Maintenance methods for machine tools

Abstract

To provide a maintenance method of a machine tool with which a machine tool can be efficiently maintained, regardless of a utilization frequency and use conditions of the machine tool.SOLUTION: In a maintenance method of a machine tool including a spindle 2 to which a tool can be detachably mounted, a spindle bearing 7 for rotationally supporting the spindle 2, and a spindle motor 8 for rotationally driving the spindle 2, deflection accuracy of the spindle 2 is regularly measured, and when the deflection accuracy of the spindle 2 obtained according to the measurement exceeds a preset threshold, inspection of the whole machine tool is conducted.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] This invention relates to a maintenance method for machine tools such as machining centers.

Background Art

[0002] When machining a workpiece, a machine tool such as a machining center is used. Machine tools generally have many movable parts.

[0003] For example, a machining center has, as movable parts, a spindle to which a tool is detachably attached, a spindle bearing that rotatably supports the spindle, and a spindle motor that rotationally drives the spindle. The spindle, the spindle bearing, and the spindle motor constitute a spindle head.

[0004] Furthermore, the machining center has, as movable parts, an X-axis feed device that relatively moves a table to which a workpiece is attached and a spindle head in the left-right direction, a Y-axis feed device that relatively moves the table and the spindle head in the front-rear direction, and a Z-axis feed device that relatively moves the table and the spindle head in the up-down direction. The X-axis feed device has an X-axis linear guide, an X-axis ball screw, and an X-axis motor. The Y-axis feed device has a Y-axis linear guide, a Y-axis ball screw, and a Y-axis motor. The Z-axis feed device has a Z-axis linear guide, a Z-axis ball screw, and a Z-axis motor.

[0005] In addition to the above, the machining center has, as movable parts, a cooling pump for circulating cooling oil in the spindle head, an automatic tool changer (so-called ATC) that automatically exchanges tools between a tool magazine that houses a plurality of types of tools and the spindle, a front door that opens and closes a front opening of a splash guard that surrounds the machining space of the workpiece, and the like.

[0006] The moving parts of machine tools, such as the spindle bearings, spindle motor, X-axis linear guide, X-axis ball screw, X-axis motor, Y-axis linear guide, Y-axis ball screw, Y-axis motor, Z-axis linear guide, Z-axis ball screw, Z-axis motor, cooling pump, automatic tool changer, front door, etc., gradually deteriorate due to wear and tear with repeated use.

[0007] Conventionally, among the moving parts of machine tools, the spindle bearings have been inspected for deterioration by periodically measuring the runout accuracy of the spindle (for example, Patent Document 1).

[0008] On the other hand, moving parts other than the main shaft bearings were not regularly inspected, and repairs or parts replacements were generally carried out only when a malfunction occurred.

[0009] However, if a malfunction occurs in a moving part and repairs or parts replacement is carried out, there is a risk of significant losses, such as the workpiece being processed becoming defective, or the machine tool being shut down while the repair or replacement of the moving part is completed, which could lead to delays in delivery.

[0010] Therefore, the inventor of the present invention considered a maintenance method in which the entire machine tool is inspected at regular intervals (for example, every three years) in order to prevent the moving parts of the machine tool from failing.

[0011] However, if machine tools are inspected at regular intervals, there is a risk that moving parts may fail before the inspection period arrives, especially if the machine tools are used frequently or under harsh conditions. On the other hand, if machine tools are used infrequently or under mild conditions, the moving parts may not have deteriorated significantly by the time the inspection period arrives, resulting in unnecessary time and cost spent on the inspection. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Publication No. 2001-347440 [Overview of the project] [Problems that the invention aims to solve]

[0013] The problem that this invention aims to solve is to provide a machine tool maintenance method that can efficiently maintain a machine tool regardless of its operating frequency or usage conditions. [Means for solving the problem]

[0014] The inventor of this invention focused on the fact that when a machine tool is in operation, not only the spindle but also other moving parts are used simultaneously. Therefore, when the spindle bearings that support the spindle deteriorate due to wear or other reasons, the other moving parts also deteriorate at the same time.

