Fig. 10 — Effect of the rotational speed on temperature; measured 1 mm below the pin tip. Fig. 12 — Sectioning scheme of material flow specimens. Figure 13A shows the specimen before welding with marker material in the longitudinal direction (parallel to welding direction). After welding, vertical cross sections of the specimen were made to observe the flow in x-direction, which is perpendicular to the welding direction (WD). It can be clearly seen in Fig. 13B that thin marker material, when placed on the RS (I), spread all over the welding zone, equivalent to pin diameter. Similarly, in Fig. 13C, marker material placed on AS (II) stirred and spread in complete welding zone. This spreading indicates a uniform stirring, either marker material is on the AS or the RS. However, in both cross sections it can be observed that marker material at the top of the specimen is not well stirred and positioned toward the AS. It is believed this unstirred area is due to a small, unthreaded part of pin near the shoulder. Furthermore, it is also observed the depth of the WZ is equivalent to the pin plunged length. It shows there was no cross flow from the plunged area to the unplunged zone at the bottom of the pin. A similar phenomenon was observed on the adjacent right and left sides of the plunged area. This restriction of WZ within the plunged area is also mentioned by Simoes and Rodrigues (Ref. 20) in their study of PMMA. In order to observe the y-direction flow (parallel to WD) of the specimen, marker materials were placed transversely (perpendicular to WD) on the AS (I), weld interface (II), and RS (III), as shown in Fig. 14A. After welding, horizontal sections were prepared. It is clear from Fig. 14B–D marker material after stirring was displaced behind the pin. The maximum displacement measured in Fig. 14C, D was remarkably very long, 11 mm, whereas the diameter of the pin is 7.5 mm. However, distribution of marker material (shown in Fig. 14C, D) was uniform, but narrowing of marker material at the end was observed. It is believed the farthest narrow part is squeezed and extruded by the pin. This extrusion phenomenon is similar to Colligan’s (Ref. 18) material flow study on FSW of aluminum alloy, in which he considered the welding process due to stirring and extrusion. As the material of the AS in Fig. 14B is prone to flow on sides, it can be said the vacant sides at the end in Fig. 14C, D can be filled by material from the AS. Thereby, it covers a complete welding zone and leaves no defects. In order to understand the complete flow during welding, flow in the zdirection was also observed. For this purpose, marker materials were placed at bottom, middle, and top of the AS and RS. It is shown in Fig. 15A, B, respectively. After welding, longitudinal sections of welded specimens were made to observe vertical movement. These are shown in Fig. 15C, D. It is clear from the sections that material at the bottom expanded up to the surfaces of both specimens. A similar case was observed for middle marker materials. Marker material at the top expelled out from the specimen and resulted in formation of flash. No difference in this upward movement of marker materials was found either on the AS or RS of specimens. A large, vertical movement of material during welding was also observed by Guerra et al. (Ref. 19), Li et al. (Ref. 15), and Seidel and Reynolds (Ref. 17) in their study on aluminum. Conclusions Systematic work was carried out on the friction stir welding of 16-mmthick Nylon 6 plates using a threaded pin tool with a small-diameter shoulder. Based on the aforementioned results and discussion, the following conclusions can be made: WELDING RESEARCH 216-s WELDING JOURNAL / JUNE 2016, VOL. 95 Fig. 11 — DSC curves of 300 rev/min with a 0deg angle Nylon 6 sample of different locations.
Welding Journal | June 2016
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