Different Methods of Composite Manufacturing
In the first of our new series on composite manufacturing, we look into how composites are made and summarise a few of the different approaches. We will delve deeper into automated methods and the areas that Loop Technology specialise in, later on in this series.
The investment and interest in manufacturing composites continues to grow as industries seek to leverage the benefits of lighter, stronger parts and components. There are many approaches to manufacturing composites and the method chosen is dependent on factors such as the complexity of the final part, cost, volume production required, access to skilled labour, industry specific tolerances, quality requirements and regulations.
Manual Layup
This involves operators manually placing layers of the reinforcement material, carbon fibre, fibreglass or aramid, onto a mould. The mould is made from materials such as aluminium, steel, fibreglass, wood, plaster, epoxy tooling board and defines the geometry of the part being manufactured. It is often coated with a release agent to ensure the composite part can be ejected easily after curing and a gel coat so the final part has a smooth surface finish.
The fabric placed is either pre-cut to the appropriate size and shape before going on to the mould or it is trimmed during the process. The exact fibre type, orientation and direction the material is placed in determines the characteristics of the final part and is a crucial stage in the process, for all types of composite manufacturing. In the case of dry fibre, resin is then applied layer by layer as the part is built up- the number of layers is determined by the required thickness and strength. The plies are then consolidated to remove air bubbles and so that the resin is evenly distributed. It is then cured at a temperature appropriate to the resin, with the part finally demoulded and ejected.
Hand layup is an open moulding technique and used to create a variety of different parts. It requires skilled, intensive labour and produces inconsistent quality when compared to automated methods. It is not ideal for high volume production and industries that have stringent tolerances, requiring parts to be manufactured to a high level of accuracy.
Resin Transfer Moulding
In resin transfer moulding (RTM), there are two moulds that are matched together (mould halves) and dry fibre sits in an enclosed space between them. Resin is injected through the mould ports under pressure and flows through the fibres so that the mould cavity is filled. The resin is then cured, the mould opened and the composite part ejected. RTM is a closed moulding technique that delivers high quality products and is used to make thousands of identical parts such as hoods, fenders and roof panels in the automotive industry. A wide range of resin systems can be used in the process including polyester, vinyl ester, epoxy and polyurethane. A variation of this process is Vacuum Assisted Resin Transfer Moulding (VARTM) in which a vacuum is applied to the closed mould and draws the resin through the layers of fibre.
Filament Winding
This method is used to manufacture cylindrical or complex shapes such as pipes, drive shafts and pressure vessels. Continuous fibres are wound around a rotating mandrel. The fibres are pulled from spools and are either pre-impregnated with resin or the dry fibre goes through a bath of liquid resin before going onto the mandrel. The benefits of filament winding are that it provides high accuracy in the patterns of fibre deposition and the ability to create highly customized parts. It is ideal for high stiffness and low porosity parts.
Braiding
Brading as a method for composites manufacturing involves arranging the fibre material into spools and then feeding them into a braiding machine. Within the braiding machine, carriers hold the spools of fibre which are then rotated around a central mandrel in a variety of patterns, including biaxial and triaxial braids. Braiding offers omnidirectional reinforcement and is often used in aerospace and automotive manufacturing where impact resistance is crucial and the components have complex geometries. It is used to manufacture composite parts such as tubes like a drive shaft, ducts and cones at a high rate, with quality, repeatability and high levels of material utilisation.
Pultrusion
This is where the fibres are pulled through a resin bath and subsequently through a heated die where they cure into a solid profile. The heat facilitates the curing process and the pressure ensures the even distribution of the resin and that the fibres are compressed into the desired shape. Pultrusion is limited to manufacturing parts with constant cross-sectional profiles such as beams and panels in the construction industry, masts in marine, railcar components and bus and truck frames.
Additive Manufacturing
Also known as 3D printing, this method involves building up the geometry of the part layer by layer. There are different methods within 3D printing – fused deposition modelling with chopped fibres, the continuous fibre reinforcement approach, powder bed fusion and resin-based printing that uses techniques such as digital light processing or stereolithography. With chopped fibres and continuous fibre reinforcement the filament gets extruded through a nozzle. The powder approach, you begin with a bed of powder and a printhead sprays a liquid binder to consolidate it together layer by layer. The resin-based method involves a vat of liquid resin mixed with tiny fibres which is then cured by lasers or light. 3D printing is used to manufacture drone frames, brackets and panels in automotive, as well as prosthetics and medical implants in the medical industry.
AFP and ATP
Automated Fibre Placement and Automated Tape placement uses robotic arms or gantries to place small strips of pre-preg tows or tapes onto a mould. The tows can be made of carbon or fibreglass, with the material pulled from spools and fed through the AFP/ATP head. The head heats the tows to activate the resin and it is placed onto the mould or the previous layers that have already been placed. After that, the part or component will often be put into an autoclave to cure the resin fully, before it is ejected. This method typically achieves a material deposition rate of around 20-50 kg per hour and is used in aerospace, automotive and renewable energy industries.
High Rate Large Scale Automation with FibreLINE
Loop Technology’s FibreLINE provides a revolutionary new method for the composite manufacturing industry, fundamentally different to all others and not available elsewhere. It is a fully automated end-to-end solution that leverages our suite of highly advanced end effectors integrated with robots or gantries to deliver cutting, sorting, picking and forming of much larger plies of composite material than any other method– up to 20 metres long. The plies are manipulated and placed onto the designated mould whilst managing shear forces to ensure no damage is done to the material, before they are then consolidated. Loop Technology also provide laser cleaning solutions for cleaning and decontaminating the mould. FibreLINE has a material deposition rate of up to 200-350 kg per hour depending on which configuration is chosen, meaning much faster rates of manufacture whilst using less factory space and with reduced energy consumption compared to other automated methods.