Working machinery

Abstract

To provide a machine tool which can suppress the occurrence of chatter-vibration in a technique that performs cutting while vibrating a tool.SOLUTION: A machine tool 10 which cuts a cutting object W by moving the cutting object W and a tool 210 while relatively vibrating the cutting object and the tool by a movement mechanism and a vibration mechanism while rotating a main shaft 110 by a rotation mechanism 120 includes a control device C as recognition means which recognizes a correspondence between an amplitude ratio expressed by a phase difference of a locus waveform for each rotation of the main shaft 110 and A / F and the difficulty of occurrence of the chatter-vibration when a feeding amount of the tool 210 to the cutting object W by the movement mechanism per one rotation of the main shaft is F, and the amplitude of the locus waveform of the tool tip is A.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to machine tools. [Background technology]

[0002] Conventionally, a technique has been known in which cutting is performed while vibrating the tool (cutting tool) to break up chips into smaller pieces (see Patent Documents 1 and 2). This technique is sometimes called low-frequency vibration cutting.

[0003] Incidentally, it is known that machine tools can experience a phenomenon called "chatter vibration," in which unstable vibrations occur during the cutting of a workpiece. In conventional cutting techniques, research into the mechanism of chatter vibration has progressed, and methods for avoiding chatter vibration have been established to some extent.

[0004] However, in the low-frequency vibration cutting technology described above, research into the mechanism of chatter vibration generation is not sufficiently advanced, and methods for avoiding chatter vibration have not yet been fully established. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 5033929 [Patent Document 2] Patent No. 6416218 [Overview of the project] [Problems that the invention aims to solve]

[0006] The object of the present invention is to provide a machine tool that can suppress the generation of chatter vibration in a cutting technique that performs cutting while vibrating the tool. [Means for solving the problem]

[0007] To solve the above problems, the present invention employs the following means.

[0008] That is, the machine tool of the present invention is a spindle to which a workpiece to be machined is attached, a rotation mechanism for rotating the spindle, a tool for cutting the workpiece to be machined, a movement mechanism for relatively moving the spindle and the tool, a vibration mechanism for relatively vibrating the spindle and the tool in a direction parallel to the moving direction by the movement mechanism, and includes a machine tool that cuts the workpiece to be machined by relatively vibrating and moving the workpiece to be machined and the tool by the movement mechanism and the vibration mechanism while rotating the spindle by the rotation mechanism, when the feed amount of the tool with respect to the workpiece to be machined by the movement mechanism per one rotation of the spindle is F and the amplitude of the locus waveform of the tool tip is A, the phase difference of the locus waveform for each rotation of the spindle, and the correspondence between the amplitude ratio represented by A / F and the difficulty of generating chatter vibration Control device using A machine tool characterized by comprising

[0009] According to the present invention, The control device , the phase difference of the locus waveform for each rotation of the spindle, and the correspondence between the amplitude ratio represented by A / F and the difficulty of generating chatter vibration are provided. Thereby, it is possible to take measures to suppress the generation of chatter vibration. Using When the cutting width of the tool in the direction perpendicular to the moving direction with respect to the workpiece to be machined is defined as the cutting width,

[0010] when cutting the workpiece to be machined without relatively vibrating the spindle and the tool by the vibration mechanism, the lower limit value of the cutting width at which chatter vibration occurs is defined as a0, and the critical cutting width lower limit value which is the minimum value of a0 is defined as L, ​When cutting the object to be cut while relatively vibrating the main shaft and the tool by the vibration mechanism, the lower limit value of the cutting width at which chatter vibration occurs from the relationship between the phase difference and the amplitude ratio is a , , a lim When the critical cutting width lower limit value, which is the minimum value of, is set as sL, before The difficulty of occurrence of chatter vibration teeth, The magnification of sL / L = s As shown .

[0012] Let r be the ratio of the length of the idle running section to the length of the entire section of the trajectory of the tip of the tool during cutting aircut Let the specific cutting resistance in the moving direction of the tool be Ky [Pa], the frequency response function be Φ [m / N], the imaginary number be i, and the angular frequency of chatter vibration be ω c [rad / s], and defining that the dynamic displacement before the k -th rotation of the main shaft is reproduced as "k -th rotation delayed reproduction", and the ratio of the length of the section for cutting the pre - machined surface created before the k -th rotation of the main shaft to the length of the entire section of the trajectory of the tip of the tool during cutting is r k When the length of the section actually cutting the object to be cut in the entire section is 1, the normalized ratio of the k -th rotation delayed reproduction region is

Number

Number

[0013] before It is preferable to include display means for directly or indirectly displaying the correspondence relationship on a display device

[0014] Thereby, the operator can easily recognize the difficulty of occurrence of chatter vibration visually

[0015] The display means may display an image on the display device that maps the distribution of the difficulty in generating the chatter vibration onto a graph in which either the horizontal axis or the vertical axis is the phase difference and the other is the amplitude ratio.

[0016] Furthermore, it is equipped with input means for inputting data to directly or indirectly obtain the phase difference and the amplitude ratio, The display means may also preferably display on the display device the likelihood of the occurrence of chatter vibration, which is derived from the phase difference and amplitude ratio obtained based on the data input to the input means. be.

[0017] The system includes input means for inputting data to directly or indirectly obtain the phase difference and the amplitude ratio, before Based on the correspondence described above, it is preferable to provide a presentation means that evaluates the likelihood of chatter vibration occurring based on the phase difference and amplitude ratio obtained from the data input to the input means, and presents multiple sets of data that are close to the data input to the input means and are even less likely to cause chatter vibration.

[0018] This allows workers to easily set conditions that make chatter vibrations less likely to occur.

