Research

Open AccessArticle

Metrology of Sheet Metal Distortion and Effects of Spot-Welding Sequences on Sheet Metal Distortion

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Enkhsaikhan Boldsaikhan

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J. Manuf. Mater. Process. 2023, 7(3), 109; https://doi.org/10.3390/jmmp7030109 - 04 Jun 2023

Viewed by 982

Abstract

Refill friction stir spot welding (RFSSW) is an emerging solid-state welding technology that demonstrates an outstanding ability to join aerospace aluminum alloys. The thermomechanical processing of RFSSW may cause variations in the workpiece in the form of distortion. This study aims to establish [...] Read more.

Refill friction stir spot welding (RFSSW) is an emerging solid-state welding technology that demonstrates an outstanding ability to join aerospace aluminum alloys. The thermomechanical processing of RFSSW may cause variations in the workpiece in the form of distortion. This study aims to establish a metrology method for sheet metal distortion with the intent to investigate the effects of RFSSW sequences on sheet metal distortion. The approach employs a robotic metrology system and the least squares method to measure and estimate the flatness of sheet metal before RFSSW and after RFSSW. The RFSSW experimentation produces five 10-spot-weld panels with five different RFSSW sequences, whereas the RFSSW sequences are based on the common practice of making sheet metal assemblies. A panel consists of two lap-welded sheets where the top sheet, a 6013-T6 aluminum alloy, is refill friction stir spot welded onto the bottom sheet, a 2029-T8 aluminum alloy. The results suggest that RFSSW sequences do have effects on sheet metal distortion. The panel with the worst distortion has a root-mean-square error of 0.8 mm as an average deviation from the ideal flatness. Full article

(This article belongs to the Special Issue Frontiers in Friction Stir Welding and Processing)

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Open AccessArticle

Effects of Friction Stir Welding Process Control and Tool Penetration on Mechanical Strength and Morphology of Dissimilar Aluminum-to-Polymer Joints

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J. Manuf. Mater. Process. 2023, 7(3), 106; https://doi.org/10.3390/jmmp7030106 - 01 Jun 2023

Viewed by 1051

Abstract

An engineering grade polymer—glass fiber-reinforced polyphenylene ether blended with polystyrene—and an aluminum alloy—AA6082-T6—were joined by friction stir welding in an overlap configuration. A comprehensive analysis was conducted of the effects of the tool penetration by adjusting the pin length and the process control [...] Read more.

An engineering grade polymer—glass fiber-reinforced polyphenylene ether blended with polystyrene—and an aluminum alloy—AA6082-T6—were joined by friction stir welding in an overlap configuration. A comprehensive analysis was conducted of the effects of the tool penetration by adjusting the pin length and the process control on the joints’ mechanical performance. To this end, a series of welds with a fixed 3° tilt angle, a travel speed of 120 mm/min, and 600 RPM of rotational speed was carried out. The analysis encompassed the mechanical strength of the fabricated joints and the mechanical energy input throughout the joining processes, the resulting cross-sectional interfaces, both on macro and micro scales, and the observed defects. The quasi-static shear tensile tests resulted in average tensile strengths varying between 5.5 and 26.1 MPa, representing joint efficiencies ranging from 10.1% to 47.4%, respectively. The joints that exhibited the lowest mechanical performance were fabricated with the highest level of tool penetration (higher pin length) with the process being position-controlled, while the best performance was recorded in joints welded with the lowest tool penetration and a force-controlled process. Nonetheless, the joint welded with a 2 mm long pin and position-controlled process exhibited a mechanical strength comparable with the highest one with a significantly lower standard deviation, a promising attribute for technological industrialization. In this way, it was found that the tool penetration, controlled by adjusting the pin length, played a significant role in the development of the joints’ morphology and, consequently, mechanical performance, whereas the process control exhibited a minor influence on the mechanical performance of the joints, but a considerable effect on process repeatability. Full article

(This article belongs to the Special Issue Frontiers in Friction Stir Welding and Processing)

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Open AccessArticle

On Friction, Heat Input, and Material Flow Initiation during Friction Stir Welding: Tool and Process Optimization

by

Max Hossfeld

J. Manuf. Mater. Process. 2023, 7(1), 34; https://doi.org/10.3390/jmmp7010034 - 31 Jan 2023

Cited by 1 | Viewed by 1736

Abstract

The Friction Stir Welding (FSW) process depends entirely upon mechanical contact between the tool and the workpiece. As a result of this, all process phenomena and process outcomes such as weld geometry and mechanical properties are governed by FSW’s frictional system. The following [...] Read more.

