Practice for Developing a Consolidation Step - P158

 

Practice for Developing a Consolidation Step
Practice document
Document Type	Practice
Document Identifier	158
Themes	Materials deposition and consolidation management
Tags	Bagging Consumables Debulking Fibre-bed compaction Consolidation Vacuum application Integrated product development Porosity
Objective functions	Cost Maintain Rate Maintain Quality Maintain
MSTE workflow	Development
Prerequisites	Integrated Product Development Practice Practice for Developing a Process Step

Overview

This page will guide the user in developing their consolidation step. Firstly highlighting some of the options to consider when selecting a type of consolidation method, then providing practice documents that describe different processes in detail. This includes conceptual screening and preliminary selection of temperature and pressure, then detailed finalization of the manufacturing (MSTE) system as a whole. The page is broken into three tabs that cover these activities.

Introduction

Consolidation refers to compacting the fibre bed and resin of a composite material system in order to achieve a desirable fibre volume fraction, and reduce/avoid gaps in the the laminate. This step contributes to the final part strength, durability, and dimensional accuracy. While a consolidation step offers numerous benefits in terms of composite part quality and performance, it is not always mandatory. The decision to implement this or not depends on the specific requirements of the application, the chosen manufacturing process, available equipment, and the desired properties of the final composite part.

Significance

The consolidation process serves several critical functions in shaping the properties of a composite part. To begin with, its primary objective is to eliminate trapped air between the layers of the material, whether it's between Prepreg layers or dry fibers (read more about Porosity). Effective consolidation further enhances the fiber volume fraction by ensuring the proper compaction of fiber and the even distribution of the matrix material. Throughout the manufacturing process, the continuous application of pressure to the material system also aids in preventing the formation of porosity. Lastly, consolidation plays a key role in achieving a smoother and more consistent surface finish for the final part.

Read more about Materials deposition and consolidation management (MDCM).

Practice

The following section follows the three process design gates of screening, selecting, and finalizing. Each of the process design gates are discussed under the consideration of each of the MSTE topics. Each MSTE topic provides questions to consider for each design gate to further advance each topic from screen to finalize.

Screen

Select

Finalize

Material

The choice of fibre and resin system is going to have an effect on how the layup will consolidate. Different fibre types and architectures have different properties (Fibre Architecture: Availability, pros and cons, and selection for my application), which can affect the way they behave when pressure is applied. For the resin system, consolidation needs to be considered when applying pressure, but also during curing. Room temperature cure or oven/autoclave cure? If it is a room temperature cure, are you applying manual pressure to the part and is that enough, or do you need a vacuum bag?

If it is an oven or autoclave cure, will there be a vacuum bag over it during cure? Is that enough to consolidate all the plies and resin, or will you need a Debulking step during layup?

Fibre orientation is critical to the final properties of the part. When performing an infusion or resin transfer moulding process, there is a risk of resin flow disturbing the fibre if there is not enough consolidation pressure to hold them in place.

• Is there a need for a debulk before infusing the resin?
• Will special precautions be made so the incoming resin does not move the fibre?
• Is the resin viscosity suitable or should it be lower?

This is also true for wet layups and prepreg layups. Using a Debulking step can aid in compacting the fibre and prevent movement.

The tackiness or stickiness of the material can affect how it is handled and laid up. Some materials may require the use of release films or peel plies to prevent the material from sticking to the tools or itself during consolidation.

Achieving the correct resin-to-fiber ratio is critical for composite performance. Proper consolidation ensures that the resin wets out the fiber evenly, avoiding resin-rich or resin-poor areas in the final part. Pre-bleeding is when resin is intentionally removed from the part under vacuum through a bleeder cloth.

If your material is a thermoplastic, consolidation must happen at temperatures above the melt temperature for semi-crystalline materials. The general rule of thumb is to apply pressure to the part at temperatures of 90°C or less above the melting temperature. Keeping in mind that the pressures and temperatures required for thermoplastic processing are higher than traditional thermosets. It is also important to consider the time the material will need to consolidate as powder coated comingled prepregs require time to fully consolidate, hot-melt prepregs can consolidate in a very short amount of time. To achieve a well consolidated thermoplastic part, the pressure must remain applied when the part is cooling until the temperature is below Tg. This inhibits the formation of voids, prevents elastic recovery in the fibres and maintains the desired shape of the part. Read more at Consolidation of Thermoplastics.

See also A267

Shape

For complicated tooling and geometries, it is important to consider if the pressure applied to the part will be uniform. Parts with varying curves and contours may require different consolidation methods to ensure that the composite material conforms to the shape without wrinkles, voids, or excessive resin pooling. Is it worth it to develop a caul plate? Is there enough space on the tool for a vacuum bag to be applied? Can a bladder be used?

If the part is complex, there may be a need to perform a hot-debulking step or a pre-bleeding step when using prepreg. Hot debulking is applying vacuum to a part as well as heat, 65°C to 90°C typically .

Parts with varying thicknesses may experience consolidation challenges. Thicker areas may require longer consolidation times or higher pressure to achieve the desired compaction, while thinner areas may be more susceptible to over-compression.

See also A268

Equipment

For automated processes such as A300 and A303 will there be enough pressure applied from the machines to ensure enough consolidation of the fibre bed?

Does the facility have integrated vacuum lines, or will vacuum pumps need to be purchased for this manufacturing process?

See also A269

Tooling & Consumables

Injection moulding and compression moulding provide very high and consistent pressures for consolidation. However, the infrastructure is expensive and the part geometry is limited.

For a vacuum bagged part, will you need an edge dam? Is there enough room on your tool to apply a vacuum bag? Is it worth it to invest in a reusable silicone vacuum bag for high volume parts?

