The tool length compensation function is an important function of the CNC machine tool and is indicated by G43, G44, and G49 in the preparation function. However, if it is not used well, it can easily cause crashes and scrap incidents. The following takes the machining center as an example to introduce several tool length compensation methods commonly used in production practice.
1 Tool length compensation function execution process
The typical instruction format is G43 Z_H_; or G44 Z_H_. The G43 command plus compensation value, also called forward compensation, is the Z coordinate movement value actually executed by the CNC after adding the programmed Z value to the preset value in the offset register specified by the H code. Correspondingly, the G44 command minus the preset compensation value is also called negative compensation.
When G43 is instructed, the actually executed Z coordinate value is Z'=Z_+(H_);
When G44 is instructed, the actual executed Z coordinate value is Z'=Z_-(H_);
This operation is not affected by the status of the G90 absolute command or the G91 incremental command. The positive value or negative value can be preset in the offset register, so the following is equivalent.
1) The positive value of the instruction G43, H is equivalent to the effect of setting the negative value of the instruction G44, H;
2) The negative value of the instruction G43, H is equivalent to the effect of setting the positive value of the command G44, H.
Therefore, under normal circumstances, in order to avoid mistakes in the input or use of instructions, according to the operator's habits in two ways:
1) Use only G43, H to set a positive or negative value:
2) H sets only a positive value, using the command G43 or G44.
The following describes the use of the first case.
The Z value in the instruction format can be 0, but H0 or H00 will cancel the tool length compensation, which is equivalent to the G49 effect, because the zero value 0 register is always set to 0 by the NC.
Under normal circumstances, to avoid errors, tool length compensation is only valid for the Z axis by setting parameters. For example, when the current instruction is G43X_H_;, the movement of the X axis is not compensated.
The compensated offset value is specified by the code following H. For example, if H1 is set to 20., H2 is set to -30., when command "G43 Z100.H1;", Z axis will move to 120.: When command "G43 Z100. H2;", Z axis will be moved to 70. Department.
When G43 (G44) and G00 and G01 appear in one block, NC will execute G43 (G44) first.
G43 (G44) can be specified in the canned cycle block. Only one H code can be commanded at this time. The tool length compensation is valid for both the Z value and the R value.
When the machine tool returns to the reference point, the tool length compensation must be canceled unless commands such as G27, G28, and G30 are used. For safety, the tool length compensation should be canceled at the end of a tooling process or at the end of a block.
Modern CNC machine tools have basically eliminated tapes, and can use chip storage programs and tool length compensation values, which can be modified at any time. However, setting and modifying compensation amounts can avoid or reduce the changes in processing programs, and thus avoid and reduce possible mistakes and changes. It is also significant that accidents do not occur. Some CNC machine tools in the factory because of improper parameter settings, resulting in storage protection switch can only be prohibited to modify the processing program, this situation is very dangerous.
2 Simplify programming with tool length compensation
The principle of NC tool length compensation can be used to simplify programming. In the preparation of machining programs, the influence of different tool lengths on the programmed values ​​is ignored, and it is possible to program only with a virtual tool of a hypothetical length. This virtual length can also be zero to simplify unnecessary calculations in programming before formal processing. Then, the difference between the actual tool length and the standard tool length is set as the tool length compensation value to the H code address used.
When trial-cutting, select a Z0 plane in the plane family on the part or fixture perpendicular to the Z axis (parallel to the X, Y axis). This plane is the Z coordinate 0 point programmed after the tool length compensation. A plane or step on a part that usually reaches the paper size is the Z0 plane, also called the reference plane of the tool. If it is a cutting blank, this plane must be established by a trial cut with a milling cutter. As shown in the figure below, the drill T1, the boring cutter T2, and the milling cutter T3 are the positions of the Z axis at the machine tool part, and the standard cutter is the position where the front end points to the Z0 plane.
