Common tool alignment methods for CNC milling machines;
The tool setting operation is divided into X, Y and Z directions. The accuracy of tool alignment will directly affect the machining accuracy. The tool setting method must adapt to the machining accuracy requirements of the parts.
According to the different tool alignment tools used, the commonly used tool alignment methods are divided into the following categories: (1) trial cutting tool alignment method; (2) Align the tools with a feeler gauge, a standard mandrel and a block gauge; (3) Tool alignment with tools such as edge finder, eccentric rod and Z-axis setter; (4) aligning the upper and lower tools; (5) dial indicator (or dial indicator) alignment method; (6) Alignment method of special tools.
In addition, according to the different tool setting positions and data calculation methods, it can be divided into unilateral tool setting, bilateral tool setting, transfer (indirect) tool setting method and "distracted zero" tool setting method (the machine tool is required to have the function of relative coordinates and zero clearing).
1. Try to cut the knife.
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 center position of the tool alignment point on the workpiece surface (which coincides with the origin of the workpiece coordinate system here) as an example (using the bilateral tool alignment method).
(1) Alignment of X and Y tools
◎ Install the workpiece on the workbench through the fixture. When clamping, the four edges of the workpiece should be reserved for tool alignment.
◎ Start the spindle to rotate at a medium speed, move the workbench and spindle quickly, make the cutter move to a position close to the left side of the workpiece at a certain safe distance, and then slow down and move to the left side of the workpiece.
◎ When approaching the workpiece, use fine adjustment operation (generally 0.0 1mm approach) to make the tool slowly approach the left side of the workpiece, so that the tool just touches the left surface of the workpiece (observe, listen to the cutting sound, see the kerf and see the chip, as long as one of the situations occurs, it means that the tool touches the workpiece), and then retreat by 0.01mm.. Write down the X coordinate values displayed in the machine coordinate system at this time, such as -240.500.
◎ Retract the tool in the positive direction of Z axis to the top of the workpiece surface, and approach the right side of the workpiece in the same way, and write down the X coordinate value displayed in the machine tool coordinate system at this time, such as -340.500.
◎ Based on this, it can be concluded that the origin of the workpiece coordinate system is {-240.500+(-340.500)}/2 =-290.500 in the machine tool coordinate system.
◎ In the same way, the Y coordinate value of the origin W of the workpiece coordinate system in the machine tool coordinate system can be measured.
(2) Tool setting in Z direction
◎ Move the tool quickly above the workpiece.
◎ Start the spindle to rotate at a medium speed, move the workbench and spindle quickly, so that the cutter can move to a position close to the upper surface of the workpiece at a certain safe distance, and then reduce the speed to make the end face of the cutter close to the upper surface of the workpiece.
◎ When approaching the workpiece, use fine adjustment operation (generally 0.0 1mm approach) to make the end face of the tool approach the surface of the workpiece slowly (note that when cutting the tool, especially the end mill, it is best to cut the tool at the edge of the workpiece, and the area where the end face of the tool contacts the surface of the workpiece is less than a semicircle, so as not to make the center hole of the end mill on the surface of the workpiece as far as possible), so that the end face of the tool just contacts the upper surface of the workpiece, and then raise the Z axis by 0.06543 , the z coordinate value of the origin w of the workpiece coordinate system in the machine tool coordinate system is-140.400.
(3) data storage
Input the measured values of X, Y and Z into the storage address G5* of the machine tool workpiece coordinate system (generally, the tool setting parameters are stored by G54~G59 codes).
(4) Start to take effect
Enter the panel input mode (MDI), input "G5*", press the start key (in "automatic" mode), and run G5* to make it effective.
(5) check
It is very important to check whether the knife is correct.
2. Use feeler gauge, standard mandrel and block gauge for tool alignment.
This method is similar to the trial cutting tool alignment method, except that the spindle does not rotate during tool alignment, and a feeler gauge (or standard mandrel or block gauge) is added between the tool and the workpiece, so that the feeler gauge cannot twitch freely. Pay attention to subtract the thickness of feeler gauge when calculating coordinates. Because the spindle does not need rotary cutting, this method will not leave traces on the surface of the workpiece, but the accuracy of tool setting is not high enough.
3. Use tools such as edge finder, eccentric rod and Z-axis setter to align the tools.
The operation steps are similar to the method of trial cutting and tool alignment, except that the tool is replaced by an edge finder or an eccentric rod.
