1. The tap quality is not good
Main materials, CNC tool design, heat treatment, processing accuracy, coating quality, etc. For example, the size difference at the transition of the tap 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 blade is too close to the welding port, resulting in the superposition of complex welding stress and stress concentration at the cross-section transition, resulting in greater stress concentration, causing the tap to break during use. For example, improper heat treatment process. During tap heat treatment, if the preheating before quenching is not preheated, the quenching is overheated or overfired, the tempering is not timely and the cleaning is too early, it may cause the tap to crack. To a large extent, this is also an important reason why the overall performance of domestic taps is not as good as imported taps.
2. Improper tap selection
High-quality taps should be selected for attacking parts with too high hardness, such as high-speed cobalt-containing steel wire taps, carbide taps, and coated taps. In addition, different tap designs are used in different work situations. For example, the number, size, angle, etc. of the chip flute head of the tap have an impact on the chip removal performance.
3. The tap does not match the processed material
This problem has been paid more and more attention in recent years. In the past, domestic manufacturers always felt that imports were good and expensive, but in fact, they were suitable. With the continuous increase of new materials and difficult processing, in order to meet this need, the variety of tool materials is also increasing. This requires the selection of suitable tap products before tapping.
4. The bottom hole diameter is too small
For example, when processing ferrous metal material M5×0.5 thread, the cutting tap should be used to make a hole with a 4.5mm diameter drill bit. If a 4.2mm drill bit is misused to make a hole, the part of the tap that needs to be cut during tapping will inevitably increase To break 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 compatible drill bit, you can choose a larger one.
5. Material problem of tapping parts
The material of the attack piece is impure, and there are local hard spots or air holes, which cause the tap to lose its balance instantly and break.
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, as long as the machine tool and clamping body have a certain accuracy to achieve the performance of the tap. It is common that the concentricity is not enough. At the beginning of tapping, the positioning of the tap is not correct, that is, the spindle axis is not concentric with the center line of the bottom hole, and the torque is too large during the tapping process, which is the main reason for the tap break.
7. Cutting fluid, poor lubricating oil quality
At this point, many domestic companies have begun to pay attention. Many companies that have purchased foreign tools and machine tools have a very deep experience. The quality of the cutting fluid and lubricants is problematic. The quality of the processed products is prone to burrs and other defects. There will also be a great reduction.
8. Cutting speed and feed rate are unreasonable
When there is a problem with machining, most domestic users reduce the cutting speed and feed rate, so that the propulsion force of the tap is reduced, and the accuracy of the thread produced by it is greatly reduced, which increases the roughness of the thread surface and the thread. Neither the diameter of the hole nor the accuracy of the thread can be controlled. Problems such as burrs are of course more inevitable. However, if the feed speed is too fast, the resulting torque is too large and the tap may easily break. The cutting speed during machine tapping is generally 6-15m/min for steel; 5-10m/min for quenched and tempered steel or harder steel; 2-7m/min for stainless steel; and 8-10m/min for cast iron. For the same material, the smaller the diameter of the tap, the higher the value, and the larger the diameter of the tap, the lower.
9. The operator's technology and skills do not meet the requirements
The above problems all require the operator to make a judgment or feedback to the technical staff, but at present most of the domestic operators do not pay enough attention. For example, when machining a blind hole thread, when the tap is about to contact the bottom of the hole, the operator does not realize that the tap is still fed at the tapping speed when the bottom of the hole is not reached, or the feed is broken due to forced feeding when the chip removal is not smooth, causing the tap to break. . It is recommended that operators strengthen their sense of responsibility.
It can be seen from the above that the causes of tap breakage can be described as various. Machine tools, fixtures, workpieces, processes, chucks and knives, etc. are all possible, and the real reason may never be found on paper alone. As a qualified and responsible tool application engineer, the most important thing is to go deep into the field, not just by imagination.