Introduction

The utility model relates to a cutter for processing internal thread, which is provided with a groove along the axial direction. It’s also called a screw tap. Taps are

Carbide Tap

divided into straight groove taps, spiral groove taps and spiral point taps (tip taps) according to their shapes.

The straight groove tap is easy to process, with low precision and high output. It is generally used for thread processing of ordinary lathe, drilling machine and tapping machine, with slow cutting speed. Spiral groove taps are mostly used for drilling blind holes in CNC machining centers, with fast processing speed, high precision, good chip removal and good alignment. There is a chip holding groove in the front of the screw tap, which is used to process through holes.

Most of the taps provided by the tool factory are coated taps, which greatly improves the service life and cutting performance compared with uncoated taps. The cutting load distribution of taps with unequal diameter design is reasonable, the machining quality is high, but the manufacturing cost is also high. Trapezoidal thread taps often adopt unequal diameter design.

Component

Machine and hand taps are standard taps for cutting common threads. Chinese tool manufacturersAnchor icon usually call high-speed steel grinding tap as machine tap, and carbon tool steel or alloy tool steel rolling (or cutting) tap as hand tap. In fact, their structure and working principle are basically the same. Generally, the tap is composed of working part and handle. The working part is divided into cutting part and calibration part. The former is grinded with cutting cone to undertake cutting work, while the latter is used to calibrate the size and shape of thread.

Purpose

It is used for processing common internal thread of nut or other machine parts (tapping). Machine tap usually refers to high speed steel grinding tap, which is suitable for tapping on machine tool; Hand tap refers to carbon tool steel or alloy tool steel rolling (or incisor) tap, suitable for manual tapping.

Tap is a kind of cutting tool for processing various medium and small size internal threads. It has simple structure and is easy to use. It can be operated by hand or on machine tools. It is widely used in production.

For small internal thread, tap is almost the only tool. The types of taps are: hand taps, machine taps, nut taps, extrusion Taps, etc.

Tapping is a relatively difficult processing procedure, because the tap is almost buried in the workpiece for cutting, the processing load of each tooth is greater than other tools, and the tap along the thread and the workpiece contact surface is very large, when cutting the thread, it must contain and remove chips, therefore, it can be said that the tap works under very bad conditions. In order to make the tapping work smoothly, all kinds of problems should be considered in advance. Such as the performance of the workpiece material, what kind of tool and machine tool to choose, how high cutting speed to choose, feed rate, etc.

Tapping on special workpiece materials

The machinability of workpiece material is the key to tapping. Now the main concern of tap manufacturers is to develop taps for special material processing. According to the properties of these materials, the geometry of the cutting part of the tap is changed, especially its rake angle and the amount of dent (hook) – the degree of dent in the front.

The maximum processing speed is sometimes limited by the performance of the machine tool. For smaller taps, the spindle speed may have exceeded the maximum spindle speed in order to reach the ideal speed [RPM = (sfm x 3.8) / tap diameter].

On the other hand, high speed cutting with a larger tap will produce a larger torque, which may be greater than the horsepower provided by the machine tool. The cutting speed can reach 250 SFM with 700 psi internal cooling tool. On the other hand, the cutting speed of the machine tool without internal cooling facilities can only reach 150 SFM. The tap is different from most metal cutting tools, because it has a very large contact area with the hole wall of the workpiece, so cooling is very important.

If the high-speed steel tap overheats, the tap will break and burn. The geometric characteristics of Noris high-performance tap are large back angle and inverted tap.

The service life of the taps can be greatly improved by the geometric shape of the taps mentioned above combined with special coating surfaces (such as tin, TiCN, CrN or TiAlN). These heat-resistant, smooth coatings reduce the cutting force and allow tapping at higher cutting speeds. In fact, the development of new high-performance taps has greatly improved the speed and power of machine tool spindle.

Carbide tap

As cemented carbide toolsAnchor icon gradually replace high-speed steel tools in turning, cemented carbide taps are more and more used in threaded hole processing. Compared with high-speed steel, cemented carbide has high hardness and brittleness. Tapping with cemented carbide taps has the problem of chip treatment. However, cemented carbide tap for processing cast iron and aluminum alloy materials, its use effect is very good, the main form of tap damage is mechanical wear.

As the automobile industry processes a large number of cast iron and aluminum alloy parts, cemented carbide taps are used to obtain long tool life. When machining workpieces of these materials, the service life of cemented carbide taps is longer than that of high speed steel taps.

In the automotive industry, the reduction of tool change time is an important factor, and the long life of cemented carbide wire will minimize the tool change time. The effect is very good when the surface coated carbide tap with small helix angle is used to tap the aluminum alloy workpiece with silicon content of 8% – 12%.

The taps made of submicron grain cemented carbide can increase the toughness of the cutting tool without reducing its hardness, which is very effective in cutting hardened steel, plastics and difficult to machine nickel base alloy.

