JPS59142046A - Control method and device for tool life - Google Patents

Abstract

PURPOSE:To allow a tool life to approximate its target value, by automatically correcting particularly a cutting speed of the cutting conditions, previously programmed in conformity with characteristics of a machine tool, tool and a workpiece, so as to continue the cutting after the point of time when the cutting speed is corrected. CONSTITUTION:After starting a workpiece 6 to be cut by a numerically controlled lathe 1, adapting the edge point of a required tool 11 to a measuring face 18 of a detector 17 at each optionally preset time in accordance with a measuring program, if a change in the flank position of said tool generated during this time is detected as the present wearing amount DELTAW (mm.), a signal corresponding to this amount DELTAW is input to a detection control circuit 22. Next, on the basis of the tool life equation V<n>T=C(V=cutting speed, T=life time of tool, n and C are both constant.), the present cutting speed Vo programmed about said tool is corrected. In such way, continuing to cut the workpiece after the point of cutting speed correction time, a tool life cab be allowed to approximate its target value.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method and apparatus for managing the life of tools used in numerically controlled machine tools.

The length of tool life time has a major impact on the economic efficiency of machining, and if tool life time is too long, it means that the selected cutting conditions, mainly cutting speed, are too slow, resulting in a decrease in machining efficiency. On the other hand, if the life time is too short, it means that the cutting speed is too fast, and in this case, the tool wears out rapidly, increasing tool costs and increasing non-cutting time due to frequent tool replacement operations. This also results in a decrease in processing efficiency. On the other hand, when machining is continued unattended at night, restrictions are likely to be placed on tool exchange operations, so it may be desirable to extend tool life even at the expense of cutting speed.

Therefore, the present invention first determines the machine tools and tools to be used according to the material, hardness, shape, dimensions, and accuracy of the workpiece to be cut, and then considers the most economical one first. The cutting conditions, especially the cutting speed, should be selected such that the desired tool life time can be obtained, and for the second gentle bending, the target predetermined tool life can be achieved even at the cost of a certain degree of economy under restrictive operating conditions. By selecting an appropriate cutting speed to obtain the desired tool life time and measuring tool wear at predetermined intervals after the start of cutting, the tool was selected as described above in order to approach the target tool life time. It is an object of the present invention to provide a novel tool life management method and device characterized by automatically correcting the cutting speed. Another object of the present invention is to obtain the most appropriate cutting speed for a given color in conjunction with the management of tool life under determined machining conditions.

Conventionally, several proposals have been made regarding tool life management systems or management methods related to labor saving or unmanned operation of numerically controlled machine tools.

The present applicant has previously developed an adaptive control lathe equipped with a cutting force sensor and a dimension measurement sensor, in which changes in machining conditions are constantly monitored by the sensor, and when tool wear progresses beyond the control range, cutting control by the tool is implemented. Japanese Patent Laid-Open No. 55-58950 proposes an automatic tool management system that enables unmanned machining by stopping, returning to the original position, replacing the tool with a previously prepared substitute tool, and continuing cutting again.

In addition, a tool life management system that predicts and determines the life of multiple tools used in each machine tool in a group management system that controls the operation of multiple machine tools using a computer is published in Japanese Patent Publication No. 51-34995. It is disclosed in Japanese Patent Application Laid-open No. 54735485. latter 2
In both of these techniques, the actual cutting usage time for each tool is calculated from a pre-given program and accumulated in the computer storage device, and the cumulative usage time of each tool and the empirically predetermined tool limit are calculated. The tool life is predicted and determined by comparing the usage time, and the wear amount for each tool is calculated and stored cumulatively, and the cumulative wear amount of each tool is compared with a predetermined tool limit wear amount. The tool life is predicted and determined using software, and the tool life is managed using software.

