The moulding process of FRP plastics begins by placing the fibre preform on or in the mould. The fibre preform can be dry fibre, or fibre that already contains a measured amount of resin called "prepreg". Dry fibres are "wetted" with resin either by hand or the resin is injected into a closed mould. The part is then cured, leaving the matrix and fibres in the shape created by the mould. Heat and/or pressure are sometimes used to cure the resin and improve the quality of the final part.
The quality of the mould determines the accuracy and surface finish of the output parts. These moulds are typically made of soft wood materials like MDF often hand crafted or made using CNC process. Using CNC can give highly accurate moulds yet lead to high cost of making the mould and long lead times barring any un-machinable features. Hand crafted moulds can be slightly cheaper but ensuring dimensional accuracy can be a challenge. Dimensional accuracy in the range of 1mm is typical for hand crafted moulds. Hand crafting takes even more time compared to CNC. Moulds measuring roughly 1000mmx1000mmx1000mm could typically take 10-14 days after meticulous planning depending on the complexity of the design.
With the advent of 3D printing even a simple process like FDM can produce moulds of great accuracy and good surface finish in a matter of days. For the above mentioned dimensions the mould can be made in a matter of 2-3 days with an accuracy of 0.2-0.3mm at roughly 1/4th the cost of CNC machining process.
Fibro Reinforced Plastics Pvt Ltd needed to make a large mould roughly measuring 1000mm3 for an aerial drone. So dimensional accuracy, structural integrity and light weight are of paramount importance in this case. The FRP process demands the mould sustain at least 70-80 0C under continuous operation for laying the fibres without any structural deformation. So the mould was fabricated using FDM process and ABS material which can sustain 80 0C under continuous operation. The entire 3D printing process took 67 hours and costed roughly 1/4th of the CNC machining process.
Below is a sample image of a part made using FRP with 3d printed mould.
FRP part made from 3D printed mould