1) The organic external tool setting tool generally uses the random check rod supplied as the tool setting tool as the standard tool, and it is loaded into the spindle. The axis is returned to the machine zero point, and then the front end of the standard tool (generally steel) is manually made. Ball) Arrival to the Z0 plane can be confirmed with a feeler gauge.
a. Subtract the standard tool length (positive value) from the Z axis value (negative value) of the machine tool coordinate system at this time. Note that the absolute value is added when the negative value is added. Set this value (negative value) as the workpiece coordinate. The Z value of the system. Next, measure the length of all machining tools on the tool setting tool, that is, the distance from the spindle end surface to the tool nose, and then use these values ​​(positive values) as the tool length compensation value for each tool.
b. Set the Z axis value (negative value) of the machine coordinate system directly to the Z value of the workpiece coordinate system. Then, the difference between the lengths of all the machining tools and the standard tool is measured on the tool setting tool, which is recorded as a positive value longer than the standard tool, a negative value shorter than the standard tool, and then used as the tool for each tool. Length compensation value.
2) Users who do not have a tool setting tool without an external tool setting tool generally use the aforementioned commands G43 and H to set a negative value. The machining tool is loaded into the spindle, the Z axis is returned to the machine zero point, and then the front end of the tool is manually brought to the Z0 plane. The Z-axis value (negative value) of the machine coordinate system at this time is directly used as the tool length compensation value for each tool. At the same time, the Z value of the workpiece coordinate system is always set to zero. This kind of tool setting process, for most CNC systems, can display the current Z coordinate value under the tool offset page, and can directly input this value to the compensation address. It should be noted that the displayed Z coordinate value is generally a relative value, and must be switched to the machine coordinate system. Otherwise, it is very easy to cause accidents.
Some operators use a tool block to confirm that the front end of the tool reaches the Z0 plane, so when the compensation value is input or the Z value of the workpiece coordinate system is converted, the thickness of the tool block is converted, and it is also easy to make mistakes by adding or subtracting. Caused an accident.
3) The tool setting point for different tools is based on the experience. In order to make the program easy to adjust, tools such as drills, milling cutters, and boring tools are set with the tool tip. However, chamfering tools such as countersinks, chamfering boring cutters, and chamfering end mills use the chamfered holes to contact the cutting edge as a tool setting point, which simplifies the conversion of the chamfering angle and the Z-axis feed length.
1 Tool length compensation function execution process
The typical instruction format is G43 Z_H_; or G44 Z_H_. The G43 command plus compensation value, also called forward compensation, is the Z coordinate movement value actually executed by the CNC after adding the programmed Z value to the preset value in the offset register specified by the H code. Correspondingly, the G44 command minus the preset compensation value is also called negative compensation.
When G43 is instructed, the actually executed Z coordinate value is Z'=Z_+(H_);
When G44 is instructed, the actual executed Z coordinate value is Z'=Z_-(H_);
This operation is not affected by the status of the G90 absolute command or the G91 incremental command. The positive value or negative value can be preset in the offset register, so the following is equivalent.
1) The positive value of the instruction G43, H is equivalent to the effect of setting the negative value of the instruction G44, H;
2) The negative value of the instruction G43, H is equivalent to the effect of setting the positive value of the command G44, H.
Therefore, under normal circumstances, in order to avoid mistakes in the input or use of instructions, according to the operator's habits in two ways:
1) Use only G43, H to set a positive or negative value:
2) H sets only a positive value, using the command G43 or G44.
The following describes the use of the first case.
The Z value in the instruction format can be 0, but H0 or H00 will cancel the tool length compensation, which is equivalent to the G49 effect, because the zero value 0 register is always set to 0 by the NC.
Under normal circumstances, to avoid errors, tool length compensation is only valid for the Z axis by setting parameters. For example, when the current instruction is G43X_H_;, the movement of the X axis is not compensated.
The compensated offset value is specified by the code following H. For example, if H1 is set to 20., H2 is set to -30., when command "G43 Z100.H1;", Z axis will move to 120.: When command "G43 Z100. H2;", Z axis will be moved to 70. Department.
When G43 (G44) and G00 and G01 appear in one block, NC will execute G43 (G44) first.
G43 (G44) can be specified in the canned cycle block. Only one H code can be commanded at this time. The tool length compensation is valid for both the Z value and the R value.
