Scenario
After placing an order, customers wait 2 weeks to receive their goods. You visit the factory, and the processing time for each workstation totals only 2 hours.
So, where is the extra 13 days and 22 hours?
Without VSM, you only see each workstation, not the waiting and inventory between workstations. VSM allows you to see the entire tree simultaneously, not just each leaf.
What is VSM
VSM (Value Stream Mapping) = Value Stream Map
One map includes:
- All process steps (Process Boxes)
- Inventory between steps (Inventory Triangles)
- Customer demand and supplier delivery (Truck Icons)
- Production scheduling and information flow (Push / Pull Arrows)
- Timeline (Bottom: Cumulative Lead Time vs. Cumulative Processing Time)
Key Metrics
Lead Time: The total time from raw material entry to finished product shipment.
Value-Added Time: The processing time that genuinely alters the product.
Typical manufacturing ratios:
- Lead Time: 5 days (7,200 minutes)
- Value-Added Time: 45 minutes
- Value-Added Ratio: 45 / 7,200 = 0.6%
99.4% of the time, the product is waiting, not being processed.
The 8 Wastes (TIMWOODS)
| English Abbr. | Chinese | Factory Example |
|---|---|---|
| T | Transportation | Unnecessary movement of materials between processes |
| I | Inventory | WIP piled up before workstations |
| M | Motion | Operator's excessive walking, reaching |
| W | Waiting | Waiting for equipment, previous station, line change completion |
| O | Overproduction | Producing quantities not requested by the customer |
| O | Overprocessing | Processing to quality specifications not required by the customer |
| D | Defects | Defective products, rework, scrap |
| S | Skills Waste | Employee capabilities not being utilized effectively |
Current State Map vs. Future State Map
The complete VSM process:
Step One: Draw the Current State Map
Faithfully record the current process—no embellishment, no omissions.
Step Two: Analyze the Current State Map
- Where inventory accumulates before which steps (Waiting Waste)
- Which steps have processing times significantly greater than Takt Time (Bottlenecks)
- Is the information flow Push (forecast-driven production) or Pull (customer demand-driven)
Step Three: Design the Future State Map
- Establish Pull flow, replacing Push scheduling with Kanban or Supermarket systems
- Identify steps that can be combined or eliminated
- Set target lead time and value-added ratio
Step Four: Develop an Improvement Plan
Mark priority improvement items with Kaizen Bursts, assign responsibilities, and set completion times.
How to Find the Highest Priority Improvement Items
Look for them in the Current State Map:
- Areas with the most inventory = areas with the poorest flow
- Waiting that accounts for the largest proportion of lead time = greatest opportunity for reduction
- The sole Push scheduling point = prime candidate for conversion to Pull
Golden Quote
"The most striking moment in VSM is when you first see on the timeline: in a 5-day lead time, the product is truly processed for only 45 minutes. At that moment, everyone suddenly understands that waste is not an exception but the norm of the entire system."