Plastic processing

Unit-5
Plastic processing
Dr. L.K. Bhagi
Associate Professor
School of Mechanical Engineering
Lovely Professional University
“Polymer Processing” may be defined as the
manufacturing activity of converting raw
polymeric materials into finished products of
desirable shape, microstructure and
properties.

Unit-5
Plastic processing
Dr. L.K. Bhagi
Associate Professor

This material is man made and is a by product of the oil industry.
PLASTICS

Plastic» Difference between Polymer and
Plastic
Polymer
The word POLYMER means ‘many’ ‘mers’
✓ A ‘mer’ is a unit
✓ Polyethylene means many ‘ethylenes’
✓ The molecular weight of a polymer (length of the chain
– number of ‘mers’) will effect the properties.
• 10-20 ethylenes – greases or oils
• 200-300 waxes
• 20,000 + polyethylene
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adhesives, lubricants, paints, films, fibers,
plastic goods, etc.

Plastic» Difference between Polymer and
Plastic
Plastic
The word plastic derives from the Greek plastikos meaning
"capable of being shaped or molded”.
Plastics are polymers, but all polymers are not plastics.
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Plastic» Applications
Construction
The Construction sector is the second highest user of plastics
after packaging.
They have great versatility and combine excellent strength
to weight ratio, durability, cost effectiveness, low maintenance
and corrosion resistance which make plastics an
economically attractive choice throughout the construction
sector.
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Electrical and Electronic
Wherever we find electricity, we also find plastics. In the
kitchen, there are the labour-saving devices that we
wouldn’t be without; Refrigerator, washing machines,
microwave ovens, kettles.
In the living room is the television, or the music system,
while at work, we may use a computer, telephone. Plastics
make progress possible, making electrical goods safer,
lighter, more attractive, and more durable.05-11-2019
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Packaging
Plastic packaging allows us to protect, preserve, store and
transport products in a variety of ways.
Without plastic packaging, a great deal of products that
consumers purchase would not make the journey to
the home or store, or survive in good condition long
enough to be consumed or used.
Durability, Safety, Hygiene, Light Weight and Design Freedom
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Transport
All forms of transport require energy to run and fuel
represents a substantial part of running costs. Cutting the
weight of cars, aeroplanes, boats and trains can cut fuel
consumption dramatically. The lightness of plastics
therefore makes them invaluable to the transport industry.
105kg of plastics, rather than metals, in a car weighing
1,000kg makes possible a fuel saving of up to 7.5%.
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Plastic» Advantages
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Advantages of plastics include:
1. Corrosion resistance and resistivity to chemicals,
2. Low electrical & Thermal conductivity,
3. Low density,
4. High strength to weight ratio, particularly when reinforced,
5. Noise reduction,
6. Wide choices of colors and transparencies,
7. Ease of manufacturing and complexity of design possibilities,
8. Relatively low cost.

Dr. L.K. Bhagi
Associate Professor

Plastic» Plastic Processing
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There are many processes for plastics. Selection of a process
depends on many factors including:
- Quantity and production rate
- Dimensional accuracy and surface finish
- Form and detail of the product
- Nature of material
- Size of final product
In general, plastics processes have three phases:
1. Heating - To soften or melt the plastic
2. Shaping / Forming - Under constraint of some kind
3. Cooling - So that it retains its shape

Plastic»
Plastic Processing Technologies
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1. Blow molding
2. Thermoforming
3. Compression molding
4. Transfer molding
5. Extrusion
6. Injection molding

Plastic»
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1. Blow molding
2. Thermoforming
4. Transfer molding
5. Extrusion

Plastic»
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1. Blow molding
2. Thermoforming
4. Transfer molding
5. Extrusion

Plastic»
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1. Blow molding
2. Thermoforming
4. Transfer molding
5. Extrusion

Plastic»
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1. Blow molding
2. Thermoforming
4. Transfer molding
5. Extrusion

