Abstract
Provided is a temperature measurement device for a rotating member of a processing device that grips a rotating member made from a metal and capable of rotating around a rotational axis, and moves in coordination with and coaxially rotates with the rotating member. This temperature measurement device is equipped with: an ideal temperature setting means for setting an ideal temperature while the rotating member is rotating; a temperature measurement means for measuring an actual temperature while the rotating member is rotating; and a detection means for detecting whether or not the difference between the actual temperature measured by the temperature measurement means and the ideal temperature set by the ideal temperature setting means exceeds a pre-set threshold at the time the actual temperature is measured.
Claims
1. A temperature measurement device for measuring a temperature of a rotary member in a machining apparatus that holds the rotary member, which is rotatable about an axis of rotation and rotates coaxially with the rotary member in cooperation with the rotary member, the temperature measurement device comprising: an ideal temperature setting means for setting an ideal temperature of the rotary member during rotation of the rotary member; a temperature measurement means for measuring an actual temperature of the rotary member during rotation of the rotary member; and a detection means for detecting whether or not a difference between the actual temperature measured by the temperature measurement means and the ideal temperature set by the ideal temperature setting means exceeds a predetermined threshold value.
2. The temperature measurement device according to claim 1, wherein the ideal temperature set by the ideal temperature setting means is calculated using predetermined calculation formula based on operation conditions of the rotary member and the temperature measurement device.
3. The temperature measurement device according to claim 1, wherein the calculation formula is
T=+T.sub.s+(T.sub.oT.sub.s)exp(t/T.sub.m) [Formula 1] where is a density, C is a specific heat, a is a coefficient of heat transfer to an outside, To is an initial temperature of a column, Ts is an external step temperature in a step response assuming rapid change, and Tm is CD/4.
4. The temperature measurement device according to claim 1, wherein the ideal temperature set by the ideal temperature setting means is determined based on a time/temperature table indicating a relationship between a predetermined time and a temperature.
5. The temperature measurement device according to claim 1, wherein the detection means detects a temperature when the difference between the actual temperature and the ideal temperature exceeds the threshold value as a limit temperature.
6. The temperature measurement device according to claim 2, wherein the ideal temperature is detected as the limit temperature when the ideal temperature exceeds the threshold value.
7. A temperature measurement device for measuring a temperature of a rotary member in a machining apparatus that holds the rotary member, which is rotatable about an axis of rotation and rotates coaxially with the rotary member in cooperation with the rotary member, the temperature measurement device comprising: a temperature measurement means for measuring an actual temperature of the rotary member during rotation of the rotary member; a temperature change detection means for detecting variability of the actual temperature measured by the temperature measurement means; and a border detection means for detecting whether or not the variability of the actual temperature detected by the temperature change detection means exceeds a predetermined condition as a limit temperature.
8. The temperature measurement device according to claim 7, wherein the measurement of the actual temperature by the temperature measurement means is performed for a predetermined time at a predetermined time interval.
9. The temperature measurement device according to claim 7, wherein the measurement of the actual temperature by the temperature measurement means is performed for each operation time during each operation of the rotary member.
10. The temperature measurement device according to claim 7, wherein a maximum temperature of the actual temperature, measured by the temperature measurement means, for each measurement time is set as an actual temperature value.
11. The temperature measurement device according to claim 7, wherein the temperature change detection means calculates a rate of change between the measured actual temperature and an actual temperature measured by that time as the variability, and the limit temperature detection means detects whether or not the calculated variability exceeds a predetermined threshold value.
12. The temperature measurement device according to claim 7, wherein the temperature change detection means calculates a difference in temperature between the measured actual temperature and an actual temperature measured by that time as the variability, and the limit temperature detection means detects whether or not the calculated variability exceeds a predetermined threshold value.
13. The temperature measurement device according to claim 8, wherein the temperature change detection means calculates an integrated value of the actual temperature for each predetermined amount of time or for each operation time as the variability of temperature, and the limit temperature detection means detects whether or not the calculated variability exceeds a predetermined threshold value.
14. The temperature measurement device according to claim 7, further comprising: an ideal temperature setting means for setting an ideal temperature of the rotary member at a predetermined time during rotation of the rotary member; and a detection means for detecting whether or not a difference between the actual temperature measured by the temperature measurement means and the ideal temperature set by the ideal temperature setting means at that time exceeds a predetermined threshold value.