This is the most commonly used method, which has high efficiency and can ensure the accuracy of tool alignment. When using the edge finder, attention must be paid to make the steel ball slightly contact with the workpiece, the workpiece to be processed must be a good conductor, and the positioning datum plane has good surface roughness. Z-axis setter is usually used to transfer (indirect) tool alignment.
Machining a workpiece usually requires more than one knife. The length of the second knife is different from that of the first knife and needs to be reset to zero. However, sometimes the zero point is removed, so the zero point cannot be found directly, or it is not allowed to destroy the machined surface. There are also some tools or occasions that are not good for direct knife. Indirect changes can be used at this time.
(1) is the first knife.
◎ For the Z of the first knife, the trial cutting method and the feeler gauge method should be used first. Write down the machine coordinate Z 1 of the origin of the workpiece at this time. After machining the first knife, stop the spindle.
◎ Place the tool setting device on the platform of the machine tool workbench (such as the large surface of a vice).
◎ In handwheel mode, move the workbench to a proper position by hand, move the spindle downward, press the bottom of the cutter to the top of the cutter, and the dial pointer rotates, preferably within one turn, write down the indicator A of the Z-axis setter at this time, and reset the relative coordinate Z-axis.
◎ Lift the spindle and remove the first knife.
(2) the second knife
◎ Mount the second knife.
◎ In handwheel mode, move the spindle downward, press the bottom of the knife to the top of the knife, and the dial pointer rotates and points to the same position as the first knife.
◎ Record the numerical value Z0 (signed) corresponding to the relative coordinates of Z axis at this time.
◎ Lift the spindle and remove the tool aligner.
◎ Add Z0 (signed) to the coordinate data of Z 1 in the original first cutter G5* to get a new Z coordinate.
◎ This new Z coordinate is the actual machine coordinate corresponding to the workpiece origin of the second tool we are looking for. Input the G5* working coordinates of the second knife, thus setting the zero point of the second knife. The other knives are aligned in the same way as the second knife.
Note: If several knives use the same G5*, the procedure should be changed to store Z0 in the length parameter of No.2 knife, and the length of the second knife should be adjusted to the correct G43H02.
4. Tip-to-tip knife method
(1) Alignment of X and Y tools
◎ Install the workpiece on the workbench of the machine tool through the fixture and replace it with the center.
◎ Move the workbench and spindle quickly, so that the tool tip moves to the top of the workpiece, find the center point of the drawing line of the workpiece, and slow down the moving speed to make the tool tip close.
◎ Use fine-tuning operation to make the tool tip slowly approach the center point of the workpiece drawing line until the tool tip of the tool tip is aligned with the center point of the workpiece drawing line, and write down the X and Y coordinate values in the machine tool coordinate system at this time.
(2) Tool setting in Z direction
Remove the top, install the milling cutter, and get the Z-axis coordinate values by other tool alignment methods, such as trial cutting method and feeler gauge method.
5. Alignment method of dial indicator (or dial indicator)
This method is usually used for tool alignment of circular workpieces.
(1) Alignment of X and Y tools
As shown in Figure 2, install the dial indicator mounting rod on the handle, or suck the magnetic seat of the dial indicator on the spindle sleeve, move the workbench to move the spindle center line (that is, the tool center) to the center of the workpiece, adjust the length and angle of the telescopic rod on the magnetic seat to make the contact of the dial indicator contact with the circumferential surface of the workpiece, (the pointer rotates about 0. 1mm) and slowly rotate the spindle by hand to make the contact of the dial indicator rotate along the circumferential surface of the workpiece. Observe the movement of the dial indicator pointer, and slowly move the X axis and Y axis of the workbench. After repeated several times, the pointer of the dial indicator is basically in the same position when the spindle rotates (the jumping amount of the pointer is within the allowable tool setting error range, such as 0.02mm). At this time, it can be considered that the center of the spindle is the origin of the X axis and the Y axis.
(2) Tool setting in Z direction
Remove the dial indicator, install the milling cutter, and use other tool alignment methods, such as trial cutting method and feeler gauge method, to get the Z-axis coordinate values.
6. Special tool alignment method
The traditional tool setting method has the disadvantages of poor safety (for example, the tip of the tool is easily damaged when using a feeler gauge to set the tool) and taking up a lot of machine time.