[0015] In other words, if a machine tool is used frequently or under harsh operating conditions, the deterioration of the spindle bearings progresses relatively quickly, and at this time, the deterioration of other moving parts also progresses relatively quickly. On the other hand, if a machine tool is used infrequently or under mild operating conditions, the deterioration of the spindle bearings progresses relatively slowly, and at this time, the deterioration of other moving parts also progresses relatively slowly. Here, the deterioration of the spindle bearings can be easily detected by measuring the runout accuracy of the spindle. Therefore, by periodically measuring the runout accuracy of the spindle and conducting a comprehensive inspection of the machine tool when the runout accuracy obtained from that measurement becomes large, it is possible to inspect the moving parts of the machine tool at the appropriate time regardless of the operating frequency or operating conditions, and to maintain the machine tool efficiently.

[0016] Based on this idea, this invention provides a maintenance method for a machine tool having the following configuration in order to solve the above-mentioned problems. [Configuration 1] A maintenance method for a machine tool having a spindle to which a tool can be detachably attached, a spindle bearing that rotatably supports the spindle, and a spindle motor that rotationally drives the spindle, A method for maintaining a machine tool, characterized by periodically measuring the runout accuracy of the spindle and performing an overall inspection of the machine tool when the runout accuracy of the spindle obtained from the measurement exceeds a preset threshold.

[0017] With this configuration, the spindle runout accuracy is measured periodically, and when the spindle runout accuracy obtained from the measurement exceeds a preset threshold, a complete inspection of the machine tool is performed. Therefore, if the machine tool is used frequently or under harsh operating conditions, the spindle runout accuracy obtained from the periodic measurements will exceed the threshold relatively early, resulting in a complete inspection of the machine tool at a relatively early stage, making it possible to detect deterioration of moving parts before failure occurs. On the other hand, if the machine tool is used infrequently or under mild operating conditions, the spindle runout accuracy obtained from the periodic measurements will exceed the threshold relatively late, resulting in a complete inspection of the machine tool at a later stage when some deterioration of the moving parts has occurred. In this way, regardless of the operating frequency or operating conditions of the machine tool, the moving parts of the machine tool can be inspected at the appropriate time, making it possible to maintain the machine tool efficiently.

[0018] [Configuration 2] The machine tool is a machining center having a table on which a workpiece to be machined with the tool is mounted, an X-axis feed device that moves the spindle head, which is composed of the spindle, the spindle bearing and the spindle motor, relative to each other in the left-right direction, a Y-axis feed device that moves the table and the spindle head relative to each other in the front-back direction, and a Z-axis feed device that moves the table and the spindle head relative to each other in the up-down direction. The X-axis feed device consists of an X-axis linear guide, an X-axis ball screw, and an X-axis motor. The Y-axis feed device is composed of a Y-axis linear guide, a Y-axis ball screw, and a Y-axis motor. The Z-axis feed device is composed of a Z-axis linear guide, a Z-axis ball screw, and a Z-axis motor. When the runout accuracy of the spindle obtained by the measurement exceeds a preset threshold value, the inspection of the spindle bearing, the spindle motor, the X-axis linear guide, the X-axis ball screw, the X-axis motor, the Y-axis linear guide, the Y-axis ball screw, the Y-axis motor, the Z-axis linear guide, the Z-axis ball screw, and the Z-axis motor is performed. The maintenance method of the machine tool according to Configuration 1.

[0019] When this configuration is adopted, regardless of the operating frequency and usage conditions of the machining center, the inspection of the spindle bearing and the spindle motor, the inspection of the X-axis linear guide, the X-axis ball screw, and the X-axis motor that constitute the X-axis feed device, the inspection of the Y-axis linear guide, the Y-axis ball screw, and the Y-axis motor that constitute the Y-axis feed device, and the inspection of the Z-axis linear guide, the Z-axis ball screw, and the Z-axis motor that constitute the Z-axis feed device can be performed at an appropriate timing. Therefore, it is possible to effectively prevent the decrease in the machining accuracy of the workpiece in the left-right direction due to the deterioration of the X-axis feed device, the decrease in the machining accuracy of the workpiece in the front-back direction due to the deterioration of the Y-axis feed device, and the decrease in the machining accuracy of the workpiece in the up-down direction due to the deterioration of the Z-axis feed device.

