Material deposition - A182

 

Material deposition
Document Type	Article
Document Identifier	182
Tags	Deposition
Prerequisites	Factory cells (where and how)

Introduction

Material deposition as a factory process step is concerned with placing (and consolidating) the constituent materials of a composite part onto the tooling. The material deposition step is highly dependent on the manufacturing process, which is likely why most processes are colloquially named after their deposition step. Material deposition processes can be broadly separated into two categories:

• Deposition of the reinforcement onto the tool followed by the deposition of matrix (Tool + Reinforcement + Matrix)
• Reinforcement and Matrix combined, then deposited onto the tool ((Reinforcement + Matrix) + Tool)

Regardless of the manufacturing process, material deposition and consolidation have direct impact on cost and final part quality. Depending on the process, material form and part shape, deposition and consolidation can consume a huge amount of time and resources in a manufacturing system, especially for complex and high performance composite parts. The combined effect of the material deposition and consolidation and the subsequent thermal transformation steps will determine local porosity, resin volume fraction leading to either resin rich or resin starved areas, and fibre misalignment.

Significance

Link to the outcome matrix

Material deposition and consolidation is a major cost driver in composite manufacturing. The capital and overhead cost of material deposition accounts for 40 - 60 % of the total cost depending on part complexity and production volume. Several manufacturing outcomes are directly related to material deposition and consolidation. This includes wrinkling, fibre waviness, Fibre volume fraction, porosity (void content), residual stress and others. Further, material deposition rate can directly impact throughput. Choosing the correct manufacturing process and appropriate material deposition processing parameters are essential to a composite manufacturing system.

Scope

This page describes material deposition as a factory step. The material, shape, tooling and equipment associated with this step are discussed. Since material deposition and consolidation is heavily process dependent, this section is linked to a comprehensive list of composite manufacturing processes where material deposition and consolidation management is expanded into greater details.

Material deposition cell

At a material deposition cell in a factory, constituent materials of a composite part are deposited into the correct position on the tool. The tool must be cleaned and have proper release agent applied beforehand. Depending on the process/part requirements, the deposition cell may require a clean room where temperature, humidity, and UV light are controlled. The clean room should have slight positive air pressure to keep the dust particles out. Inlet air should be also be filtered to minimize dust particles. Other processes/parts may not require a clean room. For different manufacturing processes, the equipment and activities in this factory cell will be different. A brief description of what the material deposition cell looks like based on the manufacturing process is listed below.

• Deposition of the reinforcement onto the tool followed by the deposition of matrix (Tool + Reinforcement + Matrix). Some typical processes in this category include:
  • Vacuum assisted resin transfer moulding (VARTM)/resin infusion (VARI): placing dry reinforcement on a rigid tool under a vacuum bag, where vacuum draws resin to impregnate the fabric
  • Light resin transfer moulding (Light RTM): placing dry reinforcement on a rigid tool under another flexible mould half, where pressure difference drives resin to impregnate the fabric
  • Resin transfer moulding (RTM): placing dry reinforcement inside a rigid closed tool, where pressure difference drives resin to impregnate the fabric
  • Forming (dry charge): dry reinforcement formed into the shape of the tool. Resin is then subsequently deposited to impregnate the fabric
  • Reaction injection moulding (RIM): placing dry reinforcement inside a rigid closed tool, resin constituents are mixed while being injected to impregnate the fabric