The consolidation process often involves the application of pressure and, in some cases, vacuum. The amount and distribution of pressure or vacuum should be carefully controlled to avoid wrinkles, voids, or excessive resin flow.

See also A270

Read Select for the next step.

Correct temperature and pressure are important to consolidate the material. Will the correct temperature be reached without an oven? Will the correct pressure be reached without an Autoclave? For every parameter that needs to be controlled by specialized equipment like an autoclave, the cost of equipment will increase rapidly. See also Room temperature transformation.

To achieve high rates in consolidation processes, pre-shaped material or pre-made vacuum application methods will increase the rate, but usually add to the cost as well. For example, using disposable vacuum bags for curing and debulking allows for variable parts and shapes at a fairly low cost. Switching to reusable vacuum bags will limit part shapes and increase cost, but will reduce the time spent on making vacuum bags per part.

Aiming for higher production rates can lead to the decline of quality. For example, a reduction of dwell time can lead to less time available for the material to undergo complete consolidation. Inadequate dwell time can result in insufficient compaction, causing voids, wrinkles, or incomplete curing. Quality can also be affected by rushing to perform tasks, this can lead to misalignment or damage to the material, affecting the consolidation quality.

Consolidation can be a very energy intensive process, so it is important to keep in mind the emission effects that come from energy hungry equipment. Optimizing cure cycles and consolidation times can minimize energy use while maintaining product quality, see Production Optimization for optimization strategies. Other strategies may include heat recovery from heated processes, or reusable vacuum bags.

Some considerations to review at this stage:

• Is there enough room on your tool to apply a vacuum bag?
• Is it worth it to invest in a reusable silicone vacuum bag for high volume parts?
• If the desired production rate is very high, is it worth it to invest in compression moulding equipment?
• Will this method of debulking slow down production rate?
• For a thermoplastic part, will there be a need for pre-consolidation and pre heating? if so, will the plies need to be tacked together to prevent them from moving beforehand?

Read Finalize for the next step.

Prototyping a few parts with slight variations of the consolidation steps will help eliminate and determine what is necessary. At this stage it will be valuable to measure porosity and the fibre volume fraction obtained in the part in order to determine how successful the consolidation of the part has been. A low amount of porosity will suggest that there has been adequate pressure and gas transport though the part. A high fibre volume fraction will indicate a high consolidation pressure on the part. Other measurements and tests may be necessary as well, for example confirming the profile and shape of the part is as it should be and that the fibres themselves have not been shifted during cure.

Read more about Porosity and How to measure reinforcement content (and corresponding matrix content). As well as Effect of consolidation in residual stress management

Consolidation During Deposition

• Debulk - Debulking
• Resin Infusion

Consolidation for Cure

• Vacuum Pressure - Vacuum Bagging
• Gas Pressure - Autoclave Pressurization System
• Tool Pressure - Hot press & A293

Thermoplastic Consolidation

• Consolidation of Thermoplastics

Explore this area further

• Practice for Developing a Consolidation Step - P158
  • Debulking - P167
  • Consolidation of Thermoplastics - P170
  • Vacuum Bagging - P168
    • Vacuum Bagging for Prepregs - P172
    • Vacuum Bagging for Vacuum Infusion - P173

Related pages

Page type	Links
Introduction to Composites Articles
Foundational Knowledge Articles
Foundational Knowledge Method Documents
Foundational Knowledge Worked Examples
Systems Knowledge Articles
Systems Knowledge Method Documents
Systems Knowledge Worked Examples
Systems Catalogue Articles
Systems Catalogue Objects – Material
Systems Catalogue Objects – Shape
Systems Catalogue Objects – Tooling and consumables
Systems Catalogue Objects – Equipment
Practice Documents	Consolidation of Thermoplastics - P170 Debulking - P167 Practice for Developing a Consolidation Step - P158 Practice for Developing a Deposition Step - P157 Vacuum Bagging - P168 Vacuum Bagging for Prepregs - P172 Vacuum Bagging for Vacuum Infusion - P173
Case Studies
Perspectives Articles

References

About	Help

Any manufacturing and/or decision making activity that occurs during any stage of the development design cycle (e.g. conceptual design to production).

In the context of Knowledge in Practice, practice refers to the systematic use of science based knowledge to reduce composites manufacturing risk, cost, and development time.

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.

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.

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

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

With regards to manufacturing, risk is the combination of the probability and consequences of undesirable manufacturing outcomes. Manufacturing risk can lead to technical issues, program/schedule delays, and cost overruns.

In composites processing, viscosity is an indicator of how easily the resin matrix will mix with the reinforcement and how well it will stay in place during processing. The lower the viscosity, the more easily resin flows. Resin viscosity ranges considerably across chemistries and formulations.

By scientific definition, viscosity is a measure of a material’s resistance to deformation. For liquids, it is in response to imposed shear stresses.

Pre-impregnated (prepreg) material refers to fibre that is already combined with resin. It is the most common material form used in aerospace.

During prepreg production, (e.g. fibres are run through a resin bath), prepreg is heated and partially cured to B Stage (< 5 % degree of cure). Thermoset prepregs (e.g. epoxy prepreg) have to be kept in a freezer at around -20 °C. At room temperature, the epoxy starts to cure.

A class of polymer, some common examples include polypropylene and polyethylene.

They soften and melt upon heating (i.e. potentially recyclable), high viscosity when melted, therefore difficult to saturate fibres. Usually needs a lot of pressure and heat to process.

A portion of the molecular polymer chains tend to ‘fold up’ into densely packed regions called crystals.