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Filament winding  simple machine: just two axes rotation of the mandrel translation of the feed eye on an axis parallel to the machine axis  complexity characterised by the number of degrees of freedom: up to six separately controlled axes usually three orthogonal and three rotational axes

Filament winding

Filament winding - tension  fibre tension is critical to the operation of a filament winding machine  normal to have fibre tensioners (closed-loop controlled servo-driven "dancers")  tension required depends on type of fibre part diameter winding pattern

Filament winding - tension  fibre tension directly affects fibre volume fraction void content and, in turn, influences the strength and stiffness of the composite part.  difficult to maintain tension on flat surfaces axial winding not a preferred orientation on cylinders.

Filament winding - impregnation  resin impregnation

Filament winding - winding patterns  hoop (90º) a.k.a girth or circumferential winding angle is normally just below 90° degrees each complete rotation of the mandrel shifts the fibre band to lie alongside the previous band.  helical complete fibre coverage without the band having to lie adjacent to that previously laid.  polar domed ends or spherical components fibres constrained by bosses on each pole of the component.  axial (0º) beware: difficult to maintain fibre tension

Filament winding - winding patterns hoop:helical: polar:

Filament winding - winding pattern  Kevlar component image from

Filament winding - geodesic path  simplest fibre orientation is the geodesic path assumes non-slip winding  once winding has commenced, fixed fibre path at any point dictated by the Clairaut angle ( r.sin a = constant) where r is local radius, a is local angle  at bosses, a = arcsin (r b /r) where r b = angle at the boss (polar opening)  exploiting friction, it is possible to achieve non- geodesic winding within limits.

Lattice structures (anisogrid)  can be produced by partial coverage and careful choice of relative band positions

Filament winding - applications  pressure vessels, storage tanks and pipes  rocket motors, launch tubes Light Anti-armour Weapon (LAW) ○ Hunting Engineering made a nesting pair in 4 minutes with ~20 mandrels circulated through the machine and a continuous curing oven.  drive shafts  Entec “the world’s largest five-axis filament winding machine” for wind turbine blades length 45.7 m, diameter 8.2 m, weight > 36 tonnes.

Fibre placement  multi-axis robot wet-winds fibre around a series of pins (or similar restraints within a mould) in a predetermined pattern.  not limited by geodesic paths  used to produce Geoform (lattice-work with coverage in specific bands)  better for thermoplastic matrix composites on-line consolidation and cooling permit use without the requirement for the fibre restraints.

Tape laying  computer-numerically controlled (CNC) technique laying prepreg reinforcement tape Cartesian framework for gross positioning (rather than a primarily rotational axis robot) rotational freedoms close to the work-piece.  used for thermoset or thermoplastic matrix  limited to flat or low curvature surfaces  high quality aerospace composites e.g. flight control surfaces and wing skins.

Pultrusion  continuous constant cross-section profile  normally thermoset (thermoplastic possible) impregnate with resin pull through a heated die ○ resin shrinkage reduces friction in the die ○ polyester easier to process than epoxy  tension control as in filament winding  post-die, profile air-cooled before gripped hand-over-hand hydraulic clamps conveyor belt/caterpillar track systems.  moving cut-off machine ("flying cutter")

Pultrusion - design  manuals by Quinn and Hartley  seek uniform thickness in order to achieve uniform cooling and hence minimise residual stress.  hollow profiles require a cantilevered mandrel to enter the die from the fibre-feed end.

Pultrusion -applications  panels – beams – gratings – ladders  tool handles - ski poles – kites  electrical insulators and enclosures  light poles - hand rails – roll-up doors  450 km of cable trays in the Channel Tunnel  plus...

Pultrusion - variations of process  pulwinding/pulbraiding: fibres are wound onto the core of the pultrusion before it enters the heated die.  pulforming: the profile is subjected to post-die shaping.

Tube rolling  a technique where pre-preg is formed onto a tapered mandrel and consolidated using shrink-wrap.  most often used to make fishing rod blanks  illustrated at

VACUUM FORMING Vacuum Forming is a technique that is used to shape a variety of plastics. In school it is used to form/shape thin plastic, usually plastics such as; polythene and perspex. Vacuum forming is used when an unusual shape like a ‘dish’ or a box-like shape is needed. To the right you can see the stages involved in vacuum forming. STEP 1 STEP 2 STEP 3 STEP 4 STEP 5 STEP 6 STEP 7 First, a former is made from a material such as a soft wood. The former is placed in the oven and a sheet of plastic (for example, compressed polystyrene) is clamped in position above the mould. The heater is then turned on and the plastic slowly becomes soft and pliable as it heats up. The plastic can be seen to 'warp' and 'distort' as the surface expands. After a few minutes the plastic is ready for ‘forming’ as it becomes very flexible. The heater is turned off and the mould is moved upwards by lifting the lever until it locks in position. The 'vacuum' is turned on. This pumps out all the air beneath the plastic sheet. Atmospheric pressure above the plastic sheet pushes it down on the mould. When the plastic has cooled sufficiently the vacuum pump is switched off. The plastic sheet is removed from the vacuum former. The sheet has the shape of the former pressed into its surface. A flat plastic sheet goes through the vacuum forming process from start to finish. for main menu