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 screw tap is too different or the design of the screw tap transition corner is not rounded, resulting in stress concentration, and easy to fracture at the stress concentration during use.
The cross screw tap 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 screw tap in use. For example, the heat treatment process is improper. In the heat treatment of screen 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 screw taps is not as good as that of imported taps.
2. Improper Tap Selection
High-quality screw taps, such as cobalt-containing HSS screw taps, hard alloy screw taps, coated screw taps, etc., should be selected for the workpiece with too much hardness. In addition, different screw tap designs are used in different workplaces. For example, the number of screw tap chip slot heads, 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 of screw taps always feel that the import of good, expensive goods, is actually suitable for good. With the continuous increase of new materials and difficulty to process, in order to adapt to this need, the variety of tool materials is also increasing. This requires before tapping, choosing the right tap product.
4. The Bottom Hole Aperture Is Small
For example, when machining the M5×0.5 thread tap screw-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 screw tap will inevitably increase during the tapping, and the screw tap will break. It is recommended to choose the right bottom hole diameter according to the type of screw 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 tools and clamping bodies are also very important, especially for high-quality screw taps, as long as a certain accuracy of machine tools and clamping body can play out the performance of the screw tap. The common thing is a lack of concentricity. At the beginning of tapping, the starting position of the screw tap is not correct, that is, the spindle axis is different from the centerline 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 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 leads to the tap screw breaking. 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, a screw tap diameter is small takes a higher value, screw tap diameter is large takes a lower value.
9. The Techniques and Skills of Operators Do Not Meet the Requirements
These problems 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 them. 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 is 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, fixtures, workpieces, processes, chuck and cutting tools, and so on may be possible, only 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 my imagination. Take the simplest example, if the tap cutting cone length is too long, tapping hit the bottom of the bottom hole and breaks, if you do not go into the field, only by guessing the tap performance, workpiece material, processing technology, etc.
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