[0020] [Configuration 3] The machining center further has a cooling pump for circulating cooling oil in the spindle head. When the runout accuracy of the spindle obtained by the measurement exceeds a preset threshold value, the inspection of the cooling pump is also performed. The maintenance method of the machine tool according to Configuration 2.

[0021] When this configuration is adopted, regardless of the operating frequency and usage conditions of the machining center, the inspection of the cooling pump for circulating cooling oil in the spindle head can be performed at an appropriate timing.

[0022] [Configuration 4] The machining center further includes an automatic tool changer that exchanges the tool between a tool magazine that houses a plurality of types of the tools and the spindle. The method for maintaining a machine tool according to Configuration 2 or 3, wherein when the runout accuracy of the spindle obtained by the measurement exceeds a preset threshold value, the automatic tool changer is also inspected.

[0023] Adopting this configuration enables the inspection of the automatic tool changer to be performed at an appropriate timing regardless of the operating frequency and usage conditions of the machining center.

[0024] [Configuration 5] The machining center has a splash guard that surrounds the machining space of the workpiece and a front door that opens and closes the front opening of the splash guard. The method for maintaining a machine tool according to any one of Configurations 2 to 4, wherein when the runout accuracy of the spindle obtained by the measurement exceeds a preset threshold value, the front door is also inspected. [[ID=...]] (Remaining tags unchanged)Adopting this configuration enables the inspection of the front door that opens and closes the front opening of the splash guard to be performed at an appropriate timing regardless of the operating frequency and usage conditions of the machining center.

[0026] [Configuration 6] Using a bar-shaped inspection jig having a cylindrical outer peripheral surface with a circumferential runout of 1 μm or less, or a bar-shaped inspection jig having a cylindrical outer peripheral surface with a circumferential runout of 3 μm or less and the phase of the runout and the measured value marked on the outer periphery, attaching the inspection jig to the spindle, and measuring the runout of the outer peripheral surface of the inspection jig when the spindle is rotated with a dial gauge to measure the runout accuracy of the spindle. The method for maintaining a machine tool according to any one of Configurations 1 to 5.

[0027] Adopting this configuration enables the runout accuracy of the spindle to be accurately measured in a short time. [Effect of the Invention] ​

[0028] The machine tool maintenance method of this invention involves periodically measuring the runout accuracy of the spindle and performing a comprehensive inspection of the machine tool when the runout accuracy obtained from the measurement exceeds a preset threshold. Therefore, if the machine tool is used frequently or under harsh operating conditions, the spindle runout accuracy obtained from the periodic measurement will exceed the threshold relatively early, resulting in a comprehensive inspection of the machine tool at a relatively early stage, making it possible to detect deterioration of the moving parts before a failure occurs. On the other hand, if the machine tool is used infrequently or under mild operating conditions, the spindle runout accuracy obtained from the periodic measurement will exceed the threshold relatively late, resulting in a comprehensive inspection of the machine tool at a later stage when the moving parts have deteriorated to a certain extent. In this way, regardless of the operating frequency or operating conditions of the machine tool, the moving parts of the machine tool can be inspected at the appropriate time, making it possible to maintain the machine tool efficiently. [Brief explanation of the drawing]

[0029] [Figure 1] Front view showing a machining center implementing a machine tool maintenance method according to an embodiment of this invention. [Figure 2] Figure 1 is a schematic front view showing the internal structure of the splash guard of the machining center. [Figure 3] Figure 2 is a partial cross-sectional view seen from the right side. [Figure 4] Enlarged cross-sectional view of the vicinity of the inspection jig in Figure 2. [Modes for carrying out the invention]

[0030] Figure 1 shows a machine tool that implements a maintenance method for a machine tool according to an embodiment of the present invention. This machine tool is a machining center 1 that processes a workpiece (not shown) fixed to a table 3 using a tool (not shown) attached to a spindle 2.

[0031] The machining center 1 has a splash guard 4 that surrounds the workpiece machining space and a front door 6 that opens and closes the front opening 5 of the splash guard 4. The splash guard 4 is an enclosure that prevents chips generated by machining the workpiece and cutting fluid sprayed towards the machining point of the workpiece from scattering to the outside. The front door 6 is provided so as to be slidable from left to right between a closed position that closes the front opening 5 of the splash guard 4 and an open position that opens the front opening 5 of the splash guard 4.

