Jawaharlal Nehru Technological University Hyderabad B.Tech II Year MANUFACTURING PROCESS Previous Question Paper (August/September - 2022 - R16)

The gating system refers to the network of channels that delivers molten metal from the pouring basin into the mold cavity. Its primary principle is to ensure the metal enters the cavity at a controlled rate, with minimal turbulence, and without trapping gases or slag, while maintaining a thermal gradient that promotes directional solidification.

A well-designed gating system must satisfy the following: the metal should enter the mold without eroding the sand, the system should be filled completely to prevent air aspiration, and the flow rate should be sufficient to fill the cavity before the metal begins to solidify.

For most non-ferrous alloys and high-quality gray iron castings, a pressurized gating system is preferred. A common, effective gating ratio is 1 : 2 : 2 (Sprue area : Runner area : Ingate area). This ratio helps in maintaining a slight back-pressure, which minimizes turbulence and prevents the aspiration of air into the molten metal stream, leading to a cleaner and more sound casting.

In die casting, molten metal is forced into a permanent metal mold (die) under high pressure. The process involves injecting the metal at high velocity into the die cavity, where it is held under pressure until it solidifies. The die is then opened, and the casting is ejected.

The advantages of die casting include:

• High production rates and excellent dimensional accuracy.
• Ability to produce complex shapes with thin walls.
• Superior surface finish, often eliminating the need for secondary machining.
• Long die life, making it economical for mass production.

The disadvantages include:

• High initial cost of dies and equipment, making it unsuitable for small production batches.
• Limited to non-ferrous alloys with lower melting points (e.g., aluminum, zinc, magnesium).
• Risk of gas porosity due to the high-velocity injection of metal.
• Size limitations on the castings that can be produced.