CNC Machining and CNC Machine Tools

Robot necessary, tap type selection, fracture analysis Daquan

First, teach you to identify the classification of taps

Tap classification

  1. according to the driver of different points: hand taps and machine taps
  2. according to machining methods: cutting taps and extrusion Taps
  3. according to the processed thread: metric coarse tooth tap, metric fine tooth tap, pipe thread tap, etc.
  4. according to its shape can be divided into straight slot tap, spiral groove tap and spiral point tap

Straight slot tap

It is the most versatile, cutting cone part can have 2,4,6 teeth, short cone for blind hole, through hole for a long cone. As long as the bottom hole deep enough, you should try to choose the cutting cone is longer, so to share the load of cutting tooth number, long service life.

Spiral groove tap

Suitable for machining screw thread blind hole, experience tells us: the processing of black metal, spiral angle selected smaller, generally at about 30 degrees, ensure the spiral tooth strength. Machining nonferrous metal, spiral angle is selected larger, at around 45 degrees, sharp cutting.

Chip tap

The salient feature is a large enough groove in the head, the processing quality by special design to achieve high. Especially in the thread processing advantages significantly. Widely used in wind power turbine, shipbuilding, mining, oil and other industries.

Tap tap

When the thread is machined, the chip is discharged forward, and the threaded tap shall be preferred to the threaded tap

Extrusion tap

According to the method of use, often divided into hand taps, machine taps, nut taps (used for thread cutting in nut machine), die tap (used for cutting and correcting die thread), pipe thread tap and taper thread tap.

Machine and hand tap

It is a standard tap for cutting ordinary thread. In fact, the structure and working principle of the two are basically the same

Two, how to choose the appropriate tap

The thread is the most common method of connecting mechanical parts, and tap is the most commonly used tools for machining internal thread. Correct selection of tap processing thread, thread connection can guarantee the quality, improve the life of tap.

Selection of tap tolerance zone

Domestic machine taps are signs of diameter tolerance zone code: H1, H2, H3 represents a different position tolerance zone respectively, but the tolerance value is equal. Tap the tolerance zone known as H4, tolerance, pitch and angle errors than machine taps, material, heat treatment, the production process is not as machine taps.H4 according to the provisions can not sign. In the internal thread tap diameter tolerance tolerance zone can processing with ratings are as follows:

Tap tolerance zone code applicable to internal thread tolerance grade

H1 4H, 5H

H2 5G, 6H

H3 6G, 7H, 7G

H4 6H, 7H

Some companies use the imported tap, the German manufacturer often labeled as ISO1 4H, ISO2 6H, ISO3 6G (ISO1-3 international standard and national standard H1-3 is equivalent), so the internal thread tolerance code and tap the tolerance zone are marked with metal processing. WeChat, the content is good, worthy of attention.

Selection of thread system

The common thread has three types: metric, imperial, unified system (also called us). The metric system is in millimeters, the thread tooth angle of 60 degrees. The metal processing WeChat, the content of good, worthy of attention. For example: M8X1-6H metric fine thread pitch diameter of 8 mm, 1 mm, inside thread tolerances of 6H belt.

Inch is the inch, the tooth angle is 55 degrees of thread. For example: BSW 1/4-20 means diameter 1/4 inches, coarse tooth pitch 20 teeth per inch, this thread is now rarely used

The other is the unified system in inches, thread tooth angle of 60 degrees. The diameter of less than 1/4 inch, commonly used number said, from 0 to 12 respectively to 1/4 inch 0.06 inch diameter specifications. The unified thread is still in the United States are currently used.

Selection of taps

We often use is: straight fluted tap, spiral tap, screw tap, squeeze tap, the performance of each one has his good points.

Straight slot taps, its strongest versatility, through holes or blind holes, non-ferrous metal or black metal can be processed, the price is the cheapest. But the poor, what to do, what not to do the best. Cutting cone part can have 2,4,6 teeth, short cone for blind hole, through hole for a long cone as long as the bottom hole deep enough, you should try to choose the cutting cone is longer, so to share the load of cutting tooth number, long service life.

Spiral Tap, suitable for thread machining blind hole, machining cutting back discharge. As a result of helix angle’s sake, tap the actual rake angle increases with increase of helix angle. The experience tells us: the processing of black metal, spiral angle selected smaller, generally around 30 degrees left and right, to ensure the spiral tooth strength. Machining nonferrous metal, spiral angle is selected larger, at around 45 degrees, sharp cutting.

Screw tap, thread processing chip forward out. Its core dimensions is relatively large, good strength, can bear larger cutting force. The processing of non-ferrous metal, black metal, stainless steel, the effect is very good, should give priority to the use of screw thread through hole tip taps.

Special tap

There are some special taps, such as screw tap interval. It get rid of a tooth, and the workpiece between the pressure and friction force of small, thin-walled internal thread processing, will not cause the deformation of thin-walled parts. There are other hollow center tap is provided with a chip, the middle hole of large diameter, specializing in the production of tens to hundreds of mm in thread.

A new type of internal thread cutter

The most worth mentioning is: an internal thread tool currently used in CNC machining center, it sets the chamfer, drilling, thread processing in one machine, using spiral interpolation, front edge cutting can be drilled, chamfer, side milling teeth can thread. A tool can be processed in the same pitch, screw holes of different diameters. Expand the scope of the use of tools, reducing the number of tools, but also greatly reduces the number of changing knife processing center.

