210s

Welding Journal | June 2016

KEYWORDS • Friction Stir Welding • Nylon 6 • Polymer • Material Flow • Threaded Pin Introduction The use of polymeric materials has grown widely in various sectors such as packaging, building, electronic, automotive, and aerospace industries. Particularly, Nylon 6 has wide engineering applications and is used in large quantities in automotive oil pans, gears, slides, cams, bearings, fluid reservoirs, and the sports industry (Ref. 1). Polymeric materials offer many advantages over metal and its alloys owing to certain distinct properties: light weight, high specific strength, high specific modulus, design flexibility, low production costs, good corrosion and environmental resistance, thermal and electrical insulation, and durability (Ref. 2). Increase in use of a particular material, on the other hand, increases the importance of the joining process. In engineering, the production of a single piece from molding is an ideal situation because it eliminates many steps of assembling. However, due to the complexity of parts and dissimilarity in joining components in some cases, efficient joining processes are necessary. Friction stir welding (FSW), among modern joining techniques, is now widely considered as a joining process, owing to its low-cost production and eco-friendly process. Moreover, by using this technique, the weld joint can be accomplished by controlling fewer parameters, such as rotational speed, feed rate, plunge depth, and tool dimension (Ref. 3). Since its inception, a variety of metal alloys has been successfully joined by this process. Investigations regarding their mechanical and microstructural properties are widely reported in literature. However, in the case of polymers, application of FSW to produce joints is a relatively new approach and requires further investigation. The nonconductor nature of polymers makes it challenging to weld them, especially in the case of a thick workpiece. However, some polymeric materials have been successfully friction stir welded up to the maximum workpiece thickness of 10 mm. The results, in order to achieve the maximum strength, are characterized through various means and reported in literature. In order to avoid the root defect fracture and to enhance the weld strength, different approaches have been adopted to eliminate this particular defect. For this purpose, Arici et al. (Ref. 4) used double passes of the tool on 5-mm-thick polyethylene (PE) sheets. Pirizadeh et. al. (Ref. 5) used a bobbin tool on 5-mm-thick acrylonitrile butadiene styrene (ABS) sheets. However, in the case of polymers with low melt viscosity or low melting temperatures, such as Nylon 6, which has a melt viscosity of 300 Pa-s at 250C (low shear rate) (Ref. 6), double passes WELDING RESEARCH Investigating Friction Stir Welding on Thick Nylon 6 Plates Exploring the effects of rotational speed on micromechanical properties, flow behavior, and thermal variations BY A. ZAFAR, M. AWANG, S. R. KHAN, AND S. EMAMIAN ABSTRACT Polymeric materials, despite being thermal insulators, are now being welded using different welding techniques. In the current work, the feasibility of the friction stir welding (FSW) process on 16mmthick Nylon 6 plates was studied. The effects of rotational speed on the weld quality were investigated by the temperature development, micromechanical properties, crystallization growth, and fracture analysis of the joints. Results showed the dependence of temperature and tensile values on rotation rates was insignificant. However, appearance of considerable defects at higher rotation rates, observed in visual and microscopic analysis, indicated that Nylon 6 is weldable only at lower rotation rates due to its low melt viscosity. Moreover, identical fracture locations during tensile tests revealed that the interface of weld zone on the retreating side was the weakest part of the joint. It can be attributed to the lack of bonding at the interface of the weld zone on retreating side and relatively low crystallinity in the retreating side region. Due to different rheological and physical properties of polymers than metals, the flow phenomenon in Nylon 6 was found to be different from that of metals, resulting in a distinct isolated pin plunged zone. A. ZAFAR (adeel_ze@ymail.com), M. AWANG (mokhtar_awang@petronas.com.my), S. R. KHAN, and S. EMAMIAN are with the department of mechanical engineering, Universiti Teknologi Petronas, Perak, Malaysia. 210-s WELDING JOURNAL / JUNE 2016, VOL. 95


Welding Journal | June 2016
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