In general, when determining the properties of the workpiece and the machine tools and tools to be used in cutting, cutting conditions such as cutting speed, depth of cut, feed, and cutting fluid have an impact on tool life, but the most prominent among these are cutting conditions such as cutting speed, depth of cut, feed, and cutting fluid. Cutting speed has a significant influence on cutting speed, and it is easy to adjust the length of tool life. Note that the depth of cut and feed are subject to restrictions such as the machining allowance of the workpiece or the state of the finished surface, and therefore cannot be freely selected as control factors for managing tool life in many cases. Traditionally, in production sites, the operator or programmer selects or specifies the required depth of cut, feed, and cutting speed based on experiential knowledge, or goes even further and performs cutting by utilizing data from accumulated tool files. Although the conditions are determined, the tool life is easily affected by changes in factors such as the material of the workpiece, hardness, stock removal, gripping means, and machine characteristics, so it is difficult to actually process while cutting with the machine. Correcting the current cutting conditions in response to the situation will yield the most appropriate results that are closest to the target life.

The present invention focuses on the fact that cutting speed is the factor that has the most decisive effect on tool life as described above, and that cutting speed can be controlled relatively easily.

Among the cutting conditions programmed in advance according to the characteristics of the tool and workpiece, the optimum cutting speed in this case is obtained by automatically correcting the cutting speed, and cutting is continued from that point onwards. The present invention will be explained in detail below based on examples.

FIG. 1 shows a headstock 3 which rotatably supports a numerically controlled lathe 1 according to the present invention, and a hydraulic chuck 5 fitted to the tip of the main spindle 4, which shows a workpiece 6. It is removably gripped by an automatic mounting device such as a colander transfer robot, and is rotated together with the main shaft 4 at an arbitrary desired rotational speed by a variable speed drive prime mover 7 such as a DC motor via an appropriate transmission mechanism.

A carriage 8 which is slidably placed on the guide surface of the bed 2 has a cross feed table 9 slidably placed on its upper guide surface, and the cross feed table 9 further allows a plurality of tools 11 to be detachably attached. A turret tool post 10 that carries and performs rotational indexing is mounted, and is moved in the Z direction parallel to the axis of the main shaft 4 and this axis through a suitable transmission mechanism such as a ball screw by feeding servo motors 12 and 13, respectively. Feeding and positioning control is performed in the perpendicular X direction according to commands from the numerical control device 20.

A heart valve stand 14 is mounted on the right side of the guide surface of the bed 2, facing the headstock 3, and is slid and tightened at any position in the Z direction. The numeral 16 cooperates with the chuck 5 of the main spindle 4 and is used for center work in which a long workpiece 6 is aligned and supported at both ends thereof for cutting.

Located on the Z-X plane including the spindle axis, the turret tool rest 1
A detector 17 for detecting the position of the cutting edge of the tool 11 is fixed to the side surface of the heart valve stand 14 facing 0, and the position of the cutting edge of the tool 11 is determined depending on whether the cutting edge is right-handed or left-handed. Similarly, when the turret tool rest 10 is actually moved by a predetermined amount of movement according to a program command from the numerical control device 20 and its cutting edge comes into contact with any of the measuring surfaces 18.1-9 of the detector 17, the tool cutting edge If there is a deviation in position, it is measured in microns and an electrical signal corresponding to the deviation is output. The detector 17 can be, for example, an analog displacement detector using a differential transformer, or a digital or optical type using Magnescale. Note that the installation position of the detector 17 is not limited to the side surface of the heart valve stand, but may be installed on an appropriate support fixed to the bed 2 near the origin position of the turret tool rest 10 so that it hits the cutting edge of the tool 11 when it returns to the origin. The detector 117 may be moved and positioned so that the detector 117 is in contact with the detector 117.

Next, the counting control device 30, which is the main component of the present invention, will be described. 22 is a detection control circuit that receives the signal from the detector 17 and converts it into a form that can be stored and processed, and the setting device 23 is This is a gauge switch for setting and inputting the target life time and limit wear amount of the tool 11 to be used and the Taylor index n in the tool life equation described later. The net cutting time of the tool, which can be calculated by the cutting program stored in the numerical control device 20, is stored in a designated location of the storage device 25, and these data are stored at any time.
It is displayed on the display 24. 26 is an arithmetic unit for calculating the wear rate, expected life time, corrected cutting speed, etc. of the tool 11 from the stored target tool life time, net cutting time, limit wear amount, and current wear amount; A comparator 28 cooperates with the numerical control device 20 to perform measurements and calculations.

