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8/11/2019 Plastics and Composites
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Forming and Shaping Plastics and
Composite Materials
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Characteristics of Forming and Shaping
Processes for Plastics and Com osite Materials
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Extruder
Figure : Schematic illustration of a typical extruder.
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Injection Molding
Figure: Injection molding with (a) plunger, (b)
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Sequence of operation
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Reaction-Injection Molding
Figure : Schematicillustration of the
reaction-injection
molding process.
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Thermoforming
Thermoforming is a manufacturing process where a plastic sheet is heated to a
pliable forming temperature, formed to a specific shape in a mold, and trimmed to
create a usable product.
The sheet or "film" is heated in an oven to a high-enough temperature that it can
be stretched into or onto a mold and cooled to a finished sha e.
Thin-gauge thermoforming is primarily the manufacture of disposable cups,containers, lids, tra s and other roducts for the food, medical, and eneral retail
industries.
-panels, refrigerator liners, utility vehicle beds etc.
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Thermoforming
Types of Thermoforming
Vacuum Forming
Vacuum forming is a plastic thermoforming process that involves forming
thermoplastic sheets into three-dimensional shapes through the application ofheat and pressure.
than injection molding, and therefore is more cost-effective.
Pressure Forming
and compressed air to force the plastic sheet against the mold.
The vacuum pulls on one side of the sheet and compressed air pushes on the
other.
Compressed air pressure reduces the cycle time and makes it possible to run atlower temperatures.
Improves the distribution of the material creating a more even wall thickness
- - .
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Thermoforming
Drape Forming
Drape forming is similar to straight vacuum forming except that after the sheet is
framed and heated it is mechanicall stretched and a ressure differential is then
applied to form the sheet over a male mould.
Faster cycle times.
Disadvantage is more scrap due to larger clamps and trim area
Plug assist forming
of a female (cavity) mold.
The limited depth of draw of female molds is improved by the use of plug
assist.
With plug assist the plastic sheet is mechanically stretched by a plug that ispushed into the hot plastic .
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Thermoforming Processes
Figure :Various thermoforming processes for thermoplastic sheet.
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Compression Molding
Figure : Types of compressionmolding, a process similar to
semipositive, and (c) flash.
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Transfer Molding
Figure : Sequence of operations in transfer molding for
thermosetting plastics. This process is particularly suitable forintricate parts with varying wall thickness.
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Sheet and Film Extrusion
Figure : Die geometry (coat-hanger die) for
extruding sheet.
Figure: Schematic illustration of the production of thin
film and plastic bags from tube first produced by an
ex ru er an en own y a r.
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Casting, Potting and Encapsulation
Figure : Schematicillustration of (a) casting, (b)
plastics.
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Calendering and Examples of Reinforced
Figure: Schematic illustration
of calendering. Sheets produced bythis process are subsequently used
.
Figure : Reinforced- plastic
components for a Honda
.
front and rear forks, a rear
swingarm, a wheel, and brake
disks.
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Prepegs
Figure : Manufacturing process for polymer-matrix composite.
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Sheet Moulding Compound
Sheet moulding compound (SMC) orsheet moulding composite is a ready to
mould fibre-reinforced polyester material primarily used in compression moulding.
SMC is made of 3 basic components: the
, ,
epoxy, phenolic or polyimide), the
reinforcements (fiberglass, graphite,
aramide), and additives which include inertfillers, pigments, UV stabilizers, catalysts,
inhibitors, and thickeners.
Figure :The manufacturing
process for producing reinforced
Often used for larger parts wherehigher mechanical strength is needed.
Is a continuous in-line process.
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Bulk moulding compound
Bulk Molding Compound (BMC) is highly filled and reinforced with short
fibers.
Glass reinforcement represents between 10% and 30%, with glass length
typically between 1/32-inch and 1/2-inch.
Generally extruded into shapes for compression, transfer, or shot molding.
The compound is delivered to
the press in the form of a ball,
slab or an extruded log and
dropped into the bottom of a
mould.
Material is flowed outward until
it assumes the shape of themould.
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Examples of Molding Processes
HandLayUp:The oldest and simplest molding technique in which reinforcing
materials and catalyzed resin are laid into or over a mould by hand.
Mainadvantages
Low Investment, any types of large
and small parts can be made, short
tooling lead time & higher glass.
Maindisadvantages
Totally labour intensive, operator
,
material waste.
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Examples of Molding Processes
Spray up: spray gun is used to simultaneously deposit fiberglass and catalyzedresin on a mould.
Advantages
Hi her out ut than hand
lay-up
Disadvantages g er nves men an
hand lay-up
Emissions
Material waste
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Examples of Molding Processes
Figure: (a) Vacuum-bag forming. (b) Pressure-bag forming.
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Filament Winding: The process of helically (spring like) wrapping reinforcements
and resin around a polar mandrel.
Main advantages
Low laborHigh strength orientation
Reproducibility
Maindisadvantage
Unsuitable for complex shapes
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Pultrusion:The process of continuously pulling a resin-impregnated reinforcement
through a die in to its final shape.
Mainadvantages
ow a or
Low waste
Disadvantages
High
investment
Long
tooling
time
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