Curvature and Radii of Lightweight Panels

Composite or "sandwich" construction is not a new concept, it incorporates the bonding of a relatively thick, high strength, low density core between thin, tough skins. These panels have higher strength-to-weight ratios than conventional plywood and reduce weight while increasing strength, dependability, durability, performance and costeffectiveness. A wide range of natural and synthetic materials are available so the optimum composite system can meet specific performance criteria.

The lightweight panels manufactured by Fusion, Multipanel and ATL Composites, including Featherlight, DuraKore and DuFLEX, are suitable for bulkheads, cabinetry, cabin soles, and built-in furniture. All panels are usually finished in 1200 mm x 2400 mm sheets, in thicknesses ranging from 10 mm to 30 mm.

The need for elaborate moulds is not necessary, the panels need only simple jigs to hold the curves while the modified epoxy cures to form a variety of corners and curves. Epoxy resin systems are used for structural applications because of their long-term stability, low shrinkage on cure and their suitability for vacuum bagging.

All cuts should be filled with a mixture of epoxy resin/hardener and a high density filler. The recommended epoxy is WEST SYSTEM Brand 105 resin with WEST SYSTEM Brand 206 Slow hardener (for the warmer months), modified with 403 Microfibre Blend. This combination will produce a strong, waterproof bond which will hold the curve when cured.

Method A: Construction of small radii corners.

Step 1: A strip of the sandwich panel is removed by cutting through the facing skin and core to the rear face
of the outside skin. The width of the strip is calculated by;
width 2n x thickness of panel x 00
360

Step 2: Apply enough modified epoxy to fill the internal angle left by the removed skin and core material.
Allow to cure. The joint should be held closed while the epoxy cures with clamps or jigs.

Step 3: Fillet the internal angle with a radius of 20 mm of modified epoxy (allow to cure) and apply an
additional layer of fibreglass cloth to the inside of the angle with an epoxy laminating system.

Method B: Construction of large radii curves.

Curves that describe angles of 60 to 90 degrees are achievable with no loss of structural integrity.

Step 1: A series of narrow parallel slots are cut into the sandwich panel along the inside of the proposed curve, through the facing skin and core to the rear face of the outside skin. In no event should the saw cuts break through the outer facing skin, which serves as a hinge. For a radius of 50 mm at 90degrees, the saw cuts are spaced at approximately 13 mm for a 13 mm thick panel.

For angles larger than 90 degrees, the cuts are shallower and wider apart; taking the opposite approach yields a radius tighter than 50 mm.

Step 2: The saw cuts are filled with a thickened epoxy mixture and immediately bent to its final shape where it is temporarily secured in position. Allow to cure. The joint should be held closed while the epoxy cures with clamps or jigs.