Thread processing is one of the very important applications of CNC machining centers, and the processing quality and efficiency of threads will directly affect the processing quality of parts and the production efficiency of machining centers.

With the improvement of CNC machining center performance and the improvement of cutting tools, the method of thread processing is also constantly improving, and the accuracy and efficiency of thread processing are gradually improving. In order to enable technicians to reasonably choose thread processing methods in processing, improve production efficiency, and avoid quality accidents, several thread processing methods commonly used in CNC machining centers are summarized as follows:

1. Tap processing method

Threaded holes with taps are the most commonly used machining method, which is mainly suitable for small diameters (D).<30)，孔位置精度要求不高的螺纹孔。

In the 80s of the 20th century, the threaded holes were all flexible tapping methods, that is, the flexible tapping chuck was used to clamp the tap, and the tapping chuck could be axial compensation to compensate for the feed error caused by the axial feed of the machine tool and the spindle speed being out of sync, so as to ensure the correct pitch. Flexible tapping chucks have complex structures, high costs, 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 configuration of CNC machining centers.

Therefore, rigid tapping has become the main method of thread processing at present.

Compared with flexible tapping chucks, spring chucks have a simple structure, cheap price, and a wide range of uses, in addition to clamping taps, they can also clamp end mills, drills and other tools, which can reduce tool costs. At the same time, the use of rigid tapping can carry out high-speed cutting, improve the efficiency of machining center use, and reduce manufacturing costs.

The processing of thread bottom hole has a great impact on the life of the tap and the quality of thread processing. Normally, the diameter of the threaded bottom hole drill bit is chosen close to the upper limit of the threaded bottom hole diameter tolerance,

For example, the bottom hole diameter of the M8 threaded hole is Ф6.7+0.27mm, and the drill bit diameter is Ф6.9mm. In this way, the processing allowance of the tap can be reduced, the load of the tap can be reduced, and the service life of the tap can be improved.

When choosing a tap, first of all, the corresponding tap must be selected according to the material being processed, and the tool company produces different types of taps according to different processing materials, and special attention should be paid when choosing.

Because taps are very sensitive to the material to be processed compared to milling cutters and boring tools. For example, using a cast iron tap to process aluminum parts can easily cause threads to fall out, buckle indiscriminately, or even break the tap, resulting in the scrapping of the workpiece. Secondly, attention should be paid to the difference between through-hole taps and blind-hole taps, the front end of the through-hole tap is longer, and the chip removal is the front chip discharge. The blind hole front end guide is short, and the chip discharge is the rear chip discharge. Machining blind holes with through-hole taps does not guarantee the depth of threading. In addition, if a flexible tapping chuck is used, it should also pay attention to the diameter of the tap handle and the width of the square, which should be the same as the tapping chuck; The diameter of the handle of the tap for rigid tapping should be the same as the diameter of the spring jacket. In short, only a reasonable selection of taps can ensure the smooth progress of processing.

1.4 CNC programming for tap processing

Programming tap processing is relatively simple. Nowadays, machining centers generally have a solidified tapping subprogram, and only need to assign values to each parameter. However, it should be noted that different CNC systems have different subprogram formats, and the meaning of some parameters is different.

For example, SIEMEN840C control system,

It is programmed in the following format: G84 X_Y_R2_ R3_R4_R5_R6_R7_R8_R9_R10_R13_.

Simply assign these 12 parameters to the program.

2. Thread milling method

Thread milling is the milling method of thread milling tools and three-axis linkage of the machining center, that is, the X and Y axes of arc interpolation and Z axis linear feed.

Thread milling is mainly used for the processing of large hole threads and threaded holes of difficult-to-machine materials. It mainly has the following characteristics:

(1) Fast processing speed, high efficiency and high processing accuracy. The tool material is generally cemented carbide material, and the tool speed is fast. The tool is manufactured with high precision and therefore the thread accuracy of milling is high.

(2) The milling tool has a wide range of applications. As long as the pitch is the same, whether it is a left-hand thread or a right-hand thread, one tool can be used, which is conducive to reducing the tool cost.

(3) Milling processing is easy to remove chips and cool, and the cutting situation is better than that of taps, especially suitable for threading of difficult-to-machine materials such as aluminum, copper, stainless steel, etc., especially suitable for threading of large parts and parts of precious materials, which can ensure the quality of threading and the safety of workpieces.

(4) Because there is no tool front guidance, it is suitable for machining blind holes with short threaded bottom holes and holes without tool retraction grooves.

Thread milling tools can be divided into two types, one is a clamp-type carbide insert milling cutter, and the other is a monolithic carbide milling cutter. Clip-on tools are suitable for a wide range of applications, including holes with a thread depth smaller than the blade length and holes with a thread depth greater than the blade length. Integral carbide milling cutters are generally used to machine holes with a thread depth less than the length of the tool.

The programming of thread milling tools is different from the programming of other tools, if the machining program is wrong, it is easy to cause tool damage or thread processing errors. The following points should be paid attention to when compiling:

(1) First of all, the threaded bottom hole should be processed well, the small diameter hole should be processed with a drill bit, and the larger hole should be bored to ensure the accuracy of the threaded bottom hole.

(2) When the cutter cuts in and out, an arc trajectory should be used, usually 1/2 turn for cutting in or out, and the Z-axis direction should travel 1/2 pitch to ensure the thread shape.Tool radius compensationThe value should be brought in at this time.

(3) The X and Y axes are interpolated for one week, and the spindle should travel a pitch along the Z axis, otherwise, it will cause the thread to be randomly fastened.

(4) Specific example procedures:Thread milling cuttersThe diameter is Φ16, the threaded hole is M48×1.5, and the threaded hole depth is 14.

The processing procedure is as follows:

3. Pick and buckle method

Large threaded holes can sometimes be encountered on box parts, and in the absence of taps and thread mills, a lathe-like method can be used.

Install a thread turning tool on the boring tool bar to boring threads.

The company once processed a batch of parts, the thread is M52x1.5, the position is 0.1mm (see Figure 1), because the position is high, the thread hole is large, can not be processed with a tap, and there is no thread milling cutter.