When programming, the positions of "tool setting point" and "tool changing point" should be correctly selected. The "tool setting point" is the starting point of the tool's movement relative to the workpiece when processing parts on a CNC machine tool. Since the program segment is executed from this point, the tool setting point is also called the "program starting point" or "tool starting point".
The principles for choosing a knife tip are:
1. It is convenient to use digital processing and simplify programming;
2. Easy to center on the machine tool and easy to inspect during processing;
3. The resulting processing error is small.
The tool setting point can be selected on the workpiece or outside the workpiece (such as on the fixture or machine tool), but it must have a certain dimensional relationship with the positioning datum of the part. In order to improve the machining accuracy, the tool setting point should be selected based on the design basis or process reference of the part. If the workpiece has a hole for positioning, the center of the hole can be selected as the tool setting point. The position of the tool is aligned with this hole, so that the "tool position point" coincides with the "tool setting point". The commonly used calibration method in the factory is to install the dial indicator on the machine tool spindle, and then rotate the machine tool spindle to make the "tool setting point" consistent with the tool setting point. The better the consistency, the higher the accuracy of tool setting. The so-called "tool positioning point" refers to the tool tips of turning tools and boring tools; drill bits; end mills and the bottom center of the end mill head and the ball head center of the ball end mill.
After the parts are installed, the workpiece coordinate system and the machine tool coordinate system have a certain dimensional relationship. After the workpiece coordinate system is set, the coordinate value of the first block starting from the tool setting point; the coordinate value of the tool setting point in the machine tool coordinate system is (X0, Y0). When using absolute value programming, regardless of whether the tool setting point coincides with the workpiece origin, they are X2 and Y2; when using incremental value programming, when the tool setting point coincides with the workpiece origin, the coordinate values of the first block are , when they do not coincide, it is (X1+X2), Y1+Y2). The tool setting point is both the starting point and the end point of the program. Therefore, the repeatability of the tool setting points should be considered during mass production. The accuracy can be checked by the coordinate values (X0, Y0) of the tool setting point from the machine origin.
The so-called "machine tool origin" refers to a fixed limit point on the machine tool. For example, for a lathe, it refers to the intersection point of the lathe spindle rotation center and the end face of the head chuck. When tool change is required during machining, the tool change point should be designated. The so-called "tool change point" is the position of the hundred tool holder when changing tools and indexing. This point can be a fixed point (such as a machining center machine tool, the position of the tool change manipulator is fixed), or it can be an arbitrary point (such as a lathe). The tool change point should be located outside the workpiece or fixture, and the tool holder should not contact the workpiece and other parts when indexing. The set value can be determined by actual measurement or calculation.
