Basic concepts of the hottest NC programming

2022-10-18
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The basic concept of NC programming

1. tool location

tool location is a reference point on the tool on which the Federal Reserve has reduced the scope of bond purchase since January 2014. The path of the relative movement of the tool location is the processing route, also known as the programming path

2. tool setting and tool setting point

tool setting refers to that the operator makes the tool location coincide with the tool setting point through certain measurement means before starting the NC program. The tool setting instrument can be used for tool setting. Its operation is relatively simple and the measurement data is relatively accurate. After positioning the fixture and installing the parts on the NC machine tool, you can also use the measuring block, feeler gauge, dial indicator, etc., and use the coordinates on the NC machine tool to set the tool. For the operator, it is very important to determine the tool setting point. The characteristics of Jinan assay micro Vickers hardness tester will directly affect the machining accuracy of parts and the accuracy of program control. In the process of batch production, the repeated accuracy of tool setting points should be considered. It is necessary for operators to deepen their understanding of CNC equipment and master more tool setting skills

(1) selection principle of tool setting point

it is easy to align on the machine tool, easy to check in processing, easy to calculate when programming, and small tool setting error

the tool setting point can select a point on the part (such as the center of the positioning hole of the part) or a point outside the part (such as a point on the fixture or machine tool), but it must have a certain coordinate relationship with the positioning datum of the part

improve the accuracy and precision of tool setting. Even if the accuracy of parts is not high or the program requirements are not strict, the machining accuracy of the selected tool setting position should be higher than that of other positions

select the part with large contact surface, easy to monitor and stable processing process as the tool setting point

the tool setting point should be unified with the design basis or process basis as far as possible to avoid the reduction of tool setting accuracy or even machining accuracy due to size conversion, which increases the difficulty of NC program or part NC machining

in order to improve the machining accuracy of parts, the tool setting point should be selected on the design basis or process basis of parts as far as possible. For example, for parts positioned by holes, it is more appropriate to take the center of the hole as the tool setting point

the accuracy of tool setting points depends not only on the accuracy of numerical control equipment, but also on the requirements of part processing. Manually check the tool setting accuracy to improve the quality of part numerical control processing. Especially in batch production, the repeated accuracy of the tool setting point should be considered, which can be checked by the coordinate value of the tool setting point relative to the origin of the machine tool

(2) selection method of tool setting point

for CNC lathe or turning milling machining center type CNC equipment, since the central position (x0, Y0, A0) has been determined by CNC equipment, the whole machining coordinate system can be determined by determining the axial position. Therefore, only one end face of the axial direction (Z0 or relative position) needs to be determined as the tool setting point

for three-dimensional NC milling machine or three-dimensional machining center, it is much more complex than CNC lathe or turning milling machining center. According to the requirements of NC program, it is not only necessary to determine the origin position of coordinate system (x0, Y0, Z0), but also related to the determination of machining coordinate systems g54, G55, g56, G57, etc., sometimes depending on the habits of operators. The tool setting point can be set on the machined part or on the fixture, but it must have a certain coordinate relationship with the positioning datum of the part. The Z direction can be determined simply by determining a plane that is easy to detect, while the X and Y directions need to select the plane and circle related to the positioning datum according to the specific part

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for four axis or five axis CNC equipment, the fourth and fifth rotating axes are added, which is similar to the selection of tool setting points for three-axis CNC equipment. Because the equipment is more complex and the CNC system is intelligent, it provides more tool setting methods, which need to be determined according to the specific CNC equipment and specific processing parts

the coordinate relationship between the tool setting point and the machine coordinate system can be simply set to be interrelated. For example, the coordinates of the tool setting point are (x0, Y0, Z0), the relationship with the machining coordinate system can be defined as (x0+xr, y0+yr, z0+zr), and the machining coordinate systems g54, G55, g56, G57, etc. can be entered through the control panel or other methods. This method is very flexible and highly skilled, which brings great convenience for subsequent NC machining

3. Zero drift phenomenon

zero drift phenomenon is caused by the environmental factors around the NC equipment. Under the same cutting conditions, for the same equipment, using the same fixture, NC program, tool, and processing the same parts, it is a phenomenon of inconsistent dimensions or reduced accuracy of third-party professional service institutions

zero drift is mainly manifested in a phenomenon of precision reduction in NC machining or can be understood as the inconsistency of precision in NC machining. The phenomenon of zero drift is inevitable in the process of NC machining, and it is common for NC equipment. Generally, it is greatly affected by the environmental factors around NC equipment, and it will affect the normal work of NC equipment when it is serious. There are many reasons affecting zero drift, mainly including temperature, coolant, tool wear, large changes in spindle speed and feed speed, etc

4. tool compensation

after a certain period of NC machining, tool wear is inevitable, which is mainly manifested in the changes of tool length and tool radius. Therefore, tool wear compensation mainly refers to tool length compensation and tool radius compensation

5. tool radius compensation

in part contour processing, because the tool always has a certain radius, such as the radius of the milling cutter, the motion path of the tool center is not equal to the actual path of the part to be processed, but needs to offset a tool radius value, which is customarily called tool radius compensation. Therefore, the radius value of the tool must be considered when NC machining the part contour. It should be pointed out that the ug/cam NC program is programmed with the ideal machining state and accurate tool radius, and the tool motion path is the tool center motion path, without considering the influence of the state of the NC equipment and the wear degree of the tool on the NC machining of parts. Therefore, whether for contour programming or tool center programming, the implementation of ug/cam NC program must consider the impact of tool radius wear, and use tool radius compensation reasonably

6. tool length compensation

on CNC milling and boring machines, when the tool is worn or replaced, so that the tool tip position is not in the programming position of the original processing, its size must be compensated by extending or shortening an offset value in the tool length direction

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