Kanban and Supermarket —— The Location, Calculation, and On-site Operation Rules of Lean Pull Production

1. Kanban and Supermarket: The "Visual Nerve" 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 supermarket are 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 inconsistent kit availability and work-in-progress (WIP). It clarifies the design of supermarkets, types of kanban, quantity calculations, and implementation pitfalls.

2. Push vs. Pull: Why Supermarkets

Supermarket (Supermarket) = controlled minimum inventory point between processes (or at the line side); the inventory upper limit is set by the number of kanbans, preventing "it's okay to stock a little more."

3. Basic Types of Kanban

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

4. 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 (standard boxes)

Common locations:

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

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

5. Kanban Quantity Calculation (Simplified Formula)

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

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

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

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

6. 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 kanban cards return upstream to trigger replenishment; no "produce first, then decide where to place"
4. Abnormal freeze — Material on hold due to quality issues is removed from the supermarket channel and does not enter the pull cycle
5. Regular audit — Weekly Gemba: Check if kanban cards are present, if the supermarket exceeds the limit

7. 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 — A-class high-turnover items use kanban, C-class items remain on MRP

Avoid "nominal pull, actual planned material release" — if the number of kanban cards remains unchanged for a long time and the supermarket is full, it indicates that the rules are ineffective.

8. Electronic Kanban and Digitalization

Advantages of electronic kanban: Real-time consumption, automatic triggering, data traceability.

Key points for implementation:

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

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

9. Common Failure Modes

10. Implementation Steps (12-Week Reference)

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

11. Interface with Quality Management

• Nonconforming products must not enter the supermarket cycle
• Incoming quality control (IQC) must pass before shelving in the supermarket (or clearly isolate the inspection area)
• Change (ECN) triggers re-evaluation of kanban quantity and packaging C
• Layered process audit (LPA) can include: whether kanban and supermarket rules are followed

12. Kanban Calculation Example (Complete Calculation)

For a certain fastener line-side supermarket:

• D = 1200 pieces/shift × 2 shifts = 2400 pieces/day
• L = 1 day (external electroplating + return transportation + inspection)
• S = 0.25 (demand fluctuation)
• C = 200 pieces/box

N = (2400 × 1 × 1.25) / 200 = 15 kanban cards → Maximum inventory 15×200 = 3000 pieces

Gemba found that the supermarket often has 4000 pieces → Root cause: Replenishment is not kanban-driven, external supplier delivers two trucks at once → Countermeasure: Bind external supplier kanban cards to single delivery quantities C.

13. Synergy with TPM and SMED

• Long changeover time → Upstream cannot replenish in small batches → Implement SMED first, then tighten N
• Frequent equipment failures → Supermarket is frequently depleted → Implement TPM alongside kanban
• Quality stoppages → Not counted as kanban consumption anomalies → Must be separately classified and statistically tracked by Andon

14. Key Points for Selecting Electronic Kanban

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

15. Integration with OTD and Lean Logistics Series

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

16. Three Daily Clearances for Team Leaders

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

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

17. Auditing and 5S

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

Kanban and supermarket 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 a kanban card—does the corresponding standard box exist in the supermarket? Is the number of boxes in the supermarket over the kanban-allowed upper limit?

Knowledge code: 7.1.3

Version: v20260702

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