MANUFACTURING WITH COMPOSITES 2 WCC WEBINAR 10 th June 2011 1
AIMS OF WEBINAR To give an overview of the most important manufacturing methods for composite materials Covering suitable materials, typical products produced Overview of main advantages and drawbacks of each method 2
Last Week s Webinar Lower cost and more mass-produced methods Hand lay-up, Vacuum bagging, Spray-up, Resin Transfer Moulding Resin Infusion Moulding Compounds 3
This Week Higher cost and more quality-critical methods Pre-pregs and autoclave, Quickstep process, Pultrusion, Filament Winding, Automatic Tape Laying Processing of Thermoplastic Composites 4
Problems with hand lay-up Poor consolidation leading to lower volume fraction of fibres Higher void content Incomplete wetting of fibres Highly dependent on operator skill Resin open to air leads to VOC emissions 5
Improvements to hand lay-up Vacuum bagging helps to reduce voids and increase fibre volume fraction Resin infusion methods help to reduce VOC emissions Both are quite slow Use of moulding compounds and sprayup methods are faster but have low fibre volume fraction and short fibres. 6
Pre-pregs and autoclave moulding 7
PRE-PREG Definition: Reinforcement fibres in a variety of forms, pre-impregnated with partially cured resin system (epoxy) or a thermoplastic. 8
Pre-Preg (usually epoxy matrix) Reinforcement is pre-impregnated with B-stage resin A-stage: soluble and fusible B-stage: swollen but not dissolved by a variety of solvents C-stage: rigid, hard, insoluble, infusible safer than liquid resins mixing done by suppliers > better quality expensive relative to dry reinforcements. 9
Pre-Preg Finite shelf life: note use-by date if out-of-date, should not be used for applications which may result in injury, loss or damage. time the roll of the material is out of cold storage will reduce its useful life (out-life) 10 normal to allow the material to warm to ambient temperature before use as condensation may form on cold material
Pre-Preg Systems Low temperature systems: cure at ~60ºC, out-life typically 3 months Medium temperature systems: cure at ~120ºC, out life typically 6 months, High temperature systems: cure at ~180ºC, out-life typically one year. Thermoplastic systems (Twintex: http://www.twintex.com) Flow at ~ 200ºC, out-life almost indefinite. 11
Pre-Preg Key considerations include: Drape formability to complex curvatures Tack stickiness De-bulk every few layers, subject the stack to vacuum in temporary bag or a vacuum table. 12
Hand lay-up of tailored prepreg Prepreg lay up prior to vacuum bagging
Pre-Preg 360 g/m 2 non crimp ±45 carbon & epoxy 1.5mm 14 PREPREG 60% fibre by volume
Autoclave only possible to apply ~1000 mbar pressure with a vacuum bag to achieve greater levels of consolidation, use an autoclave: advanced pressure cooker autoclave is a pressure vessel with pipework to allow a vacuum to be maintained in the bagged work-piece. temperature control is normally by gas- or electric-heating proportional-integral-derivative (PID) controller 15
Autoclave temp / pressure cycle
Autoclave dwell to get correct resin viscosity cure to achieve optimum properties high capital cost equipment long cycle times economics demands high autoclave loading mould tools designed to permit circulation of heated air 17 VB consumables may be a thermal barrier
Autoclave (providing heat and pressure) for maximum consolidation, low void content and high fibre fraction. Aeroform Ltd
Quick-Step Process Newer method, developed in Australia Uses a 1-sided mould, with a flexible membrane Uses heated ethylene glycol to apply pressure and heat on outside of membrane 19 Vibrations can be used to assist air removal
Quick-Step Process Much faster heat transfer from liquid to component than with gases. Can use separate tanks of ethylene glycol at different temperatures (dwell, cure and cool), to get faster temperature changes Smaller and cheaper equipment than using autoclaves 20 Faster production times
Quickstep Method 21 http://www.quickstep.com.au
Pultrusion 22
PULTRUSION Fibres are pulled from a creel through a resin bath and then on through a heated die. The die completes the impregnation of the fibre, controls the resin content and cures the material into its final shape. This cured profile is then automatically cut to length. 23
PULTRUSION 24
Materials Options Resins: Generally epoxy, polyester, vinylester and phenolic. Fibres: Any. Cores: Not generally used. 25
Advantages 26 Can be a very fast, and economic manufacturing method. Resin content can be accurately controlled. Fibre cost is minimised since the majority is taken from a creel. Structural properties of laminates can be very good since the profiles have very straight fibres and high fibre volume fractions can be obtained. Resin impregnation area can be enclosed thus limiting volatile emissions.
