There are 3 kinds of compensation in CNC machining:
☆ compensation for tool length;
☆ tool radius compensation;
☆ Fixture compensation.
These three kinds of compensation can basically solve the trajectory problem caused by the shape of the tool during machining. The following are three applications of compensation in general machining programming.
First, the tool length compensation
1. The concept of tool length
Tool length is an important concept. When we are programming a part, we must first specify the programming center of the part, and then we can establish the workpiece programming coordinate system. This coordinate system is just a workpiece coordinate system, and the zero point is generally on the workpiece. The length compensation is only related to the Z coordinate. It is not like the programmed zero point in the X and Y planes. Because the tool is positioned by the spindle cone, it does not change. The zero point for the Z coordinate is different. The length of each knife is different. For example, we need to drill a hole with a depth of 50mm and then tap the depth of 45mm, using a 250mm long drill bit and a 350mm long tap. First drill a depth of 50mm with a drill bit. At this time, the machine has set the workpiece zero point. When the tap is tapped, if both knives are machined from the set zero point, the tap is too long to be tapped longer than the drill bit, and the tool is damaged. And artifacts. At this time, if the tool compensation is set, the length of the tap and the drill bit will be compensated. After the machine zero point is set, even if the tap and the bit length are different, due to the existence of compensation, the zero point Z coordinate has been automatically turned to Z+ when the tap is operated. (or Z) compensates for the length of the tap, ensuring the correct machining zero.
2. Working use of tool length compensation
Tool length compensation is achieved by executing the G43 (G44) and H commands, and we give a Z coordinate value so that the tool moves to a point Z away from the workpiece surface after compensation. Another command G49 cancels the G43 (G44) command. In fact, we don't have to use this command because each tool has its own length compensation. When the tool is changed, it uses the G43 (G44) H command to give its own tool length compensation. The length compensation of the previous tool is automatically canceled.
3. Two ways of tool length compensation
(1) Use the actual length of the tool as the compensation for the tool length (this method is recommended). Using the tool length as compensation is to measure the length of the tool using the tool setting tool, and then input this value into the tool length compensation register as the tool length compensation. The reasons for using the tool length as the tool length compensation are as follows:
First, using the tool length as the tool length compensation can avoid continually modifying the tool length offset during different workpiece machining. Such a tool is used on different workpieces without modifying the tool length offset. In this case, each tool can be filed according to a certain tool numbering rule, and a small sign is used to write the relevant parameters of each tool, including the length and radius of the tool. In fact, many large machines Processing companies use this approach for tool management of CNC machining equipment. For those companies that specialize in tool management, it is not necessary to tell the tool face-to-face with the parameters of the tool, and even if the tool is removed due to the capacity of the magazine, the next time it is reinstalled, The value of the tool length on the label is used as the tool length compensation without further measurement.
Secondly, using the tool length as the tool length compensation allows the machine to perform the machining operation while performing the length measurement of other tools on the tool setting tool, instead of occupying the machine running time due to the tool setting on the machine tool, so that the machining can be fully utilized. The efficiency of the center. When the spindle moves to the programmed Z coordinate point, it is the spindle coordinate plus (or minus) the Z coordinate value after the tool length compensation.
(2) Use the distance between the tool tip in the Z direction and the programmed zero point (with positive and negative points) as the compensation value. This method is suitable for use when the machine is operated by only one person and there is not enough time to measure the length of the tool with the tool setter. In doing so, when machining another workpiece with a knife, the tool length compensation setting must be re-executed. When using this method for tool length compensation, the compensation value is the tool nose movement distance when the spindle moves from the Z coordinate zero point of the machine to the workpiece programming zero point. Therefore, this compensation value is always negative and large.
