JP2013188831A - Control device of machine tool and machine tool equipped with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of a machine tool and the machine tool equipped with the same capable of estimating beforehand a processing load with high accuracy irrespectively of a variation in the thickness and hardness of a workpiece and capable of making compatible both the improvement of processing efficiency and the maintenance of processing accuracy.SOLUTION: A machine tool 100 includes: cutting blades 101 cutting a workpiece; a holder 102 holding and fixing the cutting blades 101; a main spindle motor 103 rotating the cutting blades 101; a drive stage 104 moving the main spindle motor 103; an inverter 105 supplying electric power to the main spindle motor 103; a processing machine NC 106 instructing a feed speed to the drive stage 104; a cutting resistance measuring instrument 107 measuring a processing load (cutting resistance value) subjected to the cutting blade; a control device 200 instructing an appropriate feed speed to the processing machine 106; and a workpiece mounting table 109 mounting the workpiece 110.

Description

  The present invention relates to a machine tool control device that cuts a workpiece with a cutting tool and a machine tool including the same.

  In cutting, it is required to remove a part of the workpiece and obtain a required shape by bringing the cutting tool into contact with the workpiece at a predetermined relative speed. Among cutting tools, milling machines and end mills increase machining efficiency by providing a rotating body with a plurality of cutting edges. However, if the machining efficiency is increased, the machining load increases, and the machining accuracy may be impaired due to deformation and vibration of the workpiece / cutting tool. For this problem, various measures have been taken to change the machining conditions so that the machining load falls within a certain range.

  As a countermeasure against such a problem, in the machining load monitoring method disclosed in Patent Document 1, the machining load is monitored in order to reduce erroneous determination due to variations in machining load depending on cutting conditions. Specifically, the processing load monitoring for monitoring the processing load of a numerically controlled machine tool is to obtain the processing load reference data and variance from sampling data of multiple processing loads at the time of trial cutting, and calculate the variance value. Use this to set a threshold value according to the variation in the sampling data, compare the reference data with the measured data of the machining load at regular intervals by the load monitoring means, and whether the difference exceeds the threshold value Is done by detecting. That is, many trial processings are performed before the product is actually processed, the processing load at the time of product processing is predicted from the processing load at that time, and the processing conditions are changed.

  Further, in the NC machine tool feed axis control method and apparatus disclosed in Patent Document 2, the feed rate control of the NC machine tool is performed so that the displacement amount of the cutting edge of the tool due to the machining load does not exceed the target displacement amount. ing. The load calculation unit 11 calculates the load acting on the tool sequentially prior to actual machining from machining data such as workpiece shape and tool shape, machining conditions such as spindle rotation speed and feed speed, and feed axis position command. To do. In response to the result, the displacement amount calculating means 13 calculates the predicted displacement amount of the cutting edge portion of the tool, and the feed rate control means 15 calculates the target displacement of the cutting edge portion of the tool corresponding to the predicted displacement amount and the target machining accuracy. The feed rate is controlled in accordance with the comparison result. This measures the amount of displacement of the tool cutting edge when actually machining the product, and controls the feed rate so that the amount of displacement does not exceed the set value.

Japanese Patent Laid-Open No. 7-132440 Japanese Patent Laid-Open No. 9-47941

  However, in the conventional processing load monitoring system of Patent Document 1, since the actual processing conditions are determined based on the processing load measured by performing the trial processing, the workpieces during the trial processing and the actual processing are processed. When there are variations in thickness and hardness, there is a problem that the prediction accuracy of the processing load decreases.

  Further, in the conventional feed axis control method and apparatus for an NC machine tool disclosed in Patent Document 2, when the machining condition is changed based on the machining load measured at the time of actual machining, the machining condition change is not in time and is excessive. There has been a problem that machining accuracy may be impaired by machining load.

  The present invention has been made in order to solve the above-described problems. Regardless of variations in the thickness and hardness of the workpiece, the processing load can be predicted in advance with high accuracy, and the processing efficiency can be improved. An object of the present invention is to provide a machine tool control device capable of both maintaining machining accuracy.

