In a precision machining job shop, a component’s total lead time can be measured in days even when it spends only minutes being cut, deburred and inspected. The difference is often hidden between operations: jobs wait for a machine, a tool, a programme, an inspection slot or approval to proceed.
Value stream mapping (VSM) makes those delays visible. It charts the material and information flow needed to deliver a product, from customer demand through job release and machining to despatch. The aim is not simply to make individual machines busier. It is to understand the whole flow, identify constraints and design a more reliable way to meet demand.
This guide works through a hypothetical hydraulic manifold family. The figures illustrate a method; a real project should validate them against observed shop-floor data. For a broader introduction, see our guide to creating a detailed process map and the Lean Enterprise Institute’s VSM overview.
1. Select a product family and define the scope
A useful map starts with a clearly bounded family, not the entire shop. Group products with sufficiently similar process routes, equipment, materials and workholding. A suitable example is hydraulic manifold blocks that run through CNC machining centres, followed by deburring and inspection.
Use product, quantity and routing information to check that the selected family is meaningful. Then agree on the start and end points. Here, the map begins when a customer order is translated into a released job, and ends when the conforming component is despatched.
Include the information flow as well as the physical route: order entry, planning, programming, material availability, job release and quality approval. Observe actual jobs, including a changeover, instead of relying solely on written procedures. Our project scope boundary calculator can help teams define a focused improvement boundary.
2. Build the current-state map with real shop data
Assume the family receives 720 components per month, over 20 operating days. The daily requirement is 36 good components. With 540 net production minutes per day, takt time is:
Takt time = available production time ÷ customer demand = 540 ÷ 36 = 15 minutes per equivalent unit
Takt expresses the pace required to satisfy demand. It is not a target cycle time for every varied job-shop component. Compare it with family-specific operation times and the actual product mix.
The illustrative current-state routing is saw and blank preparation → CNC Op 10 → CNC Op 20 → deburr → CMM and pressure test → despatch. The map should record observed cycle, setup, downtime, quality and queue figures at each step.
| Measure | Illustrative current state |
|---|---|
| Customer demand | 36 good components/day |
| Net available time; takt | 540 min/day; 15 min/unit |
| Cycle time: saw / CNC 10 / CNC 20 / deburr / inspection | 3.5 / 11.5 / 13 / 4 / 5 min |
| Setup: CNC 10 / CNC 20 | 4 × 55 / 3 × 65 min/day |
| Unplanned downtime at CNC 20 | 65 min/day; 88% availability |
| CNC 20 OEE | 88% availability × 92% performance × 96% quality = 77.7% |
| First-pass yield: saw / CNC 10 / CNC 20 / deburr / inspection | 99% / 97% / 96% / 99% / 98% |
| Rolled throughput yield (RTY) | 99% × 97% × 96% × 99% × 98% = 89.4% |
| WIP across queues | 180 components |
| Queue and administrative time | 10 working days |
| Processing time per component | 37 min |
| Estimated lead time; process cycle efficiency | 10 days + 37 min; about 0.68% |
The ten-day queue estimate comprises 2.5 days for scheduling and job release, 1.5 days waiting on materials, three days ahead of CNC machining, 1.5 days between operations and 1.5 days for inspection and despatch. At 540 minutes per working day, the estimated elapsed lead time is 5,437 minutes: 5,400 minutes of queue and administrative delay plus 37 minutes of processing. Process cycle efficiency is processing time divided by lead time.
RTY estimates the probability that a component passes all listed steps without rework. It complements, rather than replaces, each operation’s first-pass yield. Define rework and inspection data consistently so the team is comparing like with like.
3. State the problem before selecting solutions
Problem statement: Over the last 20 operating days, the hydraulic manifold family required 36 good components per day, against a takt of 15 minutes per equivalent unit. The current route held approximately 180 components in WIP, took an estimated ten working days from release to despatch and achieved an RTY of 89.4%. CNC Op 20 recorded 65 minutes of unplanned downtime per day, while its 13-minute cycle and three 65-minute daily setups consumed more time than the available production window. The project will identify the causes and test countermeasures to improve flow, delivery and first-pass quality without compromising safety or specification.
The figures point to a capacity gap, but they do not prove what is causing it. Confirm setup definitions, check measurement reliability, review the product mix and observe the constraint in operation before deciding what to change.
