Lean Flow Tools: Value Streams, Kanban, and Standard Work
Read a value stream map, explain push versus pull, size and run a kanban signal, use point-of-use storage, and write standard work that keeps material moving.
Table of contents
Good flow means work moves from step to step without piling up or sitting idle. Most delays have nothing to do with how fast people work. They come from material waiting in a stack for its turn. The tools here help you see that waiting, build only what the next step needs, and hold on to the improvements you make.
What You Will Be Able to Do
- Read a value stream map and work out how much of the lead time adds value.
- Explain the difference between push and pull.
- Describe the main kanban types and size a simple two-bin system.
- Apply point-of-use storage and write standard work.
- Choose the measures that show whether flow is improving.
Value Stream Mapping
A value stream map is a visual diagram of every step in a process that shows how material and information flow, from the order to delivery. It separates the steps that add value from the waste around them. Where a workstation walk shows one area, a value stream map shows the whole picture, so you fix the delay that matters instead of the one that is easiest to see.
A map captures:
- Each process step and its cycle time, shown in a box.
- The inventory waiting between steps, shown as a triangle with a count.
- How orders and schedules reach each step, shown as information arrows.
- A timeline along the bottom comparing waiting time with working time.
Drawing a Map
- Pick one product or product family.
- Walk the process yourself, starting at shipping and working back to receiving. Do not map from memory.
- At each step, record cycle time, changeover time, uptime, and the number of people.
- Count the inventory between steps.
- Draw how information moves: who tells each step what to make, and how.
- Add up working time and waiting time on the timeline.
- Mark the biggest delays and draw a future-state map showing how you want the process to run.
Worked Example: Finding the Value-Added Share
A product sells 200 units a day. To turn a pile of inventory into waiting time, divide it by daily demand.
| Step | Process time | Inventory after it | Waiting time |
|---|---|---|---|
| Cut | 30 seconds | 600 units | 3 days |
| Form | 45 seconds | 400 units | 2 days |
| Assemble | 120 seconds | 800 units | 4 days |
| Pack | 45 seconds | 200 units | 1 day |
Process time adds up to 240 seconds, or 4 minutes. Waiting adds up to 10 working days. At 8 hours a day, that is 4,800 minutes.
The value-added share is 4 ÷ 4,800 = less than 0.1 percent. That looks shocking, but it is normal. Maps commonly show value-added time at less than 5 percent of total lead time. The rest is waiting, moving, and other waste, which is where the biggest gains are.
Push Versus Pull
The two systems differ in what starts the work.
| Question | Push | Pull |
|---|---|---|
| What triggers work | A forecast or schedule | Actual use downstream |
| Each step makes | What the plan says | What the next step used |
| Inventory | Builds up when plans are wrong | Stays small and capped |
| Main risk | Overproduction | Stoppage when supply is unreliable |
Think of a grocery store. Nobody stocks the shelf from a year-old forecast. When cans sell, the empty space tells the stocker to refill it. Pull works the same way: the downstream process, acting as the customer, takes what it needs, and the upstream process replaces only that amount.
Most real operations use some of both. For example, a factory may schedule its final step and pull everything upstream from there.
Kanban
Kanban is a visual signal that triggers production or material replenishment based on actual use. The word means roughly "signboard" in Japanese. The rule that makes it work is simple: no signal, no work.
| Type | How it works | Good fit |
|---|---|---|
| Two-bin | Empty the first bin, and it becomes the signal to refill while you use the second | Small parts and supplies |
| Card | A card travels with the container and returns upstream when it is used | Parts made in a nearby department |
| Floor square | A marked spot on the floor sits empty, which signals the upstream step to fill it | Larger items and carts |
| Electronic | A scan sends a signal through the inventory system | Long distances and outside suppliers |
Worked Example: Sizing a Two-Bin System
A workstation uses 40 fasteners an hour. It takes 4 hours from when a bin empties until the refilled bin comes back. Each bin must last through that wait.
- Usage during the wait: 40 x 4 = 160 fasteners.
- Add a safety margin, for example 20 percent: 160 x 1.2 = 192 fasteners.