  In order to solve the above problems, a machine tool control device according to claim 1 of the present invention includes a load measuring means for measuring a processing load when processing a workpiece by a tool having a plurality of cutting edges, Calculated by the contact cutting edge number calculating means for calculating the number of the cutting edges that simultaneously contact the workpiece after the elapsed start time, the machining load measured by the load measuring means, and the contact cutting edge number calculating means. Load predicting means for predicting a processing load according to the increased number of simultaneously contacting cutting edges based on the number of simultaneously contacting cutting edges, and changing a machining condition according to the predicted processing load Machining condition changing means.

  According to a sixth aspect of the present invention, there is provided a machine tool comprising a control device for the machine tool.

  According to the machine tool control device of the present invention, the machining load (cutting resistance value) at the time of actual machining is used to perform cutting based on highly accurate load prediction. Regardless of the variation, the machining conditions can be changed before an excessive machining load is generated, so that it is possible to suppress the occurrence of machining defects due to the overload acting.

1 is an overall schematic configuration diagram of a machine tool to which a machine tool control device according to a first embodiment is applied. It is a schematic block diagram of the signal processing apparatus which comprises the structure of the control apparatus of the machine tool which concerns on Embodiment 1. FIG. FIG. 3 is a schematic diagram showing the movement of the cutting tool during processing in the first embodiment. 6 is a diagram showing a relationship between a machining start elapsed time and a cutting resistance value obtained by calculation in Embodiment 1. FIG. It is a figure which shows the relationship between the feed rate of the cutting tool calculated | required by calculation in Embodiment 1, and a cutting resistance value. It is a whole schematic block diagram of the machine tool to which the control apparatus of the machine tool which concerns on Embodiment 2 is applied. It is a schematic block diagram of the signal processing apparatus which comprises the structure of the control apparatus of the machine tool which concerns on Embodiment 2. FIG. It is a figure which shows the relationship between the process start elapsed time in Embodiment 2, and the supplied spindle motor electric current value. It is the figure which expanded a part of FIG.

  With the machine tool control device of the present invention, even if there is a variation in the thickness and hardness of the workpiece using the machining load during actual machining, an excessive load fluctuation occurs based on highly accurate load prediction. The machining conditions can be changed to suppress the occurrence of machining defects due to overload, and both improvement in machining efficiency and maintenance of machining accuracy can be achieved regardless of variations in workpiece thickness and hardness. It is something that can be done. Hereinafter, a control device for a machine tool according to an embodiment of the present invention will be described with reference to FIGS.

Embodiment 1 FIG.
FIG. 1 is an overall schematic configuration diagram of a machine tool to which the machine tool control device according to the first embodiment is applied, and FIG. 2 is a signal constituting the configuration of the machine tool control device according to the first embodiment. It is a schematic block diagram of a processing apparatus. FIG. 3 is a schematic diagram showing the movement of the cutting tool during machining in the first embodiment, and FIG. 4 is a diagram showing the relationship between the machining start elapsed time and the cutting resistance value obtained by calculation. FIG. 5 is a diagram showing the relationship between the cutting tool feed rate and the cutting resistance value obtained by calculation.

  As shown in FIG. 1, a machine tool 100 applied to the first embodiment includes a cutting edge 101 for cutting a workpiece, and a holder 102 (holding the cutting edge 101 and the holder 102 for holding and fixing the cutting edge 101). The combination is referred to as a tool.), A spindle motor 103 that rotates the cutting edge 101, a drive stage 104 that moves the spindle motor 103, an inverter 105 that supplies power to the spindle motor 103, and a drive stage 104. A processing machine NC106 for instructing a speed, a cutting resistance measuring device (load measuring means) 107 for measuring a processing load (cutting resistance value) received by the cutting edge, and a control device 200 for instructing the processing machine NC106 with an appropriate feed speed The workpiece mounting table 109 on which the workpiece 110 is mounted.