Plastic»
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1. Blow molding
2. Thermoforming
4. Transfer molding
5. Extrusion

Plastic»
Vulcanized Rubber
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1839
Independent polymer chains to highly cross-linked polymer chains

Plastic»
Resins
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Plastic»
Resins
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Natural resins: Natural resins are
obtained from the viscous substances
secreted from the bark of trees and the
stems of other plants.
it is soluble in alcohol and related
compounds, but not in water. Once
dry, the resin will not admit water
intrusion.
Collecting
Resin from
pine trees
into a bag

Plastic»
Resins
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Synthetic resins:
is artificial synthesized high molecular polymer. Therefore,
different types of plastic can be called after the name of the
synthetic resin it is made from.
Synthetic resin is organic
compound made by combining
carbon atom, hydrogen atom, and
a small quantity of oxygen atom,
sulphur atom through certain
chemical bond.

Plastic»
Resins
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Synthetic resins:
Synthetic resin, the basic raw material of plastic, takes up
30%~60% or more of its composition. It has the function of not
only binding itself together, but also the other materials firmly
together.
As the type, property, and amount of synthetic resin change,
the physical and mechanical properties of plastic also
change. Therefore, the main properties of plastic depend on
the synthetic resin it is made from.

Plastic»
Polymerization
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The Chemical process by which monomers are combined to
form polymers is known as polymerization.
The following two methods are used to achieve polymerization
1. Addition polymerization
2. Condensation polymerization

Plastic»
Polymerization
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Plastic»
Polymerization
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In addition polymerization, two or more similar
monomers directly react to form polymers.
Addition polymerization involves the linking of
monomers with double bonds. The double bond
of one monomer breaks and links onto the
neighboring monomer. This process continues to
form polymers, some of which can be many
thousands of monomers long.

Plastic»
Polymerization
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Condensation polymerization (that yield the
condensate) takes two or more dissimilar monomers
both have hydrogen (H) and hydroxyl groups (OH)
attached to them. When they come together with an
appropriate catalyst one monomer loses H while the
other loses OH group and combine to form water (H2O),
and the remaining electrons form a covalent chemical
bond between the monomers. This reaction occurs over
and over again until you get a long chain of copolymers

Plastic»
Polymerization
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Plastic»
Additives in plastics
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Additives use:
– To improved or modify the mechanical, chemical, and
physical properties
– To prevent degradation (both during fabrication and in
service)
– To reduce materials costs
– To improve the process-ability
Typical additives include
• Filler materials,
• Plasticizer
• Stabilizers,
• Colorants,
• Flame retardants

Plastic»
Additives in plastics »Filler Material
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➢ Filler materials are most often added to polymers to improve
tensile and compression strengths, Hardness, toughness,
dimensional and thermal stability and other properties.
➢ Materials used as particulate fillers include wood flour, silica
flour, glass, clay, talc, limestone (CaCO3), and even some
synthetic polymers.
➢ Because these inexpensive materials replace some volume of
the more expensive polymer, the cost of the final product is
reduced.

Plastic»
Additives in plastics »Plasticizers
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Plasticizers are chemicals added to a polymer to make it
softer and more flexible, and to improve its flow
characteristics during forming.
The commonly used plasticizers are Phthalates (Most widely
use as plasticizer) camphore, paraffins, napathalanes,
phosphates etc.
Example depending on the proportion of plasticizer in the
mix, PVC can be obtained in a range of properties, from rigid
and brittle to flexible and rubbery.

Plastic»
Additives in plastics »Stabilizers
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➢ Polymer absorbs heat, light energy and causes crazing,
cracking, color changes, or loss of mechanical properties
➢ PVC has poor thermal properties and has used a large amount
of stabilizers, mostly cadmium based.
➢ Lead and cadmium stabilizers have been replaced with barium-
zinc, calcium-zinc, magnesium-zinc formulations.

