JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II Year MANUFACTURING PROCESS Previous Question Paper (July/August - 2021 - R16)

Casting is a primary manufacturing process in the automobile industry due to its ability to produce complex, near-net-shape components with varying mechanical properties. Typical applications include:

• Engine Components: Cylinder blocks, cylinder heads, pistons, and intake manifolds are commonly cast from aluminum or cast iron to withstand high thermal and mechanical loads.
• Transmission Parts: Gearbox housings, clutch housings, and transmission cases are typically produced using die casting for high dimensional accuracy and strength-to-weight ratios.
• Suspension and Steering: Steering knuckles, control arms, and wheel hubs are often cast to provide the necessary structural integrity and fatigue resistance.
• Braking Systems: Brake drums and brake calipers are frequently manufactured using gray or ductile iron castings due to their excellent wear resistance and thermal conductivity.
• Structural Parts: Engine mounts and various chassis brackets are cast to integrate multiple functions into a single, robust component.

Shrinkage cavities in steel castings occur during the liquid-to-solid phase transformation. As molten steel cools, it undergoes significant volumetric contraction. If the solidification front moves such that isolated pockets of liquid metal are trapped and cut off from the supply of molten metal, a void or cavity forms, typically at the thermal center or the last part to solidify.

To eliminate or reduce shrinkage cavities, the following methods are employed:

• Directional Solidification: Design the casting so that solidification proceeds from the thinnest sections toward the thickest sections, ensuring the thickest parts are connected to a reservoir.
• Use of Risers: Attach appropriately sized risers (feeders) to the thickest sections of the casting. These act as reservoirs of molten metal that feed the shrinkage demand of the casting as it cools.
• Chills: Place external metallic chills against the mold walls near thick sections to accelerate the cooling rate, forcing the solidification front to move toward the riser.
• Padding: Add extra metal (padding) to thin sections to ensure a continuous thermal gradient toward the riser, preventing premature solidification that would block the feed path.
• Insulating/Exothermic Sleeves: Use sleeves around the riser to keep the riser metal molten for a longer duration, ensuring it remains available to feed the casting until the entire part has solidified.