A central control unit consisting of a micro CPU for controlling storage processing, 29 a numerical control unit 20 and a DC motor 7
This is an interface for transmitting and receiving signals between the mechanical control panel 31 of the numerically controlled lathe 1 and the counting control device 30, which includes a control circuit.

Next, the operation of the present invention configured as described above will be explained. In general, there are many methods for determining the life of a cutting tool, such as the condition of the finished surface of the workpiece, the color or formation of chips, the state of cutting noise or chatter during cutting, changes in the shape of the cutting edge, or relying on experience. However, flank wear VB shown in FIG. 2 is an important element in the tool life criterion. It is well known that tool flank wear increases as cutting progresses, and negative effects such as increased cutting resistance, fluctuations, temperature rise, deterioration of the cut surface of the workpiece, and deterioration of dimensional accuracy become stronger. . Furthermore, as mentioned above, flank wear, which is important as a determining factor of tool life, is most affected by cutting speed, but the difference between cutting speed V (m/m1n) and tool life time (min) is expressed as an exponential function, such as the relational expression V'T=O (where n and C are both constants determined by the material of the workpiece and tool and other cutting conditions), which has been determined based on many experiments. The tool life equation holds true. n is a Taylor index, and generally the value becomes smaller as the tool is made of high-speed steel, the material is more difficult to cut, and the cutting conditions become more unstable. Generally, n=2 for ceramic tools, n=25 to 4 for continuous cutting of carbide tools, and n=6 to 8 for high speed steel tools. According to the present invention, even if the exact value of this index n is not known in advance, by repeating the calculation based on the above-mentioned life equation, it is possible to approximate the appropriate cutting speed to achieve the target tool life time. Furthermore, if the expected tool life time and corrected cutting speed are obtained through the above-mentioned measurements and calculations, the above-mentioned life equation V'T = VonTo
=C! The appropriate value of the Taylor index n can be calculated conversely from .

Figure 3 shows hard steel 545C using cutting speed V (m/m i mouth) as a parameter. This is a tool wear characteristic diagram showing that the amount of tool wear and net cutting time are approximately proportional when cutting with a carbide tool.The solid line is for rough cutting, and the dotted line is for finish cutting. The vertical axis of this diagram shows the exit wear amount W (mW) shown in Figure 2 instead of the tool flank wear ■8, and the horizontal axis shows the net cutting time (min) of the tool. It was taken from As shown in Fig. 2, the withdrawal wear amount W and flank wear amount VB of the tool are W=V
The relationship is B t a n β, and generally the front relief angle β = 6
°, so Wl=V B x O, 105. In addition, Fig. 4 shows the tool wear characteristic diagram shown in Fig. 3, line B showing the exit wear amount WB = 0.02, which is the criterion for tool life in finish cutting, and line B in rough cutting. Leaving wear amount WB is the criterion for tool life in
This is a V-T diagram drawn with the dotted line indicating =0.061+1 m as parameters, and the cutting speed V (m/m1n) and tool life time T (min) are expressed as vertical and horizontal coordinate axes, respectively.

In this case, the tool exit wear amount W was selected because the tool edge position to be detected by the aforementioned detector 17 is X-Z.
This is because the withdrawal wear amount W is detected as a deviation from the set blade edge position within the plane.

Now, when creating a machine program for the desired workpiece 6, each tool 11 to be managed is indexed to the machining position at the origin position of the turret tool rest 10 for use in the next process. A measurement program is created so that the tool cutting edge is brought into contact with a predetermined measurement surface of the detector 17, for example 18, so that the detector 17 can detect and output the deviation of the tool cutting edge position as the withdrawal wear amount W'. Then, it is stored in advance in the storage device of the numerical control device 20 so that it can be called together with the program or separately as a subprogram. Next, the above-mentioned Taylor index n is sequentially set and inputted to the target life time To (min) and critical exit wear amount Wo (portion 11n) and d of each tool 11 programmed for measurement using the digital switch of the setting device 23, respectively. It is stored in the storage device 254 of the gentleman's number notification control device 30. On the other hand, feed information such as the feed speed and feed amount based on the machine program is inputted from the numerical control device 20, and the workpiece 6 is cut during the cutting period I11 for each preset time for each tool 11. The net cutting time ΔT (min) and the accumulated net cutting time Ta2ΣΔT are calculated in the arithmetic unit 26 and stored in the memory unit 25, respectively. In addition,
Even if the net cutting time ΔT and its cumulative value Ta are calculated in advance by the program and inputted from the setting device 23, the net cutting time ΔT and its cumulative value Ta can be calculated as 'LL', or 1. A cutting force sensor may be provided in the directly controlled lathe l, and the actual net cutting time for each tool may be counted and stored by a clock generator based on the cutting force detection signal from the sensor force.