Plastic»
Additives in plastics »Flame Retardants
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Nearly all polymers burn if the required heat and oxygen are
supplied. Some polymers are more combustible than others.
Flame retardants are chemicals added to polymers to reduce
flammability by following mechanisms:
(1) Interfering with flame propagation, (2) Producing large
amounts of incombustible gases, and/or (3) Increasing the
combustion temperature of the material. The chemicals may also
function to (4) Reduce the emission of toxic gases generated
during combustion.

Plastic»
Additives in plastics »Colorants
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An advantage of many polymers over metals or ceramics is that
the material itself can be obtained in most any color. This
eliminates the need for secondary coating operations.
Colorants for polymers are of two types:
pigments and dies
Pigments are finely powdered materials that are insoluble in and
must be uniformly distributed throughout the polymer in very low
concentrations, usually less than1%. They often add opacity as
well as color to the plastic. Dies are chemicals, usually supplied
in liquid form, that are generally soluble in the polymer.

Plastic»
Classification of Polymers
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Classification of Polymers
Based on Source
Natural polymers
(Proteins, cellulose, starch,
some resins and rubber)
Semi-synthetic
polymers
Synthetic polymers
plastic (polythene), synthetic
Fibers (nylon 6,6) and synthetic
rubbers
Based on Structure
Linear polymers
High density polythene, PVC etc.
Branched chain
Polymers
Low density polythene
Cross linked
Bakelite,
melamine etc.
Mode of
polymerisation
Molecular
Forces
Addition
polymers
Condensation
Polymers
Elastomers
Fibers
Thermo
plastic
retract to its
original
position after being
stretched
high tensile
strength and high
modulus.
Thermo
setting

Plastic»
Types of Plastics
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• Plastics are mainly classifieds into two types:
depending on how they are structurally and chemically
bonded
1. Thermoplastic Plastics:
2. Thermosetting Plastics

Plastic»
Types of Plastics » Thermo plastics
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• These plastics can be softened by heating and hardened
by cooling any number of times without changing the
properties of the material.
• It is thus possible to shape and reshape these plastics by
means of heat and pressure.
• One important advantage of this variety of plastics is that
scrap obtained from old and wornout articles can be
effectively used again.

Plastic»
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The notable Properties of thermoplastic materials are:
1. They are light in weight.
2. High Strength and toughness
3. Better hardness
4. Good resistance to most of the chemical
5. They have good corrosive resistance.
6. Durability
7. They are cheap compared to metals.
8. Painting and polishing is not necessary.

Plastic»
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1. Polyvinyl chloride ( P V C )
Properties : Rigid , tough , elastic to feel.
Uses : Plumbing pipes and sanitary fittings are manufactured out
of this material. Shower curtains , window frames, flooring ,
corrugated roofing sheets , plastic coating to steel sheets tanks,
water cisterns, etc.
2. Acrylic:
Properties: Glass clear , some what brittle sound
when tapped.
Uses : Glazing , bath rooms and sinks.
THERMO PLASTIC MATERIALS

Plastic»
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3. Polyethylene ( or polythene ) – low density:
Properties: Flexible, feels like paraffin wax.
Uses ; bottles, buckets, packaging rolls.
4. Polyethylene ( or polythene )- high density:
Properties: stiff and hard, coarser than the
polythylene of low density
used as large storage bottles, water tank.
5. Polypropylene:
Properties : smooth, rigid, lightest of all
plastics – it floats in water.
Uses : cisterns, sink traps, washing machine,
food containers, appliances , car fender.

Plastic»
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6. Polystyrene: Solid state at room temperature, but flows if
heated above its glass transition temperature and becoming
solid again when cooling off.
Pure solid polystryrene is a colourless, hard plastic with
limited flexibility. Polysterene can be transparent
or can be made to take on various colours.
Uses : Refrigerator containers, food trays,
packaging, food containers, disposable cups,
plates, cutlery, CD boxes.