4. Identify the eight wastes using DOWNTIME
Use DOWNTIME to examine the route and ask where effort is disconnected from customer value:
- Defects: Rework and repeat inspection associated with first-pass losses at CNC and final inspection.
- Overproduction: Jobs released or run in large batches ahead of their need, creating more WIP.
- Waiting: Components queued for machines, materials, programmes or inspection.
- Non-utilisation of talent: Operators’ setup and improvement insights are not consistently included in method design.
- Transportation: Extra movement between separate machining, deburring and inspection areas.
- Inventory: The 180-piece WIP balance ties up space and hides flow problems.
- Motion: Time spent walking to retrieve tools, fixtures, gauges or setup information.
- Extra-processing: Repeated checks, corrections or handling that do not improve the component to its required specification.
Treat these as questions to investigate, not assumptions. For more on gathering shop-floor observations, use our guide to work sampling.
5. Design a future state around the constraint
Start by reducing the CNC changeover burden. SMED (Single-Minute Exchange of Die) separates internal tasks, which require the machine to stop, from external tasks that can be completed while it runs. A practical sequence is to observe and time setups, separate the tasks, externalise feasible work, simplify remaining internal steps, then standardise and sustain the improved method. See the Lean Enterprise Institute’s setup-reduction guidance.
For this family, test these countermeasures:
- Externalise preparation: Stage the next job’s fixture, raw material, tools, gauges, setup sheet and verified programme before the machine stops.
- Preset tools offline: Measure tools away from the machine and transfer approved offsets using a controlled method.
- Standardise work: Create a visual setup sequence, first-piece criteria and clear roles for operator, setter and inspector.
- Improve handoffs: Trial one-piece flow between compatible operations, supported by a clearly limited FIFO lane where immediate flow is impractical.
- Schedule to the constraint: Plan the CNC Op 20 sequence using demand, family compatibility and available capacity. Avoid releasing work simply to keep upstream machines occupied.
- Stabilise availability and quality: Investigate the 65 minutes of daily unplanned downtime and the main sources of rework before setting new operating standards.
The following targets are a future-state hypothesis, not a guaranteed outcome. Validate them in a controlled pilot. For example, reducing CNC 10 setups to four 20-minute changes saves 140 minutes per day; reducing CNC 20 setups to three 20-minute changes saves another 135. If CNC 20’s cycle improves from 13 to 12.2 minutes through validated process changes, its demand load becomes 439.2 run minutes plus 60 setup minutes: 499.2 minutes per day. Reducing its downtime to 20 minutes would leave 520 minutes available. This provides a narrow capacity margin, so the team should monitor variation and protect the schedule.
| Measure | Current state | Illustrative future-state target |
|---|---|---|
| CNC 10 / CNC 20 setup time | 55 / 65 min | 20 / 20 min |
| CNC 20 cycle time | 13 min | 12.2 min, after validation |
| CNC 20 unplanned downtime | 65 min/day | 20 min/day |
| CNC 20 OEE | 77.7% | About 93.4%: 96.3% × 98% × 99% |
| First-pass yields: saw / CNC 10 / CNC 20 / deburr / inspection | 99% / 97% / 96% / 99% / 98% | 99.5% / 99% / 99% / 99.5% / 99.5% |
| Rolled throughput yield | 89.4% | About 96.6% |
| WIP | 180 components | 60 components, controlled by FIFO |
| Queue and administrative time | 10 working days | 3 working days |
| Processing time; process cycle efficiency | 37 min; about 0.68% | 36.2 min; about 2.2% |
6. Sequence kaizen over 90 days
Days 1–15, Define and measure: Confirm family and demand, observe complete setups, validate cycle and queue data, and agree on baseline definitions.
Days 16–30, Analyse and test: Map the current state, verify the constraint, review downtime and rework causes, and run a cross-functional SMED event.
Days 31–60, Pilot improvements: Trial external tool presetting, setup standard work, scheduling to the constraint and a controlled FIFO lane. Review safety, quality, capacity and delivery each day.
Days 61–90, Sustain and extend: Check results against the future-state measures, update visual standards and training, assign process owners, and decide whether to extend the approach to another family.
At each review, compare actual performance with the map and revise the plan when evidence changes. The purpose of VSM is not a polished diagram; it is a shared, measurable plan for improving end-to-end flow.
Build the skills to lead improvement
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