15. The temperature measurement device according to claim 5, wherein a warning signal is generated when the limit temperature is detected.
16. The temperature measurement device according to claim 5, wherein control is performed so as to decelerate or stop the rotation of the rotary member when the limit temperature is detected.
17. The temperature measurement device according to claim 1, wherein the temperature measurement means comprises a temperature measurement element disposed at the rotary member for measuring the temperature of the rotary member and a transmission means for transmitting a temperature measurement result generated using the temperature measurement means from the temperature measurement element.
18. The temperature measurement device according to claim 1, wherein the rotary member is an end mill, a tap, a drill, or a rotary tool for friction stir joining, by which a fixed object to be machined is machined.
19. A temperature measurement device for measuring a temperature of a jig that machines a rotary member while being in contact with the rotary member in a rotary apparatus that holds the rotary member, which is rotatable about an axis of rotation and rotates coaxially with the rotary member in cooperation with the rotary member, the temperature measurement device comprising: an ideal temperature setting means for setting an ideal temperature of the jig; a temperature measurement means for measuring an actual temperature of the jig; and a detection means for detecting whether or not a difference between the actual temperature measured by the temperature measurement means and the ideal temperature set by the ideal temperature setting means at that time exceeds a predetermined threshold value.
20. A temperature measurement device for measuring a temperature of a jig that machines a rotary member while being in contact with the rotary member in a rotary apparatus that holds the rotary member, which is rotatable about an axis of rotation and rotates coaxially with the rotary member in cooperation with the rotary member, the temperature measurement device comprising: a temperature measurement means for measuring an actual temperature of the jig; a temperature change detection means for detecting variability of the actual temperature measured by the temperature measurement means; and a border detection means for detecting whether or not the variability of the actual temperature detected by the temperature change detection means exceeds a predetermined condition as a limit temperature.
21. The temperature measurement device according to claim 19, wherein the jig is a cutting tool or a turning tool.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0059] FIG. 1 is a view exemplarily showing a machining apparatus (an end mill apparatus) having a temperature measurement device according to the present invention, wherein the figure on the left is a schematic sectional view of the machining apparatus in the longitudinal direction and the figure on the right is a photograph of the machining apparatus;
[0060] FIG. 2 is a block diagram showing an example of the flow of an electric signal indicating the temperature of a cutting tool measured by a temperature measurement means;
[0061] FIG. 3 is a flowchart illustrating an example of a method of measuring the temperature of an end mill in the present embodiment;
[0062] FIG. 4 is a graph showing the relationship between an actually measured temperature and an ideal temperature (a calculated temperature) in the end mill and a machining time when an object to be machined (a material to be cut) is dry-machined and MQL-machined using the end mill, the difference between the actually measured temperature and the ideal temperature, and a threshold value indicating the limit of the difference, wherein the figure on the left is a graph at the time of dry machining and the figure on the right is a graph at the time of MQL machining (MQL: machining performed while oil is supplied to the end mill);
[0063] FIG. 5 is a graph illustrating a difference over time between an increase in the temperature of the end mill and an increase in the cutting force of the end mill in the direction of movement (the Y direction) at the time of dry machining;
[0064] FIG. 6 is a graph illustrating a difference over time between an increase in the temperature of the end mill and an increase in the cutting force of the end mill in the direction of movement (the Y direction) at the time of MQL machining;
[0065] FIG. 7 is a graph showing the relationship between an actually measured temperature in the interior of the end mill and a machining time when the side surface of an object to be machined (a material to be cut) is machined through an MQL method (the MQL method: machining performed while oil is supplied to the end mill) using the end mill, wherein FIG. 7(a) shows the relationship between the number of passes and a temperature in the interior of the tool with one side-surface machining operation (=one pass) as a unit of time, FIG. 7(b) shows the relationship between the time in the first pass (see (1) of FIG. 7(a)) and the temperature in the interior of the tool, and FIG. 7(c) shows the relationship between the time of the 124th pass (see (2) of FIG. 7(a)) and the temperature in the interior of the tool;
[0066] FIG. 8 is a graph showing the relationship between an actually measured temperature in the interior of the end mill and a machining time when the side surface of an object to be machined is dry-machined using the end mill, which shows the relationship between the number of passes and a temperature in the interior of the tool with one side-surface machining operation (=one pass) as a unit of time, wherein the maximum temperature in each pass is shown as the temperature in the interior of the tool;
[0067] FIG. 9 is a graph showing the relationship between an actually measured temperature in the interior of the end mill and a machining time when an object to be machined is grooved using the end mill while a water-soluble oil is supplied to the end mill, which shows the relationship between the number of passes and a temperature in the interior of the tool with one pass as a unit of time;
[0068] FIG. 10 is a graph showing the relationship between an actually measured temperature in the interior of the end mill and a machining time when an object to be machined (a material to be cut) is bored using the end mill while a water-soluble oil is supplied to the end mill, which shows the relationship between the number of machining operations and a temperature in the interior of the tool with one boring operation (=one machining operation) as a unit of time; and
[0069] FIG. 11 is a graph showing the relationship between an actually measured temperature in the interior of the end mill and a machining time when an object to be machined (a material to be cut) is bored using the end mill while a water-soluble oil is supplied to the end mill.
