Manufacturing Practices (BT-106) - Important Questions

Explain the principle and main parts of a centre lathe. Describe common turning operations performed on a lathe. State and derive the relationship between cutting speed $V$, spindle speed $N$ and work diameter $D$, and give the formula for metal removal rate (MRR) in turning. Use standard symbols and units.

A cylindrical job of diameter $D=100\ \text{mm}$ is to be turned to a finish diameter of $90\ \text{mm}$. The spindle speed is $N=200\ \text{rev/min}$ and feed per revolution is $f=0.25\ \text{mm/rev}$. Depth of cut per pass $d=0.5\ \text{mm}$. Calculate:

1. Cutting speed $V$ in $\text{m/min}$ using $V = \frac{\pi D N}{1000}$.

2. Material removal rate (MRR) in $\text{mm}^3/\text{min}$ using $\text{MRR} = \frac{\pi D N f d}{60}$.

3. Time required (in minutes) to remove the required material assuming the number of passes needed and that roughing is continuous.

Explain the difference between up-milling (conventional milling) and down-milling (climb milling). State advantages and disadvantages of each. Describe typical applications for both methods and specify how cutting speed $V$ is related to cutter diameter $D$ and spindle speed $N$ using $V = \frac{\pi D N}{1000}$.

Describe the principal geometry features of a twist drill (point angle, helix angle, lip relief) and their effect on drilling performance. How do you compute spindle speed $N$ (rev/min) for drilling a hole of diameter $D$ at cutting speed $V$? Provide the formula and explain the effect of feed per revolution on drilling time and chip evacuation.

Explain the classification of grinding wheels with respect to abrasive material, grit size, grade, structure and bond. Describe the purposes and procedures of dressing and truing a grinding wheel. Discuss criteria for selecting a grinding wheel for finishing hardened steels.

Compare tool materials used in machining: High Speed Steel (HSS), Cemented Carbide, Ceramic, Cubic Boron Nitride (CBN) and Polycrystalline Diamond (PCD). For each material state key properties, typical applications and limitations. Explain why coated tools (e.g., TiN, Al2O3) improve tool life.

Define cutting force components in a turning operation and explain how cutting power is calculated. If the main cutting force is $F_c$ (in N) and cutting speed is $V$ (in m/min), write the formula for cutting power $P$ in kW and explain unit conversions. Use the expression $P\ (\text{kW}) = \frac{F_c V}{60\,000}$ and show intermediate unit conversion steps.

Explain Taylor's tool life equation and its significance in selecting cutting speeds. State the equation in the form $V T^{n} = C$ and define each symbol. Given two sets of cutting data, show how to determine the tool life exponent $n$ and constant $C$ and compute the cutting speed for a desired tool life.

What factors influence surface finish in turning and milling operations? Describe how feed, tool nose radius and cutting speed affect surface roughness. State common methods to measure surface roughness and the meaning of $R_a$.

List and explain major safety precautions to be followed while working on lathes, milling machines and grinding machines. Outline a preventive maintenance checklist for a machining centre including lubrication, alignment checks and wheel balancing.

Differentiate between conventional machining and CNC machining. Give examples of common G-codes and M-codes used in CNC turning or milling and explain their basic functions. Describe the advantages of CNC machines over conventional machines for repetitive production.

Explain the purpose of jigs and fixtures in machining. Describe the principles of location and clamping, and list design considerations when creating a fixture for turning or milling operations.