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Qwestrum Engineering360 · Mechanical Engineering · Industrial Engineering

Production Planning and Control

PPC plans what, how much, and when to produce, using tools like the EOQ = √(2DS/H) for lot sizing and forecasting for demand. It coordinates routing, scheduling, dispatching, and follow-up, per industrial-engineering texts.
Exam tip: keep SI units consistent end-to-end, write the governing relation symbolically before substituting, and sanity-check magnitude and sign.

Key formulas & points

Skim these first — then read the full notes below.

  • MRP inputs: BOM, inventory, master schedule
  • Gantt chart for job scheduling; load chart for capacity
  • Make-to-stock vs make-to-order vs assemble-to-order

Topic details

Introduction

Production planning and control (PPC) is the nervous system of a factory, converting demand forecasts into executable schedules. Indian IE syllabi cover forecasting, aggregate planning, routing, scheduling, and control.

Scope in B.Tech and GATE syllabus

Lot-sizing balances ordering/setup cost against holding cost through the economic order/production quantity. Scheduling sequences jobs on machines (e.g. Johnson's rule for two machines) to minimise makespan or tardiness.

Why this topic matters in practice

Dispatching releases work and follow-up tracks progress against plan, feeding corrective control. Applying EOQ, sequencing rules, and forecasting methods numerically is the exam focus of PPC.

Key relations & formulas

EOQ=2DSHEOQ = \sqrt{\frac{2DS}{H}}
(economic order quantity)
Totalcost=DSQ+QH2+PDTotal cost = \frac{DS}{Q} + \frac{QH}{2} + PD
(ordering + holding + purchase)
MPS→MRP→shopfloorschedulingMPS → MRP → shop floor scheduling
(planning hierarchy)

Formulas (Indian textbook notation)

  • Utilisation=actualoutputcapacity×100Utilisation = \frac{actual_{output}}{capacity} \times 100%

Notation and sign conventions

Relation 1 —
EOQ=√EOQ = √
EOQ=2DSHEOQ = \sqrt{\frac{2DS}{H}}
(economic order quantity)
Write this relation with symbols exactly as in Industrial Engineering & Management — O.P. Khanna before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 2 —
Totalcost=DSQ+QH2+PDTotal cost = \frac{DS}{Q} + \frac{QH}{2} + PD
Totalcost=DSQ+QH2+PDTotal cost = \frac{DS}{Q} + \frac{QH}{2} + PD
(ordering + holding + purchase)
Write this relation with symbols exactly as in Industrial Engineering & Management — O.P. Khanna before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 3 —
MPS→MRP→shopfloorschedulingMPS → MRP → shop floor scheduling
MPS→MRP→shopfloorschedulingMPS → MRP → shop floor scheduling
(planning hierarchy)
Write this relation with symbols exactly as in Industrial Engineering & Management — O.P. Khanna before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 4 —
Utilisation=actualoutputcapacity×100Utilisation = \frac{actual_{output}}{capacity} \times 100%

Formulas (Indian textbook notation)

  • Utilisation=actualoutputcapacity×100Utilisation = \frac{actual_{output}}{capacity} \times 100%
Write this relation with symbols exactly as in Industrial Engineering & Management — O.P. Khanna before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Fundamentals and definitions

PPC starts with demand forecasting (moving average, exponential smoothing) to estimate future requirements, then aggregate planning to match capacity and demand over the medium term.

Governing relations in practice

Lot sizing uses the EOQ = √(2DS/H), which minimises the total of ordering cost (D/Q × S) and holding cost (Q/2 × H). The economic batch quantity extends this to production with a finite replenishment rate.

Design and analysis considerations

Routing fixes the sequence of operations and machines; scheduling assigns start/finish times. Johnson's rule sequences n jobs on two machines to minimise total completion time; priority rules (SPT, EDD) address single-machine problems.

Advanced theory and extensions

Dispatching authorises operations per the schedule; follow-up (expediting) compares actual to planned progress and triggers control actions. This closed loop of plan-execute-control keeps output aligned with demand — the essence of PPC.

Assumptions and validity limits

State assumptions explicitly before using any relation for production planning and control — steady state, uniform properties, linear elastic material, ideal gas, incompressible flow, etc., as applicable.
Wrong assumptions invalidate the entire solution even when the formula is correct. In Industrial Engineering viva and GATE descriptive questions, listing valid assumptions often earns separate marks.

Step-by-step problem approach

1. Read the question and list given data with SI units (common in Industrial Engineering papers).
2. Draw a neat labelled diagram where applicable — examiners in Indian universities award diagram marks even when arithmetic slips.
3. Identify which relation from this topic applies to production planning and control.
4. Use equation 1:
EOQ=√EOQ = √
.
5. Use equation 2:
Totalcost=DSQ+QH2+PDTotal cost = \frac{DS}{Q} + \frac{QH}{2} + PD
.
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.

