In metal forming processes, friction between the workpiece and the tools has both negative and positive effects. In the cases where friction opposes the flow of the workpiece material during forming, it may cause defects in the formed parts. On the other hand, in some cases friction can be useful to control the material flow and form more uniform components without defects. This book discussed the latter case and presented different metal forming processes where friction between the elastic tools and the workpiece can be used as a beneficial factor. It was also shown that friction-assisted metal forming processes can generate parts that cannot be produced, or are very difficult to fabricate using conventional metal forming processes.
Metal Forming Background
Metal forming processes are used to produce structural parts and components that have widespread applications in many industries including automobile, aerospace, appliances. Metal forming processes include a wide range of operations which deform sheet or tube metal to form the component with the desired geometry. Deep drawing is one of the most popular metal forming processes used to produce a cup like cylindrical component by radially drawing metal blank into the die cavity with the help of a punch. The cup shaped part thus produced has the depth greater than half of its diameter. The change in cross-section is achieved by plastic deformation of the initial blank. Commercial applications of this metal shaping process often involve complex geometries with straight sides and radii. In such a case, the term stamping is used in order to distinguish between the deep drawing (radial tension-tangential compression) and stretch-and-bend (along the straight sides) components.
Hydroforming is a forming technology for semi-finished goods like: tubes and sheets that aims to produce relatively small quantities of drawn parts or parts with asymmetrical or irregular contours that do not lend themselves to stamping. By hydroforming, high strength parts and to manufacture complex geometries can be obtained in one step. Even the material straining caused by fluid pressure leads to a uniform rise in yield strength in the used materials, resulting in a lower need necessary for high wall thicknesses. Hydroforming allows to overcome some of the limitations of conventional deep drawing increasing the drawing ratio and minimizing the thickness reduction of the formed parts. Some of the advantages introduced by hydroforming are: a greater flexibility and a remarkable reduction of tooling costs. Tube hydroforming is an unconventional metal forming process that uses the internal hydraulic pressure and tube end axial load to avoid rupture of the blank. Tube hydroforming is one of the most popular unconventional metal forming processes which is widely used to form various tubular components. By this process, tubes are formed into different shapes using internal pressure and axial compressive loads simultaneously to force a tubular blank to conform to the shape of a given die cavity.
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