A Novel Approach for the Detection of Geometric- and Weight-Related FSW Tool Wear Using Stripe Light Projection

Abstract

Friction stir welding (FSW) has become an up-and-coming joining method with a wide range of industrial applications. Besides the unique weld seam properties, recent investigations have focused on the process-related tool wear of shoulder and probe, which can have detrimental economic and technological effects. This paper presents a systematic quantitative characterization of FSW tool wear using stripe light projection as a novel method to detect weight and form deviations of shoulder and probe. The investigations were carried out with a robotic welding setup in which AA-6060 T66 sheets, with a thickness of 8 mm, were joined by weld seams up to a total length of 80 m. During the experimental tests, geometrical deviations of the tool induced by wear were detected for varying weld seam lengths and different measuring points on the probe and shoulder. It was shown that wear depended on welding length which in turn caused significant deviations and weight losses on shoulder and probe. Furthermore, it was demonstrated that the wear on shoulder and probe can be considered separately. It was found that there is a progressive wear rate on the shoulder and a degressive wear rate on the probe depending on the weld seam length. To demonstrate the negative impact of tool wear on shoulder and probe after 80 m weld seam length, visual and metallographic inspections and tensile tests were carried out to detect resultant irregularities in the weld seam.

Effect of friction stir welding tool hardness on wear behaviour in friction stir welding of AA-6060 T66

“…A maximum temperature of 590°C was measured in the SZ. Studies from previous work by Hasieber et al 7 show comparable maximum temperatures of 585.6°C for measurements in the tool. In addition, it could be shown that the temperature in the initial state and after a weld length of 80 m are approximately similar for the welding parameters and tool dimensions used.…”

“…The thermo-mechanical stresses and tribological interactions on the tool thereby lead to changes in the shape of the shoulder and probe. 7,12 As a result, the geometric-related FSW tool wear has been shown to cause varying material flow conditions, lateral path deviations and premature tool failure under certain circumstances with detrimental economic and technological consequences. 7 Preventive wear measures such as coatings 13 or the use of hard metals 14 can consequently help to increase tool life - and thus process efficiency - and to reduce machine downtimes due to FSW tool wear.…”

“…7,12 As a result, the geometric-related FSW tool wear has been shown to cause varying material flow conditions, lateral path deviations and premature tool failure under certain circumstances with detrimental economic and technological consequences. 7 Preventive wear measures such as coatings 13 or the use of hard metals 14 can consequently help to increase tool life - and thus process efficiency - and to reduce machine downtimes due to FSW tool wear. This requires a fundamental understanding of how the hardness influences the geometric-related tool wear during the FSW process.…”

Advances in friction stir welding by separate control of shoulder and probe

“…During the FSW process, the joining temperatures are below the material's solidus curve so that weld seam irregularities such as pores and hot cracks may be prevented due to the absence of a melting bath [3][4][5]. But FSW is simultaneously affected by process related challenges such as high process forces, tool wear, and comparative low welding speeds [6][7][8]. Hence economical aspects such as high costs for large FSW setups, preventative tool replacement, and comparatively low welding speeds restrict the application of FSW.…”

“…This simplicity has made it the most commonly used configuration in FSW despite the rough periodic surface structures and inferior mechanical fatigue properties [3,11]. Recent investigations are extensive and pointing thematic priorities such as weld seam properties of similar and dissimilar materials, varying probe/shoulder geometries, tool wear, and the interactions between tool and FSW setup [4,6,7,12,13].…”