1.4-Forming, redistibution and addition processes-polymers Flashcards
Vacuum forming- polymer stock form, products, key features
-thermoplastic sheet up to 6mm
-lightweight traysm box inserts, yoghurt pots
-moulds relatively easy but need a draft angle, air holes and rounded corners
-not cost effective for small scale production
-small scale batch and mass production
Vacuum forming process
-mould made in the shape the plastic will be formed and placed on the platen
-platen lowered to the bottom of the machine
-polymer sheet clamped over mould and heater is pulled over polymer sheet
-heat removed when polymer has softened and platen raised
-vacuum pump switched on which sucks polymer onto mould
-once cooled, platen lowered and vacuum switched off
-mould removed and excess polymer trimmed
Thermoforming- polymer stock form, products, key features
-thermoplastic sheet approx 6mm e.g. acrylic
-bath, food packaging
-good for fine detail e.g. moulding in logos
-slow process, used in industrial production
Thermoforming process
-process where plastic sheet is heated to a pliable forming temperature, formed to a specific shape in a mould, and trimmed to create a useable shape
-used to mould additional detail into the surface of polymer or mould thick polymer sheet
-similar to vacuum forming but additional mould pressed onto the surface of the polymer
Calendeing- polymer stock form, products, key features
-thermoplastic pellets
-thin polymer sheet and film
-heated rollers sqush and stretch polymer to make it thinner
-industrial production method, by specialist manufacturers
-continuous production
Calendering process
-smoorhing and rolling process
-can be used in making polymer sheet and film as well as paper making process
-hot thermoplastic extreuded between series of heated rollers to squash and stretch it. Then cooled abd cut
Line bending- polymer stock form, products, key features
-thermoplastic sheet
-acrylic boxes, shelves
-uses an electrically heated element that provides heat along a line
-slow and labour intensive, used in college
-suitable for one off or limited batch
Lamination (lay up)- polymer stock form, products, key features
-fibre composite sheets
-boat hulls, train carriages, theatre props, theme park rides
-requires a former to mould around
-polymer resin used as polymer
-a top gelcoat applied which may contain pigment
-CFRP requires an autoclave dor the product to ‘cure’
Lamination process
-mould coated with release agent e.g. wax
-gel coat is applied e.g. polyester resin
-matting is laid over formed and polymer resin brushed over
-roller used to push out air bubbles. More polyester resin applied until thick enough and then GRP is left to set
Injection moulding- polymer stock form, products, key features
-thermoplastic granules
-electrical product castings e.g. TVs
-complex 3D shapes easily made
-fast industrial production method
-high initial tooling cost
-used for large scale mass or continuous production
Injection moulding process
-polymer granules loaded into hoppper
-plastic pellets melted
-once malleable enough, they are injected with pressure into a mould cavity, which fills and solidifies to produce the final product
-shape of die determines shape of extrusion
Blow moulding- polymer stock form, products, key features
-thermoplastic tube ‘parison’
-drinks bottles, shampoo bottles, detergent bottles
-produces hollow thin walled components made of PET, LDPE, HDPE and PP
-high initial tooling cost
-used for continuous production
Blow moulding process
-polymer fed into hopper
-Archimedean screw pulls polymer through heated section melting it
-melted polymer is extruded as a tube
-mould slides close around parison and air injected into mould, forcing polymer to sides
-polymer allower to cool for few seconds, mould opens and finished bottle ejected
Rotational moulding- polymer stock form, products, key features
-thermoplastic powder of granules
-traffic cones, kayaks, water tanks
-seamless hollow components with a large wall thickness
-mould continuously rotated through heating and cooling
-large scale batch or mass
Rotational moulding process
-polymer powder or ganules are loaded into a mould, which is clamped and sealed
-transferred to an oven around 270-370 degrees celcius
-this is rotated, coating the inside of the mould with polymer
-then cooled and solidified, causing polymer to shrink slightly so it can be removed
