FRP Mold Manufacturing Process
When constructing any mold, it is essential to strike a balance between the mold's physical properties, material costs, and manufacturing time. This tutorial-based on French Nord mold-making materials and utilizing foam as the master model substrate-provides an in-depth analysis of the complete workflow for creating a master model and processing the final mold. Our aim is to help you gain a better understanding of the methods involved in manufacturing FRP molds.
Foam Substrate Preparation
In the initial phase of mold manufacturing, a Computer Numerical Control (CNC) machine is used to perform high-precision machining on the foam; this serves as the foundation for subsequent fine-finishing processes. The basis for the master model involves using a CNC machine to process polyurethane or polystyrene foam with a density of 25 kg/m³. During this stage, a fine-machining pass is executed to a depth of -8 to -12 mm.
Hand Lay-up of Foam-Compatible Resin
Once the machining of the foam master model is complete, a hand lay-up technique is employed to apply NORE CORE 854-a foam-compatible resin-to the foam's surface. First, a uniform layer of the compatible resin (approximately 0.8–1 mm thick) is applied to the foam. This layer is then covered with two layers of 300 g/m² chopped strand mat to reinforce the fiberglass structure. During the application and covering process, it is crucial to leave a 10–15 cm margin around the edges to ensure the resin fully encapsulates the substrate.
Spraying of Polyester Modeling Paste and Machining
We utilize a thin-layer spraying technique, followed by machining to a specified thickness, to achieve a mold shape with extremely high precision. NCL 809 D065 polyester modeling paste is applied via multiple thin-layer spray passes, with each layer reaching a thickness of 5–6 mm. If the required thickness for subsequent machining is 8 mm, two spray passes are necessary; if a thickness of 12 mm is required, three spray passes are performed.
Hand Lay-up of Foam-Compatible Resin
Building upon the foam master model, a hand lay-up technique is used to apply NORE CORE 854 foam-compatible resin (a styrene-free resin) to the surface of the foam substrate. First, we apply a uniform layer of compatible resin-approximately 0.8–1 mm thick-onto the foam substrate. We then overlay this with two layers of 300 g/m² chopped strand mat to reinforce the fiberglass structure. During the application and covering process, it is essential to leave a 10–15 cm margin around the perimeter to ensure the resin can fully encapsulate the substrate.
Spraying of Polyester Modeling Paste and Machining
In this step, NCL 809 D065 polyester modeling paste is applied via thin-layer spraying, with each layer reaching a thickness of 5–6 mm. If the required thickness for subsequent machining is 8 mm, two spray passes are necessary; if a thickness of 12 mm is required, three passes are needed. This step is particularly critical in the field of high-precision mold manufacturing.
Male Mold Preparation and Gelcoat Spraying
The male mold is meticulously sanded using 240–400 grit dry sandpaper, and all dust is thoroughly removed. Polishing is not required at this stage. Subsequently, a multi-pass thin-layer spraying technique is employed using NORD APPERT 230 air-drying, easy-sanding mold gelcoat to ensure the appropriate thickness is achieved-typically maintained within the 450–600 micron range.
Sanding and Polishing
Initial sanding is performed using 240–400 grit dry sandpaper, followed by the removal of any generated dust. Sandpapers of progressively finer grits are then used to achieve a smooth mold surface; this process is often combined with polishing wax for the final finishing touches. If a subsequent high-gloss gelcoat application is not required, it is recommended to sand up to 600 grit, at which point moderate surface refinement or polishing can be performed.
Demolding and Surface Treatment
A traditional mold release wax application method is utilized to ensure a smooth demolding process. An effective protective layer is created by applying 5–8 coats of mold release wax to the surface of the male mold. When demolding, it is advisable to begin by carefully testing the edges; gently tapping the mold's perimeter with a rubber or wooden mallet allows one to determine-by the sound of the tapping-whether the mold has successfully released from the substrate. Furthermore, upon completion of wet sanding and polishing, a mold cleaner should be used to thoroughly remove any polyester residue from the surface. Subsequently, a mold sealer and release agent should be applied to achieve an optimal high-gloss finish. For new molds, multiple applications are required to ensure effective mold release.
