Titanium alloys are ideal materials for aircraft and engines because of their high specific strength, mechanical properties and good corrosion resistance. But most titanium alloys have poor thermal conductivity, and the heat generated during machining will not be diffused through parts and machine tools, but concentrated in the cutting area. In some cases, temperatures up to 2 and 0000 degrees F (11093 degrees Celsius) can result in chipping and deformation, while the blade becomes dull and produces even higher heat and further reduces tool life. Cutting temperatures can be so high that titanium chips sometimes burst into flames and have largely restricted their use for a long time.
It is difficult to process titanium alloy, especially titanium small hole tapping. The main reason is that the thermal expansion of titanium alloy occurs during the tapping process. In addition, the titanium alloy after the rebound is large, easy to break into the tap. Specific can be solved by the following 2 ways. Improving the structure of the tap, increasing the taper core and reducing the width of the cutting edge of each tap or using tap taps can improve the rigidity and reduce the contact area of the machined material. In addition, the spiral groove can increase the sharp degree of the tap, reduce the cutting force, avoid the tap broken, is conducive to chip removal, so that the coolant can be easier to enter the cutting area, improve the cooling and lubrication performance of the tap. The tolerance requirements requested on the threaded hole diameter tolerances on the threaded hole design.
When tapping, improper selection of taps and improper operation, easy to cause work hardening, processing efficiency is very low, and there are broken tap phenomenon. The solution is as follows:
Select a place in place of the tap, the number of teeth should be less than the standard tap, usually 2~3 teeth. Cutting cone angle should be large, taper part is generally 3~4, thread length. In order to facilitate chip removal, a negative rake angle can be worn at the cutting cone. Use short tap as much as possible to increase the rigidity of tap. The taper part of the tap should be increased in proportion to the standard to reduce the friction between the tap and the workpiece. The processing thread bottom hole, drill and reamer reaming rough first, to reduce the hardening of bottom. The pitch of thread 0.7 ~ 1.5mm, bottom hole size can be processed into the standard thread bottombore GB on the difference and allowed to increase 0.1mm. If the position of the screw hole and the shape of the workpiece are not limited, the machine head shall be used as far as possible, so as to avoid the work hardening caused by the uneven feeding of the hand tapping and the stop at the halfway point.
Titanium screw diameter below 30mm, within the center line offset 30mm, can be the first to use oxygen acetylene bolt will be roasted red, and then a sledgehammer will clinch bolt (or Jack bending), after correction to reinforcement steel plate welding, tighten the bolts prevent recovery. If the titanium bolt spacing is wrong, it can be used for oxyacetylene flame roasted red after using a sledgehammer to clinch, steel plate in the middle of welding, filling in the future when it was dead. The bolt (more than 30mm in diameter) in great deviation, should be cut off with a piece of steel bolt, welding bolt in the middle, such as the bolt strength is not enough, in the two block of bolts on both sides of welding steel plate reinforcement, the length of not less than 3 ~ 4 times the diameter of the bolt.
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