The work of 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 sequence of parts, the main content is to determine the tool path of rough machining and empty stroke. 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. It includes the path of cutting and the non cutting empty stroke such as tool introduction and cutting out.
The shortest tool path can save the execution time of the whole machining process, and also reduce some unnecessary tool consumption and the wear of the sliding parts of the feed mechanism of the machine tool. The following figure 1 shows three taper turning methods, which are processed with rectangular circular command to analyze the reasonable determination of tool path. This method is that after each feed, the moving path of the turning tool is parallel to the generatrix of the cone. With each feed, the z-phase size increases in a certain proportion, which is the same as the common turning method, so that beginners can understand it easily. The calculation method of Z-direction dimension is based on the formula C = D-D / L. If C is 1:10, it means that 1 mm is removed from diameter x and 10 mm is added to length Z. According to this ratio, it is easy to program, and can ensure the same turning allowance every time, so that the cutting is uniform. The taper angle turning method is to keep the z-direction dimension as the drawing dimension with each X-direction feed. The taper angle of each cut is changed, and only the last cut is the taper angle required by the drawing. This taper turning method does not need to calculate the Z dimension every time, but because of the same Z dimension in machining, the machining path is longer, and the cutting allowance is not uniform, which affects the surface size and roughness of the workpiece. It is generally suitable for the taper with short taper and small allowance. Step table processing cone method, this processing method is that each time the tool path is parallel to the axis of the workpiece, many small steps are processed, and the last turning tool moves along the bevel of the cone. This processing method needs to make a 1:1 scale diagram first, otherwise it is easy to turn the waste workpiece, because it is a step shape, so the allowance is not uniform, which affects the processing quality of the cone.
Obviously, in the above three cutting routes, if the starting point is the same, the parallel turning cone route is the most reasonable, which is commonly used in production. The analysis of part drawing is the primary work in the process preparation, which directly affects the preparation and processing results of parts. It mainly includes the following contents:
Analysis of the geometric conditions of machining profile: the main purpose is to deal with the unclear dimension and closed dimension chain on the drawing.
Analyze the dimensional tolerance requirements on the part drawing to determine the processing technology to control the dimensional accuracy, such as the selection of cutting tools and the determination of cutting parameters.
Analysis of shape and position tolerance requirements: for CNC machining, the shape and position errors of parts are mainly affected by the accuracy of machine tool mechanical motion pairs. In turning, if the direction of movement along the z-axis is not perpendicular to the axis of its main axis, the shape tolerance requirement of cylindricity cannot be guaranteed; if the direction of movement along the x-axis is not perpendicular to the axis of its main axis, the position tolerance requirement of perpendicularity cannot be guaranteed. Therefore, before programming, we should consider the relevant scheme of technical processing.
Analysis of the surface roughness requirements of parts, material and heat treatment requirements, blank requirements, the number of pieces requirements is also the process arrangement and the determination of the tool path are parameters that can not be ignored. In NC turning, the program runs through the whole process of parts. Because each person’s processing method is different, the programming is also different, but the ultimate goal is to improve the production efficiency of CNC lathe, so it is particularly important to choose 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. According to each individual geometric element (i.e. straight line, oblique line, arc, etc.), the corresponding processing program is worked out, which constitutes each program of the processing program, i.e. program segment. In the process of programming, we always hope to process the parts with the least number of program segments, so as to make the program concise, reduce the probability of error and improve the efficiency of programming.