Composite Processes Explained

composite processes

Hand Lay-uP, sPRAY lAY-uP & rtm

wHAT ARE THE MAIN COMPOSITE MANUFACTURING PROCESSES?

Composite manufacturing uses a range of processes to produce strong, lightweight, and high-performance components. Choosing the right method depends on:

  • Production volume
  • Part complexity
  • Surface finish requirements
  • Budget and tooling constraints

 

In this guide, we break down three of the most widely used composite manufacturing processes:

  • Hand Lay‑Up
  • Spray Lay‑Up
  • Resin Transfer Moulding (RTM)

Later in this series, we’ll explore advanced techniques such as autoclave curing and automated composite manufacturing—and how they impact performance, cost, and efficiency.

HAND Lay Up Process?

Hand lay‑up is a manual method used to manufacture Glass Reinforced Plastic (GRP) parts. It’s ideal for:

  • Low-volume production
  • Prototyping
  • Large composite mouldings
  • Applications where low tooling cost is critical

How Hand Lay-Up Works

1. Mould Preparation

  • Clean mould (e.g. acetone)
  • Apply release agent (wax or semi-permanent)

 

2. Gelcoat Application

  • Apply by brush or spray
  • Check thickness for consistency

 

3. Reinforcement Placement

  • Place chopped strand mat (CSM)
  • Add layers for strength
  • Optional: carbon fibre, woven glass, Kevlar

 

4. Resin Wet‑Out

  • Apply resin with rollers/brushes
  • Ensure full fibre saturation
  • Allow to cure

 

5. Demoulding

  • Remove part
  • Clean mould for reuse

 

Benefits of Hand Lay Up

  • Low tooling and setup costs
  • Simple, flexible process
  • Suitable for large and custom parts

 

Limitations

  • Labour-intensive
  • Dependent on operator skill
  • Higher exposure to styrene emissions
  • Lower structural consistency vs closed moulding

 

Spray Lay Up Process

What is Spray lAY-uP?

Spray lay‑up is a semi-automated process where resin and chopped fibres are sprayed simultaneously using a chopper gun.

Best suited for:

  • Medium-volume production
  • Complex shapes
  • Faster manufacturing vs hand lay‑up

How Spray Lay-Up works?

Mould Preparation

Clean and apply release agent

Gelcoat Application

  • Apply 1–2 coats
  • Allow to become tacky

 

Spraying

Spray resin + chopped glass fibres (10–40 mm)

Common resins: polyester, vinyl ester

Compaction

  • Roll laminate to remove air
  • Add cores (foam, honeycomb) if required
 

Curing & Finishing

  • Cure at room temperature or heat
  • Trim and finish

 

Benefits of Spray Lay-Up

  • Faster than hand lay‑up
  • Lower labour requirement
  • Good for complex, curved surfaces

 

Limitations

  • Less control over fibre orientation
  • Higher resin content (heavier parts)
  • Airborne emissions and safety considerations

 

Resin Transfer Moulding (RTM)

What is RTM in Composite Manufacturing?

Resin Transfer Moulding (RTM) is a closed-mould process used to produce high-performance composite parts with excellent surface finish and consistency.

Common industries:

  • Automotive
  • Aerospace
  • Marine
  • Industrial manufacturing

How does RTM work?

Mould Preparation

  • Apply release agent
  • Apply gelcoat if needed

 

Reinforcement Placement

  • Place dry fibres into mould
  • Ensure full coverage

 

Mould Closure & Injection

  • Clamp mould shut
  • Inject resin under pressure
  • Vent air for full impregnation

 

Curing & Demoulding

  • Apply heat to cure
  • Remove finished component

 

Benefits of RTM

  • High-quality surface finish (both sides)
  • Consistent fibre-to-resin ratio
  • Reduced waste and emissions
  • Ideal for structural components

 

Limitations

  • High tooling and mould cost
  • Requires process expertise
  • Risk of defects if flow is poorly managed

 

Comparing Composite Manufacturing Processes

Process
Best For
Hand Lay-Up
Low volume, large parts, prototyping
Spray Lay‑Up
Medium volume, complex shapes
RTM
High‑quality, high‑volume structural components

How to Choose the Right Composite Process

When selecting a composite manufacturing method, consider:

  • Production volume → Hand lay-up (low), RTM (high)
  • Part complexity → Spray lay-up or RTM
  • Surface finish → RTM delivers the best results
  • Budget → Hand lay-up offers lowest upfront cost

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FAQs

Is Hand Lay-Up suitable for large parts?
Yes, but it’s labour-intensive and may require multiple operators.

Can Spray Lay-Up be automated?
Partially. The spraying process is semi-automated, but mould prep and finishing are manual.

What industries use RTM?
Automotive, aerospace, and marine industries commonly use RTM for high-performance parts.