About the processing of threads processed by CNC lathes

Speaking of CNC lathes, it can turn four standard threads, such as metric, inch, module, and diameter control. No matter what kind of thread is turned, the lathe spindle and the CNC insert must be strictly The kinematic relationship: that is, every time the spindle rotates (that is, the workpiece rotates), the CNC blade should move evenly by one (workpiece) lead pitch. The following is based on the analysis of various types of threads, to strengthen the mastery of various types of threads in order to better process various types of threads.

About the specification analysis of ordinary threads

CNC lathes also need various specifications for ordinary threads. The measurement and analysis of ordinary thread processing specifications mainly include: The following two aspects:

1. The diameter of the steel member before threading

According to the shrinkage rate of the threading profile, the diameter of the workpiece before threading D/D-0.1 P, also It is the major diameter of the thread minus 0.1 pitch, which is usually determined according to the deformation of the material, and is 0.1 to 0.5 smaller than the major diameter of the thread; Reference thread diameter, that is, the last cutting part of the thread cutter.

The diameter is: major diameter-2 times the tooth height; tooth heightu003d0.54 P (P is the thread pitch)

The amount of cutting tool used for thread cutting should be continuously reduced, and the actual cutting tool The dosage is selected according to the CNC blade material.

About the tool selection and tool setting of ordinary thread CNC inserts

If the tool is installed too high or too low or too high, when the feeding tool reaches a certain thickness, The flank surface of the milling cutter is in contact with the steel, which increases the sliding friction, and even bends the workpiece, resulting in a gnawing condition; when the cutting tool is fed, the cutting amount is difficult to discharge, and the direction of the axial force of the feeding tool is the center of the workpiece. In addition, the angle between the lead screw and the nut is too large, which causes the thickness of the eating knife to automatically continue to thicken, which in turn makes the eating knife thicker, showing the knife. At this time, the height-to-width ratio of the turning tool should be adjusted immediately, so that the cutting edge is equidistant from the center line of the workpiece (the tool can be set with the help of the tip of the tailstock). During drilling and semi-finishing, the position of the knife edge is 1% higher than the workpiece exit center position D up and D down (D represents the hole diameter of the workpiece to be processed).

The rigidity of the unstable workpiece itself cannot withstand the cutting force during cutting, resulting in excessive deflection, which changes the center height between the turning tool and the workpiece (the workpiece is lifted), resulting in sudden cutting thickness. If it increases, the phenomenon of gnawing occurs. At this time, the workpiece should be clamped firmly, and the tip of the tailstock can be used to improve the rigidity of the workpiece.

There are two kinds of tool setting methods for ordinary threads: trial tool method and automatic tool setting device. You can directly use the CNC blade for trial cutting, or you can use G50 to set the workpiece zero point, and use the workpiece movement to set the workpiece zero point for alignment. Knife. The tool setting standard for helical machining is not high, especially the Z-direction tool setting standard is not strict enough, and it can be processed according to the program processing standard.

About ordinary thread program processing

At present, in CNC lathe processing, there are generally three processing methods for thread processing: G32 straight processing, G92 Straight machining, G76 inclined machining, due to the difference of turning and programming, the machining error is also different. We must carefully analyze the application in production, and strive to process high-precision parts.

G32 straight-forward turning method, due to the synergy of the double-sided cutting edge, the high cutting speed and the difficulty in cutting, so the double-sided cutting edge is easily damaged during turning. When turning large-pitch threads, due to the large turning depth, the cutting edge is quickly damaged, resulting in a deviation of the pitch diameter of the thread; however, the precision of the toothed parts processed is relatively high, so small-pitch threading is generally used. Since its blade movement is completed by programming, the processing program is relatively long; considering that the blade is easy to wear, it is necessary to ensure frequent measurement during processing.

The G92 straight-forward turning mode is optimized for programming, and the lifting speed is faster than the G32 console command.

G76 inclined cutting method, considering the cutting side edge, the machined side edge is easy to be damaged or damaged, the machined thread surface is not straight, and the tool nose angle changes larger, resulting in poor tooth shape accuracy. However, due to unilateral cutting, the load of CNC inserts is small, chip removal is easy, and the turning thickness shows a decreasing trend. In this way, this machining method is generally suitable for machining large pitch threads. Because this processing method is easy to remove chips and has better cutting edge processing conditions, it is more convenient when the thread precision is not specified. For the machining of high-precision threads, double-tool machining can be used, which can be machined with G76 first, and can be finished with G32 machining method. But remember that the starting point of the cutting knife should be accurate, otherwise it is easy to buckle and cause the parts to be scrapped.

After the thread processing is successful, you can also carefully observe the thread profile to determine whether the thread has quality improvement measures. It will increase the major diameter of the thread. The amount of increase depends on the ductility of the material. When the thread head is sharp, the cutting amount of the knife will be reduced instead. According to this feature, the cutting amount of the thread should be correctly regarded to avoid scrap.

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