|
This
material first appeared in the I-CAR Advantage Online, which is published and
distributed free of charge. I-CAR, the Inter-Industry Conference on Auto
Collision Repair, is a not-for-profit international training organization that
researches and develops quality technical education programs related to
collision repair. To learn more about I-CAR, and to subscribe to the free
publication, visit
www.i-car.com.
|
Laminated Steels
Laminated steel is a type of "sandwiched" sheet
metal that uses two layers of steel bonded together by a polymer core. Consumer
demand for quieter vehicles is the primary reason for using this type of
material for automotive parts. One trademarked material, named Quiet Steel®, is
used on some of the newer General Motors, DaimlerChrysler, and Ford vehicles.
The core of Quiet Steel has a "visco-elastic" property that effectively reduces
vibration transferred through the panel. By reducing vibration, noise is also
reduced.
The UltraLight Steel Auto Body (ULSAB) consortium
developed a similar type of material in the 1990s. This worldwide consortium
consisted of 35 steel producers from 18 different countries with the common goal
of designing an all-steel lightweight vehicle while maintaining structural
integrity and affordability.
The ULSAB version of laminated steel was developed
along with other innovations including tailor-welded blanks, advanced
high-strength steels, and the hydroforming processes used to form steel. This
material had a polymer core of 0.650 mm between two sheets of steel. It was used
for the dash insert panel and spare tyre tub on the ULSAB unibody concept
structure that was completed in 1998. Both laminated steel parts were
lightweight and had sound-absorbing capabilities, but neither could be welded
because the polymer core was too thick. The parts were attached to the structure
with bolts, rivets, and adhesive.
The polymer core of the ULSAB laminated steel was
much thicker than the 0.025 mm core of current Quiet Steel panels.
The first body application of Quiet Steel in a
production vehicle was the cowl panel of the 2001 Ford Explorer Sport Trac. This
type of application of Quiet Steel later won the Premier Automotive Suppliers’
Commitment to Excellence (PACE) Award for the cowl panel on the Cadillac
CTS.
Currently, some of the body parts made using
laminated steel include cowl panels, lower plenums, storage tubs, and for other
areas where noise, vibration, and harshness (NVH) is a concern. Some mechanical
parts, such as the oil pan on the 2004 Ford F-150 Triton V8, are made with
laminated steel.
Using this material allows vehicle makers to
produce quieter vehicles without adding extra steps during assembly. Another
benefit is that the material is 100% recyclable compared to other non-recyclable
materials like thick carpeting, cotton shoddy, foam, and mastics. Replacing
non-recyclable materials with laminated steel may also increase the amount of
interior space in the vehicle.
Characteristics of the steel, and total thickness,
typically remain the same when a part is made with laminated steel. The
laminated material is shipped to stamping plants in a continuous coil or steel
sheets. There, the parts are stamped, E-coated, and shipped for assembly. The
material can be welded because the core is only 0.025 mm thick. Parts are
commonly attached at the factory with squeeze-type resistance spot welding
(STRSW). Other attachment methods may also be used.
DaimlerChrysler uses a windshield urethane
adhesive for attaching the laminated steel seat tubs on mini-vans with Stow N’
GoTM
seating.
Some repairability issues include identifying
parts made of laminated steel, varying recommended repair procedures, and
different joining techniques.
Currently, most locations of parts made of
laminated steel do not provide adequate accessibility for using STRSW equipment
during repairs. MIG plug welds are sometimes recommended, but weld contamination
from the polymer core may arise. Achieving adequate penetration through both
layers of steel into the backside may be another problem. Practice welds help to
identify the proper settings and techniques used to reduce contamination and
achieve proper penetration in the weld, but this can only be done if laminated
steel is available. A good practice is to keep a piece of this material in the
facility for future repairs that require sample welds.
When making test welds, it is important to use a
piece of laminated steel that closely matches the thickness of the intended
repair. The total thickness of laminated steel can range from 0.8 mm to 3.0 mm
and the polymer core can be specifically "tuned" for the type of noise the part
is designed to absorb. Differences in thickness or composition may affect the
welding characteristics of the part.