Plastic»
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7. Nylon:
Properties : High density polythene but smoother to feel.
Uses: Textiles, brush bristles, carpeting, surgical trays,
bearings, pressure tubing.

Plastic»
Types of Plastics » Thermosetting plastics
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These plastics are either originally soft or liquid or they soften
once upon heating, they harden permanently.
When they are heated in the temperature of 127-177°C, they set
permanently and further application of heat does not alter their
form or soften them.
But at temperature of about 343°C, the charring (become blackened
as a result of partial burning) occurs. The thermosetting plastics are
durable, strong and hard.
They are available in a variety of colours. They are mainly used in
engineering applications of plastics.

Plastic»
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Properties :
1. Permanently hard on heating above a certain temperature.
2. Undergoes chemical changes during manufacture.
3. Cannot be melted and reshaped.
4. Little potential for recycling.

Plastic»
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Examples and uses:
1. Polyurethanes: insulating foams, mattresses, coatings,
adhesives, car parts, print rollers, shoe soles, flooring,
synthetic fibers, etc. Polyurethane polymers are formed
by combining two bi- or higher functional monomers.
2. Bakelite, a phenol-formaldehyde resin used in electrical
insulators and plastic ware
3. Urea-formaldehyde foam used in plywood, particleboard
and medium-density fiberboard
4. Melamine resin used on worktop surfaces.
5. Epoxy resin used as the matrix component in many fiber
reinforced plastics such as glass-reinforced plastic and
graphite-reinforced plastic)

Plastic»
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1. Melamine formaldehyde:
Properties : Hardest of common plastics , heat resistant.
2. Phenolics ( Bakelite ) :
Properties : The cheapest. heavy solid plastic material, fishy smell
when burnt dark in color, heat resistant.
Uses : Bottle caps, plastic automobile parts,
bonding plywood and chip board, glues,
laminates with other materials.

Plastic»
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3. Urea formaldehyde :
PROPERTIES : Similar to phenolic but can be produced in lighter
colours.
Uses : Door furniture, light switches, and electrical fittings, glues,
bottoms, radio cabinets, etc.
4. Epoxies:
Properties: Resin and hardener.
Uses: Used as adhesives.
5. Polyesters :
Properties: produced as fibres and films.
Uses : Used for reinforced plastics.

Plastic» Difference Between Thermoplastic
and Thermosetting plastic
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Plastic» Difference Between Thermoplastic
and Thermosetting plastic
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Thermoplastic
Thermosetting

Plastic Processing
Technologies

Plastic»
Plastic Processing Technologies»
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1. Extrusion
4. Transfer molding
5. Blow molding
6. Thermoforming

Plastic» Plastic Processing Technologies»
Extrusion of Plastics
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A process in which material is forced to flow through a die
orifice to provide long continuous product whose
cross - sectional shape is determined by the shape of the
orifice/die
• Widely used for thermoplastics and elastomers to mass
produce items such as tubing, pipes, hose, structural
shapes, sheet and film, continuous filaments, and coated
electrical wire
• Carried out as a continuous process; extrudate is then cut
into desired lengths

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Components and features of a (single screw) plastic extruder

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Extruder Barrel
• Internal diameter typically ranges from 25 to 150 mm
• L/D ratios usually between 10 and 30
• Feedstock fed by gravity onto screw whose rotation moves
material through barrel
• Electric heaters melt feedstock; subsequent mixing and
mechanical working adds heat which maintains the melt

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Two Main Components of an Extruder
1. Barrel
2. Screw
• Die - not an extruder component
– Special tool that must be fabricated for particular profile to
be produced

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Extruder Screw
Feed section: feedstock is
moved from hopper and
preheated
Compression section: polymer
is transformed into fluid, air
mixed with pellets is extracted
from melt, and material is
compressed
Metering section: sufficient
pressure developed to pump it
through die opening.
Divided into sections to serve several functions:
The feeding capacity of the
screw is determined by its
geometry and speed of rotation.

