JPH06315853A - Detecting method for constituting cutting edge of turning machine - Google Patents

Abstract

PURPOSE:To accurately detect the presence of a constituting cutting edge during cutting under the cutting condition of a wide range by monitoring the thrust force applied to a cutting tool, judging whether the prescribed statistic of the thrust force exceeds the threshold value or not, and judging the presence of the constituting cutting edge. CONSTITUTION:A cutting tool 3 is fitted to a tool rest 1 via a tool holder 2, the front face or the outer shape of a work W held by a spindle 4 is cut, and a tool dynamometer having a piezoelectric element is provided on the tool holder 2 as a thrust force detecting sensor 5. The thrust force Fp among the feed component force Ff, main component force Ft, and thrust force Fp applied to the cutting tool 3 is detected by the sensor 5, and the detected signal is inputted to a calculating means 8 via a charge amplifier 6 and an A/D converter 7. The average value of the sampling data in the average time is determined, and the ratio of the average value against the standard deviation is calculated. When the ratio exceeds the threshold value, the constituting cutting edge detection signal is outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a turning machine such as a lathe, and a method for detecting a constituent cutting edge of a turning machine for detecting occurrence of a constituent cutting edge of a cutting tool during turning.

[0002]

2. Description of the Related Art In cutting, a part of a work material is melted by cutting heat and adheres to a cutting edge of a tool, which hardens to function as a cutting edge in a pseudo manner. . As shown in FIG. 15, built-up edge BUE arises the rake face a of the cutting tool T, with respect to the rake angle alpha of the cutting tool T, actually increase the rake angle of alpha _a acting on the workpiece W . Therefore, the cutting force decreases due to the formation of the constituent cutting edge BUE.

As a general tendency, as shown in FIG. 16, the forming height H of the constituent cutting edge influences the cutting speed, which occurs at a certain low speed V1 and becomes higher as the speed increases, and the intermediate speed V
It starts decreasing at 2 and completely disappears at a certain high speed (speed V3). The cutting force F decreases in proportion to the forming height H of the constituent cutting edge. Since the formation of the constituent cutting edge leads to a reduction in the cutting force in this way, a method of actively generating the constituent cutting edge and cutting is also adopted in heavy cutting and the like.

[0004]

However, there is a problem in that, when cutting is performed with the built-up edge, quality such as surface roughness of the finished surface is deteriorated. Therefore, it is necessary to avoid the formation of the constituent cutting edge in the processing that requires a good finished surface. Whether or not a configured cutting edge has occurred can be seen by visually observing the cutting tool and also by measuring the surface roughness of the machined surface, but automatically detects the configured cutting edge during automatic operation, especially during unattended operation. Is required. In this case,
A detection method by visual inspection of the tool or measurement of surface roughness cannot be adopted. Therefore, it was considered to monitor the cutting force to detect the generation of the constituent cutting edge, but the presence or absence of the constituent cutting edge varies depending on not only the cutting speed but also the cutting conditions such as the cutting depth and the cutting feed. Therefore, when automatically operating under a wide range of cutting conditions, it is difficult to automatically detect the constituent cutting edge, and a practical automatic detection method has not yet been developed.

An object of the present invention is to provide a constituent cutting edge detecting method for a turning machine capable of automatically detecting the presence or absence of the constituent cutting edge under a wide range of cutting conditions.

[0006]

A method of detecting a cutting edge of a turning machine according to the present invention monitors a back force component among a feed force component, a main force component and a back force component acting on a cutting tool, and detects the back force force during cutting. This is a method of determining the presence or absence of the constituent cutting edge depending on whether or not a predetermined statistic of the back force exceeds a threshold value.

According to a second aspect of the present invention, in the constituent edge detecting method according to the first aspect, the ratio of the average value of the back force to the standard deviation is used as the statistic to be compared with the threshold value. That is, the back force is monitored by sampling, and the average value, the standard deviation, and the ratio of the average value to the standard deviation of the sampled data of the back force during the period are calculated every predetermined period. The presence or absence of the constituent cutting edge is determined by comparing the calculated value of this ratio with a threshold value.

[0008]

[Function] The component force in each direction acting on the cutting tool varies depending on the cutting speed, cutting depth and feed conditions, even if the work material and cutting tool are the same. The configured cutting edge cannot be detected under a wide range of cutting conditions by a method such as simply comparing with a set value. However, as a result of the experiment, it was found that there is a threshold value generated by the presence or absence of the built-up edge, which does not change even if the cutting condition changes, with respect to any component force, for a certain kind of statistic. Therefore, the presence or absence of the constituent cutting edge can be detected by comparing this threshold value with its statistic. In this case, the difference in the statistic amount depending on the presence or absence of the constituent cutting edge was the largest among the three component forces. Therefore, the constituent blade edge can be detected most accurately by using the statistical amount of the back force.

