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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