Screws are one of the important applications of CNC machining centers, and their machining quality and efficiency directly affect the machining quality of parts and the production efficiency of the center.

With the improvement of the performance of machining centers and the improvement of cutting tools, the processing methods of threads are also constantly improving, and the accuracy and precision are gradually improving. In order to enable the technicians to reasonably choose the thread processing method during the processing, improve the production efficiency and avoid quality accidents.

Tap processing method – types and characteristics of tap processing.

Using taper to process threaded holes is the most common processing method, and it is mainly suitable for threaded holes with small diameters (<30) and low position accuracy requirements.

In the 1980s, flexible tapping was used for threaded holes, that is, a flexible tapping chuck was used to clamp the tap, and the tapping chuck was axially compensated to compensate for the asynchronous feed of the machine tool and the spindle speed. feed error to ensure the correct pitch. The fixture has the characteristics of complex structure, high cost, easy damage and low processing efficiency. In recent years, the performance of CNC machining centers has gradually improved, and the rigid tapping function has become the basic structure of the machining center.

Therefore, the main thread processing method at present is rigid tapping.

The tap is clamped with a rigid spring, keeping the spindle feed and spindle speed under the control of the machine.

Compared with the flexible tapping machine, the spring clamp has a simple structure, low price, and a wide range of uses. In addition to holding the tap, it can also hold tools such as end mills and drills to reduce tool costs. At the same time, the rigid tapping can realize high-speed cutting, improve the utilization rate of the machining center, and reduce the manufacturing cost.

- Determination of threaded bottom holes before tapping

The processing of the screw bottom hole has a great influence on its service life and processing quality. Generally speaking, the diameter of the threaded bottom hole drill bit is selected to be close to the upper limit of the threaded bottom hole diameter.

For example, the bottom hole diameter of the M8 threaded hole is Ф6.7+0.27mm, and the diameter of the selected drill bit is Ф6.9mm. Through this method, the machining allowance of the cone can be reduced, the load of the cone can be reduced, and the service life of the cone can be improved.

- Choice of taps

When selecting taps, first select the corresponding taper according to the material to be processed. The tool company produces taps of different specifications according to the different materials to be processed. Special attention should be paid to the selection.

Because the tapered surface is very sensitive to the material to be processed relative to the milling cutter and the boring cutter. For example, when processing aluminum parts, when using iron wire to process pig iron, it is easy to cause thread loss, random buckles or even breakage, resulting in scrapped components. Second, pay attention to the difference between taps with holes and blind holes. The length of the diversion before the holes is large, and the chip removal is the front chip removal. Has blind holes with short diversion in the front and rear chip evacuation. It is difficult to guarantee the depth of the processing line by using a hole tap to process blind holes. In addition, if you use a soft tapping chuck, you should also pay attention to the width of the tap shank and the four corners, which should be the same as the tapping; the diameter of the tap shank of the hard tapping should be the same as the diameter of the spring collet. Therefore, only a reasonable selection of taps can ensure the smooth progress of processing.

- NC programming for tap machining

Programming for tap machining is relatively simple. Now the machining center generally solidifies the tapping subroutine, just assign each parameter value. However, it should be noted that different numerical control systems have different subprogram formats, and the meanings of some parameters are different.

For example, SIEMEN840C control system, its programming format is: G84X_Y_R2_R3_R4_R5_R6_R7_R8_R9_R10_R13_. When programming, you only need to assign these 12 parameters

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