[0032] As shown in Figure 2, the machining center 1 has a spindle 2 to which a tool (not shown) can be detachably attached, a spindle bearing 7 that rotatably supports the spindle 2, and a spindle motor 8 that rotationally drives the spindle 2. The spindle 2, spindle bearing 7, and spindle motor 8 constitute the spindle head 9.

[0033] Furthermore, the machining center 1 includes a table 3 on which a workpiece (not shown) is mounted, an X-axis feed device 10 that moves the table 3 and the spindle head 9 relative to each other in the left-right direction, a Y-axis feed device 20 that moves the table 3 and the spindle head 9 relative to each other in the front-back direction, and a Z-axis feed device 30 that moves the table 3 and the spindle head 9 relative to each other in the up-down direction.

[0034] The X-axis feed device 10 consists of an X-axis linear guide 11, an X-axis ball screw 12, and an X-axis motor 13. The X-axis linear guide 11 has an X-axis rail 14 extending in the left-right direction and an X-axis slider 15 supported by the X-axis rail 14 so as to be slidable in the left-right direction. The X-axis ball screw 12 has an X-axis screw shaft 16 extending in the left-right direction and an X-axis ball nut 17 that screw-engages with the X-axis screw shaft 16.

[0035] The X-axis slider 15 and X-axis ball nut 17 are connected to the table 3 so as to move together with the table 3 in the left-right direction. The X-axis motor 13 is connected to the X-axis ball screw 12 so as to rotate the X-axis ball screw 12. The X-axis motor 13 is a servo motor that incorporates a sensor to detect the rotation angle of the motor and performs feedback control based on the difference between the rotation angle of the motor detected by the sensor and the target angle.

[0036] The Y-axis feed device 20 consists of a Y-axis linear guide 21, a Y-axis ball screw 22, and a Y-axis motor 23 (see Figure 3). The Y-axis linear guide 21 has a Y-axis rail 24 extending in the front-rear direction and a Y-axis slider 25 supported by the Y-axis rail 24 so as to be slidable in the front-rear direction. The Y-axis ball screw 22 has a Y-axis screw shaft 26 extending in the front-rear direction and a Y-axis ball nut 27 that screw-engages with the Y-axis screw shaft 26.

[0037] As shown in Figure 3, the Y-axis slider 25 and Y-axis ball nut 27 are connected to the table 3 so as to move together with the table 3 in the front-back direction. The Y-axis motor 23 is connected to the Y-axis ball screw 22 to rotate the Y-axis ball screw 22. The Y-axis motor 23 is a servo motor similar to the X-axis motor 13.

[0038] The Z-axis feed device 30 consists of a Z-axis linear guide 31, a Z-axis ball screw 32, and a Z-axis motor 33. The Z-axis linear guide 31 has a Z-axis rail 34 that extends in the vertical direction and a Z-axis slider 35 that is supported by the Z-axis rail 34 so as to be slidable in the vertical direction. The Z-axis ball screw 32 has a Z-axis screw shaft 36 that extends in the vertical direction and a Z-axis ball nut 37 that screw-engages with the Z-axis screw shaft 36.

[0039] The Z-axis slider 35 and Z-axis ball nut 37 are connected to the spindle head 9 so as to move vertically together with the spindle head 9. The Z-axis motor 33 is connected to the Z-axis ball screw 32 so as to rotate the Z-axis ball screw 32. The Z-axis motor 33 is a servo motor similar to the X-axis motor 13.

[0040] As shown in Figure 2, the machining center 1 has an automatic tool changer 40 and a cooling pump 41 that circulates cooling oil to the spindle head 9. The automatic tool changer 40 is a device (so-called ATC) that changes tools between a tool magazine 42 that stores multiple types of tools and the spindle 2.

[0041] An example of a maintenance method for the machining center 1 with the above configuration will be explained.