In the second aspect of the invention, the ratio of the average value for each predetermined period to the standard deviation is used as the statistic to be compared with the threshold value. However, by using this ratio, experimental results will be shown later. The presence or absence of the constituent cutting edge can be reliably detected under a wide range of cutting conditions.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows the configuration of a turning machine and a detection device to which the constituent blade edge detection method is applied. A cutting tool 3 is attached to a tool rest 1 via a tool holder 2, and a work material W held by a spindle 4 by the cutting tool 3 is attached.
Face turning or outer diameter cutting is performed. The turret 1 is composed of a turret or the like.

The tool holder 2 is provided with a tool dynamometer having a piezoelectric element as the back force detecting sensor 5. That is, the sensor 5 that detects the back force component F _p of the main force component F _t , the feed force component F _f , and the back force component F _p shown in FIG.
To provide. The output of the sensor 5 is amplified by the charge amplifier 6, converted into a digital value by the A / D converter 7, and input to the arithmetic means 8. The computing means 8 is composed of a dedicated microcomputer, a programmable controller of a CNC device for controlling a turning machine, or the like. The calculation of the back force measurement data by the calculation means 8
The sampling data is analyzed every fixed sampling time Ts (several milliseconds), and the sampling data is analyzed every predetermined period Ta (several hundred milliseconds).

FIG. 2 shows the processing by the arithmetic means 8 of FIG. First, sampling data (for example, several tens) of back force in a predetermined period Ta is input (step S1), and an average value of these sampling data, a standard deviation, and a ratio R of the average value to the standard deviation are calculated. Do (S
2). The average value, the standard deviation, and the ratio R thereof are calculated according to the following calculation formula.

[0013]

[Equation 1]

This calculated ratio R is compared with a preset threshold value R _t (S3). If the ratio R has not reached the threshold value R _t , the process directly returns to step S1 and the next predetermined period is reached. For Ta, the same calculation as above is repeated.
If the ratio R is larger than the threshold value R _{t in} the determination process of step S3, the constituent blade edge detection signal is output (S4), and then the process returns to step S1. In the CNC machine of turning machine,
For example, in response to the constituent blade edge detection signal, the cutting condition is controlled such that the constituent blade edge disappears, the cutting speed is controlled, or the feed is continued to continue the machining. When high accuracy is required for the finished surface, the CNC device stops the processing of the work material being processed by the generation of the component edge detection signal, discharges the work material as a defective product, and then performs the next work. The material is processed.

According to this constitutional edge detecting method, the ratio R to the standard deviation of the average value for each predetermined period is obtained for the sampling data of the back force component, and this ratio R is compared with the threshold value R _t. Since the presence / absence of the constituent cutting edge is determined, the presence / absence of the constituent cutting edge can be automatically detected under a wide range of cutting conditions in which the cutting conditions such as the cutting depth and the feed are different, as can be seen from the experimental results described later. In particular, the back force of the three force components is used for the presence / absence determination, and the back force has the largest difference in the ratio R depending on the presence / absence of the constituent cutting edge, so that the accurate presence / absence determination can be performed.

Next, an experimental example of detecting the constituent cutting edge will be shown. Figure 3 shows the experimental setup. A CNC control turning machine (WSC-6 type manufactured by Murata Machinery Co., Ltd.) is used as the turning machine, and the maximum output of the spindle motor is 7.5 kW. The workpiece W is gripped by the chuck of the spindle 14, and the cutting tool 13 attached to the turret 11 is used to carry out front face grinding. The turret 11 has a tool dynamometer 15 for detecting a main component force F _t , a feed component force F _f , and a back component force F _p of the cutting tool 13, respectively.
Set up.

The detection signals of the respective component forces F _t , F _f and F _p are amplified by the charge amplifiers 16a to 16c, respectively, and then A / C.
It is converted into a digital value by the converter 17 and input to the microcomputer 18 at a sampling time of 5 msec. The sampling data of each component F _t , F _f , F _p is
Each set period of 200 msec is analyzed. That is, the average value and the standard deviation of the component forces in each direction are calculated for 40 sampling data obtained during this period. The work material W is a thick cylindrical steel material (S45C) having an inner diameter of 32 mm and an outer diameter of 100 mm, and the cutting tool 13 is TNM.
G332-MF (Sandvik) was used. The rotation speed of the spindle 14 was 800 rpm and was always constant.

