Control device for machine tool

Abstract

To allow a tool to automatically retract without causing breakage thereto when machining abnormality or the like occurs, and thereby inhibit deterioration in productivity.SOLUTION: A control device 10 of a machine tool 1 includes: parameter setup means 13 in which parameters related to control are stored in advance; retraction means 14 for making a tool 7 retract from a workpiece W; and chip discharge means 17 for making the tool 7 discharge chips. At the timing of detecting machining abnormality, retraction operation of the tool 7 can be executed according to the retraction means 14, and at the timing of stopping the retraction operation, chip discharge operation according to the chip discharge means 17 can be executed respectively.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a control device for automatically and safely retracting a tool without breakage when an abnormality such as machining abnormality occurs in a machine tool.

Background Art

[0002] In a machine tool, in screw machining using a tap as a tool, when an abnormality occurs during machining, it is necessary to remove the tap in the middle of machining from the screw hole. When the removal operation is automatically performed by a machine, if chips are caught between the cutting edge and the created screw surface, a large load is applied to the tap, and in the worst case, breakage occurs and the workpiece becomes defective. Therefore, currently, the operation is performed manually while a person adjusts the load during the removal operation, which takes a lot of man-hours until machining is resumed and the productivity deteriorates. Therefore, a method of controlling the retraction speed during retraction has been proposed based on the information of the tap and the workpiece. For example, Patent Document 1 discloses an invention that calculates the spindle speed of the removal operation using the pitch information of the tap and the material type information of the workpiece as inputs, and retracts the tool at the calculated speed, thereby automating the removal operation without damaging the tap or the workpiece.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the technology of the above Patent Document 1, a technique has been proposed in which the spindle speed of the extraction operation without breakage is determined in advance for each material type of the workpiece, and the tool is retracted at a speed calculated based on the determined spindle speed and the pitch information of the tap using the material type information of the workpiece as an input. However, depending on the state of chip jamming between the cutting edge and the created thread surface when the machining is interrupted, simply performing a reverse rotation operation will cause a large load on the tap and prevent breakage. Fig. 1 shows the operating torque in the case where the chip jamming state during retraction is different in tap machining. The upper figure shows the case of less jamming, and the lower figure shows the case of more jamming. When there is less jamming, it can be retracted without breakage, but when there is more jamming, vibration occurs in the operating torque immediately before the machining is interrupted, and tool breakage occurs after performing the reverse rotation operation for retraction. Therefore, in the conventional invention, breakage occurs in the worst case and the workpiece becomes defective. Or, manual extraction by a person occurs, and productivity deteriorates.

[0005] Therefore, an object of the present disclosure is to provide a control device for a machine tool that can automatically retract a tool without breakage when an abnormality such as machining abnormality occurs and can suppress deterioration of productivity.

Means for Solving the Problems

[0006] In order to achieve the above object, the present disclosure mounts on a spindle that can move relative to a workpiece A tap as a tool and uses the Tap to perform the following operations on the workpiece Perform threading on A control device for a machine tool, a parameter preparation means for storing predetermined parameters related to control in advance, a retraction means for retracting the Tap from the workpiece, a chip discharge means for causing the Tap to perform a chip discharge operation, and is provided with the retraction operation of the Tap by the retraction means and the chip discharge operation of the chip by the chip discharge means are 、 each At different predetermined timings executable , The parameter preparation means stores the pitch of the chip discharge groove of the tap and the preset number of revolutions of the tap, The chip discharge means calculates the discharge operation distance of the chips from the pitch of the chip discharge groove and the number of revolutions of the tap, and causes the tap to perform a feed operation and a rotation operation by the discharge operation distance in the same direction as the machining direction It is characterized in that. Another aspect of the present disclosure is that in the above configuration, the parameter preparation means identifies in advance an operating distance that allows the chip to be discharged and the tap and the workpiece to be retracted without damage, and determines the number of tap rotations based on the identification result and the pitch. It is characterized by that. Another aspect of the present disclosure is that in the above configuration, it includes a machining diagnosis means for diagnosing whether the machining of the workpiece is normal or not. The predetermined timing for executing the retraction means is when the machining diagnosis means diagnoses that the machining is abnormal. It is characterized by that. Another aspect of the present disclosure is that in the above configuration, it includes a retraction diagnosis means for diagnosing whether the retraction operation by the retraction means is normal or not. The predetermined timing for executing the chip discharge means is when the retraction diagnosis means diagnoses that the retraction operation is abnormal and stops the retraction operation by the retraction means. It is characterized by that.

Advantages of the Invention

[0007] According to the present disclosure, the chip biting of the tool can be suppressed by the chip discharge operation of the chip discharge means, and when machining abnormalities or the like occur, the tool can be automatically retracted without breakage by the retraction means. Therefore, deterioration of productivity can be suppressed.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. FIG. 2 is a block configuration diagram showing an example of the control device of the present disclosure. The control device 10 is provided along with the machine tool 1. The control device 10 may be incorporated in a position control device (not shown) of the machine tool 1. First, the machine tool 1 includes a table 3 supported movably in the left - right direction (Y - axis direction) of the paper surface on the bed 2, a column 4 fixed on the bed 2, and a spindle head 5 supported movably in the direction perpendicular to the paper surface (X - axis direction) and the up - down direction (Z - axis direction) on the column 4. A downward spindle 6 is rotatably supported on the spindle head 5, and a tool 7 can be attached thereto.

