INJECTION MOLDING&

BLOW MOLDING

Abdul Rehman14-MCE-55

UET-Lhr

INJECTION MOLDING. BLOW MOLDING. INJECTION BLOW MOLDING.EXTRUSION BLOW MOLDING. STRETCH BLOW MOLDING.

INJECTION MOLDING Injection molding is one of the most

commonly used processing method for the plastic components.

It is defined as “ A manufacturing process for

forming objects, as of plastic or metal, by heating the molding material to a fluid state and injecting it into a mold “.

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 design and product.

So , the term to memorize in all plastic processing methods is HFC ( heating , forming , cooling ).

INJECTION MOLDING (CONTINUED) It is used to process thin walled

plastic parts for a wide variety of shapes and products .

BASIC PRINCIPLE Plastic material is melted in a heated

chamber and then injected in the mold , where it cools and finally the finished plastic part is ejected out of the

cavity .

INJECTION MOLDING MACHINE

The raw material in the form of powder/pellets is introduced through hopper into the cylinder.

MACHINE PARTS Hopper is a tapered container working with a

hopping motion to transfer grains into cylinder.

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.

PROCESS

When the plastic solidifies the ejector pins are hydraulically moved backwards .

The cavity will be filled by the pressure of the piston and the mold should not be opened until

the plastic solidifies.

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 .

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 the cavity is called the injection stage.

Cooling : The material is

cooled for at least 30-60 sec.

Ejection : The 2nd mold plate moves

back by ejector pins and the product is

tapped out .

IMPORTANT POINTS PRODUCTION RATE : Production rate depends upon the clamping and de-

clamping time of 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 to as shot volume.

PRESSURE and CYCLE TIME : The pressure applied is in the range of 35-140 MPa while

the cycle completes in 2-60 sec.

MATERIALS USED Acetate. Acrylonitrile butadiene styrene (ABS). Cellulose acetate. PVC ( poly vinyl chloride.) Polycarbonate. Polyesters.e.t.c.

ADVANTAGES Higher production rate. Minimum wastage of material. Complex geometry can easily be

produced.

DISADVANTAGES• Tooling cost higher.• High setup cost.• Large undercuts can not be formed.

APPLICATIONS

It can be used to produce thin walled plastic products of varying size and dimensions

For Example: Medical devices such as surgical syringes. Open container like buckets. Plastic housings of different tools. Daily use products such as tooth brushes.

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.

PROCEDURE

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.

TYPES OF BLOW MOLDING Extrusion blow molding. Injection blow molding. Stretch blow molding.

MAJOR DIFFERENCE: All the types have one primary

difference that is making of parison by extrusion , injection and stretching .

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 .

INJECTION BLOW MOLDING

The process is

divided into three sections

Injection.

Blowing.

Ejection.

The injection blow molding is used for the production of hollow objects in large quantities . The main applications are bottles, jars and other containers.

STRETCH BLOW MOLDING This process is divided into four steps.

Discharge : After a set time for cooling the molds open and the product is removed .

.

Stretch blow molding is also carried out by injection . Used the production of high quality containers.

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.

APPLICATIONS Different types of plastic products can

be manufactured by this process such as:

Bottles in different shapes and sizes. Jars and containers. Fluid oil tanks. Mugs. Toys. etc.