optionally preformed on stations further up the production line from upstream to downstream the production line is made up of a loading station 19 on which an operator places cold reinforcement sheets of an infrared oven 20 which heats individually each reinforcement sheet that is placed on the loading station and delivers it at the end of the oven that is further from the loading station and of a second picking up device 21 which picks up the heated sheets and can place them in two different places depending on the type of part to be made for a part using a plurality of reinforcement sheets the second picking up device 21 stacks up the reinforcement sheets exiting from the oven and then when there are enough of them places them on a pre forming rack the sheets as stacked up for pre forming purposes are inserted into a hot air oven 22 so as to bring them to the temperature at which they were on exiting from the infrared oven 20 for a part using a single reinforcement sheet the second picking up device 21 makes the reinforcement sheets available directly to the first picking up device 18 so that they can be placed immediately in the mold 17 it should be noted that the picking up device 18 made up by pressers each having two sets of needles is particularly well suited to handling heated reinforcement sheets of the twintex type and to handling them in a vertical position as applies in the production line shown in fig7 firstly the heated sheets are easy to spear and secondly the heated sheets are easy for the needles to hold because said needles are perpendicular to the plane of the sheet in addition the vertical position of.