Pinless Tool Research Articles

Influence of Tools Diameters and Plunge Depth on Mechanical Properties of Micro Friction Stir Spot Welding Materials A1100

Welding on thin aluminum alloy material is still relatively difficult, so that appropriate welding technology is needed to joint the ultra-thin aluminum material. One of the processing welding capable of solving to ultra-thin aluminium is micro friction stir spot welding μFSSW). The micro FSSW process is an adaptation of the FSW process where solid-state processes allow the welding process without changes in the basic characteristics of the workpiece. The purpose of this study was to analyze the effect parameters used in this study are pinless tool diameter and plunge depth on micro FSSW. The material used in this study was A1100 with a thickness of 0.42 mm using lap joint. The welding parameters used in this study are tool diameter and plunge depth, where each parameter has three levels. While the response variables observed were mechanical and fractures properties. To analyze maximum shear strength/load using response surface methodology (RSM). Experimental results and analysis of influence tool diameter and plunge depth on micro-friction stir spot welding μFSSW) analysis show that tool diameter and plunge depth are directly proportional to maximum shear load. Furthermore, the smallest hook defect occurs on the tool diameter 5 mm with plunge depth 500 μm.

High-Speed Deformation of Pinless FSWed Thin Sheets in AA6082 Alloy

The high-speed deformation behavior of friction stir-welded thin sheets in AA6082-T6 aluminum alloy, under biaxial balanced stretching, was investigated by means of a hemispherical punch test carried out using direct tension-compression Split Hopkinson Bar. The friction stir welding process was performed on thin sheet blanks using a pinless tool; the rotational and welding speeds were kept constant during process. The dynamic tests were carried out, with a punch speed of 4500 mm/s, at different punch stroke values until failure of the friction stir welded sample. It was seen that failure occurs along the welding line at a dome height about 11% higher than that at the onset of necking. Fractographic analysis shows that deformation is localized in the fracture zone. The results were compared with those obtained on friction stir welded blanks deformed under quasi-static condition in order to evaluate the influence of the loading rate on the weld deformation and fracture mechanisms. It was shown that joints deformed under dynamic loading condition are characterized by a dome height at the onset of necking significantly higher than the one measured under quasi-static condition.

Phase transformation during friction stir processing of dual-phase 600 steel

The objective of this work is to investigate the phase transformation during friction stir processing of dual-phase 600 steel. Friction stir processing is a microstructure modification process through high strain rate deformation at high temperature. The material undergoes appreciable microstructural changes, which reflects in the refined mechanical properties. The type of metallurgical phases and their fractions have direct impact on the mechanical properties. A coupled 3D thermo-mechanical and phase transformation model is developed to predict the temperature history, plastic deformation and phase transformation during friction stir processing. The modified Johnson–Mehl–Avrami Kolmogorov and Koistinen–Marburger equations are used to model the diffusional and non-diffusional phase transformation, respectively. Friction stir processing is performed with 1.4-mm-thick dual-phase 600 steel and pinless tool. Friction stir tool rotation frequency is varied across friction stir-processed samples, at constant traverse speed. Electron back-scattered diffraction and optical microscopy are used to analyse the phases and microstructure. Model predicts the maximum bainite and martensite volume fractions at stir zone centre. Further, more bainite and martensite formation is estimated at higher tool rotation speeds. These predictions compare well against the experimental observations. Numerical results suggest that the ferrite in the stir region is the untransformed ferrite during heating. During cooling, very small austenite grain size restricts the amount of austenite transformation to ferrite. The phases present in the stir region upon FSP are significantly affected by the amount of carbon content and the initial phases present in the steel.

Thermal Cycles and Deformation Characters During High-Speed Micro Friction Stir Welding Process of AA7075-T6 Sheets

Thermal cycles and deformations during high-speed micro friction stir welding (μFSW) under different welding conditions were studied by experimental methods. The results show that the peak temperature and elevated-temperature exposure time (t150) increased with the increasing of rotational speed and decreased with the increasing of welding speed. Increasing rotational speed or welding speed led to an increase in both heating and cooling rates. The joint fabricated by the pinless tool experienced a lower peak temperature, a shorter elevated-temperature exposure time, and a larger temperature gradient than that by the pin tool. The welded sheet presented an anti-saddle deformation character, with convex bending in a longitudinal direction and concave angular bending in a transverse direction. In comparison to the pin tool, the longitudinal maximum bending deformation, Zmax, of the joint fabricated by the pinless tool was reduced by 12.35%, and the transverse angular deformation, α, was reduced by 6.67%. In comparison to the steel backing plate, the Zmax of the joint produced using a copper backing plate was reduced by 40.66%, but the α was increased by 53.27%.

