Qingxi jinkedi talks about the programming of NC lathe machining program

In NC turning, the program runs through the machining process of the whole part. Because everyone's processing methods are different, the preparation of processing programs are also different, but the ultimate goal is to improve the production efficiency of NC lathe. Therefore, it is particularly important to select the most reasonable processing route. This paper will analyze the programming method in NC turning from the details of determining the tool path and selecting the appropriate g command.

1、 Analyze part drawings

Analysis of part drawing is the primary work in process preparation, which directly affects the preparation and processing results of parts. It mainly includes the following contents:

Analyze the geometric conditions of machining contour: the main purpose is to deal with unclear dimensions and closed dimension chains in the drawing.

Analyze the dimensional tolerance requirements on the part drawing to determine the machining process to control its dimensional accuracy, such as the selection of cutting tools and the determination of cutting parameters.

Analysis of shape and position tolerance requirements: in NC machining, the shape and position errors of parts are mainly affected by the accuracy of mechanical kinematic pairs of machine tools. In turning, if the direction of movement along the Z coordinate axis is uneven with its spindle axis, the shape tolerance requirement of cylindricity cannot be guaranteed; If the direction of movement along the X coordinate axis is not perpendicular to its main axis, the position tolerance requirement of perpendicularity cannot be guaranteed. Therefore, relevant schemes for technical processing should be considered before programming.
Analyze the surface roughness requirements of parts, material and heat treatment requirements, blank requirements and number of pieces, which are also parameters that can not be ignored for the determination of process arrangement and cutting route.

2、 Reasonably determine the cutting route and make it the shortest

Determining the tool path is the focus of machining programming. Because the tool path of finishing cutting program is basically carried out along the contour of its parts, the main content is to determine the tool path of rough machining and empty stroke. The tool path generally refers to the path that the tool moves from the tool setting point until it returns to the point and ends the machining program. Including the path of cutting and non cutting empty stroke such as tool introduction and cutting out. The shortest tool path can not only save the execution time of the whole machining process, but also reduce some unnecessary tool consumption and the wear of sliding parts of machine tool feed mechanism. The following figure 1 shows three turning cone methods, which are processed with rectangular cycle command to analyze and reasonably determine the cutting route. Fig. 1A shows the parallel turning cone method. This method is that after each feed, the turning tool moving track is parallel to the cone bus. With each feed, the z-phase size increases in a certain proportion, which is the same as the common turning cone processing method, making it easy for beginners to understand. The calculation method of Z dimension is obtained according to the formula C = D-D / L. If C is 1:10, it means that 1mm is removed from diameter x and 10mm is added to length Z. According to this ratio, it can be programmed simply, and the allowance of each turning can be guaranteed to be the same to make the cutting uniform. Fig. 1b shows the turning cone method of changing the cone angle. With each X-direction feed, keep the z-direction dimension as the drawing size. Each knife changes the cone angle, and only the last knife is the cone angle required by the drawing. This turning cone method does not need to calculate the Z dimension every time, but in machining, because the Z dimension is the same, the machining route is long, and the cutting allowance is uneven, which affects the surface dimension and roughness of the workpiece. It is generally suitable for cones with short cone surface and small allowance. Fig. 1C shows the step table processing cone method. This processing method is that each tool path is parallel to the axis of the workpiece to process many small step tables, and the last turning tool moves along the conical inclined plane. This processing method should first make a 1:1 scale diagram, otherwise it is easy to turn the waste workpiece. Because it is a step shape, the allowance is uneven, which affects the processing quality of the conical surface.

Obviously, among the above three cutting routes, if the starting point is the same, the parallel method turning cone route is the most reasonable, and this method is commonly used in production.

3、 Reasonably call g command to minimize program segments

According to each individual geometric element (i.e. straight line, oblique line, arc, etc.), the corresponding machining program is compiled, which constitutes each program of the machining program, i.e. program segment. In the preparation of machining program, it is always hoped that the machining of parts can be realized with the minimum number of program segments, so as to make the program concise, reduce the probability of error and improve the efficiency of programming.

Because NC lathe devices generally have the function of linear and circular interpolation, in addition to non-circular curve, the number of program segments can be obtained from the geometric elements of parts and each program determined by the process route. At this time, the principle of minimizing program segments should be considered. Selecting a reasonable g command can reduce the program segments, but also take into account the shortest tool path. For example, when machining the parts in Figure 1 above, if the blanks are all bar materials, you can use the linear interpolation command G01 for programming, the rectangular cycle command G90 for programming, and the compound cycle command G71 for programming, and you can process the workpiece. As shown in Figure 2 below, figure 2A shows the tool path determined by G01 command, which is the same as that determined by G90 command in Figure 2B, but when using G01, the programming is complex and there are many program segments, which are commonly used in finishing programs. Figure 2C shows the G71 machining route. Firstly, take the rectangular circular feed route, and finally take the isometric line and final contour line of the contour of the last two knives. The cutting route is not very long, the cutting amount is the same, and the cutting force is uniform. When used with G70 command, it can also make the programming simple and often used in programming. If the NC lathe used does not have this command, G90 torque line cycle command should be selected for programming first. Therefore, it should be applied flexibly in programming, and a reasonable g command should be selected for programming.