To avoid these concerns, General Motors recommends
rivet bonding for repairs that involve laminated steel parts. When repairing
laminated steel Stow N’ Go seat tubs, DaimlerChrysler recommend that the
repaired or replaced tubs be reattached with a urethane adhesive. MIG welds are
recommended for attaching the apron to the laminated steel cowl panel on the
2004 Ford F-150.
At first glance, laminated steel parts may look
identical to parts made of non-laminated steel. A closer look at the edges of
the panel may show two separate pieces of steel sandwiched together – as
pictured. To confirm, a firm tap on the part may also help identify that the
part is laminated steel. Of course, vehicle maker service information is the
best method to identify and determine proper repair processes for this new
material.
Laminated steel is a
sandwich-type material designed to reduce vibration and noise. Laminated steel
has helped vehicle makers design quieter vehicles without adding additional
assembly steps. It is a recyclable material and can reduce the amount of other
non-recyclable sound-absorbing materials added to a vehicle. Repair technicians
should be aware of the proper joining techniques to use when working with
laminated steel. Vehicle makers may also have different recommendations for
repairing these parts.
Foams
Foams seem to be the latest innovation used
throughout the vehicle for the ultimate benefit of the occupants. Foam materials
used during vehicle repairs are typically two-part materials that can change in
state and shape after they are dispensed.
Some of the first foam materials were used for NVH
control. NVH foam materials are currently broken into four categories:
sound-dampening material, flexible, rigid-type, and structural. Rigid-type foam
is broken into three sub-categories.
Sound-dampening material is an NVH foam used for
covering or sealing small openings that are easily accessible, and for
reattaching existing foam. This is a two-part product that is black, heavy
bodied, and non-expanding, much like windshield urethane or seam sealer when
compared to common two-part expanding NVH foam.
Another NVH material is flexible foam. Flexible
foam is soft, compressible, and returns to its original shape without retaining
permanent deformation.
Rigid-type foam is the NVH material that currently
has three sub-categories. These sub-categories include rigid, semi-rigid, and
pillar foam.
Each material has distinct characteristics as an
NVH control product. Rigid foam reacts differently than flexible foam when
compressed. Rigid materials have a much lower compression rate when a force is
applied and may remain permanently deformed when the force is removed. The main
difference between rigid and semi-rigid is the strength of the material. Pillar
foams are typically rigid foams with unique foam times and flow rates. This
allows them to be used in situations where foam placement is difficult.
The latest material introduced to the foam family
is referred to as structural foam. Structural foam is used for stiffening parts
of a vehicle chassis/body and for increasing occupant protection in the event of
a collision.
Along with identifying the material originally
used in the vehicle, there are other considerations that affect installing
replacement foam. These include determining the amount of material to be
installed, how to get the material to a specific location, and how to get the
foam to adhere in a specific location. Expansion rate, viscosity, and foam time
are among the variables that must be considered.
The expansion rate of a foam product is typically
given as a maximum amount. Products may have expansion rates listed as "up to
ten times." The actual expansion rate of the foam may change based on many
variables, some of which technicians can control. To determine how much material
should be installed in a part, the volume of the void to be filled should be
calculated. After determining the volume of the void, and matching that to the
approximate expansion rate of the material being used, the proper amount of
two-part foam can be determined.
Knowing the viscosity and foam time of different
foams can be helpful when determining how to place the foam in specific areas.
Sometimes, due to location and access, it is difficult to hold foam in specific
areas. When this is the case, dams can be used. Depending on where the dam is to
be placed, it can be installed either before or after parts are assembled. There
are many different acceptable materials that can be used as dams. The most
important consideration for using a dam is determining its ability to retain
moisture. Do not use materials that have the ability to retain moisture.
Overall, there are six different classifications
of foam, along with a variety of application techniques that may be required for
positioning the material. Choosing the correct replacement material is
important, as is using the proper amount of foam and properly filling the
specific area.
Did you enjoy this article?
Please consider supporting AutoSpeed with a small contribution. More Info...
|
More of our most popular articles.
|
|
|
Email a friend
Print article
|