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Jeffrey L. Klipstein Technical Service Specialist AOC
ACCE-SPE September, 2014
ABSTRACT
Today the automotive market is pursuing lighter
weight materials to reduce the overall weight of
the vehicle. This is mainly due to the ever increas-
ing demand to improve gas mileage. Past advanc-
es have shown that a lower density Sheet Molding
Compound (SMC) based on fiberglass and polyes-
ter technology, can be manufactured with suffi-
cient mechanical properties and weight reduction;
but this has been limited to structural or non-
Class A applications. However, recent advance-
ments have shown that a Class A surface with
acceptable mechanical properties can be
achieved in a 1.2 specific gravity, low density
SMC system, based on fiberglass and unsaturat-
ed polyester technology. This paper will compare
past advancements in lower density systems,
along with an insight into future work that is cur-
rently in progress.
BACKGROUND AND REQUIREMENTS
Since the 1970s, when fuel crises forced au-
tomakers to find ways to reduce weight, sheet
molding compound (SMC), a compression-molded
blend of polyester or vinyl ester resins, specialty
additives, various mineral fillers and chopped fi-
ber glass, has been part of progress towards
weight reduction. Historically SMC has offered up
to a 30 percent lower weight than the same part
made of steel. These applications include Class A
exterior body panels, underbody heat shields, and
structural parts. Automakers today expect the
painted surface of vehicles to exhibit the same
level of smoothness and gloss, regardless of the
material of construction. (1)
Today’s technology for lighter weight materials is
constantly advancing and traditional SMC materi-
als need to keep pace. Today aluminum is the
preferential material for light weighting high vol-
ume vehicles and carbon fiber composites are
receiving serious consideration, but both come at
a cost premium. Our focus has been to create a
new glass reinforced low density SMC product
with adequate mechanical properties and a Class
A surface profile.
Jim Devries, Staff Technical Specialist and Man-
ager of the Manufacturing Research Dept. at the
Ford Research Laboratory (Detroit, Mich.) pointed
out two important issues regarding the carbon
fiber SMC. One, Ford favors aluminum over car-
bon fiber and glass fiber SMC. If the cost of indus-
trial-grade carbon fiber drops to $5 per lb, he not-
ed, then it could become competitive, at least at
higher production volumes. Two, Devries posed a
tough question: If the cost of carbon fiber wasn’t
an issue, would carbon fiber suppliers be able to
meet the resulting automotive demand that, for
$5/lb carbon fiber, could be as high as 75 million
lb (~34,000 metric tonnes) per year? (2)
While aluminum is currently more expensive than
the steel it replaces, it is substantially lower cost
than carbon fiber composites. While more expen-
sive than traditional Class A SMC on an equal vol-
ume basis, low density SMC is competitive with
aluminum in terms of both cost and weight sav-
ings. Coupled with favorable manufacturing costs
for volumes up to 70,000 units per year, it pro-
vides automakers with an attractive opportunity
for saving cost and weight on lower volume and
specialty vehicles.
In order for low density SMC compound to com-
pete, it must fit existing compounding and mold-
ing infrastructure, have qualities such as ease of
molding within current parameters, good flow
properties; lower energy consumption; good me-
chanical properties, a greater ability to dissipate
heat and a smooth glossy surface. (3)
The average consumer tends to prefer a smooth
shiny surface on their car. This is highly subjective
to an individual’s eye. However for development
purposes technically a Class A surface finish refers
to the waviness in the surface of body panels in
addition to the distinctness of image (DOI), orange
peel (OP) and gloss level on the part. Class A speci-
fications have tightened in the last 5 to 10 years
but automakers and their Tier 1 suppliers normally
are faced with relying on the subjectivity of the hu-
man eye for quality control of a Class A surface pro-
file. (4)
Various types of equipment are used to determine
the smoothness and surface qualities of SMC sub-
strates. A method particularly well suited for mate-
rial development is a Laser Optical Reflected Image
Analyzer (LORIA) developed by Ashland Chemical
Company Composites Polymers Division, which is
what we use for our surface profile evaluation.
Most low density SMC at a 1.3 specific gravity is
lacking in what most may consider to be a true
Class A surface profile. A LORIA value more associ-
ated with a Class A surface profile would range in
the 65 to 100 range for index and having a dis-
tinctness of image (DOI) from 8.0-1.0 with an or-
ange peel (OP) of 80 to 100 depending on the cus-
tomer’s preference. Ideally a LORIA value of 85,
DOI of 80 and an OP of 8.0 would be considered a
good base line. Note: lower LORIA index values and
higher OP and DOI numbers are preferred.
AOC has developed new Class A resin systems and
B-sides (Thickening Systems) that when properly
formulated offer the unique combination of im-
proved mechanical properties and enhanced sur-
face profiles. Normally when the mechanical prop-
erties are enhanced the surface profile suffers for
a low density SMC compound of a 1.3 specific grav-
ity or lower. The opposite normally happens; when
the surface profile is enhanced the mechanical
properties tend to suffer. Using the new technolo-
gies, materials can be manufactured incorporating
both enhanced surface profiles and improvements
to mechanical properties.
Our goal is for the new low density SMCs to match
or exceed the properties of a standard density com-
pounds nearly as possible.
EXPERIMENTAL
The experimental section will review generic formu-
lation breakdowns that incorporate the new low
density Class A resins and their corresponding B-
sides. Together these components of the experi-
mental formulations give the desired Class A sur-
face profile along with required mechanical proper-
ties.
