Manufacturing Practices (BT-106) - Important Questions

Explain the principle and working of a centre lathe. Describe the following lathe operations with neat sketches: facing, turning, parting, grooving, taper turning and knurling. Also list typical cutting tool nomenclature and tool signature.

Derive the relation between cutting speed $V$ (in m/min), spindle speed $N$ (in rev/min) and workpiece diameter $D$ (in mm). Hence obtain the formula for spindle speed

$$N=\frac{1000\,V}{\left(\pi\,D\right)}$$

Using this relation, derive the expression for machining time $T$ (in minutes) for a turning operation given job length $L$ (mm), feed per revolution $f$ (mm/rev) and spindle speed $N$. Show all steps and give the final formula for $T$.

State and derive Taylor's tool life equation. Explain the significance of the constants in the equation

$$V\,T^{n}=C$$

where $V$ is cutting speed, $T$ is tool life, $n$ and $C$ are constants. Show how to determine the exponent $n$ from experimental data and solve a numerical example to compute tool life for a given change in cutting speed.

Explain the classification and principle of milling operations. Describe up milling and down milling and list common milling cutters with their applications. Derive the expression for material removal rate (MRR) in milling and show it in the form

$$MRR=\frac{w\,d\,f_{t}\,N}{60}$$

where $w$ is width of cut (mm), $d$ is depth of cut (mm), $f_{t}$ is feed per tooth (mm/tooth) and $N$ is spindle speed (rev/min).

Describe the principle of drilling and list types of drills (twist drill variations) and point geometries. Explain common drilling problems (e.g., chip packing, drill wandering, poor surface finish) and remedies. Derive the formula for drilling time for a given hole depth $L$, feed per revolution $f$ and spindle speed $N$, and express it as an equation.

Compare the properties, advantages and typical applications of the following cutting tool materials: High Speed Steel (HSS), Cemented Carbide (tungsten carbide), Ceramic tools and Cermets. Discuss the effect of each material on cutting speed, wear resistance and cost.

Explain the grinding process and classify grinding operations (surface grinding, cylindrical grinding, internal grinding, centerless grinding). Describe grinding wheel specifications and marking (example: A60K5V). Define dressing and truing. Also explain surface roughness parameter $R_{a}$ and methods to improve surface finish.

Describe the common mechanisms of tool wear in machining (abrasive, adhesive, diffusion, oxidation and plastic deformation). Explain methods to reduce tool wear including tool geometry changes, coatings and use of cutting fluids.

Discuss the functions of cutting fluids in machining. List types of cutting fluids, selection criteria for a given operation and environmental/health considerations. Briefly describe the concept and advantages of Minimum Quantity Lubrication (MQL).

Give an introduction to CNC machining. Describe machine coordinate systems, the role of G-codes and M-codes, and the basic structure of a simple G-code program to face a job on a CNC lathe or perform a simple contour milling pass. Discuss advantages of CNC over conventional machines.