[0042] The runout accuracy of the spindle 2 is measured at regular intervals (for example, every month). The runout accuracy of the spindle 2 can be measured as follows. First, a dedicated inspection jig 50 for measuring the runout accuracy of the spindle 2 is prepared, as shown in Figure 4. This inspection jig 50 has a shank portion 52 that is inserted into the tapered hole 51 for tool mounting of the spindle 2, and a rod-shaped portion 53 that has a cylindrical outer surface with a circumferential runout of 1 μm or less. Here, if the inspection jig 50 has a rod-shaped portion 53 with a particularly high-precision outer surface having a circumferential runout of 1 μm or less, it is possible to measure the runout accuracy of the spindle 2 accurately in a particularly short time. Alternatively, the inspection jig 50 may have a rod-shaped portion 53 with a cylindrical outer surface having a circumferential runout of 1 μm or more and 3 μm or less, and the phase of the runout of the rod-shaped portion 53 (i.e., the angular position where the runout is at its maximum value when the circumferential runout of the rod-shaped portion 53 is actually measured) and the measured value of the runout (i.e., a known value of 1 μm or more and 3 μm or less obtained by actually measuring the circumferential runout of the rod-shaped portion 53 in advance) may be used, with the phase of the runout of the rod-shaped portion 53 (i.e., the angular position where the runout is at its maximum value when the circumferential runout of the rod-shaped portion 53 is actually measured) and the measured value of the runout (i.e., a known value of 1 μm or more and 3 μm or less obtained by actually measuring the circumferential runout of the rod-shaped portion 53 in advance) may be used. In this way, it is possible to measure the runout accuracy of the spindle 2 accurately in a short time while keeping the preparation cost of the inspection jig 50 down.

[0043] Next, the inspection jig 50 is attached to the spindle 2, and the measuring probe of the dial gauge 54, which is mounted on the table 3, is brought into contact with the outer surface of the rod-shaped part 53 of the inspection jig 50. In this state, the spindle 2 is rotated at a low speed, and the runout of the outer surface of the inspection jig 50 is measured with the dial gauge 54 to measure the runout accuracy of the spindle 2. Measuring the runout accuracy of the spindle 2 using this method allows for measurement in about 10 minutes of work time, and even if the runout accuracy of the spindle 2 is measured once a month, the total work time per year is only about 2 hours, resulting in a small workload.

[0044] Then, it is determined whether the runout accuracy of the spindle 2 obtained from the above measurement exceeds a preset threshold (for example, a runout set in the range of 10 to 20 μm). If the runout accuracy of the spindle 2 exceeds the threshold, the entire machining center 1 is inspected.

[0045] Specifically, if the runout accuracy of the spindle 2 exceeds a threshold (for example, 15 μm), a day for overall inspection of the machining center 1 is set. On that day, the spindle bearing 7 and spindle motor 8 shown in Figure 2 are inspected, as are the X-axis linear guide 11, X-axis ball screw 12 and X-axis motor 13 that make up the X-axis feed device 10, as are the Y-axis linear guide 21, Y-axis ball screw 22 and Y-axis motor 23 that make up the Y-axis feed device 20 shown in Figure 3, as are the Z-axis linear guide 31, Z-axis ball screw 32 and Z-axis motor 33 that make up the Z-axis feed device 30, as well as the cooling pump 41 and automatic tool changer 40 shown in Figure 2, and the front door 6 shown in Figure 1. Then, any parts that are determined to be deteriorated due to wear or other factors as a result of the inspection are repaired or replaced.

[0046] By the way, when the machining center 1 is in operation, not only the spindle 2 but also other movable parts (spindle bearing 7, spindle motor 8, X-axis linear guide 11, X-axis ball screw 12, X-axis motor 13, Y-axis linear guide 21, Y-axis ball screw 22, Y-axis motor 23, Z-axis linear guide 31, Z-axis ball screw 32, Z-axis motor 33, cooling pump 41, automatic tool changer 40, front door 6, etc.) are used simultaneously. Therefore, when the spindle bearing 7 that supports the spindle 2 deteriorates due to wear or other reasons, the other movable parts also deteriorate at the same time.

