Tapping is a metal cutting process in which the tap is rotated into the bottom hole of the embryo of the fastener to be drilled by a certain torque to produce the internal thread. In traditional fastener manufacturing, manual tapping machine is often used for thread processing. Because in actual production, some threaded holes are not suitable for milling threads because of their location or part shape limitations. Tapping machine is a kind of machine tool which processes internal threads with taps, but sometimes in the process of tapping, the breakage of taps caused by various factors causes a lot of waste. Following is a brief introduction to the traditional manual tapping techniques and precautions of Borun Petrochemical Company.
I. Steps and Skills of Manual Tapping
The quality of manual tapping is greatly influenced by human factors, and the strength of taps with small diameter of threaded holes is low. Therefore, only by adopting correct methods can we ensure the quality of the workpiece manually tapped by fasteners.
(1) clamping of workpiece
Workpiece clamping should generally place the threaded side of the workpiece in a horizontal or vertical position. It is easy to judge and keep the tap perpendicular to the base surface of the workpiece.
(2) Location of taps
At the beginning of tapping the thread, the tap should be set straight, and then one hand to hold the tap and the other hand to turn the hinge gently. Observing whether the tap is perpendicular to the base surface of the workpiece from the front or side, and correcting it with a right-angle ruler when necessary, the direction of the tap is basically determined.
(3) Revision of taps
If the tap position is incorrect at the beginning of tapping, the tap can be screwed out with two cones to correct and then tapped with the head cone. When the cutting part of the tap enters the workpiece, it is no longer necessary to apply axial force to automatically screw in by the thread.
(4) Taper stability
When turning the hinges evenly, the operator’s hands should be balanced. Do not use too much force and sway left and right. Otherwise, it is easy to tear the threaded teeth and lead to the expansion of threaded holes and taper, and the tap will be broken.
(5) Withdrawal of tap
The screw tap is loosened with the hinged screw, and then the screw tap is screwed out, because the combination of the tapped threaded hole and the screw tap is looser. Avoid swing and vibration of tap when withdrawing, thus destroying the surface roughness of thread.
2. Treatment of tap breakage
The reasons affecting the quality of machine tool taps include: main materials, CNC tool design, heat treatment, processing accuracy, coating quality and so on. For example, the size difference of the taper section transition is too big or the transition fillet is not designed, which leads to stress concentration. When used, it is easy to fracture at the stress concentration.
(1) Technological factors of taps
Cracks in taps may occur if the taps are not preheated, quenched or overheated, tempered in time and cleaned prematurely before quenching.
(2) Selection factors of taps
For tapping parts with too high hardness, high-quality machine tool taps should be selected, such as cobalt-containing high-speed steel wire taps, carbide taps, coated taps, etc. The number, size and angle of chip removal slots of taps have an impact on chip removal performance.
(3) Material factors of workpiece
With the emergence of new workpiece raw materials, the variety of tool materials is also increasing, which requires the selection of appropriate taps before tapping. When the tapping material is impure, there are some hard spots or air holes in the part, which will cause the tap to lose its balance and break instantly.
(4) Performance factors of machine tools
Machine tools and grippers are also very important, especially for high-quality taps, as long as the accuracy of the machine tools and grippers can play the performance of taps. When tapping, that is, the axis of spindle is not concentric with the center line of bottom hole. Torque is too large during tapping, which is the main reason for tap breakage.
Selection of Special Tapping Oil
Tapping oil is the lubricating medium that must be used in thread cutting process of fasteners. High precision thread cutting process has higher requirements on cooling, lubrication, penetration and cleaning performance of tapping oil. When using waste engine oil and vegetable oil instead of special tapping oil, it is easy to have bad conditions such as burrs, and the tap life will be greatly reduced.
(1) High efficiency tapping oil has super lubricity, low friction coefficient and high extreme pressure.
(2) The special tapping oil film has strong adhesion and toughness, which can effectively protect the tap and improve the thread quality.
(3) Good cold removal performance can effectively inhibit the rise of temperature, reduce sintering and jamming, and has special effect in reducing cutting edge and broken tap.
(4) The use of special tapping oil to remove chips is more smoothly. During tapping process, a large number of iron chips will be produced. The iron chips are easy to stick to the thread hole and the top of the tap. At this time, the iron chips must be washed away with special tapping oil.
(5) Due to the use of non-corrosive vulcanization additives as the main agent, the special tapping oil has no odor and does not irritate the skin, which can effectively avoid workers’skin allergies and other problems.
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