Typical examples of NC lathe machining programming

With the development and popularization of NC machine tools, the demand of modern enterprises for technical talents who understand NC machining technology and can program NC machining will continue to increase. CNC lathe is one of the most widely used CNC machine tools. This paper discusses the programming of NC lathe parts.

CNC machine tool is a kind of Mechatronics processing equipment with high technology intensity and high degree of automation. It is the product of comprehensive application of high and new technologies such as computer, automatic control, automatic detection and precision machinery. With the development and popularization of NC machine tools, the demand of modern enterprises for technical talents who understand NC machining technology and can program NC machining will continue to increase. CNC lathe is one of the most widely used CNC machine tools. This paper discusses the programming of NC lathe parts.

1、 Programming method

There are two NC programming methods: manual programming and automatic programming. Manual programming refers to the manual programming process from part drawing analysis, process processing, data calculation, programming sheet writing, program input to program verification. It is suitable for point machining or machining of parts with less complex geometric shape, as well as occasions with simple calculation, few program segments, easy programming and so on. However, for the parts with complex geometric shape (especially the parts composed of spatial surfaces), as well as the parts with uncomplicated geometric elements but a large amount of programming, due to the tedious calculation of values during programming, heavy workload, easy to make mistakes, difficult program verification and difficult to complete by manual programming, automatic programming should be adopted. The so-called automatic programming means that most or all of the programming work is completed by computer, which can effectively solve the machining problems of complex parts. It is also the development trend of NC programming in the future. At the same time, we should also see that manual programming is the basis of automatic programming. Many core experiences in automatic programming come from manual programming, and the two complement each other.

2、 Programming steps

After getting a part drawing, first analyze the part drawing to determine the processing process, that is, determine the processing method of the part (such as the adopted fixture, clamping and positioning method, etc.), processing route (such as feed route, tool setting point, tool change point, etc.) and process parameters (such as feed speed, spindle speed, cutting speed, cutting depth, etc.). Secondly, numerical calculation shall be carried out. Most CNC systems have cutter compensation function. Only the coordinate values of the intersection (or tangent) of adjacent geometric elements of the contour need to be calculated to obtain the coordinate values of the starting point, end point and circle center of each geometric element. Finally, according to the calculated tool path coordinate value, the determined machining parameters and auxiliary actions, combined with the coordinate command code and program segment format specified by the NC system, the part machining program sheet is compiled segment by segment and input into the memory of the CNC device.

3、 Typical case analysis

CNC lathe is mainly used to process rotary parts. The typical machining surface is only outer cylinder, outer cone, thread, arc surface, grooving, etc. For example, to process parts with the shape shown in the figure, manual programming method is more appropriate. Because the programming instruction codes of different NC systems are different, they should be programmed according to the type of equipment. Take Siemens 802S CNC system as an example, the following operations shall be carried out.

(1) Determine processing route

The processing route is determined according to the principle of primary processing before secondary processing and fine processing before rough processing. The fixed cycle command is used for rough processing of the external contour, then fine processing, then turning back the tool slot, and finally processing the thread.

(2) Clamping method and selection of tool setting point

The three jaw self centering chuck is used for self centering clamping, and the tool setting point is selected at the intersection of the right end face of the workpiece and the rotation axis.

(3) Select tool

According to the processing requirements, four tools are selected, No. 1 is the rough machining cylindrical turning tool, No. 2 is the finish machining cylindrical turning tool, No. 3 is the grooving tool and No. 4 is the thread turning tool. Use the trial cutting method to set the knife, and process the end face at the same time.

(4) Determine cutting parameters

For turning the outer circle, the speed of the rough turning spindle is 500r / min, the feed speed is 0.3mm/r, the speed of the fine turning spindle is 800r / min, the feed speed is 0.08mm/r, and the speed of the spindle is 300r / min and the feed speed is 0.1mm/r during grooving and thread turning.