GlossaryKind of term: Manufacturing termChangeover time (SMED)
What is changeover time?
Changeover time is the time between the last good part of one order and the first good part of the next; SMED is a method for reducing it.
Across that whole period the machine produces no good part, even when it is already cutting again on the new job. The period covers clearing down, swapping workholding, loading and measuring tools, setting the work offset, loading the program, proving out and measuring the first part. SMED (single-minute exchange of die) is a method for reducing changeover time. Single-minute means single-digit minutes, so under ten, not one minute.
What does changeover time depend on?
SMED splits the work into internal steps, which need the machine stopped, and external steps, which can be done while the previous order still runs. Next you convert as much internal work to external as possible, and finally streamline both the internal and the external work. External work includes presetting tools outside the machine, staging workholding and stock, and checking the program beforehand. Zero-point clamping, fixed tool positions for repeat work and quick-release clamps shorten the internal part. How much there is to gain depends on the machine, the order mix and how often the same work comes back.
How does changeover time work in practice?
Changeover time is incurred per changeover, not per part; an order that passes several machines has several. How heavily it weighs per part depends on batch size and on how your estimate spreads setup: on a one-off that single part carries all of it, on a large batch it weighs little per part. Shorter changeovers can therefore make smaller batches more economical. In the estimate it makes sense to use the time your shop achieves today and to adopt a shorter one only once it has been measured over a number of batches.
What is changeover time often confused with?
Changeover time and setup time are used interchangeably on the shop floor, and in English setup often means the whole changeover. In this glossary changeover time is the measured time on the machine between two orders, clearing down the previous order included. Setup time is the planned time in the estimate to get one setup ready for a batch, per setup. What you measure as changeover and what you estimate as setup time need not be the same.
How do you see changeover time in Blake?
In Blake setup is its own line in the estimate, beside material, machining and programming, per piece and per batch, and it carries through to the quantity breaks. The result is labelled as an estimate. More on estimating.
Frequently asked questions
What is the difference between changeover time and setup time?
Changeover time is the measured time between the last good part of one order and the first good part of the next, clear-down included. Setup time is the planned time per setup and per batch in the estimate.
How do you reduce changeover time?
Do outside the machine what can be done outside it: preset tools, stage workholding and stock, check the program beforehand. Then speed up what has to happen inside, for example with zero-point clamping and fixed tool positions for repeat work.
Does SMED mean a changeover takes one minute?
No. Single-minute stands for a changeover of under ten minutes, a single-digit number. It is a target to work towards; what is achievable depends on the machine, the workholding and the work.