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The tool is the most important operation content in CNC machining, and its accuracy will directly affect the machining accuracy of the part. The tool setting method must be compatible with the machining accuracy requirements of the parts. This paper systematically describes the use of the common tool setting method of CNC milling machine (machining center) and its advantages and disadvantages, which has certain practical value. The purpose of the tool setting is to determine the position of the workpiece coordinate system origin (program origin) in the machine coordinate system by tool or tool setting tool, and input the tool setting data to the corresponding storage position or set by G92 command. It is the most important operation content in CNC machining, and its accuracy will directly affect the machining accuracy of the parts.
First, the positioning and clamping of the workpiece (preparation before the knife)
Commonly used clamps on CNC milling machines have flat jaws, indexing heads, three-jaw self-centering chucks and platform clamps. For economical CNC milling machines, flat jaw clamps are generally used for clamping workpieces. Install the pliers on the center of the milling machine table, and find and fix the <br> flat pliers. According to the height of the workpiece, put the horns with the right shape and good surface quality in the jaws of the pliers, and then put the workpiece into the workpiece. Usually, the reference surface of the workpiece faces down, close to the horn surface, and then the pliers are tightened.
Second, the determination of the knife point and the tool change point
(1) Determination of the tool point <br> The tool point is the reference point for determining the position of the workpiece coordinate system in the machine coordinate system after the workpiece is positioned and clamped on the machine tool. The tool point can be selected on the workpiece or on the clamping positioning component, but the tool point and the workpiece coordinate point must have an accurate, reasonable and simple position correspondence, which is convenient for calculating the position of the workpiece coordinate system on the machine tool. In general, the tool point is preferably coincident with the origin of the workpiece coordinate system.
(2) Determination of the tool change point <br> On a milling machine or machining center that uses a variety of tool machining, the tool needs to be changed frequently when machining the workpiece. The tool change point should be based on the tool, the fixture and the machine tool. It depends on the principle.
Third, the common tool setting method of CNC milling machine<br>The tool setting operation is divided into X, Y direction and Z direction. The accuracy of the tool will directly affect the machining accuracy. The tool setting method must be compatible with the machining accuracy requirements of the parts.
According to the different tool setting tools used, the commonly used tool setting methods are divided into the following types: (1) trial cutting knife method; (2) feeler gauge, standard mandrel and block gauge tool setting method; Tool-to-blade method such as edger, eccentric rod and Z-axis setter; (4) top-to-tool method; (5) dial gauge (or dial gauge) knife-to-tool method; (6) dedicated tool-pairing tool law.
In addition, according to the choice of tool position and data calculation method, it can be divided into single-edge tool setting, double-side tool setting, transfer (indirect) tool setting method and “minute to zero” tool setting method (requires machine tool must have relative Coordinates and clearing functions), etc.
1. Trial cutting method <br> This method is simple and convenient, but it will leave cutting marks on the surface of the workpiece, and the accuracy of the tool setting is low.
As shown in Fig. 1, the center position of the workpiece surface is taken as the example of the tool point (here, coincident with the origin of the workpiece coordinate system) (using the bilateral tool setting method).


(1) X, Y-direction tool setting ◎ The workpiece is mounted on the table by a clamp. When clamping, the position of the tool should be left on all four sides of the workpiece.
◎Start the spindle to rotate at medium speed, move the table and spindle quickly, let the tool move to a position close to the left side of the workpiece with a certain safe distance, and then reduce the speed to move to the left side of the workpiece.
◎ Use the fine adjustment operation (usually close to 0.01mm) when approaching the workpiece, and 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, see the chips, as long as When one of the cases occurs, the tool touches the workpiece, and then retracts 0.01mm. Make a note of the X coordinate value displayed in the machine coordinate system at this time, such as -240.500.
◎Retract the knife in the positive direction of Z to the surface of the workpiece. Use the same method to approach the right side of the workpiece. Write down the X coordinate value displayed in the machine coordinate system at this time, such as -340.500.
◎According to this, the X coordinate value of the workpiece coordinate system origin in the machine coordinate system is {-240.500+ (-340.500 )}/2=-290.500.
◎ Similarly, the Y coordinate value of the workpiece coordinate origin W in the machine coordinate system can be measured.
(2) Z-direction tool ◎ Move the tool quickly over the workpiece.
◎Start the spindle to rotate at medium speed, move the table and spindle quickly, let the tool move quickly to a position close to the upper surface of the workpiece, and then reduce the speed to move the tool end to the upper surface of the workpiece.
◎ Use the fine adjustment operation (usually close to 0.01mm) when approaching the workpiece, and let the end face of the tool slowly approach the surface of the workpiece. (Note that it is better to cut the edge of the workpiece at the edge of the workpiece, especially the end mill. The end surface of the knife contacts 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 hits the upper surface of the workpiece, and then raise the Z axis by 0.01mm, and record the Z value in the machine coordinate system. For example, if -140.400, etc., the Z coordinate value of the workpiece coordinate origin W in the machine coordinate system is -140.400.
(3) Data storage <br> Input the measured X, Y, and Z values ​​into the machine workpiece coordinate system storage address G5* (usually use the G54~G59 code to store the tool setting parameters).
(4) Start-up effective <br> Enter panel input mode (MDI), input "G5*", press the start button (in "automatic" mode), run G5* to make it effective.
(5) Inspection <br>Check whether the knife is correct. This step is very important.