The Friction Stir Welding (FSW) process depends entirely upon mechanical contact between the tool and the workpiece. As a result of this, all process phenomena and process outcomes such as weld geometry and mechanical properties are governed by FSW’s frictional system. The following work characterizes this system with a focus on process initialization, heat input and material flow. For this purpose, an experimental program for the isolated investigation of the frictional system was carried out. Short-term effects such as contact initiation, run-in behavior and frictional transitions are considered as well as the influences of process parameters and geometry. The system and its behavior are analyzed quantitatively and qualitatively by experiments altering the normal pressure, relative velocity, and tool geometry. The experiments demonstrate a self-similar behavior of the process, including an important wear transition which initiates the material flow, and a subsequent equilibrium of forces, heat balance, and temperatures. The interaction between the tool and the welded material is described, as is the link between the frictional interface and material flow initialization. Based on these findings, recommendations are provided for process optimization and tool design. Full article

(This article belongs to the Special Issue Frontiers in Friction Stir Welding and Processing)

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Open AccessArticle

Residual Stresses in a High- and a Medium-Entropy Alloy due to TIG and Friction Stir Welding

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Tim Richter

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Dirk Schroepfer

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Michael Rhode

J. Manuf. Mater. Process. 2022, 6(6), 147; https://doi.org/10.3390/jmmp6060147 - 18 Nov 2022

Cited by 2 | Viewed by 1055

Abstract

The new alloying concept of multi-element systems with defined entropy (HEA—high-entropy alloy; MEA—medium-entropy alloy) is gaining increasing importance in materials research. Significantly improved properties or combinations of properties are shown by some HEA/MEA systems. Thus, primarily the production and resulting microstructures of HEA, [...] Read more.

The new alloying concept of multi-element systems with defined entropy (HEA—high-entropy alloy; MEA—medium-entropy alloy) is gaining increasing importance in materials research. Significantly improved properties or combinations of properties are shown by some HEA/MEA systems. Thus, primarily the production and resulting microstructures of HEA, as well as its properties, have been investigated so far. Furthermore, processing is a main issue in transferring HEA systems from the laboratory to real components. Since welding is the most important joining process for metals, it is crucial to investigate the influence of welding to guarantee component integrity. Welding leads to residual stresses, which significantly affect the component integrity. Hence, the focus of this study is the residual stress formation and distribution in a CoCrFeMnNi HEA and ternary CoCrNi MEA using two different welding processes: tungsten inert gas (TIG) welding and solid-state friction stir welding (FSW). As a pathway for the application of HEA in this investigation, for the first time, residual stress analyses in realistic near-component specimens were performed. The residual stresses were determined by X-ray diffraction (XRD) on the surfaces of top and root weld side. The results were correlated with the local welding microstructures. The results show that both FSW and TIG generate significant tensile residual stresses on the weld surfaces in, and transverse to, the welding direction. In the case of FSW of the CoCrFeMnNi HEA, the longitudinal residual stresses are in the range of the yield strength of approx. 260 MPa in the weld zone. Full article

(This article belongs to the Special Issue Frontiers in Friction Stir Welding and Processing)

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Open AccessArticle

Fretting Fatigue as a Limiting Factor on the Durability of Friction Stir Welded Lap Joints Using AA2099-T83 and AA2060-T8E30 Aluminium Alloys

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J. Manuf. Mater. Process. 2022, 6(5), 94; https://doi.org/10.3390/jmmp6050094 - 26 Aug 2022

Cited by 3 | Viewed by 1286

Abstract

Friction stir welding (FSW) has been proposed as an alternative modern joining technology and demonstrated important benefits for the manufacturing of efficient and lightweight aircraft structures using high-strength aluminium alloys. These structures are required to be corrosion- resistant and thus, it is necessary [...] Read more.

