SMED stands for Single Minute Exchange of Die, a systematic approach to changeover and setup time reduction.
SMED is an acronym that made its way into industrial lingo for decades now. Its origins is in japanese automotive industry of the 1950s when Toyota Production System pioneers led by legendary Shigeo Shingo observed operations on shop floor.
Exchanging a die of a huge press took hours, letting the machine – a valuable resource – stopped and producing no added value. Diminishing the changeover time allowed to convert wasted time into value adding time.
After analyzing the changeover process, the thorough elimination or reduction of unnecessary tasks and better organization cut the duration of a changeover from hours to minutes.
“Single Minute”, till today misleading, does not mean in less than a minute, but in a time measured on a single digit, thus between 0 and 9 minutes, or put in the pioneers’ spirit in less than 10 minutes.
Most often, the changeover happens like the time chart below shows. It starts when the last part from actual production batch is finished and ends when the first part from new production batch is ready to be processed at normal pace.
Breakdown of changeover duration
|Finishing actual batch||Dismount tools||Change tools||Adjustments (machine stopped)||Trials||Process new batch|
The machine is usually stopped and all changeover operations happen in sequence, while the machine is stopped. The machine will start again only after completion of adjustments and trials. Sometimes after quality check and when the appointed staff gives its ok.
Most often all these operations are done without any standard method nor procedures or checklists. This means the changeover sequence and its duration is related to individual know-how, skills and habits.
Teamwork, several operators sharing changeover operations in order to minimize the stop time is also seldom. As changeovers take time, cause productivity loss and carry costs, the temptation is to dilute them in changing less often by launching bigger batches. This leads to adopt so-called Economic Order Quantity to define the production batch sizes.
The EOQ policy ends up with higher inventories and lower agility, which are opposite of what is required in the new paradigm.
Four steps to SMED
The first obvious thing noticed by the engineers was that during changeovers and setup the machine was stopped, even for operations that were totally independent of the machine itself, like preparing tools, dies or various supplies. This led to a first step of the SMED approach:
Discriminate operations that MUST be done while machine is stopped, called internal setup (IS), from those possibly done while machine runs, called external setup (ES), and useless operations. By hunting down all causes of time waste, the SMED team finally came up with a sequence of four steps to reduce changeovers:
- Suppress useless operations, convert IS operations into ES
- Simplify fittings and tightenings
- Work together!
- Suppress adjustments and trials
Quick wins are usually easy to grasp. Identify external setup tasks and treat them like that: do before the changeover, before stopping the machine for those necessary before changing over. Conversely wait until machine is restarted before doing all tasks that are external setups but can be done after changeover.
External setups prior to change are typically preparations of prerequisites:
- tools, parts
- lifting material
Besides, take opportunity to unify parts storage like boxes, crates, feeders in size and types.
External setups post change are typically recordings and tidying up:
- files, notes, tags
- tools, parts, leftovers
Internal setup tasks reduction
Some operations considered at first glance as “internal” can be converted into “external” with significant reduction of machine stoppage.
These operations can be: presets and pre heating (in external oven, with external connection…)
Once conversions done, simplify fittings and tightenings
When all operations that can be done without stopping the machine have been identified and converted, the next potential for setup time reduction lays in the reduction of the “internal” operations. Among them, fittings and tightenings are a major category. The target is to:
- suppress fittings and tightenings partially or even totally
- minimize “turning” movements: they request several grasp-release motions!
- fit at once, in a single motion
- use blocks, jigs, templates
- standardize tools, types and size of screws, nuts…
- go for ideal: use only one type of screwdriver or wrench, challenge to suppress all tools
Once the die, fixture or template for the new batch is set, it is usual to have several adjustments to go through.
These adjustments are also time-consuming and extending the duration of machine stoppage. Adjustments are to be considered as waste. Would the setting be done properly the adjustments wouldn’t be necessary.
- set standard values
- find out adjustment-less methods through physical means, like stoppers, guides, blocks…
- design custom-made tools if necessary
If a machine is critical (bottleneck), its stoppage is to be reduced to the very minimum. It is meaningful in such a case to have a team focused about that. This team is made of the operators and techies from the workcell or workshop that temporarily let their current task down to help to perform a quick changeover on the critical machine. This setup team would act like the racing pit team, each team-mate being assigned a special operation he knows well and performs flawlessly in a very short time.
Trials are like adjustments, to be considered as waste. Everything should be organized and done to make it right first time, without any need for trials.
Related: SMED Explained while doing laundry