Design of taps for titanium internal thread in aviation field

(3) Correction of the tooth angle tap

a. The angle of the common tap is equal to the angle of the threaded profile being machined. The gap angle of the side edge of the tap is 0. When the titanium alloy workpiece is cut, due to the elastic deformation and the elastic recovery, the side edge of the tap has a large friction with the workpiece, and the cutting torque is large. To improve this situation, a modified toothed angle tap can be used.

The tooth angle of the modified tooth angle tap is smaller than the tooth angle of the thread to be machined, that is, when the thread profile angle is 60°, the tooth angle of the modified tooth angle tap is generally taken as 55°. Since the tap adopts a 55° tooth angle to process the 60° angled thread, it can ensure sufficient backlash angle between the tap and the workpiece profile to improve the elastic deformation and elastic recovery of the workpiece to reduce the friction and the cutting force. decline.

b. Taper of the threaded portion of the tap.

Correct the tooth angle of the toothed angle tap to be smaller than the tooth angle of the thread to be machined. Through theoretical analysis, in order to make the tap machine the correct thread shape to be machined, the tip of each tooth of the tap must be placed on the machined edge. Threaded profile. For this reason, when grinding the tap profile, the last tooth on the tap cutting cone must be higher than the first tooth, so that the teeth of the cutting cone are lifted to the same plane for grinding, so that the taper taper taper profile has A gradually increasing larger taper, which is the required reverse taper, is the biggest difference between the modified toothed angle tap and the ordinary tap. The taper taper taper profile is a tapered taper. When the titanium alloy is processed, the cutting cone angle is 6°, and the corrected cone angle tap angle can be 39′.

c. Thread diameter of the tap.

After the tap is grounded, the median diameter of each tooth is different. Generally, the median diameter of the first calibration tooth is measured, and the angle is measured with a three-needle angle of 55°. The calculation formula of the medium diameter when processing titanium alloy is: d20=d2-0.07P.

The tap is to change the forming principle of the thread from the forming method of the standard tap to the progressive method. When the tap is tapped on the titanium alloy, the cutting torque can be reduced by 30% to 35% compared with the ordinary tap; Compared with the tapping tap, it can be reduced by 20% to 25%. This tap has high precision and is complicated to manufacture.

3 Precautions in actual use

When tapping a titanium alloy thread, it is very important to choose whether the cutting fluid is appropriate. Generally, the cutting fluid containing CI and P works well, but after using the CI extreme pressure cutting fluid, the parts must be cleaned to prevent intergranular corrosion.

The selection of the diameter of the bottom hole when tapping the titanium alloy is particularly important. The diameter of the bottom hole can be selected according to the height of the tooth (the percentage of the ratio of the actual tooth height of the screw hole to the height of the theoretical tooth height) not exceeding 70%: small diameter The height of the teeth of the coarse thread can be smaller, and the tapping height can be appropriately increased when the tapping depth is smaller than the basic diameter of the thread. The tooth height rate is too high to increase the tapping torque and even break the tap.

Third, the conclusion

As the only professional research and production enterprise for threading tools in China's aviation industry, it is committed to the research and development, manufacturing, testing and testing of military industrial sewing tools, and for the machining of titanium alloys and high-temperature alloys for the aerospace industry. Shaanxi Aviation Hongfeng Precision Machinery Tools Co., Ltd. has accumulated rich experience. It has built a good platform through the introduction of the world's advanced high-precision CNC machine tools and some imported testing equipment to ensure the screw connection of aerospace enterprises. Usage requirements. The company will continue to intensify its technological innovation and make full use of its processing advantages. Only by developing and designing tools that are difficult to process materials can it become the preferred tool supplier for modern aerospace manufacturers.

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