Extrusion Taps, suitable for processing non-ferrous metal, and the working principle of different cutting tap, it is made of metal extrusion, plastic deformation, the formation of internal threads. Thread of metal fiber extrusion is continuous, tensile, shear strength high, machining surface roughness is also good, but require a higher extrusion tap hole: too large, base metal less, causing the thread is too large, the strength is not enough. Too small, closed extrusion of metal with nowhere to go, cause the tap break. Calculation formula: diameter = bottom thread diameter -0.5 pitch.

Three, tap break 9 major problems analysis summary

  1. taps quality is not good:

The main material, the design of CNC tool, heat treatment, machining precision, coating quality and so on. For example, the tap section transition the size difference is too large or no design transition causes the stress concentration, easy to fracture in the stress concentration. When using the handle, edge at the junction of the transition section too close to the weld the distance, resulting in complex welding stress and the stress concentration at the transition section are superposed to produce larger stress concentration, resulting in tap break in use. The metal processing WeChat, the content of good, worthy of attention. For example, the improper heat treatment process. Tap during thermal treatment without preheating before quenching heating and quenching overheating and burning, not timely cleaning and tempering are likely to lead to premature tap cracks. To a large extent this is the overall performance is not as good as the imported tap tap an important reason.

Improper selection of 2. taps:

The hardness is too large should choose the high quality of the tap, such as cobalt high speed steel cone, carbide taps, coated taps. In addition, the design and application of different taps in different working occasions. For example, chip slotted number, tap size, angle and so on have influence on the chip performance.

The 3. tap does not match the machined material:

This problem has been paid more and more attention in recent years, previous domestic manufacturers always feel imported, expensive, in fact, is suitable for good. With the development of new materials and more difficult to process, in order to adapt to the needs of tool material varieties are constantly increasing. This requires the tapping, select appropriate the tap.

  1. bottom outlet aperture is small:

For example, the processing of ferrous metal materials M5 * 0.5 threads, with cutting tap should choose 4.5mm diameter drill hit bottom, if used to play 4.2mm drill hole, tapping tap required cutting part must be increased so that the tap break. Suggestions according to the different types and selection of tap material of right bottom the diameter, if not fully comply with the drill bit can choose a big level.

  1. attack pieces material problem:

The tapping material is impure, the local has excellent points or pores, resulting in taps instantly lose balance and break

  1. the machine tool does not meet the requirements of the precision of tap:

The machine tool and the clamping body is also very important, especially for the high quality of the tap, as long as the accuracy of the machine tool and the clamping body can play the tap performance. Common is concentricity enough. Tapping at the start of the tap start positioning is not correct, the center line of the main axis and the bottom is not concentric torque in the tapping process too much, this is the main reason for tap break.

  1. cutting fluid, lubricating oil quality is not good:

That many domestic enterprises began to focus on, many foreign procurement of cutting tool and machine tool company has a very profound experience, there are problems with the quality of cutting fluid, oil lubrication, the product quality is prone to burr and other adverse conditions, and life will be reduced greatly.

  1. cutting speed and feed rate unreasonable:

When processing problems, most domestic users is to reduce the cutting speed and decreasing the feed quantity, so efforts to promote tap reduction, the production of thread precision is therefore greatly reduced, so that increasing the surface roughness of the thread, the thread diameter and thread precision are free from control, burrs and other issues certainly inevitable. However, the feeding speed is too fast, resulting in the excessive torque can easily lead to broken tap. The cutting speed of the machine, the general steel materials for 6-15m/min; quenched and tempered steel or a hard steel material is 5-10m/min stainless steel; 2-7m/min; iron for 8-10m/min. in the same material, small diameter of tap high value, big diameter of tap low value.

  1. the operator’s skills and skills did not meet the requirements:

These problems are required for operation personnel to make judgments or feedback to the technical staff, but most of the current domestic operators do not pay enough attention. For example, blind hole threads, when the tap is about to contact at the bottom of the hole of the moment, the operator did not realize, still not to the bottom of the hole tapping speed to enter, or chip poor when forced to lead into the tap break. Recommended operating personnel to strengthen the sense of responsibility.

From the visible, causing tap fracture is varied, machine tool, fixture, workpiece, process, chuck and the tool and so on are possible, only empty talk may never find the real reason. As a qualified and responsible application engineer, the most important thing is the scene, rather than mere imagine.

Four, friends teach you how to identify the pros and cons of taps test methods

On the market many brands of taps, due to the use of different materials, with the specifications of the price is a lot of difference, so that buyers like smoke and mirrors, I do not know what to buy good, following a few simple methods to teach you:

Steps / methods

Look at the front end of the screw thread tap groove grinding (chamfer) cutting edge groove is uniform, whether there is a good fast, positive 7 words, 7 words or inverted U shape is not good (exit silk attack will cause two cutting, easy to break and influence the accuracy of screw

Detection of heat treatment: wire drawing cone to air a parabola (5 meters) flat falling is broken, broken shows brittleness

Knock off tap, it is plagioclase grain fracture, the fracture (10.5# fine microstructure) node, which indicated that heat treatment and material is good, flat or inclined short grain (microstructure)



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