heating plates 60 where the latter are brought to a temperature t1 which is of order for example of 80 to 120 u00b0 c at a speed of 1 5 to 2 5 u00b0 c min as shown by line a simultaneously an injection resin intended to be circulated later in the mould 50 is heated to a temperature t0 which is for example of the order of 60 to 100 u00b0 c as shown by line b this resin is preferably of the same kind as that of the pre impregnated fibres of the stack at the time t u2032 0 the temperature of the heating plates 60 reaches the value t1 which is maintained for an ageing period for the resin in the pre impregnated fibre layers in the stack which lasts a maximum of 20 minutes up to the time t1 this ageing may also apply to the resin of the adhesive films in the stack some resins however do not need to undergo ageing so that the time t1 then corresponds to time t u2032 0 at this time t1 after the temperature of the heating plates has stabilised at temperature t1 and the ageing of the resin of the stack the injection resin 62 is circulated in the mould 50 as shown in the third diagram in fig9 and as shown by line e this circulation is achieved using conventional means of the vacuum pump and resin reservoir type the circulation of the injection resin 62.