Applications & exam relevance

Production Planning and Control appears in factories, logistics, and service systems. In Indian mechanical curricula this topic is tested because it connects theory to productivity, layout, and operations.
GATE and semester exams often combine production planning and control with earlier units — revise prerequisites before attempting mixed problems.
Industry interview panels sometimes ask: "Where did you use production planning and control?" — answer with a lab, mini-project, or plant visit example if possible.

Common mistakes in exams

• Using the simple EOQ where a finite production rate (EBQ) applies
• Applying Johnson's rule to more than two machines without the extension conditions
• Confusing routing (sequence of operations) with scheduling (timing)
• Ignoring holding-cost units consistency in EOQ

Quick revision checklist

Before attempting production planning and control problems, confirm you can:
1. MRP inputs: BOM, inventory, master schedule
2. Gantt chart for job scheduling; load chart for capacity
3. Make-to-stock vs make-to-order vs assemble-to-order
Revise the solved examples in Industrial Engineering & Management — O.P. Khanna and one previous-year GATE or university paper for this unit.

Worked examples

Try the problem first — open the solution when you are ready to check.

Economic order quantity

Problem

Annual demand D = 10000 units, ordering cost S = ₹200 per order, holding cost H = ₹4 per unit per year. Find the EOQ.

Solution

EOQ = √(2DS/H) = √(2 × 10000 × 200/4) = √(4000000/4) = √1000000 = 1000 units.

Conceptual check — Production Planning and Control

Problem

In a Industrial Engineering semester or GATE paper you are asked: "State the main assumption, the governing relation, and one practical consequence of production planning and control." What should a complete answer include?

Practice questions

Most-asked interview and GATE questions for this topic — expand any item for a model answer.

  1. 1
    What is Production Planning and Control, and why does it appear in B.Tech / GATE syllabi?

    Model answer

    PPC plans what, how much, and when to produce, using tools like the EOQ = √(2DS/H) for lot sizing and forecasting for demand. It coordinates routing, scheduling, dispatching, and follow-up, per industrial-engineering texts.
  2. 2
    State the relation EOQ = √ and name each symbol.

    Model answer

    The governing relation is EOQ=√EOQ = √. Write every symbol with SI units before substituting numbers.
  3. 3
    State the relation Total cost = DS/Q + QH/2 + PD and name each symbol.

    Model answer

    The governing relation is Totalcost=DSQ+QH2+PDTotal cost = \frac{DS}{Q} + \frac{QH}{2} + PD. Write every symbol with SI units before substituting numbers.
  4. 4
    State the relation MPS → MRP → shop floor scheduling and name each symbol.

    Model answer

    The governing relation is MPS→MRP→shopfloorschedulingMPS → MRP → shop floor scheduling. Write every symbol with SI units before substituting numbers.
  5. 5
    State the relation Utilisation = actual_output/capacity × 100% and name each symbol.

    Model answer

    The governing relation is Utilisation=actualoutputcapacity×100Utilisation = \frac{actual_{output}}{capacity} \times 100%. Write every symbol with SI units before substituting numbers.
  6. 6
    Explain: MRP inputs: BOM, inventory, master schedule

    Model answer

    MRP inputs: BOM, inventory, master schedule — state the assumption range and one exam trap linked to this point.
  7. 7
    Explain: Gantt chart for job scheduling; load chart for capacity

    Model answer

    Gantt chart for job scheduling; load chart for capacity — state the assumption range and one exam trap linked to this point.
  8. 8
    Explain: Make-to-stock vs make-to-order vs assemble-to-order

    Model answer

    Make-to-stock vs make-to-order vs assemble-to-order — state the assumption range and one exam trap linked to this point.
  9. 9
    How would you correct this error in a viva: Using the simple EOQ where a finite production rate (EBQ) applies?

    Model answer

    Identify the wrong assumption or unit mix-up, rewrite the correct relation, and recompute with a one-line sanity check.
  10. 10
    How would you correct this error in a viva: Applying Johnson's rule to more than two machines without the extension conditions?

    Model answer

    Identify the wrong assumption or unit mix-up, rewrite the correct relation, and recompute with a one-line sanity check.
  11. 11
    How would you correct this error in a viva: Confusing routing (sequence of operations) with scheduling (timing)?

    Model answer

    Identify the wrong assumption or unit mix-up, rewrite the correct relation, and recompute with a one-line sanity check.
  12. 12
    How would you correct this error in a viva: Ignoring holding-cost units consistency in EOQ?

    Model answer

    Identify the wrong assumption or unit mix-up, rewrite the correct relation, and recompute with a one-line sanity check.

Exams & GATE

  • 1
    O.P. Khanna Ch. 8 — MRP explosion from BOM levels.
  • 2
    Avoid: Using the simple EOQ where a finite production rate (EBQ) applies
  • 3
    Avoid: Applying Johnson's rule to more than two machines without the extension conditions
  • 4
    Avoid: Confusing routing (sequence of operations) with scheduling (timing)

📖 Standard books (India)

  • Industrial Engineering & Management — O.P. Khanna

    Read: Syllabus unit

    Work study, PPC, and OR basics

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