Value Stream Mapping and Analysis
What the exam tests
Value stream mapping questions test whether you can select the right product family, draw a current state from observed data, calculate lead time and value-added ratio, and design a future state with a bounded plan. The exam favors maps that show material and information flow together.
Core rules and concepts
- Map one product family at a time, defined by similar process steps and equipment, not by department.
- Start at the customer end and walk the stream; record actual inventory counts, cycle times, uptime, changeover, batch sizes, and information triggers.
- A complete map has a customer/supplier box, process boxes, inventory triangles, information arrows, a timeline, and kaizen bursts.
- Lead time is inventory quantity divided by daily demand, summed across inventory points, plus processing time. Value-added ratio is value-added time divided by lead time.
- The future state should address flow, pull, leveling, and the pacemaker process. Kaizen bursts become an implementation plan, not decoration.
Worked example
A stream has 1,200 units before process A, 600 before B, and 1,800 before C; daily demand is 600. Inventory days are 2 + 1 + 3 = 6 days. Total processing time is 135 seconds. With one 8-hour shift (28,800 seconds), the value-added ratio is 135 / (6 × 28,800 + 135) ≈ 0.078%. The reasoning: the six days of inventory dominate the customer's wait, so reducing batch sizes or introducing pull at the largest inventory point usually improves lead time faster than shaving seconds off processing.
Traps that cost marks
Mapping every part number; using ERP standard times instead of observed times; drawing only material flow; treating process time as lead time; and writing a future state without owners, dates, or measurable targets.