SAMPE Journal - January/February 2021 - 16

FEATURE / SHEET MOULDING COMPOUNDS

Figure 2. a) Example of an integrated insert in a carbon fibre SMC-foam-sandwich part,
b) Schematic principle of the direct insert integration into the sandwich structure6.

been varied resulting in 35 different parameter sets.
3-point bending tests have been performed to analyse the mechanical properties of the different sandwich panels.
SMC-FOAM-SANDWICH TECHNOLOGY
A promising technology for producing geometrically complex and functional sandwich structures is
the combination of cover layers made out of sheet
moulding compounds (SMC) and rigid foam as core
material in an in-situ compression moulding process1,2. The principle of the so-called and patented
SMC-foam-sandwich technology is illustrated in
Figure 1. The SMC materials used are usually glass or
carbon fibre reinforced with fibre lengths between
25 mm and 50 mm1-3. In general, thermoset matrix
systems based on unsaturated polyester, vinyl ester
and epoxy resins are used, which depends mainly
on the area of application and component requirements, such as flame retardancy4. The rigid foams
are based on thermoplastics such as polymethacrylimide (PMI)1, 2.
The SMC-foam-sandwich components thus
produced in 180 sec to 300 sec and at mould temperatures between 130°C and 160°C are characterized by a high degree of design freedom, the possibility of complete process automation and a high
degree of functional integration2,5. Functional integration can be realized by the direct implementa-

tion of metallic force introduction elements such as
inserts and threaded sleeves. In addition to varying
the thickness of the foam core, it is also possible to
create flowing transitions to geometrically complex
monolithic SMC areas5,6.
Before the actual compression moulding, the
SMC sheets are cut to size, stacked and, if necessary,
preformed1. More complex foam core geometries
must be produced by previous preparation processes such as machining, thermal forming or shapebound foaming technologies1,5. The choice of the
respective manufacturing process for the semi-finished foam cores depends particularly on the total
quantities, the required geometry and the variety of
variants of the SMC-foam-sandwich structures to be
produced1.
In general, comparing sandwich components
to monolithic structures bending stiffness and
strength can be significantly increased without increasing weight5,6. Using the SMC foam sandwich
technology a significant reduction of production
costs of complex composite sandwich components
can be achieved compared to conventional sandwich structures due to short cycle times, a high functional integration and less reworking as well as assembly work5,6. The benefits described above make
this in-situ compression moulding process highly
economical and obtain high production rates1,5.
Moreover, load path optimised insert integra-

Figure 3. Exemplary results of the process monitoring for a) the cavity pressure and
b) the mould temperature over a compression moulding cycle.

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SAMPE Journal - January/February 2021

Table of Contents for the Digital Edition of SAMPE Journal - January/February 2021