BEST MODE FOR CARRYING OUT THE INVENTION
[0070] FIG. 1 is a view exemplarily showing a machining apparatus (an end mill apparatus) having a temperature measurement device according to a first or second embodiment of the present invention, wherein the figure on the left is a schematic sectional view of the machining apparatus in the longitudinal direction and the figure on the right is a photograph of the machining apparatus. In the machining apparatus of FIG. 1, the end mill is used as a tool. In addition to the end mill, however, a drill, a tap, or a rotary tool for friction stir joining may be used as the tool.
[0071] In FIG. 1, there is shown a machining apparatus having a temperature measurement device according to a first embodiment of the present invention in the case in which an end mill is used as a rotary member. As shown in the figure on the left, the temperature measurement device according to the first embodiment of the present invention has a main shaft, which serves as a body part that is axially rotated, and a cylindrical tool holder coaxially connected to the lower end of the main shaft for rotating in cooperation with the main shaft. The tool holder coaxially holds the end mill at the lower end thereof, and the end mill rotates in cooperation with the main shaft. In addition, as shown in the figure on the left, the temperature measurement device includes a thermocouple, which serves as a temperature measurement means, an electronic board for processing a signal from the thermocouple, a transmitter (a transmission means) for transmitting the signal processed by the electronic board to the outside, and a power supply unit (not shown). The electronic board is provided with an amplifier for amplifying an analog signal from the thermocouple and an A/D converter for converting the amplified analog signal into a digital signal.
[0072] In addition, a hollow space, which extends in the axial direction and is open at the lower end thereof, is provided in the holder, and a communication hole, which communicates with the hollow space from the outer circumference thereof, is formed in the holder. Although not shown, the communication hole is formed so as to extend in a direction that is approximately perpendicular to the axial length direction of the holder. Meanwhile, a collet nut is inserted into the tool holder near the tip of the tool holder to hold the end mill at the tip of the tool holder.
[0073] In addition, a hollow hole, which extends in the axial direction, is also provided in the end mill. Here, the hollow hole is formed through the end mill from the upper end to the lower end thereof. In this specification, however, a semi-through hole, which extends from the upper end to a portion between the upper end and the lower end thereof, may also be included as the through hole.
[0074] A thermocouple, a thermistor, a platinum resistance thermometer sensor, etc. are used as the temperature measurement element (the temperature measurement means) of the temperature measurement device, which is configured to be mounted in the through hole formed in the end mill. The temperature measurement element is configured to measure the temperature of the end mill, which rotates coaxially with the tool holder, in real time in the state of being mounted in the lower part of the through hole. In addition, the temperature measurement element is configured to transmit a signal to a personal computer for data collection and analysis via the electronic board and an external receiver.
[0075] The electronic board (a microcomputer), the A/D converter, the amplifier, and the transmitter are provided in the tool holder or at the outer circumference of the tool holder. A signal from the electronic board transmits the temperature of the end mill to the receiver via the transmitter in real time in a wireless or wired manner. The transmitter is connected to the PC for data collection and analysis, which collects and analyzes data on the temperature of the end mill.