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Breaker Plate
• Progress of polymer melt through barrel leads ultimately to the die
zone
• Before reaching die, the melt passes through a screen pack - series
of wire meshes supported by a breaker plate containing small
holes

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Breaker Plate
Functions of screen pack and breaker plate:
– Filter out contaminants and hard lumps
– Build pressure in metering section
– Improves the mixing of the plastic before entering the die

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Die Configurations and Extruded Products
• The shape of the die orifice determines the cross-sectional
shape of the extrudate.
• Common die profiles and corresponding extruded shapes:
– Solid profiles
– Hollow profiles, such as tubes
– Wire and cable coating
– Sheet and film
– Filaments

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Extrusion Advantages
• Equipment is simple and relatively inexpensive.
• Short lead time Since it uses simple dies which can be very
quickly produced.
• Relatively low tooling costs
• Overall cost of the parts produced by extrusion is low
• Practically any cross-section can be easily produced

Plastic»
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1. Extrusion
4. Transfer molding
5. Blow molding
6. Thermoforming

INJECTION MOLDING
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production of color master for
plastic injection molding parts
Extruder Operation and Control

INJECTION MOLDING
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• Injection molding is the most widely used molding process for
thermoplastics.

INJECTION MOLDING
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Injection molding is a process in which a polymer is heated to a
highly plastic state and forced to flow under high pressure into a
mold cavity, where it solidifies.
The molded part, called a
molding, is then removed from the
cavity. The process produces
discrete components that are
almost always net shape.

INJECTION MOLDING
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The mold determines the part shape
and size and is the special tooling in
injection molding.
For large, complex parts, the mold can
cost hundreds of thousands of dollars.
For small parts, the mold can be built to
contain multiple cavities, also making
the mold expensive.
Thus, injection molding is economical
only for large production quantities.

INJECTION MOLDING
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An injection molding machine consists of two principal
components: (1) the plastic injection unit and (2) the mold
clamping unit.

INJECTION MOLDING
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The injection unit is much like an extruder.

INJECTION MOLDING
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The injection unit is much like
an extruder.
It consists of a barrel that is fed from
one end by a hopper containing a
supply of plastic pellets.
Inside the barrel is a screw, in addition to turning for mixing and heating the
polymer, it also acts as a ram that rapidly moves forward to inject molten plastic
into the mold.

INJECTION MOLDING
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A non-return valve mounted near
the tip of the screw prevents the
melt from flowing backward along
the screw threads.
Later in the molding cycle the ram
retracts to its former position.
Because of its dual action, it is
called reciprocating screw, a
name that also identifies the
machine type.

INJECTION MOLDING
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The clamping unit is concerned with the operation of the mold.

INJECTION MOLDING
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The clamping unit is concerned with the operation of the mold. Its
functions are to
(1) Hold the two halves of the mold in proper alignment with each
other;
(2) Keep the mold closed during injection by applying a clamping
force sufficient to resist the injection force; and
(3) Open and close the mold at the appropriate times in the molding
cycle. The clamping unit consists of two platens, a fixed platen and
a moveable platen, and a mechanism for translating the latter.

INJECTION MOLDING
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Step1- The uncured rubber or plastic is fed into the machine in the form
of a continuous strip, powder or granules.
Step 2 - The uncured rubber is worked and warmed by an auger screw in
a temperature controlled barrel.
Step 3 - As the rubber stock accumulates in the front of the screw, the
machine is ready to make a shot.
Step 4 - With the mold held closed under hydraulic pressure, the screw is
pushed forward. This forces the rubber into the mold, similar to
the action of a syringe.
Step 5 - While the rubber cures in the heated mold, the screw turns again
to refill.
Step 6 - The mold opens and the part can be removed. The machine is
ready to make the next shot, as soon as the mold closes.

