JPH029554A - Cutting tool damage detecting device - Google Patents

Abstract

PURPOSE:To enable accurate detection of damage of a tool by providing a means which calculates a fluctuation in a cutting load force during machining as a fluctuation ratio in a percentage based on an accumulative average load force during machining made the latest given number of times and stops a machine tool according to a result of the fluctuation ratio being compared with a set value. CONSTITUTION:An average value of a cutting load force during a cutting work made the latest given number of times is calculated by a calculating means 2. A fluctuation ratio calculating means 3 calculate a ratio in which a cutting load force during each machining work, detected by a detecting part 1, is fluctuated from an average value calculated by the calculating means 2. The calculated fluctuation ratio is compared with threshold (a set value) set by a set means 5 by means of a comparing means 4. When from the comparing result, it is detected that a calculated fluctuation ratio exceeds the threshold, a tool damage occurring signal is outputted to a machine tool control device 6 from the comparing means 4 to stop operation of a machine tool and promote exchange of a tool.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a cutting tool damage detection device for detecting damage to a tool during cutting in an automatic machine tool or the like.

(Conventional technology) In today's world where automatic machine tools are frequently used, if a tool is damaged during cutting, it is not only impossible to maintain proper machining conditions, but there is also a high risk of damage to the machine tool. .

Conventionally, in order to detect such tool damage, we have focused on the fact that the cutting temperature and vibration cutting load force change due to tool damage, and by detecting these and processing the signals, we have been able to detect tool damage. I can't think of anything to detect indirectly. For example, when using variations in cutting load force, the upper and lower thresholds of the cutting load force during normal cutting are set in advance through cutting tests, and the cutting load value during actual cutting is set between the above two thresholds. A device has been proposed that compares the actual cutting load value with the actual cutting load value and determines that the tool has been damaged when the actual cutting load value exceeds the upper and lower thresholds.

(Problem to be solved by the invention) The above conventional example is as shown by A in FIG.

- When repeatedly and continuously machining the same or similar shell material, the cutting load force during machining is set to the upper and lower thresholds, because the fluctuations in the cutting load force are small even after repeated machining.
By comparing with Fmax and Fwin, it is possible to detect the fluctuation a of the cutting load force when the tool is damaged.
When the amount of wear on the cutting tool due to machining is large, such as when machining high-hardness materials, even if the machining conditions are acceptable and do not affect machining accuracy, the number of machining increases as shown by B in Figure 4. As the cutting load force increases accordingly, the cutting load force differs greatly between a new tool and a worn tool, and the cutting load force during machining is compared with the upper and lower thresholds in the same way as when machining shell material. However, it is not possible to determine whether the change in cutting load force is due to normal machining conditions or due to tool damage (indicated by b in the figure), making it difficult to accurately detect tool damage. becomes impossible.

Therefore, the present invention aims to provide a cutting tool damage detection device for machine tools that repeatedly and continuously process the same or similar workpieces, which is required as the number of machining increases due to tool wear, etc., such as when machining high-hardness materials. The aim is to enable accurate detection of tool damage even when the cutting load force changes significantly.

(Means for Solving the Problems) In order to solve the above problems, the present invention is configured as follows. That is, the present invention includes a detection unit that detects a cutting load force, a cumulative average load force calculation unit that calculates an average value of the cutting load force during the latest predetermined number of cutting operations, and an output of the detection unit that is calculated based on the cumulative a fluctuation ratio calculation means for calculating a ratio of fluctuation with respect to the output of the average load force calculation means; a comparison means for comparing the output of the fluctuation ratio calculation means with a set value;
and a machine tool control device that stops the machine tool in accordance with the output of the comparison means.

(Function) In the present invention, the cumulative average load force calculated as the average value of the cutting load force during the latest predetermined number of cutting operations (usually about 5 to 10 times before the current processing) corresponds to the current state of the cutting tool. If damage occurs to the tool that affects product dimensional accuracy or shape accuracy, the cutting load force generally changes by about 20 to 50% with respect to the cumulative average load force. Therefore, in the present invention, tool damage is detected by calculating the variation ratio of the cutting load force to the cumulative average load force during cutting as a percentage, and comparing this variation ratio with an appropriately set threshold value using a comparison means. Because it is.

Even if the cutting load force changes significantly as the number of machining operations increases, damage to the tool can be accurately detected.

(Actual Example) FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. 1st
In the figure, reference numeral 1 denotes a detection unit that detects the cutting load force during cutting, which electrically or mechanically detects the cutting load force from the main shaft motor of the cutting machine or the cutting load sensor. 2 is a cumulative average load force calculation means that calculates the average value of the cutting load force during the latest predetermined same number of machining operations (for example, 10 times before this machining); 3 is a cumulative average calculated by the cumulative average load force calculation means 2; Variation ratio calculation means 4 calculates the variation ratio of the cutting load force during machining detected by the detection unit 1 with respect to the load force as a percentage; This threshold value is set as a percentage and is usually about 20 to 50%. 6 is comparison means 4
This is a machine tool control device that stops the machine tool according to the output of the machine.