  As shown in FIG. 2, the machine tool control apparatus 200 according to the first embodiment includes a data input unit 201 that accepts tool information, workpiece information, and machining condition data, and a data storage that stores these pieces of information. A cutting edge value calculated by the cutting resistance measuring unit 107, a contact cutting edge number calculating unit (contact cutting edge number calculating means) 203 that calculates the number of cutting edges 101 that are in contact with each other at the same time based on these pieces of information; A cutting resistance value calculation unit (load predicting means) 207 that calculates a necessary cutting resistance value from the number of cutting blades that come into contact at the same time calculated by the contact cutting edge number calculation unit 203, and the drive stage 104 from the calculated cutting resistance value A feed speed calculation unit (machining condition changing means) 205 that calculates the feed speed of the machine, and a feed speed change instruction that instructs the processing machine NC 106 to change the feed speed based on the calculated feed speed And 206, in being configured.

  Next, operations of the machine tool and the control device according to Embodiment 1 will be described with reference to FIGS.

  First, the operation of the machine tool 100 will be described. The spindle motor 103 is rotated by the electric power supplied from the inverter 105, and the holder 102 and the cutting blade 101 attached to the holder 102 are rotated in conjunction therewith. The drive stage 104 is moved by an instruction from the processing machine NC 106 while the cutting edge 101 is rotating, and the cutting edge 101 comes into contact with the workpiece 110 at a predetermined feed speed F, whereby the workpiece 110 is moved. A part is cut. At this time, the machining load (cutting resistance value) received by the tool is measured by the cutting resistance measuring device 107, and the measured cutting resistance value is transferred to the control device 200. In the control device 200, an appropriate feed rate is calculated by calculation processing from the received information such as the cutting resistance value and the machining condition, and this feed rate is transferred to the processing machine NC106. Based on this, the processing machine NC 106 instructs the drive stage 104 about the feed speed. As a result, the workpiece 110 is subjected to predetermined cutting by the cutting edge 101.

  Next, the operation in the control device 200 will be described. The data input unit 201 is a part where an operator inputs information such as tool information, workpiece information, and machining conditions necessary for the control device 200. In the present embodiment, face milling is taken as an example, the tool information is the tool diameter D and the number of cutting edges z, the workpiece information is the cutting width W, the processing conditions are the tool rotation speed S and the tool feed speed F. is there. Since the machining conditions are changed during machining by the control device 200, here, the air cutting conditions before the tool contacts the workpiece 110 are indicated.

The data storage unit 202 stores information input to the data input unit 201, and the contact cutting edge number calculation unit 203 starts contact of the tool with the workpiece 110 based on the information stored in the data storage unit 202. The relationship with the number n of cutting edges that are in contact with the elapsed time t since the start of machining is calculated. The cutting resistance value calculation unit 207 determines the cutting resistance when the number n of simultaneously contacting cutting edges becomes the maximum after the measurement time point based on the calculated number n of simultaneously cutting cutting edges and the measured cutting resistance value R. A predicted value Rmax of the value R is calculated. The feed speed calculation unit 205 calculates a feed speed F such that the calculated cutting resistance value Rmax is equal to or less than a predetermined value (cutting resistance value Rf at which cutting failure occurs), and the feed speed change instruction unit 206 calculates The processing machine NC106 is instructed so that the feeding speed F is reached.

  Next, the relationship with the number n of cutting edges that come into contact with the progress of processing will be described with reference to the schematic diagram of FIG. Here, a sectional view (Z-axis plane) perpendicular to the traveling direction (X-axis) of the cutting edge 101 of the tool is shown. First, the workpiece 110 approaches the workpiece 110 while rotating with respect to the workpiece 110 as shown in FIG. At this time, the cutting edge 101 and the workpiece 110 are not in contact with each other, and the number of cutting edges in contact with each other is n = 0.

  Further, the cutting edge 101 of the tool starts to contact the workpiece 110, and as long as the contact angle θ is smaller than the opening angle α between the cutting edges 101 as shown in FIG. The state where is in contact and the state where it is not appearing alternately appear, and the number of cutting edges simultaneously contacting is n = 0 or 1. Further, as the cutting edge 101 of the tool advances toward the workpiece 110, the ratio of the number of cutting edges that are in contact with each other at the same time increases when n = 1 compared to the time when n = 0. The opening angle α of the cutting edge 101 is expressed as α = 2π / z (rad) using the number of blades z.

