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Thread processing methods commonly used in CNC machining
2020-04-07

Thread processing is one of the very important technologies of CNC machining. The quality and efficiency of thread processing will directly affect the processing quality of parts and the production efficiency of the processing center.

 

With the improvement of CNC machining performance and the improvement of cutting tools, the method of thread machining is also continuously improved, and the accuracy and efficiency of thread machining are also gradually improved. Actually, thread processing is mainly tap processing and Thread milling processing.

 

Tap processing:

 

Using taps to process threaded holes is the most commonly used processing method. It is mainly suitable for threaded holes with small diameter (D <30) and low hole position accuracy.

 

Determination of the bottom hole of thread before tapping

 

The processing of the thread bottom hole has a great influence on the life of the tap and the quality of the thread processing. Generally, the diameter of the threaded bottom hole drill is selected close to the upper limit of the tolerance of the diameter of the threaded bottom hole,

 

For example, the diameter of the bottom hole of the M8 threaded hole is Ф6.7 + 0.27mm, and the diameter of the drill bit is Ф6.9mm. 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 increased.

 

About the choice of tap

 

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

 

Compared with milling cutters and boring cutters, taps are very sensitive to the processed materials. For example, using cast iron taps to process aluminum parts can easily lead to thread loss, buckling, and even tap breakage, resulting in scrapped workpieces. Secondly, attention should be paid to the difference between through-hole taps and blind-hole taps. The leading end of the through-hole taps is longer and the chip removal is the front row of chips. The leading end of the blind hole is shorter, and the chip evacuation is the rear chip evacuation. Processing blind holes with through-hole taps does not guarantee thread machining depth. Furthermore, if a flexible tapping chuck is used, the diameter of the tap shank and the width of the square should also be the same as the tapping chuck; the tap shank diameter for rigid tapping should be the same as the diameter of the spring jacket. In short, only a reasonable choice of taps can ensure the smooth progress of processing.

 

Thread milling process:

 

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

 

Thread milling is especially suitable for the thread processing of large parts and valuable materials, which can ensure the quality of thread processing and the safety of the workpiece. It mainly has the following characteristics:

 

1.Fast processing speed, high efficiency and high processing precision. The tool material is generally cemented carbide, and the cutting speed is fast. The manufacturing precision of the tool is high, so the precision of the milled thread is high.

 

2.The scope of application of milling tools is large. As long as the pitch is the same, whether it is a left-hand thread or a right-hand thread, a tool can be used, which is beneficial to reduce the cost of the tool.

 

3.Milling processing is easy to evacuate chips and cool, and the cutting situation is better than that of taps. It is especially suitable for thread processing of difficult materials such as aluminum, copper, and stainless steel.

 

4: Because there is no tool leading end guide, it is suitable for processing blind holes with short threaded bottom holes and holes without retreating slots.

 

Precautions for CNC programming of thread milling.

The programming of thread milling tools is different from the programming of other tools. If the machining program is incorrectly edited, it is easy to cause tool damage or thread machining errors. Pay attention to the following points when preparing:

1. First, the bottom hole of the thread should be processed well, and the small diameter hole should be processed with a drill, and the larger hole should be processed by boring to ensure the accuracy of the bottom hole of the thread.

 

2. When the tool is cut in and out, the arc path should be used, usually 1/2 circle for cutting in or out, and the Z axis direction should travel 1/2 pitch to ensure the shape of the thread. The tool radius compensation value should be brought in at this time.

 

3. X, Y axis arc interpolation for one week, the main axis should travel a pitch along the Z axis direction, otherwise, it will cause thread buckle.

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