Thread machining is one of the very important applications of CNC machining center. The machining quality and efficiency of thread will directly affect the machining quality of parts and the production efficiency of machining center.
With the improvement of the performance of CNC machining center and the improvement of cutting tools, the method of thread machining is also improving, and the accuracy and efficiency of thread machining are also gradually improving. In order to enable technicians to reasonably select thread processing methods in processing, improve production efficiency and avoid quality accidents, several thread processing methods commonly used in CNC machining center are summarized as follows:
1. Tap processing method
1.1 classification and characteristics of tap processing
Using tap to process threaded hole is the most common processing method, which is mainly suitable for small diameter (d)
In the 1980s, the flexible tapping method was adopted for threaded holes, that is, the flexible tapping collet was used to clamp the tap. The tapping collet can be used for axial compensation to compensate the feed error caused by the non synchronization between the axial feed of the machine tool and the spindle speed, so as to ensure the correct pitch. The flexible tapping collet has complex structure, high cost, easy damage and low processing efficiency. In recent years, the performance of CNC machining center Gradually, the rigid tapping function has become the basic configuration of CNC machining center.
Therefore, rigid tapping has become the main method of thread machining.
That is, the tap is clamped with a rigid spring collet, and the feed of the spindle is consistent with the spindle speed controlled by the machine tool.
Compared with the flexible tapping chuck, the spring chuck has the advantages of simple structure, low price and wide application. In addition to holding the tap, it can also hold the end milling cutter, drill bit and other tools, which can reduce the tool cost. At the same time, the rigid tapping can be used for high-speed cutting, improve the use efficiency of the processing center and reduce the manufacturing cost.
1.2 determination of threaded bottom hole before tapping
The processing of threaded bottom hole has a great impact on the life of tap and the quality of thread processing. Generally, the diameter of threaded bottom hole drill is close to the upper limit of the diameter tolerance of threaded bottom hole,
For example, the bottom hole diameter of M8 threaded hole is Ф 6.7 + 0.27mm, select the drill bit diameter as Ф 6.9mm. In this way, the machining allowance of tap can be reduced, the load of tap can be reduced, and the service life of tap can be improved.
1.3 selection of tap
When selecting taps, first of all, the corresponding taps must be selected according to the processed materials. The tool company produces different types of taps according to different processing materials, and special attention should be paid to the selection.
Because the tap is very sensitive to the processed materials compared with the milling cutter and boring cutter. For example, using the tap for processing cast iron to process aluminum parts is easy to cause thread dropping, disorderly threading and even tap breaking, resulting in workpiece scrapping. Secondly, pay attention to the difference between the through-hole tap and the blind hole tap. The front-end guide of the through-hole tap is long, and the chip removal is the front-end chip. The front-end guide of the blind hole is short, and the chip removal is the front-end It is the back chip. Machining the blind hole with a through-hole tap cannot guarantee the thread machining depth. Moreover, if a flexible tapping collet is used, it should also be noted that the diameter of the tap handle and the width of the four sides should be the same as that of the tapping collet; the diameter of the tap handle for rigid tapping should be the same as that of the spring jacket. In short, only a reasonable selection of the tap can ensure the smooth machining.