2. feeler gauge, standard mandrel, block gauge tooling method<br>This method is similar to the trial-cutting knife method, except that the spindle does not rotate when the tool is placed, and a feeler gauge (or standard mandrel, Block gauge), the feeler gauge just can't be freely twitched. Note that the thickness of the feeler gauge should be subtracted when calculating the coordinates. Since the spindle does not require rotational cutting, this method does not leave marks on the surface of the workpiece, but the accuracy of the tool is not high enough.
3. Using the tools such as the edge finder, the eccentric rod and the Z-axis setter, the tooling method is similar to the trial-cutting method, except that the tool is replaced with an edge finder or an eccentric rod.
This is the most common method, high efficiency, and can guarantee the accuracy of the tool. Care must be taken when using the edge finder, so that the steel ball part is in slight contact with the workpiece, and the workpiece to be machined must be a good conductor, and the positioning reference surface has a good surface roughness. The Z-axis setter is typically used for transfer (indirect) tool setting.
It takes often more than one knife to machine a workpiece. The length of the second knife is different from the length of the first knife. It needs to be re-zeroed, but sometimes the zero point is processed, the zero point cannot be directly recovered, or the processed surface is not allowed to be destroyed, and some tools are also allowed. Or the occasion is not good for the knife directly. At this time, the method of indirect change can be used.
(1) For the first knife ◎ For the Z of the first knife, the trial cutting method, the feeler gauge method, and the like are still used first. Make a note of the machine coordinate Z1 of the workpiece origin at this time. After the first knife is finished, stop the spindle.
◎ Place the tool holder on the flat surface of the machine table (such as the large surface of the vise).
◎In the handwheel mode, use the hand to move the table to the appropriate position, move the spindle down, press the bottom of the knife to the top of the cutter, and the dial pointer rotates, preferably within one turn, note the time Z The axis A of the axis setter clears the relative coordinate Z axis.
◎ Raise the spindle and remove the first knife.
(2) Attach the second knife to the second knife ◎.
◎In the handwheel mode, move the spindle down, press the bottom end of the knife to the top of the cutter, the dial pointer rotates, and the pointer points to the same position A position as the first knife.
◎ Record the value Z0 (with sign) corresponding to the relative coordinate of the Z axis at this time.
◎ Raise the spindle and remove the tool holder.
◎ Add Z1 coordinate data in the G5* of the original first knife to Z0 (with plus or minus sign) to get a new Z coordinate. ◎ This new Z coordinate is the workpiece origin corresponding to the second knife we ​​are looking for. The actual coordinates of the machine tool are entered into the G5* working coordinates of the second tool, so that the zero point of the second tool is set. The remaining knives are the same as the second knives.
Note: If several knives use the same G5*, the step is to save Z0 into the length parameter of No. 2 knives, and use the tool length to correct G43H02 when using the second knives.
4. Top tool setting method
(1) X, Y-direction tool setting ◎ Mount the workpiece on the machine table through the clamp and replace it with the top.
◎ Quickly move the table and the spindle, move the tip to the top of the workpiece, find the center point of the workpiece line, and reduce the speed to move the tip to approach it.
◎ Use the fine adjustment operation to make the tip slowly approach the center point of the workpiece line until the top point is aligned with the center point of the workpiece line, and record the X and Y coordinate values ​​in the machine coordinate system.
(2) Z-direction tool setting <br>The top end is removed, the milling cutter is mounted, and the Z-axis coordinate value is obtained by other tool-setting methods such as trial cutting method and feeler gauge method.
5. Dial indicator (or dial gauge) knife method <br> This method is generally used for the tool setting of a circular workpiece.
(1) X, Y direction tooling <br> As shown in Figure 2, install the dial of the dial indicator on the shank, or draw the magnetic seat of the dial indicator on the spindle sleeve, and move the table to make The spindle center line (ie the tool center) is moved to the center of the workpiece, and the length and angle of the telescopic rod on the magnetic base are adjusted so that the contact of the dial indicator contacts the circumferential surface of the workpiece, and the pointer rotates about 0.1 mm. The main shaft rotates the contact of the dial indicator along the circumferential surface of the workpiece, observes the movement of the dial indicator, and slowly moves the X and Y axes of the table. After repeated iterations, the percentage of the spindle to be rotated The pointer of the table is basically at the same position (the amount of jump of the pointer is within the allowable tool setting error, such as 0.02 mm) when the head is rotated one week. At this time, the center of the spindle is considered to be the origin of the X-axis and the Y-axis.
(2) Z-direction tooling <br>The centring table is loaded with a milling cutter, and the Z-axis coordinate values ​​are obtained by other tool-setting methods such as trial cutting method and feeler gauge method.
Figure 2 dial indicator (or dial gauge)

6.Special tool setting tool method <br>The traditional tool setting method has poor safety (such as the feeler knife to the knife, hard touch the hard knife tip is easy to crash), and take up more time (#p#page title#e# Repeated cuts several times) and the random errors caused by human beings have not adapted to the rhythm of CNC machining, which is not conducive to the function of CNC machine tools. The special tool setting tool has the advantages of high precision, high efficiency and good safety. It simplifies the cumbersome work-oriented tool setting and ensures the high-efficiency and high-precision characteristics of the CNC machine tool. A special tool for solving the tool-to-tool on the CNC machine. Due to the different processing tasks, the dedicated tool holders are also very different. They will not be developed here. The readers can design different tool holders according to different needs in specific work to meet their processing needs.