Plastics and Composites

8/11/2019 Plastics and Composites

1/23

Forming and Shaping Plastics and

Composite Materials

1


2/23

Characteristics of Forming and Shaping

Processes for Plastics and Com osite Materials

2


3/23

Extruder

Figure : Schematic illustration of a typical extruder.

3


4/23

Injection Molding

Figure: Injection molding with (a) plunger, (b)

4


5/23

Sequence of operation

5


6/23

Reaction-Injection Molding

Figure : Schematicillustration of the

reaction-injection

molding process.

6


7/23

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.

7


8/23

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

- - .

8


9/23

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 .

9


10/23

Thermoforming Processes

Figure :Various thermoforming processes for thermoplastic sheet.

10


11/23

Compression Molding

Figure : Types of compressionmolding, a process similar to

semipositive, and (c) flash.

11


12/23

Transfer Molding

Figure : Sequence of operations in transfer molding for

thermosetting plastics. This process is particularly suitable forintricate parts with varying wall thickness.

12


13/23

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.

13


14/23

Casting, Potting and Encapsulation

Figure : Schematicillustration of (a) casting, (b)

plastics.

14


15/23

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.

15


16/23

Prepegs

Figure : Manufacturing process for polymer-matrix composite.

16


17/23

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.

17

.


18/23

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.

18


19/23

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.

19


20/23


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

20


21/23


Figure: (a) Vacuum-bag forming. (b) Pressure-bag forming.

21


22/23

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

22


23/23

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

23

Plastics and Composites

Documents

Transcript of Plastics and Composites