Journal of Materials Processing Technology 173 (2006) 145–150 An experimental and analytical study on dome forming of seamless Al tube by spinning process N. Akkus a,∗ , M. Kawahara b a Marmara University, Faculty of Technical Education, Istanbul, Turkey b Tokyo Metropolitan University, Graduate School of Engineering, Tokyo, Japan Received 3 November 2004; accepted 3 November 2005 Abstract The thickness distribution of a spin formed dome in an Al pressure vessel was studied experimentally and a simple formulation to predict the thickness distribution of the dome was proposed. The ends of the seamless Al tubes, which are widely used as liners in high pressure FRP composite vessels, were closed by spin forming. The thickness of the boss part of the dome may not be sufficient after forming operations, especially for high pressure vessels in which a deep thread cut is necessary for accommodating a pressure gas valve. Thus, a two-step spin forming of the Al tube end closure was proposed to improve and thicken the boss. First, the boss was deformed to a diameter smaller then the desired one. Later the dome was modified to obtain a greater boss diameter. The second forming provided a greater and better thickness distribution around the boss. Experimental work was carried out to compare the thickness distribution obtained with the conventional process and using the proposed two-step spin forming process. The ends of Al 6061-O tubes were deformed to dome shapes at an elevated temperature using a spinning machine. A simple analytical model, which was based on geometrical shape changes and an assumption of material constancy during forming, was formulated to predict the final thickness distribution of the dome. The results indicate that the proposed two-step spin forming provides a greater boss thickness than that of conventional forming. © 2005 Elsevier B.V. All rights reserved. Keywords: Spinning; End closure of tube; Pressure vessel; Dome forming; Analytical model; Boss thickness; Large deformation 1. Introduction Spinning is a process in which a flat circular sheet or a tubular form is turned and forced by a roller to deform to a predefined cir- cular shape with or without a mandrel. The spin forming process can also be classified as shear spinning, spin forging or necking, depending on how the forming takes place. Developments in NC and CNC control technology allow the production of more complicated precise shapes using spinning technology. Auto- motive parts such as two- and three-piece wheels, rims, disks, and shaft covers, single or multi pulleys, and pressure accumula- tors and home appliances such as rice cookers and large speaker bodies are specific applications of spinning processes. In some processes, spinning is the only shaping operation with little or no change in thickness between the initial blank and the finished parts. ∗ Corresponding author. E-mail address: nakkus@marmara.edu.tr (N. Akkus). Little research has been conducted on the spinning process compared with other forming processes such as deep drawing. Human controlled rollers are used in spin forming, and produc- tion need highly skilled workers until NC and CNC controlled machines became available. The human factor in the process, with big shape changes under large deformations, made analyt- ical modeling of the spinning process more complicated. Only a very small number of studies have been conducted. These studies are broadly concerned with the conventional spinning process, and studies relating to specific applications of the spin- ning process are very rare. Mainly, cone spinning is the interest of researchers. Especially in the 1960s, several reports focus- ing on analytical modeling of cone shape spinning have been published. Kalpakcioglu [1] assumed a shear mechanism for the deformation and presented a formulation involving the shear strain, shear strain rate, and tangential force to predict the param- eters. The wall thickness distribution of aluminum blanks in a cone spinning process was studied by Sortais et al. [2]. They reported the effect of the roller setting on the thickness distri- bution in under spinning, shear spinning, and over spinning. 0924-0136/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2005.11.011