Manufacturing Practices (BT-106) - Important Questions

Explain the objectives of quality control in manufacturing. Discuss the role of quality control in reducing costs, improving customer satisfaction and ensuring process reliability.

Define Statistical Process Control (SPC). Describe the basic principles of SPC and list the major types of control charts used for variables and attributes. Explain the situations in which each type is used.

Explain the construction of $\bar X$ and $R$ control charts. Derive the control limits for the $\bar X$ chart and the $R$ chart and state the meaning of each symbol used. Show the formulae for the limits in terms of the subgroup mean $\bar{\bar X}$, average range $\bar R$ and constant $A_2$, $D_3$, $D_4$.

Explain single sampling plans for acceptance sampling. Derive the probability of acceptance for a lot with defect probability $p$ and acceptance number $c$ in a sample of size $n$, i.e. show that $P_{accept} = \displaystyle\sum_{i=0}^{c} \binom{n}{i} p^{i} \left(1-p\right)^{n-i}$. Comment on how the Operating Characteristic (OC) curve is obtained from this expression.

Describe the principles, typical applications, advantages and limitations of the following non-destructive testing (NDT) methods: Ultrasonic Testing (UT), Radiographic Testing (RT), Magnetic Particle Testing (MT), Dye Penetrant Testing (PT) and Eddy Current Testing (ET).

Describe the major clauses of ISO 9001:2015 relevant to a manufacturing organization and explain how implementation of ISO 9001 improves product quality and customer confidence.

What is Total Quality Management (TQM)? Explain the key elements of TQM and briefly describe commonly used quality improvement tools such as Pareto chart, Ishikawa (fishbone) diagram and the PDCA cycle.

Explain a Gauge Repeatability and Reproducibility (Gauge R&R) study. Define repeatability and reproducibility. Describe how %R&R (percentage of total variation due to measurement system) is calculated and interpreted. If the standard deviation of R&R is $\sigma_{RR}$ and total standard deviation is $\sigma_{T}$, express %R&R using these symbols.

Differentiate between incoming inspection, in-process inspection and final inspection. Discuss the importance of sampling procedures in inspection.

Define process capability. Write the expressions for the capability indices $C_p$ and $C_{pk}$ and explain their interpretation. Use the standard notation $USL$, $LSL$, $\mu$ and $\sigma$ in your formulae, for example $C_p = \left( \frac{USL - LSL}{6\sigma} \right)$ and $C_{pk} = \left( \min\left( \frac{USL-\mu}{3\sigma}, \frac{\mu-LSL}{3\sigma} \right) \right)$.

Explain control charts for attributes: $p$-chart, $np$-chart, $c$-chart and $u$-chart. Give the control limit formula for a $p$-chart using the average proportion defective $\bar p$ and sample size $n$, i.e. $UCL_p = \left( \bar p + 3\sqrt{ \frac{\bar p\left(1-\bar p\right)}{n} } \right)$ and $LCL_p = \left( \bar p - 3\sqrt{ \frac{\bar p\left(1-\bar p\right)}{n} } \right)$ (state any conditions for $LCL_p$ ).

Explain the differences between corrective (breakdown), preventive and predictive maintenance. Describe the objectives of Total Productive Maintenance (TPM) in a manufacturing environment.

A manufacturing process is monitored using an $\bar X$ chart. Explain how you would interpret points outside control limits and non-random patterns inside control limits. Describe the steps you would take to investigate and implement corrective actions when out-of-control conditions are detected.