[0076] FIG. 2 is a block diagram showing an example of the flow of an electric signal indicating the temperature of a cutting tool measured by a temperature measurement unit. In this example, the flow of an electric signal from a thermocouple is shown. In FIG. 2, arrows indicate the flow of an electric signal indicating the temperature of the end mill measured by the thermocouple. According to the format of a signal transmission line, a wired system is shown by a solid line, and a wireless system is shown by a broken line. In this example, a zero contact compensation circuit, a potential difference amplification unit, an A/D (analog/digital) converter, and an in-device control circuit constitute a temperature reception unit. Additionally, in this example, a controller and a wireless communication device constitute a transmission unit.
[0077] In addition, as shown in FIG. 2, in this example, a wireless reception, recording, and output device constitutes an external unit. The wireless reception, recording, and output device includes a wireless reception device, a serial USB (universal serial bus) converter, a recording and calculation device such as a personal computer, and an output device such as a display or a printer, which are arranged from the upstream side to the downstream side in the direction of flow of an electrical signal. In addition, Wi-Fi (wireless fidelity), Bluetooth, wireless LAN (local Area Network), ZigBee, etc. may be used as a wireless communication standard for communication with the wireless reception device, shown by the broken line in FIG. 2.
[0078] Next, an example of a method of measuring the temperature of the end mill in the present embodiment will be described with reference to FIG. 3. In an example of the temperature measurement method, a process S1 of preparing the tool holder, a process S2 of mounting the end mill to the tip (the lower end) of the tool holder 2, a process S3 of mounting the temperature measurement element in the hollow hole formed in the end mill, a process S4 of measuring the temperature of the end mill, which rotates coaxially with the tool holder, using the temperature measurement element, and a process S5 of the electronic board (the amplifier, the A/D converter, and the microcomputer) receiving the result of measurement by the temperature measurement element may be sequentially performed.
[0079] The temperature measurement unit is disposed in the tool holder, the temperature measurement element, such as the thermocouple, connected thereto is inserted into the vicinity of a cutting edge of the tip of the end mill using a pinhole formed therein in the axial direction, and the temperature measurement element is moved to a position at which it is appropriate to measure an increase in the temperature on the contact surfaces of the end mill and an object to be machined that is generated due to frictional heat therebetween, whereby it is possible to acquire the end-point temperature of the end mill, i.e. the temperature of the tip of the end mill during machining, as a value that is extremely close to the true value of the temperature of the machining site.
[0080] Furthermore, the result of temperature measurement performed by the temperature measurement element, disposed in the end mill, during turning of the end mill is transmitted to the personal computer (a terminal for data collection and processing) via the transmitter, which is electrically connected to the temperature measurement element, whereby it is possible to accurately monitor the temperature of the tool in real time. In addition, it is possible to recognize the temperature of the tool as a sign of rupture to the end mill by analyzing variation in temperature over time. Next, a method of analyzing the temperature of the tool that is actually measured and detecting a sign of rupture will be described.
[0081] FIG. 4 is a graph showing the relationship between an actually measured temperature and an ideal temperature (a calculated temperature) in the end mill and a machining time when an object to be machined (a material to be cut) is dry-machined and MQL-machined using the end mill, the difference between the actually measured temperature and the ideal temperature, and a threshold value indicating the limit of the difference, wherein the figure on the left is a graph at the time of dry machining and the figure on the right is a graph at the time of MQL machining (MQL: machining performed while oil is supplied to the end mill). Meanwhile, the cutting conditions, the material to be cut, and the end mill are shown under respective graphs. In addition, the ideal temperature is a temperature that is calculated in real time according to a predetermined calculation formula, shown in the lower column of FIG. 4. The threshold value is a predetermined fixed value.
[0082] In the dry-machining condition, shown in the figure on the left of FIG. 4, it is revealed that the actually measured temperature starts to become increasingly distant from the ideal temperature from the vicinity of 9.0 S, the actually measured temperature increases abruptly from the vicinity of 10.8 S, and the end mill is ruptured at 11.0 S. It is understood from this figure that, if the difference between the actually measured temperature at a predetermined time t (=less than 1.0 S) before the rupture of the end mill and the ideal temperature is detected, it is possible to detect a sign of rupture. Specifically, in the figure on the left of FIG. 3, if the threshold value of the difference between the actually measured temperature and the ideal temperature is set to a predetermined temperature (20 C.), a sign of rupture appears about 1.0 S before the rupture. In the temperature measurement device according to this embodiment, when the difference between the actually measured temperature and the ideal temperature exceeds the threshold value, a warning signal is generated. Preferably, control is performed to stop the rotation of the machining apparatus.
