Hybrid multi-response optimization of friction stir spot welds: failure load, effective bonded size and flash volume as responses

Abstract

Friction stir spot welding (FSSW) is a multi-input multi-response process. Effective multi-response optimization of welds is desirable to create welds with a balance of quality responses. In order to eliminate the subjectivity (uncertainty and engineering judgment) with the existing multi-response Taguchi-based Grey relational analysis, principal component analysis (PCA) was integrated into it. The PCA helps in determining the effective optimal weighting values required for the estimation of Grey relational grade (GRG). As a result, tool rotational speed, plunge depth and dwell time were employed as input parameters while failure load (FL), expelled flash volume (EFV) and effective bonded size (EBS) of conical pin friction stir spot-welded joint of AA2219-O alloy were the chosen output responses. EFV was minimized while FL and EBS of the joints were maximized using this hybrid multi-response approach. From the analysis of variance of GRG and its response graphs, the significant parameters and their levels were obtained. Experimental results confirmed the effectiveness and robustness of this method. In addition, three critical zones were observed on the fracture surfaces of joints, namely, tool impelled unbonded zone, partially bonded zone and effective bonded/nugget zone. The weld nugget failed by circumferential nugget shear mode.

Microstructure and mechanical properties of autobody steel joined by friction stir spot welding

“…This implies that more heat input is introduced into the weld nugget at elevated temperature or at a high tool rotational speed, and this will consequently reduce the viscosity, and increase bulk material flow (plasticized material) and expulsion of more plasticized material out of the stirred zone (owing to the volume/amount of the induced plasticized material). This is in close agreement with the works of Oladimeji et al [29], and Ojo and Taban [30] as the tool rotational speed is affirmed to significantly control the expelled flash volume of friction stir spot welds. An increase in tool rotational speed is synonymous to an increase in the generated frictional heat input during the FSSW process [31,32].…”

Macro-/micro-mechanical interlocking modification on the performance of hybrid friction stir spot welded aluminum/acrylonitrile butadiene styrene joints

“…2. This incidence is observed due to the direct interrelationship between tool rotational speed and heat input [31][32][33]. The attained peak temperatures at respective tool rotational speeds are lesser than the melting temperature of the pure Al alloy (about 630oC) but are greater than the melting temperature of the ABS polymer (about 160oC).…”

Cyclic lateral behavior of friction stir spot welds of AA2219 aluminum alloy: impact of inherent flow defects

“…The hook defect is attributed to the upward material flow around the pin periphery in the conical pin welds (the tool penetration action into the bottom sheet enforces upward material flow to form the hook profile) [32][33][34][35][36]. On the other hand, the material flow underneath the shoulder surface towards the shoulder edge in the pinless welds is responsible for the microscopic toe-notch defect in the pinless weld.…”