After the numerically controlled lathe 1 starts cutting the workpiece 6, the cutting edge of the required tool 11 is brought into contact with the measurement surface 18 of the detector 17 according to the measurement program at each arbitrarily preset time as described above, and the problem that occurs during this period is measured. When the amount of change in the flank face position of the tool is detected as the current wear amount ΔW (mm ), a signal corresponding to this wear amount ΔW is input to the detection control circuit 22, and the current wear amount ΔW of the tool 11 at the time of measurement is inputted to the detection control circuit 22. The current cumulative wear amount Wa=ΣΔW is stored in the storage device 25 as W, and at the same time, the cumulative current wear amount Wa=ΣΔW is also calculated and stored.

Next, from this current wear amount ΔW and the previously calculated and stored net cutting time ΔT between measurement points of the tool 11, the arithmetic unit 26 calculates the wear rate Ga-ΔW/ΔT of the tool 11.
(mm/min), and then calculate the current measurement value using the limit exit wear amount Wo of the tool that has been set and input in advance, the measured cumulative current wear amount Wa, and the calculated wear rate Ga. Expected tool life time Te=(W
o −Wa )/()a=WB/Ga (min
) (where WR is the remaining limit wear amount at the time of measurement) is calculated by the calculation device 26. The expected life time Te calculated here is the remaining target life time at the current measurement point, which is calculated from the target life time To which was previously set and inputted from the setting device 23 and stored in the storage device 25 and the cumulative net cutting time Ta. T B = To - Ta (min) is compared in the comparator 26, and when there is a time deviation ct = TR - Te between both life times, the calculation unit 26 calculates this time deviation ( The above tool life equation VnT=C is applied so that t approaches zero.
In order to correct the current cutting speed Vo (m/min) programmed for the tool based on, the index n set and inputted earlier is used to correct the cutting speed V a =V
o°JFTR(m/min) is calculated. The above-mentioned data and calculation results regarding each tool stored in the storage device are displayed on the display 24 as desired.

The corrected cutting speed Va calculated in this way is stored in the storage device 25.
This corrected cutting speed Va is stored in the computer and sent back to the numerical control device 2o from the interface 29, and the modified cutting speed Va is then returned to the numerical control device 2o from the interface 29.
For example, the rotation speed of the DC motor 7 is controlled via the machine control panel 31 using a spindle speed override function so as to obtain the following.

In addition, the cutting speed is constant in relation to the X coordinate of the tool cutting edge position.
A numerically controlled lathe with this function is convenient because the cutting speed fV (m/min) can be directly specified in the program. In calculating the wear rate Ga of the tool mentioned above,
In the case of a new tool, since there is an influence of initial wear, appropriate measures can be taken, such as using the tool cutting edge position after this initial wear as a reference for subsequent steady wear measurement. In this way, each tool detects and accumulates the current wear amount ΔW of the cutting edge using the measurement program every time it cuts the workpiece by ΔT (min), and accordingly repeats the calculation to obtain the cutting speed IJjVa and corrects it. The tool life is set to the target value To.
When the cumulative wear amount Wa = Σ△W becomes equal to the limit wear l W o , the tool is replaced with an alternative tool prepared in the turret tool rest, or a tool replacement alarm is issued and the tool is stopped. ing. In addition to life management, in the case of finishing cutting tools, the cumulative value Wa of the current wear amount of the tool measured by the detector 17 is sent from the detection control circuit 22 to the tool position correction device 21 of the numerical control device 20 via the interface 29. , and each time the tool is called in the finishing cutting process in the machine program, the position of the cutting edge should be corrected by an amount corresponding to this wear amount Wa before cutting starts, and this correction should be canceled when processing is completed. For example, it is also equipped with an automatic measurement correction function for maintaining finished dimensional accuracy of the workpiece.

