Machine tool, machine tool control method, and machine tool control program

Abstract

The machine tool includes a spindle (180) having a communication passage connected to the through passage when a tool having a through passage formed therein is mounted, a pump (56) for pumping coolant to a first flow passage connected to the communication passage, a first valve (58A) provided in the first flow passage or the communication passage, and a second valve (58B) capable of switching at least whether to return coolant located on the first valve (58A) side of the branch point of the second flow passage to a second flow passage branching off from the first flow passage between the pump (56) and the first valve (58A). When stopping the discharge of coolant from the tool to the outside, a control unit of the machine tool executes the following processes: opening the second valve (58B) to return at least an amount of coolant existing from the first valve (58A) to an opening on the tip side of the tool to the second flow passage; and closing the first valve (58A) to fill the first flow passage between the pump (56) and the first valve (58A) with coolant.

Description

Technical Field

[0001] The present disclosure relates to a machine tool, a control method for a machine tool, and a control program for a machine tool.

Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2013 - 013968 (Patent Document 1) discloses a machine tool capable of machining a workpiece while discharging coolant from the tip of a tool. The machine tool includes a spindle and a tool in which a coolant supply passage is formed inside, and discharges coolant from the tip of the tool through the coolant supply passage.

[0003] Further, after the machining of the workpiece is completed, the machine tool executes a draw - back process of sucking the coolant remaining in the coolant supply passage. Thereby, the machine tool prevents the coolant from dripping from the tip of the tool.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the draw - back process is executed, the coolant remaining in the flow path is sucked in. Therefore, it takes time until the coolant is discharged from the tip of the tool next. Thus, a technique for shortening this time is desired.

Means for Solving the Problems

[0006] One example of the present disclosure provides a machine tool capable of machining a workpiece using a tool that has a through passage formed therein and is configured to discharge coolant to the outside from an opening at the tip of the through passage. The machine tool comprises a spindle configured to be able to mount the tool and having a connecting passage connected to the through passage when the tool is mounted, a pump for pressurizing coolant into a first flow path connected to the connecting passage, a first valve provided in the first flow path or the connecting passage, a second valve that can at least switch whether to return coolant that is on the side of the first valve beyond the branching point of the second flow path to a second flow path that branches off from between the pump and the first valve in the first flow path, and a control unit for controlling the machine tool. When the control unit stops the discharge of coolant from the tool to the outside, it opens the second valve and performs a drawback process in which at least the amount of coolant between the first valve and the opening on the tip side of the tool is returned to the second flow path, and after the drawback process is performed, it closes the first valve and performs a filling process in which the first flow path between the pump and the first valve is filled with coolant.

[0007] In one example of this disclosure, the first valve is provided on the first flow path. The length of the flow path between the first valve and the main shaft is shorter than the length of the flow path between the second valve and the main shaft.

[0008] In one example of this disclosure, the machine tool further comprises a third valve provided in a third flow path that branches off from between the pump and the first valve in the first flow path. The filling process includes opening the third valve.

[0009] In one example of this disclosure, the first valve is provided on the first flow path. The length of the flow path between the first valve and the main shaft is shorter than the length of the flow path between the third valve and the main shaft.

[0010] In one example of this disclosure, the branching point between the first channel and the third channel is located on the main axis side than the branching point between the first channel and the second channel.

[0011] In one example of this disclosure, the control unit starts the filling process after a predetermined time has elapsed since the start of the drawback process.

[0012] In another example of the present disclosure, a control method is provided for a machine tool capable of machining a workpiece using a tool having a through passage formed therein, which is configured to discharge coolant to the outside from an opening at the tip of the through passage. The machine tool comprises a spindle configured to mount the tool and having a connecting passage connected to the through passage when the tool is mounted; a pump for pressurizing coolant into a first flow path connected to the connecting passage; a first valve provided in the first flow path or the connecting passage; and a second valve that can at least switch whether to return coolant to a second flow path that branches off from the pump and the first valve in the first flow path, the coolant located on the side of the first valve beyond the branching point of the second flow path. The control method comprises the steps of opening the second valve to stop the discharge of coolant from the tool to the outside, returning at least the amount of coolant from the first valve to the opening at the tip of the tool to the second flow path, and closing the first valve after the return step to fill the first flow path between the pump and the first valve with coolant.