[0010] The control device 10 is provided with a machining information acquisition means 11, a machining diagnosis means 12, a parameter preparation means 13, a retraction means 14, a retraction diagnosis means 15, a retraction continuation determination means 16, a chip discharge means 17, and an alarm reporting means 18. The machining information acquisition means 11 acquires the control information of the machine tool 1 and the measurement signals of various sensors (not shown) as machining information. The machining diagnosis means 12 diagnoses whether the machining is normal or abnormal based on the machining information acquired by the machining information acquisition means 11. Parameters used for the control of the present disclosure are input or calculated to the parameter preparation means 13, and the values are stored therein. When an abnormality is detected by the machining diagnosis means 12, the retraction means 14 commands the machine tool 1 to perform a retraction operation to retract the tool 7 from the workpiece W. The retraction diagnosis means 15 compares the breaking torque threshold value calculated based on the set value of the parameter preparation means 13 with the machining information, diagnoses whether the retraction operation is normal or abnormal, and outputs the diagnosis result to the retraction continuation determination means 16.

[0011] When the diagnosis result of the retraction diagnosis means 15 is normal, the retraction continuation determination means 16 commands the retraction means 14 to continue the retraction operation. When the diagnosis result is abnormal, the retraction continuation determination means 16 commands the retraction means 14 to stop the retraction operation, and commands the chip discharge means 17 to perform a chip discharge operation to discharge chips. The chip discharge means 17 commands the machine tool 1 to perform a chip discharge operation in which the feeding and rotating operations of the tool 7 are carried out by a discharge operation distance calculated using the set value of the parameter preparation means 13. The alarm reporting means 18 counts both the retraction operation and the chip discharge operation as one set, compares the counted number of sets with the set number threshold value which is the set value of the parameter preparation means 13, and determines whether to stop the operation and report an alarm or continue the retraction operation.

[0012] Hereinafter, the details of the control by the control device 10 will be described based on the flowchart of FIG. 3. Step (hereinafter simply referred to as "S") 1 shown in FIG. 3 is executed by the parameter preparation means 13, S2 to S3 are executed by the machining diagnosis means 12, S4 and S15, S17 are executed by the retraction means 14, S5 to S6, S8 are executed by the retraction diagnosis means 15, S7 is executed by the machining information acquisition means 11, S9 is executed by the retraction continuation determination means 16, S10 to S11 are executed by the chip discharge means 17 and the retraction means 14, and S12 to S14, S16 are executed by the alarm reporting means 18, respectively. First, in S1, the sectional coefficient Z, tensile strength H, safety factor S of the tap serving as the tool 7, the pitch P of the chip discharge groove, and the set number threshold value Ns are input and stored. The tap rotation speed Nr is obtained by identifying an operation distance at which chips can be discharged in advance and the tap and the workpiece W can be retracted without damage, and dividing the identification result by the pitch P of the chip discharge groove, and then storing it. In S2, machining diagnosis is performed. If no machining abnormality is detected in the determination of S3, the machining diagnosis is continued in S2. If a machining abnormality is detected, a retraction operation for separating the tool 7 from the workpiece W is performed in S4. In S5, it is determined whether to continue the control. If not, the retraction operation is continued in S15. In S17, it is determined whether the retraction operation is completed. If it is completed, the process ends. If it is not completed, the process returns to S5. If the control is continued in S5, the process proceeds to S6.

[0013] In S6, the break torque threshold value Tb is calculated from the sectional coefficient Z, tensile strength H, and safety factor S of the tap by the following formula (1). Tb = 2ZH / S ··(1) At S7, the operating torque Tc of the spindle 6 during the retraction operation is measured, and at S8, the operating torque Tc is compared with the breaking torque threshold Tb. Here, if the operating torque Tc is smaller than the breaking torque threshold Tb, the retraction operation is considered normal, and if it is larger, it is considered abnormal and output to S9. At S9, if the retraction operation is normal, it is determined to continue the retraction operation, and the retraction operation is continued at S15. If the retraction operation is abnormal, it is determined to abort the retraction, the retraction operation is aborted at S10, and the discharge operation distance L is calculated by the following formula (2). L = PNr ··(2)

[0014] At S11, a chip discharge operation is performed in which the tap is fed and rotated by the discharge operation distance L. The spindle rotation speed and the feed speed of the chip discharge operation are not limited in any way, and in this embodiment, the same conditions as the machining operation are used. At S12, the set number N is counted with one set consisting of both the retraction operation and the chip discharge operation. At S13, the set number N is compared with the set number threshold Ns. The set number threshold Ns is obtained by previously checking the number of sets in which one set consists of both the retraction operation and the chip discharge operation and no damage occurs to the machine's operating axis, and using that value. If, in the determination at S13, the set number N is smaller than the set number threshold Ns (No at S13), the retraction operation is continued at S4, and if it is larger (Yes at S13), the operation is aborted at S14, an alarm is issued, and the set number N is reset and terminated at S16.

