University Tenaga National Lecturer: Habeeb Al-Ani HABEEB HATTAB HABEEB Office: BN-Block, Level-3,...

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University Tenaga National

Lecturer: Habeeb Al-Ani

HABEEB HATTAB HABEEBHABEEB HATTAB HABEEB

Office: BN-Block, Level-3, Office: BN-Block, Level-3, Room-088Room-088

Email: Email: hbuni61@yahoo.comExt. No.: 7292Ext. No.: 7292

H/P No.: 0126610058H/P No.: 0126610058

Contemporary (Modern)

Casting Processes

Metal Moulds:Metal Moulds:

Made of special metals that withstandhigh temperatures of the molten mate-rials.

Used to produce large numbers of castings.Used to produce large numbers of castings.

Used to produce small-and mediumsizeUsed to produce small-and mediumsize

Dies:Dies:- Dies for hot and cold-chamber machine are similar in construction. - Dies are made in to halves to allow Casting removal. - Metal enters the stationary half when the die is closed.- When the die opens ejector-pins for the casting to fall from the die

- Die life depends on the metal cast ( Range from 10,000 filling for brass to several million for zinc).

DiesCont…

- Vents should be considered to allow the gases to escape

-Dies are provided with water channels to cool the die after injection to metal (For rapid production)

Die casting:Die casting:

Die – Is a metal mould into which a molten material is forced to fill the cavity of the mould.

Die-casting is accomplished using either of the following methods:Die-casting is accomplished using either of the following methods:

1- Hot chamber 2- Cold chamber

Hot chamber method:

The molten pot is included within the machine. An injection cylinder in

Immersed in the molten material all times. The injection cylinder, which is actuated by air or hydraulic pressure,forces the molten metal into the mould Cavity.

The molten pot is included within the machine. An injection cylinder in

Immersed in the molten material all times. The injection cylinder, which is actuated by air or hydraulic pressure,forces the molten metal into the mould Cavity.

This method is used to cast low-melting point alloys (Zinc, tin, and lead). Relatively high-melting temperature metals are not cast using this method because high temperatures cause damage to hot chamber machines.

Hot chamber method (Die casting)Cont…

PrinciplePrinciple

Cont…

Metal is injected into the mould by an cylinder (plunger).

The plunger maintains the pressure required during solidification (this also can be performed using compressedair). At this time the mould is closedby another cylinder.

Metal is injected into the mould by an cylinder (plunger).

The plunger maintains the pressure required during solidification (this also can be performed using compressedair). At this time the mould is closedby another cylinder.

Hot chamber method (Die casting)

Cont…

After the metal solidification the pressure is relieved, the opens and the casting is ejected by knockout pins (ejector-pins).

Hot chamber method (Die casting)

Cont… Hot chamber method (Die casting)

Cold chamber method:

The molten material is poured into the Injection cylinder by mechanical meansor hand. The molten material is taken from a separate container (Furnace).

This method is used to cast alloys with relatively high-melting temperatures and pressures.

PrinciplePrincipleCont…

The metals are not molten in a self-contained pot ladle the molten metalis poured in a cavity before the plunger.Cold chamber machines are designed to withstand high temperatures of thePoured metals and to provide pressureDuring the solidification process.

Cold chamber method (Die casting)

Cont… Cold chamber method (Die casting)

A- The mould is closed with cores and the metal is ready to be poured by a ladle. B- The plunger forces the metal into the cavity.c- After the metal solidifies, the cores are withdrawn.D- Die opens and the casting is ejected

Advantage of Die casting:Advantage of Die casting:

1- Rapid Process

2- The core and die are permanent

3- Smooth surfaces of casting

4- Minimizes machining and cutting processes (less waste material than in sand castings)

Advantage of Die casting

5- The wall thickness is more uniform than in sand castings.

6- Waste material is low because thesprue, runners and gates are re-melted.

Cont…

7- Tolerances are less than in sand Castings.

1- High cost of equipment and dies (sodie casting is used in mass production)

2- Undesirable chilling of the casting (The solution: High temperature must be sustained before removing the casting)

Disadvantage of Die casting:Disadvantage of Die casting:

Disadvantage of Die casting

3- Metal with high coefficient of contraction should be removed from the mould immediately because of the inability of the mould to contract with the casting.

Cont…

4- Used mainly for low melting point materials.

Features of die casting of Brass and high melting

point metals:

Features of die casting of Brass and high melting

point metals:

The difficulty faced in die casting ofbrass is the damage and rapid oxida-tion of steel dies because of the high melting temperature. This problem has been overcome by performingthe die casting at low a temperatureas possible.

Features of D. cas. of Brass and high melt. point metalsCont…

So metal is can be injected in a semi-liquid or plastic state to perform casting operations at lower tempe-rature.

There are two variations of die castingProcess for BRASS:

NEXT SLIDE

a- Compression chamber is built in theDie .

b- Compression chamber is separatefrom the die .

Lower pressure permanentmoulds:

- A mould is mounted over a furnace.

- The furnace is sealed through a stalk into the cavity.

Advantage: Dense, clean and AccurateCasting, less secondary machining andCutting operations.

Lower pressure permanent mouldsCont…

Gravity or permanent-MouldCasting :Gravity or permanent-MouldCasting :

No pressure is used (only gravity). It Is used for ferrous and non-ferrous metals.

