Keywords:reasons for screw tap fracture
1. The Poor quality screw tap:
Main materials,tool design,heat treatment, machining accuracy, coating quality, etc. For example, the size of the transition section of the tap is too different or the design of the transition corner is not rounded, resulting in stress concentration, easy to fracture at the stress concentration during use. The cross section transition at the junction of shank and blade is too close to the welding port, resulting in the complex welding stress superimposed with the stress concentration at the cross section transition, resulting in a large stress concentration, which leads to the fracture of the tap in use. For example, the heat treatment process is improper. In the heat treatment of taps, cracks may occur if the taps are not preheated before quenching, overheated or overburned during quenching, not tempered in time and cleaned too early.This is also an important reason why the overall performance of domestic taps is not as good as that of imported taps.
2. Improper tap selection:
High quality taps, such as cobalt-containing HSS taps, hard alloy taps, coated taps, etc., should be selected for the workpiece with too much hardness. In addition, different tap designs are used in different workplaces. For example, the number of tap chip slot head, size, Angle and so on have an impact on the chip performance.
3. The tap does not match the processed material:
The problem is taken seriously more and more in recent years, before the domestic manufacturers always feel that the import of good, expensive good, it is actually suitable for good. With the continuous increase of new materials and difficult to process, in order to adapt to this need, the variety of tool materials are also increasing. This requires before tapping, choose the right tap product.
4. The bottom hole aperture is small:
For example, when machining M5×0.5 thread in ferrous metal, the cutting tap should be used to drill the bottom hole with a 4.5mm diameter bit. If the 4.2mm bit is used to drill the bottom hole, the cutting part of the tap will inevitably increase during the tapping, and the tap will break. It is recommended to choose the right bottom hole diameter according to the type of tap and workpiece material, if there is not a full match of the drill bit can choose a larger stage.
5. Tapping material problem:
The workpiece material is not pure, and there are some hard points or pores in local parts, which causes the tap to lose balance instantly and break.
6. The machine tool does not meet the precision requirement of tap:
Machine tool and clamping body is also very important, especially for high quality taps, as long as a certain accuracy of machine tool and clamping body can play out the performance of the tap. The common thing is lack of concentricity. At the beginning of tapping, the starting position of the tap is not correct, that is, the spindle axis is different from the center line of the bottom hole, and the torque is too large in the tapping process, which is the main reason for the tap breaking.
7. Poor quality of cutting fluid and lubricating oil:
Many domestic enterprises have begun to pay attention to this point, many companies have purchased foreign tools and machine tools have a very deep experience, cutting fluid, lubricating oil quality problems, processed product quality is easy to appear burr and other bad conditions, at the same time, life will also be greatly reduced.
8. Unreasonable cutting speed and feed:
When processing problems, most of the domestic users is to reduce cutting speed and reduce feeding, such tap propulsion strength is reduced, the production of thread accuracy was greatly reduced, it increased the roughness on the surface of the screw thread, thread aperture and cannot control precision, burr problem, of course, such as more inevitable. However, the feed speed is too fast, resulting in excessive torque is also easy to lead to the tap broken. The cutting speed of machine attack, general steel material is 6-15m/min; Quenched and tempered steel or hard steel material is 5-10m/min; Stainless steel is 2-7m/min; Cast iron is 8-10m/min. In the same material, tap diameter is small take a higher value, tap diameter is large take a lower value.
9. The techniques and skills of operators do not meet the requirements:
These problems above all need operators to make a judgment or feedback to technical personnel, but the vast majority of domestic operators do not pay enough attention to. For example, when processing blind hole thread, when the tap is about to contact the bottom of the hole, the operator did not realize that the tapping speed is still not at the bottom of the hole, or forced to feed when the chip is not free, resulting in the tap broken. It is recommended that operators strengthen their sense of responsibility.
As can be seen from the above, the causes of tap fracture can be described as a variety of machine tools, fixture, workpiece, process, chuck and cutting tools and so on May be possible, only by paper talk may never find the real cause. As a qualified and responsible tool application engineer, the most important thing is to go into the field, not just by imagination. Take the simplest example, if the tap cutting cone length is too long, tapping hit the bottom of the bottom hole and break, if you do not go into the field, only by guessing the tap performance, workpiece material, processing technology, etc. How do I know?
Link to this article：China Hardware Tells You Nine Reasons for Screw Tap Fracture
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