Why is the Machine Tap Broken Again?

Why is the Machine Tap Broken Again?

Maybe All technicians engaged in machining have encountered the breakage of machine tap. Why is your tap broken again? For check the following 9 reasons:

1. The Machine tap is bad quality.

Main raw material, the design of CNC tool, heat treatment, machining precision, the quality of coating, etc.

For example:

The difference in size at the transition of the tap section is too large or no transition fillet is designed, which leads to stress concentration, then it’s easy to fracture at the stress concentration. The section transition at the junction of shank and flute is too close to the weld joint, resulting in the superposition of complex welding stress and stress concentration at the section transition, resulting in larger stress concentration, then leads to a fracture in use.

The heat treatment process is improper. During heat treatment of taps, cracks may occur if the taps are not preheated before quenching, or quenching is overheated or burnt, if tempering is not carried out in time, and if cleaning is carried out too early.  To a large extent, this is also an important reason why the overall performance of domestic taps is inferior to that of imported taps.

What’s the Heygo Machine taps’ raw material and heat treatment?

Material: HSS-Vanadium, custom made by our supplier according to DIN standard, with good red hardness and better wear resistance, same with Japan brand.

Salt Bath Heat treatment: Two times preheating, quenching in different temperature, stepped cooling, 3-4 times tempering. Quenching 5-10 degree, tempering 3-5 degree higher than the competitor, precision management ensure the heat treatment stability.

2. The choice of machine tap is unsuitable.

For workpiece with high hardness, high-quality machine taps should be selected, such as cobalt-containing high-speed steel machine taps, solid carbide machine taps, coated machine taps, etc. In addition, different tap designs are applied in different working situations. For example, the number, size, and angle of the chip groove of the tap have an impact on the chip removal.

3. The machine tap could not be matched with working material.

In recent years, more and more attention has been paid to this problem. In the past, domestic manufacturers always thought imported goods were good and expensive ones were good. Actually, suitable ones are good. With the increasing number of new material and the difficulty of machining, the variety of cutting tool material is also increasing in order to meet this need. So it requires selecting a kind of suitable machine tap before tapping.

4. The diameter of the bottom hole is small.

For example, when processing M5×0.5 threads of ferrous metal material, the cutting tap should be used with a 4.5mm diameter drill bit to make the hole. If the 4.2mm drill bit is misused, the part that the machine tap needs to cut during tapping will inevitably increase, thus causing the tap to break. It is suggested to choose the correct diameter of the bottom hole according to the type of tap and the material of the workpiece. If there is no completely matching drill bit, the larger one can be selected.

5. Material of Workpiece

The cutting workpiece is made of impure material, with some hard points or pores, which causes the tap to lose balance and break off instantly.

6. The machine tool could not meet the precision requirements of machine tap.

Machine tools and chucks are also very important, especially for high-quality taps, only a certain precision machine tools, and chucks can give full play to performance.  The common problem is not sufficient concentricity. At the beginning of tapping, the starting position of machine tap is not correct, i.e. the principal axis is not in the same line as the center line of the bottom hole, and the torque is too large during tapping, which is the main reason about tap broken.

7. Cutting fluid and lubricating oil is of poor quality.

Many domestic enterprises have begun to pay attention to this point. Many companies that have purchased foreign cutting tools and machine tools have a deep understanding. If the quality of cutting fluid and lubricating oil has problems, the quality of processed products is prone to burrs and other undesirable conditions. At the same time, the service life will be greatly reduced.

8. Cutting speed and feed are not reasonable.

When problems occur in the process, most users in China reduce cutting speed and feed, so the propulsive force is reduced, and the thread precision is greatly reduced, thus increasing the roughness of thread surface, making the thread diameter and precision uncontrollable, and burrs or other problems inevitable. However, when the feed speed is too high, then causing high torque will make the machine tap easily break. Generally, the cutting speed of steel during machining is 6-15m/min. Quenched and tempered steel or harder steel is 5-10m/min. Stainless steel is 2-7m/min. Cast iron is 8-10m/min. For the same material, the smaller the tap diameter, the bigger the number, and the larger the smaller.

9. The technology and skills of the operator did not meet the requirements.

All these problems need operators to make judgments or feedback to technicians, but at present most of the domestic operators do not pay enough attention to them. For example, when processing blind hole threads, the tap is about to touch the bottom of the hole, while the operator does not realize and still use the cutting speed as before. Or the tap is broken due to forcing to feed when chip removal is not smooth. It is suggested that operators should strengthen their sense of responsibility.

From the above, it can be seen that there are many causes for machine tap breakage. Machine tools, chucks, workpieces, techniques, and tools are all possible. The real causes may never be found by mere theory. As a qualified and responsible tool engineer, the most important thing is to go deep into the site and not just imagine.