SC QUALITY GUILDValue stream map and takt time
SCQUALITYGUILD.COM/TOOLS/VALUE-STREAM-MAP-TAKT.HTML
Enter the available time, customer demand and the data box for each process to get takt time, days of inventory, production lead time, process cycle efficiency and a drawn current-state map.
ON THE EXAM · CSSGB I.B.1, I.B.2 · FREE · NOTHING YOU TYPE LEAVES YOUR BROWSER
Q-BotClick for an explanation of this tool.For educational use. This page is a study aid. The method behind it has far more depth and detail than one page and one tool can cover, and what you see here is not everything the method offers or everything this site offers. For full understanding and application, use the governing standards and texts, and seek further education, training or qualified advice. Results depend on the data you enter, so check them before relying on them.
What a value stream map shows
A value stream map follows one product family from raw material to the customer and records both the material flow and the information flow. The current-state map is drawn from a walk of the floor, starting at shipping. Each process box carries a data box: cycle time (C/T), changeover time (C/O), uptime and the number of operators. Inventory triangles show the queue in front of each step. The conventions used here follow Rother and Shook's Learning to See.
Takt time
Takt time = available working time per period ÷ customer demand per period. Available time excludes planned breaks and meetings but does not deduct unplanned downtime or changeovers; those show up as uptime and C/O on the data box. Takt is a pace set by the customer, not a measure of the process. Comparing each step's C/T with takt shows which steps cannot keep up (C/T over takt) and how many operators the work content needs if it were balanced: total C/T ÷ takt.
The timeline and process cycle efficiency
- Inventory is converted to days of demand: units in the triangle ÷ daily demand. This is Little's law: lead time = work in process ÷ completion rate.
- The production lead time is the inventory days plus the processing time.
- Process cycle efficiency (PCE) = value-added time ÷ total lead time. A PCE well under 1 percent is normal for a batch-and-queue process. The point is not the exact figure but where the time goes: waiting in inventory.
Common traps
- Mapping the whole plant instead of one product family.
- Using design or standard cycle times instead of times observed on the floor.
- Treating takt as a target for each operator rather than the customer's pace; a step under takt with poor uptime can still miss it.
- Drawing a future state that only moves boxes; it should add flow, pull and a pacemaker. Use the waste walk to find the wastes and the kaizen planner to run the improvements.
On the CSSGB exam
Expect to compute takt time from shifts, breaks and demand, convert inventory to days, total a lead-time ladder, calculate PCE and identify the step whose cycle time exceeds takt. Know the standard icons: process box, data box, inventory triangle, push arrow, supermarket and the timeline.