Automotive Worldwide

Multi-thickness laser welded blanks: Tailored Blanks

Extract from the product catalogue -European edition

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Please contact us if you have a specific requirement that is not included in the range of products and services covered by this catalogue.We are also reachable by the e-mail address automotive.request@arcelormittal.com.

 

We are also reachable by the e-mail address automotive.request@arcelormittal.com.  

Multi-thickness laser welded blanks: Tailored Blanks

Introduction

Tailored Blanks, a business unit of ArcelorMittal with design and production facilities in most parts of the world, is a leading producer of laser welded blanks (LWB). These products, widely used in automotive chassis and body-in-white (BIW) components, are made by welding together flat steel sheets of different thicknesses, grades and coatings. They decrease the weight of the vehicle and improve safety by enhancing crash performance. At the same time, laser welded blanks have been shown to reduce the total cost of the vehicle structure. In today's vehicles, the body in white typically includes some 20 tailored blank applications.

Laser welded blank technology

Laser welded blanks have the advantage of providing the "best material in the right place in the right thickness". This concept makes it possible to vary steel thickness and quality without post-joining operations or sheet overlap and thus to avoid the additional weight that would otherwise arise.

Tailored Blanks offers three different types of laser welded blanks:Blanks of relatively simple geometry with linear weld seams, for high productivity or laser welded blanks of complex shape with non-linear weld seams, for weight optimization;Spot-welded or remote laser welded patchwork blanks, suitable for components requiring local reinforcement;It is of course possible to combine patchwork blanks with the two laser welding techniques.

Three types of welded blank technology

Applications

Laser welded blanks are now widely used by all vehicle and equipment manufacturers and both the number of applications and the total number of welded blanks employed in the vehicle are steadily increasing.

Most widespread applications and steel grades offered, based on the most recent production technologies

Customer support

Teams of engineers specializing in the development of laser welded blanks are available to work with customers from the initial vehicle design stage onwards. To ensure maximum responsiveness, the same engineer provides support throughout the process up to and including industrialization.

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ArcelorMittal's R&D teams and development engineers can provide full support for tailor-welded blank design, choice of steel grades, forming strategy and feasibility studies. This support significantly reduces prototyping costs and times.

Steel grades

Laser welded blanks can now be made from an extensive range of steels, including, advanced high strength steel grades such as Dual Phase and TRIP, with all types of coatings.

The advantages of laser welded blanks made of ordinary high strength steels also apply to welded blanks made of very high strength steels and of Usibor® 1500 for hot stamping.

These steels are used to further reduce the weight and increase the strength of the welded blank.

The advantages of high strength steels are further enhanced when they are combined with milder steel grades in welded blanks to adjust local formability in deep-drawn parts.

Potential optimization of components using the tailored blanks concept

The most recent trend in body in white design is the use of welded blanks made of advanced high strength steel: The cost advantages of using welded blanks are further enhanced by the use of very high strength steel. With increasing steel prices it becomes even more crucial to combine materials, and the use of advanced high strength steel supports greater part integration;The ArcelorMittal offering includes a broad range of very high strength steels.

Thanks to its fully operational dedicated welding process, Tailored Blanks can offer its customers laser welded blanks made from ArcelorMittal's entire range of high strength steels.

This table shows all the possible combinations

Unique analysis tools

To support its customers in developing new laser welded blank solutions, Noble International has devised the tools and expertise required for each stage of the evaluation process.

At the preliminary stage and design stage, it is essential that the feasibility of the planned solution be assessed in terms of formability; this requires the use of digital simulation tools based on finite element analysis.

To provide fast and accurate predictions of the fracture risk margins described above, ArcelorMittal has developed two dedicated models that are unique in the tailored blanks market:

Forming Limit Curve specific to laser welded blanks: fracture prediction for the weakest metal parallel to the weld line;Failure model for butt-welded joints: prediction of weld seam fracture in the perpendicular direction.

These tools have been adapted to the full range of laser welded blank solutions, including those using very high strength steel grades.

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These tools have been adapted to the full range of laser welded blank solutions, including those using very high strength steel grades.

Forming Limit Curves for welded blanks

It has been demonstrated on many occasions that the Forming Limit Curve (FLC) of the weakest metal does not by itself accurately predict the appearance of necking phenomena close to butt welded joints, even though fracture occurs in the weakest metal.

To overcome this difficulty, ArcelorMittal has developed a dedicated digital analysis tool for these configurations to support accurate prediction of fracture risk when drawing a component from a laser welded blank.

Example of the use of the laser welded blank forming limit curve, the only way to predict fracture observed in practice during drawing:

Fracture on real part

Simulation without welded blank FLC for material A1 and B1

The welded blank FLC predicts fracture during drawing simulation

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Simulation with welded blank FLC for material A1 and B1

Laser welded blank FLCs are an essential tool for accurately predicting necking.

