Tool setting of CNC lathe is an important skill in machining. The accuracy of tool setting determines the machining accuracy of parts. The efficiency of tool setting directly affects the processing efficiency of parts. Tool setting is very important to the machining operation of machine tools.
After the CNC lathe is turned on, it must return to zero (reference point). The purpose is to establish a unified benchmark for position measurement, control, and display of the CNC lathe, that is, the tool returns to the origin of the machine tool. The origin of the machine tool is usually at the maximum positive stroke of the tool. , its position is determined by the machine position sensor.
After the machine tool returns to zero, the distance between the position of the tool (tool tip) and the machine origin is fixed. Therefore, for the convenience of tool setting and processing, the position of the tool tip after the machine tool returns to zero can be regarded as the machine origin. Tool setting is the operation process of establishing the workpiece coordinate system in the machine tool coordinate system of the CNC machine tool, and making the origin of the workpiece coordinate system coincide with the programming origin.
Measure the distance between the tool nose programming point in the machine tool coordinate system and the machining origin in the X and Z directions by trial cutting or non-contact methods, and set the value into the machine tool parameters, and establish the workpiece coordinate system by calling the program, and the base point in the program. The absolute coordinate value is based on the origin of the established workpiece coordinate system, and the contour of the part is processed.
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1. The principle of tool setting
The purpose of tool setting is to establish the workpiece coordinate system. Intuitively speaking, tool setting is to establish the position of the workpiece in the machine tool workbench. In fact, it is to find the coordinates of the tool setting point in the machine tool coordinate system.
For CNC lathes, the tool setting point must first be selected before processing. The tool setting point refers to the starting point of the tool's movement relative to the workpiece when the workpiece is processed by the CNC machine tool. The tool setting point can be set on the workpiece (such as the design datum or positioning datum on the workpiece), or it can be set on the fixture or machine tool. If it is set at a certain point on the fixture or machine tool, the point must be consistent with the positioning datum of the workpiece. Preserve dimensional relationships with a certain degree of precision.
When setting the tool, the point of the finger point should coincide with the point of the setting point. The so-called point of the tool refers to the positioning reference point of the tool. For the turning tool, the point of the tool point is the tip of the tool. The purpose of tool setting is to determine the absolute coordinate value of the tool setting point (or workpiece origin) in the machine tool coordinate system, and to measure the tool position deviation value of the tool. The accuracy of the tool point alignment directly affects the machining accuracy.
In the actual processing of workpieces, the use of one tool generally cannot meet the processing requirements of the workpiece, and usually multiple tools are used for processing. When using multiple turning tools for machining, the geometric positions of the tool tip points will be different after the tool change when the tool change position remains the same, which requires different tools to be able to Make sure the program runs normally.
In order to solve this problem, the CNC system of the machine tool is equipped with the function of tool geometric position compensation. Using the tool geometric position compensation function, it is only necessary to measure the position deviation of each tool relative to a pre-selected reference tool in advance and input it to the CNC system. In the specified group number in the tool parameter correction column, use the T command in the processing program to automatically compensate the tool position deviation in the tool path. The measurement of the tool position deviation also needs to be realized through the tool setting operation.
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2. Tool setting method
In CNC machining, the basic methods of tool setting include trial cutting method, tool setting instrument and automatic tool setting. This article takes CNC milling machine as an example to introduce several commonly used tool setting methods.
1. Trial cutting and knife setting method
This method is simple and convenient, but it will leave cutting marks on the surface of the workpiece, and the accuracy of tool setting is low. Take the tool setting point (here coincident with the origin of the workpiece coordinate system) at the center of the workpiece surface as an example to adopt the bilateral tool setting method.
(1) Tool setting in x, y direction.
① Install the workpiece on the workbench through the fixture. When clamping, the four sides of the workpiece should be reserved for tool setting.
