Page 408 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

388 Chapter 16 Sheet-Metal Forming Processes and Equipment

desired path. In addition to its flexibility, an advantage of nibbling is that intricate
slots and notches, such as those shown in Fig. 16.4b, can be produced with standard
punches. The process is economical for small production runs because no special
dies are required.

Scrap in Shearing. The amount of scrap (trim loss) produced in shearing operations
can be significant and can be as high as 30% on large stampings (see Table 40.3).
Scrap can be a significant factor in manufacturing cost, and it can be reduced sub-
stantially by efficient arrangement of the shapes on the sheet to be cut (nesting, see
Fig. 16.55). Computer-aided design techniques have been developed to minimize the
scrap from shearing operations.

I6.2.2 Tailor-welded Blanks
In the sheet-metal-forming processes to be described throughout this chapter, the
blank is usually a one-piece sheet of one thickness cut from a large sheet. An im-
portant variation from these conditions involves laser-beam butt welding (see
Section 3O.7) of two or more pieces of sheet metal with different shapes and thick-
nesses. The strips are welded to obtain a locally thicker sheet or add a different
material and are then coiled.
Because of the small thicknesses involved, the proper alignment of the sheets
prior to welding is important. The Welded assembly subsequently is formed into a
final shape (see Example 16.2). This technique is becoming increasingly important,
particularly to the automotive industry. Because each subpiece now can have a dif-
ferent thickness, grade, coating, or other property, tailor-vvelded blanks possess the
needed properties in the desired locations in the blank. The result is

° Reduction in scrap
° Elimination of the need for subsequent spot Welding (i.e., in the making of the
car body)
° Better control of dimensions
° Improved productivity.

EXAMPLE l6.2 Tailor-welded Sheet Metal for Automotive Applications

An example of the use of tailor»Welded sheet metals It also makes possible the use of different materials in
in automobile bodies is shown in Fig. 16.7. Note that one component, weight savings, and cost reduction in
five different pieces are blanked first, which includes materials, scrap, equipment, assembly, and labor.
cutting by laser beams. Four of these pieces are 1 mm There are increasing applications for this
thick, and one is 0.8 mm thick. The pieces are laser type of production in automobiles. The various
butt welded and then stamped into the final shape. In components shown in Fig. 16.8 utilize the advan-
this manner, the blanks can be tailored to a particular tages outlined above. For example, note in Fig. 16.8(b)
application, not only as to shape and thickness, but that the strength and stiffness required for the
also by using different-quality sheets-with or With- support of the shock absorber are achieved by
out coatings. Welding a round piece onto the surface of the large
Laser-Welding techniques are highly developed; sheet. The sheet thickness in such components is
as a consequence, Weld joints are very strong and varied (depending on its location and on its
reliable. The growing trend toward Welding and contribution to such characteristics as stiffness and
forming sheet-metal pieces makes possible significant strength) and thereby makes possible significant
flexibility in the product design, structural stiffness, weight savings without loss of structural strength and
formability, and crash behavior of an automobile. stiffness.