How To Make A Mould for Carbon Fiber Parts

Introduction

Creating a mould for carbon fiber parts is a precise process that requires careful planning and execution. Carbon fiber composites are widely used in aerospace, automotive, and sports industries due to their high strength-to-weight ratio (tensile strength of 500-700 MPa and modulus of 70-300 GPa). A well-made mould ensures the final part meets dimensional tolerances of ±0.1 mm and surface finish requirements (Ra < 0.8 µm).

Materials and Tools Required

• Master Pattern: Typically made from CNC-machined aluminum (6061-T6) or high-density polyurethane foam (density 30-50 lbs/ft³).

• Mould Material: Epoxy resin systems (viscosity 300-500 cPs) with fiberglass or carbon fiber reinforcement.

• Release Agents: Semi-permanent polymer-based coatings (PTFE or PVA) with 5-10 µm thickness.

• Gel Coat: High-temperature resistant (up to 150°C) with 0.5-1.0 mm thickness.

• Vacuum Bagging Supplies: Peel ply (50 g/m²), breather fabric (100 g/m²), and vacuum film (0.1 mm thick).

Step-by-Step Mould Making Process

1. Pattern Preparation

The master pattern must have a surface roughness < 0.4 µm Ra. Apply 3-5 layers of mould release wax (carnauba-based) with 20-minute intervals between coats. Buff to a high gloss finish using 2000-grit polishing compound.

2. Gel Coat Application

Spray or brush a 0.75 mm thick gel coat layer (mixed with 1.5% MEKP catalyst). Maintain ambient temperature at 22±2°C and relative humidity below 60% during curing (45-60 minutes).

3. Structural Laminate

Apply the first layer of 300 g/m² fiberglass mat with epoxy resin (mix ratio 100:30 resin to hardener). Subsequent layers use 200 g/m² carbon fiber fabric in a 0/90° orientation. Vacuum bag at 0.8-0.9 bar pressure for 12-24 hours at 25°C.

4. Demoulding

After full cure (7 days at room temperature or 2 hours at 80°C), carefully separate the mould using air wedges. The mould should have a thermal expansion coefficient of 20-30 µm/m·°C to match carbon fiber parts.

Key Technical Parameters

Application Scenarios

Aerospace Components

Moulds for aircraft winglets require CTE matching to carbon fiber (0.5-2.0 µm/m·°C) and must maintain vacuum integrity at 0.1 mbar for 8-hour cure cycles.

Automotive Body Panels

Production moulds for hoods and doors typically use nickel-shell tooling with 0.05 mm surface accuracy, capable of 5-minute cycle times at 140°C.

Sports Equipment

Bicycle frame moulds often incorporate 3D-printed PLA patterns with 0.1 mm layer resolution, later coated with epoxy for final tooling.

Medical Devices

MRI-compatible component moulds require non-metallic materials with dielectric properties (ε_r < 3.5 at 1 MHz).

Maintenance Procedures

Cleaning

After each use, clean with isopropyl alcohol (99% purity) and lint-free wipes. For stubborn release agent buildup, use specialized solvent cleaners with pH 6.5-7.5.

Surface Repair

Fill scratches deeper than 0.2 mm with epoxy putty (hardness Shore D 85), then sand with progressively finer grits (400→1200→2000).

Storage

Store moulds at 20±5°C and 40-60% RH. Apply a protective wax coating (5-10 µm) for long-term storage (>3 months).

Periodic Inspection

Check for dimensional drift using CMM every 50 cycles (tolerance ±0.1 mm). Verify surface gloss remains >85 GU (60° measurement angle).

Advanced Techniques

Invar Tooling

For ultra-precision aerospace moulds, Invar 36 (Fe-Ni alloy) provides CTE of 1.2 µm/m·°C between 20-100°C, but requires CNC Machining with 0.01 mm tolerance.

Ceramic Moulds

Used for high-temperature curing (up to 350°C), these moulds have thermal conductivity of 1.5 W/m·K and can maintain ±0.03 mm accuracy over 500 cycles.

Additive Manufactured Tools

Direct metal laser sintered (DMLS) aluminium moulds achieve 20 µm feature resolution and can be produced in 72 hours for Rapid Prototyping.

Safety Considerations

• Wear NIOSH-approved respirators when sanding (P100 filters for particles<0.3>

• Maintain VOC levels below 50 ppm during resin application

• Use explosion-proof equipment when working with acetone (flash point -20°C)

• Ensure adequate ventilation (minimum 10 air changes per hour)