Next, when the contact angle θ exceeds the opening angle α of the cutting edge 101, the plurality of cutting edges 101 come into contact at the same time. As shown in FIG. 3C, under the condition of α <θ <2α, the number of cutting edges that are in contact with each other is n = 1 or 2, and as shown in FIG. 3D, 2α <θ <. Under the condition of 3α, the number of cutting edges that are in contact at the same time is n = 2 or 3. After that, the number n of cutting blades that are simultaneously in contact while maintaining the same relationship increases. However, since the contact angle θ does not change when the cutting width W becomes a constant value, the increase in the number of cutting edges that are simultaneously contacted also stops. The contact angle θ at that time can be obtained by θ = 2sin ⁻¹ (W / D), where D is the tool diameter.

In addition, the elapsed time tn from the start of the machining in which the number n of cutting edges that are simultaneously contacted is expressed by the following equation.
tn = 30 × D × (1-COS (nπ / z)) / F (1)
Here, n is assumed to be 1,..., M−1 (m: maximum number of cutting edges that are in contact with each other at the same time), and D> Wd (Wd: width of the workpiece).

  As a specific example, the relationship between the number n of cutting edges that are in contact with each other and the cutting resistance value R will be described with reference to FIG. In this graph, the horizontal axis indicates the elapsed time t after the tool (cutting edge 101) starts to contact the workpiece 110, and the vertical axis indicates the calculation result of the cutting resistance value R. The machining conditions were as follows: cutting width W = 77 mm, tool diameter D = 100 mm, number of cutting edges z = 8, tool rotation speed S = 382 rpm, tool feed rate F = 856 mm / min, and axial cut g = 3 mm. Immediately after the start of contact (start of machining), the number of cutting edges that are in contact at the same time is n = 0 or 1, and n = 1 in a region where cutting resistance is generated. As the feed of the tool progresses, the time during which cutting resistance is generated becomes longer and changes from n = 1 to 2 at around t1 = 0.3 sec. Similarly in this region, the time of n = 2 becomes longer as the tool feed proceeds. Furthermore, n = 2 changes to 3 around t2 = 1.1 sec. Similarly, in this region, the time of n = 3 becomes longer, but reaches a cutting width of 77 mm at t = 1.26 sec, and thereafter becomes a steady state.

In this embodiment, based on the above results, the maximum cutting resistance value at the maximum cutting edge number m (n = 3 in this example) simultaneously contacting from the maximum cutting resistance value R1 or R2 at n = 1 or 2. Rmax (= R3) is predicted, and the feed speed F is changed so as to be equal to or less than a predetermined cutting resistance value Rf at which cutting chatter failure does not occur. In the calculation of the cutting resistance value R, for example, it can be calculated by the product of the specific cutting resistance k (N / mm ² ), which is the cutting resistance value R per unit area, and the cutting cross-sectional area A. Assuming that the angle formed by the tool traveling direction and the straight line connecting the cutting edge and the tool center is θ, it is expressed as A = d × F / S / z × cos θ. FIG. 5 shows the result of calculating the maximum cutting resistance values R1, R2, and R3 at n = 1, n = 2, and n = 3, respectively, with the cutting edges that are simultaneously in contact with each other and θ being a variable. Here, a general carbon steel was selected as a workpiece, and a specific cutting resistance k = 2,000 (N / mm ² ) was used.

  For example, when the cutting resistance value R is 3500 N or more in a prior investigation, the maximum contact resistance simultaneously from the maximum cutting resistance value R2 when n = 2 is known for chatter failure. A method for predicting the maximum cutting resistance value Rmax with the number m of cutting edges (n = 3 in this example) will be described. When the feed rate F at the time of air cut is 856 mm / min, the maximum cutting resistance value R at n = 2 is R = 3083N. At this time, no defect occurs, but when n = 3, the maximum cutting resistance value R3 becomes R = 4044N (> 3,500N), and a defect occurs. Therefore, since the straight line of n = 3 is represented by R = 4.723 × F, F> 741 mm / min satisfying R> 3,500N is calculated, and F = Automatic adjustment to 667 mm / min. However, the tolerance for occurrence of defects is arbitrary.

