28
Improving Global Quality of Life
Through Optimum Use and Innovation of Welding and Joining Technologies
Finally, testing of welds will be extended to all periods of the life-cycle of the welded structures. In addition
to the fabrication and service phase, they will also significantly contribute to life-cycle extension (repair)
procedure of the critical components.
4.2
High energy density welding processes and material response
High energy density (HED) welding simply refers to Laser Beam Welding (LBW) and Electron Beam Welding
(
EBW) processes. The benefits offered by HED fusion welding are narrow, deep weld penetration, high
welding speeds, low heat input (and hence low distortion and heat affect) and precision. EBW is somewhat
mature and has various well-accepted applications including packaging (e.g. pressure sensors) and aerospace
components. There have been attempts to broaden application to high production (e.g. automotive)
manufacturing, but incompatibility of vacuum systems with the demands of large scale production have
prevented these applications. In contrast, LBW has benefited from continual development of new laser
sources with new capabilities and is somewhat more compatible with the demands of high production and
large component manufacturing, so it enjoys a broader range of applications.
Nonetheless, challenges of high equipment cost, lack of system portability, laser safety, lack of robustness to
manufacturing environments (particularly, the need for cleanliness of optical surfaces) continue to hamper
LBW applications. Smaller, more efficient laser sources or central laser generators with fibre distribution
system would help with LBW portability. Practical, robust cost-competitive out-of-vacuum capability would
promote EBW applications. Eliminating root defects in partial penetration LBW would assist its application,
and laser systems with multiprocess capability (i.e. cut, drill, weld, machine interchangeably on the same
system) would be more economical. The general need for off-line process planning for virtual manufacturing
are the same as for other joining processes, but the models and needs for HED processes are unique.
The continuously disappearing global resources in metals require and make it economically advantageous
to join dissimilar materials according to function. Bi-metal segment saws need wear resistant teeth and
a carrier for fastening. With continuous wear the teeth may be sharpened by grinding down to the holes
of the rivets
(
Figure 4.5
).
High speed steel costs today 10 times more than carbon steel. It is evident, that
such a bi-metal design is cost effective and works as well as made from full HSS. The preferred process with
minimum energy consumption for joining is electron beam welding.
A similar application with the same underlying concept is EB welding of worm gears consisting of bronze
and steel. The expensive bronze is only used where its lubricating characteristics and wear resistance are
required at the outer circumference. There are many such examples already taking place today and with
rising material cost, in the future, these applications of joining dissimilar materials will increase.
Figure 4.5
Segment of a cold saw of high speed
steel EB-welded to carbon steel in annealed
condition. This saves 50% of the expensive high-
speed steel (Reproduced courtesy: Probeam)
Figure 4.6
Combination of steel and bronze,
30
mm deep electron beam weld (Reproduced
courtesy: Probeam)
