified layer WL, it is also possible to calculate the indentation load ratio η, the first indentation load L1, the second indentation load L2, the third indentation load L3, and the first residual stress in the X-axis direction at each indentation depth h, i.e., the X-axis stress σ. x And the second residual stress in the Y-axis direction, i.e., the Y-axis stress σ Y Therefore, the stress within the processed metamorphic layer WL can be evaluated together with the calculation of the processed metamorphic layer depth Z.

[0069] Based on the above, the method for measuring the modified layer WL of the workpiece W, the method for processing the workpiece W, the computing device 38, and the machine tool 10 of this embodiment can easily evaluate the state of the modified layer WL of the processed surface of the workpiece W on the machine tool 10.

[0070] An apparatus for measuring the machining altered layer using a conventional machine tool that does not integrate the load sensor 46 into the spindle head 18 and does not consider the measurement of the machining altered layer will be described. In this case, a load sensor for measuring the indentation load L can be installed inside the indenter holder 40. Furthermore, a general-purpose personal computer is used as the computing device, and the indentation depth detection unit 38a, stop control unit 38b, and depth calculation unit 38c are installed as application software on this personal computer. The personal computer is then connected to the user interface of the machine tool's NC device. By installing this machining altered layer measuring apparatus on a conventional machine tool, the aforementioned method for measuring the machining altered layer and the workpiece machining method can be implemented, thereby enabling the application of… Figure 1 It has the same functions as machine tool 10. That is, the processing modified layer measuring device can be said to be a processing modified layer measuring kit that encapsulates various indenters, indenter holders with built-in load sensors, personal computers and application software that can be connected to the machine tool's control device.

[0071] The above describes the method for measuring the modified layer WL of workpiece W, the method for machining workpiece W, the computing device 38, and the implementation of the machine tool 10. However, the present invention is not limited to the above-described embodiments. For example, instead of a vertical machine tool with a vertical spindle orientation, a horizontal machine tool with a horizontal spindle orientation may be used. In addition to the above, it should be understood by those skilled in the art that various modifications of the above-described embodiments are possible.

[0072] Explanation of reference numerals in the attached figures

[0073] 10. Machine tool; 20. Spindle; 22. X-axis feed device; 26. Z-axis feed device; 32. Y-axis feed device; 36. NC control unit; 38. Calculation unit (machined modified layer measuring device); 38a. Indentation depth detection unit; 38b. Stop control unit (indenter head indentation stop control component); 38c. Depth calculation unit (machined modified layer depth calculation component); 42. Indenter head; 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 pyramid indenter head; VI. Vickers pyramid indenter head; WL. Machined modified layer.

Claims

1. A method of measuring a machined modified layer of a workpiece, the method of measuring the machined modified layer of the workpiece being characterized by comprising: replacing a tool with a press head for pressing into the workpiece attached to a main shaft; pressing the press head into the workpiece using a feed device of a machine tool; measuring a press-in load for pressing in the press head and a press-in depth of the press head into the workpiece in real time; calculating a press-in load coefficient as a coefficient when the press-in load is functionally approximated by the press-in depth in real time; stopping the press head from being pressed into the workpiece when a rate of change of the press-in load coefficient with respect to the press-in depth becomes a value sufficiently close to 0 from a negative value; and calculating a machined modified layer depth by multiplying the press-in depth of the press head at the time of stopping the press-in by a depth conversion constant.

2. The method of measuring the machined modified layer of the workpiece according to claim 1, wherein the press head is pressed in along a normal direction of a surface of the workpiece.

3. The method of measuring the machined modified layer of the workpiece according to claim 1, wherein, with respect to the press-in load measured when the press head is pressed in, a time point at which a moving average value of an amount of change of the press-in load in real time exceeds a predetermined threshold value is taken as a load start point of the press-in load.

