Casting & Its types in metals

Presented byHasnain nazir sherwani

B.Sc mechanical engineering

Swedish college of engineering and technology,wah cantt.

• Casting is the process of producing metal/alloy component parts of desired shapes by pouring the molten metal/alloy into a prepared mold (of that shape) and then allowing the metal/alloy to cool and solidify. The solidified piece of metal/alloy is known as a CASTING or FOUNDRY”.

EXAMPLES OF CAST PARTS

Crank handle formed by casting; some areas were machined and assembled after casting

EXAMPLES OF CAST PARTS

Complex part formed by casting

CASTING TERMINOLOGYFlask

The box containing the mold

Cope

The top half of any part of a 2-part mold

Drag

The bottom half of any part of a 2-part mold

Core

A shape inserted into the mold to form internal cavities

Mold Cavity

Hollow mold area in which metal solidifies

Riser

Extra cavity to store additional metal to prevent shrinkage

Gating System

Channels used to deliver metal into the mold cavity

Pouring Cup

The part of the gating system that receives poured metal

Sprue

Vertical channel

Runners

Horizontal channels

Parting Line / Parting Surface

Separate the cope and drag of a 2-part mold

Draft

Taper on a pattern that allows removal from the mold

Casting

The process and product of solidifying metal in a mold

CATEGORIES OF METAL CASTING PROCESSES1. Expendable mold processes - mold is sacrificed to remove part

TYPES: Sand Casting, Shell mold Casting,, Mold Casting,

Investment Casting

• Advantage: more complex shapes possible

• Disadvantage: production rates often limited by time to make mold rather than casting itself

2. Permanent mold processes - mold is made of metal and can be used to make many castings

TYPES:Die Casting, Permanent Mold Casting, Centrifugal Casting

• Advantage: higher production rates

• Disadvantage: geometries limited by need to open mold

Process Advantages Disadvantages Examples

Sand Wide range of metals, sizes, shapes, low cost

poor finish, wide tolerance

engine blocks, cylinder heads

Shell mold better accuracy, finish, higher production rate

limited part size connecting rods, gear housings

Expendable pattern

Wide range of metals, sizes, shapes

patterns have low strength

cylinder heads, brake components

Plaster mold complex shapes, good surface finish

non-ferrous metals, low production rate

prototypes of mechanical parts

Ceramic mold complex shapes, high accuracy, good finish

small sizes impellers, injection mold tooling

Investment complex shapes, excellent finish

small parts, expensive jewellery

Permanent mold good finish, low porosity, high production rate

Costly mold, simpler shapes only

gears, gear housings

Die Excellent dimensional accuracy, high production rate

costly dies, small parts, non-ferrous metals

precision gears, camera bodies, car wheels

Centrifugal Large cylindrical parts, good quality

Expensive, limited shapes

pipes, boilers, flywheels

IMPORTANT METAL CASTING METHODS

• Sand CastingHigh Temperature Alloy, Complex Geometry, Rough Surface Finish

• Investment CastingHigh Temperature Alloy, Complex Geometry, Moderately Smooth Surface Finish

• Die CastingHigh Temperature Alloy, Moderate Geometry, Smooth Surface

SAND CASTING

• The most ancient , useful casting process

• Nearly all alloys can be sand casted ,

e.g. steel, nickel, titanium

• Mold can be used only one time

• Parts ranging in size from small to very large

• Production quantities from one to millions

• Sand casting typically has a low production rate.

• Use of a furnace, metal, pattern, and sand mold in this process

• Mold-making -

A sand mold is formed by packing sand into each half of the mold.

• Clamping -

Binding of the both halves of molds

• Pouring -

Molten metal ladled and poured into the mold.

• Cooling -

The solidification and cooling of molten metal for a predetermined solidification time

• Removal/Shakeout -

After predetermined time has passed, breaking the mold

• Trimming -

Removing the extra parts called flash by cutting from casting

Sand Casting process cycle

Factors effecting the quality of sand cast : Strength - Ability of the sand to maintain its shape.

Permeability - Ability to allow venting of trapped gases through the sand .Permeability is determined by the size and shape of the sand grains.

Thermal stability - Ability to resist damage, such as cracking, from the heat of the molten metal.

Collapsibility - Ability of the sand to collapse, or more accurately compress, .

Reusability - Ability of the sand to be reused for future sand molds.

• Advantages : Can produce very large parts.

Many material options.

Low tooling and equipment cost.

Scrap can be recycled.

Short lead time possible.

• Disadvantages: Poor material strength.

Poor surface finish and tolerance.

Secondary machining often required.

Low production rate.

High labor cost.

• Applications: Engine blocks and manifolds, machine bases, gears, pulleys

Aluminum piston for an internal combustion engine: as-cast and after machining.

• Investment casting is one of the oldest manufacturing processes

• molten metal is poured into an expendable ceramic mold

• The mold is formed by using a wax pattern

• Using ceramic slurry that hardens into the mold

• Investment casting also called "lost-wax casting"

• Lost -wax processes increases production time and cost

INVESTMENT CASTING

• Pattern creation -

• Mold creation -

• Immersing -

Investment Casting Process Cycle

(a) Wax pattern (pattern creation)

(b) Multiple patterns assembled to wax sprue

(c) Shell built immerse into ceramic slurry immerse into fine sand (few layers)

• Wax removal -

• Pouring -

• Casting removal -

(d) dry ceramic melt out the wax fire ceramic (burn wax)

(e) Pour molten metal (gravity) cool, solidify [Hollow casting: pouring excess metal before solidification

(f) Break ceramic shell (vibration or water blasting)

• Advantages: Can form complex shapes

Many material options

High strength parts

Excellent surface finish and accuracy

Little need for secondary machining

• Disadvantages:

Time Consuming process

High labor cost

High tooling cost

Long lead time possible

• Applications: Turbine blades, pipe fittings, lock parts, hand tools, jewelry.

• Produces geometrically complex metal parts

• Reusable molds used, called dies.

• A furnace, metal, die casting machine, and die is used

• The metal, typically a non-ferrous alloy such as aluminum or zinc, .

• After the molten metal is injected into the dies,

it rapidly cools and solidifies into the final part, called the casting.

DIE CASTING

• Clamping - Preparation, binding and clamping of mold

• Injection -Molten metal is transferred to the die

• Cooling - Solidification and cooling of molten metal

• Ejection - The removing of cast by hydraulic mechanism

• Trimming -. Cutting the extra metal by sawing

Die casting process cycle

DIE CASTING PROCESS

DIE CASTING EQUIPMENT • Two types of die casting machines are :-

• Hot chamber die casting machine

• Cold chamber die casting machine• PARTS FORMED BY DIE CASTING

HOT-CHAMBER DIE CASTING• Used for metal/alloys with low melting temperatures, such as zinc, tin,

and lead.

• Clamping of the die

• Molten metal poured in a chamber

• Injecting the metal by forcing plunger

• Metal flows through a goose neck

• Low pressure required around 1000 - 5000 psi

• After the solidification , ejection of cast part by hydraulic system .

Hot chamber die casting process1)Clamping. 2)Injection

3) Cooling

4) Ejection

Cold Chamber Die Casting

• Used for alloys with high melting temperatures e.g. aluminum

• Clamping the die

• Horizontally injection..

• High Pressure is required around 2000 - 20000 psi.

• Solidification for predetermined time

• After solidification, the part can be ejected by the clamping unit.

Cold chamber die casting process