When the imaginary tool tip is numerically programmed, it is assumed that the turning tool has a sharp point, and the tool nose radius R is 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1.0 mm, and the like. In the case of the tool setting, the center of the arc of the tool tip is not easily aligned directly with the tool position or the reference position, and it is easy to align the position if the imaginary tool tip is used. Theory and practice show that there is no error when the surface of the outer circle, inner hole, etc. parallel to the z-axis is programmed by the imaginary tool tip, but less cutting or overcutting occurs when turning the right end face, taper and arc. The phenomenon that the actual path of the tool is inconsistent with the contour of the workpiece to be cut, resulting in machining errors. CNC machining accuracy is affected by many factors of the machining system consisting of machine tools, fixtures, tools and workpieces, and they are the main source of machining errors. Therefore, CNC machining requires that the tolerances assigned to the programming in the tolerances of the parts only account for a small part. Should be controlled within 10% 20% of the tolerance requirements of the parts, otherwise it will seriously affect the pass rate of CNC machining.
The error reason analysis is as shown in the figure. When programming with the imaginary tool tip as the reference, the numerical control system issues commands according to the imaginary tool nose position and controls the tool movement trajectory, and the objective existence of the tool arc radius makes the imaginary tool tip in the actual knife. Does not exist physically.
From the geometrical analysis, there is a certain difference in size and shape between the imaginary tool tip and the actual tool edge arc. The cutting point does not coincide with the imaginary tool tip point, so the cutting edge of the tool cannot cut off the imaginary tool tip and the actual The material between the cutting edges produces less cutting; or too much material is cut between the imaginary cutting edge and the cutting point on the cutting edge to cause overcutting, resulting in dimensional error, shape error and surface roughness.
In order to ensure and improve the machining accuracy of the parts, we should try to make the cutting path of the tool consistent with the contour of the workpiece. There are two ways to do this: 1 change the program to make the tool cutting path consistent with the part contour; 2 use the tool nose radius compensation command to reduce the offset between the actual machining path and the programmed path without changing the program. By changing the program to achieve the same path between the cutting path and the contour of the part, the program is complicated, which is not conducive to simplifying the program, resulting in an increase in programming workload. The use of the tool nose arc compensation command makes it easier to achieve compensation without changing the program. The purpose of the error.
The principle of the less-cut and over-cut 3 tool nose arc radius compensation command caused by the tool nose radius R and the function of the common tool nose radius compensation command G40: Cancel the tool nose radius compensation, that is, according to the program The path is fed and the error is no longer compensated. G41: Tool left compensation means that when the tool moves along the tool path to the feed direction, the tool is on the left side of the workpiece to compensate for the error caused by the radius of the tool nose. G42: Tool right compensation means that when the tool moves along the tool movement path to the feed direction, the tool is on the right side of the workpiece to compensate for the error caused by the radius of the tool nose arc.
Application of the tool nose radius compensation command (1) G41 or G42 command <3> must be used together with the G00 and G01 commands, and when the contour is cut, the compensation is canceled with the command G40, so that the tool returns to the initial position, avoiding the next In a round of machining, compensation at a new position will result in machining errors.
(2) When there is taper or arc on the workpiece, the radius compensation must be established in the previous block of the precision car taper or arc. Generally, the radius compensation is established in the block when cutting the workpiece.
(3) The tool nose radius value of the tool must be filled in the tool nose radius of the tool compensation parameter setting page, as shown in the RADIUS item. At this time, the CNC device of the machine tool will automatically calculate the compensation amount that should be moved. As the basis for the tool nose radius compensation.
When the tool compensation command used in the tool compensation parameter setting page is converted, that is, when G41 is changed to G42 (or G42 is replaced by G41), it is better to cancel the tool compensation command through G40 in the middle. In summary, only from the relationship between the programming principle of CNC machining and the radius of the tool nose arc, the reason why the programming imaginary tool tip and the actual cutting point of the blade do not coincide with each other is discussed, and the principle and method of reducing such error in the numerical control system are clarified.
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