• Reinforcement and matrix combined, then deposited onto the tool ((Reinforcement + Matrix) + Tool). Some typical processes in this category include:
  • Wet layup: dry reinforcement are placed into an open tool as resin is applied to impregnate the reinforcement
  • Spray-up: chopped reinforcement strands and resin are sprayed into an open mould simultaneously
  • Pultrusion: resin impregnates dry reinforcement, which then pass through a die
  • Filament winding (wet winding): continuous reinforcement filament is impregnated with liquid resin and wound onto a mandrel
  • Filament winding (Towpreg winding): continuous pre-impregnated reinforcement is wound onto a mandrel
  • Forming (Pre-preg): pre-impregnated reinforcement is formed to the shape of the tool
  • Compression moulding (SMC/BMC): place reinforcement and matrix in two mould halves, close in a hot press to form the shape
  • Hand layup prepreg (Autoclave/Out-of-autoclave) processing - A291: placing pre-impregnated reinforcement on a rigid tool under a vacuum bag
  • Automated fibre placement (AFP)：robot placing narrow pre-impregnated reinforcement on a rigid tool
  • Automated tape layup (ATL): robot placing pre-impregnated reinforcement tape on a rigid tool
  • Bladder moulding: place reinforcement and matrix against the wall of the mould cavity, use a bladder to consolidate
  • Tube Rolling: Roll pre-impregnated reinforcement on to a tube
  • Centrifugal casting: deposit dry reinforcement and resin against the inner surface of a rotating mould
  • Continuous Lamination: resin impregnates dry reinforcement on a conveyor system

Remarks on deposition, consolidation and thermal transformation

Depending on the manufacturing process, material deposition, consolidation and thermal transformation can be achieved in the same factory cell/step. Examples:

• When the resin is impregnating the dry reinforcement during a wet lay-up process, a roller is typically used to consolidate the laminate
• When impregnated filament is wound onto the mandrel during a filament winding process, the tension on the filament consolidates the already deposited material
• In the case of pultrusion and continuous lamination, reinforcement and matrix are combined, consolidated and cured in the same factory cell For more information on the specific processing parameters, materials, shapes, tooling and equipment of these manufacturing process, please visit Materials deposition and consolidation management

Explore this area further

• Material deposition - A182
  • Compression moulding - A302
  • Hand layup prepreg (Autoclave/Out-of-autoclave) processing - A291
  • Vacuum assisted resin transfer moulding (VARTM)/resin infusion (VARI) - A290
  • Wet layup - A296

References

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The individual materials that combine to form the composite material. The constituent materials are separate and distinct on a macroscopic level.

Engineered materials (designed to have specific properties) made from two or more constituent materials with different physical or chemical properties. The constituents remain separate and distinct on a macroscopic level within the finished structure.

The continuous material phase that binds the reinforcement together, maintains shape, transfers load, protects the reinforcement from environment and damage, and provides the composite support in compression.

Desirable characteristics:

• Moisture/chemical resistance
• Low density
• Processability

For polymer matrix composites (PMCs), resin refers to the matrix; the continuous material phase that binds the reinforcement together, maintains shape, and transfers load. Resins are divided into two main groups: thermosets and thermoplastics.

Volume fraction of either matrix or fibres with respect to total composite volume (matrix + fibre).

Outcomes represent the range of response/sensitivity to factory system attributes. Those that fail to satisfy manufacturing requirements are known as defects. Examples of manufacturing outcomes include process parameter outcomes, material structure outcomes, and material performance outcomes.

An individual station within a factory where a given set of tasks are accomplished (also known as a "work cell"). Some cells may directly add value to the product (e.g. deposition), while others may serve support roles that are critical to maintaining part quality (e.g. receiving, storage, inspection & shipping).

A single unit of fibre reinforcement that cannot be separated further without breaking it. It often has a circular cross section that is formed by the dies used to create it or its precursor material. Many filaments are manufactured in parallel to produce a strand or tow. The number of filaments in a strand or tow is often references by how many thousands of filaments comprise the tow. e.g. an 18k tow is made up of ~18000 filaments.

The act of combining reinforcement fibre, resin to shape on a mould (tool).

There are three main methods to combine resin and fibre to deposit onto a tool (i.e. material deposition):

• Wet Processes: Mixing liquid resin and dry fibre directly in the mould, e.g. Wet Compression Moulding process for parts in BMW 7 series
• Liquid Composite Moulding (LCM) processes: Infusing dry fabric with resin using a pressure gradient, e.g. High Pressure Resin Transfer Moulding process (HP RTM) for parts in BMW i3
• Prepreg Processes: Laying up using prepreg where resin and fibre are already combined, e.g. Automated Tape Laying (ATL) process for some of the parts in Boeing 787.