Talking about the processing of common thread on C

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Talking about the processing of ordinary threads on CNC lathes

four standard threads, metric, inch, modulus and diameter control, can be turned on CNC lathes. No matter which thread is turned, the strict motion relationship between the lathe spindle and the tool must be maintained: that is, every rotation of the spindle (that is, the workpiece rotates), the tool should move a lead distance evenly. Through the analysis of ordinary threads, we can strengthen our understanding of ordinary threads in order to better process ordinary threads

I. dimensional analysis of ordinary threads

NC lathes need a series of dimensions for the processing of ordinary threads. The calculation and analysis of the dimensions required for ordinary thread processing mainly includes the following two aspects:

1. The diameter of the workpiece before thread processing

considering the expansion of the thread processing profile, the diameter of the workpiece before thread processing d/d - 0.1p, that is, the major diameter of the thread is reduced by 0.1 pitch, Generally, it is 0.1 to 0.5 smaller than the major diameter of the thread according to the small deformation capacity of the material

2. The feed amount of thread machining

the feed amount of thread can refer to the bottom diameter of thread, that is, the final feed position of thread cutter

the minor diameter of thread is: major diameter - twice the tooth height; Tooth height =0.54p (P is the pitch)

the feed amount of thread processing should be continuously reduced, and the specific feed amount should be selected according to the tool and working material

II. Tool loading and tool setting of ordinary thread cutters

if the turning tool is installed too high or too low, when the cutting tool reaches a certain depth, the rear face of the turning tool will support the workpiece, increase the friction, and even bend the workpiece, causing the phenomenon of tool gnawing; If it is too low, the chip is not easy to be discharged. The turning tool diameter Yaming indicates that the direction of the force is the center of the workpiece. In addition, the clearance between the transverse lead screw and the nut is too large, which leads to the deepening of the cutting depth, thus lifting the workpiece and biting the knife. At this time, the height of the turning tool should be adjusted in time to make its tip equal to the axis of the workpiece (the tool can be adjusted by using the center of the tailstock). During rough turning and semi fine turning, the position of the tool tip is about 1% d higher than the out center of the workpiece (d represents the diameter of the workpiece to be machined)

the workpiece is not clamped firmly, and the rigidity of the workpiece itself cannot bear the cutting force during turning, resulting in excessive deflection, which changes the center height of the turning tool and the workpiece (the workpiece is raised), resulting in a sudden increase in the cutting depth and knife gnawing. At this time, the workpiece should be clamped firmly, and the tailstock center can be used to increase the rigidity of the workpiece

the tool setting methods of ordinary thread include trial cutting tool setting and automatic tool setting by tool setting instrument. You can directly use the tool for trial cutting and tool setting, or you can use G50 to set the workpiece zero point and use workpiece shift to set the workpiece zero point for tool setting. There are several 10 lines in the large-scale plastic market. The requirements for tool setting are not very high, especially the z-direction tool setting is not strictly limited, which can be determined according to the programming processing requirements

III. programming processing of ordinary thread

in the current CNC lathe, there are generally three processing methods for thread cutting: G32 straight cutting method, G92 straight cutting method and G76 oblique cutting method. Due to different cutting methods, different programming methods lead to different processing errors. We should carefully analyze the operation and use, and strive to process parts with high precision

1. G32 straight cutting method, because both edges work at the same time, the cutting force is large, and it is difficult to arrange cutting, so the two cutting edges are easy to wear during cutting. When cutting threads with large pitch, due to the large cutting depth, the blade wears faster, resulting in the error of the pitch diameter of the thread; However, the tooth shape accuracy of its processing is high, so it is generally used for small pitch thread processing. Because its tool moving cutting is completed by programming, it is mainly used for processing: the tensile machine is used to stop stretching, tightening, bending, shearing, peeling and other mechanical properties of metal and non-metal materials, and the mechanical force application program used for the experiment is long; Since the blade is easy to wear, frequent measurement should be done during processing

2. G92 direct cutting method simplifies programming and improves efficiency compared with G32 instruction

3. G76 oblique cutting method, because it is processed with a single edge, the processing edge is easy to be damaged and worn, so that the processed thread surface is not straight, and the tool tip angle changes, resulting in poor tooth shape accuracy. However, because it works with a single edge, the tool load is small, chip removal is easy, and the cutting depth is decreasing. Therefore, this machining method is generally applicable to the machining of large pitch threads. Because this processing method is easy to remove chips and the working condition of the blade is good, this processing method is more convenient in the case of low thread accuracy requirements. When machining high-precision threads, it can be completed by two knives, i.e. rough turning with G76 machining method first, and then fine turning with G32 machining method. However, it should be noted that the starting point of the tool should be accurate, otherwise it is easy to buckle randomly, causing parts to be scrapped

4. After the thread processing is completed, the thread quality can be judged by observing the thread profile, and measures can be taken in time. When the thread crown is not sharp, increasing the cutting amount of the knife will increase the major diameter of the thread, and the increase depends on the plasticity of the material. When the crown has been sharpened, increasing the cutting amount of the knife will reduce the major diameter in proportion. According to this feature, the cutting amount of the thread should be treated correctly to prevent scrap

IV. detection of ordinary threads

for general standard threads, thread ring gauge or plug gauge is used to measure. When measuring the external thread, if the "through end" ring gauge of the thread is just screwed in, but the "stop end" ring gauge cannot be screwed in, it means that the processed thread meets the requirements, otherwise it is unqualified. When measuring internal thread, use thread plug gauge to measure in the same way. In addition to the measurement of thread ring gauge or plug gauge, other measuring tools can also be used to measure. Such a large increase is mainly due to the continuous decline of extruder imports since October last year. The pitch diameter of the thread is measured with a thread micrometer, the pitch diameter of the trapezoidal thread and the pitch diameter of the worm are measured with a tooth thickness vernier caliper, and the pitch diameter of the thread is measured with a measuring needle according to the three needle measurement method. (end)

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