4. The method of measuring the machined modified layer of the workpiece according to any one of claims 1 to 3, wherein the press head is provided as a square-based pyramid press head or a rhombic-based pyramid press head having a long axis and a short axis of a base surface, the method of measuring the machined modified layer comprises: before machining of the workpiece, pressing the square-based pyramid press head and the rhombic-based pyramid press head into a reference test piece in a stress-free state made of the same material kind as the workpiece using the feed device of the machine tool, thereby measuring a press-in load and a press-in depth, and calculating a press-in load ratio of the rhombic-based pyramid press head with respect to the square-based pyramid press head at the same press-in depth; pressing the rhombic-based pyramid press head having the long axis of the base surface oriented in a first direction into the workpiece using the feed device of the machine tool, thereby measuring a press-in depth of the rhombic-based pyramid press head into the workpiece and a first press-in load for pressing in the rhombic-based pyramid press head; pressing the rhombic-based pyramid press head having the long axis of the base surface oriented in a second direction orthogonal to the first direction into the workpiece using the feed device of the machine tool, thereby measuring a press-in depth of the rhombic-based pyramid press head into the workpiece and a second press-in load for pressing in the rhombic-based pyramid press head; and pressing the square-based pyramid press head into the workpiece using the feed device of the machine tool, thereby measuring a press-in depth of the square-based pyramid press head into the workpiece and a third press-in load for pressing in the square-based pyramid press head. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The first residual stress in the first direction and the second residual stress in the second direction at each indentation depth are calculated based on the indentation load ratio, the first indentation load, the second indentation load, and the third indentation load.

5. A workpiece processing method of performing a measurement of a processing modification layer of a surface of a workpiece after rough processing of the workpiece mounted on a table of a machine tool is performed using a tool attached to a spindle of the machine tool, and performing finish processing after the measurement of the processing modification layer, the workpiece processing method characterized by comprising: replacing the tool after the rough processing, and attaching a presser for indenting the workpiece to the spindle; indenting the presser into the workpiece using a feed device of the machine tool; measuring an indentation load for indenting the presser and an indentation depth of the presser into the workpiece in real time; calculating an indentation load coefficient as a coefficient when the indentation load is functionally approximated by the indentation depth in real time; stopping the indentation of the presser into the workpiece when a rate of change of the indentation load coefficient with respect to the indentation depth becomes a value sufficiently close to 0 from a negative value; calculating a processing modification layer depth by multiplying the indentation depth of the presser at the time when the indentation is stopped by a depth conversion coefficient; and performing the finish processing when the calculated processing modification layer depth is smaller than a finish processing allowance of the workpiece.

6. A machine tool of performing a measurement of a processing modification layer of a surface of a workpiece mounted on a table after processing of the workpiece is performed using a tool attached to a spindle of the machine tool, the machine tool characterized by comprising: a presser capable of being attached to the spindle instead of the tool, and capable of forming an indentation by indenting into the workpiece using a feed device of the machine tool; an indentation load detector measuring a real-time indentation load of the presser with respect to the workpiece; an indentation depth detector measuring a real-time indentation depth of the presser into the workpiece; a presser indentation stop control means calculating an indentation load coefficient as a coefficient when the indentation load is functionally approximated by the indentation depth in real time, and stopping the indentation of the presser into the workpiece when a rate of change of the indentation load coefficient with respect to the indentation depth becomes a value sufficiently close to 0 from a negative value; and a processing modification layer depth operation means calculating a processing modification layer depth by multiplying the indentation depth of the presser at the time when the indentation is stopped by a depth conversion constant.

7. A processing modification layer measurement device attached to a machine tool of performing processing of a workpiece mounted on a table using a tool attached to a spindle of the machine tool, and performing a measurement of a processing modification layer of a surface of the workpiece on the machine tool, the processing modification layer measurement device characterized by comprising: a presser capable of being attached to the spindle instead of the tool, and capable of forming an indentation by indenting into the workpiece using a feed device of the machine tool; a presser holder mounting the presser in a detachable manner, and having a sensor detecting an indentation load of the presser with respect to the workpiece; and a presser indentation stop control means calculating an indentation load coefficient as a coefficient when the indentation load is functionally approximated by the indentation depth in real time, and stopping the indentation of the presser into the workpiece when a rate of change of the indentation load coefficient with respect to the indentation depth becomes a value sufficiently close to 0 from a negative value. ​ ​ An arithmetic device capable of being connected to a control device of the machine tool, calculates in real time a press-in load coefficient which is a coefficient when a function approximation of the press-in load by the press-in depth is performed, stops the press-in of the presser to the workpiece when a rate of change of the press-in load coefficient with respect to the press-in depth becomes a value sufficiently close to 0 from a negative value, and calculates a processing metamorphic layer depth by multiplying the press-in depth at the time when the press-in of the presser is stopped by a depth conversion constant.

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