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There
is a general concern today, coming from car manufacturers, governments,
environmentalists and consumers, related to safety, economy and
environmental issues in car manufacturing.
Lightweight
auto body structures helping to improve fuel efficiency without compromising
either quality or safety, is one of the most important trends in car
manufacturing. The success in body weight reduction can be achieved by using
high strength steels and innovative manufacturing technologies and processes
such as hydro-formed components, tailored blanks and laser welding. A
reduction of about 25% in the bodyweight as proven to be possible using this
approach (ULSAB – Ultra Light Steel Auto Body) with remarkable
improvements in some properties as torsion and bending.
Tailored
blanks are becoming increasingly popular for the production of structural
components in the automotive industry, resulting in increased safety levels,
a reduction in weight and number of components, high safety levels, improved
accuracy, less processing time and design possibilities. Tailored blanks
enable design engineers to locate various steels within the part precisely
where their attributes are most needed, therefore removing any mass that
does not contribute to performance. Designed for structural performance and
weight savings, tailored blanks eliminate reinforcements and can promote
cost savings.
The
major applications of tailored blanks either under development or in
production include door inners, body sides, rails and pillars as presented
in the figure below.
Possible
uses for Tailored Blanks in a car-body
More
than 15 car manufacturers already use tailored blanks for over 20 different
applications on more than 50 vehicle platforms.
Tailored
blanks applications by world-wide manufacturers.
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Manufacturer
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Common
applications
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Europe
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Audi
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Door inner, engine rail,
floor
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BMW
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Door inner, engine rail
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MB
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Body side, door inner, floor,
side pillar
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VW
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Door inner, engine rail,
floor, side pillar
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Volvo
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Side pillar, engine rail
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Others
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Body side, door inner,
engine rail
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Japan
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Toyota
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Body sides (average four
tailored blanks per car)
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Nissan
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Body side
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Honda
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Door inners
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Others
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One or two applications
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The
possibility of improvement in structural integrity and strengthening of
strategic locations of components is achieved in tailored blanks through a
combination of sheet thickness, steel qualities and surface coatings.
Several welding technologies are feasible for the production of tailor
welded blanks. However, only laser (both
CO2 and Nd:YAG) and resistance mash seam are firmly established
in production facilities. The emergence of a new laser tool, the diode,
opens new opportunities to be explored by researchers and manufacturers.
There
are different opinions in the industry regarding the advantages and
disadvantages of different technologies. Next table summarises the generally
perceived advantages and disadvantages of the different welding technologies,
as expressed in a survey of several automobile manufacturers. Several
critical areas of concern pertain to:
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welding system reliability (process control);
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cost (investment and operating costs);
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weld bead strength and hardness;
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effects of steel coatings on weld quality;
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effects of welding on steel coatings (corrosion resistance of
weld with coated steels);
-
weld
seam geometry (concavity and convexity).
Perceived differences in weld technologies for welding
tailored blanks.
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Tailor
Welded Blank Welding Technologies
- Perceived Differences
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Technology
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Advantages
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Disadvantages
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Comments
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Laser – CO2
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- Flexible
- Weld appearance,
- Resistance to corrosion
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- Expensive
- Process complexity
- Fit up/clamping
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Single most common technology used.
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Laser –Nd:YAG
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(Same as CO2)
- Greater flexibility with fibber optic delivery.
- Non-linear capability.
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- Expensive
- Low power
- Fit up/clamping
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Has more potential, as increased power becomes available. New systems
are just beginning production.
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Resistance Mash Seam
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- More reliable
- Less expensive
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- Weld bead Corrosion
- Weld bead Thickness
- Linear Process (straight line welds)
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Electron Beam (non Vacuum)
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- Fast-high power
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- Undeveloped systems
- Expensive
- Stationary weld head
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High-frequency Induction
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- Fast
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- Undeveloped,
- Limited weld length,
- Weld end concern
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Recently put into production by Volvo.
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Laser
technology provide several advantages over other processes to weld tailor
blanks, as, for example, non contact processing, high welding speed, small
heat affected zone, considerable flexibility, better corrosion resistance,
low distortion, single sided access, high tolerance to coating and high
torsion stiffness of components.
Stamping
of the welded tailor blank enable the production of several components as,
doors’ inners, body sides, rails and pillars. The formability performance
of laser welded tailor blanks is also a key issue in the automotive industry
due to the complexity of the operation and suitable computer models are
being searched to simulate and optimise the position of the weld and to
determine the optimum tool design and its relation to the press forming
parameters.
Although,
most of the tailor blanks applications in the automotive industry, nowadays,
involve linear welds in steels, non linear welds as well as tailor blanks in
aluminium constitute, today, potential fields of increase of product ranges.
It can be said that the possibilities of tailored blanking are far from the
point of exhaustion. When the concept is integrated since the design phase
of the auto body structure of the vehicle, optimum use can be made of the
full potential of tailored blanks for series production. Automotive industry
experts estimate that the demand for tailored blanks will increase 10 times
in the next years.
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