Next, the operation of this embodiment will be explained using the flowchart shown in FIG.

In addition, in Fig. 2, i indicates the processing factory number when repeatedly and continuously cutting products of the same shape or similar shape.
N indicates a predetermined number of processing times for calculating the cumulative average load force by the cumulative average load force calculating means 2.

First, in step 7, the threshold value setting means 5 sets the threshold value X, which is used by the comparison means 4 to determine tool damage, as a percentage. This threshold value X varies depending on processing conditions, material to be cut, etc., and is determined by cutting tests and the like. After that, the cutting process is started, and the first arbitrary process will be described below. In step 8, the cutting load force fi during i@th machining is
is detected by the detection unit. At this time, a reproducible value such as an average load force during cutting or a peak value is used as the cutting load force fi. Next, in step 9, the cumulative average load force F during the N machining times before the current (i-th) machining, that is, the cumulative average load force F during the machining times from i-N@ to the i-1-th machining is calculated. Thereafter, in step 10, the amount of variation in the cutting load force fi detected in step 8 with respect to the cumulative average load force F calculated in step 9 is calculated as a fluctuation ratio ΔF, which is the absolute value of a percentage based on the cumulative average load force F. Then, the process proceeds to step 11, where it is determined whether the variation ratio ΔF calculated in step 10 is smaller than the threshold value
Return to and proceed to the next processing.

If the judgment is NO, the tool is damaged and step 1
Proceeding to step 2, a tool damage occurrence signal is output to the machine tool control device 6 to stop the machine tool and prompt the tool to be replaced.

In this way, by determining tool damage based on the variation ratio based on the cumulative average load force that differs for each machining process, it is possible to determine whether the cutting load force increases due to tool wear or other factors as the number of machining increases, such as when machining high-hardness materials. Even if the cutting load force changes, the cumulative average load force also changes according to the change in the cutting load force, so the third
As shown in the figure, if the cutting conditions are normal, the variation ratio will not change significantly even if the number of machining increases, and the variation ratio will change significantly only when tool damage occurs, so the variation due to tool damage. The ratio variation C can be correctly determined, and tool damage can always be accurately detected regardless of the material of the workpiece.

In addition, by using the cumulative average load force as a standard when calculating the variation ratio, it is possible to eliminate factors that are not reproducible, such as variations in machining allowance and material hardness or vibration during clamping, which are included in the cutting load force detected by the detection unit. Since the influence of damage on detection accuracy can be significantly reduced, it becomes possible to detect even minute tool damage that was difficult to detect in the past.

Furthermore, the threshold value of the variation ratio for damage determination is very often 20 to 30% in normal machining, and if it is set within this range, damage detection can be practically achieved with sufficient accuracy. Therefore, it is no longer necessary to repeat the cutting test many times to quantitatively understand the threshold value as in the past, and it is possible to significantly shorten the adjustment time when setting up the device.

(Effects) As explained above, according to the present invention, the variation in cutting load force during each machining process is calculated as a percentage variation ratio based on the cumulative average load force during the latest predetermined number of machining cycles, and this variation Since tool damage is determined based on the ratio, tool damage can be detected accurately even when the cutting load force fluctuates greatly with each machining cycle, such as when machining high-hardness materials.
In addition, by using the cumulative average load force as the standard for the variation ratio, the influence of changes in cutting load force due to non-reproducible factors such as variations in material hardness on damage determination can be suppressed, and detection accuracy can be dramatically improved. Furthermore, since it is easy to set the threshold value for determining damage, the complexity of adjustment when installing the device can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a flow chart for explaining the operation of an embodiment of the present invention, and FIG. 3 is a diagram showing the number of machining operations in an embodiment of the present invention. FIG. 4 is a diagram showing changes in the variation ratio, and FIG. 4 is a diagram showing changes in cutting load force with respect to the number of machining operations in a conventional cutting tool damage detection device. 1...Detection section. 2... Cumulative average load force calculation means, 3...
...... Fluctuation ratio calculation means, 4...
・Comparison means, 6...Machine tool control device. Presenter: Nippondenso Co., Ltd. Agent, Patent Attorney: Masaaki Suzuki (2 others)

Claims (1)

[Claims] a detection unit that detects cutting load force; a cumulative average load force calculation unit that calculates the average value of cutting load force during the latest predetermined number of cutting operations; A fluctuation ratio calculation means for calculating a ratio of fluctuation with respect to the output, a comparison means for comparing the output of the fluctuation ratio calculation means with a set value, and a machine tool control device for stopping the machine tool according to the output of the comparison means. A cutting tool damage detection device characterized by comprising: