Tool setting is the main operation and important skill in CNC machining. Under certain conditions, the accuracy of tool setting can determine the machining accuracy of parts. At the same time, the efficiency of tool setting also directly affects the efficiency of CNC machining. It is not enough to only know the tool setting methods. It is also necessary to know the various tool setting methods of the CNC system and the calling methods of these methods in the machining program. At the same time, it is necessary to know the advantages and disadvantages of the various tool setting methods and the conditions of use.

 

 

 

 

 

1. Principle of knife setting

The purpose of tool calibration is to establish the workpiece coordinate system. Intuitively, tool calibration is to establish the position of the workpiece on the machine tool table. In fact, it is to find the coordinates of the tool calibration point in the machine tool coordinate system. For CNC lathes, the tool setting point must be selected before machining. The tool setting point refers to the starting point of the tool 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 aligned with the workpiece positioning reference Maintain a certain precise dimensional relationship.

 

When setting the tool, the tool position point should coincide with the tool setting point. The so-called tool position point refers to the positioning reference point of the tool. For turning tools, the tool position point is the tool tip. 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. When actually processing a workpiece, using one tool generally cannot meet the processing requirements of the workpiece, and usually multiple tools are used for processing. When multiple turning tools are used for machining, when the tool change position is unchanged, the geometric position of the tool tip point will be different after the tool change. This requires different tools to start machining at different starting positions. Ensure that the program runs normally.

 

In order to solve this problem, the machine tool numerical control system is equipped with the function of tool geometric position compensation. Using the tool geometric position compensation function, as long as the position deviation of each tool relative to a preselected reference tool is measured in advance, it is input to the numerical control system In the specified group number in the tool parameter correction column, use the T command in the machining program to automatically compensate the tool position deviation in the tool path. The measurement of tool position deviation also needs to be realized by tool setting operation.

 

 

Second, the method of knife setting

 

In CNC machining, the basic methods of tool setting include trial cutting, tool setting instrument setting and automatic tool setting. This article takes the CNC milling machine as an example to introduce several common tool setting methods.

 

1. Trial cutting method

 

This method is simple and convenient, but it will leave cutting marks on the surface of the workpiece, and the tool setting accuracy is low. As shown in Figure 1, taking the tool setting point (here coincides with the origin of the workpiece coordinate system) at the center of the workpiece surface as an example, the bilateral tool setting method is used.

 

(1) Tool setting in x, y direction.

 

①The workpiece is mounted on the worktable through the fixture. When clamping, the four sides of the workpiece should be reserved for tool setting positions.

 

②Start the spindle to rotate at medium speed, quickly move the worktable and spindle, so that the tool quickly moves 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.

 

③When approaching the workpiece, use the fine-tuning operation (usually 0.01mm) to approach, let the tool slowly approach the left side of the workpiece, so that the tool just touches the left side surface of the workpiece (observe, listen to the cutting sound, see the cut 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 coordinate system at this time, such as -240.500.

 

④ Withdraw the tool in the positive z direction to above the surface of the workpiece, approach the right side of the workpiece in the same way, and write down the coordinate value displayed in the machine coordinate system at this time, such as -340.500.

 

⑤According to this, the coordinate value of the origin of the workpiece coordinate system in the machine tool coordinate system can be obtained

 

{-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.

 

① Move the tool quickly to the top of the workpiece.

 

②Start the spindle to rotate at medium speed, quickly move the worktable and spindle, so that the tool quickly moves to a position close to the upper surface of the workpiece with a certain safety distance, and then reduce the speed to move the tool end face close to the upper surface of the workpiece.

 

③Use the fine-tuning operation (usually 0.01mm) when approaching the workpiece, and let the tool end surface slowly approach the surface of the workpiece (note that it is best to cut the tool at the edge of the workpiece when the tool is especially an end mill, and the end surface of the tool is in contact with the surface area of ​​the workpiece. If it is smaller than a semicircle, try not to make the center hole of the end mill under the surface of the workpiece), make the end face of the tool just touch the upper surface of the workpiece, and then raise the axis again, and write down the z value in the machine coordinate system at this time, -140.400 , The coordinate value of the origin W of the workpiece coordinate system in the machine tool coordinate system is -140.400.

 

(3) Input the measured x, y, z values ​​into the storage address G5* of the machine tool workpiece coordinate system (usually use G54～G59 codes to store the tool setting parameters).

 

(4) Enter the panel input mode (MDI), enter "G5*", press the start key (in automatic mode), and run G5* to make it effective.

 

(5) Check whether the tool setting is correct.

 

2. Feeler gauge, standard mandrel, block gauge tool setting method

 

This method is similar to the trial cutting tool setting method, except that the spindle does not rotate during tool setting. A feeler gauge (or standard mandrel or block gauge) is added between the tool and the workpiece, and the feeler gauge just cannot twitch freely. Pay attention to the calculation In the case of coordinates, the thickness of the feeler gauge should be subtracted. Because the spindle does not need to rotate for cutting, this method will not leave traces on the surface of the workpiece, but the tool setting accuracy is not high enough.

 

3. Tool setting method using edge finder, eccentric rod and axis setter

 

The operation steps are similar to the trial cutting method, except that the tool is replaced by an edge finder or an eccentric rod. This is the most commonly used method. High efficiency, can ensure the accuracy of tool setting. When using the edge finder, you must be careful to make the steel ball part slightly contact the workpiece, and the workpiece to be processed must be a good conductor, and the positioning reference surface has a good surface roughness. The z-axis setter is generally used for transfer (indirect) tool setting.

 

4. Transfer (indirect) knife setting method

 

Processing a workpiece often requires more than one knife. The length of the second knife is not the same as the length of the first knife. It needs to be re-zeroed, but sometimes the zero point is processed and the zero point cannot be retrieved directly or not. It is permissible to damage the machined surface, and some tools or occasions are not good for direct tool setting. In this case, indirect change can be used.

 

(1) On the first knife.

 

①For the first knife, still use trial cutting method and feeler gauge method. Note down the machine coordinate z1 of the workpiece origin at this time. After the first tool is processed, stop the spindle.

 

②Put 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 to move the worktable to a suitable position, move the spindle down, press the top of the tool setter with the bottom end of the knife, the dial pointer rotates, preferably within one circle, and record the axis at this time Set the indicator of the setter and clear the relative axis.

 

④ Make sure to raise the spindle and remove the first knife.

 

(2) On the second knife.

 

① Install the second knife.

 

②In the handwheel mode, move the spindle down, press the top of the tool setter with the bottom end of the knife, the dial pointer rotates, and the pointer points to the same 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.

 

⑤Add z0 (plus or minus sign) to the z1 coordinate data in G5* of the original first tool to obtain a new coordinate.

 

⑥ This new coordinate is the actual coordinate of the machine tool corresponding to the workpiece origin of the second tool, and input it to the second tool

 

In G5* working coordinates, in this way, the zero point of the second tool is set. The rest of the knife is the same as the second knife.

 

Note: If several tools use the same G5*, step 5) and 6) change to store z0 in the length parameter of the second tool, and call tool length compensation G43H02 when using the second tool for machining.

 

 

5. Top knife setting method

 

(1) Tool setting in x, y direction.

 

① Install the workpiece on the machine tool table through the fixture and replace the center.

 

②Move the worktable and the spindle quickly, let the top move to the top of the near workpiece, find the center point of the workpiece line, reduce the speed and move the top to approach it.

 

③Use the fine-tuning operation to make the center slowly approach the center point of the workpiece line until the tip of the center is aligned with the center point of the workpiece line, and write down the x and y coordinate values ​​in the machine coordinate system at this time.

 

(2) Remove the center, install the milling cutter, and use other tool setting methods such as trial cutting and feeler gauge to obtain the z-axis coordinate value.

 

6. Dial indicator (or dial indicator) tool setting method (usually used for round workpiece tool setting)

 

(1) Tool setting in x, y direction.

 

Install the mounting rod of the dial indicator on the tool holder, or attach the magnetic seat of the dial indicator to the spindle sleeve, move the worktable to move the spindle center line (ie the tool center) approximately to the center of the workpiece, and adjust the magnetic seat The length and angle of the telescopic rod make the contact of the dial indicator touch the circumferential surface of the workpiece, (the pointer rotates about 0.1mm) slowly rotate the main shaft by hand to make the contact of the dial indicator rotate along the circumferential surface of the workpiece, and observe The movement of the dial indicator pointer, slowly move the axis and the axis of the worktable. After many times of repetition, the dial indicator pointer is basically at the same position when the main shaft is rotated (when the meter head rotates one week, the amount of movement of the pointer is Within the allowable tool setting error, such as 0.02mm), the center of the spindle can be considered as 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, feeler gauge method, etc. to obtain the z-axis coordinate value.

 

7. Tool setting method with special tool setting device

 

Traditional tool setting methods have disadvantages such as poor safety (such as feeler gauge setting, hard hitting the tip of the knife, easy to crash), which takes up more time (such as trial cutting requires repeated cutting several times), and large random errors caused by humans. The rhythm of CNC machining is not conducive to the function of CNC machine tools. Tool setting with a special tool setting device has the advantages of high precision, high efficiency, and good safety. It simplifies the tedious work of tool setting guaranteed by experience, and ensures the high efficiency and high precision of CNC machine tools. A special tool that is indispensable for tool setting on a CNC machine.