JP5127603B2 - Processing method and processing apparatus - Google Patents

Description

  The present invention relates to a machining method and a machining apparatus for correcting thermal displacement of a tool due to cutting heat or the like during machining in a machining apparatus that performs cutting or the like with high accuracy.

  Factors that deteriorate the processing accuracy of a processing machine include a change in environmental temperature, heat generation of the machine itself by a spindle and a motor, and thermal displacement of each part of the machine due to cutting heat during processing. As a countermeasure against thermal displacement of a tool, for example, as disclosed in Patent Document 1, there is a method of cooling by injecting high-pressure coolant onto a tool being processed. Further, as disclosed in Patent Document 2, there is a method of forming a tool with a low thermal expansion material. In Patent Document 3, a temperature sensor is provided in the tool, and the thermal displacement amount of the tool is estimated and corrected. A method has been proposed.

JP-A-6-134648 Japanese Patent Laid-Open No. 5-318275 JP-A 63-2645

  However, the method of cooling the tool as in the above-described conventional example has a problem that the temperature of the tool is not constant and is thermally displaced when there is a change in cutting heat during machining. When the tool temperature during actual machining is measured, for example, a graph as shown in FIG. 4 is obtained. FIG. 4 shows the result of measuring the temperature of a tool when an end face turning is performed from the outside of the workpiece toward the center at a cutting depth of 10 μm, a spindle rotation speed of 3800 rpm, and a scanning speed of 50 μm / s. It is a graph which shows. From this graph, it can be seen that after the temperature of the tool rises from the start of machining, the temperature of the tool decreases toward the center of the workpiece, and the temperature cannot be kept constant by the method of cooling the tool.

  Further, the method of forming the tool with the low thermal expansion material has a problem that the cost is increased.

  In the method using the temperature sensor, there is a problem that the measurement accuracy is deteriorated because the cutting oil used at the time of processing adheres to the temperature sensor, and there is a problem that it is necessary to set up the temperature sensor every time the tool is changed.

  An object of the present invention is to provide a machining method and a machining apparatus capable of correcting a thermal displacement of a tool due to cutting heat during machining without using a special tool or a temperature sensor and improving machining accuracy. Is.

  To achieve the above object, a machining method according to the present invention is a machining method for machining a workpiece by a tool driven according to a machining program, wherein a first removal amount per unit time is calculated based on the machining program. A step, a second step of calculating a temperature change of the tool being processed from the removal amount, a third step of estimating a thermal displacement amount of the tool from the temperature change, and canceling out the thermal displacement amount of the tool A fourth step of correcting the command value of the machining program as described above.

  The processing apparatus of the present invention is a processing apparatus that rotates a workpiece in accordance with a processing program and drives the tool in a cutting direction and a scanning direction to perform end face turning processing. Based on the processing program, the removal amount per unit time Means for calculating the thermal displacement amount of the tool from the removal amount, and means for correcting the command value of the machining program so as to cancel out the thermal displacement amount of the tool. And

  Since the amount of removal per unit time is calculated based on the machining program and the thermal displacement of the tool due to cutting heat is estimated, the thermal displacement of the tool during machining can be corrected without using a special tool or sensor. Enables high-precision processing at low cost.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  As shown in FIG. 1, a machining apparatus that performs end face turning with a tool 1 includes a machining program input device 7, a removal amount calculator 8, a calorific value calculator 9, a temperature change calculator 10, a thermal displacement calculator 11, a machining. A program correction device 12, an NC device 13 and the like are provided. The removal amount per unit time is calculated by the removal amount calculator 8 from the machining conditions including the rotation speed, feed speed (scanning speed), and cutting amount input to the machining program input device 7 and the cutting edge shape of the tool. Based on the calculated removal amount per unit time, the calorific value calculator 9, the temperature change calculator 10 and the thermal displacement calculator 11 estimate (calculate) the calorific value due to processing, the temperature change of the tool, and the thermal displacement amount of the tool. . The machining program correction device 12 creates a command value corrected so as to cancel out the thermal displacement amount, and outputs the command value from the NC device 13 to the machining device. In this way, the thermal displacement of the tool 1 due to the cutting heat is corrected.

  Alternatively, as shown in FIG. 2, the output of the removal amount calculator 8 is introduced into the temperature change calculator 10, and the tool 1 is calculated by a calculation formula using constants determined by the tool shape, the tool material, and the material of the workpiece 4. The structure which calculates | requires a temperature change may be sufficient.

  As shown in FIG. 1, a machining apparatus for end face turning according to the present embodiment holds a tool 1, a tool holder 2 for fixing the tool 1, a tool holder 2, and a cutting direction (Y in end face turning) Direction) and an XY table 3 driven in the scanning direction (X direction). A spindle 5 that holds the workpiece 4 and rotates at high speed about the Y axis is supported by a surface plate 6.

  The control system includes a machining program input device 7, a removal amount calculator 8, a calorific value calculator 9, a temperature change calculator 10, a thermal displacement calculator 11, and a machining program correction device 12 that corrects the machining program. , NC device 13 and the like, and arrows indicate the flow of data.

