Fromability Analysis of AA5052 Alloy for Single - Point Incremental Hole Flanging Process

Abstract

Single Point Incremental Forming technique is advantageous in terms of complex contour forming, high formability, and low-cost setup, especially in prototype manufacturing and job production of sheet metal parts. The technique has been implemented to perform the hole flanging operation by researchers. The hole-flanging using Single Point Incremental Forming incorporates the advantages of the technique in the flange forming. The formability in the flange forming is analysed by measurement of the thickness of the flange, the height of the flange, and by finding the limit forming ratio. Moreover, the deformation mechanism is evaluated by analysing the strain distribution on the strain space diagram. Similar to the forming of conical and pyramidal shapes, the necking is suppressed in the Single Point Incremental Hole Flanging (SPIHF) too. However, due to the presence of the hole in the sheet metal, the strain distribution is different. The strain distribution also depends on the single stage and multistage strategies used for the flange forming. The majority of the studies are on the multistage flange forming of conical or cylindrical flanges on the sheet of aluminum alloys, but the forming of flanges of other shapes may have different deformation mechanisms. A comparative study of the single-stage and multistage strategies has been studied and analysis has been presented in this thesis. Moreover, the square flange forming using the single-stage SPIHF has been analysed. Further, a novel tool is proposed to achieve grain refinement on the aluminium alloy during the SPIHF process and the experimental study has been carried out to analyse the effect of the use of proposed tool on the grain structure. A fixture and tools have been developed to perform SPIHF using Vertical Machining Center. The detailed analysis of the formability of the AA5052 alloy in the hole-flanging using the Single Point Incremental Forming technique has been carried out being a potential material for marine and other industrial applications. In the preliminary experiments, the effect of the tool diameter on the Limit Forming Ratio (LFR) in SPIHF of AA1050 alloy has been studied. The large tool diameter (12 mm) resulted in better formability with higher LFR (1.81) as compared to small tool diameter (8 mm) which gave the lower LFR (1.56). Moreover, the experimental study has been carried out on the formability of AA5052 alloy in single-stage and multi-stage SPIHF. The LFR of 1.81 and 2.0 were obtained in the single-stage and the multi-stage strategies respectively, which shows that higher formability could be achieved in the later. However, the stretching of the flange reduced when the larger tool was used. Further, the effect of process parameters (spindle speed, feed rate and step depth) on the flange quality was evaluated based on the Taguchi method. The results suggest that the step depth is the most effective parameter whereas the spindle speed and feed rate have a high interactive effect. To establish the use of the Single-Point Incremental Forming method in forming flange shapes other than the cylindrical, the square shape flange forming has been carried out. In the available literature, it was performed using the multistage method. In this work, the single stage method has been implemented for the same. The deformation modes on the flange have been analysed. The Limit Forming Ratio for the same has been defined and it has been obtained for the AA5052-H32 material using an experimental study. The non-rotating tool resulted in the Limit Forming Ratio of 1.26 which reduced to 1.20 when a rotating tool was used. Moreover, the effect of the corner radius of the pre-cut square hole on the formability has been evaluated by forming the flanges with three different pre-cut hole corner radius of 6 mm, 8 mm, and 10 mm. The higher corner radius increased the Limit Forming Ratio to 1.35. Further, to improve the hardness of the AA5052-H32 material, a novel tool has been proposed. The novel tool has its axis eccentric to the spindle axis and hence generated an alternate contact pattern during the forming process. The grain structure of the as-received material and the formed flanges has been analysed by Electron Back Scattered Diffraction (EBSD) measurement. The results showed that the rotating tool refined the grain structure of the material, moreover, the proposed eccentric tool increased the grain refinement. The strain hardening has been observed on the flange formed by the novel tool and the microhardness increased. In summary, this work has provided a better understanding of the single-stage and multistage Single Point Incremental Hole Flanging of cylindrical shapes. Also, the implementation of the single-stage strategy to form a square flange has been evaluated and an attempt has been made to improve the process by proposing a novel tool which was used for strain hardening of AA5052-H32 material.