In Jection Moulding

8/11/2019 In Jection Moulding

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INJECTION MOULDING

Designed b y :-Monde Sagar Baban

(13721)


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D

EFINATION

Injection molding is a manufacturing process

where heated molten plastic is forced into a

mold cavity under pressur.


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T

YPES

Reaction injection moulding.

Liquid injection moulding.

Gas assist injection moulding.

Co-injection moulding.2-shot injection moulding.

Fusible core injection moulding.

Rapid injection moulding.


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REACTIONINJECTION

MOULDING

Process for molding polyurethane, epoxy, and

other liquid chemical systems. A mixture of two

to four components in the proper chemical ratio

is accomplished by a high-pressure

impingement-type mixing head, from which themixed material is delivered into the mold at low

pressure, where it reacts (cures).


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L

IQUID

INJECTION

MOULDING

Process that involves an integrated system for

proportioning, mixing, and dispensing dual-

component liquid resin formulations and

directly injecting the resultant mix into a mold

which is clamped under pressure. See Injectionmolding.


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GASASSISTINJECTION

MOULDING

Plastic molding process in which a high-

pressure gas is co-injected along with the

plastic part to produce discrete internal hollow

sections. It differs from blow molding in that

one large hollow product is not created; rather,a solid piece with hollow sections is produced.


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C

O

INJECTION

MOULDING

This is a process that creates a skin and core

material arrangement in a molded part. The skin

material is injected first into the mold cavity,

and is immediately followed by a core material.

As the skin material flows into the cavity, thematerial next to the cavity walls freezes and

material flows down a center channel. When the

core material enters it displaces the skin

material in the center of the channel by pushingthe skin ahead. As it flows ahead it continues to

freeze on the walls producing the skin layer


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2 SHOTINJECTIONMOULDING

This technology produces a part with two

different raw materials or colors in a single

operation. The machine has two injection units:

one vertical and one horizontal. By using a

rotating mold, the machine automaticallyproduces a substrate of one resin or color and

overmolds the part with the second resin or

color


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FUSIBLEINJECTIONMOULDING

It is used in the manufacture of molded

components with cavities or undercuts, which

would not be possible with tools having

demoldable cores


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R

APID

INJECTION

MOULDING

Rapid Injection Molding allows us to make

prototype injection molded parts in a

production thermoplastic resin in 2-5 weeks.

These parts may be used for full functional and

fit testing as well as test marketing.


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PROCESSES

Clamping

Inject ion

Cool ing

Eject ion


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C

LAMPING

Prior to the injection of the material into the mold,

the two halves of the mold must first be securely

closed by the clamping unit. Each half of the mold is

attached to the injection molding machine and one

half is allowed to slide. The hydraulically poweredclamping unit pushes the mold halves together and

exerts sufficient force to keep the mold securely

closed while the material is injected. The time

required to close and clamp the mold is dependent

upon the machine - larger machines (those withgreater clamping forces) will require more time. This

time can be estimated from the dry cycle time of the

machine.


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I

NJECTION The raw plastic material, usually in the form of pellets, is

fed into the injection molding machine, and advancedtowards the mold by the injection unit. During thisprocess, the material is melted by heat and pressure.The molten plastic is then injected into the mold very

quickly and the buildup of pressure packs and holds thematerial. The amount of material that is injected isreferred to as the shot. The injection time is difficult tocalculate accurately due to the complex and changingflow of the molten plastic into the mold. However, the

injection time can be estimated by the shot volume,injection pressure, and injection power.


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C

OOLING

The molten plastic that is inside the mold begins to

cool as soon as it makes contact with the interior

mold surfaces. As the plastic cools, it will solidify

into the shape of the desired part. However, during

cooling some shrinkage of the part may occur. Thepacking of material in the injection stage allows

additional material to flow into the mold and reduce

the amount of visible shrinkage. The mold can not

be opened until the required cooling time has

elapsed. The cooling time can be estimated fromseveral thermodynamic properties of the plastic and

the maximum wall thickness of the part.


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E

JECTION

After sufficient time has passed, the cooled partmay be ejected from the mold by the ejectionsystem, which is attached to the rear half of themold. When the mold is opened, a mechanism isused to push the part out of the mold. Force must

be applied to eject the part because during coolingthe part shrinks and adheres to the mold. In order tofacilitate the ejection of the part, a mold releaseagent can be sprayed onto the surfaces of the moldcavity prior to injection of the material. The time thatis required to open the mold and eject the part can

be estimated from the dry cycle time of the machineand should include time for the part to fall free ofthe mold. Once the part is ejected, the mold can beclamped shut for the next shot to be injected.


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ADVANTAGES

The injection molding process has several advantages over othermolding processes. The following is a short list of what you canexpect from utilizing Injection Molding as your form of production.

Injection molding allows for high production output rates.

When producing your product you may use inserts within the mold.You may also use fillers for added strength.

Close tolerances on small intricate parts is possible with InjectionMolding.

More than one material may be used at the same time when utilizingco-Injection Molding.

There is typically very little post production work required becausethe parts usually have a very finished look upon ejection.

All scrap may be reground to be reused, therefor there is very littlewaste.

Full automation is possible with Injection Molding.


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DISADVANTAGES

The molding process has several disadvantages toother molding processes. The following is a shortlist of some of the disadvantages to InjectionMolding.

This is not a preferred method of manufacturing forshort production runs. This is mainly due to the costof tooling and the cost of operation. However B.J.Molding can handle smaller runs than most shops.

Design and development of parts that will work wellwith Injection Molding often takes a very long time.Many parts are just not suited to the process.


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A

PPLICATIONS

Injection molding is used to create many things

such as wire spools, packaging, bottle caps,

automotive dashboards, pocket combs, some

musical instruments (and parts of them), one-

piece chairs and small tables, storagecontainers, mechanical parts (including gears),

and most other plastic products available today.

Injection molding is the most common modern

method of manufacturing parts; it is ideal forproducing high volumes of the same object.


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T

OOLING

B

ASICS

Cavity Plate

Cavity

MouldingCore

Core Plate

Basic mould consisting of cavity and core plate

Runner

Cavity

Gate

NozzleSprue

Melt Delivery


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T

OOLING

FOR

A

PLASTIC

CUP

Runner

Part

Cavity

Nozzle

Part

Cavity

Knob

Stripper

plate

Runner

Part

Cavity

Nozzle


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In Jection Moulding

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