Tap classification, selection, and fracture problems

First, teach you to identify the classification of taps

Tap classification

1. According to the drive different points: hand taps and machine taps

2. According to the processing method: cutting tap and extrusion tap

3. According to the thread to be processed: metric coarse tap, metric fine tap, pipe thread tap, etc.

4. According to its shape, it is divided into straight groove tap, spiral groove tap and screw tip tap.

Straight groove tap

It has the most versatility. The cutting cone can have 2, 4, and 6 teeth. The short cone is used for non-through holes and the long cone is used for through holes. As long as the bottom hole is deep enough, the cutting cone should be used as long as possible, so that the teeth sharing the cutting load are more and the service life is longer.

Spiral groove tap

More suitable for processing non-through hole thread, experience tells us: processing ferrous metal, the spiral angle is chosen to be smaller, generally around 30 degrees, to ensure the strength of the helical teeth. For the processing of non-ferrous metals, the helix angle is chosen to be a little larger, and it can be cut at about 45 degrees.

Content chip tap

Its distinctive feature is to open a large enough chip pocket in the head, using a special design to achieve higher processing quality. Especially in the large thread processing advantages. Widely used in wind power, steam turbines, shipbuilding, mining and other industries.

Screw tap

The chips are discharged forward when the thread is machined, and the threaded taps are preferred for the through-hole threads.

Extrusion tap

According to the method of use, it is often divided into hand taps, machine taps, nut taps (for cutting threads on nut processing machines), die taps (for cutting and correcting die threads), pipe thread taps and taper threads Tap.

Machine and hand taps

It is a standard tap that cuts ordinary threads. In fact, the structure and working principle of the two are basically the same.

Second, how to choose the right tap

Threads are the most common method of joining mechanical parts, and taps are the most common tool for machining internal threads. Correctly selecting the internal thread of the tap can ensure the quality of the threaded connection and improve the service life of the tap.

Select tap tolerance zone

Domestic machine taps are marked with medium diameter tolerance band code: H1, H2, H3 respectively indicate different positions of the tolerance band, but the tolerance values ​​are equal. The tolerance of the hand tap is coded as H4. The tolerance value, pitch and angle error are larger than the machine tap. The material, heat treatment and production process are not as good as the machine tap. H4 can be marked as not required. The internal thread tolerance band grades that can be machined by the tap diameter tolerance band are as follows:

Tap tolerance band code for internal thread tolerance band

H1 4H, 5H

H2 5G, 6H

H3 6G, 7H, 7G

H4 6H, 7H

Some companies use imported taps, and German manufacturers often mark ISO1 4H, ISO2 6H, ISO3 6G (the international standard ISO1-3 is equivalent to the national standard H1-3), so that the tap tolerance is coded and the machined internal thread can be processed. The tolerance bands are marked.

Select the thread system

There are three common types of common threads: metric, imperial, and unified (also known as the US). The metric is a thread with a tooth angle of 60 degrees in millimeters. For example: M8X1-6H represents a metric fine thread with a diameter of 8 mm, a pitch of 1 mm, and a 6H internal thread tolerance band.

Inch is a thread with a tooth angle of 55 degrees in inches. For example, BSW 1/4-20 means 1/4 inch in diameter and coarse pitch is 20 teeth per inch. This thread is currently rarely used.

Another uniform system is a thread with a tooth angle of 60 degrees in inches. The diameter is less than 1/4 inch, commonly used number, from 0 to 12 respectively indicate the diameter specification of 0.06 inch to 1/4 inch. The main use in the United States is still the uniform thread.

Select the type of tap

We often use: straight groove taps, spiral groove taps, screw taps, extrusion taps, and their performance has their own advantages.

Straight groove taps, which have the most versatility, can be processed through or without through holes, non-ferrous metals or ferrous metals, and are the cheapest. But the pertinence is also poor, everything can be done, and nothing is done best. The cutting cone portion can have 2, 4, and 6 teeth, a short cone for the through hole, and a long cone for the through hole. As long as the bottom hole is deep enough, the cutting cone should be used as long as possible, so that the teeth sharing the cutting load are more and the service life is longer.