  First, the cutting amount and scanning speed by the XY table 3, the rotation speed of the spindle 5, and the cutting edge shape of the tool 1 are input to the machining program input device 7. The removal amount per unit time by cutting is calculated by the removal amount calculator 8 from the information input to the machining program in this way. The removal amount based on the machining program is calculated by the following method.

  FIG. 3A shows the positional relationship between the tool 1 and the workpiece 4 in the end face turning. In the figure, the cutting amount M1 of the tool 1 into the workpiece 4, the scanning direction R1 of the tool 1, the rotation direction R2 of the workpiece 4 fixed to the spindle 5, and the movement amount M2 of the tool 1 per rotation. The removal area is M3. Further, assuming that the rotation center O of the main shaft 5, the radial distance D from the rotation center O of the main shaft 5 to the tool 1, and the tool position 1a before one rotation, the movement amount M2 of the tool 1 per one rotation is the tool scanning speed. Is divided by the rotational speed of the work piece 4. The removal area M3 where the tool 1 contacts the workpiece 4 is calculated based on the obtained movement amount M2 and cutting amount M1 of the tool 1 per rotation and the cutting edge shape of the tool 1. Further, the removal length in the circumferential direction per unit time is obtained from the rotational speed of the workpiece 4 and the radial distance D from the rotation center O, and the removal amount per unit time is calculated from the removal length and the removal area M3. The Here, since the radial distance D varies with the machining time, the removal amount varies with time.

  Next, the calorific value calculator 9 calculates the calorific value per unit time due to machining from the removal amount per unit time and the material of the workpiece 4. As a first method for obtaining the calorific value, there is a method of calculating based on the cutting theory. As a second method for determining the amount of heat generation, a database of the amount of removal per unit time and the amount of heat generation per unit time by cutting according to the material of the workpiece 4 is created in advance and read from this database. There is a way. For example, the removal amount per unit time at the time of temperature measurement shown in FIG. 4 is obtained as shown in FIG. 5, and the heat generation amount with respect to the removal amount per unit time can be obtained from FIGS. By performing such basic experiments under a plurality of processing conditions, a database of calorific values can be created.

  The temperature change calculator 10 calculates the temperature change of the tool 1 during machining by unsteady thermal analysis using a finite element method. The boundary conditions of the analysis are the calorific value obtained by cutting, the heat transfer coefficient of the tool in a state where the cutting oil is attached, the temperature of the working atmosphere, the material and shape of the tool. Here, the heat transfer coefficient is identified by measuring the temperature of the tool while using cutting oil.

  The thermal displacement calculator 11 calculates the amount of thermal displacement of the tool by performing structural analysis from a finite element model created by temperature change.

  The machining program correction device 12 creates a command value corrected so as to cancel out the thermal displacement amount of the tool 1 estimated by the thermal displacement calculator 11 from the machining program input to the machining program input device 7. The NC device 13 outputs a command value by the machining program in which the thermal displacement amount of the tool 1 is corrected in this way, and drives the XY table 3.

  Since the thermal displacement of the tool due to the cutting heat is estimated from the removal amount per unit time, the thermal displacement of the tool due to the cutting heat can be corrected with high accuracy without using a special tool or sensor.

  Note that the present embodiment is not limited to the above-described end face turning, and can be similarly applied to other machining in which the removal amount per unit time changes during machining.

  FIG. 2 shows a processing apparatus according to the second embodiment. This is a processing device for end face turning, holding the tool 1, the tool holder 2 for fixing the tool 1, and the tool holder 2, and the cutting direction (Y direction) and the scanning direction (X direction) in the end face turning. XY table 3 to be driven. A spindle 5 that holds the workpiece 4 and rotates at high speed about the Y axis is supported by a surface plate 6.

  The control system includes a machining program input device 7, a removal amount calculator 8, a temperature change calculator 10, a thermal displacement calculator 11, a machining program correction device 12, an NC device 13, etc. The flow is shown.

  First, the cutting amount and scanning speed by the XY table 3, the rotation speed of the spindle 5, and the cutting edge shape of the tool 1 are input to the machining program input device 7. From the input information, the removal amount per unit time by cutting is calculated by the removal amount calculator 8. This removal amount is calculated by the following method.

  FIG. 3A shows the positional relationship between the tool 1 and the workpiece 4 in the end face turning. In the figure, the cutting amount M1 of the tool 1 into the workpiece 4, the scanning direction R1 of the tool 1, the rotation direction R2 of the workpiece 4 fixed to the spindle 5, and the movement amount M2 of the tool 1 per rotation. The removal area is M3. Further, assuming that the rotation center O of the main shaft 5, the radial distance D from the rotation center O of the main shaft 5 to the tool 1, and the tool position 1a before one rotation, the movement amount M2 of the tool 1 per one rotation is the tool scanning speed. Is divided by the rotational speed of the work piece 4. The removal area M3 where the tool 1 contacts the workpiece 4 is calculated based on the obtained movement amount M2 and cutting amount M1 of the tool 1 per rotation and the cutting edge shape of the tool 1. Further, the removal length in the circumferential direction per unit time is obtained from the rotational speed of the workpiece 4 and the radial distance D from the rotation center O, and the removal amount per unit time is calculated from the removal length and the removal area M3. The Here, since the radial distance D varies with the machining time, the removal amount varies with time.

