CNC Machining Tips for Beginners

1. Analyze the part pattern and determine the processing process
Analyze the material, shape, size, precision, blank shape and heat treatment requirements of the parts, determine the correct processing method, positioning and clamping, processing sequence, tools used and cutting amount, etc., that is, formulate the processing technology. This link is an important link of CNC programming. Its main purpose is to determine the process route of CNC machining, the amount of cutting and the positioning and clamping of the workpiece. The first is the division of CNC machining processes, such as machining end faces, turning outer circles, grooving, cutting, etc.; secondly, the selection of tools, which should be reasonably selected; and then the arrangement of the process sequence, which requires that in the process of determining the process, the The processing route is short, the feed and tool change times are small, and the functions of the CNC machine tool are fully utilized to make the processing safe, reliable and efficient.
The tool path refers to the movement trajectory and direction of the tool position relative to the workpiece during the machining process. It not only includes the content of the work steps, but also reflects the order of the work steps. When arranging the finishing process that can be carried out with one or more cuts, the final contour of the parts should be continuously processed by the last cut. At this time, the advance and retreat position of the processing tool should be considered properly. Try not to arrange cutting in and out or tool change and pause in the continuous contour, so as to avoid elastic deformation caused by sudden changes in cutting force, resulting in smooth connection contours. Defects such as scratches, sudden changes in shape, or retained knife marks.

2. Numerical calculation
According to the size requirements of the part, the processing route and the set coordinate system, the calculation of the coordinate value of the motion track is carried out. For simple parts composed of arcs and straight lines, it is only required to calculate the coordinates of the intersection or tangent point of each geometric element on the contour of the part to obtain the coordinates of the starting point, end point, and arc center of each geometric element. If the CNC system has no tool compensation function, it should also calculate the movement path of the tool position point. For complex parts composed of non-circular curves, since CNC machine tools usually only have the function of linear and plane circular arc interpolation, they can only be processed by the method of approximation of branch line segments or arc segments. The coordinate value of the intersection point (that is, the node) of the processing curve.
For simple planar motion trajectories, the calculation of the coordinate values of each geometric element is often done manually. For the trajectory is very complex, or three-dimensional, the calculation of coordinate values is often done by means of a computer. For CNC machined parts, in order to facilitate programming and coordinate between dimensions, it is best to quote the dimensions from a reference, and the relevant coordinate dimensions are directly given, and the coordinate values can be directly seen from the diagram by using the absolute programming method. If not, it's best to switch over.

3. Write the program list
According to the calculated motion track coordinates and the determined processing sequence, tool number, cutting parameters and auxiliary actions, etc., according to the specified instruction code and program format, the processing program sheet is written block by block. When writing a program, care should be taken to make the program simple, convenient and intuitive. When we establish the workpiece coordinate system, the CNC lathe generally sets the origin of the program on the right end surface of the workpiece. The CNC machining program is composed of a series of program segments, and the program segments are composed of instruction words.
Before programming, you must first understand the basic format of the program segment, the format, function and use of common instructions. In fact, there are not many basic processing instructions, such as G00, G01, G02, G03, etc.; Mark the coordinates of the points on the route, so that it is not easy to travel when programming; then write the program list. The general steps of program writing are summarized as follows: program number---program content---program end.

4.The division of processing procedures
(1). Tool concentration and sequencing method is to divide the process according to the tools used, and use the same tool to process all the parts that can be completed on the part. In other parts that they can finish with the second knife and the third. In this way, the number of tool changes can be reduced, the idle time can be compressed, and unnecessary positioning errors can be reduced.
(2). Sorting method by processing parts For parts with a lot of processing content, the processing part can be divided into several parts according to its structural characteristics, such as inner shape, outer shape, curved surface or plane. Generally, the plane and positioning surface are processed first, and then the holes are processed; the simple geometric shapes are processed first, and then the complex geometric shapes are processed; the parts with lower precision are processed first, and then the parts with higher precision requirements are processed.
(3). Sequential method for rough and finish machining For parts that are prone to machining deformation, shape correction is required due to the possible deformation after rough machining. Therefore, generally speaking, the processes for rough and finish machining must be separated. To sum up, when dividing the process, it must be flexibly controlled according to the structure and manufacturability of the parts, the function of the machine tool, the amount of CNC machining content of the parts, the number of installations and the production organization status of the unit. In addition, it is recommended to adopt the principle of process concentration or the principle of process dispersion, which should be determined according to the actual situation, but must strive to be reasonable.