② Start the spindle to rotate at a medium speed, move the table and the spindle quickly, let the tool quickly move to a position close to the left side of the workpiece with a certain safety distance, and then reduce the speed to move close to the left side of the workpiece.
③ When approaching the workpiece, use fine-tuning operation (generally 0.01mm) to approach, let the tool slowly approach the left side of the workpiece, so that the tool just touches the surface of the left side of the workpiece (observe, listen to the cutting sound, see the cutting marks, and see the chips, as long as If a situation occurs, it means that the tool touches the workpiece), and then retract 0.01mm. Write down the coordinate value displayed in the machine tool coordinate system at this time, such as -240.500.
④Retract the tool along the z positive direction, reach above the workpiece surface, approach the right side of the workpiece in the same way, and record the coordinate value displayed in the machine tool coordinate system at this time, such as -340.500.
⑤According to this, it can be obtained that the coordinate value of the origin of the workpiece coordinate system in the machine tool coordinate system is {-240.500+(-340.500)}/2=-290.500.
⑥Similarly, the coordinate value of the origin of the workpiece coordinate system in the machine tool coordinate system can be measured.
(2) Z direction tool setting.
①Move the tool quickly above the workpiece.
② Start the spindle to rotate at a medium speed, move the worktable and the spindle quickly, let the tool move quickly to a position close to the upper surface of the workpiece with a certain safety distance, and then move at a lower speed so that the end surface of the tool is close to the upper surface of the workpiece.
③ When approaching the workpiece, use the fine-tuning operation (generally 0.01mm) to approach, so that the end face of the tool slowly approaches the surface of the workpiece (note that when the tool is especially an end mill, it is best to cut the knife at the edge of the workpiece, the area where the end face of the tool touches the surface of the workpiece less than a semicircle, try not to make the center hole of the end mill under the surface of the workpiece), so that the end face of the tool just touches the upper surface of the workpiece, and then raise the axis again, record the z value in the machine tool coordinate system at this time, -140.400 , then the coordinate value of the workpiece coordinate system origin W in the machine tool coordinate system is -140.400.
(3) Input the measured x, y, z values into the storage address G5* of the workpiece coordinate system of the machine tool (generally use G54~G59 codes to store tool setting parameters).
(4) Enter the panel input mode (MDI), input "G5*", press the start button (in automatic mode), run G5* to make it effective.
(5) Check whether the tool setting is correct.
2. Feeler gauge, standard mandrel, block gauge knife setting method
This method is similar to the trial cutting tool setting method, except that the spindle does not rotate during tool setting, and a feeler gauge (or standard mandrel, block gauge) is added between the tool and the workpiece. In this way, the thickness of the feeler gauge should be subtracted from the coordinates. Because the spindle does not need to rotate for cutting, this method will not leave marks on the surface of the workpiece, but the accuracy of tool setting is not high enough.
3. Tool setting method using tools such as edge finder, eccentric rod and axis setter
The operation steps are similar to the method of trial cutting and tool setting, except that the tool is changed to an edge finder or an eccentric rod, which is the most commonly used method. High efficiency, can guarantee the accuracy of tool setting. Care must be taken when using the edge finder, so that the steel ball part is in slight contact with the workpiece. At the same time, the workpiece to be processed must be a good conductor, and the positioning reference plane has a good surface roughness. The z-axis setter is generally used for transfer (indirect) tool setting methods.
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4. Transfer (indirect) knife setting method
It is often necessary to use more than one knife to process a workpiece. The length of the second knife is different from the length of the first knife, and it needs to be re-zeroed. However, sometimes the zero point is processed and cannot be directly retrieved. It is allowed to damage the processed surface, and some tools or occasions are not easy to directly set the tool. At this time, the method of indirect change can be used.
(1) For the first knife
① For the first knife, still use the trial cutting method, feeler gauge method, etc. first. Write down the machine tool coordinate z1 of the workpiece origin at this time. After the first tool is processed, stop the spindle.
