JNTU
JNTU B.Tech II PRODUCTION TECHNOLOGY Previous Question Paper (July/August - 2021 - R13)
Answer any five questions. All questions carry equal marks.
Main
Explain the principle of investment casting process with neat sketch. Also discuss the advantages, limitations and applications of investment casting process.
Answer
Investment casting, also known as the lost-wax process, is a precision casting method that produces complex, high-accuracy parts by using a disposable wax pattern coated in a ceramic shell. The process begins by creating a wax pattern of the desired part, which is then attached to a wax gating system to form a tree assembly. This assembly is dipped into a ceramic slurry and coated with fine sand (stucco) repeatedly to build a strong, heat-resistant shell. Once the shell hardens, it is heated in an autoclave or furnace to melt and remove the wax, leaving a hollow cavity. The ceramic mold is then fired to increase its strength and preheated before molten metal is poured into it. After the metal solidifies, the ceramic shell is broken away to reveal the finished casting.
A typical sketch would show the following sequence: (1) Wax pattern injection, (2) Wax tree assembly, (3) Ceramic shell coating (dipping and stuccoing), (4) Dewaxing (melting out the wax), (5) Firing the mold, (6) Pouring molten metal, and (7) Knockout and cleaning of the final metal part.
Advantages:
- Capable of producing extremely complex shapes with intricate details that are difficult to machine.
- Excellent surface finish and high dimensional accuracy, often eliminating the need for further machining.
- Suitable for a wide range of metals and alloys, including those that are difficult to forge or machine (e.g., superalloys).
- Minimal material waste due to the precision of the near-net-shape casting.
Limitations:
- High production cost per unit due to the labor-intensive process and expensive mold materials.
- Limited by size and weight; generally unsuitable for very large or heavy castings.
- Long lead times for pattern production and shell preparation.
- Not economically viable for low-complexity parts that could be produced by simpler casting methods.
Applications:
- Aerospace components like turbine blades and nozzle guide vanes.
- Medical implants such as artificial joints and dental prosthetics.
- Intricate components for firearms, jewelry, and high-performance automotive engines.
- Precision parts for instruments and complex industrial machinery.
Illustrate and describe the process of Die casting.
Answer
Die casting is a permanent mold casting process where molten metal is forced under high pressure into a metallic mold cavity, known as a die. The process involves injecting molten metal into the die at high velocities, followed by rapid solidification under pressure to ensure high dimensional accuracy and surface finish.
Key steps include:
- The die is cleaned and lubricated to facilitate part ejection.
- The die is closed and clamped tightly.
- Molten metal is injected into the die cavity using a plunger or piston system.
- The metal is held under pressure until it solidifies.
- The die is opened, and the casting is ejected using ejector pins.
There are two primary types: Hot-chamber die casting, where the injection mechanism is submerged in the molten metal, suitable for low-melting-point alloys like zinc; and Cold-chamber die casting, where molten metal is ladled into the injection chamber, used for high-melting-point alloys like aluminum and copper.
Explain different types of allowances used in patterns making.
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The voltage-length characteristics of a DC arc is given by
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Explain the process of forge welding.
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Compare and distinguish spot welding and projection welding.
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Explain the principle of thermit welding with applications, advantages and limitations.
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Write the principle of operation along with application, advantages and limitations of explosive welding process.
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What is magnetic arc blow? Mention the causes and remedies of for magnetic arc blow.
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Write the principle of operation along with applications, advantages and limitations of TIG welding process.
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Discuss the possible defects and reasons for them in welding.
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Write a note on control of hot rolling mills.
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A number of cold rolling passes are required in a two high rolling mill to reduce the thickness of a plate from 50mm to 20mm. The roll diameter of 700mm and the coefficient of friction at the roll work interface is 0.1. It is required that the draft in each pass must be the same. Assuming no front and back tensions, determine, the minimum no. of passes and the draft in each pass.
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What are the various equipment used in extrusion of metals? Briefly describe them.
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Write the expression for determining the force required to produce an extrusion and discuss the effect of various parameters on the extruding force.
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