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CTMA: Operations and Production Management

CTMA · Work through your exam, one topic at a time.

All guide sections

Operations and Production Management

Operations and Production Management covers how inputs become outputs efficiently and reliably: forecasting demand, sizing capacity, planning materials, controlling quality, and improving flow. CTMA items here are usually quantitative, or they ask you to diagnose a system - push versus pull, where the bottleneck sits - from a short description.

Core rules

  • Takt time = available production time ÷ customer demand. It sets the required pace, not the speed of any one machine.
  • Little's Law: work-in-process = throughput × flow time. Useful for lead-time and inventory questions.
  • EOQ = √(2DS/H), where D is annual demand, S order cost, H holding cost per unit per year. Assumes constant demand, fixed order cost, no quantity discounts, no shortages.
  • MRP explodes the bill of materials using lead times; it is push-based and inherits forecast error. Kanban is pull-based and needs stable, leveled demand.
  • Lean targets the wastes (overproduction, waiting, transport, overprocessing, inventory, motion, defects); value stream mapping exposes them. JIT cuts inventory but also removes the buffer that hides variability.
  • SPC: control charts separate common-cause from special-cause variation. Specification limits are not control limits. Cp/Cpk compare process spread with tolerance.
  • Theory of Constraints: identify the constraint, exploit it, subordinate everything else, elevate it.

Worked example

A cell runs one 7.5-hour shift (27,000 s); demand is 480 units/day; total work content is 280 s.

  • Takt = 27,000 ÷ 480 = 56.25 s/unit.
  • Minimum stations = 280 ÷ 56.25 = 4.98, so 5 stations.
  • Efficiency = 280 ÷ (5 × 56.25) = 99.6%. Five is the theoretical minimum; real lines carry balance delay, so a six-station line at about 83% efficiency is often the practical answer.

Traps

  • Using 24 hours or 365 days when the stem supplies operating time only.
  • Confusing cycle time (what a station takes) with takt time (what the market requires).
  • Forgetting yield: required input = good output ÷ yield.
  • Reading Cpk below 1.0 as "out of control"; capability and stability are separate questions.
  • Applying EOQ when the stem states quantity discounts or highly variable demand.