[0013] In other examples of the present disclosure, a control program is provided for a machine tool capable of machining a workpiece using a tool configured to discharge coolant to the outside from an opening at the tip of the through passage. The machine tool comprises a spindle configured to mount the tool and having a connecting passage connected to the through passage when the tool is mounted; a pump for pressurizing coolant into a first flow path connected to the connecting passage; a first valve provided in the first flow path or the connecting passage; and a second valve that can at least switch whether to return coolant to a second flow path that branches off from between the pump and the first valve in the first flow path if the coolant is on the side of the first valve beyond the branching point of the second flow path. The control program described above causes the machine tool to perform the following steps when it wants to stop the discharge of coolant from the tool to the outside: open the second valve and return at least the amount of coolant from the first valve to the opening on the tip side of the tool back into the second flow path; and after the return step, close the first valve and fill the first flow path between the pump and the first valve with coolant.

[0014] The above and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description relating to the invention, which will be understood in conjunction with the accompanying drawings. [Brief explanation of the drawing]

[0015] [Figure 1] This is a diagram showing the external appearance of a machine tool. [Figure 2] This figure shows an example of a coolant mechanism. [Figure 3] This figure shows the control flow of the coolant mechanism in steps S1 and S2. [Figure 4] This figure shows the control flow of the coolant mechanism in steps S3 and S4. [Figure 5] This figure shows an example of the hardware configuration of the control unit. [Figure 6] This flowchart shows the pre-processing steps for tool changes. [Figure 7] It is a flowchart showing the flow of workpiece processing.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, each embodiment according to the present invention will be described while referring to the drawings. In the following description, the same parts and components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated. Note that each embodiment and each modification described below may be selectively combined as appropriate.

[0017] <A. Machine Tool 100> First, referring to FIG. 1, a machine tool 100 according to an embodiment will be described. FIG. 1 is a view showing the appearance of the machine tool 100.

[0018] As used in this specification, the "machine tool" is a concept encompassing various devices having a function of machining a workpiece. The machine tool may be a horizontal machining center, a vertical machining center, a lathe, or other cutting machines, grinding machines, compound machining machines, 5-axis machining machines, etc. Further, the machine tool is not limited to performing only removal machining, and may perform addition machining in addition to removal machining.

[0019] The machine tool 100 has a tool storage unit 40A and a machine tool main body 40B. Each of the tool storage unit 40A and the machine tool main body 40B is partitioned by a cover.

[0020] The tool storage unit 40A is provided with a magazine 150 and an ATC (Automatic Tool Changer) 160. The machine tool main body 40B is provided with a spindle head 170.

[0021] The spindle head 170 includes a spindle barrel 175 and a spindle 180. The spindle 180 is rotatably supported by the spindle barrel 175 about its axial direction as the rotation center.

[0022] One tool selected from the magazine 150 is mounted on the spindle 180. More specifically, the machine tool 100 drives the magazine 150 and moves one tool (hereinafter also referred to as the "next-use tool") corresponding to the machining process to the first tool change position. Further, the machine tool 100 drives the spindle head 170 and moves the tool mounted on the spindle 180 (hereinafter also referred to as the "used tool") to the second tool change position. Thereafter, the ATC 160 exchanges the next-use tool waiting at the first tool change position with the used tool waiting at the second tool change position. The tool exchange is performed through the door D provided in the partition between the processing machine main body 40B and the tool storage section 40A. The door D is a slide-type door and is opened and closed by a drive source such as a motor. Thereafter, the machine tool 100 machines the workpiece using the next-use tool mounted on the spindle 180.

[0023] Further, the machine tool 100 is provided with an operation panel 400. The operation panel 400 includes a display 405 for displaying various information related to machining and operation keys 406 for receiving various operations on the machine tool 100.

[0024] <B. Coolant mechanism> Next, referring to FIG. 2, the coolant mechanism provided inside the machine tool 100 will be described. FIG. 2 is a diagram showing an example of the coolant mechanism.

