Augos Factory / Learn / Variation and standard work
Learn · variation, standard work and Six Sigma
Variation is a process signal, not a verdict on people.
In short
Process variation is how much the same task's duration or result changes from one time to the next. When a standard task such as a changeover takes seven minutes one day and forty the next, something is not settled. It is usually the method, tooling or materials. Standard work fixes the best known method so it can be repeated, then improved.
Reading variation
Where the variation is decides who acts
| Where the variation is | What it usually signals | Who acts |
|---|---|---|
| Within one task on one line | No settled method, tooling or material for the task | Engineering: standard work, quicker changeovers |
| Between operators on the same task | The best operator's method has not been passed on | Supervisors: the best operator trains, trainees close the gap. Best operator › |
| Between teams or shifts on the same task | The best team's method has not spread | Training: copy what the best team does |
| Between sites on the same task | One site has solved what the others have not | Group operations: move the best practice across sites |
A task that varies wildly usually lacks a method, a tool or a part, rarely effort. That is why each operator is compared with the line's own best task by task, and coaching starts with the method and the tools. The shop-floor charter ›
Measuring it
How do you measure process variation?
For task durations, the median and the quartiles are more useful than the average and the standard deviation. A few very long events skew the average.
recommended = median − median absolute deviation, from at least ten events
spread = interquartile range = 75th percentile − 25th percentile
outliers = events beyond 1.5 × the interquartile range
A wide spread with a fast recommended time is the clearest opportunity in a plant: the fast version already exists, it just isn't repeated.
An early Augos study
One task, three sites, a tenfold spread
At a three-site steel processor, the typical best coil change ranged from 6.6 to 11.2 minutes between sites. The spread at the least consistent site was 12.5 times that at the most consistent. The fastest site was not the steadiest, so each had something the others could copy. Coil set-up remained that client's largest addressable loss.
Coil changes by site: the spread
Illustrative dotsThe same coil change at three sites of one steel processor, each centred on its own typical time. The band shows how widely each site's changes scatter, relative to the steadiest site.
An early Augos study · one anonymised steel processor, three sites, 2,934 coil changes. Band widths are each site's standard deviation relative to the steadiest site; the dots are illustrative. Site, products and people removed.
Standard work
Three elements of standard work
- Takt time: the pace customer demand sets.
- Work sequence: the order of steps the best method uses.
- Standard work in process: the materials and parts that must be ready for the sequence to run.
Six Sigma
Six Sigma is the reduction of variation
Six Sigma projects follow DMAIC: define, measure, analyse, improve, control. The measure and control steps need the same thing as kaizen: the same task, measured the same way, every time it happens.
Questions
Variation, answered
Isn't variation just people working at different speeds?
Rarely. When the same task varies widely, look first at method, tooling and materials. Effort is the least common cause.
Why the median rather than the average?
One very long stop can drag the average up for weeks. The median shows the typical event, and the quartiles show the spread.
How many events do you need?
At least ten for a recommended time. Both benchmarks use every event in the calendar year to date, outliers set aside.
Find your widest spread.
Thirty minutes with a manufacturing specialist: which tasks vary most on a line like yours, and the fastest version your team already does.
- Every task timed
- Typical, recommended and spread
- Prices in rand, ex VAT
A manufacturing specialist replies within two business hours to set a 30-minute call.