[0019] Furthermore, it is equipped with input means for inputting data to directly or indirectly obtain the phase difference and the amplitude ratio, before Based on the correspondence described above, it is also preferable to provide a correction means that evaluates the likelihood of chatter vibration occurring based on the phase difference and amplitude ratio obtained from the data input to the input means, and corrects the phase difference and amplitude ratio to make chatter vibration even less likely to occur under conditions close to the data input to the input means.

[0020] This allows machining to be performed under conditions that are close to those entered by the operator, and that are even less prone to chatter vibration.

[0021] The aforementioned moving mechanism is A first moving mechanism that moves the spindle and the tool relative to each other with respect to the axial direction of the spindle, It has a second moving mechanism that moves the main spindle and the tool relative to each other in a direction perpendicular to the axial direction, The vibration mechanism is A first vibration mechanism that causes the spindle and the tool to vibrate relative to each other with respect to the axial direction of the spindle, It has a second vibration mechanism that causes the main spindle and the tool to vibrate relative to each other in a direction perpendicular to the axial direction, A first cutting mode is characterized by rotating the spindle with the rotation mechanism while moving the workpiece and the tool while vibrating them relative to each other in the axial direction of the spindle using the first moving mechanism and the first vibrating mechanism, The present invention may include a second cutting mode in which, while the spindle is rotated by the rotation mechanism, the workpiece is cut by moving the workpiece and the tool while vibrating them relative to each other in a direction perpendicular to the axial direction using the second moving mechanism and the second vibrating mechanism.

[0022] Furthermore, the above configurations can be combined and adopted as much as possible. [Effects of the Invention]

[0023] As described above, according to the present invention, in a cutting technique that involves vibrating a tool, the occurrence of chatter vibration can be suppressed. [Brief explanation of the drawing]

[0024] [Figure 1] Figure 1 is a schematic diagram of a machine tool according to an embodiment of the present invention. [Figure 2] Figure 2 is an explanatory diagram of the operation of a machine tool according to an embodiment of the present invention in the first cutting mode. [Figure 3] Figure 3 is an explanatory diagram of the operation of a machine tool according to an embodiment of the present invention in the second cutting mode. [Figure 4] Figure 4 is an explanatory diagram of the cutting characteristics. [Figure 5] Figure 5 is an explanatory diagram illustrating how to recognize the likelihood of chatter vibration occurring. [Figure 6] Figure 6 shows an example of an image mapping the distribution of the difficulty in generating chatter vibrations. [Figure 7] Figure 7 is a flow chart of the operation control of a machine tool according to an embodiment of the present invention. [Figure 8] Figure 8 is an explanatory diagram of the formula for deriving the lower limit of the cutting width at which chatter vibration occurs. [Figure 9] Figure 9 is an explanatory diagram of the formula for deriving the lower limit of the cutting width at which chatter vibration occurs. [Figure 10] Figure 10 is an explanatory diagram of the formula for deriving the lower limit of the cutting width at which chatter vibration occurs. [Figure 11] Figure 11 is an explanatory diagram of the formula for deriving the lower limit of the cutting width at which chatter vibration occurs. [Figure 12] Figure 12 is an explanatory diagram of the formula for deriving the lower limit of the cutting width at which chatter vibration occurs. [Figure 13] Figure 13 is an explanatory diagram of the formula for deriving the lower limit of the cutting width at which chatter vibration occurs. [Figure 14] Figure 14 is a table listing the definitions of the symbols. [Figure 15] Figure 15 is a table listing the definitions of the symbols. [Modes for carrying out the invention]

[0025] The embodiments for carrying out this invention will be described in detail below with reference to the drawings, based on examples. However, unless otherwise specifically stated, the dimensions, materials, shapes, and relative arrangements of the components described in these embodiments are not intended to limit the scope of this invention to those components alone.

[0026] (Examples) A machine tool according to an embodiment of the present invention will be described with reference to Figures 1 to 13. In Figures 1 to 3 and 8, for the sake of explanation, the directions of three mutually orthogonal axes (X-axis, Y-axis, and Z-axis) are shown. The axis direction of the spindle 110 is the Z-axis, and the X-axis and Y-axis are mutually orthogonal and also orthogonal to the Z-axis.

[0027] <Machine tool configuration> Referring to Figure 1, the configuration of the machine tool 10 according to an embodiment of the present invention will be described. Figure 1 is a schematic diagram of the machine tool 10 according to an embodiment of the present invention, and is a diagram that simply shows the configuration of each part. The machine tool 10 comprises a spindle 110 to which the workpiece W is attached, a rotating mechanism 120 for rotating the spindle 110, and a tool (cutting tool) 210 for cutting the workpiece W. A chuck for holding the workpiece W is provided at the tip of the spindle 110. The rotating mechanism 120 can employ known technologies such as various motors.

[0028] Furthermore, the machine tool 10 is equipped with a moving mechanism for relatively moving the spindle 110 and the tool 210. The moving mechanism according to this embodiment has a first moving mechanism 130 and a second moving mechanism 220. The first moving mechanism 130 is a mechanism for relatively moving the spindle 110 and the tool 210 with respect to the axial direction of the spindle 110 (Z-axis direction). The second moving mechanism 220 is a mechanism for relatively moving the spindle 110 and the tool 210 with respect to a direction perpendicular to the Z-axis direction (X-axis direction). Various known technologies such as linear servo motors, ball screw mechanisms, and rack and pinion mechanisms can be used as these moving mechanisms.

