August 2019 Volume 1

FORGING RESEARCH

e. Spinning Extrusion

f. Cross Rolling [5]

g. Tube Hydroforming

h. Extrusion and FrictionWelding

Figure 1-2: Manufacturing methods that can be used to produce Hollow Shafts

FIA MAGAZINE | August 2019 52 The flow forming, in Figure 1-2 d, works by deforming a rotating tube into a stepped axisymmetric part using mandrels and rollers. Flow forming locally shears the material between the roller and the mandrel and displaces it axially. Mechanical properties of the product are enhanced by cold working. Because the exterior shape of the work-piece is determined by kinematic motion of rollers, the flow forming is able to form several steps at various axial positions with simple tool design at low tool cost. However, it is difficult to produce shaft with large flange using flow forming technique [6]. As is shown in Figure 1-2 e and Figure 1-2 f, spinning extrusion combined with cross rolling can be used to manufacture hollow shafts with several steps and undercuts. The spinning extrusion produces a hollow axisymmetric part from a sold billet. In this process the spinning roller is used to shape the exterior of the part while the punch forms the interior section. Cross wedge rolling forms various diameters on the work-piece in axial direction using two moving wedge shaped tools. Spinning extrusion resembles flow forming and thus has similar advantages. It is however, difficult to produce products with deep holes using this method [7]. Although high productivity and high tolerance can be achieved with cross wedge rolling method, the inherent complexity in tool and process design has hindered utilization of this technique in industry [8]. Tube hydroforming is another manufacturing method that can be used to produce hollows shaft (Figure 1-2 g). With this method a tube is plastically deformed to conform to the die cavity shape by fluid pressure. The tube can also be fed axially to supply material to the die cavity. Although the work-piece manufactured by tube hydroforming process benefits from strain hardening and is usually

shaped in one operation, the ratio of flange diameter to wall thickness has an upper limit [9]. Additionally, long cycle time is another disadvantage of the tube hydroforming process. Figure 1-2 h shows a schematic figure of a hollow shaft manufactured by a combination of backward can extrusion and friction welding. First, two halves are produced by backward can extrusion and later joined by friction welding. The backward can extrusion is usually implemented in several operations. Depending on the material and length of the extruded cup, intermediate annealing and surface treatment (e.g., phosphate coating) may be needed. In addition, a turning operation is usually added between the extrusion and welding to improve weldability andwelding seamquality. Due to the numerous operations and the high manufacturing cost, extrusion followed by friction weld is hardly applied in mass production [4]. Although there are different ways that hollow shafts could be produced as highlighted above, to meet the demand in the automotive, aerospace, maritime, and other industries which employ solid shafts, any new manufacturing process must meet the following criteria: mass production potential, short cycle time, structural integrity, and cost effectiveness. 1.2. Objectives The overall objective of the project is to reduce the weight of various power transmission shafts by developing an economical process to mass produce hollow shafts with good quality from tubular blanks. The project is divided into three stages: investigation stage, development stage, and testing stage. In the investigation stage, the conceived manufacturing process sequence of high-power-density