INJECTION MOLDING
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Common defects in injection molded:
Short shots. As in casting, a short shot is a molding that has
solidified before completely filling the cavity. The defect can
be corrected by increasing temperature and/or pressure. The
defect may also result from use of a machine with insufficient
shot capacity, in which case a larger machine is needed.

INJECTION MOLDING
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Flashing
Flash, also called “burrs”, is an excess of molding material that
appears as a thin lip or protrusion at the edge of a component.
Flashing occurs when the polymer melt is squeezed into the
parting surface between mold plates; it can also occur around
ejection pins.

INJECTION MOLDING
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Sink marks. These are defects usually related to thick molded
sections. A sink mark occurs when the outer surface on the
molding solidifies, but contraction of the internal material
causes the skin to be depressed below its intended profile.

INJECTION MOLDING
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Advantageous
• Fast production.
• Low labour costs.
• High-output production.
• Multiple materials can be used at the same time.
• Can be used to produce very small parts.
Limitations
• High initial tooling and machinery cost.
• Small number of parts can be costly.

Plastic»
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1. Extrusion
3. Compression Molding
4. Transfer molding
5. Blow molding
6. Thermoforming

COMPRESSION MOLDING
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Compression molding process consists of two steps, preheating
and pressurizing.
Compression molding is generally used for thermosetting plastic.

COMPRESSION MOLDING
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Process Description

COMPRESSION MOLDING
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Step 1- A piece of uncured rubber is placed in the mold.
Step 2 - The mold is closed up and held under hydraulic pressure
while the rubber cures due to temperature.
Step 3 - When the mold opens the part can be removed. The
excess rubber, called flash, needs to be trimmed off the part.
The process employs thermosetting resins in a partially cured
stage, either in the form of granules, putty-like masses, or
preforms.
Compression molding is a high-volume, high-pressure method
suitable for molding complex, high-strength fiberglass
reinforcements.

COMPRESSION MOLDING
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Advantages
• Lowest cost
• More uniform density
• Uniform shrinkage due to uniform flow
• Improved impact strength due to no degradation of
fibers during flow
• Dimensional accuracy
• Residual stresses are minimized

COMPRESSION MOLDING
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Materials used in this process
A. Thermosetting polymers
B. Thermoplastic:
• Ultra High Molecular Weight Polyethylene (UHMWPE)
• Long fiber reinforced thermoplastics

COMPRESSION MOLDING
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Advantages
• Large curing time
• scrap cannot be reprocessed.
Applications & products
• Dinnerware
• Buttons
• Electrical Appliance Housings
• Radio Cases

Plastic»
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1. Extrusion
4. Transfer molding
5. Blow molding
6. Thermoforming

TRANSFER MOLDING
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• In the transfer molding, polymer charge is transferred
from the transfer pot to the mold. The mold is cooled and
molded part is ejected.
• Generally, thermoset plastics (such as epoxy, polyester,
phenol-formaldehyde, vinyl ester, silicone) are processed
by transfer molding process, but certain thermoplastic
materials can also be processed.
• This process is widely used to encapsulate items such as
integrated circuits, plugs, connectors, pins, coils etc.

TRANSFER MOLDING
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• The required amount of polymer charge is weighted and
inserted into the transfer pot.
2. The transfer pot is heated by the heating element above
the melting temperature of the polymer charge.
3. The plunger is used to push the liquid polymer charge
from the transfer pot into the mold cavity.
4. The mold cavity is held closed until the resin gets cured.
The mold cavity is opened and the molded part can be
removed.

TRANSFER MOLDING
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• This is similar to compression molding and injection
molding
• But the different from compression molding in that the
mold is enclosed rather than open to the fill plunger
• In injection molding we use heat to melt the material and
then press to make the casting. But in transfer molding we
use only pressure to make the casting.