[0029] Furthermore, the machine tool 10 has a spindle 110 and a direction parallel to the direction of movement by the moving mechanism. The system is equipped with a vibration mechanism that vibrates the tool 210 relative to itself. The vibration mechanism according to this embodiment has a first vibration mechanism 140 and a second vibration mechanism 230. The first vibration mechanism 140 is a mechanism that vibrates the spindle 110 and the tool 210 relative to each other with respect to the axial direction of the spindle 110 (Z-axis direction). The second vibration mechanism 230 is a mechanism that vibrates the spindle 110 and the tool 210 relative to each other with respect to a direction perpendicular to the Z-axis direction (X-axis direction). These vibration mechanisms can employ various known technologies that can reciprocate the vibration of the object to be vibrated.

[0030] A first vibration mechanism 140 is fixed to a movable table 131, which is configured to be movable in the Z-axis direction by a first moving mechanism 130. The first vibration mechanism 140 then configures a rotation mechanism 120, which rotates the spindle 110, to vibrate in the Z-axis direction. With this configuration, the workpiece W is configured to be movable in the Z-axis direction by the first moving mechanism 130 (see arrow S1), to vibrate in the Z-axis direction by the first vibration mechanism 140 (see arrow T1), and to be rotatable by the rotation mechanism 120 (see arrow R).

[0031] The second vibration mechanism 230 is fixed to a movable table 221, which is configured to be movable in the X-axis direction by the second moving mechanism 220. Therefore, the tool 210 is configured to be movable in the X-axis direction by the second moving mechanism 220 (see arrow S2) and to be vibrated in the X-axis direction by the second vibration mechanism 230 (see arrow T2).

[0032] The machine tool 10 is equipped with a control device C that controls the operation of the various mechanisms described above. The machine tool 10 is also equipped with an input means 311 for the operator to input data such as machining conditions to the control device C, and a display device 312 for displaying various information. Specific examples of the input means 311 include a keyboard, keypad, and mouse. Specific examples of the display device 312 include a display that shows images. The control device C also plays the role of a display means for displaying various information on the display device 312.

[0033] In this embodiment, in order to move and vibrate the workpiece W and the tool 210 relative to each other in two axial directions, the workpiece W is configured to be movable and vibrable in the Z-axis direction, and the tool 210 is configured to be movable and vibrable in the X-axis direction. However, the tool 210 may be fixed, and the workpiece W may be configured to be movable and vibrable in two axial directions, thereby enabling the workpiece W and the tool 210 to move and vibrate relative to each other in two axial directions. Similarly, the workpiece W may be fixed, and the tool 210 may be configured to be movable and vibrable in two axial directions, thereby enabling the workpiece W and the tool 210 to move and vibrate relative to each other in two axial directions.

[0034] Furthermore, in this embodiment, a configuration is shown in which the moving mechanism and the vibration mechanism are provided independently and controlled independently. However, a configuration that combines the functions of both the moving mechanism and the vibration mechanism is also acceptable. For example, by using a linear servo motor and controlling the linear servo motor to move and vibrate the workpiece W or the tool 210, the same operation as when the moving mechanism and vibration mechanism are provided and operated independently can be achieved.

[0035] Furthermore, this embodiment shows a configuration in which the workpiece W and the tool 210 are moved and vibrated relative to each other in two axial directions. However, a configuration in which the workpiece W and the tool 210 are moved and vibrated relative to each other in three axial directions can also be adopted. That is, in addition to the above configuration, a configuration can also be provided in which the workpiece W and the tool 210 are moved and vibrated relative to each other in the Y-axis direction as well.

[0036] With the machine tool 10 configured as described above, the spindle 110 is rotated by the rotation mechanism 120, and the workpiece W and the tool 210 are moved while being vibrated relative to each other by the moving mechanism and the vibration mechanism, thereby enabling cutting of the workpiece W. Machine 10 is capable of performing cutting operations using at least a first cutting mode and a second cutting mode. This will be explained below.

[0037] <Cutting Mode> The cutting modes will be explained with reference to Figures 2 and 3. Figures 2 and 3 are explanatory diagrams of the operation of the cutting modes in a machine tool according to an embodiment of the present invention. Figure 2 shows the operation in the case of the first cutting mode, with Figure 2(a) showing the workpiece W and tool 210 as viewed in the Y-axis direction and Figure 2(b) showing them as viewed in the Z-axis direction. Figure 3 shows the operation in the case of the second cutting mode, with Figure 3(a) showing the workpiece W and tool 210 as viewed in the Y-axis direction and Figure 3(b) showing them as viewed in the Z-axis direction.

[0038] First, with reference to Figure 2, the cutting operation in the first cutting mode will be explained. In this case, cutting is performed by rotating the spindle 110 with the rotation mechanism 120, while moving the workpiece W and the tool 210 in the Z-axis direction while vibrating them relatively with the first moving mechanism 130 and the first vibrating mechanism 140. The operator only needs to input data related to the rotational speed of the spindle 110 per unit time, the feed rate by the first moving mechanism 130 (feed rate in the direction of arrow S1 in Figure 2), the radial cutting width, and the frequency and amplitude of the vibration by the first vibrating mechanism 140 into the input means 311. Regarding the data to be input, it is possible to set it to input various data directly, or to input various data indirectly. In other words, even if the necessary data is not directly input, it is also possible to set it to input data that can be derived through calculation.

[0039] Referring to Figure 3, the cutting operation in the second cutting mode will be explained. In this case, cutting is performed by rotating the spindle 110 with the rotation mechanism 120, while moving the workpiece W and the tool 210 in the X-axis direction while vibrating them relatively with the second moving mechanism 220 and the second vibration mechanism 230. The operator only needs to input data related to the rotational speed of the spindle 110 per unit time, the feed rate by the second moving mechanism 220 (feed rate in the direction of arrow S2 in Figure 3), the cutting width in the axial direction, and the frequency and amplitude of the vibration by the second vibration mechanism 230 into the input means 311. As described above, the input data can be set to be entered directly or indirectly.

