Kanban and Supermarkets —— Site Selection, Kanban Calculation, and On-site Operation Rules for Lean Pull Production

One, Kanban and Supermarkets: The "Visual Nervous System" of the Pull System

The value stream map (VSM) shows a supermarket, but the site stocks materials in large batches according to MRP; production line material calls rely on WeChat groups, and kanban becomes a decoration on the whiteboard.

Kanban and supermarkets are at the core of lean pull production: downstream consumption, upstream replenishment, and inventory with an upper limit—using physical or electronic signals to replace predictive push production.

This article is aimed at factories that have implemented 5S and have a basic cell line structure but still experience unstable kit availability and work-in-progress (WIP). It clarifies the design of supermarkets, types of kanban, quantity calculation, and common pitfalls in implementation.

Two, Push vs Pull: Why Supermarkets

Supermarket (Supermarket) = A controlled minimum inventory point between processes (or at the line side); the inventory upper limit is set by the number of kanbans, preventing "a little extra doesn't matter."

Three, Basic Types of Kanban

Regardless of whether they are paper or electronic, the principle remains the same: no kanban, no production, no movement.

Four, Where to Set Up Supermarkets? How Many?

Prerequisites for setting up a supermarket:

• Upstream process is relatively stable (acceptable changeover time)
• Downstream consumption predictable within a reasonable range
• Materials are unitized for packaging (standard boxes)

Common locations:

1. Raw materials → Line-side supermarket
2. Semi-finished products → Inter-process supermarket
3. Finished products → Shipping supermarket (linked to OTD)

Not suitable for supermarkets: One-piece flow is stable, suppliers deliver directly to the line side with perfectly synchronized takt times (rare).

Five, Kanban Quantity Calculation (Simplified Formula)

Number of Kanbans N = (D × L × (1 + S)) / C

• D = Daily consumption rate (units/day)
• L = Lead time for replenishment (days), including production, transportation, and acceptance
• S = Safety factor (fluctuation, typically 0.1～0.3)
• C = Number of units per box (standard packaging)

Example: D=800, L=0.5 days, S=0.2, C=50 → N = (800×0.5×1.2)/50 ≈ 10 kanbans

Verification needed: Maximum supermarket inventory = N × C should not exceed on-site space and financial constraints.

Six, Supermarket Operation Management Rules

1. First In, First Out (FIFO) —— Ensured by physical storage or labeling
2. Fixed location, fixed quantity —— Number of boxes in the supermarket ≤ kanban upper limit
3. Kanban circulation path —— Empty kanbans return upstream to trigger replenishment, no "produce first, then decide where to place"
4. Abnormal freeze —— Material on hold for quality issues is removed from the supermarket channel and does not enter the pull cycle
5. Regular review —— Weekly Gemba: Check if kanbans are present, if the supermarket is overstocked

Seven, Relationship with Planning and MRP

• MRP can retain the planning function for long-cycle materials, imported parts, and non-repetitive items
• Repetitive, stable items are gradually incorporated into the kanban pull system, with MRP only maintaining master data and safety stock parameters
• For mixed-line production: ABC classification —— High-turnover A items use kanban, C items remain on MRP

Avoid "nominal pull, actual planned input" —— If the number of kanbans remains unchanged for a long time while the supermarket is overstocked, it indicates the rules are failing.

Eight, Digitalization and Electronic Kanban

Advantages of electronic kanban: Real-time consumption, automatic triggering, data traceability. Key points for implementation:

• Consistency with on-site actions —— Scanning/button press = traditional kanban withdrawal
• Network outage contingency —— Paper backup or local cache rules
• No additional operational steps —— Otherwise, frontline workers will bypass the system

Refer to the lean logistics series and water spider delivery articles for a complete supermarket + delivery solution.

Nine, Common Failure Modes

Ten, Implementation Steps (12-Week Reference)

Metrics: Line-side WIP value, kit availability rate, number of urgent insertions, supermarket turnover days.

Eleven, Interface with Quality Management

• Nonconforming products must not enter the supermarket cycle
• Materials must be shelved in the supermarket only after passing incoming quality control (IQC) (or clearly isolated in a pending inspection area)
• Changes (ECN) trigger re-evaluation of kanban quantities and packaging C
• LPA can include: whether kanban and supermarket rules are followed

Twelve, Kanban Calculation Example (Full Calculation)

For a certain fastener line-side supermarket:

• D = 1200 units/shift × 2 shifts = 2400 units/day
• L = 1 day (external electroplating + transport back to the factory + inspection)
• S = 0.25 (demand fluctuation)
• C = 200 units/box

N = (2400 × 1 × 1.25) / 200 = 15 kanbans → Maximum inventory 15×200 = 3000 units

Gemba found the supermarket often piled with 4000 units → Root cause: Replenishment not kanban-driven, suppliers deliver two trucks at once → Countermeasure: Bind external kanban to single delivery quantity C.

Thirteen, Synergy with TPM and SMED

• Long changeover times → Upstream struggles to replenish in small batches → Implement SMED first, then tighten N
• Frequent equipment failures → Supermarket is frequently depleted → Run TPM and kanban in parallel
• Quality line stops → Not counted as abnormal consumption in the kanban system → Requires separate Andon classification and statistics

Fourteen, Key Points for Selecting Electronic Kanban

• Whether it supports dual-box (dual-card) kanban logic
• Whether consumption signals can integrate with Andon (automatically light up for material shortages)
• Whether historical records can be exported for auditing FIFO
• Whether ERP material issuance is enforced to follow kanban before release

Fifteen, Integration with OTD and Lean Logistics Series

The high-read section 7.4 Lean Logistics covers layout and water spider; the kanban supermarket is the pull logic layer. Combining these three elements constitutes a complete value stream improvement.

Sixteen, Three Daily Checks for Team Leaders

1. Are kanbans circulating, and are any missing?
2. Is the supermarket inventory ≤ the kanban upper limit?
3. Are there any "temporary material boxes" without kanbans?

For mixed-line production with multiple SKUs, different colored kanbans or electronic kanban SKU fields can be used to prevent wrong material delivery; quality isolation areas must be physically separated from the supermarket channel to avoid the misconsumption of held materials.

Seventeen, Audits and 5S

LPA can include: whether the supermarket area maintains 5S, and whether labels match the kanban C value—on-site visualization is the sustainability guarantee for the pull system. In the early stages, it is recommended to conduct a 30-minute Gemba weekly focusing on three questions: kanban, supermarket upper limit, and FIFO. When combining water spider and FIFO channels in the design, kanban triggers replenishment tasks rather than directly driving large-batch movements, balancing response speed and WIP upper limits.

Kanban and supermarkets are not just "logistics techniques," but a management mechanism that exposes fluctuations, limits WIP, and enforces replenishment based on consumption—when done correctly, quality and delivery often improve simultaneously.

On-site 30-second inspection: Randomly check one kanban—Is the corresponding standard box in the supermarket? Is the number of boxes in the supermarket over the kanban-allowed upper limit?

Knowledge Number: 7.1.3

Version: v20260702

Author: Quality Excellence Think Tank Quality Excellence Think Tank is dedicated to providing systematic professional knowledge, methodologies, and practical tools for quality management practitioners, helping companies continuously improve their quality capabilities.