A new model for predicting elongation parallel to the weld seam

To assess the risk of fracture parallel to the weld seam, ArcelorMittal R&D has developed a new model.

The model is based on the interaction of several physical phenomena:Mechanical (mechanical characterization, etc.);Metallurgical (chemical composition, etc.);Thermal (power, speed, etc.).

Comparison of experimental elongation results and results of the new ArcelorMittal prediction model: excellent correlation across the board

The comparison between experimental results and model predictions shows an excellent correlation for all very high strength steels tested.

These two specific tools used to analyze welded blank solutions enable Tailored Blanks to provide improved customer support as part of co-engineering studies covering the full range of welded blank solutions, including those using very high strength steels.

Hot stamped welded blank solutions

The increasing demand for weight reduction in order to cut CO2 emissions is driving the development of ever more innovative solutions aimed at achieving weight savings while maintaining or improving performance at no additional cost.

It has already been demonstrated that solutions combining the use of very high strength steels and welded blanks offer the advantages of both technologies.

Hot stamped laser welded blank solutions have been developed for this purpose.

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These solutions optimize thickness and material utilization through the use of laser welded blank technology while maximizing mechanical performance through the use of hot stamped Usibor® 1500.

A dedicated welding process

To cope with the specific properties of Usibor® 1500 and in particular its aluminum coating, ArcelorMittal has developed a dedicated welding process that ensures optimum performance of the welded joint and functional performance of the final part.

Comparison of the behavior of two Usibor® 1500 laser butt-welded joints, one using a conventional process and the other the dedicated Tailored Blanks process: in the latter case, the weak point is the weaker material and not the welded zone.

ArcelorMittal has carried out technology and product development work in order to provide robust hot stamped laser welded blank solutions that guarantee all the expected functions.

By way of illustration, it was essential, at the design stage, to be able to guarantee that the weld would under no circumstances constitute a weak point in the structure concerned.

Given that guarantee, engineers designing body in white structures are able to consider these solutions using conventional methods, without having to introduce sophisticated weld fracture models when calculating crash performance.

Ductibor® 500: extensive hot stamped welded blank applications

As indicated in the chapter on products for hot stamping, Ductibor® 500 was developed for a single purpose: to offer hot stamped welded blank solutions comprising zones of high crash deformability ensuring a high level of energy absorption.

The successful development of Ductibor® 500 supports all applications relating to car body crash behavior, even the most demanding in terms of energy absorption, such as front and rear beams.

The illustration to the left shows typical deformation of a B-pillar made of a Usibor® 1500 /Ductibor® 500 hot stamped welded blank solution during a lateral collision. The lower part using Ductibor® 500 ensures control of the crash deformation and the energy absorption needed to achieve good overall crash behavior of the structure.

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Potential hot stamped laser welded blank applications using Usibor® 1500 and Ductibor® 500. Up to 60 kg hot-stamped steel components per vehicle → 20% of BIW mass

Crash characterization of Usibor® 1500 /Ductibor® 500 welded blank solutions

Usibor® 1500 /Usibor® 1500 and Usibor® 1500 /Ductibor® 500 butt welded solutions have been characterized in great detail in order to validate their functional behavior and to provide customers with the data they require in order to consider implementing such a solution in the vehicle preliminary design or design stage.

Crash behavior characterization of Usibor® 1500 /Ductibor® 500 welded blank solutions: bending (left) -Courtesy of Adam Opel GmbH - and compression (right)

The crash tests presented above demonstrated the following points:No fracture in the weld zone;Perfect stability of the structure;The Ductibor® 500 zone deforms, ensuring its energy absorption function;The Usibor® 1500 zone does not deform, ensuring its anti-intrusion function.

Ductibor® 500 has also undergone full mechanical characterization (high speed tensile test, Hopkinson bar tests, etc.); full material data sheets can be provided.

The robustness and functional performance of Usibor® 1500 /Usibor® 1500 and Usibor® 1500 /Ductibor® 500 hot stamped tailor welded blank solutions have thus been well documented and validated.

These solutions constitute a new, highly effective tool available to automobile body engineers that enables them to achieve weight, performance and cost optimization.

Lighter and safer vehicles for today and tomorrow: Usibor 1500 /Ductibor 500 solutions

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Automakers have opted for Usibor® 1500 /Ductibor® 500 laser welded blanks generic steel solutions in new platforms

B-Pillar Application: Usibor® /Ductibor® tailored blanks proposal vs. monolithic

Monolithic reference

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Low material utilization (up to 67%)Large scrap rateHigh material cost

Tailored Blanks concept

No cost penalty for laser welded blanks due to higher material utilization (>85%)Any thickness optimization will induce weight and cost savings in favor of LWBUsibor® 1.75 mm /Ductibor® 1.5 mm LWB will be 8.5% lower in weight and 6.5% lower in cost compared to 1.75 mm monolithic /partial hardening

© ArcelorMittal | Last update: 25-04-2018

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