The experimental results and their consideration will be described. Figure 4
The change in the three-component force of the cutting force when the cutting speed is gradually changed by face milling is shown. The feed f was 0.1 mm / rev and the depth of cut a was 0.2 mm / rev, both of which were kept constant.
The cutting tool 13 was fed from the center side of the work material W to the outer diameter side. Therefore, the cutting speed V is 80 to 250 m / mi
gradually increasing between n. The constituent cutting edge was generated from the start of cutting and disappeared when the cutting speed reached 153 m / min. This critical cutting speed can be easily found by measuring the surface properties (surface roughness) of the work material W (see FIG. 3D). The three-component force shows a similar change with the growth of the constituent cutting edges, and both have the maximum value at the critical speed, and even if the cutting speed is further increased, the same value continues.

FIG. 5 is a diagram showing the boundaries of the constituent cutting edges when the feed f is gradually changed and the cutting speed V is changed according to the cutting depth. In the same figure (A), the cutting depth a is 0.
2 mm, (B) is 0.4 mm, and (C) is 0.6 mm. From the figure, it can be seen that the boundary formed by the constituent cutting edges affects not only the cutting speed and the feed but also the cutting depth.

As a characteristic statistic of the cutting force that can be used for determining the presence or absence of the constituent cutting edge, there are two possible values, an average value and a standard deviation. Therefore, FIG. 6 shows the average value and the standard deviation (STD) calculated for each of the 40 sampling data obtained as described above for each predetermined force for each predetermined period. The figure shows the results calculated from the data of FIG. From the figure, it can be seen that the magnitude of the cutting force and the state of its change can be used to determine the presence or absence of the constituent cutting edge.

However, the magnitude of the cutting force and its change are
Since it varies depending on the cutting conditions, the tool shape, etc., it is difficult to determine the threshold value for detecting the constituent cutting edge under a wide range of cutting conditions. For example, in FIGS. 7 to 9, the feed depth f is 0.1, 0.1 with the cutting depth a being constant (0.4 mm).
The standard deviation of each component force when set to 5 and 0.20 mm / rev is shown, respectively. As can be seen by comparing these figures, the threshold σ _t value for the standard deviation of each component force increases as the cutting depth increases. Therefore, monitoring the standard deviation of the cutting force is not sufficient to detect the built-up edge under a wide range of cutting conditions.

However, this problem is solved by calculating the ratio R to the standard deviation of the mean value. Figure 1
Each graph of 0 shows the ratio R for each component force when the cutting depth is constant (0.4 mm) and the feed f is 0.10, 0.15, and 0.20 mm / rev. In each graph in the figure, the horizontal axis is the cutting speed V (m / min)
Is taken and the vertical axis shows the ratio R. According to the figure, if the cutting depth a is constant, the threshold R _t value of the ratio R is a constant value under a wide range of cutting speed V and feed f for any cutting component force. I know that I can make a decision.

In each graph of FIG. 11, the feed f is constant (0.
1 mm / rev) and the cutting depths a are 0.2, 0.
The ratio R for each component force when 4 and 0.6 mm
Are shown respectively. According to the figure, if the feed f is constant, the threshold value R _{t of the} ratio R is set for any cutting component force.
It can be seen that can be determined as a constant value under a wide range of cutting speed V and cutting depth a. Moreover, the threshold value R _t for the same cutting component force shown in FIGS. 10 and 11 is the same value. This means that the threshold value R _{t of the} ratio R can be determined to be a constant value under a wide range of cutting conditions if the combination of the cutting tool and the work material is the same.

Of the three component forces, which component force has the highest sensitivity to the detection of the component cutting edge is what the average value of the ratio R is with and without the component cutting edge. You can tell by asking for the difference. FIG. 12 shows the average value of the ratio R calculated for the presence or absence of the constituent cutting edge for each feed rate. According to the figure, the difference in the ratio R depending on the presence or absence of the constituent cutting edge is the largest in the back force. Similar results are shown in FIG. The figure shows the difference in the ratio R depending on the presence or absence of the constituent cutting edge when the cutting depth is different. From these results, the ratio R to the standard deviation of the mean value of the back force is
It can be seen that can be used to detect the presence or absence of the constituent cutting edge.

FIG. 14 shows the result of actually detecting the presence or absence of the constituent cutting edge by monitoring the back force and calculating the ratio R of the average value to the standard deviation for each predetermined period. In this cutting test, face grinding was performed and the spindle rotation speed was 800 rpm.
The feed was 0.1 mm / rev and the depth of cut was 0.4 mm. The result of the presence / absence judgment of the constituent cutting edge is shown in FIG. The fact that this result is correct is proved by directly measuring the surface texture of the work material (FIG. 7C).

