Tapping is one of the most problematic processing types, and some misoperations during processing will cause the thread tap to break. When using CNC machine tools, the lack of correct tapping operation or inferior taps can easily cause the thread taps to break and cause unnecessary losses.
Now we will analyze some of the main reasons and troubleshooting methods that lead to tap breakage during the tapping process one by one to avoid tap breakage, wear, and other problems in the tapping process.
1. The quality of the thread tap is not good
Possible situations that affect the thread tap’s quality: the primary material, CNC tool design, heat treatment, machining accuracy, coating quality, etc.
For example, the size difference at the thread tap section’s transition is too significant. 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 thread to tap to break during use.
For example, improper heat-treatment process. During the machining tap’s heat treatment, 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.
2. Improper selection of thread taps:
High-quality thread cutting taps should be used for tapping parts with too high hardness, such as cobalt-containing high-speed steel wiretaps, cemented carbide tips, and coated taps. Besides, different tap designs are used in various workplaces.
For example, the number, size, angle, etc., of the chip flute of the metal thread taps impact 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 metal thread taps may break due to their insufficient strength. They cannot resist the cutting resistance of tapping.
The mismatch between the tap and the processed material has been paid more and more attention in recent years.
It is suitable. With the continuous increase of new materials and complex processing, the variety of tool materials also increases to meet this need. This requires choosing the right tap product 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.
3. Excessive wear of the thread tap
Another widespread situation is that after the tap has processed several threaded holes, the cutting resistance becomes more extensive due to the tap’s excessive wear, which causes the tap to be broken.
Countermeasures: First of all, it is recommended to use the Sentaiyinger 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; besides, the use of thread gauges (T /Z) Can easily judge the tap situation.
4. Axial synchronization error
During the machining center’s tapping process, many taps are broken because of the error in the synchronization between the spindle rotation and the axial feed of the machine tool, which increases the axial tension (or pressure) on the taps and causes the taps to break. However, the synchronization error is almost impossible to avoid the machining center’s rigid tapping (or CNC lathe) significantly when the tap is retracted (reversed).
Countermeasures: Use Sentai Inge V handle, which completely solves axial synchronization error compensation for rigid tapping.
5. 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 number 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;
Simultaneously, adjust the cutting parameters appropriately to ensure that the iron filings can be removed smoothly; if necessary, A variable spiral angle tap can be used to ensure that the iron filings can be discharged smoothly.
6. Mismatch between taps and processed materials
This problem has been paid more and more attention recently by thread tap manufacturers.
With the continuous increase of new materials and difficulty processing, the variety of tool materials is also constantly increasing to meet this need. This requires choosing the right tap product before tapping.
For different processing conditions, other processing materials, the types of thread taps selected are also different. The types of cutting taps selected are different for the two different processing conditions of holes and blind holes.
For materials with long chips, such as steel, in the case of a through-hole, select a straight flute tap, and the chips will go down, and in the case of a blind hole, choose a spiral tap. The chips will go up. For short chip materials, such as cast iron, iron chips can be contained in the chip flute, so both holes and blind holes can be processed with straight flute taps.
In another case, the downward chips formed by the left-hand tap are separated. This type of tap is suitable for situations where the workpiece and the tooling are relatively close, and the chip removal space is not enough.
In the production of spot welding machines, we often see that spiral groove taps are used to process through-holes, an incorrect use method. There are three reasons:
First, spiral flute taps are used for upward chip removal. To achieve this effect, the tap’s structure is more complicated, the rigidity is not good, and the chip transmission stroke is long, and it is easy to jam during the spiral flute transmission. Circumstances are causing chipping or breaking.
Second, the number of teeth cutting in front of the two types of taps is not the same. Spiral flute taps generally have 2 to 3 cutting teeth, while straight flute taps have 3 to 5 cutting teeth. The life of the tap is proportional to the number of cutting teeth.
Third, fluted spiral taps are more expensive than straight fluted taps, and the economy is not good. On the other hand, we should choose taps with different geometries for cutting taps and processing different materials. There are various angles on the tap, such as rake angle, relief angle, guide angle, blade inclination, etc.
The design of these angles is based on the characteristics of different materials. For example, steel and cast iron, because the steel chip is relatively long, the tap’s rake angle is designed to be more significant. In contrast, cast iron’s iron filings are generally debris, and the rake angle is relatively small, even 0°.
For example, when processing the M5×0.5 thread of ferrous metal material, a 4.5mm diameter drill should be used to make the bottom hole when using a cutting tap. If a 4.2mm drill is used to make the bottom hole by mistake, tap when tapping. The part that needs to be cut will inevitably increase, causing the tap to break.
