1. SANDWICH CONSTRUCTION
PRINCIPLES OF SANDWICH CONSTRUCTION
Two facings, which are relatively thin and of high strength,
a core is enclosed which is relatively thick and light and which has adequate stiffness in a direction normal to the faces of the panel.
Many alternative forms of sandwich construction may be obtained by combining different facing and core materials.
The facings may be steel, aluminium, wood, fibre-reinforced plastic or even concrete.
The core may be made of cork, balsa wood, rubber, solid plastic material (polyethylene), rigid foam material (polyurethane, polystyrene, phenolic foam), mineral wool slabs or from honeycombs of metal or even paper.

2. panel with a polyurethane or polystyrene core
panel with a metal or paper honeycomb core
panel with a mineral wool core

3. Steel–polymer–steel and
For a symmetric sandwich section with a low modulus core, the bending stiffness and the bending stiffness-to-weight rato are given by
Steel–polymer–steel and
aluminum–polymer–aluminum are two commercially available sandwich materials developed for body structures as well as for body panels.
where, Es = modulus of the skin material,
Ρs = density of the skin material,
b = width of the section,
t = thickness of the skins and
d = distance between the skins.
Sandwich panels with carbon fiber reinforced polymer in the skins and a polymer foam core can provide much higher weight saving opportunity for body applications.

5. SANDWICH MATERIALS vibration damping group lightweight construction
The inner and outer skins typically consist of five or seven layers of various material thickness and type, dependent on the specific strength required at different locations, and optimized by finite element analysis.
The actual form of the body panel material is essentially a sandwich of aluminium honeycomb between layers of multi-ply carbon fibre reinforced resin.

6. SEQUENTIAL CO-INJECTION OR SANDWICH MOLDING
Each of the five parts comprises a rigid polyurethane foam core of 110 kg/m3 density. Glass-fibre mat is preformed and wrapped around the foam core before being placed into the low pressure injection tool. To ensure accurate location, the glass mat is retained in the part line of the tool. Polyester resin is then injected into the tool which impregnates the glass fiber and completes the sandwich construction.

8. ADVANTAGES
lightweight nature of the thermoplastic core
stiffness,
corrosion resistance
surface appearance of the metallic outer layers.

9. DISADVANTAGES
this material type is only viable for components that are assembled into the body after the painting process
this material is not weldable and must be assembled by a cold joining process of either adhesive bonding or mechanical fastening.