Top 10 problems of tap breakage

Analysis and summary of 10 major problems of tap breakage
1. The tap quality is not good
Main materials, CNC 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. To a large extent, this is also an important reason why the overall performance of domestic taps is not as good as that of imported taps.
Countermeasures: choose high-quality and reliable tap brands and more suitable tap series.
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.
For difficult-to-machine materials such as precipitation stainless steel and high-temperature alloys with high hardness and good toughness, the tap may break due to its insufficient strength and cannot resist the cutting resistance of tapping.
In addition, the problem of the mismatch between the tap and the processed material 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.
Countermeasures: Use high-strength material taps (such as powdered high-temperature steel, etc.) to improve the strength of the tap itself; at the same time, improve the surface coating of the tap to improve the surface hardness of the thread; in extreme cases, even manual tapping may be a feasible method.
3. Excessive wear of the tap
Another very common situation is that after the tap has processed several threaded holes, the cutting resistance becomes larger due to the excessive wear of the tap, resulting in the tap being broken.
Countermeasures: First of all, it is recommended to use Sentai Inge V shank, which will obviously delay the wear of the tap, thereby improving the service life of the tap; at the same time, the use of high-quality tapping lubricating oil can also effectively delay the wear of the tap; in addition, use the thread gauge (T /Z) The tap condition can be easily judged.
4. Axial synchronization error
During the tapping process of the machining center, a large number of broken taps are caused by the error in the synchronization between the rotation of the machine tool spindle and the axial feed, which increases the axial tension (or pressure) the taps are subjected to, resulting in the breakage of the taps. The synchronization error is almost impossible to avoid completely in rigid tapping of machining centers (or CNC lathes), especially at the moment when the tap is retracted (reversed).
Countermeasures: Use Sentai Inge V-shank, which completely solves the problem of axial synchronization error compensation for rigid tapping.
5. Difficulty in chip breaking and chip evacuation
For blind hole tapping, a helical groove rear chip removal tap is usually used. If the iron chips are wrapped around the tap and cannot be discharged smoothly, the tap will be blocked, and a large number of processed materials (such as steel and stainless steel and high temperature alloys, etc.) are tapped. Machining is often difficult to break chips.
Countermeasures: first consider changing the helix angle of the tap (usually there are several different helix angles to choose from), try to make the iron filings be removed smoothly; at the same time adjust the cutting parameters appropriately, the purpose is also to ensure that the iron filings can be removed smoothly; if necessary Variable helix angle taps can be selected to ensure smooth discharge of iron filings.
6. The hole diameter of the bottom hole is too small
For example, when processing M5×0.5 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 that needs to be cut by the tap will inevitably increase during tapping. , 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.
7. 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.
8. 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.
9. The quality of cutting fluid and lubricating oil is not good
Many domestic enterprises have begun to pay attention to this point. Many companies that have purchased foreign tools and machine tools have a very profound experience. There are problems with the quality of cutting fluid and lubricating oil, and the quality of processed products is prone to burrs and other adverse conditions. will also be greatly reduced.
10. 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.
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. As a qualified and responsible tool application engineer, the most important thing is to go deep into the field, not just imagine. For the simplest example, if the length of the tap cutting cone is too long, it hits the bottom of the bottom hole and breaks when tapping. If you don’t go deep into the field, you can only guess how the tap performance, workpiece material, processing technology, etc. will be known.