Casting Process

The casting or foundering process is the oldest manufacturing process in which liquid molten metal is poured into a perforated casting cavity of refractory material. Allow liquid metal to solidify; after solidification, the casting metal can be removed by breaking the mold. The casting process produces pistons, mill rolls, wheels, cylinder blocks, liners, and machine tool beds.

Critical Steps in the Casting Process:

Pattern Making:

• A pattern (a replica of the final product design) is created using wood, plastic, or metal.
• This is used to form the cavity in the mold.

Mold Making:

• A mold is created by packing molding material (like sand, plaster, or metal) around the pattern.
• The mold includes a cavity shaped like the final product.

Melting:

• The material (e.g., metal or alloy) is heated in a furnace until it becomes liquid.

Pouring:

• The molten material is poured into the mold cavity through channels.

Cooling and Solidification:

• The liquid material cools and solidifies into the shape of the mold cavity.

Removing the Casting:

• Once solidified, the mold is removed. For sand molds, they are often broken apart.

Cleaning and Finishing:

• Excess material, like sprues and gates, is removed.
• The casting is cleaned, and additional processes (grinding, polishing, or machining) may be performed for final finishing.

Different terminology used in the casting process is molding sand, baking sand, facing sand, loam sand, parting sand, CO₂ sand, flak, pattern, parting line, sprue, runner, ingate, riser, chill, and chaplets.

Molding sand:
Molding sand is the refractory material used to make the mold. It is a mixture of silica, clay, and moisture to get the required properties.

Baking sand:
Baking sand consists of refractory material, and it is made of used sand or burnt sand.

Facing sand:
Facing sand is the carbonaceous material sprinkled on the inner surfaces of the molding cavity to obtain a better surface finish.

Loam Sand:
Gree or dry sand with at least 50% clay and dries hard is called loam sand. It also contains fire clay. It has 18 to 20% moisture and produces a good surface finish.

Parting sand:
Separating the molds from adhering to each other by separating a fine, sharp, dry sand called parting sand. It also can be used to keep green sand from sticking to the pattern. It is clean, clay-free silica sand.

CO₂ sand:
In the sand-in-place of clay, sodium silicate (Na₂SiO₃) is used, called Carbon dioxide (CO₂) sand. When the CO₂ is supplied into this sand, the CO₂ will chemically react with sodium.

Flak:
Flak is the molding box used for holding the sand. Based on the situation, it can be called cope, drag, cheek, etc.

Drag:
The lower molding flask is called drag.

Cope:
The upper molding flask is called cope.

Cheek:
The middle molding flask used in the three-piece pattern is called cheek.

Pattern:
The pattern is the replica of the casting to be produced.

Parting line:
The parting line is the dividing line between the two flasks.

Sprue:
Sprue is the connecting passage between the pouring basin and the runner. It controls the flow of molten metal.

Runner:
The runner is the passage used to regulate the flow of molten liquid.

Ingate:
The ingate is the last gating point where molten metal enters the cavity.

Riser:
The riser is the reservoir of molten metal provided in the casting process to compensate for the liquid shrinkage during solidification.

Chill:
Chill is the metallic piece used to obtain directional solidification.

Chaplets:
Chaplets support the cores inside the mold cavity to take care of its weight and the mold cavity to take care of its weight and overcome the buoyancy forces.

Advantages of the casting process:

• Molten metal flows into a small ant section in the molten cavity. Hence, any complex shape can be quickly produced.
• Practically any material can be cast.
• The ideal method is to produce small quantities.
• Due to the low cooling rate from all directions, the casting properties are the same.
• Any size of casting can be produced up to 200 tons.
• Casting is often the cheapest and most direct way of producing a shape with specific desired mechanical properties.
• Certain metals and alloys, such as highly creep-resistant metal-based alloys for gas turbines, cannot be worked mechanically and can be cast only.
• Heavy equipment like machine leads, ship’s propeller, etc., can be thrown easily in the required size rather than fabricating them by joining several small pieces.
• Casting is best suited for composite components requiring different properties in various directions. These are made by incorporating preferable inserts in a casting. For example, aluminum conductors into slots in iron armature for electric motors wear-resistant skins onto shock-resistant components.

Limitations of the casting process:

• The dimensional accuracies and surface finish are less than those in the normal sand casting process.
• Defects are unavoidable.
• Sand casting is labor-intensive.