Disadvantages Limited to constant or near constant cross-section components Heated die costs can be high 27
Main Applications Beams and girders used in roof structures, bridges, ladders, frameworks. 28
Pultrusion (ACCS) Advanced Composite Construction System components: plank... and connectors used in Aberfeldy and Bonds Mill Lock bridges
Pulwinding 30
Pulwinding Combination of pultrusion and filament winding Gives some fibres along tube axis And some in hoop direction Can give optimum set of properties Added expense 31
Pulwinding 32
Filament Winding 33
FILAMENT WINDING This process is primarily used for hollow, generally circular or oval sectioned components, such as pipes and tanks. Fibre tows are passed through a resin bath Then wound onto a mandrel in a variety of orientations. Orientation controlled by the fibre feeding mechanism, and rate of rotation of the mandrel. 34
Filament Winding
Materials Resins: Any, e.g. epoxy, polyester, vinylester, phenolic, can also be used with thermoplastic tapes such as Twintex. Fibres: Any. The fibres are used straight from a creel and not woven or stitched into a fabric form. Cores: Any, although components are usually single skin. 36
Main Advantages Can be a very fast and therefore economic method of laying material down. Resin content can be controlled by metering the resin onto each fibre tow through nips or dies. Fibre cost is minimised since there is no secondary process to convert fibre into fabric prior to use. 37 Structural properties of laminates can be very good since straight fibres can be laid in a complex pattern to match the applied loads.
Main Disadvantages The process is limited to convex shaped components. Fibres cannot easily be laid exactly along the length of a component. Mandrel costs for large components can be high. The external surface of the component is unmoulded, and therefore cosmetically unattractive. 38 Low viscosity resins usually need to be used with their attendant lower mechanical and health and safety properties.
Typical Applications Chemical Pipelines (high pressure capability and resistance to corrosion) Chemical Storage Tanks Pressurised gas cylinders Firefighters air tanks (low weight) Marine spars and masts 39
Automatic Tape Laying 40
Tape Placement Modification to filament winding Used mainly with prepregs Robotic control Accurate placement of tape sections prior to curing 41
Thermoplastic matrix composites 42
Thermoplastics Need to be melt processed High viscosity of molten thermoplastics limits fibre incorporation Higher process temperatures can limit fibre incorporation Fibre matrix bond can be less reliable Higher toughness than thermosets Recyclable 43
Conventional Processing Of Reinforced Thermoplastics When thermoplastics are reinforced with particles or short fibres, they can be processed like unfilled thermoplastics 44 Good summary of methods on British Plastics Federation Website: www.bpf.co.uk Injection moulding Extrusion Thermoforming
Glass Mat Thermoplastics (GMT) Similar to sheet moulding compound Short glass fibres or woven rovings added to thermoplastics Either of these: At the end of an extruder as a laminating process Into a thermoplastic slurry 45 Sheets of reinforced thermoplastics produced
Glass Mat Thermoplastics (GMT)
Glass Mat Thermoplastics (GMT)
Glass Mat Thermoplastics (GMT) Longer fibres / higher volume fraction than with extrusion or injection moulding Sheets can then be thermoformed Quite widely used in automotive sector More recyclable than SMC / BMC 48
Thermoforming Sheet material with reinforcement already incorporated. Co-mingled. Heated to soften. Pressed between matched moulds. Vacuum formed. Cooled. 49
Pultrusion With Thermoplastics It is possible to modify the pultrusion process to work with thermoplastics Instead of passing fibres through a resin bath, they are drawn through molten thermoplastic Thermoplastic normally fed by an extruder 50 Coating and shaping done together
Pultrusion With Thermoplastics One good example of this is sheets of carbon-fibre reinforced PEEK produced by pultrusion Sheets can then be laid up to form laminate Laminate can then be thermoformed / press-formed into contoured shapes 51
Twintex Produces co-mingled glass / thermoplastic filaments Most common with PP, though PET also available Continuous glass fibres combined with thermoplastic fibres 52
Twintex Glass content 60% or 75% by weight Supplied as: Rovings Woven fabrics Pellets Consolidated plates Can then be: Compression moulded Filament wound Pultruded Vacuum formed 53 http://www.twintex.com
All-Polymer Composites A method of using highly oriented thermoplastic tapes or fibres Woven fabrics laid up (with no separate matrix) Heated to melt outer surface of fibres Layers bonded together Orientation of fibres retained Can then be thermoformed Eg CURV - Polypropylene Gives enhanced stiffness and strength over conventional thermoplastics 54 (http://www.curvonline.com)
CURV
CURV Applications 56
SUMMARY A wide range of process methods. Considerable scope for combining elements of different methods. Always a balance between speed and cost of production, quality of part, capital equipment requirements. In all cases, considerable control required. 57
Thank you for your attention Any questions???