  Thereby, at the time of cutting, the tool is set such that the maximum cutting resistance value Rmax at the maximum number m of cutting edges that are simultaneously in contact with the workpiece is within a predetermined range (the cutting resistance value Rf that does not cause defects). By calculating the feed rate F of (cutting edge) and adjusting the feed rate based on this result, fluctuations in the cutting resistance value can be minimized and the occurrence of machining defects can be reduced.

In FIG. 5, the maximum cutting resistance value R at each n is calculated as d = 3 mm and k = 2,000 (N / mm ² ), but the thickness and hardness of the workpiece vary. However, since the relationship between the cutting resistance value R and the feed rate F changes in a proportional relationship, the maximum number m of cutting edges simultaneously contacting from the maximum cutting resistance value R of n = 2 (in this example, , N = 3), the maximum cutting resistance value Rmax can be similarly predicted. Note that if the cut d is too large and the axial length of the cutting edge is insufficient, a processing failure will occur even if the control device of the present invention is used, so the upper limit of the thickness of the workpiece is expected. It is desirable to set the cutting depth.

  Thus, according to the machine tool control device according to Embodiment 1, cutting is performed based on high-precision load prediction using the processing load (cutting resistance value) at the time of actual processing. Regardless of variations in the hardness and thickness of the workpiece, the machining conditions can be changed before an excessive load is generated, so that there is an effect that it is possible to suppress the occurrence of machining defects due to the overload acting.

Embodiment 2. FIG.
FIG. 6 is an overall schematic configuration diagram of a machine tool to which the machine tool control device according to the second embodiment is applied, and FIG. 7 is a signal constituting the configuration of the machine tool control device according to the second embodiment. It is a schematic block diagram of a processing apparatus. FIG. 8 is a diagram showing the relationship between the machining start elapsed time and the supplied spindle motor current value in the second embodiment, and FIG. 9 is an enlarged view of a part of FIG.

  In the first embodiment, the cutting resistance value generated thereafter is predicted by using the cutting resistance value corresponding to the number of cutting edges in contact with each other at the same time. Although this method can predict the cutting resistance value with the highest accuracy, it may be difficult to directly measure the cutting resistance value on the machine tool. Therefore, in the second embodiment, the maximum load is predicted by using the current value supplied to the spindle motor of the machine tool that is relatively easy to measure as an index of the machining load.

  The difference between the overall schematic configuration diagram of the machine tool according to the second embodiment shown in FIG. 6 and the overall schematic configuration diagram of the machine tool according to the first embodiment shown in FIG. 1 is installed in the first embodiment. There is no cutting resistance measuring device 107, and instead a current measuring device 308 is installed, and accordingly, the cutting resistance value calculating unit provided in the control device according to the first embodiment shown in FIG. 2 is replaced. 7 is that the current value calculation unit 408 is provided in the control device according to the second embodiment shown in FIG. 7, and the other components are the same as those in the first embodiment, and thus the description thereof is omitted.

  Next, the operation of the machine tool control apparatus according to Embodiment 2 will be described with reference to FIGS.

  First, the operation in the machine tool 300 will be described. The spindle motor 303 is rotated by the electric power supplied from the inverter 305, and the holder 302 and the cutting blade 301 attached to the holder 302 are rotated in conjunction therewith. The drive stage 304 is moved in response to an instruction from the processing machine NC306 while the cutting edge 301 is rotating, and the cutting edge 301 is brought into contact with the workpiece 310 at a predetermined feed speed F, whereby the workpiece 310 is moved. A part of is cut. At this time, the power supply from the inverter 305 is adjusted in order to maintain the rotation of the spindle motor 303 according to the processing load (cutting resistance value) received by the tool (including the holder 302 to which the cutting blade 301 is attached). In this embodiment, since the current of the spindle motor 303 is mainly increased or decreased according to the machining load, the current change amount (load measuring means) 308 is used as an alternative index for the change amount of the cutting resistance value. The measured current value of the spindle motor 303 is transferred to the control device 400. The control device 400 calculates an appropriate feed speed from information such as the measured current value and the machining conditions by arithmetic processing, and transfers this feed speed to the processing machine NC306. Based on this, the processing machine NC306 instructs the feed speed F to the drive stage 304. As a result, the workpiece 310 is subjected to predetermined cutting by the cutting edge 301.

