Industrial Engineering
Industrial Engineering tests productivity, work measurement, facility and operations design, quality control, and reliability. Expect calculations in EOQ, line balancing, process capability, control charts, and time standards, plus interpretation of what the numbers mean for capacity and quality.
Core rules
- Productivity = output/input; partial measures use one input, total factor uses all inputs.
- Standard time = observed time × rating factor + allowances.
- EOQ = sqrt(2DS/H), where D is annual demand, S order cost, H holding cost per unit per year.
- Line balance efficiency = sum of task times/(number of stations × cycle time).
- Cp = (USL − LSL)/(6σ); Cpk = min[(USL − μ), (μ − LSL)]/(3σ).
- Control limits come from process variation, not specification limits.
Worked example
Annual demand is 10,000 units, ordering cost is 500 per order, and holding cost is 20% of a 50 unit cost, so H = 10 per unit-year. EOQ = sqrt(2 × 10,000 × 500/10) = sqrt(1,000,000) = 1000 units. Orders per year = 10,000/1000 = 10. Average inventory is about 500 units, ignoring safety stock. If demand or holding cost changes, recalculate rather than scaling the old EOQ linearly.
Traps
- Mixing annual demand with monthly holding cost.
- Using specification width in place of process variation for Cp.
- Reporting Cp as capable when Cpk is low because the process is off-centre.
- Ignoring allowances in standard time.
- Balancing a line to the longest task rather than the required cycle time.