② Put the tool setter on the flat surface of the machine tool table (such as the large surface of the vise).
③In the handwheel mode, use the hand crank to move the worktable to a suitable position, move the spindle down, press the top of the tool setting device with the bottom of the knife, and the pointer on the dial will rotate, preferably within one circle, and record the axis at this time. Set the indication of the device and clear the relative coordinate axis to zero.
④ Raise the main shaft and remove the first knife.
(2) Against the second knife.
① Install the second knife.
②In the handwheel mode, move the spindle downwards, press the top of the tool setting device with the bottom end of the knife, the dial pointer rotates, and the pointer points to the same display A position as the first knife.
③Record the value z0 (with sign) corresponding to the relative coordinate of the axis at this time.
④ Raise the spindle and remove the tool setter.
⑤ Add z0 (with plus or minus sign) to the z1 coordinate data in G5* of the original first knife to get a new coordinate.
⑥This new coordinate is the actual coordinate of the machine tool corresponding to the workpiece origin of the second tool to be found, and input it into the G5* work coordinate of the second tool, so that the zero point of the second tool is set . The other knives are set in the same way as the second knife.
Note: If several tools use the same G5*, then step ⑤ and ⑥ should be changed to store z0 in the length parameter of No. 2 tool, and call tool length correction G43H02 when using the second tool for machining.
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5. Top knife setting method
(1) Tool setting in x, y direction.
① Install the workpiece on the machine table through the fixture, and replace it with the top.
②Quickly move the worktable and spindle, let the tip move close to the top of the workpiece, find the center point of the workpiece line, and move at a reduced speed to make the tip approach it.
③Use the fine-tuning operation to make the tip slowly approach the center point of the workpiece line until the tip point is aligned with the center point of the workpiece line, and record the x and y coordinate values in the machine tool coordinate system at this time.
(2) Remove the top, install the milling cutter, and use other tool setting methods such as trial cutting method, feeler gauge method, etc. to obtain the z-axis coordinate value.
6. Dial gauge (or dial gauge) knife setting method
Dial indicator (or dial gauge) tool setting method (generally used for tool setting of circular workpieces)
(1) Tool setting in x, y direction.
Install the dial indicator rod on the tool handle, or attach the magnetic seat of the dial indicator to the spindle sleeve, move the worktable so that the center line of the spindle (that is, the center of the tool) is approximately moved to the center of the workpiece, and adjust the magnetic seat Adjust the length and angle of the telescopic rod so that the contact of the dial indicator touches the peripheral surface of the workpiece, (the pointer rotates about 0.1mm) slowly rotate the main shaft by hand, so that the contact of the dial indicator rotates along the peripheral surface of the workpiece, observe The easy movement of the pointer of the dial indicator, slowly move the shaft and shaft of the workbench, and after repeated repetitions, the pointer of the dial indicator is basically at the same position when the main shaft is turned (when the head rotates a circle, the jump of the pointer is at Within the allowable tool setting error, such as 0.02mm), it can be considered that the center of the spindle is the axis and the origin of the axis.
(2) Remove the dial indicator and install the milling cutter, and use other tool setting methods such as trial cutting method, feeler gauge method, etc. to obtain the z-axis coordinate value.
7. Special tool setting tool setting method
The traditional method of tool setting has the disadvantages of poor safety (such as feeler gauge tool setting, it is easy to damage the tip of the knife head-on), takes up a lot of machine time (such as repeated cutting times for trial cutting), and has the disadvantages of large random errors caused by human beings. It can't adapt to the rhythm of CNC machining, and it is not conducive to the function of CNC machine tools. Using a special tool setting device for tool setting has the advantages of high tool setting accuracy, high efficiency, and good safety. It simplifies the tedious tool setting work guaranteed by experience and ensures the high efficiency and high precision of CNC machine tools. It has become a A special tool that is indispensable for tool setting on CNC machining machines.
