Effect of Pin Geometry and Orientation on Friction and Wear Behavior of Nickel-Coated EN8 Steel Pin and Al6061 Alloy Disc Pair

Most mechanical systems (in particular, gear transmission system) undergo relative motion which results in increased friction phenomenon (friction coefficient, stresses, and wear rate) and thereby results in loss of efficiency. Mechanical parts undergo relative motion in different geometry configurations and orientations that induce a different state of stress as a result of friction. Till date, attempts are being made to minimize the friction with full sphere pin geometry configuration. The present work focused to reduce the frictional and wear rate, and experiments are conducted with tribo-pairs. i.e., nickel-coated pin surface slide against Al6061 alloy disc. The friction studies are carried out at different loads and geometries of pin surfaces (sphere and hemisphere configured at different orientations such as full sphere and hemisphere configured at 0°, 45°, and 90°) to induce different stress states with reference to sliding directions. Change in the geometry of EN8 pin material and their orientation with reference to sliding direction resulted in a different state of stress. The resulting stress levels were examined under the scanning electron microscope, which revealed the mechanisms of adhesion, abrasion, and extrusion. At a lower magnitude of orientation and load, the extent of asperity breaking lessens and material removal from pin surface decreases. Abrasion wear mechanism was observed corresponding to full sphere configuration on Al 6061 disc, whereas adhesive wear mechanisms are seen with hemisphere pins. The amount of aluminum transfer on pin surface with a hemisphere pin is comparatively more than that of full sphere configuration. At a lower magnitude of state of stress, the mechanism of sliding was dominated by the adhesion effect. At a higher level of state of stress, the mechanism of sliding was dominated by abrasion and extrusion.

Investigation on Friction Stir Weldability Characteristics of AA7075-T651 and AA6061-T6 Based Nanocomposites

Friction stir welding (FSW) is an emerging solid-state process and alternative to fusion welding, wherein frictional heat is generated between a nonconsumable rotating steel tool and the work substrate. The present study focuses on the influence of the operating attributes like tool pin contact geometry, welding speed, and tool rotational speed on dissimilar aluminum matrix nanocomposites. AA6061-T6 and AA7075-T651 aluminum alloy plates were joined via double-pass FSW with the inclusion of 5 vol. % of nanoscale h-BN particles. Welding was performed with four rotational speeds (600, 800, 900, and 1000 rpm), three traversing speeds (30, 40, and 60 mm/min), and three distinct tool pin geometry (cylindrical, threaded cylindrical, and square), respectively. Besides, unreinforced and reinforced weldments were analyzed for mechanical properties like tensile strength and microhardness. Microstructural characterization was also carried out using FESEM and XRD techniques. The findings concluded that the reinforced samples welded using a cylindrical tool and double-pass strategy showcased homogenous distribution of nanoparticles with grain refinement, thereby exhibiting improved strength and hardness.

Pin Angle Thermal Effects on Friction Stir Welding of AA5058 Aluminum Alloy: CFD Simulation and Experimental Validation

The friction stir welding (FSW) of tool pin geometry plays a critical role in the final properties of the produced joint. The tool pin geometry directly affects the generation of heat and the flow of internal materials during the FSW process. The effects of the FSW tool pin angle on heat generation and internal flow have not been quantitatively investigated in detail. In this manuscript, a validated Computational Fluid Dynamic (CFD) model was implemented to analyze the effects of pin angle on the thermo-mechanical action during the FSW process of AA5058 Al-Mg alloy. Experimental test results validate the thermal outcomes of the used model. The obtained results revealed that, when the pin angle is increased, the heat generation decreases while the mechanical action of the tool increases. The internal heat distribution at a higher pin angle is symmetrical. The higher mechanical action of the tool decreases the viscosity of the internal materials and increases stirring action (materials flow) around the pin. Furthermore, plastic flow near the tool increased stirring action and formed a larger stir zone in the joint area.

Effect of Tool Pin Geometry on the Microhardness and Surface Roughness of Friction Stir Processed Recycled AA 6063

Friction stir processing was experimented on recycled aluminum alloy 6063 to investigate the effects of varying friction stir tool pin geometry and friction stir processing parameters on the microhardness and surface roughness. Different tool pin geometry has great influence on the outcome as it alters the ability to provide localized heating and better material flow. This study was performed using two different types of tool pin geometry, namely, the cylindrical threaded and the taper threaded pins, across varying rotational speeds and feed rates. The mechanical properties of the processed workpiece were inspected and analyzed in terms of microhardness, microstructure, and surface roughness. The results show that the taper threaded tool offers the highest improvement in microhardness up to 63% at the lowest rotational speed and highest feed rate at 1150 rpm and 30 mm/min, respectively, and this is supported by microscopy images showing finer grains with the compact and homogenous distribution. The taper threaded tool also provided a better surface roughness than the cylindrical threaded tool. However, the surface produced by cylindrical threaded at 30 mm/min feed rates is as smooth and consistent as that of taper threaded tool.