[0083] In the MQL-machining condition, shown in the figure on the right of FIG. 4, the actually measured temperature starts to become increasingly distant from the ideal temperature from the vicinity of 21.0 S, the actually measured temperature increases greatly from the vicinity of 24.1 S, and the end mill is damaged (but is not yet ruptured) at about 26.0 S, and the actually measured temperature decreases greatly after that. It is understood from this figure that, if the difference between the actually measured temperature a predetermined amount of time t (=less than 2.0 S) before the rupture of the end mill and the ideal temperature is detected, it is possible to detect a sign of rupture. Specifically, in the figure on the right of FIG. 3, if the threshold value of the difference between the actually measured temperature and the ideal temperature is set to a predetermined temperature (50 C.), a sign of rupture appears about 2.0 S before the rupture. In the temperature measurement device according to this embodiment, when the difference between the actually measured temperature and the ideal temperature exceeds the threshold value, a warning signal is generated. More preferably, control is performed to stop the rotation of the machining apparatus.
[0084] Even if the machining conditions are changed from these, it is understood in a tool made of a metal that, if the threshold value of the difference between the actually measured temperature and the ideal temperature is set and the difference between the actually measured temperature and the ideal temperature is detected using the set threshold value as the limiting condition, it is possible to prevent damage to the end mill and the rupture of the end mill by detecting a sign of damage and rupture due to frictional wear and controlling the operation of the apparatus in advance. It has been verified that this applies equally to the above metal rotary member (tool), in addition to the end mill. In addition, it has been verified that it is possible to detect a sign of rupture and damage in the same manner even on a tool that is not ruptured or damaged but exceeds the durability limit thereof and needs to be replaced.
[0085] Next, the difference over time between an increase in the temperature of the end mill and an increase in the cutting force of the end mill in the direction of movement (the Y direction) at the time of dry machining and MQL machining in different conditions will be described with reference to FIGS. 5 and 6.
[0086] In a rotary type machining apparatus, it is possible to measure the cutting force of a tool in the direction of movement (the Y direction). The cutting force in the direction of movement (the Y direction) abruptly increases immediately before the rupture of the tool or damage to the tool. If the cutting force is measured, therefore, it is possible to detect a sign of rupture or damage. Since a change in the cutting force occurs abruptly within a short time immediately before rupture or the like, however, the case in which it is possible to detect a sign of rupture and damage but it is not possible to perform control so as to stop the operation of the apparatus in time is also considered. In contrast, there are many cases in which an increase in temperature is detected at an earlier stage than an increase in cutting force. In that sense, there are many cases in which it is possible to control the operation of the apparatus further in advance by using a method of foreseeing rupture or the like due to an increase in temperature, as in the temperature measurement device according to this embodiment. The verification results thereof are shown in FIGS. 5 and 6.
[0087] It is revealed that it is possible to detect a sign of rupture or the like about 1 second earlier for the dry machining of FIG. 5 and about 2 seconds earlier for the MQL machining of FIG. 6 when an increase in temperature is detected than when an increase in the cutting force of the tool in the direction of movement (the Y direction) is detected.
[0088] Next, a method of analyzing the actually measured temperature of a tool that has been actually measured and detecting a sign of rupture in a temperature measurement device according to a second embodiment of the present invention will be described. A machining apparatus having a temperature measurement device according to a second embodiment of the present invention is the same as the machining apparatus shown in FIGS. 1 to 3, and therefore a description thereof will be omitted.