[0025] As shown in Figure 2, the machine tool 100 includes coolant flow paths F1 to F3, a control unit 50, a coolant tank 52, a motor driver 54, a pump 56, a pressure-holding valve 58A (first valve), a drawback valve 58B (second valve), an orifice valve 58C (third valve), and a spindle 180. The names of each valve are assigned to make it easier to identify each valve based on the main function performed by each flow path F1 to F3, and should not be interpreted restrictively as meaning that each valve has that function on its own. For example, the drawback valve 58B may realize the drawback function on its own, or it may realize the drawback function in cooperation with other fluid equipment such as ejectors. Similarly, the orifice valve 58C can be controlled to any opening degree and may realize the function of an orifice on its own, or it may realize the function in cooperation with other fluid equipment such as separately provided orifices.

[0026] One end of the flow path F1 is connected to the coolant tank 52. The other end of the flow path F1 is connected to a connecting passage L1 formed within the main shaft 180. For the sake of explanation, the side of the coolant flow path closer to the coolant tank 52 will also be referred to as the "upstream side," and the side of the coolant flow path closer to the main shaft 180 will also be referred to as the "downstream side."

[0027] Flow path F2 branches off from flow path F1 at branching point P2. That is, one end of flow path F2 is connected to flow path F1. The destination of the other end of flow path F2 is arbitrary. In the example in Figure 2, the other end of flow path F2 is connected to the coolant tank 52. In another example, the other end of flow path F2 may be connected to a storage unit other than the coolant tank 52.

[0028] Flow path F3 branches off from flow path F1 at branching point P3. In other words, one end of flow path F3 is connected to flow path F1. The destination of the other end of flow path F3 is arbitrary. In the example in Figure 2, the other end of flow path F3 is connected to the coolant tank 52. As another example, the other end of flow path F3 may be connected to a storage unit other than the coolant tank 52.

[0029] A communication passage L1 is formed inside the spindle 180. The communication passage L1 penetrates the inside of the spindle 180 along its axial direction.

[0030] Various types of tools can be mounted on the spindle 180. In the example shown in Figure 2, a tool T with a through passage L2 is mounted on the spindle 180. The through passage L2 extends from the connection surface between the tool T and the spindle 180 to the tip of the tool T, and penetrates the tool T along the axial direction of the spindle 180. Note that the opening of the through passage L2 formed in the tool T is not limited to being formed on the base end face or tip face of the tool T, but may also be an opening on the side of the tool T, for example.

[0031] The through passage L2 inside the tool T is connected to the communication passage L1 inside the spindle 180 when the tool T is mounted on the spindle 180.

[0032] The control unit 50 controls various devices within the machine tool 100. The configuration of the control unit 50 is arbitrary. The control unit 50 may consist of a single control unit or multiple control units. As an example, the control unit 50 includes at least one of a PLC (Programmable Logic Controller) and a CNC (Computer Numerical Control).

[0033] The components controlled by the control unit 50 include, for example, the pump 56, the pressure-holding valve 58A, the drawback valve 58B, and the orifice valve 58C.

[0034] The pump 56 is located in the flow path F1 and pumps coolant from the coolant tank 52 into the flow path F1. The force with which the coolant is pumped is controlled by the control unit 50.

[0035] More specifically, a motor 55 is connected to the pump 56. The motor 55 is driven by a motor driver 54. The motor driver 54 consists of a control circuit and an inverter, etc. The motor driver 54 receives a control signal input from the control unit 50 and outputs an alternating current with a frequency corresponding to the control signal to the motor 55. This changes the rotational speed of the motor 55, and controls the flow rate of the coolant pumped into the flow path F1.

[0036] The pressure-holding valve 58A is installed in the flow path F1 or the communication passage L1. In the example shown in Figure 2, the pressure-holding valve 58A is installed in the flow path F1. Furthermore, the pressure-holding valve 58A is installed downstream of the pump 56.

[0037] The pressure-holding valve 58A is configured to be switchable between at least two states, an open state and a closed state, in response to a control command from the control unit 50. The opening degree of the pressure-holding valve 58A may be adjustable or constant.

