CAD/CAM /CIM (ME-704) - Important Questions

Explain the principle of CNC interpolation. Differentiate between linear and circular interpolation in CNC machines and discuss how the controller generates axis commands to realize these motions. Describe the mathematical basis used by CNC controllers to convert a circular arc defined by center and radius into incremental axis motions.

Write a complete CNC part program (G and M codes) for milling a rectangular pocket $80\,\text{mm}\times 60\,\text{mm}$ to a depth of $10\,\text{mm}$ using a $12\,\text{mm}$ endmill. Include tool change, spindle speed, coolant on/off, roughing and finishing passes, and program comments. Specify feed and spindle speed calculations where required.

Explain cutter radius compensation in CNC milling. For a given straight line segment from point $P_1(x_1,y_1)$ to $P_2(x_2,y_2)$ and a cutter of radius $R$, show how the tool center path is offset from the programmed path. Provide the expression for the offset vector normal to the segment and explain how the sign of compensation affects the offset direction.

Calculate the spindle speed $N$ (in rpm), feed rate $V_f$ (in mm/min), and machining time $T_m$ (in min) for a turning operation given the following data: cutting speed $V$ in m/min, work diameter $D$ in mm, length of cut $L$ in mm, and feed per revolution $f$ in mm/rev. Use the standard relations for turning and show the formulas used. $$N = \frac{1000\,V}{\pi\,D}$$ $$V_f = f\,N$$ $$T_m = \frac{L}{V_f}$$ Then compute numerical values for $V=120\,\text{m/min}$, $D=50\,\text{mm}$, $L=200\,\text{mm}$ and $f=0.2\,\text{mm/rev}$.

Describe canned cycles used in CNC drilling operations. Explain the purpose of peck drilling (G83) and write an example G-code block to drill a hole to depth $-25\,\text{mm}$ with peck depth $5\,\text{mm}$, include dwell and retract parameters.

Explain the role of a post-processor in a CAM system. List the typical data transformations performed when converting generic CAM toolpaths into machine-specific NC code and discuss common issues encountered when post-processing for machines with rotary or compound axes.

Discuss toolpath strategies used in 3-axis milling for roughing and finishing free-form surfaces. Compare zigzag (raster), offset (contour-parallel), and trochoidal toolpaths with respect to material removal rate, surface finish, tool load, and suitability for high-speed machining.

Explain parametric NC programming and the use of subprograms. Provide a concise example where a subprogram is written to drill a hole and is called multiple times with different coordinates or depths using parameters or looping constructs.

Describe the process of NC program verification and simulation before actual machining. List at least five common causes of tool collision and propose preventive measures that should be verified in the simulation stage.

Explain the coordinate systems used in CNC machines including machine coordinates, work (part) coordinates, and tool coordinate system. Describe methods to set a work offset such as $\text{G54}$ using touch-off and probing procedures and list the steps an operator follows to establish $\text{G54}$ for a new part.