Numerical and experimental research of the process of reducing the diameter of a S355J2G2W steel pipe by necking

Abstract

Abstract. The article presents the results of research the process of reducing the diameter of pipe ends using the necking method, which are applied to the ends of pressure hoses. The aim of the research was to determine the possibility of reducing the diameter of the S355J2G2W steel pipe by cold necking. The research was carried out using numerical analysis, which was verified experimentally. The software Simufact.forming was used for numerical research of the pipe endnecking process. Experimental tests were carried out using specially designed and made dies and a hydraulic press. As a result of the tests, we determined the pushing force for various friction conditions and the clamping force of the die for four types of grease. The article also presents experimental results of measurements of wall thickness of the pipe being reduced (diameter before and after leaving the die). The test results showed a large influence of the type of grease on: upsetting and elongation of the pipe, flow and the quality of the material surface. The test results showed the effect of the cone angle of the standard die made on the buckling phenomena during the necking process. On the basis of the conducted research, tools for changing the diameter of pipes with theoretically unlimited length were designed. IntroductionNecking is a shaping method, used to reduce diameter or cross-section of pipes, rods and vascular elements by acting on them with an external compressive force. The necking process can be carried out using rotary shaping on roll crushers equipped with a specified number of forming rollers (neckspinning) [1,2,3,4], or with the use of stationary tools, i.e. dies with appropriate geometry [5]. Neck-spinning is most often used in the production of vascular components such as pressure containers -fire extinguishers, industrial gas cylinders, gas storage cylinders. On spinning lathes, operations are performed to close the bottom of the vessel and necking operations, which are usually carried out on a hot surface with simultaneous flame heating where the tool contacts the material.The necking with dies consists in applying pressure to the face of the blank and pressing it into the conical die hole [8]. The process is most often carried out on vertical or horizontal hydraulic presses. The change in diameter can be carried out only on a specific part of the pipe or on its entire length, then a very important aspect is the correct guiding of the pipe, in order to prevent its loss of stability and buckling. The length of the shaped part of the pipe is also dependent on the machine construction and the maximum stroke. The limiting deformation during pipe necking operation is limited by the loss of stability which occurs at = 0,025. In addition, the reduction of the pipe diameter by this method can be carried out as free and with the internal pipe guide using a rod. The method with guiding is used in cases of possible loss of stability of the pipe after leaving the die.