Spiral groove taps are more suitable for machining non-through-hole threads, and the chips are discharged backwards during processing. Due to the helix angle, the actual cutting front angle of the tap increases as the helix angle increases. Experience tells us that the processing of ferrous metals, the spiral angle is chosen to be smaller, generally around 30 degrees, to ensure the strength of the helical teeth. For the processing of non-ferrous metals, the helix angle is chosen to be a little larger, and it can be cut at about 45 degrees.

Screw tip tap, the chips are discharged forward when the thread is machined. Its core size is relatively large in design, strong in strength, and can withstand large cutting forces. The processing of non-ferrous metals, stainless steel, and ferrous metals is very good, and the threaded taps should be preferred for through-hole threads.

Special tap

There are some special taps, such as tapping taps. It removes one tooth at intervals, and the pressure and friction between the workpiece and the workpiece are small, and the internal thread of the thin-walled member is processed, and the thin-walled member is not deformed. Others include a chip tap with a chip hole in the middle and a large diameter internal thread of tens to hundreds of millimeters.

New internal thread cutter

The most noteworthy is: an internal threading tool used in CNC machining centers, which integrates chamfering, drilling and threading. With the machine tool helical interpolation, the front end of the tool can be drilled, chamfered, side The teeth can be milled with internal threads. A tool can machine screw holes with the same pitch and different diameters. The use of the tool has been expanded, the number of tools has been reduced, and the number of tool changes in the machining center has been greatly reduced.

The extrusion tap is more suitable for processing non-ferrous metals. Unlike the above-mentioned cutting tap, the working principle is that the metal is extruded to deform and form an internal thread. The extruded internal thread metal fiber is continuous, tensile strength, high shear strength, and the surface roughness of the machine is also taught. However, the bottom hole of the extrusion tap is required to be high: too large, the amount of base metal is small, resulting in The thread diameter is too large and the strength is not enough. Too small, the closed extruded metal has nowhere to go, causing the tap to break. The calculation formula is: bottom hole diameter = internal thread nominal diameter - 0.5 pitch.

Third, the analysis and summary of 9 major problems of tap fracture

1. The quality of the tap is not good:

Main materials, CNC tool design, heat treatment, machining accuracy, coating quality and more. For example, the difference in size of the transition of the tap section is too large or there is no design transition fillet to cause stress concentration, and it is easy to break at the stress concentration during use. The cross-section transition at the intersection of the shank and the blade is too close to the weld, resulting in a complex weld stress superimposed on the stress concentration at the cross-section transition, resulting in a large stress concentration, causing the tap to break during use. For example, the heat treatment process is improper. When the tap is heat treated, it may cause cracks in the tap if it is not preheated, quenched or overheated, not tempered in time and cleaned prematurely before quenching. To a large extent, this is also an important reason why the overall performance of domestic taps is not as good as imported taps.

2. The tap is not properly selected:

For high-strength tapping parts, high-quality taps, such as cobalt-containing high-speed steel taps, hard alloy taps, coated taps, etc., should be used. In addition, different tap designs are used in different work situations. For example, the number of chips, the size, the angle, etc. of the tap have an effect on the chip removal performance.

3. The tap does not match the processed material:

This problem has received more and more attention in recent years. In the past, domestic manufacturers always felt that the import was good and the price was good. In fact, it was suitable. As new materials continue to increase and are difficult to machine, the variety of tool materials is constantly increasing to accommodate this need. This requires the selection of a suitable tap product before tapping.

4. The bottom hole diameter is too small:

For example, when machining a black metal material M5×0.5 thread, the cutting tap should use a drill hole with a diameter of 4.5 mm to make a bottom hole. If a 4.2 mm drill bit is misused to make a bottom hole, the cutting part of the tap must be increased when tapping. And then break the tap. It is recommended to select the correct bottom hole diameter according to the type of tap and the material of the tapping piece. If the drill bit is not fully matched, you can choose a larger one.

5. Attack material problem:

The material of the attack piece is not pure, and there are too hard points or pores in the part, which causes the tap to lose balance and break.