[0040] <Cutting characteristics> Figure 4 shows a graph illustrating the change in the relative movement of the tip of the tool 210 relative to one rotation of the spindle. Figure 4(a) shows the case without vibration. In other words, it is a graph of cutting performed without vibration by a vibration mechanism, and can also be said to be a graph of cutting when using a general machine tool (NC lathe) that does not have a vibration mechanism. Figure 4(b) is a graph of cutting with vibration.

[0041] In each graph, the solid line n represents the graph for the nth rotation of the spindle 110, the dashed line n-1 represents the graph for the (n-1)th rotation of the spindle 110, and the dotted line n-2 represents the graph for the (n-2)th rotation of the spindle 110. Furthermore, in these graphs, W0 indicates the portion of the workpiece W that is not cut by the tool 210 even after the nth rotation of the spindle 110, and W1 indicates the portion of the workpiece W that is cut by the tool 210 after the nth rotation of the spindle 110. Additionally, F represents the relative movement of the tool 210 relative to the workpiece W due to the moving mechanism. In the absence of vibration, F corresponds to the movement (feed rate) of the tool tip of the tool 210 per spindle rotation. In contrast, with vibration, the movement of the tool tip of the tool 210 relative to the workpiece W includes the movement due to the moving mechanism plus the movement due to vibration. Therefore, F represents the average movement of the tool tip of the tool 210 per spindle rotation. It can be called the amount (feed amount).

[0042] In the case of non-vibratory cutting, it can be understood that during the rotation of the spindle 110, the thickness (cutting thickness) of the portion to be cut (the portion that becomes chips) is constant.

[0043] On the other hand, in the case of cutting with vibration, depending on the vibration conditions (amplitude and frequency), during the rotation of the spindle 110, an idle running section where the tool 210 does not contact the workpiece W can be provided. In the illustrated graph, TA indicates the section where the workpiece W is cut by the tool 210, and TB indicates the idle running section. From this, it can be understood that the chips can be finely divided.

[0044] <Chattering vibration> As described in the background art, in machine tools, it is known that a phenomenon called "chattering vibration" occurs in which unstable vibrations occur during the cutting of a workpiece. When chattering vibration occurs, chattering marks are formed on the workpiece or the tool may be damaged, so it is necessary to perform machining under conditions where chattering vibration does not occur. Whether chattering vibration is occurring can be detected not only by the experience of the operator but also by using information obtained from various sensors and the like in the machine tool.

[0045] The inventors of the present application have obtained the knowledge that chattering vibration can be suppressed more in the case of cutting with vibration (hereinafter, appropriately referred to as "low-frequency vibration cutting") than in the case of cutting without vibration (so-called conventional cutting). The reason for this will be described later.

[0046] In the graph shown in FIG. 5, the horizontal axis represents the rotational speed [r / min], and the vertical axis represents the cutting width [mm]. In this graph, the transition of the cutting width (the lower limit value) at which chattering vibration occurs with respect to the rotational speed is shown. The graph for conventional cutting is a0, and the graph for low-frequency vibration cutting is a lim is. Here, let the critical cutting width lower limit value, which is the minimum value of a0, be L, and a lim the most Let sL be the lower limit of the critical cutting width, which is a small value. The likelihood of chatter vibration occurring can be expressed by the ratio sL / L=s.

[0047] Here, a lim This can be expressed by the following (Equation 1).

number

[0048] The derivation of this formula will be explained later.

[0049] Here, let F be the feed rate of the tool 210 relative to the workpiece W by the moving mechanism per rotation of the spindle, and let A be the amplitude of the trajectory waveform of the tool tip. In the machine tool 10 according to this embodiment, Control device C is The relationship between the phase difference of the trajectory waveform for each rotation of the main spindle 110, the amplitude ratio expressed as A / F, and the likelihood of chatter vibration occurring is as follows: Use.

[0050] Figure 5 above shows a lim The graph above shows an example of the above phase difference and amplitude ratio A / F at a certain value. Figure 6 shows images where s was calculated and mapped under conditions where these phase difference and amplitude ratio A / F were changed. In Figure 6, the horizontal axis is the phase difference [πrad] and the vertical axis is the amplitude ratio A / F. The solid lines in the figure are contour lines, and s decreases in the order of region R1, region R2, region R3, region R4, region R5, and region R6. This indicates that chatter vibrations are less likely to occur as the region approaches R1. However, since chatter vibrations are not the only factor determining suitable conditions for machining, approaching R1 does not necessarily mean that the machine is more suitable for machining.

[0051] As described above, in the machine tool 10 according to this embodiment, the control device C determines the relationship between the phase difference of the tool tip trajectory waveform for each rotation of the spindle 110, the amplitude ratio expressed as A / F, and the likelihood of chatter vibration occurring. UseTherefore, according to the machine tool 10 of this embodiment, measures can be taken to suppress the occurrence of chatter vibration.

[0052] For example, the control device C can directly or indirectly display the above correspondence on the display device 312. This allows the operator to suppress the occurrence of chatter vibration by machining under conditions that are less likely to occur based on the correspondence displayed on the display device 312. The timing of the display of the above correspondence on the display device 312 is not limited. For example, it may be displayed before the operator inputs the machining conditions so that the operator can input the machining conditions while looking at the displayed content. Alternatively, it may be displayed after the operator has entered the desired machining conditions into the input means 311 but before machining begins, allowing the operator to choose whether or not to change the machining conditions. Furthermore, if chatter vibration occurs after machining has started after the operator has entered the desired machining conditions into the input means 311, it may be displayed to prompt the operator to change the machining conditions. A more specific example is described below.