[0038] When the pressure-holding valve 58A is closed, the flow of coolant between the branching point P3 and the spindle 180 is stopped. On the other hand, when the pressure-holding valve 58A is open, the coolant can flow between the branching point P3 and the spindle 180. In this case, the coolant pumped by the pump 56 flows in the order of the flow path F1, the connecting passage L1, and the through passage L2, and is discharged from the tip of the tool T to the workpiece being machined. A spindle 180 equipped with such a coolant discharge function is also called a coolant-through spindle.

[0039] In the example shown in Figure 2, the pressure-holding valve 58A is located in the flow path F1, but the installation location of the pressure-holding valve 58A is not limited to the flow path F1. For example, the pressure-holding valve 58A may be located in the communication passage L1 within the main shaft 180.

[0040] The drawback valve 58B is installed, for example, on a flow path F2 that branches off from flow path F1. The drawback valve 58B is a valve that can at least switch whether or not to return coolant located on the side of the pressure-holding valve 58A beyond the branching point P2 to flow path F2, which branches off from between the pump 56 and the pressure-holding valve 58A in flow path F1.

[0041] For example, the drawback valve 58B is configured to be switchable between at least two states, an open state and a closed state, in response to a control command from the control unit 50. The opening degree of the drawback valve 58B may be adjustable or constant.

[0042] When the drawback valve 58B is closed, the flow of coolant in the flow path F2 is stopped. On the other hand, when the drawback valve 58B is open, the coolant can flow through the flow path F2.

[0043] Typically, the drawback valve 58B is located upstream of the holding pressure valve 58A. In other words, the length of the coolant flow path between the holding pressure valve 58A and the spindle 180 is shorter than the length of the coolant flow path between the drawback valve 58B and the spindle 180.

[0044] The orifice valve 58C is installed on the flow path F3, which branches off from the flow path F1 at branching point P3, and controls the flow of coolant in the flow path F3. An orifice FR is separately provided upstream of the orifice valve 58C in the flow path F3 as a fluid resistance. In other words, the opening and closing of the orifice valve 58C allows switching between applying the fluid resistance FR to the coolant flowing through the flow path F3. The branching point P3 between flow path F2 and flow path F3 is located downstream of the branching point P2 between flow path F1 and flow path F2.

[0045] The orifice valve 58C is configured to be switchable between at least two states, an open state and a closed state, in response to a control command from the control unit 50. The opening degree of the orifice valve 58C may be adjustable or may be constant.

[0046] When the orifice valve 58C is in the closed state, the flow of the coolant in the flow path F3 is stopped. On the other hand, when the orifice valve 58C is in the open state, the coolant can flow through the flow path F3.

[0047] Typically, the orifice valve 58C is provided upstream of the pressure maintaining valve 58A. In other words, the length of the coolant flow path between the pressure maintaining valve 58A and the main shaft 180 is shorter than the length of the coolant flow path between the orifice valve 58C and the main shaft 180.

[0048] In the above description, an example in which the draw-back valve 58B is provided on the flow path F2 and the orifice valve 58C is provided on the flow path F3 has been described. However, the draw-back valve 58B may be provided on the flow path F3 and the orifice valve 58C may be provided on the flow path F2.

[0049] <C. Control Mode of Coolant Mechanism> Next, with reference to Figures 3 and 4, the control modes of the coolant mechanism, including the pump 56, the pressure-holding valve 58A, the drawback valve 58B, and the orifice valve 58C, will be described. Figure 3 shows the control flow of the coolant mechanism in steps S1 and S2. Figure 4 shows the control flow of the coolant mechanism in steps S3 and S4. In this embodiment, the pressure-holding valve 58A, the drawback valve 58B, and the orifice valve 58C are normally closed valves that remain closed when no voltage is applied. In other words, each valve is normally closed, but it opens when a command signal is input from the control unit 50. Needless to say, even if each valve were a normally open valve that remains open when no voltage is applied, it would be possible to achieve the same functionality as in this embodiment by appropriately setting the control signals.

