Department of Metallurgical Engineering

Gandhi Institute of Engineering and

Technology, Gunupur - 765022

SupervisorDr. Ajaya Kumar Pradhan

Presented ByHariballabha Mahanta

Introduction:

Metal Casting is one of the oldest materialsshaping methods known. Casting meanspouring molten metal into a mold with acavity of the shape to be made, and allowingit to solidify. The solidified object is calledthe casting.

The mold, into which the metal is poured, ismade of some heat resisting material. Sandis most often used as it resists the hightemperature of the molten metal.Permanent molds of metal can also be usedto cast products.

Steps involved in making a casting:1. Make the pattern out of Wood , Metal or Plastic.

2. Prepare the necessary sand mixtures for mould

and core making.

3. Prepare the Mould and necessary Cores.

4. Melt the metal/alloy to be cast.

5. Pour the molten metal/alloy into mould and

remove the casting from the mould after the

metal solidifies.

6. Clean and finish the casting.

7. Test and inspect the casting.

8. Remove the defects, if any.

9. Relieve the casting stresses by Heat Treatment.

10. Again inspect the casting.

11. The casting is ready for shipping.

Casting steps (Schematic)

Schematic diagram of casting

mould:

Classification of casting

Processes:Casting processes can be classified into

following FOUR categories:1. Conventional Molding Processes Green Sand Molding

a. Dry Sand Molding

b. Flask less Molding

2. Chemical Sand Molding Processesa. Shell Molding

b. Sodium Silicate Molding

c. No-Bake Molding

3. Permanent Mold Processesa. Gravity Die casting

b. Low and High Pressure Die Casting

4. Special Casting Processesa. Lost Wax

b. Ceramics Shell Molding

c. Evaporative Pattern Casting

d. Vacuum Sealed Molding

e. Centrifugal Casting

1. Green Sand Molding:Green sand is the most diversified molding method used

in metal casting operations. The process utilizes a mold made

of compressed or compacted moist sand. The term "green"

denotes the presence of moisture in the molding sand. The

mold material consists of silica sand mixed with a suitable

bonding agent (usually clay) and moisture.

Advantages:

Most metals can be cast by this method.

Pattern costs and material costs are relatively low.

No Limitation with respect to size of casting and type of metal or alloy used

Disadvantages:

Surface Finish of the castings obtained by this process is not good and machining is often required to achieve the finished product.

Few important casting processes

2. Dry Sand Molding:

When it is desired that the gas forming materialsare lowered in the molds, air-dried molds aresometimes preferred to green sand molds. Twotypes of drying of molds are often required.

Skin drying and

Complete mold drying.

In skin drying a firm mold face is produced.Shakeout of the mold is almost as good as thatobtained with green sand molding. The mostcommon method of drying the refractory moldcoating uses hot air, gas or oil flame. Skin dryingof the mold can be accomplished with the aid oftorches, directed at the mold surface.

3. Shell Molding Process:

It is a process in which, the sand mixed with athermosetting resin is allowed to come in contact with aheated pattern plate (200 oC), this causes a skin (Shell) ofabout 3.5 mm of sand/plastic mixture to adhere to thepattern..

Then the shell is removed from the pattern. The cope anddrag shells are kept in a flask with necessary backupmaterial and the molten metal is poured into the mold.

This process can produce complex parts with good surfacefinish 1.25 µm to 3.75 µm, and dimensional tolerance of0.5 %.

A good surface finish and good size tolerance reduce theneed for machining. The process overall is quite costeffective due to reduced machining and cleanup costs.

The materials that can be used with this process are castirons, and aluminum and copper alloys.

4. Sodium Silicate Molding

Process In this process, the refractory material is coated with

a sodium silicate-based binder. For molds, the sandmixture can be compacted manually, jolted orsqueezed around the pattern in the flask.

After compaction, CO2 gas is passed through thecore or mold. The CO2 chemically reacts with thesodium silicate to cure, or harden, the binder. Thiscured binder then holds the refractory in placearound the pattern. After curing, the pattern iswithdrawn from the mold.

The sodium silicate process is one of the mostenvironmentally acceptable of the chemicalprocesses available.

The major disadvantage of the process is thatthe binder is very hygroscopic and readilyabsorbs water, which causes a porosity in thecastings.. Also, because the binder creates sucha hard, rigid mold wall, shakeout andcollapsibility characteristics can slow downproduction.

Some of the advantages of the process are: A hard, rigid core and mold are typical of the

process, which gives the casting good dimensional tolerances;

good casting surface finishes are readily obtainable;

Advantages of metal casting:

Casting is one of the most versatilemanufacturing process.

Casting provides the greatest freedom ofdesign in terms of shape, size and theproduct quantity.

Casting imparts uniform directionalproperties and better vibration capacity tothe cast parts.

Casting produces machinable parts.

Shapes difficult and uneconomic to obtainotherwise may be achieved through castingprocess.

( Contd..)

A product may be cast as one piece, there by

eliminating the need of metal joining

processes.

Very heavy and bulky parts which are

otherwise difficult to get fabricated may be

cast.

Metals (like cast iron) difficult to be shaped by

other manufacturing processes may be cast.

Casting can be designed for equal distribution

of loads and for minimum stress concentration

in order to achieve more strength and

increased service life.

Casting process can be mechanized and

usefully employed for mass production of

components.

Limitations of metal casting: Dimensional accuracy and surface finish of the

castings made by sand casting processes are a

limitation to this technique.

Many new casting processes have been

developed which can take into consideration the

aspects of dimensional accuracy and surface

finish.

Some of these processes are die casting process,

investment casting process, vacuum-sealed

molding process, and shell molding process.

The metal casting process is a labor intensive

process

Applications of Casting:

Transportation vehicles

Turbine vanes

Power generators

Railway crossings

Agricultural parts

Aircraft jet engine parts

Sanitary fittings

Communication, Construction and Atomic Energy applications, etc..

Different Sections in Foundry:

1) Pattern making

2) Sand mixing & preparation

3) Mould and core making

4) Mould assembly & handling

5) Melting

6) Pouring

7) Shaking out

8) Fettling & finishing

9) Heat treatment

10) Inspection & testing

Reference:1. A text book of Production Technology Vol. I /

O.P. Khanna / Dhanpat Rai Publications

2. A text book of Production Technology (Manufacturing Processes) / P. C. Sharma / S. Chand & Company Ltd

3. Manufacturing Technology (Second Edition) / P N Rao / Tata McGraw-Hill Publishing Company Ltd

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http://nptel.iitm.ac.in/