  Next, the operation in the control device 400 will be described. The data input unit 401 is a part where an operator inputs information such as tool information, work piece information, and processing conditions necessary for the control device 400. Also in this embodiment, face milling similar to that in Embodiment 1 is taken as an example, and input information is also the same.

  The data storage unit 402 stores the information input to the data input unit 401, and the contact cutting edge number calculation unit 403 is based on the information stored in the data storage unit 402 and the tool (the holder 302 to which the cutting blade 301 is attached). Is calculated at the same time as the elapsed time t from the start of contact with the workpiece 310 (machining start). Based on the measured spindle motor current value I at the elapsed time t at which the calculated number n of simultaneously contacting cutting edges changes, the current value calculating unit 408 determines the maximum number of cutting edges simultaneously contacting after the measurement time point. A predicted maximum current value Imax is calculated. The feed rate calculation unit 405 calculates a feed rate F such that the calculated maximum current value Imax is equal to or less than a predetermined current value If where a cutting defect occurs, and the feed rate change instruction unit 406 calculates the calculated feed rate F. To the processing machine NC306. The difference from the first embodiment is that instead of measuring the cutting resistance value R, the current value I supplied from the inverter 305 to the spindle motor 303 is used.

As a specific example, FIG. 8 shows the relationship between the measured machining start elapsed time t and the spindle motor current value during actual machining. According to this, as the elapsed time t elapses, the spindle motor current value I increases, and at the maximum number of cutting edges m (n = 3 in this example) that are in contact at the same time, the increase stops at 40 to 45 A. However, under the influence of the fluctuation of the cutting resistance value R, the current value continues to vibrate periodically with a width of about 4 to 5A. On the other hand, the period of change in the spindle motor current value I with respect to the machining load supplied from the inverter 305 in this example is 0.017 sec, and the cutting resistance value R calculated in the first embodiment is shorter than this period. The moving average, which is a value obtained by calculating the average for each period while moving the range with the pitch, is also shown in FIG. According to this, the spindle motor current value I and the cutting resistance value R with respect to the elapsed time t show the same upward trend, and the fluctuation of the moving average of the cutting resistance value R becomes 0.3 sec. In the vicinity of 1 sec, the inventors have found a phenomenon that the fluctuation of the spindle motor current value I is 2 A or less over 0.1 sec and the fluctuation of the current value I is small and becomes a substantially constant value. It has been clarified that the current values I1 and I2 correspond to the cutting resistance value R in the elapsed time when the maximum number of cutting edges simultaneously contacting changes from n = 1 to 2 and n = 2 to 3.

  That is, the spindle motor current value I1 at the elapsed time t1 (n = 1 to 2) or the elapsed time t2 (n = 2 to 3) at which the predicted maximum number n of simultaneously contacting blades changes (increases). By carrying out the measurement of the value I2, the change in the current value is small even if there is a slight deviation in the measured elapsed time, so the accuracy is high and the maximum current value Imax with the maximum number of cutting edges m simultaneously contacting is calculated. be able to. In the present embodiment, using the above phenomenon, the maximum current value Imax at the maximum number m of cutting edges (n = 3 in this example) simultaneously contacting is obtained using the measured current value I1 or I2. Predict. The predicted current value Imax is compared with the current value If where the failure occurs, which is obtained by prediction or actual measurement. If the current value Imax is smaller than the current value If where the failure occurs, the feed speed F is not changed and the predicted current value Imax is predicted. If the current value Imax is larger than the current value If at which defects occur, the occurrence of defects can be reduced by changing the feed rate F as in the first embodiment.

  In the above embodiment, the case where the maximum current value Imax is predicted using the current value I1 at the elapsed time t1 or the current value I2 at the elapsed time t2 has been described. However, the current value I near t1 or t2 is described. It is also possible to increase the accuracy by using the average value of. Next, a method using this average value will be described with reference to FIG. 9 which is an enlarged view of a part of FIG. 8, taking the case of the elapsed time t1 as an example. First, if t1 is calculated using Equation 1 under the same conditions as in the first embodiment, t1 = 0.267 sec. Further, the first cutting edge at the start of machining may not be a predetermined depth of cut and may be smaller than the predicted cutting resistance depending on the initial position of the workpiece of the tool. Actually, since the machining time ts for one blade is added to t1 as an error, the actual elapsed time tr is in the range of t1 <tr <t1 + ts. Here, since ts = 60 S / z, when a numerical value is substituted, ts = 0.02. Therefore, the current value can be measured with high accuracy by averaging the current value I in the range from t1 = 0.267 to t1 + ts = 0.287. In actual operation, it is preferable to average in the processing time (−0.5 ts to 2.0 ts) for 2 to 3 blades with t + 0.5 ts as the center in consideration of measurement variation.