[0050] Step S1 describes the state of the coolant mechanism during workpiece machining. In step S1, the control unit 50 opens only the holding valve 58A. That is, the drawback valve 58B and the orifice valve 58C remain closed. Then, the control unit 50 controls the pump 56 to pump the coolant into the flow path F1. The coolant pumped through the flow path F1 is discharged from the tip of the tool T via the connecting passage L1 and the through passage L2.

[0051] Subsequently, the control unit 50 receives a command to stop the discharge of coolant from the tool T, or a command to replace the tool T. As a result, the control unit 50 stops driving the pump 56 and performs the drawback process shown in step S2.

[0052] More specifically, in step S2, the control unit 50 switches the drawback valve 58B from the closed state to the open state. The control unit 50 also maintains the pressure-holding valve 58A in the open state. The orifice valve 58C is maintained in the closed state. The control unit 50 then returns at least the amount of coolant from the pressure-holding valve 58A to the opening on the tip side of the tool T back to the flow path F2. Typically, any coolant remaining in the communication passage L1, through passage L2, and flow path F1 is discharged from the flow path F2. This prevents the coolant from dripping from the tool T or the spindle 180.

[0053] Preferably, a suction mechanism such as an ejector (not shown) is provided at the branching point P2 or the flow path F2. During the drawback process, coolant supplied from, for example, the pump 56 at a predetermined flow rate or pressure flows into the ejector, thereby exerting a suction effect downstream of the branching point P2. As a result, the coolant downstream of the branching point P2 flows back from the flow path F1 into the flow path F2.

[0054] The control unit 50 performs the filling process shown in step S3 after the drawback process has been executed. More specifically, in step S3, the control unit 50 closes the pressure-holding valve 58A from the open state. Subsequently, the control unit 50 drives the pump 56 to fill the flow path F1 between the pump 56 and the pressure-holding valve 58A with coolant. This shortens the time it takes for the coolant to be discharged from the tip of the tool T when the tool T having the through passage L2 is newly mounted on the spindle 180.

[0055] Furthermore, during the coolant filling process in step S3, the control unit 50 closes the drawback valve 58B, as shown in the example in Figure 4. This prevents the coolant from flowing out of the flow path F2.

[0056] Furthermore, during the coolant filling process in step S3, the orifice valve 58C may be in an open or closed state. As shown in the example in Figure 4, the control unit 50 keeps the orifice valve 58C in an open state. If the orifice valve 58C is in an open state, even if the pump 56 is not completely stopped and is kept running at the lowest operating frequency, it is possible to prevent the pressure of the coolant in the flow path from rising too high above a predetermined value. Therefore, even when the discharge and stopping of coolant is repeated, it is possible to prevent the increase in power consumption caused by repeatedly completely stopping and starting the pump 56 as in the conventional method.

[0057] Preferably, the pressure-holding valve 58A is provided on the spindle 180 side of the flow path F1. The spindle 180 side refers to the vicinity of the spindle 180 on the flow path F1. As an example, the spindle 180 side represents the flow path between the center of the flow path F1 and the spindle 180. As another example, the spindle 180 side represents the flow path between branch point P2 or branch point P3 and the spindle 180. By providing the pressure-holding valve 58A on the spindle 180 side, the coolant is filled up to the vicinity of the spindle 180. As a result, the time until the coolant is discharged from the tip of the tool T can be further shortened. Furthermore, while achieving this reduction in the time until coolant discharge begins, energy savings can also be achieved by eliminating the repeated starting and stopping of the pump 56.

[0058] The control unit 50 performs the process shown in step S4 after the coolant filling process is completed. More specifically, in step S4, the control unit 50 closes the orifice valve 58C from the open state. The pressure holding valve 58A is kept closed, and the drawback valve 58B is kept closed. After that, the control unit 50 stops the pump 56.

[0059] Incidentally, in the above description, an example in which the pump 56 is stopped in step S4 has been described. However, when the pump 56 is a variable displacement pump driven by an inverter, the control unit 50 needs to continue driving the pump 56 at the minimum driving frequency. In this case, in step S4, the control unit 50 drives the pump 56 at the minimum driving frequency while maintaining the orifice valve 58C in the open state. The minimum driving frequency is lower than the driving frequency of the pump 56 in step S3.

