injection moulding

1. MOULDING AND ITS TYPES

2. Moulding
 The term moulding process refers to the method of maki
ng the mould and the materials used.
 Moulding processes have certain features in common-
1. The use of pattern.
2. Some type of aggregate mixture comprising a refractory and bi
nders.
3. A means of forming the aggregate mixture around the pattern.
4. Hardening of aggregate or developing its bond while in contact
with the pattern.
5. Withdrawal of the pattern from the mould.
6. Assembly of the mould and core pieces to make a complete m
ould, metal then being poured into the mould.

3. Moulding
 Classification of Moulding Processes:

4. Types of Moulding Sands
 Green Sand:
 Natural sand prepared as a mixture of silica sand with 18-30 %
clay and 6-8 % moisture.
 Fine, soft, light and porous.
 The name ‘Green sand’ employs for damped i.e. it contains
moisture and the mould made of this sand is used immediately
to pour the molten metal.
 Easily available and has low cost.

5. Types of Moulding Sands
 Dry Sand:
 Green sand that has been dried or baked in between 250° to
550° in suitable oven after the making mould and cores, is cal
led dry sand.
 More strength, rigidity and thermal stability.
 Suitable for larger castings.

6. Types of Moulding Sands
 Parting Sand:
 It is used to keep away the green sand from sticking to the patt
ern and to allow the sand on the parting surface of the flasks to
separate without clinging.
 It is free from clay and is dry.
 It is washed and non sticky sand

7. Types of Moulding Sands
 Core Sand:
 Used to make core.
 Should be stronger than the moulding sand.
 It is made by mixing core linseed oil with silica sand,
 It is also called as soil sand

8. Backing sand

9. Facing sand

10. Properties of Moulding Sand
1. Refractoriness:
 The ability of moulding sand to withstand high temperatures w
ithout breaking down or fusing.
 The degree of refractoriness depends on SiO2 content and sh
ape & grain size of the particle.
 To enhance the proporty, sand should have lower percentage
of lime, magnesia, alkali, oxides of metals.
 Refractoriness is measured by Sinter point rather than its melt
ing point. ( At sintering temperature, the moulding sand adher
es to the casting)

11. Properties of Moulding Sand
2. Permeability:
Also referred as porosity, is the property of sand allow the escape
of any air, gases or moisture present or generated in the mould wh
en the molten metal is poured into it.
Liquid metals cause evolution of gases due to their reaction with
moulding sand ingredients.
Permeability is a function of:
1. Grain size
2. Grain shape
3. Moisture and clay contents in the moulding sand.

12. Properties of Moulding Sand
3. Cohesiveness:
Also referred to as the strength of sand.
It is property of moulding sand by virtue which the sand grain part
icles interact and attract each other within the moulding sand.
Moulding sand should be capable of withstanding the compressiv
e and erosive force exerted by liquid metal while filling the cavity.
Low strength mouldings result in defective castings.
It depends upon the grain size, sand particle shape and size, moi
sture content and density,
strength inversely affect the porosity

13. Properties of Moulding Sand
4. Flowability:
It is the ability of the sand to get compacted and behave like a flui
d.
It will flow uniformly to all portions of pattern when rammed and di
stribute the ramming pressure evenly all around in all directions.
In general, flow ability increases with decrease in green strength,
an, decrease in grain size.
flow ability also varies with moisture and clay content.
It is also called as plasticity fluidity.

14. Properties of Moulding Sand
5. Adhesiveness:
It is property of moulding sand to get stick or adhere with foreign
material such sticking of moulding sand with inner wall of mouldin
g box.
It helps the sand to retain the mould cavity and stay in the box.

15. Types of moulding

16. Floor moulding

17. • It is used for large casting
manufacturing.
• Pit is dug in the floor of foundry with
bed of charcoal placed at the bottom of
pit to help the escape of gases.
• cope is placed over the pit to complete
the assembly.
• Sand is rammed and wall of pit are
bricklined and plastered with Liam
sand.
• Moulds are baked before pouring.
• Gates , runner, riser, pouring basin are
made in cope.
• crane are used to lift the cope and
Pit moulding

18. Machine moulding

19. What does processing of
plastic means ?
 All the methods used for processing of plastics like
Injection molding, blow molding , thermoforming ,
extrusion e.t.c. , have a raw material i.e. plastic in some form
which is then heated , formed and cooled to get the desired
designand product.
So , the term to memorize in all plastic processing methods is
HFC ( heating , forming , cooling )

20. INJECTION MOLDING
(CONTINUE
D)
It is used to process thin walled plastic parts fora
wide variety of shapes and products .
BASIC PRINCIPLE
Plastic materialis melted in a heated chamberand
then injected in the mold , where it cools and
finally the finishedplastic part isejected outof the
cavity .

