Top 10 Reasons and Solutions for Tap Breaks

What causes the tap to break during the tapping process? Today I will list the following 10 reasons and solutions for your reference in your work.

  • The tap quality is not good

Main materials, CNC tool design, heat treatment conditions, machining 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 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 and heating, quenching is overheated or burned, not tempered in time, and 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.

Countermeasures: Choose high-quality and reliable tap brands and more suitable tap series.

  • Improper selection of taps

High-quality taps should be used for tapping parts that are too hard, such as cobalt-containing high-speed steel taps, cemented carbide taps, and coated taps. In addition, different tap designs are used in different workplaces. For example, the number, size, angle, etc. of the chip flute of the tap have an impact on the chip removal performance.

For difficult-to-machine materials such as precipitated 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 taps and the processed materials has been paid more and more attention in recent years. In the past, domestic manufacturers always felt that the imported ones were better, and the expensive ones were better. With the continuous increase of new materials and difficulty in processing, in order to meet this need, the variety of tool materials is also constantly increasing. This requires the selection of suitable tap products before tapping.

Countermeasures: Use high-strength material taps (such as powdered high-temperature steel, etc.) to increase the strength of the tap itself; at the same time, improve the surface coating of the tap to increase the surface hardness of the wire; in extreme cases, even manual tapping may be a feasible method.

  • Excessive tap wear

Another very common situation is that after the tap is processed with several threaded holes, the cutting resistance becomes larger due to the excessive wear of the tap, which causes the tap to be broken.

Countermeasures: First, it is recommended to use the V handle, which will significantly delay the wear of the tap, thereby increasing the service life of the tap; at the same time, the use of high-quality tapping lubricants can also effectively delay the wear of the tap; in addition, use a thread gauge (T/Z) can easily judge the tap situation.

  • Axial synchronization error

During the tapping process of the machining center, a large number of taps are broken because of the error in the synchronization between the spindle rotation and the axial feed of the machine tool, which makes the axial tension (or pressure) of the taps increase, causing the taps to break. The synchronization error is almost impossible to completely avoid for rigid tapping in machining centers (or CNC lathes), especially when the tap is retracted (reversed).

Countermeasures: Use the V handle, which completely solves the problem of axial synchronization error compensation for rigid tapping.

  • Difficult chip breaking and chip removal

For blind hole tapping, the spiral groove rear chip discharge tap is usually used. If the iron filings are wound on the tap and cannot be discharged smoothly, the tap will be broken, and a large amount of processed materials (such as steel and stainless steel and high-temperature alloys) will be tapped. Processing is usually difficult to break chips.

Countermeasures: First consider changing the helix angle of the tap (usually there are several different helix angles available), try to make the iron filings can be removed smoothly; at the same time adjust the cutting parameters appropriately, the purpose is to ensure that the iron filings can be eliminated smoothly; if necessary A variable spiral angle tap can be used to ensure that the iron filings can be discharged smoothly.

  • The bottom hole diameter is too small

For example, when machining M5×0.5 threads of ferrous metal materials, when using a cutting tap, a 4.5mm diameter drill should be used to make the bottom hole. 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. , And then break the tap. It is recommended to choose the correct diameter of the bottom hole according to the type of tap and the material of the tapping part. If there is no suitable drill bit, you can choose a larger one.

  • Material problem of attacking parts

The material of the tapping part is impure, and there are excessive hard spots or pores in some parts, which cause the tap to lose balance and break instantly.

  • The machine 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 axis of the spindle 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 to break.

  • The quality of cutting fluid and lubricating oil is not good

Many companies that have purchased foreign tools and machine tools have a very deep experience. The quality of cutting fluids and lubricating oils has problems, and the quality of processed products is prone to burrs and other bad conditions. At the same time, the service life There will also be a great reduction.

  • 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 is greatly reduced, which increases the surface roughness of the thread. 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. For the same material, the smaller tap diameter takes a higher value, and the larger tap diameter takes a lower value.

The above problems require the operators to make judgments or give feedback to the technicians, but most of the domestic operators do not pay enough attention to them. 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 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 a tap. Machine tools, fixtures, workpieces, processes, chucks and tools, etc. are all possible. You may never find the real cause just by talking about it on paper. As a qualified and responsible tool application engineer, the most important thing is to go to the site, not just rely on imagination. Whether you want to find the carbide taps or threading inserts, you can contact us.

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