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