1、 Tool setting
The tool position is the reference point on the tool. The relative motion path of the tool position is the machining path, also called the programming path.
2, tool pairing and tool pairing point
Tool setting is the index control operator to make the tool point coincide with the tool setting point by certain measurement means before starting the CNC program. The tool setting tool can be used for tool setting. The operation is relatively simple and the measurement data is relatively accurate. After positioning the fixture and mounting the part on the CNC machine, the machine is set up using a measuring block, plug gauge, micrometer, etc. and using the coordinates on the CNC machine. The determination of the tool point is very important to the operator, and it directly affects the machining accuracy of the part and the accuracy of the program control. In the process of mass production, attention should be paid to the repeatability of the tool point. Operators need to deepen their understanding of CNC equipment and acquire more tool setting skills.
(1) Principles of tool setting point selection
Easy to align on the machine, easy to check during machining, easy to calculate during programming, and small tool setting error. Tool setting point can choose a part of a point (such as the center part of the positioning hole), or a part other than a point (such as a point on the fixture or the machine tool), but there must be a certain coordination relationship between the parts of the positioning datum. In order to improve the accuracy of tool setting and alignment, the machining accuracy of the selected alignment position should be higher than the machining accuracy of other positions even if the accuracy of the part is not high or the program requirements are not strict.
Select the part with large contact surface, easy monitoring and stable machining process as the tool setting point. Tool setting point should be unified with the design or process benchmark as far as possible to avoid reducing tool setting accuracy or even machining accuracy due to size conversion and increasing the difficulty of CNC program or CNC machining of the part. In order to improve the machining accuracy of the part, should be as far as possible in the design basis or process basis of the part to choose the tooling point. For example, for parts with hole positioning, it is more appropriate to use the center of the hole as the tool setting point. The accuracy of the tool setting point of the tool setting instrument depends not only on the accuracy of the CNC equipment, but also on the requirements of the part processing. Especially in mass production, the repetition accuracy of the tool setting point needs to be considered, which can be checked by the coordinate value of the tool setting point relative to the machine origin.
(2) the tooling point selection method
For CNC lathe or milling machine machining center type CNC equipment, as the center position (X0, Y0, A0) is determined by the existing CNC equipment, determining the axial position can determine the entire machining coordinate system. Therefore, only the end face (Z0 or relative position) of the axial direction needs to be determined as the cutting point.
For three-coordinate machining center, three-coordinate CNC milling machine or relatively complex CNC turning machining center, according to the requirements of the CNC program, it is necessary to determine not only the coordinates of the origin position (X0, Y0, Z0), but also with the processing and the determination of coordinates G54, G55, G56, G57, etc. Sometimes it also depends on the habits of the operator.
Tooling point can be located on the part being machined, can also be positioned in the fixture, but must have a certain coordinate relationship with the positioning datum of the part, Z direction can simply determine the plane, easy to detect, while X, Y direction according to the positioning datum, the specific part of the circle to determine the need to choose.
For four-axis or five-axis CNC equipment, the fourth and fifth axis of rotation is added, similar to the three-coordinate CNC equipment tool position selection. Because the equipment is more complex and the CNC system is more intelligent, it provides more tool setting methods, which need to be determined according to the specific CNC equipment and specific machining parts.
The coordinate relationship between the tool point and the machine coordinate system can be simply set to inter-correlation. For example, the tool point coordinates are (X0, Y0, Z0), and the relationship with the machining coordinate system can be defined as (X0+Xr, Y0+Yr, Z0+Zr), and the machining coordinate system G54, G55, G56, G57, etc., as long as they are entered through the control panel or other means. The method is flexible, proficient, and brings great convenience for subsequent CNC machining. Once the machine collides due to the wrong programming parameters input, the impact on the machine accuracy is fatal. So for high precision CNC lathe, it is necessary to eliminate the collision accident.
(3) The main causes of collision
A. Incorrect input of tool diameter and length.
B. Incorrect input of workpiece dimensions and other related geometric dimensions, and incorrect initial positioning of the workpiece.
C, the machine workpiece coordinate system is not set correctly, or the machine tool zero point reset during processing, resulting in changes. Most machine collisions occur during the rapid movement of the machine tool.
So the operator should pay special attention to the machine tool in the initial stage of the implementation of the program and the machine tool in the replacement of tools, once the program editing errors, tool diameter and length input errors, it is easy to collision.
At the end of the program, the CNC axis retires the tool in the wrong order of action, may also occur collision. To avoid the above collisions, CNC operators in the operation of the machine tool, to give full play to the five senses, observe the machine tool without abnormal movement, no sparks, no noise and abnormal noise, no vibration, no burnt smell. If abnormal conditions are found, the program should be stopped immediately. After the machine problem is solved, the machine can continue to work.