Formulation Components for Low Density SMC
Abbreviations for Formulations:
A1 - Using AOC Proprietary Resin System 1 with
proprietary B-side 1
A2 - Using AOC Proprietary Resin System 2 with
proprietary B-side 1
A3 - Using AOC Proprietary Resin System 3 with
proprietary B-side 2
850LD – CSP Composites Technology using
AOC proprietary resin and B-side
B1 - Using AOC Proprietary Resin System 4 with
proprietary B-side 3
B2 - Using AOC Proprietary Resin System 3 with
proprietary B-side 3
The SMC was manufactured on a 24" Finn and
Fram SMC laboratory machine except for the CSP
850LD which was processed on their production
equipment. The A and B-side pastes for each 24”
formula were blended on a Cowles high shear mix-
ing system. Laser Optical Reflected Image Analyzer
(LORIA) was used for our surface profile measure-
ments.
Mechanical and Surface Property Testing
Test panels for the sheet molding compounds were
molded on a 100 ton hydraulic press in a 12" X 12"
plaque tool for samples A1 through A3. The 850 LD
mechanical data was supplied by CSP composites.
The Mechanical property testing for compression
molded panels was performed and compared to
the Ford Low Density Structural Specification for
Mechanical Properties WSS-M3D188-A. The LORIA
profile data for a typical low density SMC is com-
pared against the new low density SMC’s which is
represented in Table #1. The corresponding physi-
cal property data for both typical and new low den-
sity SMC's is represented in Table #2
Advances in Low Density SMC for Automotive Class A Applications, continued
Table 1. LORIA Data
As can be seen from the data comparison,
the typical LD system has poor LORIA val-
ues, but good mechanical properties, where
the new systems have both good values for
LORIA and good mechanical properties.
Advances in Low Density SMC for Automotive Class A Applications, continued
Table 2. Mechanical Properties (5)
Table 3. Mechanical Tables # 3 and 4 show how the new low density sys-
tems compare to a typical standard density SMC.
Advances in Low Density SMC for Automotive Class A Applications, continued
Table 4. Mechanical Properties (6)
Extensive paint and adhesive bonding perfor-
mance testing is nearing completion. To date all
results are looking positive.
Description Index O P DOI
Standard Density 87 9.3 94
A1 54 9.6 97
A2 71 8.8 89
850LD 73 8.2 85
A3 61 8.5 88
Table 4. LORIA Data
Table 5. Cross Hatch Data & Photo
There is additional work going on to lower the specific gravity yet further, while maintaining mechan-
ical properties and LORIA values. Tables 6 & 7 give some insight into our progress. Further work is
required to boost Tensile and Flexural modulus.
Advances in Low Density SMC for Automotive Class A Applications, continued
Table# 5 shows initial cross-hatch adhesion
work that has been done for evaluating au-
tomotive primer to bare substrate. This da-
ta was provided by CSP.
Cross Hatch Adhesion Test
Table 6. Mechanical Properties
Description Index O P DOI
B1 68 8.4 87
B2 86 7.8 82
Table 7. LORIA Data
Advances in Low Density SMC for Automotive Class A Applications, continued
Advances in Low Density SMC for Automotive Class A Applications , continued
In addition, the above mentioned systems
have cold tool to cold part shrinkage val-
ues as follows in Table 8. The minus sign
signifies expansion.
Description
mils/in.
A1 -0.29
A2 -0.44
A3 -0.29
850LD -0.38
B1 -0.37
B2 -0.16
Table 8. Shrinkage Data
SUMMARY AND NEXT STEPS
None of the sheet molding compounds discussed ex-
hibited any issues during the manufacture and mold-
ing of the material. The new resins combined with their
corresponding B- sides displayed 1.2 specific gravity
results that were favorable to the Ford Low Densi-
ty Structural Specification for Mechanical Properties
WSS-M3D188-A and comparable to the surface pa-
rameters mentioned above for a Class A system. We
are currently focusing on the A3 version. This version
appears to offer the best path in maintaining good me-
chanical properties, while improving the LORIA surface
profile. Production evaluations are underway.
Additionally, the work that is ongoing to further reduce
the relative density while maintaining mechanical
properties and LORIA surface profiles looks encourag-
ing.
We believe that the work done to improve the mechan-
ical properties and surface profile will increase the op-
portunity for the automotive industry to consider usage
of low density polyester SMC in their future designs. It
will additionally give other markets the opportunity to
consider SMC as an alternative material for light
weighting and surface profile.
ACKNOWLEDGEMENTS
I would like to acknowledge The AOC Closed Mold
Technical Service Organization and The CSP Compo-
sites Group for making this paper possible. In addition
I would like to acknowledge all the lab personnel for
completing the required testing for this paper.
BIBLIOGRAPHY
1. http://www.compositesworld.com/articles/
innovation-driving-automotive-smc.
2. http://www.compositesworld.com/columns/a-
convergence-of-market-outlooks
3. http://www.thefreelibrary.com/LowDensity
+ S M C + T a c k l e s + S t r u c t u r a l + A u t o + P a r t s -
a066498799
4. http://www.compositesworld.com/articles/
automotive-composites-taking-subjectivity-out-of-
class-a-surface-evaluation
5. Ford Unsaturated Polyester (UP), Low Density, Non
-Class A', WSS-M3D188-A 40% Glass Fiber Rein-
forced Sheet Molding Compound
6. Ford Unsaturated Polyester (UP), Impact Modified,
28% Glass Fiber Reinforced SheetMolding Com-
pound, WSS-M3D184-A
Jeffrey L. Klipstein Technical Service Specialist AOC
ACCE-SPE September, 2014
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