[0089] FIG. 7 is a graph showing the relationship between an actually measured temperature in the interior of the end mill and a machining time when the side surface of an object to be machined (a material to be cut) is machined through an MQL method (the MQL method: machining performed while oil is supplied to the end mill) using the end mill, wherein FIG. 7(a) shows the relationship between the number of passes and a temperature in the interior of the tool with one side-surface machining operation (=one pass) as a unit of time, FIG. 7(b) shows the relationship between the time in the first pass (see (1) of FIG. 7(a)) and the temperature in the interior of the tool, and FIG. 7(c) shows the relationship between the time of the 124th pass (see (2) of FIG. 7(a)) and the temperature in the interior of the tool. Meanwhile, as shown in FIGS. 7(a) to 7(c), the maximum temperature in each pass is shown as the temperature in the interior of the tool. Meanwhile, in an experimental example of FIG. 7, a 5 coated high-speed steel end mill made of SUS 304 material was used as the end mill, and cutting conditions were as follows: a cutting speed Vc=80 m/min, a feed rate per blade fz=0.02 mm, a cutting depth in the radial direction ae=1.25 mm, and a cutting depth in the axial direction ap=7.5 mm. [0062]
[0090] Referring to FIG. 7(b), it is revealed that, since oil is supplied to the end mill, the temperature in the interior of the tool per pass first increases from a temperature approximate to room temperature, reaches the maximum temperature (about 200 C. in FIG. 7(b)), is generally maintained without change, and decreases when machining is finished.
[0091] When the passes (round marks in the figure) are repeated, as shown in FIG. 7(a), the temperature increases gently until about the 100th pass is reached, the temperature increases somewhat greatly in 110th to 120th passes, the temperature increases more abruptly when the 120th pass is exceeded, and the tool is ruptured in the 124th pass. As shown in FIG. 7(c), it is revealed that the temperature in the interior of the tool in the last path, i.e. 124th pass, has a maximum temperature of about 400 C., an increase in the temperature in the interior of the tool is not found at the halfway point in the same manner as in other passes, and the temperature in the interior of the tool increases abruptly from about 18 sec, whereby the tool is damaged suddenly. Even when an increase in temperature is detected within this pass, therefore, the time until rupture is short, thus making it undesirable as a predictor of rupture.
[0092] In addition, for the temperature measurement device according to the first embodiment of the present invention described above, when the maximum temperature of the temperature in the interior of the tool per pass increases to a predetermined temperature or higher, as shown in FIG. 7(a), it is determined that the tool is not yet ruptured. In the example, as shown in FIG. 7(a), the temperature increase magnitude is not so large in about the 110th to 120th passes, whereby it is difficult to determine which temperature to set as a threshold value. If the threshold value is set to too low, even a time having no relation with rupture may be determined as a sign of rupture when measurement accuracy and an error at the time of actual cutting are considered. On the other hand, if the threshold value is set to too high, it is not possible to capture a sign of rupture until the 120th pass is exceeded, and it is not possible to foresee rupture even if the threshold value is set in the case in which the temperature increases suddenly and rupture occurs in the last pass or immediately before it.
[0093] Meanwhile, in the example of FIG. 7(a), a rate of increase of temperature (the variability of temperature) is obviously greatly changed when the 100th pass is exceeded. It is revealed that the variability of temperature is greater than the magnitude of actual temperature increase. In the temperature measurement device according to the second embodiment of the present invention, an increase in the variability of temperature is captured and detected as a sign of rupture. A detailed method determining the same as a limit temperature when the variability of temperature is captured and found to be higher than a predetermined variability will be described below.
[0094] Next, another experimental example will be considered.
[0095] FIG. 8 is a graph showing the relationship between an actually measured temperature in the interior of the end mill and a machining time when the side surface of an object to be machined is dry-machined using the end mill, which shows the relationship between the number of passes and a temperature in the interior of the tool with one side-surface machining operation (=one pass) as a unit of time, in the same manner as in FIG. 7(a), wherein the maximum temperature in each pass is shown as the temperature in the interior of the tool.
[0096] Meanwhile, in the example of FIG. 8, the cutting conditions are the same as those in the example of FIG. 7 except that the side surface of the object is machined by dry machining.
[0097] When the passes (round marks in the figure) are repeated, as shown in FIG. 8, the temperature increases gently until about the 25th pass is reached. The rate of increase of temperature is higher than that of FIG. 7(a), which, however, is considered to result from the reduction in cooling efficiency for dry-machining conditions. The temperature increases abruptly when the 25th pass is exceeded, and the tool is ruptured in the 28th pass.
[0098] In the example of FIG. 8, it is revealed that a rate of increase of temperature (the variability of temperature) is obviously greatly changed when the 20th pass is exceeded and that the variability of temperature is greater than the magnitude of actual temperature increase. Even in this example, therefore, an increase in the variability of temperature is captured and detected as a sign of rupture, and, when variability higher than a predetermined variability is detected, it is possible to determine the same as a limit temperature.
