SMED: How to Cut Changeover Time

A changeover is the time between the last good unit of one job and the first good unit of the next: swapping a tool, cleaning down, setting up for a new product. SMED stands for single-minute exchange of die. It is a method for cutting that time, developed by Shigeo Shingo for Toyota and other Japanese manufacturers in the 1950s and 1960s.

"Single-minute" means under ten minutes, a single-digit number of minutes. The goal is not always reachable, but large reductions usually are.

Why changeovers matter

Long changeovers push businesses into big batches. If it takes an hour to switch products, it feels wasteful to switch often, so you make a week's worth at once. That ties up cash in stock and makes customers wait for anything not in the current batch.

Shorter changeovers let you make smaller batches more often, at the same total cost. The same idea applies outside manufacturing: resetting a treatment room, changing a print job or switching a kitchen from breakfast to lunch service.

The four stages

1. Record the changeover. Video one complete changeover. List every step with its time.
2. Separate internal and external steps. Internal steps can only be done while the machine is stopped. External steps could be done while it is still running: fetching tools, finding the next job's paperwork, preheating.
3. Convert internal steps to external. Prepare as much as possible before stopping, for example by presetting a spare tool off the machine.
4. Streamline what is left. Replace bolts with quick-release clamps, mark settings so they do not need adjusting, and have two people work in parallel.

An illustration

A small printing firm's press takes 45 minutes to change between jobs. The video shows that 15 minutes are spent finding the next job's plates and ink and 10 minutes cleaning tools that could be cleaned after the press restarts. Moving those to before and after the stop cuts the changeover to 20 minutes before any equipment is changed.

What do your changeovers cost?

Enter how often you change over and for how long. If stopped time also costs you output that you could have sold, add an hourly value for it.

In the example, 10 changeovers a week at 45 minutes each, over 46 weeks, comes to 345 hours a year. With two people at £25 an hour, that is £17,250 of labour, before any lost output is counted.

Making it stick

Write the new changeover down as a standard operating procedure, with photos. Keep the tools and parts for it in a fixed, labelled place. Time the next five changeovers and display the times beside the machine.