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Título :

TAILORED WELDED BLANKS: AN OVERVIEW OF APPLICATIONS IN THE AUTOMOTIVE INDUSTRY

Resumo :

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.

 

Manufacturer

Common applications

Europe

Audi

Door inner, engine rail, floor

BMW

Door inner, engine rail

MB

Body side, door inner, floor, side pillar

VW

Door inner, engine rail, floor, side pillar

Volvo

Side pillar, engine rail

Others

Body side, door inner, engine rail

Japan

Toyota

Body sides (average four tailored blanks per car)

Nissan

Body side

Honda

Door inners

Others

One or two applications

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:

  •     welding system reliability (process control);

  •     cost (investment and operating costs);

  •     weld bead strength and hardness;

  •     effects of steel coatings on weld quality;

  •     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.

Tailor Welded Blank Welding Technologies - Perceived Differences

Technology

Advantages

Disadvantages

Comments

Laser – CO2

- Flexible

- Weld appearance,

- Resistance to corrosion

- Expensive

- Process complexity

- Fit up/clamping

Single most common technology used.

Laser –Nd:YAG

  (Same as CO2)

- Greater flexibility with fibber optic delivery.

- Non-linear capability.

- Expensive

- Low power

- Fit up/clamping

Has more potential, as increased power becomes available. New systems are just beginning production.

Resistance Mash Seam

- More reliable

- Less expensive

- Weld bead Corrosion

- Weld bead Thickness

- Linear Process (straight line welds)

Second most common technology used. Can be less expensive than laser, but not in all cases.

Electron Beam (non Vacuum)

- Fast-high power

- Undeveloped systems

- Expensive

- Stationary weld head

Has been in production for thick frame parts – being researched for sheet steel

High-frequency Induction

- Fast

- Undeveloped,

- Limited weld length,

- Weld end concern

Recently put into production by Volvo.

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.

Autor :

Helena Gouveia

Instituto de Soldadura e Qualidade Lisboa, Portugal

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