In the process of NC process analysis, first of all, the process analysis of the part drawing should be carried out to analyze whether the structural process of each part of the part conforms to the characteristics of NC machining
1. The dimension marking of part drawing should conform to the convenience of programming
In the NC machining drawing, it is better to use the same datum to quote the dimension or give the coordinate size directly. This marking method is not only convenient for programming, but also convenient for coordinating the setting and calculation of design datum, process datum, testing datum and programming zero point.
2. The geometric element conditions of the contour structure of parts should be sufficient
In programming, all geometric elements that constitute the contour of the part should be defined. When analyzing the part drawing, it is necessary to analyze whether the conditions of various geometric elements are sufficient. If not, it is impossible to program or model the parts to be processed.
3. Can machining accuracy and dimensional tolerance required by parts be guaranteed
Although the machining accuracy of CNC machine tools is very high, for some special cases, such as the processing of thin-walled parts, due to the poor rigidity of thin-walled parts, the cutting force generated during machining and the elastic yielding of thin-walled parts are easy to produce vibration of the cutting surface, which makes the dimensional tolerance of thin-walled thickness difficult to guarantee, and its surface roughness also increases When its thickness is less than 3 mm, we should pay attention to this problem in technology.
4. Are the geometric types and dimensions of the internal and external contour of the part unified
In NC programming, if the geometric types of the inner contour and outer contour of the part are the same or similar, consider whether it can be programmed in the same program to reduce the tool specification and tool change times as far as possible, so as to reduce the auxiliary time and improve the machining efficiency. It should be noted that the diameter of the tool is often limited by the radius r of the inner contour arc.
5. Can larger diameter tools be used in the process structure design of parts
Using larger diameter milling cutter to process can reduce the number of tool passes and improve the tool rigid system. Not only the machining efficiency is improved, but also the processing quality of the surface and bottom surface of the workpiece is also improved.
6. The fillet radius of the groove bottom or the fillet radius r at the intersection of the base plate and the edge plate should not be too large
Because the large diameter of the cutter contacting with the milling plane D = d-2r, where D is the diameter of the milling cutter. When D is constant, the larger the fillet radius R (as shown in Fig. (1), the worse the ability of milling cutter end edge to mill plane, the lower the efficiency and the worse the manufacturability.. When R reaches a certain degree, it must be processed with ball end milling cutter, which should be avoided. When D is larger and R is smaller, the area of milling surface is larger, the ability of machining plane is stronger, and the milling technology is better. Sometimes, when the bottom surface area of milling is large and the bottom arc R is also large, two milling cutters with different R can be used to cut twice.
7. Principle of ensuring the unification of standards
If the parts are re installed on the other side after milling one side, due to the non-uniform datum, it is often difficult to connect the cutter due to the re installation of the parts, and the contour position and size on the positive and negative sides are not coordinated after machining. Therefore, it is necessary to make full use of the appropriate hole of the part itself or the reference edge of the part contour or specially set the process hole (such as adding process boss on the blank or setting the reference hole on the allowance to be removed in the subsequent process) as the positioning reference, so as to ensure the accuracy of the relative position after two clamping processes.
8. Consider the deformation of parts
When the parts are deformed in the process of NC milling, not only the machining quality of the parts is affected, but also the phenomenon of skipping cutter sometimes occurs. At this time, we should consider the milling process, separate the rough and finish machining as far as possible, or use the symmetrical method to remove the allowance. Of course, heat treatment can also be used to solve the problem.
About the author