An Investigation in to Tool Wear Detection in Friction Stir Welding

Paul FlemingThomas Bloodworth

David LammleinTracie Prater

George E. CookAlvin StraussD. M. Wilkes

David DeLappThomas Lienert

Matt Bement

Friction Stir Welding

Recently (1991) developed solid state welding technique

Uses mechanical stirring to join metals

Yields high weld strength

Can be used to join aluminum

The FSW Tool

Numerous tool designs exist Smooth Threaded Fluted

(Khaled)

FSW Tool Wear

There is extensive study of tool wear in related fields such as cutting tool wear and milling tool wear, but little for FSW

This is because of both FSW's newness and also because FSW is currently typically used on soft metals and wear is often neglible.

However this may not always be the case

FSW Tool Wear

The paper “Tool wear in the friction-stir welding of aluminum alloy 6061 20% Al2O3: a preliminary study“ investigates FSW tool wear for a threaded tool When welding the above metal, an FSW tool of 01

steel hardened to a Rockwell C hardness of 62 showed the following wear patterns

FSW Tool Wear

(Prado)

Detecting Tool Wear

This research focuses on means of discovering tool wear in FSW automatically to prevent the use of a worn tool to be allowed to proceed unnoticed.

Experimental Design

An FSW tool was constructed out of a mild tool steel to increase the wear rate

Bead on plate welds were run repeatedly and the forces incurred were recorded

Experimental Design

Show Movie

Results

After 20 welds the tool had worn to the point shown (compared with unused tool)

Worn tool on left Threads have been

worn down

Analysis

Dynamometer collects data at 1000Hz: Fx, Fy, Fz, Mz

The average force for each direction was calculated and plotted across runs

AnalysisFx

Analysis

The progression appears to be a decrease in the force experienced by the dynamometer

This trend is demonstrated in each direction

AnalysisFz

AnalysisTorque

Analysis

This decreasing force and torque can probably be directly related to the loss of threads

This decrease would then serve as a good indicator of tool wear

However, it is also shown that the forces involved vary for other reasons and make a precise estimator based on this alone impractical

Frequency Based Analysis

The frequencies in the recorded force signals could also serve as indicators of tool wear

The following shows the recorded forces for the recorded wear runs

Frequency Based Analysis

Other Possibilities

Acoustic Emissions Computer Vision

Detection of Tool Wear in FSW

This automatic detection is important for the increased industrial application of FSW, as joining of more difficult materials will become more common

Forces recorded during the weld can serve as indicators of tool wear when forces involved in welding have dropped below a certain threshold

References George E. Cook, Reginald Crawford, Denis E. Clark, and Alvin M. Strauss. Robotic friction stir welding.

Industrial Robot, 31(1):55–63, November 2004.

Terry Khaled. An outsider looks at friction stir welding. Technical report, Federal Aviation Administration, 2005.

R. A. Prado, L. E. Murr, D.J. Shindo and K.F. Soto. Tool wear in the friction stir welding of aluminum alloy 6061 + 20% Al2O3: a preliminary study. Scripta Materialia. 2001