Page 444 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

24 Chapter 16 Sheet-Metal Forming Processes and Equipment

the laser acts as a localized heat source, thus reducing the strength of the sheet metal
at specific locations, improving formability, and increasing process flexibility.
Applications include straightening, bending, embossing, and forming of complex tu-
bular or flat components.

Microforming. This is a more recent development and describes a family of
processes that are used to produce very small metallic parts and components.
Examples of minitaturized products include a wristwatch with an integrated digital
camera and one gigabyte of a computer storage component. Typical components
made by microforming include small shafts for micromotors, springs, screws, and a
variety of cold-headed, extruded, bent, embossed, coined, punched, or deep-drawn
parts. Dimensions are typically in the submillimeter range, and weights are on the
order of milligrams.

Electrohydraulic Forming. Also called underwater spark or electric-discharge
forming, the source of energy in this forming process is a spark between electrodes
that are connected with a short, thin wire. The rapid discharge of the energy from a
capacitor bank through the wire generates a shock wave, similar to those created by
explosives. The energy levels are lower than those in explosive forming, being typi-
cally a few k]. The pressure developed in the water medium is sufficiently high to
form the part. Electrohydraulic forming is a batch process and can be used in mak-
ing various small parts.

Gas Mixtures. As an energy source in this process, a gas mixture in a closed con-
tainer is ignited. The pressure generated is sufficiently high to form sheet-metal
parts. Although not often used in practice, the principle of this process is similar to
that used for the generation of pressure in an internal combustion engine.

Liquefied Gases. Liquefied gases (such as liquid nitrogen) also have been used to
develop pressures sufficiently high to form sheet metals. When allowed to reach
room temperature in a closed container, liquefied nitrogen becomes gaseous and ex-
pands, developing the necessary pressure. Although not used in practice, the process
is capable of forming relatively shallow parts.

CASE STUDY I6.3 Cymbal Manufacture

Cymbals (Fig. 16.51a) are an essential percussion cast into mushroom-shaped ingots and then cooled
instrument for all forms of music. Modern drum-set by ambient temperature. It then is rolled successively
cymbals cover a wide variety of sounds-from deep, (up to 14 times), with water cooling the metal with
dark, and warm to bright, high-pitched, and cutting. each pass through the rolling mill. Special care is
Some cymbals sound musical, while others are taken to roll the bronze at a different angle with
“trashy” A wide variety of sizes, shapes, weights, each pass, to minimize anisotropy, impart preferred
hammerings, and surface finishes (Fig. 16.51b) is grain orientation, and develop an even, round shape.
available to achieve the desired performance. The as-rolled blanks are then reheated and stretch
Cymbals are produced from metals-such as formed (pressed) into the cup or bell shape that
B20 bronze (80% Cu-20% Sn with a trace of silver), determines the cymbal’s overtones. The cymbals then
B8 bronze (92% Cu-8% Sn), nickel-silver alloy, are center drilled or punched to create hang holes
and brass-by various methods of processing. The and trimmed on a rotary shear to approximate final
manufacturing sequence for producing B20 bronze diameters. This operation is followed by another
cymbals is shown in Fig. 16.52. The metal is first stretch-forming step to achieve the characteristic