[0015] Fig. 4 shows the change in the operating torque of the spindle 6 when the control of this embodiment is applied. By monitoring the operating torque during the retraction operation with the breaking torque threshold after diagnosing an abnormality in machining, performing a chip discharge operation when the breaking torque threshold is exceeded, and performing the retraction operation again when the operating torque does not exceed the breaking torque threshold, it can be seen that the tap can be retracted from the workpiece without breakage.

[0016] As described above, the control device 10 of the machine tool 1 of the above-described embodiment includes a parameter preparation means 13 in which parameters related to control are stored in advance, a retraction means 14 that retracts the tool 7 from the workpiece W, and a chip discharge means 17 that causes the tool 7 to perform a chip discharge operation. At the timing when a machining abnormality is detected, the retraction operation of the tool 7 by the retraction means 14 and the chip discharge operation by the chip discharge means 17 at the timing when the retraction operation is stopped are each executable. According to this configuration, the chip discharge operation by the chip discharge means 17 suppresses the biting of chips of the tool 7, and the tool 7 at the time of occurrence of a machining abnormality can be automatically retracted by the retraction means 14 without breakage. Therefore, deterioration of productivity can be suppressed.

[0017] Hereinafter, modification examples of the present disclosure will be described. In the above-described embodiment, the retraction operation is performed by the retraction means when a machining abnormality occurs. However, the retraction operation is not limited to the occurrence of a machining abnormality, and the present disclosure can also be applied to a case where the retraction operation is performed for collision prevention or the like during normal machining. The chip discharge means may also be executed not only at the timing when the retraction operation is stopped, but also when removing a tap from a screw hole at the end of normal machining. In the above-described embodiment, together with the retraction diagnosis means, a retraction continuation determination means for determining whether or not to continue the retraction operation is provided. However, the retraction continuation determination means may be omitted, and the retraction operation may be stopped based on the abnormality diagnosis of the retraction operation by the retraction diagnosis means. The retraction diagnosis means may include the process of retraction continuation determination.

[0018] The machining diagnosis means may use a method of comparing machining information with a preset threshold value to diagnose whether it is normal or abnormal, or a method of diagnosing whether it is normal or abnormal using a mathematical model obtained by learning machining information using machine learning without any problem. In addition, the machine tool is not limited to the above-described embodiment. The tool is not limited to a tap.

Description of Reference Numerals

[0019] 1 ·· Machine tool, 2 ·· Bed, 3 ·· Table, 4 ·· Column, 5 ·· Spindle head, 6 ·· Spindle, 7 ·· Tool, 10 ·· Control device, 11 ·· Machining information acquisition means, 12 ·· Machining diagnosis means, 13 ·· Parameter preparation means, 14 ·· Retracting means, 15 ·· Retracting diagnosis means, 16 ·· Retracting continuation determination means, 17 ·· Chip discharging means, 18 ·· Alarm reporting means, W ·· Workpiece.

Claims

1. A control device for a machine tool that mounts a tap as a tool on a spindle that can move relative to a workpiece and performs threading on the workpiece using the tap, comprising: parameter preparation means for pre-storing predetermined parameters related to control; retraction means for retracting the tap from the workpiece; chip discharge means for causing the tap to perform a chip discharge operation, and comprising: the retraction operation of the tap by the retraction means and the chip discharge operation by the chip discharge means can be executed at different predetermined timings respectively; the parameter preparation means stores the pitch of the chip discharge groove of the tap and a preset tap rotation speed; the chip discharge means calculates a chip discharge operation distance from the pitch of the chip discharge groove and the tap rotation speed, and causes the tap to perform a feed operation and a rotation operation by the discharge operation distance in the same direction as the machining direction. A control device for a machine tool characterized by this.

2. The parameter preparation means has previously identified an operation distance at which chips can be discharged and the tap can be retracted without damage to the tap and the workpiece, and determines the tap rotation speed based on the identification result and the pitch. The control device for a machine tool according to claim 1, characterized by this.

3. Comprising machining diagnosis means for diagnosing whether the machining of the workpiece is normal or not, the predetermined timing for executing the retraction means is when machining is diagnosed as abnormal by the machining diagnosis means. The control device for a machine tool according to claim 1 or 2, characterized by this.

4. Comprising retraction diagnosis means for diagnosing whether the retraction operation by the retraction means is normal or not, the predetermined timing for executing the chip discharge means is when the retraction diagnosis means diagnoses the retraction operation as abnormal and stops the retraction operation by the retraction means. The control device for a machine tool according to any one of claims 1 to 3, characterized by this.

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