2011 International Conference on Mechanical and Aerospace Engineering (CMAE 2011) 604 EFFECT OF COLD FLOW FORMING DEFORMATION ON THE TENSILE PROPERTIES OF 15CrMoV6 STEEL 1 Defence Research & Development Laboratory (DRDL) Kanchanbagh, Hyderbad-500058, India Email: bpodder@drdl.drdo.in 2 Defence Metallurgical Research Laboratory (DMRL) Kanchanbagh, Hyderbad-500058, India Email: chandan_mondal@yahoo.com Abstract- Present study reports the variation in tensile properties of 15CrMoV6 steel tube at various stages of reverse flow forming using a 13mm thick annealed preform. A seamless tube of 270mm diameter and more than 1000 mm length has been manufactured by three pass flow forming process. Evolution of tensile properties in terms of yield strength, ultimate tensile strength (UTS) and percentage of elongation has been monitored after each flow forming pass. It has been observed that with the increase in number of passes, strength of the flow formed tubes increases rapidly with considerable drop in elongation values. The present study demonstrate that a combination of very high strength (UTS=933MPa) with reasonable ductility could be achieved in the as-flow formed condition without any subsequent heat treatments by choosing suitable process parameters. Keywords- Flow forming; 15CrMoV6 Steel; Tensile properties; Ductility. I. INTRODUCTION Flow-forming, commonly known as tube spinning, is an advanced chip less, net-shape, cold metal forming process. The process is capable of producing precise, thin walled tubes. During the process, a shorter and thicker preform is deformed into a thinner and longer tube over a rotating mandrel with the help of one or more rollers. Depending upon the material being formed and final thickness requirement of the flow formed tube, the total reduction in thickness needs to be carried out in a number of forming passes. Due to the inherent advantages of the process, it has found wide acceptability in defense, aerospace and automobile industries. The process can broadly be classified in two categories viz., forward and reverse flow forming. In case of the forward flow forming (Fig.1), direction of material flow is in the direction of axial movement of the rollers and support of tailstock is mandatory during the process. Whereas, material flow takes place in the opposite direction of roller axial movement for the reverse flow forming (Fig.2) and drive ring is necessary to transfer the rotational movement of the mandrel into the work-piece. Over the years several experimental and analytical studies have been carried out to understand the mechanics of the process and to estimate the forming forces [1-4]. The experimental investigations have mainly been focused on the shear spinning of long tubes using various critical aerospace materials [5]. Finite Element Method has also been used to study the deformation characteristics and the axial displacement distribution [6]. Although the mechanics of the process is reasonably well understood, there is a lack of the literature on the correlation between flow forming parameters and the resultant mechanical properties. Such studies assume a greater significance to the process designers as an optimum balance of strength and ductility could be achieved by selection of suitable process parameters. The aim of the present investigation is to study the effect of deformation on the mechanical properties of flow formed 15CrMoV6 tubes and to obtain a combination of high strength and moderate ductility in the flow formed tube. Tube, thus, produced will be used for a critical aerospace application requiring an optimum balance of tensile strength and ductility. Figure 1. Schematic diagram of forward flow forming. Figure 2. Schematic diagram of backward flow forming. Chandan Mondal 2 Bikramjit Podder 1 ,G.Gopi 1 K.Ramesh Kumar 1 , D.R. Yadav 1 978-1-4244-95 06 -1 C /11/$26.00 2011 IEEE