Friction stir welding (FSW) has been proposed as an alternative modern joining technology and demonstrated important benefits for the manufacturing of efficient and lightweight aircraft structures using high-strength aluminium alloys. These structures are required to be corrosion- resistant and thus, it is necessary to use technologies such as surface treatments and sealants in their manufacturing and assembly. In this work, the feasibility of combining innovative Cr-free surface treatments, sealants and FSW technology was investigated with the focus on the durability of the joints in fatigue. FSW lap joints were produced using AA2099-T83 extrusions and AA2060-T8E30 sheets in the as-received or surface-treated condition. A sealant was also applied in some cases at the overlapping interface before the FSW process. Static tensile tests and fatigue tests were carried out applying hoop-stress loading conditions. Different fracture modes were identified depending on the stress levels applied in the fatigue tests: High stress levels resulted in fractures in the HAZ of the FSW joints, while the specimens tested at low stress levels showed fractures out of the FSW joint. In general, FSW joints produced using surface-treated aluminium components and sealant presented improved fatigue life and extended durability in comparison with non-treated aluminium joints. The surface treatments and sealant at the interface of AA2099-T83 extrusions and AA2060-T8E30 sheets reduced the friction and local damage produced due to the sliding movement during the fatigue tests, minimizing the fretting fatigue effect, which was found to be the main limiting factor on the durability and fatigue life of the FSW joints. Full article

(This article belongs to the Special Issue Frontiers in Friction Stir Welding and Processing)

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Open AccessArticle

Optimization of Friction Stir Welding Parameters in Hybrid Additive Manufacturing: Weldability of 3D-Printed Poly(methyl methacrylate) Plates

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J. Manuf. Mater. Process. 2022, 6(4), 77; https://doi.org/10.3390/jmmp6040077 - 20 Jul 2022

Cited by 7 | Viewed by 1784

Abstract

In this work, the expansion of friction stir welding (FSW) in parts made via material extrusion (MEX) 3D printing was investigated. Poly(methyl methacrylate) (PMMA) plates were joined in a full factorial experimental design. The effects of three FSW parameters (weld tool pin geometry, [...] Read more.

In this work, the expansion of friction stir welding (FSW) in parts made via material extrusion (MEX) 3D printing was investigated. Poly(methyl methacrylate) (PMMA) plates were joined in a full factorial experimental design. The effects of three FSW parameters (weld tool pin geometry, rotating speed, and travel speed) on the weld results were studied. The tensile strength was investigated using statistical modeling tools. A morphological characterization study was also conducted on the weld zone, with microscopy. The state of the material during the FSW process was monitored via real-time temperature measurements. The feasibility of the process was verified. The results show high industrial merit for the process. The highest tensile strength was reported for the sample welded with the frustum tool, at 1400 rpm and a 9 mm/min travel speed (the highest studied), with a welding efficiency > 1. This can be attributed to the reduced porosity of the weld area compared to the 3D printed structure, and indicates a high potential for joining 3D-printed PMMA sheets via the FSW process. Full article

(This article belongs to the Special Issue Frontiers in Friction Stir Welding and Processing)

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Open AccessEditor’s ChoiceArticle

Effect of Rotation Speed and Steel Microstructure on Joint Formation in Friction Stir Spot Welding of Al Alloy to DP Steel

by

Hadi Torkamani

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Javier Vivas Méndez

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Clement Lecart

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Egoitz Aldanondo Begiristain

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Pedro Alvarez Moro

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Marta-Lena Antti

J. Manuf. Mater. Process. 2022, 6(1), 24; https://doi.org/10.3390/jmmp6010024 - 15 Feb 2022

Cited by 2 | Viewed by 2351

Abstract

In this work, friction stir spot welding of 5754 aluminum alloy to dual phase steel was investigated using two different ratios of martensite and ferrite (0.38 and 0.61) for steel sheet initial microstructure and varying tool rotation speed (800, 1200 and 2000 rpm). [...] Read more.

In this work, friction stir spot welding of 5754 aluminum alloy to dual phase steel was investigated using two different ratios of martensite and ferrite (0.38 and 0.61) for steel sheet initial microstructure and varying tool rotation speed (800, 1200 and 2000 rpm). The effect of these parameters on the joint formation was evaluated by studying the plunging force response during the process and the main characteristics of the joint at (i) macrolevel, i.e., hook morphology and bond width, and (ii) microlevel, i.e., steel hook and sheet microstructure and intermetallic compounds. The plunging force was reduced by increased tool rotation speed while there was no significant effect from the initial steel microstructure ratio of martensite and ferrite on the plunging force. The macrostructural characterization of the joints showed that the hook morphology and bond width were affected by the steel sheet initial microstructures as well as by the tool rotation speed and by the material flow driver; tool pin or shoulder. At microstructural level, a progressive variation in the ratio of martensite and ferrite was observed for the steel hook and sheet microstructure. The zones closer to the tool presented a fully martensitic microstructure while the zones away from the tool showed a gradual increase in the ferrite amount until reaching the ratio of ferrite and martensite of the steel sheet initial microstructure. Different types of FexAly intermetallic compounds were found in three zones of the joint; the hook tips, in the hooks close to the exit hole and in the corner of the exit hole. These compounds were characterized by a brittle behavior with hardness values varying from 456 to 937 HV01. Full article