PrinciplePrinciple

The die is closed using a cylinder and the molten metal is simply poured intothe mould cavity by hand or mechani-cal means. The metal fills the cavitybecause of the pressure created by the head of the metal poured (no plu-nger) is used to keep the casting underpressure).

Gravity or permanent-mould casting Cont…

Casting cycle:

Pouring, cooling, ejecting, and setting the coresPouring, cooling, ejecting, and setting the cores

Gravity or permanent-mould casting Cont…

Advantage: Good finish and surface ofthe castings, capability of maintainingsmall tolerances. Disadvantage: Good High cost of equ-ipment and dies.

Centrifugal Casting:Centrifugal Casting:

1- The mould rotates while the metal solidifies.

PrinciplePrinciple

Centrifugal Casting:

1- High cost of equipment and dies (sodie casting is used in mass production)

2- Undesirable chilling of the casting (The solution: High temperature must be sustained before removing the casting)

Advantage:

1- No need of cores for cylindrical castings.

2- Good dense of the metal.

3- Thin walled castings can be produced.

centrifugal casting Cont…

Methods of centrifugal casting

This method is used to produce pipes,bars, cylinders and other symmetricobjects. The mould rotates about itshorizontal or vertical axis. THREE orTWO types:

1- True Centrifugal Casting

b- Using a thick, highly insulated sand interface between the mould wall andthe casting. In this case, the solidifica-tion will start from the casting centerand from the wall at the same time.

a- Using a massive thick metal mould with a thick refractory coating. As a result of this design, the solidification will proceed from the mould wall toward the casting centre.

Finding the centrifugal force CF:

The centrifugal force is created by themould rotation about its axis. If too lowA centrifugal force is applied, the metal will slide, slip or rain.

Horizontal

Vertical

/ Methods of centrifugal casting

The mould is completely full of metal.The centre of the casting is solid but with less density then it is in the surf-ace of the casting. Usually, the centreof the casting will be removed using machining processes.

2- Simicentrifugal Casting

Advantage: Good dense surface of the metal, especially near the surface.

centrifugal casting Cont… / Methods of centrifugal casting

/ Methods of centrifugal casting

Several cavities are located around the mould axis. As the mould is rotated,the CF encourages the metal to fill the cavities through radial gates.

3- Centrifuging

Advantage: Not limited to symmetricalobjects.

centrifuging casting Cont… / Methods of centrifugal casting

Precision or investment Casting:Precision or investment Casting:

This process is used to cast unmachi-nable alloys and radioactive metals (Poor machinability).

Advantage:

1-Intricate and smooth casting.

2-Good for unmachinable metals and itCan replace die-casting.

Precision or investment Casting:

Disadvantage:

1- Very expensive.

Cont…

2- Limited to small parts.

3- some difficulties when cores are used .

Type of Precision or investment Casting

1-“Lost Wax” precision casting process.

A wax pattern is used to form a cavityIn the mould. The Wax pattern is cove-red with plaster investment. When thisplaster becomes hard the plaster mould will be heated. As a result, theWax pattern will melt away from the mould leaving a cavity having all the details of the Wax pattern.

Schematic illustration of investment castingSchematic illustration of investment casting

1. WAX INJECTION : Wax replicas of the desired castings are produced by injection molding. These replicas are called patterns.

2. ASSEMBLY : The patterns are attached to a central wax stick, called a sprue, to form a casting cluster or assembly.

3. SHELL BUILDING : The shell is built by immersing the assembly in a liquid ceramic slurry and then into a bed of extremely fine sand. Up to eight layers may be applied in this manner.

4. DEWAX : Once the ceramic is dry, the wax is melted out, creating a negative impression of the assembly within the shell.

5. CONVENTIONAL CASTING: In the conventional process, the shell is filled with molten metal by gravity pouring. As the metal cools, the parts and gates, sprue and pouring cup become one solid casting.

6. KNOCKOUT: When the metal has cooled and solidified, the ceramic shell is broken off by vibration or water blasting.

7. CUT OFF: The parts are cut away from the central sprue using a high speed friction saw.

8. FINISHED CASTINGS: After minor finishing operations, the metal castings--identical to the original wax patterns--are ready for shipment to the customer.

Type of Precision or investment CastingCont…

2-Plaster Mould Casting.

1- Mold is made of plaster 2- Mixed with water and additives and poured over a pattern 3- After plaster sets, pattern is removed and the mold is dried at 120 C 4- Have low Permeability – gases can not escape 5- Patterns are made of:

-Al alloys, -Thermosetting plastics-Brass or Zinc alloys

6-Have fine details and good surface finish 7-Form of precision casting

Plaster moulds are also not permanentbecause they are destroyed when the casting is removed.

Continuous Castings

Continuous casting process consists of continuously poring the molten metal into a mould that has the capability forrapidly chilling the metal to the pointof solidification and then withdrawingIt from mould.

Continuous casting

Continuous casting and hot rolling plant

Asarco process

The mould is built in the furnace. The molten metal is fed by gravity into the mould from furnace. At the mould exit,the metal solidifies and it is withdrawnby rolls. The exit consists of a graphitedie that forms the final shape of the withdrawn product. The graphite die isbuild in a cooling jacket, which uses water to cool the product at the mouldexit. The products: Bars, Rods.

Next Lecture:Metal Cutting

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University Tenaga National Lecturer: Habeeb Al-Ani HABEEB HATTAB HABEEB Office: BN-Block, Level-3,...

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