Mixed-Model Production: Multiple Products on One Line

Mixed-model production is a lean manufacturing approach where multiple product variants are produced on the same production line in a leveled, repeating sequence. Rather than running large batches of a single model before switching to the next, mixed-model production intermixes products throughout the day to match the proportional demand for each. This manufacturing glossary entry explains how mixed-model production works, its measurable benefits, and the critical role of scheduling.

What Is Mixed-Model Production?

Consider a line that produces three products: Model A (demand: 200/week), Model B (demand: 100/week), and Model C (demand: 50/week). Total weekly demand is 350 units, or 70 per day across 5 working days.

Batch approach: Run 200 of A (3 days), then 100 of B (1.5 days), then 50 of C (0.5 day). Model C customers wait all week for their product. Upstream suppliers receive a lumpy demand signal.

Mixed-model approach: Produce a daily mix reflecting the demand ratio — A:B:C = 4:2:1. The daily sequence repeats: AABABAC AABABAC... Every model ships every day. Upstream processes receive a smooth, predictable demand signal.

Mixed-model production is the practical implementation of Heijunka (production leveling). Heijunka provides the principle; mixed-model production is how it looks on the shop floor.

How Mixed-Model Production Works in Practice

Implementing mixed-model production requires several foundations:

Fast Changeovers

Switching between models must be quick — ideally under a minute for an assembly line, under 10 minutes for machining operations. SMED is the essential prerequisite. If changing from Model A to Model B takes 2 hours, mixed-model production is economically impossible.

Standardized Work with Variation

Standard work documents must handle model variations. Common approaches include: color-coded work instructions, model-specific pick lists displayed by the system, and fixtures designed to accommodate multiple variants with quick adjustments.

Product Design Commonality

Mixed-model production is easier when products share common platforms, components, and processes. Design for manufacturing principles maximize commonality while allowing customer-facing variety.

Level Scheduling

A Heijunka box or scheduling system determines the daily model sequence. The sequence is designed to:

• Distribute changeover effort evenly (avoid clustering difficult changeovers)
• Level component consumption (avoid surges in demand for variant-specific parts)
• Match the proportional demand ratio

Flexible Workforce

Operators must be cross-trained on all models. Work content varies by model — some variants take longer than others. Standard work and line balancing account for this variation.

Example with Numbers

An automotive component supplier producing brake assemblies for 5 vehicle platforms transitioned from batch to mixed-model production:

Before (batch production):

• Ran one platform per day, switching platforms daily
• Changeover between platforms: 35 minutes
• Finished goods buffer required: 3 days of stock for each platform = 15 days total
• Finished goods inventory: $1.2M
• Customer lead time: 5 days (average wait for the next batch run of their platform)

After (mixed-model production):

• All 5 platforms produced daily in a repeating sequence
• Changeover reduced to 4 minutes through SMED (fixtures, tooling, and programs pre-staged)
• Finished goods buffer reduced to 1 day of stock for each platform = 5 days total
• Finished goods inventory: $420,000 — 65% reduction, freeing $780,000 in working capital
• Customer lead time: 1 day — 80% reduction
• Line efficiency held steady at 92% despite the more frequent changeovers because each changeover was so short
• Upstream material flow smoothed significantly — component suppliers received daily level signals instead of weekly lumpy orders, reducing their expediting by 40%

Why Mixed-Model Production Matters for Production Scheduling

Mixed-model production transforms scheduling challenges:

• Leveled schedules are more achievable: A mixed-model schedule smooths the load across the day and week, eliminating the peaks and valleys that cause overtime and idle time. Production scheduling software like RMDB generates level-loaded schedules that align with mixed-model sequencing.
• Simpler material planning: When every product is made every day, material consumption is predictable and level. MRP calculations become more stable, and supplier signals are smoother.
• Reduced finished goods: Daily production of every model means less finished goods buffer is needed to cover the gap between production batches and customer orders.
• Sequence optimization: RMDB can optimize the mixed-model sequence to minimize total changeover time — for example, scheduling transitions between models that share similar setups adjacently.
• Responsiveness: If a customer's demand shifts from Model A to Model B, a mixed-model system adjusts the daily ratio immediately. A batch system cannot respond until the next batch cycle.

The lean manufacturing guide describes mixed-model production as the mature state of a lean production system — the point where Heijunka, SMED, and standard work converge to create truly demand-responsive manufacturing.

Related Terms

• Heijunka — The production leveling principle that mixed-model production implements on the shop floor.
• SMED — The changeover reduction methodology that makes frequent model switches economically viable.
• Batch Production — The traditional approach of producing one model at a time that mixed-model production replaces.

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See all lean and scheduling terms in the Manufacturing Glossary.