Role of tool design on thermal cycling and mechanical properties of a high-speed micro friction stir welded 7075-T6 aluminum alloy

AA7075-T6 sheet welds that were 0.5 mm thick were fabricated by micro friction stir welding (μFSW) using a pinless tool as well as a pin tool. The experiments were conducted at a higher rotational speed of 6000 rpm and a higher welding speed of 1200 mm/min than those that are used in conventional FSW. The heat generation, peak temperature and elevated-temperature exposure time (t150) of the joints fabricated by the pin tool were higher than those fabricated by the pinless tool at the same shoulder penetration depth. The minimum ratio of the thickness reduction at the center of the friction stir weld was 0% for the pinless tool at a penetration depth of 0.14 mm. In comparison to those for the joints fabricated by the pin tool, the joint fabricated by the pinless tool showed less softening and better tensile properties. For the welds fabricated by the pin tool, the tensile properties increased with increasing penetration depth. In the case of welds made by the pinless tool, the tensile specimens failed at the transition region between the stir zone and the thermomechanically affected zone on the retreating side due to the local thickness reduction. However, the tensile specimens failed at the center of the stir zone due to kissing bond defects in the joints produced by the pin tool.

Cladding thick Al plate onto strong steel substrate using a novel process of multilayer-friction stir brazing (ML-FSB)

Friction stir brazing (FSB) using a pinless tool together with a braze was developed to extend bond area over friction stir lap welding. When using a large pinless tool of Ø40 mm to clad 10 mm thick 5083Al plate to 16Mn steel by FSB with Zn braze, the thermomechanical effect was sufficient to achieve wetting on Al side by dissolving Al into molten Zn, but joint could not be formed due to poor wettability on steel side. To enhance mechanical disruption of oxide film on the steel, multilayer FSB (ML-FSB) process was proposed by adding a thin (3 mm thickness) and soft aluminum sheet as interlayer. The first FSB pass created bonding between the thin interlayer and steel substrate with 4.7 μm thick FeAl3 without Zn residue, having 55 MPa shear strength. The second FSB pass created bonding between the thin interlayer and thick 5083Al clad with a diffusion zone with a little Zn, having 50 MPa shear strength. This work provided a new way to fabricate “thick clad” layered composite with “strong substrate”, and suggested that mechanical route for strong substrate and metallurgical route (eutectic reaction) for Al for removing oxide film should be preferential and available in FSB.

Relationship between tool tilt angle, shoulder plunge depth and process energy input for pin-less friction stir welded thin Ti-6Al-4V sheets

This paper reports on the initial process development towards evaluating pin-less friction stir welding as a feasible alternative joining technology for Ti-6Al-4V sheets. Initial research results were derived from “bead on plate” welds with a pin-less tool on 3 mm Ti-6Al-4V sheets to assist with decision making for joining 1 mm Ti-6Al-4V sheets. The study evaluates the shared influence of tool tilt angle and shoulder plunge depth on weld profile and process energy input for a pin-less tool. An experimental approach was followed, performing bead on plate welds with three tool tilt angles (0°, 1° and 2°) respectively at shoulder plunge depths from 0.15 mm to 0.25 mm in 0.05 mm increments. From critically evaluating the hardness profile and heat effected area below the tool shoulder, the shared influence of tool tilt angle and shoulder plunge depth could be analysed to give an indication of the best parameter combination for performing solid state welds on 1 mm Ti-6Al-4V sheet. Additionally, the thinning effect on the weld region was evaluated and compared to welds made with a pin. Future work will include quantifying surface residual stresses on the material and the relationship these stresses exhibits with the varying tool tilt and shoulder plunge depth. This work will assist in selecting weld parameter combination that will minimize tensile residual stresses in critical areas. Knowledge gained from this study forms the basis for the overall process development for joining 1 mm Ti-6Al-4V sheets by pin-less friction stir welding.