[0047] Therefore, when the machining center 1 is maintained using the method of this embodiment, if the machining center 1 is operated frequently or under harsh operating conditions, the runout accuracy of the spindle 2 obtained by periodic measurements will exceed the threshold relatively early. As a result, a comprehensive inspection of the machining center 1 will be performed at a relatively early stage, making it possible to detect deterioration of the moving parts before a failure occurs in the moving parts. On the other hand, if the machining center 1 is operated infrequently or under mild operating conditions, the runout accuracy of the spindle 2 obtained by periodic measurements will exceed the threshold relatively late. As a result, a comprehensive inspection of the machining center 1 will be performed at a later stage when the moving parts of the machining center 1 have deteriorated to a certain extent. In this way, regardless of the operating frequency or operating conditions of the machining center 1, the moving parts of the machining center 1 can be inspected at the appropriate time, making it possible to maintain the machining center 1 efficiently.

[0048] In the above embodiment, a 3-axis machining center 1 was used as an example of a machine tool for maintenance, but this invention can also be applied to other types of multi-tasking machines, such as 5-axis machining centers. [Explanation of Symbols]

[0049] 1 Machining Center 2 spindle 3 tables 4 Splash Guard 6 Front Doors 7. Main shaft bearings 8. Main shaft motor 9. Spindle head 10 X-axis feed device 11 X-axis linear guide 12 X-axis ball screw 13 X-axis motor 20 Y-axis feed device 21 Y-axis linear guide 22 Y-axis ball screw 23 Y-axis motor 30 Z-axis feed device 31 Z-axis linear guide 32 Z-axis ball screw 33 Z-axis motor 40 Automatic tool changer 41 Cooling pump 42 Tool Magazine 50 Inspection fixtures 54 Dial Gauge

Claims

1. A spindle (2) to which a tool can be detachably attached, a spindle bearing (7) that rotatably supports the spindle (2), a spindle motor (8) that rotationally drives the spindle (2), a table (3) to which a workpiece to be machined by the tool is attached, an X-axis feed device (10) that moves the spindle head (9), composed of the spindle (2), the spindle bearing (7), and the spindle motor (8), relative to the table (3) in the left-right direction, and moves the table (3) and the spindle head (9) relative to each other in the front-back direction. The machine has a Y-axis feed device (20), a Z-axis feed device (30) that moves the table (3) and the spindle head (9) relative to each other in the vertical direction, a cooling pump (41) that circulates cooling oil to the spindle head (9), an automatic tool changer (40) that exchanges tools between a tool magazine (42) that houses multiple types of tools and the spindle (2), a splash guard (4) that surrounds the machining space of the workpiece, and a front door (6) that opens and closes the front opening (5) of the splash guard (4). The X-axis feed device (10) consists of an X-axis linear guide (11), an X-axis ball screw (12), and an X-axis motor (13). The Y-axis feed device (20) consists of a Y-axis linear guide (21), a Y-axis ball screw (22), and a Y-axis motor (23). In a maintenance method for a machine tool that is a machining center, the Z-axis feed device (30) is composed of a Z-axis linear guide (31), a Z-axis ball screw (32), and a Z-axis motor (33). A method for maintaining a machine tool, characterized by periodically measuring the runout accuracy of the spindle (2), and when the runout accuracy of the spindle (2) obtained from the measurement exceeds a preset threshold, inspecting all of the movable parts of the machine tool, namely the spindle bearing (7), the spindle motor (8), the X-axis linear guide (11), the X-axis ball screw (12), the X-axis motor (13), the Y-axis linear guide (21), the Y-axis ball screw (22), the Y-axis motor (23), the Z-axis linear guide (31), the Z-axis ball screw (32), the Z-axis motor (33), the cooling pump (41), the automatic tool changer (40), and the front door (6).

2. A method for maintaining a machine tool according to claim 1, comprising using a rod-shaped inspection jig (50) having a cylindrical outer surface with a circumferential runout of 1 μm or less, or a rod-shaped portion (53) having a cylindrical outer surface with a circumferential runout of 1 μm or more and 3 μm or less, wherein the rod-shaped inspection jig (50) has markings on its outer surface indicating the phase, which is the angular position where the runout is maximum when the circumferential runout of the rod-shaped portion (53) is measured, and a measured value of 1 μm or more and 3 μm or less obtained by measuring the circumferential runout of the rod-shaped portion (53) in advance, and attaching the inspection jig (50) to the spindle (2), and measuring the runout of the outer surface of the inspection jig (50) with a dial gauge (54) when the spindle (2) is rotated, thereby measuring the runout accuracy of the spindle (2).

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