Model Mix Sequencing is the design of the order in which different product models or variants are produced within a mixed-model system.

The objective is to create a practical sequence that supports:

  • customer demand;
  • workload balance;
  • material replenishment;
  • changeover constraints;
  • stable flow.

It is more detailed than simply deciding how much of each product to make.

Start with leveled demand

Heijunka helps level product mix and volume over time.

Model Mix Sequencing translates that leveled requirement into a repeating production order.

For example, instead of producing:

A A A A B B C

the sequence may be:

A B A C A B A

depending on demand proportions and process capability.

Protect takt and workload balance

Different models may require different work content.

A poor sequence can create:

  • repeated overload;
  • operator waiting;
  • downstream congestion;
  • uneven material consumption.

Takt Time provides the required customer rhythm, while sequencing should keep actual work content manageable around that rhythm.

Consider sequence-dependent changeovers

Some product transitions are more difficult than others.

Examples include:

  • color change;
  • tooling change;
  • cleaning requirement;
  • temperature change.

The best sequence may reduce difficult transitions without creating large batches.

SMED helps reduce changeover time so the production system can sequence smaller quantities with less penalty.

Connect sequencing to EPEI

EPEI indicates how frequently every part in a family can be produced.

A shorter EPEI supports more frequent model repetition.

The sequence should fit the realistic changeover and available-capacity conditions.

Design material flow around the sequence

Mixed-model sequencing changes material consumption.

The logistics system should know:

  • what comes next;
  • required quantity;
  • delivery timing.

Mizusumashi or other standardized replenishment methods can support frequent, predictable mixed-model material movement.

Avoid hidden batching

A schedule may appear mixed while operators quietly regroup products into larger batches because:

  • changeovers are difficult;
  • material is not ready;
  • instructions are unclear.

Observe the actual sequence at the Gemba.

The production rule must be executable.

Use visual sequence control

Useful methods may include:

  • heijunka box;
  • sequence board;
  • electronic dispatch list;
  • model cards.

The visual should make the next required model unambiguous.

Monitor sequence adherence

Schedule Attainment can reveal whether the production system actually follows the intended plan by item and time window.

Repeated sequence deviation may indicate:

  • unrealistic plan;
  • material shortages;
  • process instability;
  • excessive changeover burden.

Common mistakes

Leveling volume without defining model sequence, ignoring work-content differences, optimizing changeovers by creating large batches, designing the sequence separately from material flow, changing sequence constantly, and measuring only total output rather than whether the intended mix was produced are common mistakes.

Practical sequence

  1. define demand by model.
  2. determine the leveled mix.
  3. understand model work content.
  4. identify difficult transitions.
  5. establish a repeating sequence.
  6. check takt and workload.
  7. align material replenishment.
  8. make the sequence visible.
  9. monitor adherence and abnormalities.
  10. refine the pattern as demand or process capability changes.

The practical lesson

Model Mix Sequencing converts a leveled production plan into an executable order.

Stable mixed-model flow depends on sequence, not only on total volume.

This topic also connects with Production Sequence Adherence. Use that method when the improvement requires the related operating or management discipline.