Dieless friction stir extrusion joining of aluminum alloy sheets with a pinless stir tool by controlling tool plunge depth

Abstract The present work explains dieless friction stir extrusion joining for aluminum alloy sheets, AA5052-H32 and AA6061-T6, of 2 mm thickness each. The joints are strengthened by metallurgical bonding as well as mechanical interlocking. The hook defect and the pinhole formation in friction stir spot welding are successfully eliminated in this new process. Experimental investigation of the effect of tool plunge depth on the formation of the joint and its performance is comprehensively discussed with mechanical performance tests, macro/ microstructuture analysis, hardness measurement, joint morphology and failure mode analysis. The joints possess shear fracture load of 7.7 kN, which is superior than that of friction stir spot welding and conventional friction stir forming. Higher tool plunge depth level ranging from 0.45–0.50 mm is found to be optimum choice for fabricating spot joints with better joint strength and aesthetic appearance. Slight increase in tool plunge depth yields significant improvement in the mechanical interlocking (collar growth). The zones identified through microstructural analysis, which are subjected to severe plastic deformation and frictional heat flux possess significant recrystallization and grain refinement. Reduction in hardness is observed over the joint spot than that of the parent metal. Morphological features of the joint are affected by increase in the plunge depth beyond the optimum range. The critical zones in the joint, which leads to pin failure and bonding delamination failure are also identified.

Enhanced microstructure and mechanical properties of boiler steel via Friction Stir Processing

Abstract The main objective of the current investigation is to achieve strengthening of SA210 Grade A1 boiler steel using friction stir processed (FSPed) using pinless WC tool with plunge depth of 1 mm, transverse speed as 40 mm/min and tool-spindle rotational speeds of 800 revolutions per minute and 1400 rpm respectively with two numbers of passes in each case. through The microstructural refinement and mechanical properties like tensile and hardness for base steel were studied and compared with friction stir processed steel. The initial grain sizes of the selected boiler steel (25 µm) has been reduced to 7.8 µm and 5.9 µm respectively with increase in rotational speed. The microhardness and tensile strength was evaluated of all the FSPed samples. The microhardness of the FSPed samples was enhanced by factor of 1.72 and 2.38 in comparison to base steel respectively with the increase in rotational speeds; this may be due to phase transformation (austenite to martensite and ferrite) verified by Image processing software “Image-J” and refinement in grain size as per Hall-Petch equation. The ultimate tensile strength was improved by 7.2% and 15% respectively in comparison to base metal, which may be accredited to enlarge in grain boundaries which hinder the dislocation movement. The characterization was done by optical microscopy and Electron Back Scattered Diffraction (EBSD) analyses with an intend to suggest mechanisms behind grain size refinement and phase transformation.

Effect of pinless tool shoulder diameter on dieless friction stir extrusion joining of AA 5052-H32 and AA 6061-T6 aluminum alloy sheets

A new spot joining process called dieless friction stir extrusion is proposed, in which simultaneous mechanical interlocking (collar formation) and metallurgical bonding is the key aspect of joint formation. The pinless flat stir tool eliminates pinhole and hook formation, the common defects of friction stir spot welding. Aluminum alloy sheets such as AA 5052-H32 and AA 6061-T6 are spot joined and the effect of change in tool shoulder diameter (10–18 mm) on joint strength and joint formation is evaluated. Lap shear fracture load of 6.22 kN obtained at optimum tool shoulder diameter of 14 mm is higher than that of conventional spot joining techniques. Macrostructure analysis revealed that increase in tool shoulder diameter results in poor mechanical interlocking. Consequently, pin shear failure is common at highest tool shoulder diameter. Critical weak zones of failure are identified. The change in tool shoulder diameter has significant impact on the external joint morphology.

Effect of a Zinc Interlayer on a Cu/Al Lap Joint in Ultrasound-Assisted Friction Stir Welding

This study proposes a welding process, ultrasound-assisted friction stir welding of dissimilar Al/Cu metals. Zinc foil is melted using the heat generated by a pinless stirring tool, and the molten intermediate layer is stirred by ultrasonic cavitation to achieve an effective connection. The metallurgical reaction behavior of the joint under the action of the sound field was studied, and the effects of different microstructures on the joint performance were analyzed. Specifically, the following observations were reported in this study: (1) When ultrasound assistance was used, the cavitation effect changed the brittle intermetallic compounds of Al2Cu from a continuous distribution to a block distribution, and the mechanical properties of the joint were greatly improved; (2) the effects of the thickness of the zinc were also determined. The results showed that the highest shear tensile force was obtained when the thickness of the zinc foil was 0.2 mm. When the thickness was 0.3 mm, the ultrasound effect was weakened. The copper-side interface generated a zigzag-shaped Al4.2Cu3.2Zn0.7 layer with a thickness of 3.4 μm and had a continuous distribution. Increasing the thickness of the zinc to 0.5 mm, however, drastically decreased the mechanical properties of the joint due to incomplete melting of the zinc layer.

