ArcelorMittal Touts New Ultra-Strong Structural Parts for Vehicles
The steelmaker predicts North American automotive customers alone will adopt more than 4 million, hot-stamped, laser-welded blanks during the next two years.
Automotive aluminum seems to be getting all the headlines lately, but steel suppliers are fighting back by spotlighting innovative forming technologies and advanced high-strength steel grades they say can create stronger, lighter and more crashworthy structures at much lower cost than aluminum.
One of the industry’s showcase examples is what Honda’s Acura luxury division says is the world’s first 1-piece stiffener ring for the driver and front passenger door areas on the ’14 Acura MDX CUV.
Combining the A-pillar, B-pillar, roof rail and lower frame member, the 1-piece door ring replaces multiple parts spot welded together to better manage collision energy.
It significantly increases the ability to absorb and redirect crash energy in front and side impacts, and manage roof loads in the event of a rollover, Acura says.
Blake Zuidema, director-global R&D, automotive product applications for steel supplier ArcelorMittal, says the ring played a key role in enabling the MDX to receive the highest rating for the Insurance Institute for Highway Safety’s small-offset crash test, which is proving to be one of the industry’s most challenging.
“You can see in the crash test virtually no deformation in the door-ring area. The doors were actually able to be opened afterwards,” Zuidema says. And even though the door ring is exceptionally strong, it actually helped the automaker trim 8.8 lbs. (4 kg) from the body structure as well, he says.
The door ring combines two sophisticated steel fabricating technologies, laser-welded tailored blanks and hot stamping, into a new highly advanced process that is becoming an increasingly popular method of creating strong, lightweight steel parts, Zuidema says.
Laser-welded tailored blanks are created by welding together different thicknesses and strengths of steel alloys like a quilt to create parts that are customized for specific applications, thick and strong where they need to be and thin and light in lower-stress areas.
Hot stamping is a process where blanks are heated to very high temperatures to become more malleable and easily formed. The hot blanks then are placed in stamping presses with specially cooled dies to be formed into parts.
When the stamping dies press the metal blanks into complex shapes, the sheet metal cools suddenly and the steel undergoes metallurgical changes that turn it into a much stronger material known as press-hardened steel.
“The press-hardened steels provide some of the highest-strength components that are found in cars today,” Zuidema says.
MDX 'Perfect Example' of Dual Technology
The critical components that prevent intrusion into the passenger compartment during crashes need to be the strongest possible for maximum crashworthiness, but they also can’t add too much to overall vehicle weight for fuel-economy reasons, meaning lighter, thinner-gauge steel needs to be used wherever feasible.
“The MDX is a perfect example of how we can use hot stamping and laser welding together to get the right gauge in the right part of the car,” Zuidema says.
“We’ve been working with Honda for a number of years developing that application and launching on the new MDX. This is a technology that takes hot stamping to the next level.”
“Other people are doing hot-stamping; (it’s) one of those technologies automakers are all applying,” MDX Chief Engineer Jim Keller told WardsAuto last year.
“But typically, hot stamping is done with separate stampings that are joined together as an assembly. In the MDX, this whole structure is now one complete assembly.”
The door ring starts at ArcelorMittal’s giant Indiana Harbor mill in East Chicago, IN, with the production of Usibor 1500, an aluminum-silicon coated high-strength steel. The steel is prepped at a facility in Dearborn, MI, then shipped to ArcelorMittal Tailored Blanks in Pioneer, OH, where it undergoes another process that makes it easier to weld into the body-in-white on the vehicle assembly line.
The finished laser-welded blanks then are shipped to Magna’s Cosma International operating unit in Eagle Bend, TN, where they are hot stamped into the finished door ring before heading to Honda’s production facility in Lincoln, AL, to become part of the Acura MDX.
Zuidema says virtually every automaker the steelmaker supplies has shown interest in the concept.
ArcelorMittal predicts North American automotive customers, alone, will adopt more than 4 million, hot-stamped, laser-welded blanks during the next two years. In Europe too, various automakers are studying the door ring for their next models.
While aluminum certainly is making gains in automotive, continued advances such as hot-stamped laser-welded blanks are enabling steel to remain the most cost-effective solution for creating lightweight vehicle bodies, Zuidema says.
“It is by no means game over for steel. We are stepping up and doing what is necessary to achieve even greater weight reductions and keep steel viable as a lightweight material for making future cars.”