6. The machine does not meet the precision requirements of the tap:

Machine tools and clamping bodies are also very important, especially for high-quality taps, as long as the machine tool and the clamping body of a certain precision can achieve the performance of the tap. It is common that the concentricity is not enough. At the beginning of tapping, the tap is not positioned correctly, that is, the spindle axis 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 break.

7. Cutting fluid, the quality of lubricating oil is not good:

Many domestic enterprises have begun to pay attention to it. Many companies that have purchased foreign tools and machine tools have a very deep understanding. The quality of the cutting fluid and lubricating oil is problematic. The quality of the processed products is prone to burrs and other life problems. There will also be a big reduction.

8. Cutting speed and feed rate are unreasonable:

When there is a problem in processing, most domestic users are reducing the cutting speed and reducing the feed rate, so that the pushing force of the tap is reduced, and the thread precision of the production is greatly reduced, thereby increasing the roughness of the thread surface, the thread. Aperture and thread accuracy are uncontrolled, and problems such as burrs are of course more inevitable. However, if the feed speed is too fast, the resulting excessive torque will easily cause the tap to break. The cutting speed during machine attack is 6-15m/min for general steel; 5-10m/min for quenched and tempered steel or harder steel; 2-7m/min for stainless steel; and 8-10m/min for cast iron. In the same material, the diameter of the tap is slightly higher, and the diameter of the tap is larger.

9. Operator skills and skills do not meet the requirements:

All of the above problems require the operator to make judgments or feedback to the technical staff, but at present most of the operators in China do not pay enough attention. For example, when machining a blind hole thread, when the tap is about to contact the bottom of the hole, the operator does not realize that the tapping speed is still given when the tap is not reached, or the chip is broken when the chip is not smooth. . It is recommended that operators strengthen their sense of responsibility.

It can be seen from the above that the causes of tap breaks can be varied, such as machine tools, fixtures, workpieces, crafts, chucks and knives, etc., and the real reason may never be found on paper alone. As a qualified and responsible tool application engineer, the most important thing is to go deep into the field, not just imagine.

Fourth, netizens teach you how to identify the pros and cons of the tap

There are many taps on the market. Because of the different materials used, the price of the same specification is also quite different, so that the purchaser looks like a fog, I don’t know which one to buy. Here are a few simple ways to teach you:

Step / method

See if the thread cutting edge (chamfering) at the front end of the tap groove is uniform, and whether there is a fast opening in the cutting groove, the good shape is a positive 7-shape, and the bad one is inverted 7 or U-shaped (it will cause two cuts when exiting the wire tapping, Easy to break and affect the accuracy of the thread

Detecting the heat treatment condition: the drawing cone is parabolic in the air (about 5 meters), whether it is broken under the flat line, and the breaking indicates that the brittleness is large.

Knock the tap and see that the fracture is obliquely long. The grain in the fracture (metallographic structure 10.5#) is fine, indicating that the heat treatment and material are good, flat or oblique, and the grain (metallographic structure) is not measured. it is good.

Precautions

The quality of the tap depends mainly on its original material, heat treatment, groove shape, precision, equipment, speed and material to be processed, hardness, quality of the operating staff, etc., and more! When selecting the tap, pay special attention to the original material of the tap, heat treatment and groove type. For different processing holes, it is recommended to select different types of taps!

In practice, it is very important to grind the cutting edge. Especially for the stainless steel series, it can be divided into several times, and the length of the guide should be lengthened. The cutting edge should be ground to the lower corner to increase the strength of the tap. At the same time, cooling and lubrication should be Keep up (using the pump), the service life of the tap is also relatively long! In short, it is specifically treated on a case-by-case basis.

Five, tap product recommendation

OSG 2014 new product: ALL-MIGHT all-round tap

In the future, it will be almost all of the processing materials such as mild steel, stainless steel, carbon steel, alloy steel and aluminum alloy; or tapping machines, general-purpose machines, machining centers, existing processing machinery worldwide; or from 5 ~80m / min such a large span of processing conditions. Only one OSG A tap can be used with ease. In addition, in order to correspond to a larger customer base, in 2014, the A tap introduced a new DIN standard and a long handle.

Features and advantages:

·Important sharp tip style

·Highly wear resistant CPM material

·V coating with high abrasion resistance

·Good chip evacuation unequal guide groove design

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