The threaded bottom hole diameter is marked in the tap sample, or the formula (bottom hole diameter = thread diameter-pitch) can be used to obtain the bottom hole diameter. For spiral groove taps, the approximate bottom hole diameter can also be calculated according to the formula (bottom hole diameter = thread diameter-pitch/2). For blind holes, the depth of the bottom hole also needs to be considered.
Since the front end of the tap has several cutting teeth, its diameter is relatively small and cannot be regarded as a compelling thread. Therefore, the bottom hole depth should also consider the depth of the cutting teeth and the size of the tap’s pointed end.
In production, there have also been instances where the bottom hole is not deep enough, and the tip of the tap hits the bottom of the hole, causing the tap to break.
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.
8. The workpiece material’s problem is not pure, and there are excessive hard spots or pores in some parts, causing the tap to lose balance and break instantly. (For example, workpieces like cast steel)
9. The machine tool does not meet the machine tap’s accuracy requirements
The machine tool and the clamping body are also essential, especially for high-quality taps. Only a certain precision of the machine tool and the clamping body can exert the tap’s performance.
Commonly, there is not enough concentricity. At the beginning of tapping, the starting position of the tap is incorrect. 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.
10. The quality of cutting fluid and lubricating oil is not good
Many domestic companies have begun to pay attention to this. Many companies that have purchased foreign tools and machine tools have a profound understanding of cutting fluid and lubricating oil and the processed products. The quality is prone to burrs and other undesirable conditions, and the service life will be significantly reduced.
11. Unreasonable cutting speed and feed rate
When machining problems occur, most domestic users reduce the cutting speed and reduce the feed rate to reduce the tap’s advancement. The thread accuracy of its production is significantly reduced.
This increases the thread’s surface roughness, and the threaded aperture and thread accuracy cannot be controlled. Of course, problems such as burrs are 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 more rigid steel; 2-7m/min for stainless steel; 8-10m/min for cast iron. When the same material is used, the smaller tap diameter takes a higher value, and the larger tap diameter takes a lower value.
12. The operator’s technology and skills do not meet the requirements:
The above problems require the operator to make a judgment or give the technician feedback, but most operators in China do not pay enough attention to it.
For example, when processing blind hole threads, the tap is about to touch the bottom of the hole, and 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, 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 solely rely on imagination,
The above are some of the common reasons that cause the tap to break. It is hoped that these problems will be avoided as much as possible during use.
At the same time, when using manual taps, the following points should also be noted.
What should be paid attention to When using thread taps?
When tapping with a tap on the clamp table by hand, pay attention to the following points.
1. Align the tap with the eye hole, a judge with your eyes, and make the tap and the plane of the workpiece perpendicular. The center of the working screw hole should be in a straight line with the tap’s center.
2. Rotate the tap and observe from the front and the side to check whether it is aligned, that is, whether the tap is perpendicular to the working plane. If necessary, use a square ruler to test whether it is aligned from the front and back sides, if it is aligned. , Then rotate the tap for two revolutions and still use the above method to check the alignment.
3. When tapping, if you feel the forward rotation is laborious, do not force the rotation. It would help if you stopped immediately, go backward a quarter turn to remove the chips accumulated around the cutting part of the tap and the hole, and then continue the forward attack.
4. If it is not correct, the tap should be turned upside down and re-aligned. Otherwise, the tapped screw hole will be tilted.
5. The force must be even when tapping. You can hold the wrench with one hand and the tap with the other to rotate it evenly, or press the twist with both hands and rotate it evenly.
6. The spanner used should be suitable for the size of the tap. When it is laborious to twist the spanner, never extend the sleeve on the spanner.
7. After the tapping is completed, a tap cannot be moved back together after loosening the tap with a wrench when the tap is turned back. This should be particularly careful to prevent damage to the thread and the tap in the screw hole.
8. After taking out the tap, pour out the swarf accumulated in the threaded hole or pour it out with oil, take it out with a hook, or blow it out with compressed air. Please do not blow it with your mouth to prevent iron filings from flying into your eyes.
9. When tapping, if there is a rock in the material or cannot be tapped, you can use a three-tap tap to return to the tapped part to reduce the cutting force and then continue to tap with the head tap.
10. When the tap will enter the bottom hole that has been drilled on the workpiece, hold it with your hand to avoid collision between the tap and the workpiece.
11. When tapping on the machine tool, it is best to use a tapping tool with a protective device to prevent the tap from breaking due to excessive force.
12. The tapping length is accurately positioned on the machine tool or tapping tool. The tapping attempt cannot be equal to the depth of the hole. Generally, it should be 1~2 mm less than the bottom hole’s deep, and sometimes it can be smaller. The specific can be based on the standard. Pre-drilling is required.
13. When tapping through-hole threads on the machine tool, it is best to take the tap out through the workpiece instead of turning it out to prevent possible damage to the tapped thread. If the through-hole thread is not tapped, the machine spindle can be rotated in the opposite direction, back out of the tap.