(This article belongs to the Special Issue Frontiers in Friction Stir Welding and Processing)

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Open AccessArticle

Mechanical Properties and Failure Mechanisms of Refill Friction Stir Spot Welds

by

Guruvignesh Lakshmi Balasubramaniam

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Enkhsaikhan Boldsaikhan

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Gratias Fernandez Joseph Rosario

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Saravana Prabu Ravichandran

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Shintaro Fukada

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Mitsuo Fujimoto

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Kenichi Kamimuki

J. Manuf. Mater. Process. 2021, 5(4), 118; https://doi.org/10.3390/jmmp5040118 - 01 Nov 2021

Cited by 6 | Viewed by 3106

Abstract

Refill friction stir spot welding (RFSSW) is an innovative solid-state welding technology for aluminum structures. The presented study aimed to evaluate the mechanical properties of refill spot welds and their failure mechanisms with the use of industrial test standards. The mechanical properties of [...] Read more.

Refill friction stir spot welding (RFSSW) is an innovative solid-state welding technology for aluminum structures. The presented study aimed to evaluate the mechanical properties of refill spot welds and their failure mechanisms with the use of industrial test standards. The mechanical properties of refill spot welds were compared with those of rivet joints with comparable joint sizes. Static load tests indicated that RFSSW coupons demonstrate higher ultimate shear strengths but slightly lower ultimate tension strengths than those of rivet coupons. Fatigue test results indicated that both RFSSW coupons and rivet coupons demonstrate comparable performances during low-load-level fatigue lap shear tests but RFSSW coupons outperform rivet coupons during high-load-level fatigue lap shear tests. The failure mechanisms of refill spot welds were characterized in terms of external loading, parent metal properties, and weld properties. Refill spot weld failures included parent metal tensile failures, nugget pullouts, and interfacial failures. A refill spot weld may demonstrate one or a combination of these mechanical failures. Although the mechanical tests of refill spot welds demonstrated promising results with predictable failure mechanisms, the metallurgical evolution involved in RFSSW remains a subject to study. Full article

(This article belongs to the Special Issue Frontiers in Friction Stir Welding and Processing)

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Open AccessArticle

A Comparative Study on Fatigue Response of Aluminum Alloy Friction Stir Welded Joints at Various Post-Processing and Treatments

by

Soran Hassanifard

and

Ahmad Varvani-Farahani

J. Manuf. Mater. Process. 2021, 5(3), 93; https://doi.org/10.3390/jmmp5030093 - 20 Aug 2021

Cited by 2 | Viewed by 2194

Abstract

The present study examines the fatigue of friction stir welded (FSW) aluminum 6061, 7075, 1060 joints followed by (i) in situ and sequential rolling (SR) processes, (ii) plastic burnishing (iii) solution-treatment artificial aging (STA), (iv) local alloying through depositing thin copper foils, and [...] Read more.

The present study examines the fatigue of friction stir welded (FSW) aluminum 6061, 7075, 1060 joints followed by (i) in situ and sequential rolling (SR) processes, (ii) plastic burnishing (iii) solution-treatment artificial aging (STA), (iv) local alloying through depositing thin copper foils, and (v) inserting alumina powder in the weld nugget zone (NZ). The microstructural features and fatigue life of post-processed joints were compared with those of as-welded joints. The in situ rolling technique offered simultaneous rolling and welding operations of aluminum joints, while through the sequential rolling process, the top surface of FSW joints was rolled after the welding process. The fatigue life of in situ rolled samples was increased as the ball diameter of welding tool increased. The fatigue life of friction stir welded joints after a low-plasticity burnishing process was noticeably promoted. The addition of 1 wt.% alumina in the NZ of joints resulted in a significant elevation on fatigue life of friction stir spot welded joints, while an increase in alumina powder to 2.5 wt.% adversely affected fatigue strength. Weld NZ was alloyed through the insertion of copper foils between the faying surfaces of joints. This localized alloy slightly improved the fatigue life of joints; however, its effects on fatigue life were not as influential as STA heat-treated or in situ rolled joints. The microstructure of weld joints was highly affected through post-processing and treatments, resulting in a substantial influence on the fatigue response of FSW aluminum joints. Full article

(This article belongs to the Special Issue Frontiers in Friction Stir Welding and Processing)

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