Casting Process B.Tech Notes: It is a manufacturing process in which a liquid material is poured into a mold with a hollow cavity of the desired shape and then allowed to solidify. The solidified part is known as a casting, which is broken or ejected out of the mold to complete the process. Casting is widely used to create complex shapes that would be difficult or uneconomical to make by other methods.
Types of Casting Processes
Sand Casting – Casting Process B.Tech Notes
- Overview: Involves packing sand around a pattern that is removed to leave a cavity in the sand mold.
- Advantages: Low cost, adaptable to large sizes and complex shapes.
- Disadvantages: Poor surface finish, large grain size, less accurate dimensions.
Investment Casting (Lost Wax Casting)
- Overview: Uses a wax pattern coated with a refractory ceramic material. Once the ceramic material hardens, the wax is melted out, creating a mold cavity.
- Advantages: High precision, excellent surface finish, can produce complex geometries.
- Disadvantages: Higher cost, time-consuming process.
Die Casting
- Overview: Involves forcing molten metal under high pressure into a mold cavity. The molds are usually made of high-quality steel.
- Advantages: High production rates, excellent dimensional accuracy, smooth cast surfaces.
- Disadvantages: High tooling costs, limited to metals with low melting points.
Centrifugal Casting
- Overview: Uses a rotating mold to create parts with a cylindrical shape. The centrifugal force pushes the molten metal against the mold walls.
- Advantages: High material purity, excellent mechanical properties, good dimensional accuracy.
- Disadvantages: Limited to cylindrical shapes, high equipment cost.
Continuous Casting
Casting Process B.Tech Notes
- Overview: Molten metal is continuously poured into a mold and solidified as it is drawn out of the mold.
- Advantages: High efficiency, good surface finish, consistent quality.
- Disadvantages: High initial cost, complex setup.
Casting Materials
Ferrous Metals
- Cast Iron: Good fluidity, excellent machinability, widely used for engine blocks and machinery.
- Steel: Strong, tough, used for critical applications like structural components and tools.
Non-Ferrous Metals – Casting Process B.Tech Notes
- Aluminum: Lightweight, good corrosion resistance, used for automotive and aerospace components.
- Copper Alloys: Good thermal and electrical conductivity, used in plumbing and electrical applications.
- Zinc: Low melting point, good for die casting, used in automotive and hardware components.
Steps in the Casting Process
Pattern Making | Casting Process B.Tech Notes
- Creating an exact replica of the final product to form the mold cavity.
- Materials used: Wood, plastic, metal.
Mold and Core Making
- Preparing the mold that holds the cavity for casting. Cores are used to create hollow sections within the casting.
- Sand molds, ceramic molds, metal molds are commonly used.
Melting and Pouring
Melting the metal in a furnace and pouring it into the mold cavity.
Types of furnaces: Cupola, electric arc, induction.
Solidification and Cooling
- Allowing the molten metal to solidify and cool within the mold.
- Cooling rates affect grain structure and mechanical properties.
Shakeout and Fettling – Casting Process B.Tech Notes
- Removing the casting from the mold and cleaning off excess material.
- Processes include removing gates, risers, and parting lines.
Heat Treatment
Optional step to enhance mechanical properties through processes like annealing, quenching, and tempering.
Inspection and Testing
Ensuring the casting meets quality standards through visual inspection, dimensional checks, and non-destructive testing methods (e.g., X-ray, ultrasonic).
Defects in Castings
Porosity | Casting Process B.Tech Notes
- Caused by trapped gas bubbles or shrinkage during solidification.
- Solutions: Improved mold design, proper venting, controlled pouring.
Inclusions
- Non-metallic materials trapped within the casting.
- Solutions: Clean molten metal, proper gating and filtration.
Cold Shuts – Casting Process B.Tech Notes
- Incomplete fusion where two streams of molten metal meet.
- Solutions: Increased pouring temperature, better gating design.
Hot Tears – Casting Process B.Tech Notes
- Cracks formed due to restrained contraction during solidification.
- Solutions: Proper mold design, controlled cooling rates.
Misruns | Casting Process B.Tech Notes
- Incomplete filling of the mold cavity.
- Solutions: Increased pouring temperature, better gating system, adequate venting.
Conclusion | Casting Process B.Tech Notes
Casting is a versatile manufacturing process capable of producing a wide range of complex shapes and sizes. By understanding the different casting methods, materials, and potential defects, manufacturers can optimize the process to produce high-quality castings efficiently. The choice of casting process depends on factors such as the type of material, desired properties, production volume, and cost considerations.
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