JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II AIRCRAFT PRODUCTION TECHNOLOGY Previous Question Paper (October - 2020 - R16)
Answer any five questions
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Main
Explain the steps used in investment casting with neat sketches. Also discuss the applications, advantages and disadvantages of investment casting.
Answer
Investment casting, also known as the lost-wax process, is a precision casting technique used to produce complex, near-net-shape components with excellent surface finish and dimensional accuracy. The process involves the following sequential steps:
- Pattern Creation: Wax patterns are produced by injecting molten wax into a metal die. For complex shapes, multiple wax parts may be assembled into a single pattern cluster.
- Tree Assembly: Individual wax patterns are attached to a central wax sprue and runner system to form a 'tree' or cluster, allowing multiple parts to be cast simultaneously.
- Investment (Shell Building): The wax cluster is dipped into a ceramic slurry and then coated with fine sand (stucco). This process is repeated several times to build a thick, strong ceramic shell around the wax patterns.
- Dewaxing: The ceramic shell is placed in an oven or autoclave, where the wax melts and drains out, leaving a hollow cavity that corresponds to the desired part shape.
- Firing: The empty ceramic shell is fired at high temperatures to harden the ceramic and remove any residual wax, ensuring the mold is ready for pouring.
- Pouring: Molten metal is poured into the preheated ceramic shell. Preheating helps the metal flow into thin sections and reduces thermal shock.
- Knockout and Finishing: Once the metal solidifies, the ceramic shell is broken away (knockout). The individual parts are cut from the sprue, and the gates are ground off and finished.
Advantages: It offers exceptional dimensional accuracy and surface finish, allows for the casting of intricate geometries that are impossible to machine, and is suitable for almost any alloy, including high-melting-point metals like superalloys.
Disadvantages: The process is relatively expensive due to the cost of dies and the labor-intensive nature of shell building, and it is generally limited to smaller parts and lower production rates compared to sand casting.
Applications: It is widely used in the aerospace industry for turbine blades, impellers, and engine components, as well as in the medical field for surgical implants and in the automotive industry for high-performance engine parts.
Explain about the types of soldering.
Answer
Soldering is a metal joining process where a filler metal with a melting point below 450°C is melted and distributed between two or more close-fitting parts. The primary types of soldering are:
- Soft Soldering: Uses lead-tin alloys as filler metal. It is performed at temperatures below 450°C and is commonly used for electrical connections and sheet metal work where high mechanical strength is not required.
- Hard Soldering (Brazing): Performed at temperatures above 450°C using filler metals like silver or copper alloys. It provides significantly higher joint strength than soft soldering.
- Silver Soldering: A specific type of hard soldering using silver-based alloys, offering excellent corrosion resistance and high strength, often used in precision engineering and aircraft components.
- Sweat Soldering: A technique where surfaces are tinned individually, placed together, and then heated until the solder melts and creates a bond between the surfaces.
Discuss about the steps used in moulding with a neat sketch.
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Explain the various parts and working principle of drilling machine with a neat sketch.
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Explain about the following:
a) Punching b) Drawing c) Spinning d) Bending e) Louvering.
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Explain about ECM process with its advantages, disadvantages and applications.
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Explain the working principle of abrasive jet machining with a neat sketch.
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Explain about the X-Ray and holography technique for testing.
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Explain about the particle size distribution in additive manufacturing.
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Discuss about the physical properties of powder materials used in AM.
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