In CNC lathes, four types of standard threads can be turned in metric, inch, modulus, and diameter. No matter which thread is turned, a strict movement relationship must be maintained between the lathe spindle and the tool: that is, every revolution of the spindle (ie, the workpiece Turning), the tool should move the distance of one (workpiece) lead evenly. The following analysis of common threads enhances understanding of ordinary threads to better process ordinary threads.
First, the size of ordinary thread analysis The CNC lathe requires a series of dimensions for the processing of common threads. The dimensional calculation analysis required for ordinary thread processing mainly includes the following two aspects:
1, the diameter of the workpiece before threading
Considering the expansion amount of the thread processing profile, the diameter of the workpiece before threading is D/d-0.1P, that is, the thread diameter minus 0.1 pitch is generally smaller than the large diameter of the thread by 0.1 to 0.5 according to the deformation capacity of the material.
2, thread processing feed
The amount of thread added to the tool can refer to the thread bottom diameter, which is the final feed position of the thread knife.
Thread diameter is: Large diameter - 2 times tooth height; tooth height = 0.54P (P is pitch)
The feed rate for thread processing should be continuously reduced, and the specific feed rate should be selected according to the tool and work material.
Second, ordinary thread cutter loading and knife If the turning tool is installed too high or too low, then when the knife is to a certain depth, the flank of the turning tool resists the workpiece, increases the friction force, and even bends the workpiece topside, resulting in a sickle phenomenon; if it is too low, then Chips are not easy to discharge, the direction of the radial force of the turning tool is the center of the workpiece, and the gap between the feed screw and the nut is too large. As a result, the depth of the knife is automatically deepened, and the workpiece is raised and a guillotine blade appears. At this time, the height of the turning tool should be adjusted in time to make the height of the tool tip and the workpiece axis equal (using the tailstock tip to set the knife). In roughing and semi-finishing, the position of the tool tip is 1%D higher than the center of the workpiece (D indicates the diameter of the workpiece being machined).
The workpiece is not clamped. The rigidity of the workpiece itself cannot withstand the cutting force during turning, resulting in excessive deflection, changing the center height of the turning tool and the workpiece (the workpiece is raised), resulting in an abrupt increase in the depth of cut. At this time, the workpiece should be firmly clamped, and the tailstock tip can be used to increase the rigidity of the workpiece.
The method for setting the normal thread is the test method. The tool setting tool and the tool setting tool automatically set the tool. You can use the tool to cut the tool directly. You can also use the G50 to set the workpiece zero, and use the workpiece to set the workpiece zero to perform tool setting. The requirements for thread processing and tool setting are not very high. In particular, there is no strict limitation on the Z-direction tool setting, which can be determined according to the programming requirements.
Third, the ordinary thread programming In the current CNC lathes, there are generally three machining methods for thread cutting: G32 in-line cutting, G92 in-line cutting, and G76 oblique cutting. Due to different cutting methods and different programming methods, machining errors are also caused. different. We must carefully analyze the operation and use, and strive to produce high-precision parts.
1. G32 straight cutting method, because the two sides of the blade work at the same time, the cutting force is large, and the cutting is difficult, so when the cutting, the two cutting edges are easy to wear. When cutting a thread with a large pitch, the cutting edge wears quickly due to a large depth of cut, resulting in an error in the diameter of the thread. However, since the precision of the tooth shape is high, it is generally used for small-pitch thread processing. Because the cutting movement of the tool is done by programming, the machining procedure is long; because the cutting edge is easy to wear, the measurement must be done during processing.
2. The G92 in-line cutting method simplifies programming and improves efficiency over the G32 instruction.
3, G76 oblique cutting method, because of the single-sided edge processing, processing blade is easy to damage and wear, so that the thread surface is not straight, the tool angle changes, resulting in poor teeth accuracy. However, due to its single-edge operation, the tool load is small, chip evacuation is easy, and the depth of cut is decremental. Therefore, this processing method is generally applicable to large-pitch thread processing. Due to the ease of chip evacuation in this processing method, the cutting edge working condition is better, and the machining method is more convenient in the case where the accuracy of the thread is not high. In the machining of high-precision threads, two-pass machining can be used. The G76 machining method is used for the roughing, and the G32 finishing method is used. However, it should be noted that the starting point of the tool must be accurate, otherwise it is easy to buckle and cause parts to be scrapped.
4, after the completion of thread processing can be observed by looking at the thread thread type thread quality in time to take measures, when the thread crest is not sharp, increase the cutting amount of the knife will make the thread larger diameter, increase the amount of material depending on the plastic, When the crest of the crest has been sharpened, the incision of the knife is increased, and the diameter of the chopper is reduced in proportion. According to this feature, the cutting amount of the screw thread must be correctly treated to prevent scrapping.
Fourth, the detection of ordinary thread
For general standard threads, thread ring gauges or plug gauges are used. When measuring the external thread, if the “over-end” ring thread just advances and the “end-end” ring ring does not advance, then the processed thread meets the requirements, otherwise it fails. When measuring internal threads, use a threaded plug gauge to measure in the same way. In addition to thread ring gauge or plug gauge measurement, other gauges can also be used for measurement. Measure the diameter of the thread with a thread micrometer. Measure the diameter of the trapezoid thread and the thickness of the teeth of the worm with a tooth thickness vernier caliper. Use the measuring needle according to the three needles. Measure the thread diameter.