  Next, the temperature change calculator 10 calculates the temperature change of the tool 1 from the removal amount per unit time. A calculation formula used to calculate the temperature change of the tool 1 is shown below.

  In the above equation, ΔT (t) is the temperature change amount, V (t) is the removal amount per unit time, and t is the time from the start of processing. A, B, and C are constants determined by the shape and material of the tool 1, the processing environment, and the material of the workpiece 4, and are identified by performing processing in which the removal amount changes while actually measuring the temperature of the tool 1. To do. For example, the removal amount per unit time at the time of temperature measurement shown in FIG. 4 is obtained as shown in FIG. 5 by the machining program, and identification can be performed as follows from FIG. 4 and FIG.

  A is a slope in a range from a to b in which time has elapsed from the start of machining in the graph of FIG. 4 and the temperature change of the tool is constant, and in the graph of FIG. 5, the range from a to b in the graph of FIG. And the slope in the range from c to d, which is the same time as.

  B is obtained by substituting the value c at t = 0 in FIG. 4, the value f at t = 0 in FIG. 5, and A obtained previously in the above equation and calculating t = 0.

  C is a delay time from c to a in FIG. 4 and is determined by repeatedly adjusting the above equation so as to match FIG.

  Thus, by obtaining A, B, and C, the temperature change of the tool can be calculated from the removal amount per unit time.

  From the temperature change of the tool 1 calculated by the temperature change calculator 10, the thermal displacement calculator 11 calculates the thermal displacement amount using the following formula.

  Here, ΔL (t) is a thermal displacement amount, D is a thermal expansion coefficient determined by the material of the tool 1, and ΔT (t) is a temperature change amount. FIG. 3B shows a method of fixing the tool 1 with the tool holder 2, and the tool 1 is fixed to the tool holder 2 with a set screw 14. L is the length from the place where the tool 1 is fixed with the set screw 14 to the tip of the tool, as shown in FIG.

  The machining program correction device 12 creates a command value obtained by correcting the thermal displacement amount of the tool estimated by the thermal displacement calculator 11 from the machining program input to the machining program input device 7. The NC device 13 outputs a command value by the machining program in which the thermal displacement amount of the tool is corrected in this way, and drives the XY table 3.

  Since the thermal displacement of the tool due to the cutting heat is estimated from the removal amount per unit time, the thermal displacement of the tool due to the cutting heat can be corrected with high accuracy without using a special tool or sensor.

  Note that the present embodiment is not limited to the above-described end face turning, and can be similarly applied to other machining in which the removal amount per unit time changes during machining.

FIG. 3 is an explanatory diagram for explaining Example 1; FIG. 6 is an explanatory diagram for explaining Example 2; It is explanatory drawing explaining the method of calculating the removal amount per unit time in Example 1, 2, and the thermal displacement of a tool. It is a graph which shows the temperature change of the tool at the time of performing end face turning. It is a graph which shows the change of the removal amount when performing end face turning.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tool 2 Tool holder 3 XY table 4 Workpiece 5 Spindle 6 Surface plate 7 Machining program input device 8 Removal amount calculator 9 Heat generation amount calculator 10 Temperature change calculator 11 Thermal displacement calculator 12 Machining program correction device 13 NC device

Claims (6)

In a machining method for machining a workpiece with a tool driven according to a machining program,
A first step of calculating a removal amount per unit time based on the machining program;
A second step of calculating a temperature change of the tool being processed from the removal amount;
A third step of estimating a thermal displacement amount of the tool from the temperature change;
And a fourth step of correcting a command value of the machining program so as to cancel out the thermal displacement amount of the tool.   The machining method according to claim 1, wherein, in the third step, a thermal displacement amount of the tool is calculated from the temperature change and the material and shape of the tool.   The machining method according to claim 1 or 2, wherein, in the second step, a temperature change of the tool during machining is calculated from a removal amount per unit time and a material of the workpiece.   In the second step, the calorific value during processing is obtained from a database of calorific value per unit time created in advance according to the amount of removal per unit time and the material of the workpiece, and the calorific value and the tool The processing method according to claim 1, wherein a temperature change of the tool being processed is calculated from the material and shape of the tool. The machining method according to claim 3, wherein in the second step, the temperature change of the tool is obtained by the following equation.

Where ΔT (t): temperature change amount
V (t): removal amount per unit time
A, B, C: Constants determined by workpiece material, tool material and shape In a processing apparatus that rotates a workpiece according to a processing program and drives a tool in a cutting direction and a scanning direction to perform end face turning,
Means for calculating a removal amount per unit time based on the machining program;
Means for calculating a thermal displacement amount of the tool from the removal amount;
And a means for correcting a command value of the machining program so as to cancel out the thermal displacement amount of the tool.

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