With the development of processing technology, in recent years, titanium alloys have been widely used in the manufacture of aircraft engine compressors, hoods, exhaust devices and other parts, as well as the manufacture of aircraft frame beams and other structural frame parts. Tapping of titanium alloys, especially small holes with M6mm or less, is quite difficult. Mainly because the chips are small, it is easy to bond with the blade and the workpiece, resulting in a large surface roughness value and a large torque.
When tapping is not properly selected and improper operation is easy to cause work hardening, the processing efficiency is extremely low and the tap breaks sometimes. The solution is as follows:
Preferably use a thread-in-place tap, the number of teeth should be less than the standard tap, generally 2 to 3 teeth. The cutting cone angle should be large, and the taper part is generally 3 to 4 thread lengths. In order to facilitate chip evacuation, a negative inclination angle can also be ground on the cutting cone. Try to use short taps to increase the rigidity of the taps. The inverted cone part of the tap should be properly enlarged compared to the standard to reduce the friction between the tap and the workpiece.
When processing the threaded bottom hole, first rough-drill and then ream the hole to reduce the work hardening of the bottom hole. For threads with a pitch of 0.7 to 1.5mm, the size of the bottom hole can be processed to the upper difference of the standard thread bottom hole specified by the national standard and allowed to be increased by 0.1mm.
If it is not restricted by the position of the screw hole and the shape of the workpiece, try to use machine tapping as far as possible to avoid the processing hardening caused by uneven tapping and manual stop tapping.
Titanium alloy is an ideal manufacturing material for aircraft and engines due to its high specific strength, good mechanical properties and good corrosion resistance. However, due to its poor machinability, it has long restricted its application to a large extent.