Stamp forming of continuous glass fibre reinforced polypropylene

A thermoforming technique, known as stamp forming, has been used to process unidirectional glass fibre reinforced polypropylene (PP). A novel hemispherical mould with built-in hold-down arrangement was designed. This mould was used at room temperature to form parts from pre-heated flat pre-consolidated laminates. Pre-consolidated laminates are heated by contact heating in an external heater above the melting temperature of the PP polymer matrix; they are then formed in the cold matched metal tool. Typical cycle times to process the pre-consolidated laminates (including pre-heating time of the pre-consolidated laminates) are in the range of 2 min. Useful processing conditions, such as stamping temperature, stamping velocity and hold-down pressure required for the stamp forming of this composite are determined. The effects of die geometries and laminate dimension on the 'fibre buckling' are studied. Finally, the thickness distribution in stamped parts is investigated in relation to different directions of fibre orientation. (C) 1997 Elsevier Science Limited.