EXPERIMENTAL INVESTIGATION OF

ULTRASONIC VIBRATION-ASSISTED TAPPING

Author: Kei Lin-Kuo

Presenter: Adam HainingDate: October 28, 2009

INTRODUCTION 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.

REFERENCES

PROBLEM 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.

PROBLEM 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.

PREVIOUS FINDINGS 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

DESIGN

DESIGN PARAMETERSTap size (mm): M3×0.5, M3.5×0.6Workpiece material: Titanium Round Bar TB340C

(chemical composition, 99.8Ti; tensile strength, 447MPa;yield strength, 327MPa)

Vibration frequency (Hz): 18,000–20,000Vibration amplitude (m): 6–24Vibration wave type: SineSpindle speed (rpm): 50Tapping fluid: Dry, machine oil

DESIGN Tap Stages, Forces, and Torques

DESIGN Tap Stages, Forces, and Torques

continued

RESULTS

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

RESULTS

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

RESULTS

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

RESULTS

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

RESULTS

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

CONCLUSION 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.

CONCLUSION 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.

CONCLUSION 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.

CONCLUSION 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.

EXPERIMENTAL INVESTIGATION OF ULTRASONIC VIBRATION-ASSISTED

TAPPINGAuthor: Kei Lin-Kuo

Presenter: Adam HainingDate: October 28, 2009

QUESTIONS?