[0060] <D. Hardware Configuration of Control Unit 50> Referring to FIG. 5, the hardware configuration of the control unit 50 shown in FIG. 2 above will be described. FIG. 5 is a diagram showing an example of the hardware configuration of the control unit 50.

[0061] The control unit 50 includes a control circuit 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, a communication interface 104, and an auxiliary storage device 120. These components are connected to an internal bus 109.

[0062] The control circuit 101 is constituted by, for example, at least one integrated circuit. The integrated circuit can be constituted by, for example, at least one CPU, at least one GPU (Graphics Processing Unit), at least one ASIC (Application Specific Integrated Circuit), at least one FPGA (Field Programmable Gate Array), or a combination thereof.

[0063] The control circuit 101 controls the operation of the control unit 50 by executing various programs, such as the control program 122. The control program 122 is a program for realizing the various processes shown in Figures 3 and 4 above. Based on receiving an execution command for the control program 122, the control circuit 101 reads the control program 122 from the auxiliary storage device 120 or ROM 102 into the RAM 103. The RAM 103 functions as working memory and temporarily stores various data necessary for the execution of the control program 122.

[0064] The communication interface 104 is an interface for performing periodic communication with external devices using a field network. These external devices include, for example, the pump 56, the pressure-holding valve 58A, the drawback valve 58B, and the orifice valve 58C. Examples of field networks include EtherCAT®, EtherNet / IP®, CC-Link®, or CompoNet®.

[0065] The auxiliary storage device 120 is, for example, a storage medium such as a hard disk or flash memory. The auxiliary storage device 120 stores the control program 122 and the like. However, the storage location of the control program 122 is not limited to the auxiliary storage device 120, and it may also be stored in the storage area of ​​the control circuit 101 (for example, cache memory), ROM 102, RAM 103, or an external device (for example, a server).

[0066] Further, the control program 122 may be provided not as a single program but as part of an arbitrary program. In this case, various processes according to the present embodiment are realized in cooperation with an arbitrary program. Even a program that does not include such partial modules does not deviate from the spirit of the control program 122 according to the present embodiment. Further, part or all of the functions provided by the control program 122 may be realized by dedicated hardware. Further, the control unit 50 may be configured in the form of a so-called cloud service in which at least one server executes part of the processing of the control program 122.

[0067] <E. Flowchart related to preprocessing of tool change> Next, referring to FIG. 6, a flowchart related to the preprocessing of tool change by the above-described ATC 160 will be described. FIG. 6 is a flowchart showing the flow of preprocessing of tool change.

[0068] The processing shown in FIG. 6 is realized by the control unit 50 of the machine tool 100 executing the above-described control program 122. In other aspects, part or all of the processing may be executed by a CNC, circuit elements, or other hardware.

[0069] In step S110, the control unit 50 determines whether or not it has received a tool change command to remove the above-described tool T (see FIG. 2) from the spindle 180. When the control unit 50 determines that it has received the tool change command (YES in step S110), the control is switched to step S112. Otherwise (NO in step S110), the control unit 50 ends the processing shown in FIG. 6.

[0070] In step S112, the control unit 50 controls the above-described pump 56 to stop the discharge of coolant from the tool T. Here, the pump 56 may be driven continuously at, for example, the lowest drive frequency or may be completely stopped.

[0071] In step S114, the control unit 50 starts the coolant drawback process. More specifically, the control unit 50 opens the pressure holding valve 58A, opens the drawback valve 58B, and closes the orifice valve 58C. As a result, the coolant remaining in the communication passage L1, through passage L2, and flow path F1 is discharged from flow path F2.

[0072] The control unit 50 switches control from step S114 to step S116 after a predetermined time has elapsed since the start of the drawback process in step S114. This predetermined time may be set in advance or may be set arbitrarily by the user. As an example, this predetermined time is set to be longer than the time required to return a certain amount of coolant from the holding pressure valve 58A to the opening on the tip side of the tool T back to the flow path F2. This ensures that coolant does not drip from the tool T or the spindle 180.

