Manufacturing Practices (BT-106) - Important Questions

Define accuracy, precision and measurement uncertainty. Explain different sources of uncertainty in measurements and outline a step-by-step procedure to estimate the combined standard uncertainty for a dimensional measurement.

Explain the working principle of a Coordinate Measuring Machine (CMM). Describe the main types of CMM probes, typical applications in manufacturing inspection and how a CMM is used to determine geometric form errors of a machined component.

Explain Statistical Process Control (SPC). For subgroup size $n$ samples, give formulas for control limits of the $\bar{x}$ (X-bar) and $R$ charts. Show the expressions for the upper and lower control limits of $\bar{x}$ and $R$ charts in terms of $\bar{\bar{x}}$, $\bar{R}$, $A_2$, $D_3$ and $D_4$. Also describe how to interpret common patterns of assignable causes from these charts.

Describe the single-sampling acceptance plan for inspection by attributes. Explain the meaning of Acceptance Quality Limit (AQL) and Lot Tolerance Percent Defective (LTPD). Given a lot size and an AQL, outline the method to determine sample size $n$ and acceptance number $c$ (no detailed table needed; describe the principles and decision criteria).

List and briefly explain four commonly used non-destructive testing (NDT) methods used in manufacturing (e.g., Radiography, Ultrasonic Testing, Magnetic Particle Testing, Dye Penetrant Testing). For each method state suitable materials, types of defects detectable, and typical advantages and limitations.

Explain the importance of calibration and traceability in metrology. Describe a standard calibration procedure for a 0–25 mm micrometer using gauge blocks and state how measurement results are made traceable to national standards.

Define the arithmetic average roughness $Ra$ and the mean peak-to-valley roughness $Rz$. Give the mathematical expression for $Ra$ for a surface profile $y(x)$ over evaluation length $L$ as an integral. Also describe the instruments commonly used to measure surface roughness.

Define runout, straightness and squareness errors in machine tools. Describe common causes of each and list methods used for detection and correction (for example use of dial indicators, laser alignment, test bars, and precision squares).

Describe control charts for attributes: the $p$-chart and the $c$-chart. Give the center line and the formulas for the upper and lower control limits for the $p$-chart: $$UCL_p = \bar{p} + 3 \sqrt{\frac{\bar{p} \left(1-\bar{p}\right)}{n}}, \quad LCL_p = \bar{p} - 3 \sqrt{\frac{\bar{p} \left(1-\bar{p}\right)}{n}}$$ and for the $c$-chart: $$UCL_c = \bar{c} + 3 \sqrt{\bar{c}}, \quad LCL_c = \bar{c} - 3 \sqrt{\bar{c}}$$. Explain conditions of use for each chart and how over-dispersion or under-dispersion affects interpretation.

Explain the key elements of an ISO 9001 quality management system relevant to a manufacturing organisation. Describe the roles of documentation, corrective and preventive actions (CAPA), and the Plan–Do–Check–Act (PDCA) cycle in continual improvement.