In the CNC lathe can be switched metric, inch system, modulus and diameter control of four standard thread, no matter what kind of thread turning, lathe spindle and the tool must maintain a strict relationship between the movement:That the spindle per revolution (that is, the workpiece revolution), the tool should be evenly moving a (workpiece) lead distance. The following through the analysis of ordinary threads, to strengthen the understanding of the ordinary thread, in order to better the processing of ordinary thread.
First, the general thread size analysis.
CNC lathe on the processing of ordinary threads require a series of dimensions, general thread size calculation and analysis required mainly include the following two aspects:
1.the workpiece diameter before threading
Consider the amount of expansion of the thread processing tooth shape, the diameter of the workpiece before the thread processing D / D-0.1P, that is, the major diameter of the thread by 0.1 pitch, generally smaller than the thread diameter 0.1 to 0.5 small deformation capacity.
2.thread processing feed
Thread into the amount of knife can refer to the thread bottom diameter, that is, the final position of the thread knife into the knife.
Thread trails are: large diameter -2 times the tooth height; tooth height = 0.54P (P is the pitch)
The amount of thread infeed should be reduced, the specific amount of feed according to the choice of tools and working materials.
Second, the general thread cutter equipment and knife
Tool installed too high or too low too high, then the knife to a certain depth, the lathe knife to withstand the workpiece after the knife face, increasing friction, and even the top bend the workpiece, resulting in eating knife phenomenon; too low, then Chip is not easy to discharge, the radial direction of the tool is the workpiece center, together with the horizontal crossbar into the gap between the nut and nut is too large, resulting in automatic deepening depth of the eater to raise the workpiece lifted, eating knives appear. At this point, the lathe height should be adjusted in time, so that the tip and workpiece axis is high (the tailstock can be used on the knife). In roughing and semi-finishing, the tip position is about 1% higher than the center of the workpiece (D is the diameter of the workpiece being machined).
Insufficient workpiece clamping The rigidity of the workpiece itself can not withstand the cutting force when turning, resulting in excessive deflection, changing the center height of the turning tool and the workpiece (the workpiece is raised), the sudden increase of cutting depth, , This time should be firmly clamp the workpiece, the tailstock can be used to increase the rigidity of the workpiece.
The common thread method of the knife has the method of trial and error on the knife and the tool on the knife automatically, you can use the tool to test the knife, you can also use the G50 to set the workpiece zero, the workpiece is set to move the workpiece zero to the knife. Requirements of the thread processing knife is not very high, especially the Z to the knife is not strictly limited, according to programming requirements may be.
Third, the ordinary thread programming.
In the current CNC lathes, thread cutting generally has three kinds of processing methods: G32 straight-ahead cutting method, G92 straight-ahead cutting method and G76 oblique cutting method, due to the different cutting methods, programming methods, resulting in processing errors different. We have to carefully analyze the operation and use, strive for the processing of high-precision parts.
1, G32 straight-ahead cutting method, because both sides of the blade work at the same time, cutting force larger, and row cutting difficult, so cutting, the two cutting edges easy to wear. In the cutting of larger thread pitch, the larger the depth of cut, the faster the blade wear, resulting in the thread diameter error; but the processing of the tooth-shaped high accuracy, it is generally used for small-pitch thread. Because of its cutting tools are moving to cut by programming to complete, so a longer processing procedures; Because the blade is easy to wear, so to do the groundwork measurement.
2, G92 straight-ahead cutting method simplifies programming, improve the efficiency compared with G32 instruction.
3, G76 oblique-cutting method, as a single-edged blade processing edge easily damaged and worn, so that the processing of non-straight thread surface, the tip angle changes, resulting in poor accuracy of the dentition. However, because of its single-edged work, the tool load is small, chip evacuation is easy, and the depth of cut is decreasing. Therefore, this processing method is generally suitable for large-pitch threading. More CNC knowledge WeChat search public number "CNC programming teaching" free tutorials, because this processing method is easy to chip removal, blade processing conditions are better, less demanding in the thread accuracy of this processing method is more convenient. In the processing of high-precision thread, the use of two-knife processing can be completed, both with the G76 roughing roughing method, and then use the G32 processing method fine car. However, we must pay attention to the starting point of the tool to be accurate, otherwise easy to buckle, causing parts scrapped.
4, the thread can be processed through the completion of the thread to determine the quality of thread to take timely measures, when the top of the thread crest is not sharp, the increase of the amount of the knife cut will increase the thread diameter will increase, depending on the amount of plastic material may be increased, when When the top of the tooth has been sharpened to increase the amount of incision into the large diameter reduced proportionally, according to this feature to correctly cut the amount of thread to prevent scrap.
Fourth, the detection of ordinary thread
For the general standard thread, thread ring gauge or plug gauges are used to measure. In the measurement of external thread, if the thread "over" ring gauge just precession, and "stop" ring gauge does not enter, then the processed thread to meet the requirements, on the contrary unqualified. When measuring the internal thread, use the thread plug gauge and measure it in the same way. In addition to the thread gauge or plug gauges can also measure the use of other gauges, measuring the thread diameter with a micrometer micrometer caliper with traverse caliper measuring trapezoidal thread diameter thickness and worm pitch diameter tooth thickness, the amount of needle according to the three-pin Measuring method of measuring thread diameter.
