Page 439 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

Section 16 9 Spmmng

Spinnability is found to be related to the tensile reduction of area of the material,
just as is bendability (see Fig. 16.18). Thus, if a metal has a tensile reduction of area
of 50% or higher, its thickness can be reduced by as much as 80% in just one
spinning pass. For metals with low ductility, the operation is carried out at elevated
temperatures by heating the blank in a furnace and transferring it rapidly to the
mandrel.

Tube Spinning. In tube spinning, the thickness of hollow, cylindrical blanks is re-
duced or shaped by spinning them on a solid, round mandrel using rollers (Fig. 16.46).
The reduction in wall thickness results in a longer tube. This operation may be carried
out externally or internally; thus, various external and internal profiles can be pro-
duced from cylindrical blanks with constant wall thickness. The parts may be spun
forward or bac/award; this nomenclature is similar to that of direct and indirect extru-
sion, as described in Section 15.2. The maximum thickness reduction per pass in tube
spinning is related to the tensile reduction of area of the material, as it is in shear spin-
ning. Tube spinning can be used to make rocket, missile, and jet-engine parts, pressure
vessels, and automotive components, such as car and truck Wheels.
Incremental Forming. Incremental forming is a term applied to a class of processes
that are related to conventional metal spinning. The simplest version is incremental
stretch expanding, shown in Fig. 16.47, Wherein a rotating blank is deformed by a
steel rod with a smooth hemispherical tip to produce axisymmetric parts. No special
tooling or mandrel is used, and the motion of the rod determines the final part shape
in one or more passes. The strain distribution Within the workpiece depends on the
tool path across the part profile, and proper lubrication is essential.
CNC incremental forming uses a CNC machine tool (see Section 373) that is
programmed to follow contours at different depths across the sheet-metal surface.
In this arrangement, the blank is clamped and is stationary, and the tool rotates to
assist forming. Tool paths are calculated in a manner similar to machining (Part IV),
using a CAD model of the desired shape as the starting point (see Fig. 202).
Figure 16.47b depicts an example of a part that has been produced by CNC incre-

mental forming. Note that the part does not have to be axisymmetric.
The main advantages of incremental forming are low tooling costs and high
flexibility in the shapes that can be produced. CNC incremental forming has been

'F'
Clamp 3 `1.f;
\
B|ank

__ .___ ___ '

Rotating

(fi) tool (D)

FIGURE I6.47 (a) Illustration of an incremental~forming operation. Note that no mandrel is
used and that the final part shape depends on the path of the rotating tool. (b) An automotive
headlight reflector produced through CNC incremental forming. Note that the part does not
have to be axisymmetric. Source: After ]. jeswiet, Queen’s University, Ontario.