Analysis on the tapping of internal thread of stainless steel pipe fittings

Stainless steel materials are now popular, mainly because of environmental reasons. The internal threads on stainless steel fittings are usually tapped using taps. Due to the high viscosity of the stainless steel material and the poor chip breaking performance, it is easy for the chip to scratch the workpiece thread or the taper chipping during the tapping process, which affects the processing efficiency and the thread quality.

In order to extend the service life of the tap and improve the quality of thread processing, the following points should be noted:

1. Design and manufacture of taps

(1) Use a better tap material. The addition of special alloying elements to ordinary high-speed tool steel can significantly improve the wear resistance and toughness of the tap.

(2) Coating the surface of the tap thread with titanium nitride can significantly improve the wear resistance, heat resistance and lubricity of the tap.

(3) Appropriately increase the front angle of the tap. However, it should be noted that if the front angle of the tap is too large, it is easy to cause the tapping of the tap and the threading of the tapped thread when retracting the knife.

(4) Appropriately increase the amount of tapping back. However, it should be noted that if the amount of backhoe is too large, it is easy to cause the chip to be inserted into the back corner of the tap when the knife is retracted, and the threaded finish is not good.

(5) Reasonably select the tool heat treatment method to take into account the hardness and toughness of the tap.

2, the reasonable use of taps

Different chip orientations should be considered when machining different types of workpieces. If necessary, the new taps also need to be ground. The principle of grinding is to remove the chips from the chip pocket as much as possible during the tapping to prevent the thread from being scratched.

An example is as follows: Machining Coupling (SPU): It is best to use a vertical tapping machine (or a three-head tapping machine) for tapping of the coupling. The grinding method of the tap is: 1 lengthening the front guide of the tap, so that the tap gradually enters the cutting to improve the service life of the tap; 2 grinding the rake angle on each blade of the tap, but the first sharpening should not be too long (about 3 - 4MM), can be gradually lengthened in the future. The standard for judging the quality of the edge rake is that the chips are horned out of the coupling end face during tapping, and the tapped thread is not damaged. When the tapping is carried out for a period of time, if the quality of the tapped thread is found to be poor, a long edge inclination can be added.