Value Stream Mapping & Waste
Key Takeaways
- Value stream mapping visualizes material and information flow to separate value-added from non-value-added time.
- The seven wastes (TIMWOOD) are Transport, Inventory, Motion, Waiting, Overproduction, Over-processing, and Defects.
- Current-state maps show today’s flow; future-state maps design a leaner target with pull, flow, and less waste.
- On CSSGB scenarios, classify steps as VA, NNVA, or NVA and link symptoms (queues, travel, excess stock) to TIMWOOD wastes.
- VSM baselines lead time and process cycle efficiency in Define/Measure and guides Improve countermeasures.
Value Stream Mapping & Waste (CSSGB BoK I.B.2 — Understand)
Quick Answer: Value stream mapping (VSM) draws current and future material and information flow to expose waste. The seven wastes (TIMWOOD)—transport, inventory, motion, waiting, overproduction, over-processing, and defects—drive most NVA time. Green Belts read maps to classify VA vs NVA and recommend leaner future states.
Value stream mapping shows how a product or service family moves from request to delivery. Unlike a simple flowchart, a VSM includes process boxes, inventory triangles, information flows (schedules, forecasts, electronic orders), a timeline of value-added vs wait time, and data boxes (cycle time, changeover, uptime, operators). On the CSSGB exam, I.B.2 is at the Understand level: interpret maps and waste types.
Why VSM Matters for Green Belts
Most of lead time is waiting and inventory, not touch time. VSM makes that imbalance visible. Typical metrics:
- Lead time (LT): total elapsed time from start to finish.
- Process / value-added time (VA): time when the product is actually transformed.
- Process cycle efficiency (PCE): VA time ÷ total lead time (often only a few percent before improvement).
If lead time is 10 days and pure processing time is 2 hours, PCE is tiny—opportunity is mostly flow and inventory reduction, not only speeding operators.
VSM usually supports Define and Measure: baseline the stream, agree on the product family, and quantify waste. Improve implements future-state design (pull, cells, smaller lots). Control locks in standard work so waste does not return.
Value-Added vs Non-Value-Added
| Classification | Definition | Examples |
|---|---|---|
| Value-added (VA) | Changes form/fit/function the customer pays for | Machining to print, assembling parts, resolving a customer issue |
| Necessary non-value-added (NNVA) | Required today by regulation, safety, or technology | Mandatory inspection, certain approvals, sterilization |
| Non-value-added (NVA) waste | Consumes resources without customer value | Waiting, rework, excess transport, overproduction |
Inspection is usually NNVA (or pure waste if it exists only because quality is poor). Rework of defects is NVA—do not call it value-added just because it restores the product; the customer did not ask to pay twice for the same transformation.
The Seven Wastes (TIMWOOD)
| Letter | Waste | Description | Typical symptoms |
|---|---|---|---|
| T | Transport | Unnecessary movement of product or materials | Long arrows between distant processes; forklift trips |
| I | Inventory | Excess raw, WIP, or finished goods | Large inventory triangles; high days of supply |
| M | Motion | Unnecessary movement of people | Spaghetti paths; reaching, searching, walking |
| W | Waiting | Idle people, machines, or product | Long timeline bars between process boxes |
| O | Overproduction | Making more/sooner than needed | Push schedules; piles before the next process |
| O | Over-processing | Extra steps beyond customer requirement | Redundant approvals, over-tight tolerances |
| D | Defects | Scrap, rework, wrong information | Scrap counts, rework loops, inspection fails |
Related exam language:
- Excess inventory / storage → Inventory waste (often with transport into/out of storage).
- Unused space → Often inventory, poor layout, or motion/transport waste.
- Test/inspection → Frequently NNVA; if it exists only because upstream defects are high, the deeper waste is Defects.
- Rework → Defects waste.
- Transportation → Transport waste.
Overproduction is often called the worst waste because it creates inventory, hides defects, and forces extra transport and storage. Pull systems and takt alignment attack overproduction at the source. (Some sources add an eighth waste: unused human talent.)
Current-State vs Future-State Maps
Current-state map
Built from direct observation (Gemba) and data, not only procedure manuals:
- Select a product or service family with similar steps.
- Walk and document material flow and wait points.
- Record process data: cycle time, changeover, uptime, batch size, operators.
- Draw inventory and wait times between steps.
- Draw information flow (MRP push vs kanban pull).
- Build the timeline; compute lead time vs VA time.
A current-state map might show five departments, multi-day queues, weekly batch releases, and low PCE—justifying a project charter and focusing the team.
Future-state map
Designs how the stream should operate. Common features:
- Produce to takt or a pacemaker process.
- Continuous flow or small-lot flow where practical.
- Pull (supermarket/kanban) where continuous flow is not yet possible.
- Fewer handoffs and shared cells.
- Leveling (heijunka) of mix and volume.
- Simpler information loops and scheduling.
- Targets: shorter lead time, higher PCE, lower inventory days.
The gap between current and future state becomes the implementation plan (kaizen bursts, DMAIC Improve actions). The map is not the improvement itself—execution is.
Exam Scenario Interpretation
Use this checklist on CSSGB stems:
- What does the customer want? Defines value.
- Where is time spent? Waiting bars and inventory triangles → Waiting/Inventory.
- Made before a signal? → Overproduction / push.
- Long travel between steps? → Transport; consider layout/spaghetti.
- Operators walking/searching? → Motion.
- Extra reviews, polishing, duplicate data entry? → Over-processing.
- Scrap, returns, rework loops? → Defects.
- Required by regulation? May be NNVA—still minimize and error-proof it.
Scenario A: Orders wait three days in a shared inbox, then travel across campus for a wet-signature approval that adds nothing beyond an available electronic approval. Wastes: Waiting, Transport, and Over-processing. Future state: electronic approval at the pacemaker step; eliminate the campus trip.
Scenario B: A line builds two weeks of finished goods “just in case” while defects surface only at final test. Primary wastes: Overproduction and Inventory, with delayed Defects. Future state: smaller lots, pull from shipping, and in-process checks closer to the source.
Linking VSM to Lean Concepts and SIPOC
VSM operationalizes I.B.1 concepts: takt is the demand rate the future state must meet; flow and JIT/pull are design choices; TOC may identify the constrained process box; Gemba validates current-state data; perfection drives iterative remapping after each wave.
Do not confuse VSM with SIPOC. SIPOC is a high-level Define tool (suppliers, inputs, process, outputs, customers). VSM is a deeper, time-and-inventory-rich picture of one value stream. Both can appear on the same project; they answer different questions.
Open-book exam tips: Memorize TIMWOOD with one example each; remember PCE = VA / lead time; current state = as-is and future state = to-be with less waste and pull/flow; inspection/test is not automatically VA; rework is not VA; excess space and “just-in-case” stock map primarily to Inventory (often fed by overproduction).
On a value stream map, products sit for two days between machining and assembly while a forklift later moves them to a distant warehouse before the next step. Which wastes are most clearly present?
What is the primary purpose of creating both a current-state and a future-state value stream map on a Green Belt project?