Bobbin Tool Friction Stir Welding of Aluminum Thick Lap Joints: Effect of Process Parameters on Temperature Distribution and Joints’ Properties

Bobbin tool friction stir welding (BT-FSW) is characterized by a fully penetrated pin and double-sided shoulder that promote symmetrical solid-state joints. However, control of the processing parameters to obtain defect-free thick lap joints is still difficult and needs more effort. In this study, the BT-FSW process was used to produce 10 mm AA1050-H14 similar lap joints. A newly designed bobbin tool (BT) with three different pin geometries (cylindrical, square, and triangular) and concave shoulders profile was designed, manufactured, and applied to produce the Al alloy lap joints. The experiments were carried out at a constant tool rotation speed of 600 rpm and a wide range of various welding travel speeds of 200, 400, 600, 800, and 1000 mm/min. The generated temperature during the BT-FSW process was recorded and analyzed at the joints’ center line, and at both advancing and retreating sides. Visual inspection, macrostructures, hardness, and tensile properties were investigated. The fracture surfaces after tensile testing were also examined. The results showed that the pin geometry and travel speed are considered the most important controlling parameters in BT-FSW thick lap joints. The square (Sq) pin geometry gives the highest BT-FSW stir zone temperature compared to the other two pins, cylindrical (Cy) and triangular (Tr), whereas the Tr pin gives the lowest stir zone temperature at all applied travel speeds from 200 to 1000 mm/min. Furthermore, the temperature along the lap joints decreased with increasing the welding speed, and the maximum temperature of 380 °C was obtained at the lowest travel speed of 200 mm/min with applying Sq pin geometry. The temperature at the advancing side (AS) was higher than that at the retreating side (RS) by around 20 °C. Defect-free welds were produced using a bobbin tool with Cy and Sq pin geometries at all the travel welding speeds investigated. BT-FSW at a travel speed of 200 mm/min leads to the highest tensile shear properties, in the case of using the Sq pin. The hardness profiles showed a significant effect for both the tool pin geometry and the welding speed, whereas the width of the softened region is reduced dramatically with increasing the welding speed and using the triangular pin.

ANALYTICAL AND NUMERICAL THERMAL ANALYSIS ON FRICTION STIR WELDING USING POLYGONAL TOOL PIN

Frictional heat generation in the tool/matrix interface followed by the stirring of material along the weld line causes plasticized solid state joining in friction stir welding. In this paper, the existing torque based thermo-mechanical model for the tools with cylindrical pins is remodified for the polygonal tool pin profile by introducing novel multiplication factors with respect to the number of sides in the tool pin geometry. The variation in the effective heat supply with respect to the chosen pin geometry was analyzed. A comparative analysis of the proposed analytical model with the existing model was also carried out to understand the accuracy of the proposed model. Furthermore, a transient thermal numerical modelling was carried out in the view of understanding the change in process peak temperature in the stir zone and change in temperature gradient along the heat affected zone with respect to the change in pin geometry for the opted set of process input parameters. An analytically estimated heat-input-based numerical model was adopted in the present study. It was observed that the process peak temperature was directly proportional to the number of sides in the tool pin. ABSTRAK: Penjanaan haba geseran antara muka pada alat/matrik diikuti dengan pengacauan material sepanjang garis kimpalan menyebabkan keadaan plastik pepejal melekat bersama geseran kimpalan pengacau. Kajian ini berkaitan tork sedia ada berdasarkan model mekanikal-terma bagi alat pin silinder yang terubah suai bagi profil pin alat poligon dengan memperkenalkan faktor gandaan berdasarkan bilangan sisi geometri alat pin. Perubahan pada bekalan haba efektif berdasarkan geometri pin pilihan telah dikaji. Analisis bandingan pada model analitik yang dicadang bersama model sedia ada, telah dilakukan bagi memahami ketepatan model cadangan. Tambahan, model transien numerikal terma telah dibuat bagi memahami proses perubahan suhu puncak ketika zon pengacauan dan perubahan gradien suhu sepanjang zon terkena haba perubahan geometri pin pada set proses parameter input terpilih. Kajian ini mengaplikasi model numerik berdasarkan input anggaran haba secara analitik. Dapatan kajian menunjukkan suhu puncak proses adalah berkadar langsung dengan bilangan sisi pin alat.

Experimental analysis on friction stir welding using flat-faced pins in AA2024-T3 plate

In friction stir welding, lesser tool life restricts the usage of non-circular pin in friction stir welding tool eventhough it delivers comparatively better weld joints than circular pin. Process peak temperature during the process affects the shear strength of the flowing material around the tool pin. Maintaining the process peak temperature as low as possible improves the properties in heat affected zone but on the other hand it increases the stress on the tool pin.Especially on the usage of non-circular pin, the pin surface experiences uneven stress distribution and causes premature tool failure. In this paper, optimum thermal environment through proper selection of process parameters and dwell period with respect to the pin geometry are analysed. A comparative analysis is also made to understand the impact of increase in flat surfaces in the pin surface on weld quality in the view of developing a suitable thermal environment that can improve tool life without compromising joint strength. Apart from this, optimum dwell period for the chosen tool pin geometry is analysed based on the empirical softening temperature of the material.

Improvement of thermal EHL by selecting bush-pin geometry based on an investigation for industrial chains

Purpose This study aims to investigate the influence of geometry of bush-pin pair from a perspective of optimal lubrication through a thermal elastohydrodynamic lubrication model for finite line contact. Design/methodology/approach A constitutive equation: Ree-Eyring fluid is used in the calculations. The real chain sizes, i.e. equivalent radius of curvature, bush length, length of the rounded corner area and rounded corner radius, are jointed investigated. Moreover, the effects of the length of the rounded corner area and the radius of rounded corner are investigated. Findings It is found that the current standard of the chain might not consider the importance of lubrication, and the lubrication state can be improved effectively by choosing an optimal radius of rounded corner and the length of the corner area. Originality/value By optimally selecting sizes, the occurrence of high pressure, high temperature rise and near zero film thickness at the ends of bush, especially under heavier load, can be effectively avoided. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2020-0031/