1. METAL CASTING
LECTURE 12

2. CASTING Basically involves
i. Pouring molten metal into a mould patterned after the part to be made WITHOUT TURBULANCE , SERIES OF EVENTS TAKES PLACE
INFLUENCE SIZE, SHAPE, UNIFORMITY OF THE GRAINS FORMED,
AND THUS THE OVERALL PROPERTIES.
ii. Allow it to cool HEAT TRANSFER DURING SOLIDIFICATION
iii. Remove from the mold INFLUENCE OF THE TYPE OF MOULD MATERIAL
SIMILARITY WITH POURING CAKE MIX INTO A PAN

3. POURING CAKE MIX INTO A PAN (MOULD) & BAKING IT
POURING CAKE MIX INTO A PAN (MOULD) & BAKING IT   *SELECT THE KIND AND SIZE OF PAN, *CONTROL THE COMPOSITION OF THE MIX, * CAREFULLY POUR THE MIX, * SET THE PROPER BAKING TEMPERATURE, * SET THE TIMER FOR PROPER BAKING TIME, * LEAVE THE CAKE IN THE MOULD FOR A CERTAIN AMOUNT OF TIME BEFORE REMOVING.   (CASTING OF PLASTICS & CERAMICS - DIFFERENT)

4. Knowledge of certain fundamental relationships is essential to produce good quality economic castings This knowledge helps in establishing proper techniques for mould design and casting practice.   Castings must be free from defects, must meet the required strength, dimensional accuracy, surface finish

5. ADVANTAGES OF CASTING PROCESS
Process is cheap
More suitable for mass production
Most suitable for manufacturing complex/complicated/intricate shaped products.
Large parts weighing several tonnes and also small components weighing a few grams can be cast.
No limitation on the size of component.
Directional properties absent in castings. Components with uniform properties as well as with varying properties at different locations can be cast.
By use of cores, saving in machining of holes achieved.
Internal stresses are relieved during solidification in many types of castings.
Even some materials which cannot be made by other processes made by casting: eg. Phosphor-Bronze.

6. Outline of production steps in a typical sand casting operation
- pattern making - Core making - Gating system
Moulding
Mould
Sand
Melting
Pouring
casting
Heat Treat
Clean
Inspect
Furnaces
Solidification
Shakeout
Addl. Heat Treatment
Defects, pressure tightness, dimensions
Outline of production steps in a typical sand casting operation

7. PATTERN
Model of a casting constructed such that it forms an impression in moulding sand

8. PATTERN 1st step- Prepare model (pattern) Differs from the casting
Differences Pattern Allowances.
To compensate for metal shrinkage,
Provide sufficient metal for machining
Easiness in moulding
As Shrinkage allowance, Draft allowance, Finishing allowance, Distortion or camber allowance, Shaking or rapping allowance

9. MATERIAL Types- many WOOD. METAL Al, CI, Brass,
3. For special casting processes, Polystyrene which leaves mould as gas when heated also used.
Types- many
Simple-Identical patterns; Complex, intricate- with number of pieces. Single or loose piece; Split; gated; Match Plate; Sweep; Segmental; Skeleton(frame, ribbed), skell; Boxed Up; Odd shaped etc. Sketches

10. Material
1. WOOD. (+) Cheap, easily available, light, easiness in surfacing, preserving (by shellac coating), workable, ease in joining, fabrication (-) Moisture effects, wear by sand abrasion, warp during forming, not for rough use. Must be properly dried/ seasoned, free from knots, straight grained Egs. Burma teak, pine wood, mahogany, Sal, Deodar, Shisham, Walnut, Apple tree

11. 2. METAL: For durability, strength Egs: Al alloys, Brass, Mg alloys, Steel, cast Iron for mass production (first, wooden pattern is made, then cast in the metal) Type of material depends on shape, size, number of castings required, method of moulding etc.