With the rapid development of science and technology and social production, mechanical products are becoming more and more complex, and society has put forward higher and higher requirements for the quality and productivity of mechanical products. In aerospace, shipbuilding, military and computer industries, parts have high precision, complex shapes, and small batch sizes, which require CNC machine tools. CNC machine tools have strong adaptability to parts changes, and only need to change the corresponding program to replace parts. To give full play to the role of CNC machine tools, not only must there be good tools, but more importantly, programming, that is, according to the characteristics of different parts, a reasonable and efficient processing program is prepared.
As far as the application is concerned, although the processing flexibility of the CNC lathe is superior to that of the ordinary lathe, it has been proved that there is a certain gap between the production efficiency of a certain type of parts and the ordinary lathe. Therefore, improving the efficiency of CNC lathes becomes the key, and the rational use of programming skills and the preparation of high-efficiency machining programs can have unexpected effects on improving machine efficiency. Through several years of programming practice and teaching, the author has explored some programming skills. The specific exploration is as follows: 1 Reasonable selection of various cycle cutting instructions In the GSK980TD CNC system, there are more than ten kinds of cutting cycle machining instructions for CNC lathes. Each type of command has its own processing characteristics, and the machining accuracy after machining is different. The respective programming methods are also different. We should carefully analyze and select them when selecting, and strive to process high-precision parts.
There are two machining instructions for thread cutting cycle machining: G92 straight cutting and G76 diagonal cutting. Due to the different cutting methods of the cutting tool (), the respective programming methods are different, and the machining accuracy of the thread segments after machining is also different. The G92 thread cutting cycle uses a straight feed method for thread cutting. The thread diameter error is large. However, the accuracy of the tooth shape is high, and it is generally used for the processing of high-precision thread with small pitch. The machining program is long and needs to be measured frequently during machining. The G76 thread cutting cycle adopts the oblique feed method for thread cutting, and the tooth shape accuracy is poor, but the processability is reasonable and the programming efficiency is high. This machining method is generally suitable for machining large pitch and low precision threads. This processing method is simpler and more convenient when the thread precision is not high. Therefore, we must master the respective processing characteristics and scope of application, and select these cutting cycle instructions according to the machining characteristics of the workpiece and the precision required by the workpiece. For machining high-precision, large-pitch threads, G92 and G76 can be used in combination, that is, the G76 is used for roughing and then G92 is used for finishing. It should be noted that the starting point for rough finishing should be the same to prevent the occurrence of thread buckles.
2Flexible use of the call subroutine function to put the command field related to the part geometry in a subroutine, and put the command field about the machine control and the command field of the cut part in the main program, each time a part is machined, the main The program calls the subroutine once by calling the subroutine command. After the machining is completed, it jumps back to the main program. It is necessary to process several parts and call several sub-programs, which is very beneficial to increase or decrease the number of parts processed per cycle. The processing program prepared in this way is also relatively simple and clear, and is easy to modify and maintain. It is worth noting that since the parameters of the subroutine remain unchanged in each call, and the coordinate moment of the spindle changes, in order to adapt to the main program, relative programming statements must be used in the subroutine.
3 Flexibly use the MO command MO as the program pause command. In order to control the accuracy of the workpiece during the rough finishing of the part, the MO command can be added after the roughing is finished to pause the program, and the size is verified by measurement. If there is an error in the size, it can be modified by the tool compensation to ensure the accuracy of the part.
4 Correct selection of program origin When CNC turning programming, first select a point on the workpiece as the program origin, and use this as the origin to establish a workpiece coordinate system. Reasonable determination of the workpiece coordinate system is important for NC programming and workpiece alignment during machining. The selection of the program origin should be as simple as possible, such as simple programming, small size conversion, and small processing error. In order to improve the machining accuracy of parts and facilitate calculation and programming, we usually set the program origin to the intersection of the workpiece axis and the right end face, the left end face and the front end face of the workpiece. Try to make the programming reference coincide with the design and assembly basis.
5 flexible use of special G code to ensure the processing quality and accuracy of the parts 5.1 delay G04 command, the so-called delay G04 command, its role is to artificially limit the running of the machining program, in addition to the common general use, in the actual CNC machining In the middle, the delay C04 command can also be used for some special purposes.
5.1.1 When there is a large change in the spindle speed, the C04 command can be set. The purpose is to stabilize the spindle speed and then machine the part to improve the surface quality of the part.
5.1.2 In the processing of parts with short processing time of large batches, the start button is frequently used. In order to reduce the operator's malfunction due to fatigue or frequent buttons, the G04 command is used instead of the start of the first part. The delay time is set according to the loading and unloading time of one part. After the operator skillfully masters the NC machining program, the delay command time can be gradually shortened, but it must be guaranteed a certain safety time. The part machining program is designed as a cyclic subroutine. The G04 command is designed in the main program that calls the cyclic subroutine. If necessary, the design selection plan stops the M01 command as the end or check of the program.
5.1.3 When tapping the center thread with a tap, it is necessary to use the elastic collet to tap the teeth to ensure that the tap will not break when it taps to the bottom of the thread, and set the G04 delay command at the bottom of the thread to make the tap for non-feed cutting. The time of delay should ensure that the spindle stops completely. After the spindle stops completely, it will reverse according to the original forward rotation speed, and the tap will retreat according to the original lead.
5.2 Relative coordinates U, W and absolute coordinates X, Z code. The relative programming mentioned here is based on the position of the tool tip as the coordinate origin, and the tool tip is programmed to be displaced relative to the coordinate origin. That is to say, the relative programmed coordinate origin is often transformed, and the operation is to control the displacement based on the current tool tip point. Then, when the continuous displacement is performed, a cumulative error is inevitably generated. Absolute programming has a relatively uniform reference point, that is, the origin of coordinates, in the whole process of machining, so its cumulative error is smaller than relative programming. In CNC turning, the accuracy of the radial dimension of the workpiece is higher than the axial dimension. Therefore, when programming, the radial dimension is preferably absolutely programmed. Considering the convenience of machining, the axial dimension is relatively programmed, but for important Axial dimensions are also available in absolute programming. In addition, in order to ensure some relative position of the parts, according to the requirements of the process, flexible use of relative programming and absolute programming.
The CNC machine tool integrates modern precision machinery, computer, communication, hydraulic, pneumatic, optoelectronic and other multidisciplinary technologies, effectively solving complex, precise and small batches of variable parts processing problems, and can meet high quality, high efficiency and variety. The requirements of small batches of flexible production methods are adapted to the needs of rapid replacement of various mechanical products. CNC lathes are characterized by high efficiency, high precision and high flexibility, and are increasingly used in machinery manufacturing.
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