[0053] For example, by displaying an image on the display device 312 that maps the distribution of resistance to chatter vibration, as shown in Figure 6, the operator can select a phase difference and amplitude ratio that makes chatter vibration less likely to occur. In Figure 6, the horizontal axis is the phase difference [πrad] and the vertical axis is the amplitude ratio A / F, but it is also possible to display an image that maps the distribution of resistance to chatter vibration by setting the horizontal axis to the amplitude ratio A / F and the vertical axis to the phase difference [πrad].

[0054] Specifically, for example, after the operator inputs the desired machining conditions into the input means 311, an image like the one shown in Figure 6 may be displayed to clearly indicate the location on the map where the input conditions correspond. This allows the operator to re-enter machining conditions that are close to the input conditions but less prone to chatter vibration if the original machining conditions were likely to cause chatter vibration. The input means 311 should be configured to accept data for obtaining the phase difference and amplitude ratio directly or indirectly. In other words, it is also acceptable to configure it to accept data that can be derived through calculation, even if the phase difference and amplitude ratio are not directly input.

[0055] Furthermore, the display device 312 can also display the phase difference, amplitude ratio, and likelihood of chatter vibration occurring in text. Specifically, for example, it can display on the display device 312 that "Phase difference = XX [πrad], amplitude ratio A / F = YY, likelihood of chatter vibration occurring is s times lower than conventional cutting." In this case, for example, after the operator inputs the desired machining conditions into the input means 311, the display device 312 can display several machining conditions that are close to the input conditions but are even less likely to cause chatter vibration, allowing the operator to change the machining conditions as appropriate.

[0056] Thus, based on the above correspondence, the control device C can evaluate the likelihood of chatter vibration occurring, derived from the phase difference and amplitude ratio obtained based on the data input to the input means 311. Furthermore, the control device C can also function as a presentation means that presents multiple data sets that are close to the data input to the input means 311 and are even less likely to cause chatter vibration.

[0057] Furthermore, while we have so far described an example where the above correspondence is directly displayed on the display device 312, it is also possible to adopt a configuration in which the above correspondence is indirectly displayed on the display device 312.

[0058] For example, if the vibration frequency (number of vibrations per rotation of the main spindle) due to the vibration mechanism is D and the amplitude feed ratio is Q, then the relationships A = QF + F / (2D) and A / F = Q + 1 / (2D) exist. Also, there is a relationship between the phase difference φ and the vibration frequency D such that φ = 2π(D - int[D]) (0 ≤ φ < 2π). Thus, since there is a correlation between the phase difference φ and the amplitude ratio A / F and the vibration frequency D and the amplitude feed ratio Q, the relationship between the vibration frequency D and the amplitude feed ratio Q and the difficulty of generating chatter vibration can also be displayed on the display device 312. In other words, the relationship between the phase difference φ and the amplitude ratio A / F and the difficulty of generating chatter vibration can also be displayed indirectly.

[0059] The method of display is the same as described above. That is, the display device 312 can display an image on a graph in which either the horizontal or vertical axis represents frequency D and the other represents amplitude feed ratio Q, mapping the distribution of the difficulty in generating chatter vibrations. In addition, the display device 312 can also display the correspondence between frequency D, amplitude feed ratio Q, and the difficulty in generating chatter vibrations in text.

[0060] Furthermore, if there is a correlation with the phase difference φ and the amplitude ratio A / F, other numerical values ​​besides the frequency D and amplitude feed ratio Q may be used, and the correspondence between these other numerical values ​​and the difficulty of generating chatter vibrations may be displayed on the display device 312.

[0061] Whether the control device C directly or indirectly displays the above correspondence on the display device 312 should be determined according to the numerical values ​​entered by the operator into the input means 311. That is, if the operator inputs a phase difference φ and an amplitude ratio A / F as processing conditions into the input means 311, it is preferable to directly display the correspondence between the phase difference φ and the amplitude ratio A / F and the likelihood of chatter vibration occurring on the display device 312. Also, if the operator inputs a vibration frequency D and an amplitude feed ratio Q as processing conditions into the input means 311, it is preferable to display the correspondence between the vibration frequency D and the amplitude feed ratio Q and the likelihood of chatter vibration occurring on the display device 312.

[0062] The above explanation described a case where the control device C directly or indirectly displays the above correspondence on the display device 312, allowing the operator to readjust the processing conditions as appropriate. However, it is also possible to adopt a configuration in which the control device C corrects the processing conditions instead of the operator readjusting them.

[0063] In other words, as described above, the control device C can evaluate the likelihood of chatter vibration occurring based on the phase difference and amplitude ratio obtained from the data input to the input means 311, based on the above correspondence. Furthermore, the control device C can also function as a correction means to correct the phase difference and amplitude ratio to make chatter vibration even less likely to occur under conditions close to the data input to the input means 311. In this case, the machine tool 10 performs machining using machining conditions corrected by the control device C without the operator having to readjust the machining conditions. Of course, it is also possible to allow the operator to select between a mode in which they readjust the machining conditions and a mode in which the control device C corrects the machining conditions.

[0064] <Machine tool motion control> Referring to Figure 7, an example of the operation flow of the machine tool 10 will be explained. When the operation of the machine tool 10 starts (step SS), the machine tool 10 performs machining operations based on the input machining conditions (step S1). During the machining operation, the control device C successively determines whether or not it has received a command signal indicating the chatter vibration suppression conditions (step S2). If this command signal is not received The machining operation continues until a machining completion command signal is received (step S3). The chatter vibration suppression condition suggestion command signal may be issued when the operator presses a designated button or the like when they recognize that chatter vibration is occurring. Alternatively, the control device C may generate the command signal when it detects that chatter vibration is occurring based on data obtained from various sensors.

