Jeffrey L. Klipstein ACCE SPEa 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

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





850LD – CSP Composites Technology using

AOC proprietary resin and B-side

B1 - Using AOC Proprietary Resin System 4 with


B2 - Using AOC Proprietary Resin System 3 with


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.


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.


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.


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

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

Documents

Jeffrey L. Klipstein ACCE SPEa 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