There are many reasons for the breakage of a tap. Machine tools, fixtures, workpieces, processes, chucks and tools, etc. are all possible. You may never find the real reason just by talking about it. As a qualified and responsible tool application engineer, the most important thing is to go to the site, not just rely on imagination.
1. Reasons for the breakage of machine tool taps
1. The quality of machine tool taps is not good
Main materials, CNC tool design, heat treatment, machining accuracy, coating quality, etc. For example, the size difference of the transition part 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 point during use.
The section transition at the junction of the shank and the blade is too close to the welding port, which leads to the superposition of complex welding stress and the stress concentration at the section transition, resulting in a large stress concentration, which causes the tap to break during use. For example, improper heat treatment process. During the heat treatment of the tap, if it is not preheated before quenching, overheated or overfired, tempered not in time, and cleaned 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 selection of machine tool taps
High-quality machine tool taps should be selected for tapping parts with too much hardness, such as cobalt-containing high-speed steel taps, carbide taps, and coated taps. In addition, different tap designs are used in different workplaces. For example, the number, size, angle, etc. of chip flutes of machine tool taps have an impact on chip removal performance
3. The machine tap does not match the processed material
This issue has received more and more attention in recent years. In the past, domestic manufacturers always felt that imported goods were good, but expensive goods were good. In fact, they were suitable. With the continuous increase of new materials and difficulty in processing, in order to meet this need, the variety of tool materials is also increasing. This requires choosing the right tap product before tapping.
4. The bottom hole diameter is too small
For example, when machining M5×0.5 threads of ferrous metal materials, the tap of a cutting machine tool should be used to make the bottom hole with a 4.5mm diameter drill bit. If a 4.2mm drill bit is used to make the bottom hole by mistake, the cutting part of the tap will inevitably increase during tapping. Large, which in turn causes the tap to break. It is recommended to select 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
The material of the tapping part is impure, and there are excessive hard spots or pores locally, which causes the tap to lose balance and break instantly.
6. The machine tool does not meet the accuracy requirements of the tap
Machine tools and clamping bodies are also very important, especially for high-quality taps. only a certain precision of machine tools and clamping bodies can exert the performance of the tap. It is common that there is not enough concentricity. At the beginning of tapping, the starting position of the tap is incorrect, that is, the spindle axis 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 tap to break.
7. Cutting fluid and lubricating oil are of poor quality
Many domestic companies have begun to pay attention to this point. Many companies that have purchased foreign tools and machine tools have a very deep experience. The quality of cutting fluids and lubricants has problems, and the quality of processed products is prone to burrs and other bad conditions. There will also be a great reduction.
8. Unreasonable cutting speed and feed
When there is a problem in processing, most domestic users reduce the cutting speed and reduce the feed rate, so that the pushing force of the tap is reduced, and the precision of the thread produced by it 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 inevitable. However, if the feed speed is too fast, the resulting torque is too large, which can easily cause the tap to 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; 8-10m/min for cast iron. In the case of the same material, the smaller tap diameter takes a higher value, and the larger tap diameter takes a lower value.
9. The operator's technology and skills did not meet the requirements
All of the above problems require the operators to make judgments or give feedback to the technicians, but at present, most operators in China do not pay enough attention to them. For example, when machining blind hole threads, when the tap is about to touch the bottom of the hole, the operator does not realize that it is still fed at the tapping speed when the bottom of the hole is not reached, or the tap is broken by forced feeding when chip removal is not smooth. . It is recommended that operators strengthen their sense of responsibility.
It can be seen from the above that there are many reasons for the breakage of the tap. Machine tools, fixtures, workpieces, processes, chucks and tools, etc. are all possible. You may never find the real reason just by talking about it. As a qualified and responsible tool application engineer, the most important thing is to go to the site, not just rely on imagination. 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 site, just guess how the tap performance, workpiece material, processing technology, etc. know how to know
In fact, neither traditional tapping equipment nor expensive CNC equipment can solve the above-mentioned problems in principle. Because the machine cannot identify the working condition of the tap and the most appropriate torque required, it will only repeat the processing according to the preset parameters. only use the thread gauge at the end to detect the processed
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