On the CNC lathe, four standard threads of metric, inch, modulus and caliper can be turned. No matter which thread is turned, the spindle between the lathe and the tool must maintain a strict motion relationship: that is, the spindle rotates once (ie the workpiece) Turn one turn), the tool should evenly move the distance of one (the workpiece) lead. The following analysis of ordinary threads enhances the understanding of ordinary threads for better machining of common threads.
First, the size analysis of ordinary thread
CNC lathes require a series of sizes for the processing of ordinary threads. The calculation of the dimensions required for ordinary thread processing mainly includes the following two aspects:
1. Workpiece diameter before thread machining
Considering the amount of expansion of the thread-cutting type, the diameter of the workpiece before threading is D/D-0.1P, that is, the diameter of the thread is reduced by 0.1 pitch. Generally, the deformation ability of the material is smaller than the large diameter of the thread by 0.1 to 0.5.
2, thread processing feed amount
The thread feed amount can refer to the thread bottom diameter, that is, the final feed position of the thread cutter.
The thread diameter is: large diameter - 2 times the tooth height; tooth height = 0.54P (P is the pitch)
The amount of thread feed should be continuously reduced. The specific amount of feed is selected according to the tool and working material.
Second, the general threading tool loading and tool setting
If the turning tool is installed too high or too low or too high, when the knife reaches a certain depth, the flank of the turning tool will bear against the workpiece, increase the friction, and even bend the workpiece to cause a sickle phenomenon; if it is too low, then The chip is 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 screw and the nut is too large, so that the depth of the knife is constantly deepened, so that the workpiece is lifted and a file is formed. At this time, the height of the turning tool should be adjusted in time so that the tool tip is at the same height as the axis of the workpiece (the tip of the tailstock can be used to align the blade). In roughing and semi-finishing, the tool nose position is about 1%D higher than the center of the workpiece (D indicates the diameter of the workpiece to be machined).
The workpiece is not clamped. The rigidity of the workpiece itself cannot withstand the cutting force during turning. Therefore, the excessive deflection is generated, and the center height of the turning tool and the workpiece is changed (the workpiece is raised), and the cutting depth is suddenly increased. At this time, the workpiece should be clamped firmly, and the tailstock tip can be used to increase the rigidity of the workpiece.
For the common thread, the tool setting method is the trial cutting method and the tool setting tool. The tool can be directly cut with the tool. The workpiece zero point can also be set with G50, and the workpiece zero point can be set by the workpiece to perform the tool setting. The threading tool is not very demanding, especially the Z-direction tooling is not strictly limited, and can be determined according to the programming requirements.
Third, the programming 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 result in machining errors. different. We must carefully analyze the operation and use, and strive to process parts with high precision.
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 the two cutting edges are easy to wear during cutting. When the thread with a large pitch is cut, the cutting edge wears faster due to the large cutting depth, which causes an error in the diameter of the thread; however, the precision of the processed tooth shape is high, so it is generally used for small pitch thread processing. Since the cutting of the tool is performed by programming, the machining program is long; since the blade is easy to wear, it is necessary to perform the measurement in the machining.
2. The G92 straight-cut cutting method simplifies programming and improves efficiency compared to the G32 command.
3. G76 oblique cutting method, because of the single-side cutting process, the machining blade is easy to be damaged and worn, so that the thread surface of the machining is not straight, the cutting edge angle changes, and the tooth shape accuracy is poor. However, due to its single-sided blade operation, the tool load is small, the chip removal is easy, and the cutting depth is decreasing. Therefore, this processing method is generally suitable for large pitch thread processing. Since the processing method is easy to remove chips, the blade processing condition is good, and the processing method is more convenient when the thread precision is not high. When machining high-precision threads, it can be completed by two-knife. The G76 machining method is used for roughing, and then the G32 machining method is used for finishing. However, it should be noted that the starting point of the tool should be accurate, otherwise it will be easy to buckle and cause the parts to be scrapped.
4. After the thread processing is completed, the thread quality can be judged by observing the thread shape. When the thread crest is not pointed, increasing the cutting amount of the knife will increase the diameter of the thread, and the increase amount depends on the plasticity of the material. When the crest has been sharpened, the cutting amount of the knife is increased, and the large diameter is proportionally reduced. According to this feature, the cutting amount of the thread should be correctly treated to prevent scrapping.
Fourth, the detection of ordinary thread
For standard standard threads, threaded ring gauges or plug gauges are used for measurement. When measuring the external thread, if the thread "over the end" ring gauge is just screwed in, and the "stop end" ring gauge does not advance, it means that the thread processed meets the requirements, and vice versa. When measuring internal threads, use the thread plug gauge to measure in the same way. In addition to the thread ring gauge or plug gauge measurement, other gauges can be used for measurement. The thread diameter is measured by a thread micrometer, and the tooth thickness of the trapezoidal thread and the tooth diameter of the worm pitch are measured by the tooth thickness vernier caliper. The measuring method measures the diameter of the thread.