Forming mechanism and rules of mandreless neck-spinning on corrugated pipes

Aluminum corrugated pipe has been applied in broad areas including aerospace, petrol industries due to its lightweight and good corrosion resistance. The existing welding processing method of corrugated pipes has many disadvantages, such as weld seam, long time of manufacturing, high cost, and sensitivity of weld areas to cracks, etc. Thus this paper proposed a method using mandreless neck-spinning forming process to manufacture the corrugated pipes. Based on ABAQUS/Explicit, an elastic-plastic finite element model for the mandreless neck-spinning process is established. Stress and strain distributions during the spinning process are analyzed, and the results show that the fillet between the straight wall area and the inclined wall area is the stress-strain concentration area, which has great effect on the thickness reduction and crack of the corrugated pipe. Furthermore, the single factor experiments were designed to study the effects of process parameters on the forming quality. Finally, the experiments have been carried out to verify the feasibility of this spinning method and simulations. The results show that: the mandrel speed is the most influential factor on the forming quality, a big rotation speed of mandrel leads to a bad wall straightness and inaccurate dimension of ripple area; Roller fillet radius also has a significant influence on the forming quality, and a small fillet radius results in the incomplete plastic state and a considerate amount of springback at the end of the process. A relatively big feed rate would lead to a large accumulation of material in front of the roller and severe reduction of wall thickness during the spinning process.