When the machine tool returns to the reference point, the tool length compensation must be canceled unless commands such as G27, G28, and G30 are used. For safety, the tool length compensation should be canceled at the end of a tooling process or at the end of a block.
Modern CNC machine tools have basically eliminated tapes, and can use chip storage programs and tool length compensation values, which can be modified at any time. However, setting and modifying compensation amounts can avoid or reduce the changes in processing programs, and thus avoid and reduce possible mistakes and changes. It is also significant that accidents do not occur. Some CNC machine tools in the factory because of improper parameter settings, resulting in storage protection switch can only be prohibited to modify the processing program, this situation is very dangerous.
2 Simplify programming with tool length compensation
The principle of NC tool length compensation can be used to simplify programming. In the preparation of machining programs, the influence of different tool lengths on the programmed values ​​is ignored, and it is possible to program only with a virtual tool of a hypothetical length. This virtual length can also be zero to simplify unnecessary calculations in programming before formal processing. Then, the difference between the actual tool length and the standard tool length is set as the tool length compensation value to the H code address used.
When trial-cutting, select a Z0 plane in the plane family on the part or fixture perpendicular to the Z axis (parallel to the X, Y axis). This plane is the Z coordinate 0 point programmed after the tool length compensation. A plane or step on a part that usually reaches the paper size is the Z0 plane, also called the reference plane of the tool. If it is a cutting blank, this plane must be established by a trial cut with a milling cutter. As shown in the figure below, the drill T1, the boring cutter T2, and the milling cutter T3 are the positions of the Z axis at the machine tool part, and the standard cutter is the position where the front end points to the Z0 plane.
1. Drill T1 2. Boring T2 3. Milling cutter T3 4. Standard tool 5. Workpiece setting tool reference plane
1) The organic external tool setting tool generally uses the random check rod supplied as the tool setting tool as the standard tool, and it is loaded into the spindle. The axis is returned to the machine zero point, and then the front end of the standard tool (generally steel) is manually made. Ball) Arrival to the Z0 plane can be confirmed with a feeler gauge.
a. Subtract the standard tool length (positive value) from the Z axis value (negative value) of the machine tool coordinate system at this time. Note that the absolute value is added when the negative value is added. Set this value (negative value) as the workpiece coordinate. The Z value of the system. Next, measure the length of all machining tools on the tool setting tool, that is, the distance from the spindle end surface to the tool nose, and then use these values ​​(positive values) as the tool length compensation value for each tool.
b. Set the Z axis value (negative value) of the machine coordinate system directly to the Z value of the workpiece coordinate system. Then, the difference between the lengths of all the machining tools and the standard tool is measured on the tool setting tool, which is recorded as a positive value longer than the standard tool, a negative value shorter than the standard tool, and then used as the tool for each tool. Length compensation value.
2) Users who do not have a tool setting tool without an external tool setting tool generally use the aforementioned commands G43 and H to set a negative value. The machining tool is loaded into the spindle, the Z axis is returned to the machine zero point, and then the front end of the tool is manually brought to the Z0 plane. The Z-axis value (negative value) of the machine coordinate system at this time is directly used as the tool length compensation value for each tool. At the same time, the Z value of the workpiece coordinate system is always set to zero. This kind of tool setting process, for most CNC systems, can display the current Z coordinate value under the tool offset page, and can directly input this value to the compensation address. It should be noted that the displayed Z coordinate value is generally a relative value, and must be switched to the machine coordinate system. Otherwise, it is very easy to cause accidents.
Some operators use a tool block to confirm that the front end of the tool reaches the Z0 plane, so when the compensation value is input or the Z value of the workpiece coordinate system is converted, the thickness of the tool block is converted, and it is also easy to make mistakes by adding or subtracting. Caused an accident.
3) The tool setting point for different tools is based on the experience. In order to make the program easy to adjust, tools such as drills, milling cutters, and boring tools are set with the tool tip. However, chamfering tools such as countersinks, chamfering boring cutters, and chamfering end mills use the chamfered holes to contact the cutting edge as a tool setting point, which simplifies the conversion of the chamfering angle and the Z-axis feed length.
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