[0065] When the machining work is completed, for example, the operator presses the finish button, which sends a machining completion command signal. The control device C receives this command signal (step 3) and terminates the operation of each mechanism, thereby ending the operation of the machine tool 10 (SE). In step S2, if the control device C receives a command signal to present chatter vibration suppression conditions, it temporarily stops the machining operation (step S4). The control device C then displays the chatter vibration suppression conditions on the display device 312 (step S5). In this case, as described above, the display device 312 can display an image mapping the distribution of the likelihood of chatter vibration occurring, or it can display the likelihood of chatter vibration occurring in text. As a result, when the operator inputs new machining conditions into the input means 311, the control device C changes to the newly input machining conditions and operates the machine tool 10 to perform the machining operation (step S6).

[0066] Subsequently, the control device C sequentially determines whether or not it has received a command signal indicating chatter vibration suppression conditions (step S7). Unless this command signal is received, the machining operation continues until a machining completion command signal is received (step S8). In step S8, when the control device C receives a machining completion command signal, the operation of the machine tool 10 ends when the control device C terminates the operation of each mechanism, etc. (SE). Also, in step S7, if the control device C receives a command signal indicating chatter vibration suppression conditions, the machining operation is temporarily suspended (step S4). The subsequent flow is as described above.

[0067] <Formula for determining the lower limit of the cutting width at which chatter vibration occurs> Lower limit value a of cutting width at which chatter vibration occurs lim We will now explain how to derive the formula (Formula 1 above) for [the desired result]. Figures 14 and 15 show a list summarizing the definitions of the formulas and symbols used in the diagrams, which will be explained below.

[0068] High-frequency vibrations can occur during machining, potentially degrading the surface finish or causing damage to the tool. This phenomenon is called chatter vibration, and in cutting processes, a type of chatter vibration called regenerative chatter vibration is particularly common. In regenerative chatter vibration, vibrations that occurred during the previous cutting rotation remain as undulations on the machined surface, and these vibrations are regenerated in the current cutting rotation as fluctuations in the cutting thickness. In this case, the phase difference between the vibration from the previous rotation and the vibration in the current cutting rotation determines whether the current vibration is amplified or attenuated, and amplified vibrations make chatter vibrations more likely to occur. Whether or not chatter vibrations occur depends on the relationship between this phase difference, the magnitude of the cutting resistance load, and the vibration transmission characteristics of the closed-loop structure composed of the tool and material from which the vibrations are transmitted.

[0069] In low-frequency vibration cutting, chatter vibrations of a higher frequency are superimposed on the low-frequency vibrations. However, since no cutting force acts during the free-swinging phase of vibration cutting, the amplitude of dynamic displacement decreases due to the damping of the system in free vibration. Furthermore, as shown in Figure 4(b), in vibration cutting, the dynamic displacement of the machined surface is reproduced not only from one spindle rotation before (n-1 rotation), but also from two spindle rotations before (n-2 rotation) and even earlier. As a result, the stability of chatter vibration in low-frequency vibration cutting is improved compared to normal cutting, and applying low-frequency vibration cutting has a chatter vibration suppression effect.

[0070] Whether or not chatter vibration occurs, or in other words whether or not unstable vibration occurs, depends on the stability limit. While boundary conditions can be determined by calculating a diagram, the improvement in stability compared to normal cutting can be determined by deriving the stability limit in low-frequency vibration cutting. The stability limit in low-frequency vibration cutting is explained below.

[0071] First, let's explain low-frequency vibration cutting. In low-frequency vibration cutting, cutting is performed while the tool is vibrated in the cutting feed direction in synchronization with the spindle rotation. Figure 8 shows a schematic of vibration cutting synchronized with spindle rotation, and the relationship between tool feed and vibration direction. In actual machining, the number of tool vibrations per spindle rotation is specified, and the feed motion on the spindle side of the lathe and the spindle rotation speed are controlled by NC. Therefore, synchronization of spindle and tool vibration is achieved by NC control. In addition, since sinusoidal vibration is superimposed along the machining path that processes the target shape, it is possible to accurately process the specified shape while vibrating the tool.

[0072] Figures 9 and 10 show the tool tip movement trajectories for conventional cutting (cutting without vibration) and vibratory cutting, respectively. In the figures, the hatched area represents the area where cutting is taking place, and its height corresponds to the cutting thickness h [m] in the feed direction at the main cutting edge.

[0073] Figure 9 shows the tool tip movement trajectory during conventional cutting when the spindle feed rate F = 0.03 mm / rev is set. In conventional cutting, the tool tip moves at a constant feed rate F, so the cutting thickness h is always constant. Also, the magnitude of the cutting thickness h is the same as the set feed rate F.

[0074] On the other hand, the tool movement trajectory in low-frequency vibration cutting can be considered as a constant cutting feed component superimposed with a sinusoidal vibration component that vibrates in synchronization with the spindle phase, as shown in Figure 10. In this case, the relationship between the cutting edge position Yn [m] in the feed direction and the spindle phase θ [deg] in vibration cutting after n spindle rotations is defined as follows, using the number of vibrations D per spindle rotation, the ratio Q of the vibration amplitude to the feed amount F [m / rev], and the amplitude A [m] of the sinusoidal vibration component.

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[0075] The cutting edge movement trajectory in Figure 10 was drawn using equations 2 and 3 under the conditions F=0.03mm / rev, D=1.5, and Q=1.5. Here, if we define the phase difference [rad] between the current tool movement trajectory and the trajectory one rotation before the spindle as shown in Figure 8, then φ can be expressed as follows.

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[0076] When the phase of the tool path one rotation ago and the current tool path are aligned (φ=0,2π), the tool path one rotation ago and the current tool path are always parallel, and therefore continuous chips are ejected. On the other hand, currently Under the condition where the vibration of the tool and the vibration of the spindle one rotation ago are in opposite phase (φ=π), the trough of the current vibration trajectory intersects with the peak of the previously machined surface, allowing chips to be broken up even with smaller amplitudes.

