Industrial Engineering and Production Management: Work Study to Quality Control
Work study and productivity
Method study follows select–record–examine–develop–install–maintain. Time study sets standard time = observed time × rating factor + allowances. Productivity is output per input, improved by reducing work content or idle time, not merely by speeding up operators.
Quantitative tools
- EOQ = √(2DS/H), with D annual demand, S ordering cost, H holding cost per unit per year; total cost is minimum at EOQ.
- Break-even quantity = F/(p − v), with F fixed cost, p price and v variable cost per unit.
- PERT expected time t_e = (a + 4m + b)/6; CPM uses deterministic durations.
- Control charts: X̄ and R for variables, p and c for attributes; control limits come from process data, not drawing tolerances.
- Line balancing assigns tasks so station time ≤ cycle time, minimising idle time.
Worked example
Annual demand 10 000 units, ordering cost ₹100, holding cost ₹5 per unit-year. EOQ = √(2 × 10 000 × 100/5) = √400 000 = 632.5, so about 633 units per order. Orders per year = 10 000/633 ≈ 15.8; at EOQ, ordering cost and holding cost are each about ₹1 580, confirming the balance.
Traps
- Using monthly demand with an annual holding cost.
- Confusing slack with float on the critical path (zero).
- Treating specification limits as control limits.
- Computing PERT variance as (b − a)/6 instead of ((b − a)/6)².