RateProof Capacity Study
How to run a capacity verification study
A capacity verification study proves, with cycles timed on the production line, that a supplier can make the volume a customer has contracted for. This guide covers when a customer asks for one, how to run it, the arithmetic behind the verdict, and what the report has to show.
What the study proves
A capacity plan says what a line should make. A capacity verification study shows what it does make. The supplier runs the line under normal conditions, with its normal crew and shift pattern, times real cycles at every operation, and sets the demonstrated capacity of each operation against the rate the customer requires.
The result is a verdict for every operation. A line can only ship what its most heavily loaded operation can make once scrap and downtime are paid for, so the real work of the study is finding that operation, the constraint, and stating how much margin it has.
- Required capacity
- The parts per day the customer has contracted for, over the working pattern the line runs.
- Net available time
- Scheduled minutes minus planned downtime for each machine, times the machines running the operation.
- Effective cycle time
- The measured cycle time divided by the parts each cycle makes.
- Demonstrated capacity
- Net available time in seconds divided by effective cycle time, reduced by the scrap rate. Only good parts count.
- Utilization
- The share of an operation's capacity, or of its time, the requirement consumes. Lower is safer.
- Constraint operation
- The operation with the highest utilization. It sets the capacity of the whole line.
When a customer asks for one
Customers ask for a capacity verification study when they need evidence rather than a quote. The usual triggers:
- Before a new part launches, often as part of the production part approval package, so the customer knows the line can carry the volume before it depends on it.
- When volume goes up. A higher schedule, a new program sharing the line, or a change to the working pattern means the earlier study no longer answers the question.
- When the process moves or changes. New tooling, a moved or rebuilt machine, a new site or a new subcontractor resets what the line has demonstrated.
- When deliveries fall behind. Missed shipments and expedited freight usually lead to a request to show, with data, where the capacity went.
- At planned intervals, for parts the customer treats as high volume or high risk.
The customer normally supplies the required rate and the form the result goes on. Ask early whether any equipment is shared with other parts: if a machine also runs work for other customers, only the hours allocated to this part count toward its capacity.
How to run it
- Fix the required rate. Convert the customer's volume to parts per day over the working pattern you will actually run. 20,000 parts a week over 5 working days is 4,000 parts per day. Use the figure the customer contracted, not the figure the line usually ships.
- List every operation in process order. For each one record shifts per day, hours per shift, parallel machines and parts per cycle. Include the operations nobody worries about: a wash or a test station can be the constraint.
- Total the planned downtime for each machine. Breaks and lunch, changeovers, planned maintenance, any other scheduled stops, and an honest allowance for unplanned stops. Leaving the unplanned allowance out overstates capacity.
- Time real cycles at the line. Time consecutive cycles during normal production, with the normal crew and normal material, not the best operator on the best hour. Keep every lap. If a cycle is an outlier, set it aside where a reviewer can still see it.
- Run the line and tally it. Record good parts, scrap and downtime hour by hour through the run. The tally shows whether the timed cycles hold up over hours of production.
- Compute each operation, then the line. Work out net available time, effective cycle time, demonstrated capacity, the requirement at each operation and its utilization, then name the constraint. The next section works through the arithmetic.
- Report the result and the actions. Every operation at high risk or failing needs a cause and a countermeasure before the customer signs off.
The arithmetic, worked through
A housing line has three operations in sequence: machining, a batch wash, and a leak test. Every operation runs 3 shifts of 8 hours, and the customer requires 4,000 parts per day.
| Operation | Parallel machines | Parts per cycle | Planned downtime per machine, minutes | Measured cycle, seconds | Scrap, percent |
|---|---|---|---|---|---|
| Machining | 4 | 1 | 150 | 64 | 1 |
| Wash | 1 | 12 | 90 | 240 | 0 |
| Leak test | 2 | 2 | 120 | 70 | 2.5 |
The wash is the operation that teaches the most, so here it is step by step.
