Page 437 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

Section 16.9 Spinning 4| 7

FIGURE l6.44 View of the tube-hydroforming press,
with bent tube in place in the forming die.

expanded, there is significant wall thinning, especially The assembly shown has 76 holes that are
at the corners, because of friction at the tube-die pierced inside the hydroforming die. The ends are
interface. The pressure sequence hydroforming then sheared to length. The 10 components in the
process is therefore used on this part, as shown in hydroformed closure are then assembled through
Fig. 16.43b. In this approach, a first pressure stage robotic gas-metal arc welding (see Section 30.4.3) and
(prepressure stage) is applied as the die is closing, with threaded fasteners to aid in serviceability.
causing the tube to partially fill the die cavity and form Compared to the original stamped design, the
the cross-sectional corners. After the die is completely hydroformed design has four fewer components, uses
closed, the internal pressure is increased to lock in the only 20 welds as opposed to 174 for the stamped
form and provide support for hole piercing. This design, and weighs 10.5 kg versus 14.1 kg. Further-
sequence has the benefit of forming the sharp corners more, the stiffness of the enclosure is increased by as
in the cross section by bending, as opposed to pure much as 150% in some directions. In addition, the
stretching in conventional hydroforming. The result- cooling system surface area is increased by 43% in
ing wall thickness is much more uniform, producing the new design.
a more structurally sound component. Figure 16.44
shows a part being hydroformed. Source: Courtesy of B. Longhouse, Vari-Form, Inc.

l6.9 Spinning

Spinning is a process that involves the forming of axisymmetric parts over a mandrel
by the use of various tools and rollers-a process is similar to that of forming clay
on a potter’s wheel.

Conventional Spinning. In conventional spinning, a circular blank of flat or pre-
formed sheet metal is placed and held against a mandrel and rotated while a rigid
tool deforms and shapes the material over the mandrel (Fig. 16.45a). The tool may
be activated either manually or (for higher production rates) by computer-controlled
mechanisms. The process typically involves a sequence of passes, and it requires
considerable skill. Conventional spinning is suitable particularly for conical and