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Through Optimum Use and Innovation of Welding and Joining Technologies
Improving Global Quality of Life
9.6.2
Materials development
High-tensile steel materials have been developed and utilised, and this has contributed to weight reduction
by use of smaller gauges. If ultra-high-tensile steels are introduced, however, spring back of stamped sheets
will become a problem. In welding jigs, fitting accuracy of ultra-high-tensile steel will be certainly inferior to
former steels. Welding techniques such as the increase of electrode pressure force and countermeasures
for electrode abrasion need to be investigated. Thin gauge sheets should not be applied to areas of the
vehicle which influence the rigidity of the auto body due to potentially reduced safety of passengers.
It is important therefore that applied portion must be selected thoroughly by use of structural analysis
simulation.
As well as high-tensile steel, galvanised steel is necessary for automobiles from the viewpoint of corrosion
resistance. For more than 20 years, galvanised steel has been utilised in the body for the purpose of
preventing red rust which spoils the external appearance. It also has been adopted in the chassis parts for
the purpose of preventing a decline of the strength which depends on plate thickness. In Japan, galvanised
steel, thinly coated by hot-dipping can be supplied, but in consideration of the cooperation between Japan
and foreign countries, recently the thickness of galvanised coating was unified. This change is making the
coating thicker in chassis parts, and it is thought to be more difficult to weld in the case of arc welding in
which porosity and spatter are increased considerably. Modern welding processes are able to deal with this
challenge however.
To overcome the limitations of steel, the application of aluminium has been investigated, and it is used in
covers such as the lid and hood of vehicles. There appear to be no obstacles to welding of vehicles so far.
There are two issues with the application of aluminium however. The first is the price of material which is
the main constraint on the production of an aluminium car. In the near future, however, the price of petrol
will probably be raised through the exhaustion or oligopoly of petroleum resources, so lighter vehicles will
be advantageous. The second subject is a lack of agreement on the value of aluminium vehicles from the
view point of life cycle assessment (LCA). A large amount of CO
2
gas is exhausted at each stage in the alumina
smelting process and when smelting waste aluminium. To offset this amount of gas it is calculated that
180,000
km of vehicle travel is needed in the case of all new material, and 100,000 km travelling is needed in
case of all recycled material. Considering that the average vehicle life is about 10 years, it cannot be assumed
that the application of aluminium in the automotive industry will lead to reductions of the total exhausted
CO
2
gas. It will be necessary to develop complete recycling technology to reclaim body material from waste
aluminium bodies. To prepare for the aluminium vehicle age, one of the challenges is to develop welding
techniques which will efficiently join recycled materials.
9.6.3
Welding processes and challenges
Transistor inverter type power sources and electromotive pressure guns have been developed for use in the
automotive industry, and now the advancement in this field seems to have slowed. Recently laser welding
was applied to tailored blank welding for the purpose of raising the yield rate of material, and this technique
contributed to optimum arrangement of plate thickness and strength of materials. New applications of laser
welding for body assembly are popular. This process has been introduced to prevent the decrease of body
assembly rigidity.
In resistance spot welding, which does not make continuous joints and requires holes merely to generate
electrode pressure, the joint efficiency and the rigidity of body assembly decreases and these factors are
regarded as issues for the use of resistance spot welding. Currently, however, more attention is given to the
weak points of laser welding, such as low adaptability to fitting accuracy of the basematerial in lap-filet joints,
and deviation of focus point in butt joints duringmass production applications. To overcome these challenges,
laser-arc hybrid welding and laser brazing are being trialled by almost all makers. Countermeasures for other
issues with laser welding, such as porosity generation and irregular bead formation, are now in progress.
9
Needs and challenges of major industry sectors for future applications