[0077] Next, we will explain how to calculate the stability limit in low-frequency vibration cutting. Figures 11 and 12 show a one-degree-of-freedom vibration model during low-frequency vibration cutting. Figure 11 shows the case when φ=π (only the regeneration effect from 1 or 2 rotations prior), and Figure 12 shows an example where φ≠π, with D=1.8,Q The value =2.2 indicates the case where the effect of playback from three rotations prior is included.

[0078] Chatter vibrations occur in different directions depending on where the rigidity is weakest, such as in the tool, machine structure, or the shape of the material being machined. In this model, it is assumed that the rigidity of the tool structure in the feed direction is very small compared to the direction of the main force component, and chatter vibration occurs in the feed direction. In other words, the quasi-static change in cutting thickness at low frequencies due to vibratory cutting is superimposed with the dynamic change in cutting thickness due to the vibration of the tool structure at higher frequencies.

[0079] In conventional cutting, regenerative chatter vibration occurs because only the vibration from the spindle rotation before the current rotation is reproduced. On the other hand, in vibratory cutting, not only the vibration of the tool from the spindle rotation before the current rotation, but also the motion trajectory of the tool from two or more rotations before the current cutting thickness is affected. Therefore, the cutting thickness h in vibratory cutting is expressed as follows.

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[0080] Y(t) is the cutting edge position [m] in the feed direction of the vibratory cutting at time t[s], h vc The cutting thickness [m], h changes quasi-statically due to the tool trajectory of vibratory cutting. d Dynamic cutting thickness [m] due to chatter vibration, y d is the dynamic displacement of the tool [m]. Also, k(t) means that the position where the cutting edge is cutting at time t is the region of the pre-machined surface created before k rotations of the spindle, and the possible values ​​of k(t) are natural numbers (1, 2, 3...). Note that in Figure 11, the pre-machined surface corresponds to the trajectory of the (n-2)th rotation, so k(t)=2, and in Figure 12, the pre-machined surface corresponds to the trajectory of the (n-1)th rotation, so k(t)=1. Y(t) can be calculated by transforming equations 2 and 3 using the spindle rotation period T [s] as follows.

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[0081] Quasi-static cutting thickness h vc The change in cutting thickness h is due to the tool motion of the machine tool's feed drive system and does not affect the growth of chatter vibration; therefore, the stability of the system is determined by the cutting thickness h, which includes the effects of past dynamic displacements from more than one spindle rotation prior. d It can be evaluated by considering only the changes in [the variable].

[0082] As shown in Figure 11, under the condition φ=π, the pre-machined surface is created by the tool motion one and two rotations prior to the spindle rotation. That is, the dynamic cutting thickness h dIt is only affected by past dynamic displacements from one and two rotations prior to the spindle rotation. On the other hand, as shown in an example in Figure 12, when φ≠π, the cutting thickness h d It may be affected by past dynamic displacements from more than three rotations of the main spindle.

[0083] We define "k-rotation delayed regeneration" as the regeneration of the dynamic displacement before the spindle k rotations. In the k-rotation delayed regeneration region, the position between the current dynamic displacement and the past dynamic displacement transferred to the previously machined surface. The phase shift εk [rad] is the angular frequency ω of the chatter vibration. c It is defined using [rad / s] as follows:

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[0084] Using the phase shift εk, the equivalent dynamic cutting thickness h in the cutting section excluding the idle section is calculated. de [m] can be defined as follows:

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[0085] however,

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[0086] In other words, equivalent dynamic cutting thickness h deThis is the average of the dynamic cutting thickness in each section within the cutting zone. On the other hand, in the idle zone, no material is removed, so no cutting force acts on the cutting edge, and the amplitude of the dynamic displacement decreases due to the damping effect of the system in free vibration. Therefore, the presence of an idle zone may improve the stability limit of the system. Considering the stabilizing effect of the idle zone, the equivalent dynamic cutting force F in vibratory cutting is calculated. y,e [N] can be defined as follows:

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[0087] Here, a is the radial cutting width [m], and Ky is the specific cutting resistance in the feed direction [Pa]. In this case, the dynamic displacement y d This can be defined as follows, using the frequency response function Φ[m / N] of the tool structure.

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[0088] The frequency response function Φ is obtained by Laplace transforming the equation of motion of a one-degree-of-freedom spring-mass-damper system, where the equivalent mass is m [kg], the damping coefficient is c [N / (m·s)], and the stiffness is k. stif It is defined using [N / m] as follows:

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[0089] In summary, the block diagram of the entire vibratory cutting process is shown in Figure 13. Note that Figure 13 is a block diagram of regenerative chatter in vibratory cutting, taking into account the ratio of the multiple rotational delay regeneration section to the cutting section.

[0090] Here, the critical cutting width is a lim Let [m] be the characteristic equation obtained by combining equations 8 and 9, and equation 11, from which a lim This leads to (equation 1 above).

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[0091] Since the specific cutting resistance Ky and the response function Φ are constants that depend on the combination of tool and workpiece material, and the compliance of the tool structure, the critical cutting width a obtained from Equation 1 is... lim (1-r aircut , and

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[0092] By comparing the critical cutting width obtained in low-frequency vibration cutting with the critical cutting width in conventional cutting, the improvement in the stability limit in low-frequency vibration cutting can be determined. The feed rate of the conventional cutting used for this comparison is the same as the average feed rate of the low-frequency vibration cutting.

