Main material, tool design, heat treatment, machining accuracy, coating quality, etc. For example, the size difference at the transition of the tap cross-section is too large or the transition fillet is not designed to cause stress concentration, and it is easy to break at the stress concentration during use. The cross-section transition at the junction of the shank and the blade is too close to the weld, resulting in the superposition of complex welding stress and the stress concentration at the cross-section transition, resulting in a large stress concentration, which causes the tap to break during use. For example, improper heat treatment process. When the tap is heat treated, if it is not preheated before quenching and heating, quenching is overheated or over-burned, not tempered in time and cleaned too early, it may cause cracks in the tap. This is also an important reason why the overall performance of domestic taps is not as good as that of imported taps.
2. Improper selection of taps:
For tapping parts with too much hardness, high-quality taps should be used, such as cobalt-containing high-speed steel taps, carbide taps, coated taps, etc. In addition, different tap designs are used in different work situations. For example, the number, size, angle, etc. of the chip flute heads of the tap have an impact on the chip removal performance.
3. The tap does not match the material being processed:
This problem has been paid more and more attention in recent years. In the past, domestic manufacturers always thought that imported products were good and expensive, but they were actually suitable. With the continuous increase of new materials and difficult processing, in order to meet this demand, the variety of tool materials is also increasing. This requires selecting a suitable tap product before tapping.
4. The hole diameter of the bottom hole is too small:
For example, when machining M50.5 threads of ferrous metal materials, a 4.5mm diameter drill bit should be used to make a bottom hole with a cutting tap. If a 4.2mm drill bit is misused to make a bottom hole, the part of the tap that needs to be cut during tapping will inevitably increase. , which in turn breaks the tap. It is recommended to choose the correct bottom hole diameter according to the type of tap and the material of the tapping piece. If there is no fully qualified drill bit, you can choose a larger one.
5. Tackling material problem:
The material of the tapping piece is not pure, and there are hard spots or pores in some parts, which will cause the tap to lose its balance and break instantly.
6. The machine tool does not meet the accuracy requirements of the tap:
The machine tool and clamping body are also very important, especially for high-quality taps, only a certain precision machine tool and clamping body can exert the performance of the tap. It is common that the concentricity is not enough. At the beginning of tapping, the starting position of the tap is incorrect, that is, the axis of the spindle is not concentric with the centerline of the bottom hole, and the torque is too large during the tapping process, which is the main reason for the break of the tap.
7. The quality of cutting fluid and lubricating oil is not good:
Many domestic enterprises have begun to pay attention to this point. Many of them have purchased foreign countries and have a very profound experience. There are problems with the quality of cutting fluid and lubricating oil. The quality of the processed products is prone to burrs and other bad conditions, and the service life will also be very long. decrease.
8. Unreasonable cutting speed and feed:
When there is a problem in processing, most domestic users reduce the cutting speed and feed rate, so that the propulsion force of the tap is reduced, and the thread accuracy of its production is greatly reduced, which increases the roughness of the thread surface. The hole diameter and thread accuracy cannot be controlled, and problems such as burrs are of course more unavoidable. However, if the feed speed is too fast, the resulting torque is too large and the tap is easily broken. The cutting speed during machine attack is generally 6-15m/min for steel; 5-10m/min for quenched and tempered steel or harder steel; 2-7m/min for stainless steel; 8-10m/min for cast iron. For the same material, the smaller the tap diameter takes the higher value, and the larger the tap diameter takes the lower value.
9. The operator's technology and skills do not meet the requirements:
The above problems all require operators to make judgments or give feedback to technicians, but at present, most operators in China do not pay enough attention. For example, when processing blind hole threads, when the tap is about to touch the bottom of the hole, the operator does not realize that the tap is still fed at the tapping speed before reaching the bottom of the hole, or the tap is broken due to forcible feeding when the chip evacuation is not smooth. . It is recommended that operators strengthen their sense of responsibility.
It can be seen from the above that there are various reasons for the breakage of taps, including machine tools, fixtures, workpieces, processes, chucks and tools, etc. It is possible that the real reason may never be found just on paper.