Net available time
Three shifts of eight hours is 1,440 scheduled minutes per machine. The washer loses 90 minutes to planned downtime, which leaves 1,350 minutes. There is one washer, so that is the operation's net available time.
Effective cycle time and demonstrated capacity
One wash cycle takes 240 seconds and cleans a basket of 12 parts, so the effective cycle time is 20 seconds per part. 1,350 minutes times 60, divided by 20, is 4,050 parts. The wash scraps nothing, so its demonstrated capacity is 4,050 parts per day.
The requirement at this operation
Set against the contracted 4,000, the wash reads 98.7 percent: high risk, but passing. That comparison is wrong. Every part the wash cleans still has to pass the leak test, which rejects 2.5 percent, so the wash has to make 4,000 divided by 0.975, which is 4,102.6 parts per day, shown rounded up as 4,103. Divide that requirement by the 4,050 the wash demonstrated and its part capability utilization is 101.2 percent.
Machine utilization
The second measure asks how much of the washer's time the requirement consumes. It takes the contracted 4,000 and adds the scrap of this operation and every later one as an overproduction allowance, 2.5 percent here. At 20 seconds a part that is 1,366.7 minutes of running. Add the 90 minutes of planned downtime and the wash needs 1,456.7 of its 1,440 scheduled minutes, a machine utilization of 101.1 percent.
The higher of the two measures governs. The wash fails at 101.2 percent and it is the constraint: the line cannot ship 4,000 parts a day until the wash gains capacity, whatever the other operations show.
Two other results are worth reading. Machining passes on output at 85.6 percent, but its machine utilization is 87.0 percent, so time rather than output binds it: each of its 4 machines gives up 150 minutes a day to planned downtime. The leak test sits at 91.3 percent, high risk. It passes, with no margin for a bad shift.
The risk bands follow the thresholds customer capacity forms use: below 85 percent is low risk, from 85 medium, from 90 high, and at 100 percent or more the operation fails. An operation whose planned downtime consumes its whole schedule fails on its own terms, with no time available.
The free capacity verification calculator runs this same arithmetic in your browser. Enter the three operations above to see each one's results, then replace them with your own line.
What the report must show
A customer reads a capacity report to check the arithmetic and to judge whether the evidence is real. A report that holds up shows:
- The required rate and where it came from: the contracted volume, the working pattern, and the parts per day they produce.
- Every operation in process order, with shifts, hours, machines, parts per cycle, each downtime allowance and the scrap rate.
- The cycle evidence. How many cycles were timed at each operation, when, and the average used. Outliers set aside stay visible, struck through, so nothing is quietly removed.
- The figures for each operation: net available time, effective cycle time, demonstrated capacity, the requirement at that operation, both utilization measures and which one governs.
- A risk band for every operation, and the constraint operation named.
- The production run: good parts, scrap and downtime by hour, with planned against observed cycle time, scrap and downtime, so a reviewer can see where the run disagreed with the plan.
- Actions for every operation at high risk or worse, each with an owner and a date.
- Who ran it, where and when: part number, supplier, site, the engineer, and the date of the run.
Rounding should always fall on the safe side. Requirements round up and capacities round down, so the report never credits the line with a part it did not demonstrate. The capacity study template lists every field and formula a report like this rests on.
Mistakes that sink a study
- Quoted cycle times instead of measured ones. The study exists to replace the quote with evidence.
- Every operation set against the contracted rate. An operation upstream of scrap has to make more than the contract, as the wash shows.
- No allowance for unplanned downtime. No line runs a whole day without an unplanned stop, and the customer knows it.
- Shared equipment counted at full time. Only the hours allocated to this part are available to it.
- A showcase run. Extra staff, hand picked material or the best operator produce a number the line will not repeat on an ordinary day.
- Studying only the operation everyone expects to bind. The wash in the example was nobody's first guess.