21. INJECTIONMOLDING
MACHINE
⚫The raw material in the form of powder/pellets is
introduced through hopper into thecylinder

22. Machine parts
⚫Hopper is a tapered container working with a hopping
motion to transfergrains intocylinder
⚫Inside the cylinder there is a piston /plunger which is used
to move the material from cylinder into the mold
⚫Heating arrangement is placed above and below the
cylinder .
⚫The mold is in two halves , it has a mold cavity and the
mold has two ejector pins.

23. Process
⚫As soon as the plastic is melted it will be pushed by the
piston into the sprue through which the material
would go into the mold cavity .
⚫The cavity will be filled by the pressure of the piston
and the mold should not be opened until the plastic
solidifies.
⚫When the plastic solidifies the ejector pins are
hydraulically moved backwards .

24. Stages of Injection molding
⚫Clamping : The two halves of mold are tightly closed before
the molten plastic is injected.
⚫Injection : Injection of raw material from hopper into
cylinder to thecavity is called the injection stage.
⚫Cooling : The material is cooled forat least 30-60 sec
⚫Ejection : The 2nd mold plate moves back by ejector pins
and the product is tapped out

25. IMPORTANT POINTS
 PRODUCTION RATE :
Production rate depends upon the clamping and de-clamping
timeof the mold halves.
 INJECTION TIME:
The filling process should be optimal not too slow in order to
stop the production of cracks.
 SHOT VOLUME :
The amount of material that is injected into the mold is
referred toas shotvolume
while the
 PRESSURE and CYCLE TIME :
The pressure applied is in the range of 35-140 MPa
cyclecompletes in 2-60 sec

26. MATERIALS USED
⚫Acetate
⚫Acrylonitrile butadienestyrene (ABS)
⚫Celluloseacetate
⚫PVC ( polyvinyl chloride)
⚫Polycarbonate
⚫Polyesters
e.t.c.

27. ADVANTAGES
⚫Higher production rate
⚫Minimum wastageof material
⚫Complexgeometry caneasily be produced
DISADVANTAGES
• Tooling cost higher
• High setup cost
• Large undercuts can not be formed

28. APPLICATIONS
⚫It can be used to produce thin walled plastic products of
varying size and dimensions e.g.
⚫Medical devices such as surgical syringes
⚫Open container like buckets
⚫Plastic housings of different tools
⚫Daily use products such as tooth brushes

29. BLOW MOLDING
⚫“ It is a plastic processing technique which is used to
produce hollow plastic parts by inflating a heated
plastic until it fills a mold and forms the desired shape”
⚫The raw material used for processing in blow molding is
called parison
⚫Parison is a preform tube that is hollow and it has a hole
at one end

30. PROCEDURE
I. First the parison is obtained by means of
extrusion or injection molding process
II. Above the preform there isa blower and the
preform is
• positioned between two split halves of the mold.
III. The mold closes over the tube and the hot air is
injected from the blower into the hollow tube . The air
expands the tube against the sides of the mold
IV. After sufficient cooling , the mold opens to release

32. Important Process
Parameters
⚫Cooling temperature of plastic material
⚫Air pressure required ( usually 2-4 Mpa)
⚫Cooling time
o Pressure is exerted both axially and radially , both
cavities are pressurized with a non-reactive gas such as
argon.

33. Types of Blow molding
⚫Extrusion blow molding
⚫Injection blow molding
⚫Stretch blow molding
⚫MAJOR DIFFERENCE:
All the types have one primary
making of parison by extrusion
difference that is
, injection and
stretching .

34. INJECTION BLOW MOLDING
⚫The injection blow molding is used for the production of
hollow objects in large quantities . The main applications are
bottles, jars and othercontainers.
⚫The process is divided intothree sections
i) Injection
ii) Blowing
iii) Ejection

35. EXTRUSION BLOW MOLDING
⚫In this process the blow molding machine is based on a standard
extruder barrel and screw assembly to plasticize the polymer.
⚫The polymer is heated inside the barrel , the molten polymer is
led through a right angle and through a die to emerge as a
hollow section.
⚫When the parison has moved enough length it is cut through by
a knife and fits inside the bottle mold .
⚫The bottle mold moves toward the jet where the air blows and
the product is obtained after cooling .

37. ADVANTAGES
⚫Low tooling costs .
⚫Fast production rates .
⚫Ability to mold complex parts .
⚫ Little scrap generated .
⚫ Large hollow shape can be produced .
⚫ Produced parts can be recycled .
DISADVANTAGES
• Limited to hollow parts .
• Thick parts cannot be manufactured.

38. Applications
⚫Different typesof plastic productscan be
manufactured by this processsuch as:
 Bottles in different shapes and sizes
 Jarsand containers
 Fluid oil tanks
 Mugs
 Toys etc