[0093] Up to this point, we have discussed the case where the rigidity of the tool structure in the feed direction is very small compared to the direction of the main force component. However, even when the direction of chatter vibration is different, as described above, we can derive the variation in cutting force from the variation in cutting cross-sectional area due to chatter vibration, determine the critical cutting width, and set its lower limit as the conventional cutting value. By making comparisons, we can determine the percentage improvement in the stability limit. [Explanation of Symbols]

[0094] 10 Machine tools 110 Main shaft 120 rotation mechanism 130 First moving mechanism 131 Mobile platform 140 First vibration mechanism 210 Tools 220 Second moving mechanism 221 Mobile platform 230 Second vibration mechanism 311 Input means 312 Notification methods C Control device W Cutting Object

Claims

1. The spindle to which the workpiece to be cut is attached, A rotating mechanism for rotating the main shaft, A tool for cutting the aforementioned object to be cut, A moving mechanism for moving the spindle and the tool relative to each other, A vibration mechanism that causes the main shaft and the tool to vibrate relative to each other in a direction parallel to the direction of movement by the aforementioned moving mechanism, Equipped with, A machine tool that cuts a workpiece by rotating the spindle with the rotation mechanism, while moving the workpiece and the tool while vibrating them relative to each other using the moving mechanism and the vibration mechanism, When F is the amount of tool feed from the moving mechanism to the workpiece per rotation of the spindle, and A is the amplitude of the trajectory waveform of the tool tip, A machine tool characterized by comprising a control device that uses the relationship between the phase difference of the trajectory waveform for each rotation of the spindle, the amplitude ratio expressed as A / F, and the difficulty in generating chatter vibration.

2. When the cutting width is defined as the width of the cutting by the tool in the direction perpendicular to the movement direction with respect to the object to be cut, When cutting the workpiece without causing relative vibration between the spindle and the tool by the vibration mechanism, the lower limit of the cutting width at which chatter vibration occurs is a ０ a ０ Let L be the minimum value of the critical cutting width lower limit. When cutting the workpiece while the spindle and the tool are vibrated relative to each other by the vibration mechanism, the lower limit of the cutting width at which chatter vibration occurs is determined from the relationship between the phase difference and the amplitude ratio. lim a lim When the minimum value of the critical cutting width, which is the lower limit of the critical cutting width, is denoted as sL, The machine tool according to claim 1, characterized in that the likelihood of chatter vibration occurring is expressed by a factor of sL / L = s.

3. The ratio of the length of the idle section to the total length of the trajectory of the tip of the tool during cutting is r. ａｉｒｃｕｔ Let Ky [Pa] be the specific cutting resistance in the direction of movement by the tool, Φ [m / N] be the frequency response function, i be the imaginary number, and ω be the angular frequency of chatter vibration. ｃ [rad / s] is defined as the regeneration of the dynamic displacement before k rotations of the spindle, and "k-rotation delayed regeneration" is defined as the ratio of the length of the section cutting the pre-machined surface created before k rotations of the spindle to the total length of the trajectory of the tip of the tool during cutting, and r ｋ The normalized ratio of the k-rotation delay regeneration region, where the length of the section in which the workpiece is actually being cut in the entire section is set to 1, is [Math 1] Let ε be the phase difference between the current dynamic displacement and the past dynamic displacement transferred to the pre-processed surface ｋ When it is lim then the a [Math 2] The machine tool according to claim 2, characterized in that it is derived by the method described above.

4. The machine tool according to claim 1, 2, or 3, further comprising a display means for directly or indirectly displaying the correspondence relationship on a display device.

5. The machine tool according to claim 4, characterized in that the display means displays an image on the display device which maps the distribution of the difficulty in generating the chatter vibration onto a graph in which either the horizontal axis or the vertical axis is the phase difference and the other is the amplitude ratio.

6. The system includes input means for inputting data to directly or indirectly obtain the phase difference and the amplitude ratio, The machine tool according to claim 4, characterized in that the display means displays on a display device the likelihood of chatter vibration occurring, which is derived from the phase difference and the amplitude ratio obtained based on the data input to the input means.

7. The system includes input means for inputting data to directly or indirectly obtain the phase difference and the amplitude ratio, The machine tool according to claim 1, 2, or 3, characterized in that it includes a presentation means that evaluates the likelihood of chatter vibration occurring based on the phase difference and amplitude ratio obtained from the data input to the input means based on the aforementioned correspondence, and presents a plurality of data sets that are close to the data input to the input means and are even less likely to cause chatter vibration.

8. The system includes input means for inputting data to directly or indirectly obtain the phase difference and the amplitude ratio, Based on the aforementioned correspondence, the likelihood of chatter vibration occurring, derived from the phase difference and amplitude ratio obtained based on the data input to the input means, is evaluated, and the phase difference is determined to be as close as possible to the data input to the input means, and to make chatter vibration even less likely to occur. The machine tool according to claim 1, 2, or 3, characterized by comprising a correction means for correcting the phase difference and the amplitude ratio.

9. The aforementioned moving mechanism is A first moving mechanism that moves the spindle and the tool relative to each other with respect to the axial direction of the spindle, It has a second moving mechanism that moves the main spindle and the tool relative to each other in a direction perpendicular to the axial direction, The vibration mechanism is A first vibration mechanism that causes the spindle and the tool to vibrate relative to each other with respect to the axial direction of the spindle, It has a second vibration mechanism that causes the main spindle and the tool to vibrate relative to each other in a direction perpendicular to the axial direction, A first cutting mode is characterized by rotating the spindle with the rotation mechanism while moving the workpiece and the tool while vibrating them relative to each other in the axial direction of the spindle using the first moving mechanism and the first vibrating mechanism, The machine tool according to claim 1, 2, or 3, characterized in that it has a second cutting mode, in which the workpiece is cut by rotating the spindle with the rotation mechanism, and moving the workpiece and the tool while vibrating them relative to each other in a direction perpendicular to the axial direction using the second moving mechanism and the second vibrating mechanism.

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