[0073] In step S116, the control unit 50 starts the coolant filling process. More specifically, the control unit 50 closes the pressure-holding valve 58A, closes the drawback valve 58B, and opens the orifice valve 58C. Subsequently, the control unit 50 drives the pump 56 to pump the coolant into the aforementioned flow path F1. As a result, the coolant fills the flow path from the coolant tank 52 to the pressure-holding valve 58A.

[0074] The control unit 50 switches control from step S116 to step S118 after a predetermined time has elapsed since the start of the filling process in step S116. This predetermined time may be set in advance or may be set arbitrarily by the user. As an example, it may be set to be longer than the time required to fill the flow path between the coolant tank 52 and the pressure holding valve 58A with coolant.

[0075] In step S118, the control unit 50 controls the ATC 160 to execute a tool change process. More specifically, the control unit 50 removes the tool T mounted on the spindle 180 and mounts the next tool to be used specified in the machining program on the spindle 180.

[0076] <F. Flowchart related to machining process> Next, referring to FIG. 7, a flowchart related to the machining process of the workpiece will be described. FIG. 7 is a flowchart showing the flow of the machining process of the workpiece.

[0077] The process shown in FIG. 7 is realized by the control unit 50 of the machine tool 100 executing the above control program 122. In other aspects, part or all of the process may be executed by a CNC, circuit elements, or other hardware.

[0078] In step S150, the control unit 50 determines whether or not it has received the input of an NC program, which is a machining program for machining the workpiece, for example. When the control unit 50 determines that it has received the NC program (YES in step S150), it switches the control to step S160. Otherwise (NO in step S150), the control unit 50 ends the process shown in FIG. 7.

[0079] In step S160, the control unit 50 determines whether or not the machining is performed using the above tool T (see FIG. 2) in which the through passage L2 is formed. As an example, when a pre-registered tool is called in the machining program, or when an M code for turning on the through spindle coolant is detected in the machining program, the control unit 50 determines that the machining is performed using the tool T in which the through passage L2 is formed. When the control unit 50 determines that the machining is performed using the above tool T (YES in step S160), it switches the control to step S162. Otherwise (NO in step S160), the control unit 50 switches the control to step S166.

[0080] In step S162, the control unit 50 opens the pressure holding valve 58A, closes the draw-back valve 58B, and closes the orifice valve 58C.

[0081] In step S164, the control unit 50 drives the pump 56 so that the coolant is discharged from the tool T.

[0082] In step S166, the control unit 50 drives the spindle 180 according to the machining program and executes the machining process of the workpiece.

[0083] <G. Others> In the coolant mechanism of the above-described embodiment, the flow path F3 and the orifice valve 58C were provided. However, for example, when it is not necessary to continuously drive the pump 56 all the time, a configuration in which the flow path F3 and the orifice valve 58C are omitted may be used. Alternatively, even when it is necessary to continuously drive the pump 56 at the lowest driving frequency at which the discharge capacity is the smallest, when the pressure holding valve 58A is closed, the draw-back valve 58B on the flow path F2 may be opened, and a part of the coolant discharged from the pump 56 may be returned to the coolant tank 52 through the flow path F2. In such a modification, the draw-back valve 58B is preferably not an on-off valve but a control valve whose opening degree can be adjusted. During the draw-back process, the draw-back valve 58B may be opened to the opening degree for draw-back, and during the filling process, the opening degree of the draw-back valve 58B may be controlled to a filling opening degree smaller than the opening degree for draw-back. By doing so, a predetermined flow path resistance can be generated in the flow path F2 during the filling process. That is, it is possible to prevent all the coolant discharged from the pump 56 from returning to the coolant tank 52 through the flow path F2, and only a part of the coolant discharged from the pump 56 can be returned to the coolant tank 52 from the flow path F2. Therefore, it becomes possible to perform the filling process while continuously driving the pump 56 for the portion downstream of the branch point of the flow path F2 in the flow path F1 and up to the portion where the pressure holding valve 58A is provided.