TRANSFER MOLDING
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TRANSFER MOLDING
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Step 1 - A piece of uncured rubber is placed into a portion of the mold
called the “pot”.
Step 2 - The mold is closed up and under hydraulic pressure the
rubber is forced through the small hole into the final cavity.
The mold is held closed while the rubber cures.
Step 4 - Mold is opened and the part can be removed. The flash and
the gate may need to be trimmed.

TRANSFER MOLDING
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Pros:
▪ Fast setup time and lower setup costs
▪ Low maintenance cost
▪ Plastic parts with metal inserts can be made
▪ Design flexibility
▪ Dimensionally stable
Cons:
▪ Wastage of material
▪ Production rate lower than injection molding
▪ Air can be trapped in the mold

TRANSFER MOLDING
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Applications
• Natural gas industry
• Electrical industry
• Hydraulic industry
• Wind turbine blades
• Medical composites
• Aerospace and automobile parts
• Bathroom fixtures, car body, helmets, etc…

Plastic»
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1. Extrusion
4. Transfer molding
5. Blow molding
6. Thermoforming

BLOW MOLDING
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Molding process in which air pressure is used to inflate soft
plastic into a mold cavity
• Important for making one-piece hollow plastic parts with
thin walls, such as bottles
• Because these items are used for consumer beverages in
mass markets, production is typically organized for very
high quantities

BLOW MOLDING
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Accomplished in following steps:
1. Plasticizing(make plastic ) or melting the resin
2. Fabrication of a starting tube, called a parison
(The parison is a tube-like piece of plastic with a hole
in one end).
3. Inflation of the tube to desired final shape
4. Ejection of the part
5. Trimming and finishing of the part

BLOW MOLDING
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BLOW MOLDING
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Forming the parison is accomplished by either
Blow molding process
Extrusion blow
molding
Injection blow molding

BLOW MOLDING
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Extrusion Blow Molding
(1) Extrusion of parison (2) Parison is pinched at the top and sealed at
the bottom (3) the tube is inflated so that it takes the shape of the
mold cavity; and (4) mold is opened to remove the solidified part.

BLOW MOLDING
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Injection Blow Molding
(1) Parison is injection molded around a blowing rod (2) injection mold
is opened and parison is transferred to a blow mold; (3) soft polymer is
inflated to conform to the blow mold; and (4) blow mold is opened and
blown product is removed.

BLOW MOLDING
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Some typical APPLICATIONS are
➢ HDPE : High Density Polyethylene (stiff bottle, toys, cases,
drum)
➢ LDPE : Low Density Polyethylene (flexible bottle)
➢ PP : Polypropylene (higher temperature based bottles)
➢ PVC : Polyvinyl Chloride (oil resistant containers)
➢ PET : Polyethylene terephthalate (Water Bottles)

Plastic»
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1. Extrusion
4. Transfer molding
5. Blow molding
6. Thermoforming (Disposable Cup Thermoforming Machine)

THERMOFORMING
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In its basic operation, a flat thermoplastic sheet of specific size is
clamped in place, heated to its softening temperature, then forced
against the contours of a mold or form by either air or vacuum
pressure or by mechanical means.
Once cooled, the thermoformed part retains the shape of the mold
or form.
Materials: PVC, PE, HIPS, ABS and PC.

THERMOFORMING
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THERMOFORMING
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THERMOFORMING » Vacuum Thermoforming
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Advantage:
• Operated comparatively low vacuum pressure.
• Relatively cheap.
Disadvantage:
• Uneven wall thickness at the corner of the product.
• Bad finishing or non uniform plastic concentration.
• Therefore the thinnest area occur at the corner, near
the clamp

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• Alternative to vacuum forming.
• Here, the air pressure is forced to the preheated sheet
into cold mold. The air pressure is much higher than the
vacuum forming.
• The basic difference between vacuum forming is the
heated sheet is pressured from above the mold cavity.
• Due to high pressure, the heated sheet can be deformed
in fraction of a second.
(High production rate)
THERMOFORMING » Pressure Thermoforming

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Advantage:
• High production rate .
• Efficient for large parts.
• Low tooling cost.
Disadvantage:
• Limited shape complexity.

