Author: Kei Lin-Kuo Presenter: Adam Haining Date: October 28, 2009

 Purpose: Explore ultrasonic vibration-assisted tapping of titanium to lengthen tap tool life, decrease the necessary tapping torque, and obtain a better surface finish of the tapped surface.

 Titanium and other hard materials have a low modulus of elasticity, which causes springback when cold worked. The springback increases frictional forces when tapping, which in turn requires a larger torque, and causes the tap to break in the workpiece.

 F15 Jet is made of approximately 26% titanium. Steel rivets are used, but if tapping can be done easier in titanium, all of the rivets can be replaced with titanium nuts. Since aircraft take tens and hundreds of thousands of these, it will significantly reduce the weight of the aircraft.

 Vibration reduces tapping torque by a range of ¼ to 2/3 the regular tapping torque  Vibration increases a tap’s lifetime by up to 10,000 pieces per tool

Tap size (mm): M3×0.5, M3.5×0.6 Workpiece material: Titanium Round Bar TB340C (chemical composition, 99.8 Ti; tensile strength, 447MPa; yield strength, 327MPa) Vibration frequency (Hz): 18,000–20,000 Vibration amplitude (m): 6–24 Vibration wave type: Sine Spindle speed (rpm): 50 Tapping fluid: Dry, machine oil

 Tap Stages, Forces, and Torques

 Tap Stages, Forces, and Torques continued

 Significant reduction in the tapping torque was seen with vibration, but not for the axial force.

 Vibration reduces the maximum torque (stage 2) by 28% for the M3x0.5 tap, and by 8% for the m3.5x0.6 tap

 Adding oil to the vibration reduces the maximum torque by an additional 16%

 The best tapping condition was the situation where the assisting vibration frequency matched the resonance frequency.

 The profile of the thread was studied by magnifying it 25x. There was no noticeable effect on the profile due to the vibration.

 For smaller size tapping of pure titanium metal, imposing an ultrasonic vibration can beneficially affect the tapping process in terms of reducing the tapping torque, and thereby decreasing the likelihood of tap breakage.

 Within the adjustable range of the ultrasonic vibration generator, it was verified that vibration-assisted tapping performed at the resonance frequency would have the lowest tapping torque generated.

 Introduction of cutting fluid during tapping had a beneficial effect in terms of reducing the tapping torque, though the degree of reduction was less than that realized by vibration.

 The smaller the tap size was, the greater the degree of the tapping torque reduction could be.  No adverse effect on the profile of the internal threads was noted when vibration-assisted tapping was employed.

Author: Kei Lin-Kuo Presenter: Adam Haining Date: October 28, 2009