  In other words, during cutting, the current value I of the spindle motor is measured by the current measuring device 308 at the elapsed time t when the number n of simultaneously contacting cutting edges is predicted by the contact cutting edge number calculation unit 403, and the current value calculation is performed. The unit 408 obtains the spindle motor current value Imax at the maximum number of cutting edges m simultaneously contacting from the current value I, and the feed speed calculation unit 405 compares this current value Imax with the current value If where cutting failure occurs. Then, the feed rate F of the tool (cutting edge) where no defect occurs is calculated. Based on this result, the feed speed change instructing unit 406 can instruct the processing machine NC306 to adjust the feed speed, thereby minimizing the variation in the cutting resistance value and reducing the occurrence of machining defects. .

As described above, according to the machine tool control device according to the second embodiment, even when it is difficult to directly measure the cutting resistance value, by using the spindle motor current value, machining during actual machining is performed. Since the load can be estimated and cutting is performed based on highly accurate load prediction, an excessive load is generated regardless of variations in the hardness and thickness of the workpiece as in the first embodiment. Since the machining conditions can be changed before starting, there is an effect that the occurrence of machining defects due to the overload acting can be suppressed.

  In addition, in the said embodiment, although the case where the tool side which attached the cutting blade was moved was demonstrated, in the case where the workpiece mounting base side which mounts a workpiece is moved, or both are moved. Needless to say, the same effect can be obtained.

  Also, within the scope of the present invention, the embodiments can be freely combined, or the embodiments can be appropriately modified or omitted.

  Moreover, in the figure, the same code | symbol shows the same or an equivalent part.

100, 300 Machine tool 200, 400 Control device 101, 301 Cutting edge 102, 302 Holder 103, 303 Spindle motor 104, 304 Drive stage 105, 305 Inverter 106, 306 Machine NC
107 Cutting resistance measuring device 109,309 Workpiece mounting table 110,310 Workpiece 201,401 Cutting edge 202,402 Data input section 203,403 Contact cutting edge number calculation section 205,405 Feed speed calculation section 206,406 Feed Speed change instruction unit 207 Cutting resistance value calculation unit 408 Current value calculation unit

Claims (6)

Load measuring means for measuring a processing load at the time of processing a workpiece by a tool having a plurality of cutting edges;
Contact cutting edge number calculating means for calculating the number of cutting edges that simultaneously contact the workpiece after the processing start elapsed time;
Based on the machining load measured by the load measuring means and the number of simultaneously contacting cutting edges calculated by the contact cutting edge number calculating means, the machining load is determined in accordance with the increased number of simultaneously contacting cutting edges. A load prediction means for predicting;
A machine tool control device comprising: machining condition changing means for changing a machining condition in accordance with the predicted machining load.   2. The machine tool control device according to claim 1, wherein the machining condition changed by the machining condition changing means is a moving speed of the tool with respect to the workpiece.   3. The machine tool control device according to claim 1, wherein the load measuring unit is a cutting resistance measuring device that measures a machining load applied to the tool. 4.   3. The machine tool control device according to claim 1, wherein the load measuring unit is a current measuring device that measures a current flowing in a motor that rotationally drives the tool. 4.   The load predicting means is based on a current value measured by the current measuring instrument after an elapsed time of the start of the machining, in which an increase in the number of cutting blades in contact with the contact cutting edge number calculating means is predicted. The machine tool control device according to claim 4, wherein a current value is calculated in accordance with an increase in the number of cutting blades that are simultaneously in contact with each other, and the machining load is predicted.   A machine tool comprising the machine tool control device according to any one of claims 1 to 5.

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