Steels_ Metallurgy and Applications, Third Edition

106 Steels: Metallurgy and Applications

per minute for 2.0 mm strip. A good fit-up between the pieces to be joined and

good joint beam alignment is, however, necessary for these rates to be employed.

Simulative forming tests showed that cup heights of 80-100% of those of the

parent material may be obtained with the weld before failure. The situation

is more complicated when the sheet components have a significantly different

thickness.

Laser-welded blanks are used in automotive construction for components such

as door inners, monosides and longitudinal rails, as previously illustrated in

Figure 1.33. The benefits depend on the part and on the production volumes.

Laser seam welding is also now used for vehicle construction to produce contin-

uous joints and improve torsional stiffness. The number of applications is small

at present but is likely to increase in the future. The narrow weld results in low

distortion. Close tolerances are, however, required on joint fit-up.

?dig and TIG welding

These abbreviations refer to metal inert gas and tungsten inert gas respectively.

Both processes are arc welding methods in which an inert gas is used to protect

the weld. In the MIG process the weld is prepared using a consumable electrode

which melts to form part of the weld metal. In the TIG process a non-consumable

tungsten electrode is used and the weld metal comes from the pieces to be joined.

Mechanical joining

One of the simplest methods of joining along a straight edge is to use what
is called lock forming or clinching, as illustrated in Figure 1.105. Modifications
of this method are particularly suitable for the manufacture of box sections, as
shown in Figure 1.106. Another technique involves the use of a pneumatic tool
which cuts holes in the pieces to be joined and bends two tags through the holes
to make a joint, as illustrated in Figure 1.107.
Press joining provides a further technique for joining sheet materials. 157 The
tooling for this method is illustrated in Figure 1.108 and consists of a punch, an

,, ,,,

(a) Double lock seam

(b) Pittsburgh lock seam

Figure 1.105 Two forms of lock seaming 155