Automotive Engineering - May 2019 - 21

COVER STORY

UNIVERSITY OF MICHIGAN

"The end game in automotive
primary body and chassis
structure will contain significant
carbon-fiber composites."
Press-hardening adds cost, but those grades are
"still well below that $2.00-$3.00 per pound saved
threshold," Dr. Taub explained. He said the steel industry is developing 1,200 to 1,400 MPa products that are
sufficiently ductile to be stamped at room temperature-with even stronger grades to follow.
"The high-strength steels we used to say were limited to 10-to-15 percent weight reduction will soon be
capable of delivering up to 25 percent reductions," he
told the plastics engineers.
ALUMINUM: Because it's not as ductile as steel,
manufacturers can't yet stamp aluminum sheet in the
same extreme shapes as steel offers, Dr. Taub noted.
But the industry "has gotten much better at forming
parts out of aluminum. And it has solved the joining
problem that put it at a disadvantage to steel spotwelding," by adopting mechanical fastening and even
new processes to spot-weld aluminum to steel.
With a density that is 2.5 times less than comparable
steel, "aluminum has quickly become the weight-saving
material of choice for closures, where it's now being delivered at below $2.00 per pound saved," Dr. Taub said.
But the fundamentally higher cost of making aluminum, due to the energy-intensive nature of refining
bauxite, continues to make it a premium-priced play.
In addition, the industry is beginning to reach the limit
of its rolling-mill capacity-which may cause restrictions of material availability. According to Dr. Taub,
"OEMs developing new vehicles with extra aluminum
content must team up with one of the aluminum companies to build up that capacity in rolling."
Those challenges aside, F-150 is on track for record
sales, "and more OEMs are talking about additional
aluminum content on vehicles," Dr. Taub reported.
COMPOSITES: "So far, we know that the lightestweight vehicle we can make is in carbon-fiber composite," stated Dr. Taub, who is also senior technical
advisor at the American Lightweight Materials
Manufacturing Innovation Institute.
Making carbon fiber the material of choice for automotive structures faces numerous challenges. While
many OEMs and Tier 1s are committed to working on it
in low volume projects, BMW has walked away from its
multi-million-dollar venture with SGL Carbon that
spawned BMW's novel i3 and i8 models-built on a
supply chain that stretched from Germany all the way
AUTOMOTIVE ENGINEERING

Materials expert Dr.
Alan Taub is a veteran
of General Electric,
Ford, and General
Motors. He has been a
University of Michigan
professor since 2012.
to northern Washington state.
"I am a believer that the end game in automotive primary body
and chassis structure will contain significant carbon-fiber composites-it's the material that can give us the most weight savings," Dr.
Taub said.
So, what's it going to take to get there?
First, carbon fiber must meet all impact standards-difficult for a
super-stiff material that fractures under extreme impact rather than
deforms like metals. "The good news is we've learned how to model
it, and it now gives higher specific energy absorption," he noted.
Then there's the molding time to produce a part-still a nagging
issue. According to Dr. Taub, composites researchers are working to
get the largest part of the vehicle-the floorpan-down to less than 1
minute in the mold. "We've reduced that process from eight minutes
seven years ago to about four minutes today, and the one-minute
cycle is starting to look possible," he told the SPE audience. "We're
still looking for that instant cure."
The next technology shift likely will be to thermoplastic-resin carbon fiber composites that offer the same structural properties with
much-reduced molding time.
Cost of the material's precursor, as well as the process used to convert it into high-strength carbon fiber, are also the focus of materials
scientists and process engineers. "There is lots of work going on to
reduce costs in all areas-we've gone from $20 per pound to $10 per
pound, and we're moving toward $7," Dr. Taub reports. He adds that
closed-loop recycling for the material still needs to be established:
"That's the end game for composites. I believe they can win eventually on every other single item including cost and cycle time."
The mobility industry has migrated from single-material-intensive
vehicles (i.e., F-150) to the concept of right material, produced the
right way and engineered into the right part of the vehicle. "Now, the
design engineers can go into ANSYS or whatever tool they use and
select their material of choice; the component engineers can make
that part in complex shapes, while the manufacturing engineers handle the multiplicity of materials and forms," Dr. Taub noted. "And the
joining engineers? They're the ones everybody is investing in."
May 2019 21

Automotive Engineering - May 2019

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