From these experimental results, it is proved that the method for detecting the built-up edge of the present invention can be actually applied to the detection of the built-up edge under a wide range of cutting conditions. In addition, although the above-mentioned experimental example shows only the case of face-cutting, the same result can be obtained also in the case of outer-diameter cutting. In the above-mentioned embodiment, the threshold value is determined from the surface property (surface roughness) of the work material W by the method of determining the disappearance time of the constituent cutting edge in the sampling data. The threshold value determined by the method of obtaining the point of time at which the constituent cutting edge occurred in the process of gradually decelerating from was approximately the same value. Further, in the embodiment, as the statistic amount to be compared with the threshold value for determining the presence or absence of the constituent cutting edge, the ratio of the average value to the standard deviation is used, but if the statistic amount is set to a fixed value for the threshold value. Alternatively, a statistic other than the above ratio may be used for determining the presence or absence of the constituent cutting edge.

[0027]

EFFECT OF THE INVENTION The method of detecting the constituent cutting edge of the turning machine according to the present invention monitors the back force acting on the cutting tool, and determines whether the predetermined cutting force of the back force exceeds a threshold value. Since the presence / absence is determined, it is possible to automatically and accurately detect the presence / absence of the constituent cutting edge during cutting under a wide range of cutting conditions.

In particular, in the case of the structure of claim 2, the average value and the standard deviation and the ratio of the average value to the standard deviation are calculated for each sampling period of the back force component, and the ratio is calculated. Since the presence or absence of the component cutting edge is judged by comparing the statistical amount, which is the value, with the threshold value, a constant threshold value can be set under a wide range of cutting conditions, as evidenced by experimental results, and It is possible to easily and accurately detect the presence or absence of the constituent cutting edge.

[Brief description of drawings]

FIG. 1A is a conceptual diagram of a detection device to which a constituent blade edge detecting method according to an embodiment of the present invention is applied, and FIG. 1B is an explanatory diagram showing a cutting component force of a constituent blade edge.

FIG. 2 is a flowchart showing a data processing process in the constituent blade edge detection method of the embodiment.

FIG. 3 is an explanatory diagram of equipment used for an experiment for detecting a configured cutting edge.

FIG. 4 is a graph showing detection results of three-dimensional component force of cutting force and surface roughness in the same detection experiment.

FIG. 5 is a graph showing the influence of cutting conditions on the formation of constituent cutting edges.

FIG. 6 is a graph showing changes in the average value and standard deviation of the cutting force associated with the formation of the constituent cutting edges.

FIG. 7 is a graph showing a change in the standard deviation of the cutting force due to the generation of the constituent cutting edge when the feed is 0.10 mm.

FIG. 8 is a graph showing changes in the standard deviation of the cutting force due to the generation of constituent blade edges when the feed is set to 0.15 mm.

FIG. 9 is a graph showing changes in the standard deviation of the cutting force due to the generation of the constituent cutting edge when the feed is 0.20 mm.

FIG. 10 is a graph showing changes in the ratio of the average value of the cutting force to the standard deviation for each of three types of feed.

FIG. 11 is a graph showing changes in the ratio of the average value of the cutting force to the standard deviation for each of three types of cuts.

FIG. 12 is a graph showing an average value of the above ratios with and without a constituent cutting edge, when the feed is changed.

FIG. 13 is a graph showing an average value of the ratios according to presence or absence of a constituent cutting edge when the cutting depth is changed.

FIG. 14 is an explanatory diagram of an experimental result in which the constituent blade edge is detected by the method of the embodiment.

FIG. 15 is an explanatory diagram showing a general state of formation of a cutting edge and a change in rake angle.

FIG. 16 is a graph showing a general relationship between a cutting force and a change in height of a constituent cutting edge with a change in cutting speed.

[Explanation of symbols]

1 ... tool rest, 3 ... cutting tool, 4 ... spindle, 5 ... back component force sensor, 8 ... operation unit, W ... workpiece, F _p ... back component force

Claims (2)

[Claims] 1. A feed component force, a main component force, which acts on a cutting tool,
Of the back force components, a back force component is monitored, and a component cutting edge detection method for a turning machine that determines the presence or absence of a component blade edge based on whether or not a predetermined statistic of the back component force exceeds a threshold value during cutting. 2. The constituent blade edge detection method according to claim 1, wherein the back force component is monitored by sampling, and an average value and a standard deviation of the back force component sampling data during the period are provided. A method of detecting a constituent cutting edge of a turning machine, wherein a ratio of the average value to a standard deviation is calculated, and the calculated value of the ratio is used as a statistic used for comparison with the threshold value.