Study on Low Axial Load Friction Stir Lap Joining of 6061-T6 and Zinc-Coated Steel

Friction stir lap joining of 6061-T6 and zinc-coated steel was performed using a high rotation speed and small tools with different pin lengths. During the welding process, the average axial force ranged from 0.2 to 1.1 kN, which is smaller than that for conventional friction stir welding. Satisfactory surface formation was achieved using a pinless tool and smaller plunge depth. The highest failure load of 2.26 kN was achieved for a pin length of 0.3 mm, plunge depth of 0.3 mm, and welding speed of 50 mm/min. The specimen fractured at the advance side of the 6061-T6 base metal. A continuous and compact interface layer with a thickness of 5.2 μm was formed. The main component of the intermetallic compound at the interface was Fe4Al13. The intermetallic compound was tightly connected and bound to the steel galvanized sheet and aluminum side.

Study of microstructure evolution, mechanical properties and hot corrosion behavior of friction stir processed boiler steel

In this investigation, commonly used boiler steel (SA210) was friction stir processed (FSPed) using pinless tool with plunge depth of 1 mm, transverse speed as 30 mm min−1 and tool-spindle rotational speeds of 600 revolution per minute (rpm), 300 rpm, and 150 rpm respectively with three number of passes in each case. Scanning Electron Microscopy (SEM) and Optical Microscopy (OM) analyses were done in order to characterize the Friction Stir Processed specimens. Prediction of the grain size distribution after friction stir processing under different rotational speeds was done using Electron Back Scattered Diffraction (EBSD). The initial grain sizes of the selected boiler steel (25 μm) has been decreased to 7.3 μm, 4.3 μm, and 1.75 μm respectively with decrease in rotational speed. The microhardness and tensile strength was evaluated of all the FSPed samples. The microhardness of the FSPed samples was enhanced by factor of 2, 2.5 and 3 in comparison to base steel respectively with the decrease in rotational speeds; this may be due to phase transformation (austenite to martensite and ferrite) verified by Image processing software "Image-J" and refinement in grain size as per Hall-Petch equation. The ultimate tensile strength was improved by 8%, 16% and 25% respectively in comparison to base metal, which may be accredited to enlarge in grain boundaries which hinder the dislocation movement. FSPed steel having grain size of 1.75 μm offered 68% resistance to hot corrosion in comparison to base steel. The enhanced corrosion resistance might be attributed to the increased microhardness, fine grain structures and the presence of protective oxides on the top surface layer.

Microstructure and mechanical properties of friction lap-butt welded ultra-thin galvanized steel sheets

In this study, a Lap-Butt joint (LBJ) of ultra-thin galvanized steel sheets with satisfactory joint properties had been produced by friction lap welding (FLW) using a pinless tool. The LBJ had a lap form but with the butt joint thickness and without the altitude intercept at back side. The LBJ was produced by the smooth material flow and plastic deformation of the top sheet. An interlayer consisting of Fe and Fe3Zn10 was observed at the interface. The dynamic recrystallization zone (DRZ) and heat affected zone (HAZ) were observed in the LBJs. The influences of FLW parameters on microstructural change and shear strength were investigated. The maximum fracture load of LBJ is equivalent to 95% fracture load of the base metal. The grain refinement induced by dynamic recrystallization increased the strength of top sheet.

Friction Stir Spot Brazing of Low Carbon to Galvanized Steel

Friction stir spot brazing of low carbon to galvanized steel was carried out using a pin-less tool, and the effect of tool rotational speed on the microstructure and mechanical properties of the joints was investigated. With the increase in rotational speed as a result of the higher Zn molten formation and also more diffusion of atomic iron toward the this molten phase, thicker interface, which mainly consisted of α-Fe(Zn), was achieved. No intermetallic compounds or cracking was detected at the joint interface. With the increase in rotational speed, the joint strength increased which could be due to higher diffusion rate as well as interface mechanical interlocking.