The dl15ni series nickel alloy special taps produced by Noris company can continuously tap more than 200 screw holes on Inconel 718 under certain conditions, which can only be achieved by regrinding before.

Characteristic

Taps are usually divided into single or group taps. Small and medium sized through hole threads can be tapped with a single tap at one time. When processing blind holes or large-size screw holes, group taps are commonly used, that is, more than two taps are used to complete the processing of one screw hole in turn. There are two kinds of design of group taps: equal diameter and unequal diameter. For taps of equal diameter design, only the length of each tap is different; For the taps with unequal diameter design, the sizes of each thread are different, and only the last one has complete tooth profile.

Tap classification

  • According to different driving: hand tap and machine tap
  • According to the processing method: cutting tap and extrusion tap
  • According to the processed thread: metric coarse tap, metric fine tap, pipe thread tap, etc
  • According to its shape, it can be divided into straight groove tap, spiral groove tap and spiral point tap
  • According to the tapping direction of tap, it can be divided into parallel tap and reverse tap

Tap type

  • Straight groove tap: The straight groove tap has the best versatility and the strongest rigidity. Therefore, generally in the processing of materials with higher hardness (such as: quenched steel above 40HRC) and chips with powder particles (such as cast iron and cast aluminum), straight groove taps are preferred.
  • Spiral groove tap: Spiral groove taps are more suitable for processing through-hole threads (also known as blind holes), and the chips are discharged upward during processing. Because of the helix angle, the actual cutting rake angle of the tap will increase with the increase of the helix angle. Experience tells us: for materials with high hardness, the helix angle should be selected smaller, generally around 30 degrees, so as to ensure its own rigidity and prolong the life of tap. When processing non-ferrous metals, such as copper, aluminum, magnesium and zinc, which are not very hard, the helix angle should be larger, which can be about 45 degrees. The cutting is sharper, which is conducive to chip removal.
  • Edge angle tap: When machining thread, the chip is discharged forward, and the edge angle tap is preferred for through-hole thread. Because its design is based on the straight groove tap, and then use the grinding wheel to cut a cut obliquely at the edge, so its own rigidity can be comparable to the straight groove tap.
  • Extrusion tap: Different from the first three types of cutting taps, the extrusion taps are processed through the plastic deformation of the material itself, and the internal thread shape is extruded in the bottom hole by extrusion. Therefore, the processing material should not be too hard. The advantage of this method is that it does not produce chips, so 90% of the machining problems can be eliminated. However, due to extrusion molding, there is a small groove on the top of the processed internal thread, so it is not suitable for the work with higher sealing requirements.

How to use tap?

  • When tapping, first insert the tap to make the tap center line consistent with the drilling centerline.
  • Rotate the two hands evenly and add a little pressure to make the tap feed, and there is no need to add pressure after feed.
  • Each time the tap is turned, it reverses about 45 ° To cut off the chips to avoid blocking.
  • If the tap is difficult to rotate, do not increase the rotating force, otherwise, the tap will break.

How to choose taps?

Thread is the most common method to connect mechanical parts, and tap is the most commonly used tool to process internal thread. Proper selection of taps for internal thread processing can ensure the quality of thread connection and improve the service life of taps.

Select tap tolerance zone

All domestic machine taps are marked with pitch diameter tolerance zone Codes: H1, H2 and H3 respectively indicate the same position of tolerance zone, but the tolerance values are different.

The tolerance zone code of hand tap is H4, the tolerance value, pitch and angle error are larger than machine tap, and the material, heat treatment and production process are not as good as machine tap. H4 may not be marked according to regulations.

The grade of tolerance zone of internal thread that can be processed by pitch diameter tolerance zone of tap is as follows: the code of tolerance zone of tap is applicable to the grade of tolerance zone of internal thread

H1 4H、5H
H2 5G、6H
H3 6G、7H、7G
H4 6H、7H

Some enterprises use imported taps. German manufacturers often mark them as iso14h, iso26h and iso36g (international standard iso1-3 is equivalent to national standard h1-3). In this way, the code of tolerance zone of taps and the tolerance zone of Machinable internal threads are marked.

How to choose the standard of tap thread?

There are three common systems of common thread: metric system, English system and unified system (also known as American system). Metric system is a thread with 60-degree tooth angle in mm. For example: m8x1-6h represents the tolerance zone of 8 mm diameter metric fine thread, 1 mm pitch and 6h internal thread.

Inch system is a thread with 55-degree tooth angle in inches. For example: BSW 1 / 4-20 means 1 / 4-inch diameter, coarse pitch 20 teeth per inch, this thread is rarely used. Another unified system is in inches, tooth angle of 60 degrees of thread.

The diameter is less than 1 / 4 inch, which is usually indicated by numbers. From No. 0 to No. 12, the diameter specifications are 0.06 inch to 1 / 4 inch respectively. The United States still mainly uses unified thread.