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THERMOFORMING»Mechanical Thermoforming

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• Here, positive and negative molds are brought against
heated plastic sheet, forcing it to the assumed shape.
• Air between the die and sheet is evacuated by using
vacuum pump, and sheet conforms to the mold shape.
• Formed part is cooled and ejected.

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Advantages:
• Better dimensional control.
• Opportunity for surface detailing of both sides of the
parts.
Disadvantages:
• Two mold halves are required
• Relatively costly.

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Applications:
Thermoforming has many applications like
▪ Food packaging
▪ Automotive parts
▪ Aircraft windscreens
▪ Vehicle doors etc.

THERMOFORMING
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Plastic» Product Design Guidelines
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• Strength and stiffness
– Plastics are not as strong or stiff as metals
– Avoid applications where high stresses will be encountered
– Creep resistance is also a limitation
Creep resistance can be defined as a material's ability to resist
any kind of distortion when under a load over an extended
period of time
– Strength-to-weight ratios for some plastics are competitive
with metals in certain applications

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• Impact Resistance
– Capacity of plastics to absorb impact is generally good;
plastics compare favorably with most metals because in
case of metals brilltle-ness may be present.
• Service temperatures
– Limited relative to metals and ceramics
• Thermal expansion
– Dimensional changes due to temperature changes much
more significant than for metals

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• Many plastics are subject to degradation from
sunlight and other forms of radiation
• Plastics are soluble in many common solvents
• Plastics are resistant to conventional corrosion
mechanisms that afflict many metals.
• Metals degrade because of corrosion

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• Wall thickness
– Uniform wall thickness is desirable in an extruded cross
section
– Variations in wall thickness results in non-uniform plastic
flow and uneven cooling which tend to warp extrudate
Extrusion

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Extrusion
• Hollow sections
– Hollow sections complicate die design and plastic flow
– Desirable to use extruded cross-sections that are not hollow
yet satisfy functional requirements

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Extrusion
• Corners
– Sharp corners, inside and outside, should be avoided in
extruded cross sections
– They result in uneven flow during processing and stress
concentrations in the final product

Product Design Guidelines: Moulding
• Economic production quantities
– Each part requires a unique mold, and the mold for any
molding process can be costly, particularly for injection
molding
– Minimum production quantities for injection molding are
usually around 10,000 pieces
– For compression molding, minimum quantities are 1000
parts, due to simpler mold designs
– Transfer molding lies between injection molding and
compression molding

• Part complexity
– An advantage of plastic molding is that it allows multiple
functional features to be combined into one part
– Although more complex part geometries mean more costly
molds,
– It may nevertheless be economical to design a complex
molding if the alternative involves many individual
components that must be assembled

• Wall thickness
– Thick cross sections are wasteful of material, more likely to
cause warping due to shrinkage, and take longer to harden
• Reinforcing ribs
– Achieves increased stiffness without excessive wall
thickness
– Ribs should be made thinner than the walls they reinforce
to minimize sink marks on outside wall

• Corner radii and fillets
– Sharp corners, both external and internal, are undesirable in
molded parts
– They interrupt smooth flow of the melt, tend to create
surface defects, and cause stress concentrations in the part
• Holes
– Holes are quite feasible in plastic moldings, but they
complicate mold design and part removal

• Draft
– A molded part should be designed with a draft on its sides
to facilitate removal from mold
– Especially important on inside wall of a cup-shaped part
because plastic contracts against positive mold shape
– Recommended draft:
• For thermosets, ~ 1/2 to 1
• For thermoplastics, ~ 1/8 to 1/2

• Tolerances
– Although shrinkage is predictable under closely controlled
conditions, generous tolerances are desirable for injection
moldings because of
• Variations in process parameters that affect shrinkage
• Diversity of part geometries

Plastic processing

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