Principles for selecting tool setting points
The tool setting point is the starting position of the machining program. When selecting the tool setting point in CNC machining, the following principles must be followed: first, it is convenient to use digital processing and simplify programming; Secondly, it is convenient to align on the machine tool, and it should also be convenient to check in the processing process; Finally, it is also required that the machining error caused should be as small as possible.
In addition, it needs to be understood that the tool setting point can be selected on the workpiece or outside the workpiece, such as fixture or machine tool. However, the determination of "tool setting point" must have a certain dimensional relationship with the positioning datum of the part.
In general, in order to improve the machining accuracy of parts, CNC machining usually selects the tool setting point on the design basis or process basis of parts as far as possible. For example, for workpiece positioned by holes, the center of holes can be selected as the tool setting point. Then, use this hole to align the position of the tool, so that the tool setting point coincides with the tool location, that is, the tool tip of the turning tool and boring tool, the drill tip of the drill bit, the center of the bottom surface of the head of the end mill and end mill, and the center of the ball head of the ball end mill. The commonly used alignment method in processing plants is to install the dial indicator on the spindle of the machine tool, and then rotate the spindle to make the tool location consistent with the tool setting point. The higher the consistency, the higher the accuracy of tool setting.
Annotation method of coordinate value
When the parts are installed, the workpiece coordinate system and the CNC machine coordinate system have a definite dimensional relationship. In the workpiece coordinate system, the coordinate value of the first program segment from the tool setting point is the coordinate value (x0, Y0) of the tool setting point in the machine coordinate system. If it is programmed according to the absolute value, the coordinate values are (X2, Y2) regardless of whether the tool setting point coincides with the workpiece origin; If it is programmed according to the incremental value, when the tool setting point coincides with the workpiece origin, the coordinate value of the first program segment is (X2, Y2), and when it does not coincide, it is (x1 + X2, y1+y2).
Because the tool setting point is both the starting point and the end point of the CNC machining program, we must pay attention to the repeated accuracy of the tool setting point in the batch processing of parts. Whether the accuracy is reliable can be checked by checking the coordinate values (x0, Y0) between the tool point and the origin of the machine tool.
Principle of selecting tool change point
When it is necessary to change the tool during processing, the correct tool change point should be specified to make the tool holder complete the transposition and tool change at the appropriate position. The tool change point can be a fixed point. Take the machining center machine tool as an example, the position of its tool change manipulator is fixed. Sometimes, the change point can also be any point, such as an ordinary lathe. As for the specific position, the tool change point should be set outside the workpiece or fixture to ensure that the tool holder will not touch the workpiece and other parts during rotation. Its set value can be determined by actual measurement method or calculation.