- Round up to a practical size: 200 per bin.
Check real usage after a few weeks. If bins never run close to empty, the quantity can come down, and that frees up cash and space.
Keeping Kanban Honest
Kanban fails in a few predictable ways. Cards get lost, so a part stops being made. People build ahead "to stay busy," which is push all over again. People hoard extra bins, so the signal stops meaning anything. Defects get passed downstream, and the next step runs short. Keep the rules visible, count the cards or bins on a schedule, and fix the cause when a station runs out.
Point-of-Use Storage
Point-of-use storage means bringing tools and parts to the place where the work is done. If an assembler uses a torque wrench every few minutes, it belongs within reach of the station. A warehouse packing station keeps tape, labels, and box sizes at hand. A maintenance crew can keep a stocked cart for one machine's routine service, so nobody walks back to the shop for each item.
Keep only what the work uses, in small amounts, with a marked location. If the storage turns into clutter or forces awkward reaching, it has defeated the purpose. Keep shelves and bins at safe, comfortable heights.
Standard Work
Standard work is the current best known way of doing a task, written down so that it is done the same way each time. It usually records:
| Element | What it says |
|---|---|
| Work sequence | The steps, in order |
| Timing | Takt time and the time for each step |
| Standard work in process | How many units sit at the station |
| Quality checks | What to check and how often |
| Safety | Hazards, PPE, and key precautions at each step |
To write it:
- Watch the job with the people who do it, and time each step over several cycles.
- Pick the best current method with the team, not for them.
- Write it with photos and few words, and post it at the workstation.
- Train everyone on it, on every shift.
- Change it when someone finds a better way, and retrain.
Standard work is a baseline, not a straitjacket. You cannot improve a process that changes every time someone does it, because you cannot tell what helped. And an improvement that never gets written into the standard fades when the person who made it moves on.
Measuring Progress
Track a few measures and watch the trend over time. A single reading says little.
| Measure | What it is | Good direction |
|---|---|---|
| Lead time | Time from order to shipment | Down |
| Work in process | Units sitting on the floor | Down |
| First pass yield | Units right the first time | Up |
| OEE | Availability x performance x quality | Up |
| PM compliance | Scheduled maintenance done on time, target 90 percent or higher | Up |
| Floor space | Space used for production vs. storage | More for production |
| Safety incidents | Injuries and near misses | Down, with honest reporting |
Common Mistakes
| Mistake | What it costs |
|---|---|
| Mapping from a desk instead of walking the process | The map shows the plan, not what really happens |
| Adding kanban on top of a forecast schedule | Two systems fight and inventory grows |
| Setting bin sizes once and never checking | Shortages or wasted space |
| Writing standard work without the operators | People ignore it |
| Making a map and never acting on it | All the effort, none of the benefit |
Check Your Understanding
1. A value stream map shows 6 minutes of process time and 15 working days of lead time at 8 hours a day. What is the value-added share?
Fifteen days is 7,200 minutes, and 6 ÷ 7,200 is less than 0.1 percent. The best target is the waiting between steps, not the process time.
2. A department builds to a monthly forecast and keeps running out of one part while overflowing with another. What would pull change?
Each part would be replaced only as it is used, so the part that sells gets rebuilt and the one that does not stops piling up.
3. A line uses 25 seals an hour. It takes 6 hours to get a refill, and the team adds a 10 percent margin. How big should each bin be?
25 x 6 = 150, and 150 x 1.1 = 165. Round up to a practical size, such as 170 or 175.
4. An operator finds a better way to load a part, and everyone on that shift starts using it. What still has to happen?
Update the standard work, confirm it is safe and holds quality, and train the other shifts. Otherwise the improvement stays with one group and may be lost.
Key Takeaways
- A value stream map shows the flow of material and information and exposes the waiting between steps.
- Value-added time is commonly less than 5 percent of total lead time.
- Push builds to a forecast. Pull builds only when actual demand triggers it.
- Kanban signals replace what was used, and no signal means no work.
- Point-of-use storage brings tools and parts to where the work happens.
- Standard work is the current best method and the baseline for the next improvement.