[0099] FIG. 9 is a graph showing the relationship between an actually measured temperature in the interior of the end mill and a machining time when an object to be machined is grooved using the end mill while a water-soluble oil is supplied to the end mill, which shows the relationship between the number of passes and temperature in the interior of the tool with one pass as a unit of time, in the same manner as in FIGS. 7(a) and 8. Meanwhile, in the example of FIG. 9, the cutting conditions are the same as those in the examples of FIGS. 7 and 8, except that the object is grooved while the water-soluble oil is supplied to the end mill.
[0100] When the passes (round marks in the figure) are repeated, as shown in FIG. 9, the temperature increases gently until about the 85th pass is reached. After that, the temperature increases abruptly, and the tool is ruptured in the 90th pass.
[0101] The example of FIG. 9 is an example in which the temperature decreases while the temperature increases gently and in which, in particular, it is difficult to estimate a sign of rupture if the threshold value is set based only on the magnitude of actual temperature increase itself. Consequently, a combination with a method of detecting the difference between the actual temperature and the ideal temperature to determine whether the difference between the actual temperature and the ideal temperature is within a predetermined range of threshold value, as in the first embodiment of the present invention, may be considered.
[0102] In the example of FIG. 8, it is revealed that a rate of increase of temperature (the variability of temperature) is obviously greatly changed when the 20th pass is exceeded and that the variability of temperature is greater than the magnitude of actual temperature increase. Even in this example, therefore, an increase in the variability of temperature is captured and detected as a sign of rupture, and, when variability higher than a predetermined variability is detected, it is possible to determine the same as a limit temperature.
[0103] FIG. 10 is a graph showing the relationship between an actually measured temperature in the interior of the end mill and the number of machining operations (the number of boring operations) when an object to be machined (a material to be cut) is bored using the end mill while a water-soluble oil is supplied to the end mill, which shows the relationship between the number of machining operations and temperature in the interior of the tool with one boring operation (=one machining operation) as a unit of time. Meanwhile, as shown in FIG. 10, the maximum temperature during each machining process is shown as the temperature in the interior of the tool.
[0104] Meanwhile, in the experimental example shown in FIG. 10, boring was performed using a drill, a 10 coated high-speed steel drill made of SUS 304 material was used as the drill, and cutting conditions were as follows: a cutting speed Vc=15 m/min, a feed rate per rotation f=0.15 mm/rev, and a depth d=1.5 mm.
[0105] When the machining operations (round marks in the figure) are repeated, as shown in FIG. 10, the temperature increases gently until the number of machining operations is about 90. When the number of machining operations is 90, the temperature increases suddenly, and then the drill is ruptured.
[0106] FIG. 11 is a graph showing the relationship between the actually measured temperature in the interior of the end mill and the number of machining operations (the number of boring operations) when an object to be machined (a material to be cut) is bored using the end mill while a water-soluble oil is supplied to the end mill, in the same manner as in FIG. 10. A 8 coated high-speed steel drill made of SUS 304 material is used as the drill, and a cutting speed Vc and a feed rate per rotation f are the same as those in FIG. 10 and a depth d=12 mm as cutting conditions.
[0107] When the machining operations (round marks in the figure) are repeated, as shown in FIG. 11, the temperature increases gently until the number of machining operations is about 11. When the number of machining operations is 12 or 13, the temperature increases suddenly, and then the drill is ruptured.
[0108] Next, concrete methods of calculating the variability of temperature will be illustrated. For example,
[0109] (1) a method of calculating the rate of change between a measured actual temperature and an actual temperature measured by that time as the variability of temperature,
[0110] (2) a method of calculating the difference in temperature between a measured actual temperature and an actual temperature measured by that time as the variability of temperature, and
[0111] (3) a method of calculating the integrated value of an actual temperature for each predetermined amount of time or for each operation time as the variability of temperature may be illustrated.
[0112] Although the embodiments of the present invention have been described with reference to the accompanying drawings, the detailed construction of the present invention is not limited to the embodiments. The scope of the present invention is limited by the scope of the claims, rather than the description of the embodiments. Furthermore, the scope of the present invention includes all changes within the meaning and scope equivalent to the scope of the claims.
