Manufacturing Practices (BT-106) - Important Questions

Describe the classification of patterns used in foundry practice. Explain the materials commonly used for pattern making and discuss the various allowances provided on patterns including $\text{shrinkage allowance}$, $\text{machining allowance}$ and $\text{draw/draft}$.

Discuss the composition of molding sand and explain the importance of each component. Describe the standard tests for moulding sand, namely permeability test, compressive strength test and compactibility test, and explain how the results influence mould quality.

Explain the core making process in casting. Describe the types of core materials, core prints, core boxes and the common core-making methods (hand core, sand core with cold-box and shell core).

What is a gating system in sand casting? Explain the functions of a gating system and describe common elements (sprue, runner, gate, riser). Discuss the principles for designing a gating system to minimize turbulence and defects.

Explain the purpose of risers (feeders) in casting and classify types of risers. State Chvorinov's rule for solidification time and explain how it is used in riser design. Provide the Chvorinov relation: $$t = C \left( \frac{V}{A} \right)^{2}$$ where $t$ is the solidification time, $V$ is the volume and $A$ is the surface area.

Define directional solidification. Explain how directional solidification is achieved in castings and how it helps to avoid shrinkage defects.

List common casting defects (such as blowholes, porosity, cold shuts, misruns, shrinkage, inclusion defects and hot tearing). For each defect, explain the typical causes and suggest remedial measures to prevent it.

Compare the following casting processes: green sand casting, shell moulding, investment (lost-wax) casting and die casting. For each process, state the principle, advantages, limitations and typical applications.

Explain die casting. Differentiate between hot-chamber and cold-chamber die casting machines, mentioning working principle, suitable alloys and advantages/disadvantages of each.

Describe the working principles, advantages and limitations of the following melting furnaces used in foundries: cupola furnace, induction melting furnace and electric resistance (crucible) furnace.

Using Chvorinov's rule $$t = C \left( \frac{V}{A} \right)^{2}$$ calculate the solidification time $t$ for a casting having volume $V = 2.0\times 10^{-3}\,\text{m}^{3}$ and surface area $A = 0.12\,\text{m}^{2}$ given the mould constant $C = 0.45\,\text{s}\,\text{m}^{-2}$. (Do not perform rounding beyond appropriate significant figures.)

Discuss typical defects related to cores (such as core blow, core wash and core shift). Explain the causes of these defects and the preventive measures used in core production and moulding practice.