Influence of base material characteristics and process parameters on frictional heat generation during Friction Stir Spot Welding of steels

Frictional heat generation, in Friction Stir Spot Welding of steels, was assessed by producing welds with pinless tools. In order to analyse the influence of base material characteristics on heat generation, spot welds were produced, using varied process parameters, in DC01, DX51D and HC420 LA steel sheets (1 mm thick). Uncoated and coated sheets, with galvanised films of different thicknesses, were tested in order to assess the influence of surface properties on heat generation. The welding thermal cycles were measured using thermography and hardness measurements were done to evaluate the influence of the maximum temperature, maintenance time and cooling rates on welds properties. It was found that the main factors influencing the frictional heat generation are, by order of importance, the tool diameter, the tool rotation speed and the presence of low melting point coatings. Differences in frictional heat generation, for the different base materials, were only registered when welding with a 10 mm diameter tool. The analysis of the average welds hardness enabled to conclude that the hardness increase in the weld region, relative to the base material, is determined by the maximum temperature reached during welding and by the grain size of the base material.

Friction stir spot soldering galvanized steel using tin interlayer

Friction stir spot soldering of galvanized steel plates was carried out using Sn interlayer with a pin-less tool without any form of brazing flux and the effect of tool rotational speed on the microstructure and mechanical properties of the joints was investigated. According to the rotational speeds, some intermetallic compounds were detected in the joint interface. Also, the intermetallic thickness increment was achieved with an increase in the rotational speed. As a solder joint, the shear test showed an outstanding result in the sample soldered at 1600 rpm and the fracture occurred in the base metal, which means the joint strength is higher than that of galvanized steel. However, at the other rotational speed fracture occurred along the interface at lower loads.

Projection friction stir spot welding: a pathway to produce strong keyhole-free welds

ABSTRACTThis paper introduces a novel facile method, called projection friction stir spot welding, to produce a keyhole-free friction stir welds based on a pinless tool method involving using a specially designed projection on the surface of the backing anvil. The projection plays two key roles contributing to the bonding mechanism and the joint strength: (i) encouraging the material flow perpendicular to the joint interface and (ii) bending the joint interface at the edge of the projection. The process enables pathway to produce keyhole-free welds with superior mechanical performance in steel sheets compared to the other spot welding techniques.

Effect of FSP parameters and tool geometry on microstructure, hardness, and wear properties of AA7075 with and without reinforcing B4C ceramic particles

The aim of this work is to produce a surface composite by incorporating B4C particles on the surface of AA7075 alloy through friction stir processing (FSP) using both a pinless and a cone pin tool. The influence of friction stir processing parameters on the microstructure, hardness, and wear properties of the processed surface composites was investigated. The studied parameters include rotational tool speed (400 and 600 rpm) and number of passes (1, 2, 3, and 4 passes). Microstructural analysis and microhardness profiles were performed on cross sections of FSPed samples at different depths. Wear behavior of the processed samples was evaluated by means of dry sliding tests. The results indicate that (i) increasing the number of passes results in improving the distribution of B4C reinforcing particles, (ii) samples processed with the pinless tool displayed a more homogeneous distribution of the reinforcement in the outer layer of the material with respect to the samples processed with the cone pin, (iii) the addition of B4C particles improved the wear resistance of the AA7075 alloy even if it led to a raise in the coefficient of friction.

Pinless tool for FSSW of AA 6061-T6 aluminum alloy

Pinless tools have been proposed to eliminate pinhole problems during friction stir welding; while strength of the joint could be decreased. Two probe tools with pin lengths of 2 and 3 mm and two pinless tools with the scroll groove and L-shaped grooves were used for lap welding of 2 mm thick 6061-T6 aluminum alloy sheets. The average tensile shear strength of the weld created by the long probe tool was about 3 times larger than that of the joint fabricated by the short probe tools. This difference was related to the larger stir zone and higher volume of the displaced metal resulted from the higher plunge depth, the higher heat input and more severe stirring induced by the long probe tool. The pinless welds were stronger due to the larger effective cross section area and absence of the keyhole. The application of the proposed pinless tool with L-shaped grooves produced welds with the average tensile shear strength of 2595 N in comparison to 2222 N of the welds created by the pinless tool with the scroll groove. This slight improvement was resulted from the larger stir zone and more severe stirring caused by the grooves with sharp corners.