[0084] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope of equivalents of the claims are intended. [Explanation of symbols]

[0085] 40A Tool storage compartment, 40B Machine body, 50 Control unit, 52 Coolant tank, 54 Motor driver, 55 Motor, 56 Pump, 58A Pressure holding valve, 58B Drawback valve, 58C Orifice valve, 100 Machine tool, 101 Control circuit, 102 ROM, 103 RAM, 104 Communication interface, 109 Internal bus, 120 Auxiliary storage device, 122 Control program, 150 Magazine, 170 Spindle head, 175 Spindle cylinder, 180 Spindle, 400 Control panel, 405 Display, 406 Operation keys, D Door, F1 Flow path, F2 Flow path, F3 Flow path, FR Fluid resistance, L1 Connecting passage, L2 Through passage, P2 Branch point, P3 Branch point, T Tool.

Claims

1. A machine tool capable of machining a workpiece using a tool having a through passage formed therein and configured to be able to discharge coolant to the outside from an opening at a tip end side of the through passage, a main shaft configured to be able to mount the tool and having a communication passage connected to the through passage when the tool is mounted; a pump for pumping a coolant to a first flow passage connected to the communication passage; a first valve provided in the first flow path or the communication passage; a second valve capable of switching at least whether to return the coolant located on the first valve side of a branch point of the second flow path to a second flow path branched off from the first flow path between the pump and the first valve; and a control unit for controlling the machine tool, The control unit is a drawback process in which, when the discharge of the coolant from the tool to the outside is stopped, the second valve is opened and at least an amount of coolant present from the first valve to the opening on the tip side of the tool is returned to the second flow path; the first valve is closed after the drawback process is performed, and a filling process is performed to fill the first flow path between the pump and the first valve with coolant.

2. The first valve is provided on the first flow path, 2. The machine tool according to claim 1, wherein a length of a flow passage between the first valve and the spindle is shorter than a length of a flow passage between the second valve and the spindle.

3. The machine tool further includes a third valve provided in a third flow path branching off from the first flow path between the pump and the first valve, The machine tool according to claim 1 or 2, wherein the filling process includes a process of opening the third valve.

4. The first valve is provided on the first flow path, 4. The machine tool according to claim 3, wherein a length of a flow passage between the first valve and the spindle is shorter than a length of a flow passage between the third valve and the spindle.

5. The machine tool according to claim 3 , wherein a branch point between the first flow path and the third flow path is provided closer to the spindle than a branch point between the first flow path and the second flow path.

6. The machine tool according to claim 1 or 2, wherein the control unit starts execution of the filling process after a predetermined time has elapsed since execution of the drawback process was started.

7. A method for controlling a machine tool capable of machining a workpiece using a tool having a through passage formed therein and configured to be able to discharge coolant to the outside from an opening at a tip end side of the through passage, comprising: The machine tool comprises: a main shaft configured to be able to mount the tool and having a communication passage connected to the through passage when the tool is mounted; a pump for pumping a coolant to a first flow passage connected to the communication passage; a first valve provided in the first flow path or the communication passage; a second valve capable of switching at least whether to return the coolant located on the first valve side of a branch point of the second flow path to a second flow path branched off from the first flow path between the pump and the first valve, The control method includes: When the discharge of the coolant from the tool to the outside is stopped, the second valve is opened, and at least an amount of the coolant existing from the first valve to the opening on the tip side of the tool is returned to the second flow path. and closing the first valve after performing the returning step, and filling the first flow path between the pump and the first valve with coolant.

8. A control program for a machine tool capable of machining a workpiece using a tool having a through passage formed therein and configured to be able to discharge coolant to the outside from an opening at a tip end side of the through passage, The machine tool comprises: a main shaft configured to be able to mount the tool and having a communication passage connected to the through passage when the tool is mounted; a pump for pumping a coolant to a first flow passage connected to the communication passage; a first valve provided in the first flow path or the communication passage; a second valve capable of switching at least whether to return the coolant located on the first valve side of a branch point of the second flow path to a second flow path branched off from the first flow path between the pump and the first valve, The control program causes the machine tool to When the discharge of the coolant from the tool to the outside is stopped, the second valve is opened, and at least an amount of the coolant existing from the first valve to the opening on the tip side of the tool is returned to the second flow path. a step of closing the first valve after the returning step is performed, and filling the first flow path between the pump and the first valve with coolant.

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