In the above embodiment, a numerically controlled lathe has been described, but the present invention can be similarly applied to numerically controlled machine tools such as machining centers that use rotary tools.

As described above, the present invention focuses on the fact that tool wear is most sensitively affected by cutting speed and that cutting speed can be easily controlled and adjusted, and the present invention automatically measures tool wear periodically during cutting. As a result, cutting is performed while automatically correcting the programmed cutting speed in response to environmental conditions, which eliminates the need to manually judge tool life, which previously relied on the experience and intuition of workers at production sites. By adding a simple detector and counting control device to a conventional numerically controlled machine tool, the cutting speed can be adjusted based on the characteristics of the numerically controlled machine tool, the tool used, and the target workpiece. It is possible to periodically inspect the progress of tool wear during machining based on characteristics such as material and hardness, and automatically adjust the cutting speed for subsequent machining on the spot. The most reasonable result can be obtained to maintain the tool life close to the target tool life that can be considered realistic. In addition, when unmanned operation at night using a numerically controlled machine tool with a small number of spare alternative tools, it is possible to achieve the target tool life by slightly lowering the cutting speed, etc. production. Furthermore, a large amount of cutting technology data, including the appropriate cutting speed accumulated through actual cutting and the appropriate Taylor index n calculated from this cutting speed and tool life time, can be used immediately in the subsequent creation of a cutting program. Not only can it be used, it can be fully utilized as a tool file in production factories, and it can also be used as a larger data bank in the future.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example in which the present invention is implemented in a numerically controlled lathe, Fig. 2 is an explanatory diagram of the wear state of the cutting tool edge,
FIG. 3 is a withdrawal wear characteristic diagram when hard steel material is cut with a cemented carbide tool, and FIG. 4 is a V-T diagram in FIG. 3. ■...Numerical control lathe, 6...Workpiece, 7 DC motor for driving spindle, 10 - Turret tool post, 11 Tool, 17
Detector, 20... Numerical control device, 23 Setting device, 30...
・Counting control device, 31 ・Machine control panel 0 Patent applicant: Ikegai Iron Works Co., Ltd., Figure 2, Section 4

Claims (1)

[Claims] 1) In a method for managing the life of a tool for cutting a workpiece into a desired shape using a numerically controlled machine tool, the target life time, the limit wear amount, and the index n of the relational expression described below are determined in advance. The current wear amount of the tool that progresses through cutting under the programmed command cutting conditions is measured and memorized at set time intervals, and the measured current wear amount and the tool wear amount within the set time are measured and memorized. The wear rate and expected life time of the tool at the time of measurement are calculated from the net cutting time and the limit wear amount set above, and the target life time and expected life time of the tool are compared. If there is a deviation, the cutting speed is determined. The cutting speed is calculated from the relational expression V'T=O between A tool life management method comprising automatically controlling cutting speed so that the deviation approaches zero. 2) In a device that manages the life of a tool that cuts a workpiece into a desired shape using a numerically controlled machine tool, a variable speed drive device that generates a cutting speed between the workpiece and the tool according to programmed command cutting conditions. , a detector that measures and outputs the current wear amount of the tool by relative movement with the tool attached to the tool holding device of the numerically controlled machine tool, the target life time of the tool, the limit wear amount, and the index n of the relational expression described below. a setting device for setting and inputting the information, a storage device for storing the set target tool life time, limit wear amount, index n, and the measured current wear amount and one net cutting time of the tool between measurement points, respectively; A calculation device that calculates the tool wear rate and expected life time from the stored current wear amount, net cutting time, and limit wear amount, and compares the stored target tool life time with the calculated expected life time. Including a comparator, when there is a deviation between the two compared tool life times, the cutting speed is calculated in the arithmetic unit from the relational expression vnT-〇 between the cutting speed ■ and the tool life time T, and the above-mentioned method is used for subsequent cutting. A count that automatically controls the cutting speed so that the deviation from the target tool life time approaches zero by correcting the prime mover rotation speed of the variable speed drive device, which is related to the commanded cutting speed by the program, based on the calculated cutting speed. A tool life management device equipped with a control device.