With the improvement of the performance of CNC machining center and the improvement of cutting tools, the method of thread processing is constantly improved, and the accuracy and efficiency of thread processing are also gradually improved. Thread processing is one of the most important applications of CNC machining. The quality and efficiency of thread processing will directly affect the machining quality of parts and the production efficiency of machining center. In order to enable the process personnel to reasonably choose the thread processing method in the processing, improve the production efficiency and avoid the quality accident, several thread processing methods commonly used in CNC machining are summarized as follows:
- Tap processing method
1.1 classification and characteristics of tap processing
The tap is the most commonly used processing method for threaded hole, which is mainly applicable to the small diameter (d < 30) and low accuracy requirement of hole position.
In the 1980s, the flexible tapping method was adopted for the threaded hole, that is, the flexible tapping chuck was used to clamp the tap, and the tapping chuck could be used to compensate the feed error caused by the machine tool’s axial feed and spindle speed, so as to ensure the correct pitch. Flexible tapping chuck has complex structure, high cost, easy damage and low processing efficiency. In recent years, the performance of CNC machining has gradually improved, and the rigid tapping function has become the basic configuration of CNC machining.
Therefore, rigid tapping has become the main method of thread processing.
In other words, the rigid spring chuck is used to hold the tap, and the spindle feed and spindle speed are 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 the tap, it can also clamp the end mill, drill and other tools, which can reduce the cost of the tool. At the same time, the use of rigid tapping can make high-speed cutting, improve machining efficiency and reduce manufacturing costs.
1.2 the bottom hole of thread before tapping
The processing of thread bottom hole has great influence on the life of tap and the quality of thread processing. In general, the drill diameter of the bottom hole is close to the upper limit of the diameter tolerance of the bottom hole,
For example, the diameter of the bottom hole of the M8 thread hole is Ф 6.7 + 0.27mm, and the diameter of the drill bit is selected to be Ф 6.9mm. In this way, the machining 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.
1.3 selection of taps
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 the different processing materials, and special attention should be paid to the selection.
Because the tap is very sensitive to the processed material relative to milling cutter and boring cutter. For example, using taps for processing cast iron to process aluminum parts is easy to cause thread missing, thread disorderly and even tap breaking, resulting in workpiece scrapping. Secondly, we should 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 longer, and the chip removal is the front row chip. The leading edge of the blind hole is short, and the chip removal is the back row chip. The processing depth of thread can not be guaranteed when the blind hole is machined with through-hole tap. Furthermore, if flexible tapping chuck is used, the diameter of tap shank and the width of four sides should be the same as that of tapping chuck; the diameter of shank of rigid tapping should be the same as that of spring jacket. In short, only reasonable selection of taps can ensure the smooth processing.
1.4 NC programming of tap machining
The programming of tap machining is simple. Now the machining center generally solidifies the tapping subroutine, which only needs to assign the parameters. However, it should be noted that the meaning of some parameters is different due to different NC systems and different formats of subroutines.
For example, Siemens 840C control system, its programming format is: g84x_ Y_ R2_ R3_ R4_ R5_ R6_ R7_ R8_ R9_ R10_ R13_。 In programming, only these 12 parameters need to be assigned.
- CNC thread milling method
2.1 features of thread milling
Thread milling is to use thread milling tool, machining center three axis linkage, namely x, Y axis arc interpolation, Z axis linear feed milling method.
Thread milling is mainly used for machining large hole thread and thread hole of difficult to machine material. It has the following characteristics:
(1) high speed, high efficiency and high precision. The cutting tool material is generally cemented carbide material, and the cutting speed is fast. The manufacturing precision of cutting tool is high, so the precision of thread milling is high.
(2) milling tools are widely used. As long as the pitch is the same, whether it is * * thread or right-hand thread, one tool can be used, which is conducive to reducing the cost of the tool.
(3) milling is easy to chip removal and cooling. Compared with the tap, the cutting condition is better, especially suitable for the screw thread processing of difficult to machine materials such as aluminum, copper, stainless steel, etc,
It is especially suitable for thread processing of large parts and components of valuable materials, which can ensure the quality of thread processing and the safety of workpiece.
(4) because there is no tool front-end guide, it is suitable for machining blind holes with short thread bottom holes and holes without undercut groove.
2.2 classification of thread milling tools
Thread milling tools can be divided into two types, one is the machine clip type carbide blade milling cutter, the other is the integral cemented carbide milling cutter. It can be used for machining holes with thread depth less than blade length and holes with thread depth greater than blade length. Integral cemented carbide milling cutter is generally used for machining holes with thread depth less than tool length.
2.3 NC programming of thread milling
The programming of thread milling tool is different from that of other tools
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