Analysis on the Causes of Tap Fracture

1. The operator’s technology and skills do not meet the requirements:

The above problems need operators to make judgments or feedback to technicians, but most domestic operators do not pay enough attention to them at present. For example, when processing blind hole threads, when the tap is about to contact the hole bottom, the operator is not aware that the tap is still fed at the tapping speed when the hole bottom is not reached, or forced feeding when chip removal is not smooth, causing the tap to break. It is suggested that the operators should strengthen their sense of responsibility.

2. 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 the machine tools and clamping bodies with a certain accuracy can give play to the performance of taps. 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 spindle axis is not concentric with the centerline of the bottom hole, and the torque is too large during tapping, which is the main reason for the tap breaking.

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 thought that imports were good and expensive, but in fact they were suitable. With the continuous increase of new materials and difficult machining, in order to meet this need, the variety of tool materials is also increasing. It is necessary to select appropriate tap products before tapping.

4. Poor tap quality:

Main materials, tool design, heat treatment, machining accuracy, coating quality, etc. For example, the size difference at the transition of tap section is too large or no transition fillet is designed, resulting in stress concentration, which is easy to fracture at the stress concentration when using. The section transition at the junction of the handle and the blade is too close to the weld crater, resulting in the superposition of complex welding stress and the stress concentration at the section transition, resulting in large stress concentration, which leads to the fracture of the tap in use. For example, improper heat treatment process. During the heat treatment of tap, if the tap is not preheated before quenching and heating, the quenching is overheated or burnt, the tap is not tempered in time, and the tap is cleaned too early, cracks may occur on the tap. This is also an important reason why the overall performance of domestic taps is inferior to that of imported taps.

5. Improper tap selection:

High quality taps should be selected for tapping parts with too high hardness, such as cobalt high speed wire taps, carbide taps, coated taps, etc. In addition, different tap designs are used in different working situations. For example, the number, size and angle of the chip removal slot of the tap have an impact on the chip removal performance.

6. The cutting speed and feed rate are unreasonable:

When problems occur in processing, most domestic users reduce the cutting speed and feed rate, so that the driving force of the tap is reduced, and the thread accuracy of its production is greatly reduced. This increases the roughness of the thread surface, and the diameter and accuracy of the thread can not be controlled. Of course, problems such as burrs are unavoidable. However, if the feed speed is too fast, the resulting torque is too large and the tap is easy to break. Cutting speed during machine tapping, generally 6-15m/min for steel; 5-10m/min for quenched and tempered steel or hard steel; 2-7m/min for stainless steel; 8-10m/min for cast iron. For the same material, the higher value shall be taken for smaller tap diameter, and the lower value shall be taken for larger tap diameter.

7. The bottom hole diameter is too small:

For example, processing ferrous material M5 × When 0.5 thread is used, the cutting tap should be used to drill the bottom hole with a 4.5mm diameter drill bit. If a 4.2mm drill bit is used to drill the bottom hole by mistake, the cutting part of the tap must be increased during tapping, thus breaking the tap. It is recommended to select the correct bottom hole diameter according to the type of tap and the material of tapping parts. If there is no fully compliant drill, a larger one can be selected.

8. Tapping material problem:

The tap material is impure, and there are some hard spots or air holes in some parts, which causes the tap to lose balance instantly and break.

9. Poor quality of cutting fluid and lubricating oil:

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 understanding. The quality of cutting fluid and lubricating oil has problems, and the quality of processed products is prone to burrs and other undesirable conditions. At the same time, the service life will also be greatly reduced.

There are many reasons for the tap fracture. It is necessary to conduct specific analysis based on the site conditions to find the real reason.