Three compensation methods commonly used in CNC machining
Three compensation methods commonly used in CNC machining
There are three types of compensation in NC machining: these three types of compensation can basically solve the trajectory problem caused by the shape of the tool during processing. The following is the application of three kinds of compensation in general machining programming.
I. Tool length compensation:
1. The concept of tool length Tool length is an important concept. When we program 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 only 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 taper hole without changing. 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 a depth of 45mm, using a drill with a length of 250mm and a tap with a length of 350mm. First use a drill to drill a depth of 50mm. At this time, the machine tool has set the workpiece zero point. When replacing the tap with a tap, if both tools start processing from the set zero point, the tap will be too long because the tap is longer than the drill, which will damage the tool. And artifacts. At this time, if tool compensation is set, the length of the tap and drill bit is compensated. At this time, after the zero point of the machine tool is set, even if the length of the tap and the drill bit are different, due to the existence of compensation, the Z coordinate of the zero point has automatically moved to Z + (Or Z) compensates the length of the tap to ensure the correct machining zero point.
2. The work of tool length compensation The tool length compensation is implemented by executing the instructions containing G43 (G44) and H. At the same time, we give a Z coordinate value so that the tool moves to the place where the distance from the workpiece surface is Z after compensation. . The other command G49 cancels the G43 (G44) command. In fact, we don't need to use this command, because each tool has its own length compensation. When the tool is changed, the G43 (G44) H command is used to give its own tool length compensation. The length compensation of the previous tool is automatically cancelled.
3.Two ways of tool length compensation
1) Use the actual length of the tool as the tool length compensation (this method is recommended). To use the tool length as compensation is to use the tool setter to measure the length of the tool, and then enter this value into the tool length compensation register as the tool length compensation. The reasons for using tool length as tool length compensation are as follows:
First of all, using the tool length as the tool length compensation can avoid constantly modifying the tool length offset in different workpiece processing. Such a tool can be used on different workpieces without modifying the tool length offset. In this case, you can make a file for each tool according to a certain tool numbering rule, and use a small label to write the relevant parameters of each tool, including the length and radius of the tool. In fact, many large machinery Processing enterprises adopt this approach to the tool management of CNC machining equipment. For those companies that have a tool management department, they do n’t need to tell the tool parameters face to face with the operator. At the same time, even if the tool is removed due to the capacity of the tool magazine and the next time it is reinstalled, only The tool length value on the label is used as the tool length compensation without further measurement.
Second, using the tool length as the tool length compensation allows the machine tool to measure the length of other tools on the tool setting tool while it is running, without having to occupy the machine's operating time because of tool setting on the tool, which can make full use of the processing. Center efficiency. In this way, when the spindle moves to the programmed Z coordinate point, it is the Z coordinate value after the spindle coordinate plus (or subtracting) the tool length compensation.
2) Use the distance between the tool tip and the programmed zero in the Z direction (there is a difference between positive and negative) as the compensation value. This method is applicable when the machine tool is operated by only one person and there is not enough time to measure the length of the tool with the tool setter. In this way, when machining another workpiece with one tool, the tool length compensation setting must be performed again. When using this method for tool length compensation, the compensation value is the tool tip movement distance when the spindle moves from the machine tool Z coordinate zero point to the workpiece programming zero point. Therefore, this compensation value is always negative and large.
2. Tool radius compensation:
1. The concept of tool radius compensation is just like the use of tool length compensation, which basically does not need to consider the tool length when programming, because with tool radius compensation, we can not consider too much the diameter of the tool when programming. Tool length compensation is applicable to all tools, while tool radius compensation is generally only used for milling tools. When the milling cutter is processing the outer or inner contour of the workpiece, the tool radius compensation is used. When the end milling cutter is used to process the end surface of the workpiece, only the tool length compensation is needed. Because tool radius compensation is an instruction that is difficult to understand and use, many people are reluctant to use it in programming. But once we understand and master it, it will bring great convenience to our programming and processing.
When the programmer is going to compile a program for machining the shape of a workpiece with a milling cutter, first of all, a detailed calculation of the coordinate values according to the workpiece's overall dimensions and the radius of the tool is required to clarify the path taken by the tool center. The radius of the tool used at this time is only the radius of this milling cutter. After working hard to write the program, it was found that this milling cutter is not suitable for switching to a tool of another diameter, and the programmer must take the pains to recalculate the tool center. The coordinate value of the route taken. This is not too big for a simple workpiece, and recalculation is too difficult for a mold with a complicated shape.
The machining of the shape of a workpiece is divided into rough machining and finishing machining. After the rough machining program is compiled, the rough machining is completed. After rough machining, the external dimensions of the workpiece have changed, and then the coordinate value of the tool center for finishing machining must be calculated, and the workload is even greater. At this time, if tool radius compensation is used, these troubles are all solved. We can ignore the tool radius and program according to the workpiece size, and then put the tool radius as the radius compensation in the radius compensation register. It is also possible to temporarily change the milling cutter or to perform rough and fine machining. We only need to change the compensation value of the tool radius to control the size of the workpiece. The program is basically not used for a little modification.
2. Use of tool radius compensation The use of tool radius compensation is performed by commands G41 and G42. The compensation has two directions, that is, left and right along the vertical direction of the cutting direction of the tool. Compensation is in accordance with the left-hand rule; G41 is a left-compensation that conforms to the left-hand rule; G42 is a right-compensation that complies with the right-hand rule. 3 Right and left hand rules for tool radius compensation When using G41, G42 for radius compensation, special attention should be paid to the tool movement direction and coordinates that make the compensation effective. The starting position of the tool radius compensation is very important, and the path processed by the incorrect tool is prone to error.
3. Fixture offset compensation:
Just like tool length compensation and radius compensation, the programmer can ignore the length and size of the tool, and 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 small workpieces, the tooling can clamp 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. Fixture offset is performed using fixture offset instructions G54 to G59. Another method is to use the G92 command to set the coordinate system. After one workpiece is processed, G92 is used to reset the new workpiece coordinate system when processing the next workpiece. The above are three types of compensation commonly used in CNC machining, which bring great convenience to our programming and machining, and can greatly improve work efficiency.
E-mail:alice..........com
WhatsApp:86-155-6681-6110