Second, the tool radius compensation
1. The concept of tool radius compensation
Just as the tool length compensation is used, basically no need to consider the length of the tool during programming. Because of the tool radius compensation, we can not consider too many tool diameters when programming. Tool length compensation is available for all tools, while tool radius compensation is generally only used for milling tools. When the milling cutter processes the outer or inner contour of the workpiece, the tool radius compensation is used. When the end face of the workpiece is machined with the end mill, only the tool length compensation is required. Because tool radius compensation is an instruction that is difficult to understand and use, many people in programming are reluctant to use it. But once we understand and master it, it will bring great convenience to our programming and processing. When the programmer is ready to program a shape that uses a milling cutter to machine the shape of a workpiece, it is first necessary to carefully calculate the coordinate values based on the external dimensions of the workpiece and the radius of the tool to clarify the route taken by the tool center. The tool radius used at this time is only the radius value of the milling cutter. When the program is painstakingly compiled, it is found that the milling cutter is not suitable for changing the tool of other diameters, and the programmer has to recalculate the tool center without any difficulty. The coordinate value of the route taken. This is not a big problem for a simple workpiece, and recalculation is too difficult for a complex mold. The shape of a workpiece is divided into roughing and finishing, so that the roughing is completed after the roughing program is programmed. Because the rough shape of the workpiece has changed, and then the coordinate value of the finished tool center is calculated, the workload is even larger. At this point, if the tool radius compensation is used, these troubles are solved. We can ignore the tool radius and program according to the workpiece size, then place the tool radius as radius compensation in the radius compensation register. Temporary replacement of the milling cutter or rough finishing is also possible. We only need to change the tool radius compensation value to control the size of the workpiece. It is basically not used for the program.
2. Use of tool radius compensation
The use of tool radius compensation is performed by commands G41, G42. The compensation has two directions, that is, the left and right sides in the vertical direction of the cutting feed direction of the tool are compensated, which conforms to the left and right hand rules; G41 is the left compensation, which conforms to the left hand rule; G42 is the right compensation, which conforms to the right hand rule, as shown in Fig. 3. Shown. Figure 3 Left and right hand rules for tool radius compensation When using G41, G42 for radius compensation, special attention should be paid to making the effective tool movement direction and coordinates. The tool radius compensation is important. If the path is not correct, the path is easy to make mistakes, as shown in Figure 4. Figure 4 Tool radius compensation of the starting position If the G42 compensation is valid for the tool from position 1 to 2, the milling cutter will cut out an A-B bevel as shown in Figure 4. The correct pass should be to make the radius compensation valid before the tool has cut the workpiece, and then perform normal cutting. As shown in Fig. 4, the compensation is validated first by moving the milling cutter from position 1 to position 3, and then cutting from position 3 to position 2 continues the following cutting, and the A-B bevel does not occur. Therefore, when using G41, G42 for radius compensation, the following steps should be taken: ☆ set the tool radius compensation value; ☆ let the tool move to make the compensation effective (the workpiece can not be cut at this time); ☆ correctly cancel the radius compensation (this time can not Cutting the workpiece). Remember to use G40 to disable the compensation when the cutting is complete and the tool compensation is over. The use of the G40 also encounters the same problem of making the compensation effective. It is necessary to wait for the tool to be completely cut and safely push out the workpiece before executing the G40 command to cancel the compensation.
Third, fixture offset compensation
Just like tool length compensation and radius compensation, the programmer can ignore the length and size of the tool. The fixture offset allows the programmer to use the fixture offset regardless of the position of the workpiece fixture. When a machining center is processing a small workpiece, the tool can hold several workpieces at a time. The programmer does not need to consider the coordinate zero point of each workpiece during programming, but only needs to program according to the respective programming zero point, and then use the fixture. Offset to move the programmed zero point of the machine on each workpiece. The fixture offset is performed using the clamp bias commands G54 to G59. Another way is to set the coordinate system using the G92 command. When a workpiece is machined, use G92 to re-set the new workpiece coordinate system when machining the next workpiece. The above are three kinds of compensation commonly used in CNC machining, which brings great convenience to our programming and processing, and can greatly improve work efficiency.
