Manufacturing Practices (BT-106) - Important Questions

Explain the mechanics of orthogonal cutting. Using the shear plane model, derive the relationship between cutting force, shear stress and shear plane area. Discuss assumptions of the model and limitations in practical machining.

For a turning operation, derive the expression for material removal rate (MRR). Calculate the MRR in $\mathrm{mm^3/min}$ when work diameter $D=100\ \mathrm{mm}$, spindle speed $N=600\ \mathrm{rpm}$, feed per revolution $f=0.2\ \mathrm{mm/rev}$ and depth of cut $d=2\ \mathrm{mm}$. Use the appropriate formula for turning and show all steps.

Define and explain the significance of cutting tool geometry parameters: rake angle, clearance (relief) angle, cutting edge angle and nose radius. Discuss how each parameter affects cutting forces, chip flow and surface finish.

Compare the common cutting tool materials: High Speed Steel (HSS), Cemented Carbide, Ceramic, Cubic Boron Nitride (CBN) and Polycrystalline Diamond (PCD). For each material discuss typical applications, advantages and limitations.

State Taylor's tool life equation and explain the physical meaning of each term. A tool manufacturer gives $\:V T^{n}=C\:$ with $n=0.2$ and $C=250$. Calculate the tool life $T$ when cutting speed $V=50\ \mathrm{m/min}$. Also calculate the cutting speed for a desired tool life of $T=30\ \mathrm{min}$.

Derive the approximate relation between average surface roughness $R_{a}$, feed per revolution $f$ and tool nose radius $r$ for turning. Use the commonly used approximation $R_{a}\approx \frac{f^{2}}{8r}$ and explain assumptions. Calculate $R_{a}$ when $f=0.25\ \mathrm{mm/rev}$ and $r=0.8\ \mathrm{mm}$.

Describe the different types of chips formed in metal cutting: continuous, discontinuous (segmented), and built-up edge (BUE). Explain the conditions under which each type is formed and their practical consequences.

A face milling cutter of diameter $D=80\ \mathrm{mm}$ has $Z=8$ teeth. The desired cutting speed is $V=60\ \mathrm{m/min}$ and feed per tooth $f_{z}=0.08\ \mathrm{mm/tooth}$. Calculate the spindle speed $N$ in $\mathrm{rpm}$ and the table feed $V_{f}$ in $\mathrm{mm/min}$. Also compute the theoretical metal removal rate (MRR) assuming depth of cut $d=3\ \mathrm{mm}$ and full width of cut.

Explain the principles of grinding. Describe the characteristics of a grinding wheel (abrasive type, grit size, bond, grade and structure) and explain the purpose and methods of wheel dressing and balancing.

Enumerate the functions of cutting fluids (coolants and lubricants) in machining operations. Discuss methods of application and key selection criteria for cutting fluids.

A batch of 500 identical turned parts is to be produced. For each part, rough turning requires a lengthwise cut of 100\ \mathrm{mm} at feed $f=0.25\ \mathrm{mm/rev}$ with spindle speed $N=900\ \mathrm{rpm}$. Calculate the cutting time per part and the total cutting time for the batch. If the machine operating cost is $$20$ per hour, compute the machining cost for the batch (ignore tool change and non-cutting times).

Compare conventional (manual) machining and CNC machining in terms of accuracy, productivity, flexibility, initial investment and typical applications. Discuss situations where each is preferred.