1、 Reasons for the fracture of machine tool taps

1. Poor quality of machine tool taps

Main materials, CNC tool design, heat treatment conditions, machining accuracy, coating quality, etc. For example, if the size difference at the transition point of the tap section is too large or there is no designed transition fillet, stress concentration may occur, which can lead to fracture at the stress concentration point during use.

The distance between the section transition at the junction of the handle and the blade and the weld is too close, resulting in complex welding stress and stress concentration at the section transition overlapping, causing significant stress concentration and leading to the fracture of the tap during use. For example, improper heat treatment process. During the heat treatment of the tap, if it is not preheated before quenching, overheated or burnt during quenching, not tempered in time, and cleaned too early, it may lead to 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.

2. Improper selection of machine tool taps

High quality machine tool taps, such as cobalt containing high-speed steel wire taps, hard alloy taps, coated taps, etc., should be selected for tapping parts with excessive hardness. In addition, different tap designs are applied in different work environments. For example, the number, size, angle, and other factors of the chip removal groove of the machine tool tap have an impact on the chip removal performance

3. The machine tool tap does not match the material being processed

This issue has received increasing attention in recent years. Previously, domestic manufacturers thought that imported goods were good and expensive, but in fact, they were suitable and good. With the continuous increase and difficulty in processing of new materials, the variety of tool materials is also constantly increasing to meet this demand. This requires selecting a suitable tap product before tapping.

4. The bottom hole diameter is too small

For example, when processing M5 × 0.5 threads of black metal material, a cutting machine tap should be used to drill the bottom hole with a 4.5mm diameter drill bit. If a 4.2mm drill bit is mistakenly used to drill the bottom hole, the part that the tap needs to cut will inevitably increase during tapping, causing the tap to break. It is recommended to choose the correct diameter of the bottom hole based on the type of tap and the material of the workpiece. If there is no drill bit that fully meets the requirements, a larger one can be chosen.

5. Material issues with the attacking components

The material of the tapping is impure, with some areas having hard spots or pores, causing the tap to instantly lose balance and break.

6. The machine tool did not meet the accuracy requirements of the tap

Machine tools and clamping bodies are also very important, especially for high-quality taps. Only machine tools and clamping bodies with a certain precision can fully utilize the performance of taps. The common issue is insufficient 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, resulting in excessive torque during the tapping process, which is the main reason for the tap to break.

7. Poor quality of cutting fluid and lubricating oil

Many domestic enterprises have begun to pay attention to this point, and many companies that purchase foreign cutting tools and machine tools have a very profound experience. If there are quality problems with cutting fluids and lubricants, the quality of the processed products is prone to defects such as burrs, and the service life will also be greatly reduced.

8. Unreasonable cutting speed and feed rate

When there are problems with machining, most domestic users reduce the cutting speed and feed rate, resulting in a decrease in the pushing force of the tap and a significant reduction in the accuracy of the produced threads. This increases the roughness of the thread surface, making it difficult to control the diameter and accuracy of the threads. Problems such as burrs are also inevitable. However, if the feed speed is too fast, the excessive torque can also easily cause the tap to break. The cutting speed during machine attack is generally 6-15m/min for steel materials; The speed for quenched and tempered steel or harder steel materials is 5-10m/min; Stainless steel is 2-7m/min; Cast iron is 8-10m/min. When using the same material, a smaller tap diameter is taken as the higher value, and a larger tap diameter is taken as the lower value.

9. The operator's skills and techniques did not meet the requirements

The above issues require operators to make judgments or provide feedback to technical personnel, but currently the vast majority of operators in China do not pay enough attention to them. For example, when processing blind hole threads, at the moment when the tap is about to contact the bottom of the hole, the operator is not aware and still feeds in at the tapping speed before reaching the bottom of the hole, or forcibly feeds in when chip removal is not smooth, causing the tap to break. Suggest that operators strengthen their sense of responsibility.

As can be seen from the above, there are various reasons that can cause tap breakage, such as machine tools, fixtures, workpieces, processes, clamps, and cutting tools, etc. It may never be possible to find the real cause just by talking on paper. As a qualified and responsible tool application engineer, the most important thing is to go deep into the field, not just rely on imagination. For example, if the length of the cutting cone of a tap is too long and it hits the bottom of the bottom hole during tapping, it will break. If you don't go deep into the site and only rely on guessing the tap performance, workpiece material, processing technology, and so on, how can you know

In fact, neither traditional tapping equipment nor expensive CNC equipment can effectively solve the above problems in principle. Because the machine cannot recognize the working condition of the tap and the most appropriate torque required, it will only repeatedly process according to pre-set parameters. Only use a thread gauge to check the processed part at the end