For most people, changing a single tyre can easily take 15 minutes. For a Formula One pit crew, changing four tyres takes less than 15 seconds. This is living proof that changeover times can be reduced by analysing each element to see if it can be eliminated, moved, simplified or streamlined. In manufacturing maintenance, single-minute exchange of dies (SMED) is a system for dramatically reducing the time it takes to complete equipment changeovers.
For a long time the belief was held that the effect of changeovers on production could be reduced through long runs or large lots. This ‘solution’, however, increases the inventory of finished goods, and the resulting cost of working capital could offset the savings in terms of lower unit cost.
The concept of ‘economic lot size’ is based on the lot size where the sum of set-up cost and inventory holding cost is at a minimum. Though theoretically correct, this concept was based on the flawed assumption that set-up time is a given and can’t be reduced. But then Shigeo Shingo, a Japanese engineering genius, showed the West a technique through which changeovers could be reduced to below 10 minutes on most equipment. He called the technique single-minute exchange of dies or SMED. His pioneering work led to documented reductions in changeover times averaging 94%, i.e. from 90 minutes to less than 5 minutes.
Perform your maintenance regimen at pace
The time required for maintenance can be reduced substantially through proper planning and preparation. The ideal is to have all the spare parts, skilled persons and tools ready before production is stopped. The maintenance department, similar to the F1 pit crew, can then move in to deal with the problem in the quickest time possible. Care must, however, be taken not to compromise workmanship for speed.
Apply the three SMED steps in the following way:
1. Prepare properly
The primary goal is to reduce the downtime for maintenance by eliminating any waste of time, e.g. operators waiting for maintenance personnel, people searching for parts or tools and delays in fault-finding. Though the best solution will obviously depend on your equipment, manning levels and plant layout, consider some of these options:
- Allocate maintenance personnel to specific areas and ensure that they spend the bulk of their time in the area, instead of waiting for something to happen in the workshop
- Have a controlled satellite workshop in the area where maintenance personnel can do basic work
- Teach the operators to do basic fault-finding before calling the maintenance personnel
- Allow access to the maintenance store after hours and reduce the paperwork involved in drawing spares
- Improve the communication system so that maintenance personnel can be contacted more easily, e.g. through the use of radios or cell phones
2. Streamline the work
Streamline maintenance tasks by considering the following:
- Allow the operator to assist the maintenance personnel
- Reduce the time needed for fasteners and couplings — consider clamps, fewer bolts, split-thread bolts, pear-shaped holes, etc.
- Have fixed settings and reference points to eliminate adjustments
- Standardise components, e.g. PLCs and fasteners
- Try to reduce the amount of walking while working on a machine
- Streamline the process of spares or services procurement
- Eliminate the need for rework — the maintenance person should remain at the machine until stable production has been achieved
- Develop and use standard job plans for executing maintenance tasks
3. Evaluate actual performance (simulations)
Simulations are a highly effective way for the maintenance department to measure its true effectiveness. The analysis should be done judiciously and in partnership with maintenance personnel to incorporate their ideas, and to ensure that they do not feel policed or manipulated in any way.
Take the following into account when performing a simulation:
- The exercise is not a ‘time and motion’ study on maintenance personnel performance — this must be made clear before any such exercises are undertaken
- A simulation can be used to measure any area where the team would like to check the conformity to specified business processes
- The simulated time should be chosen so as to force the use of the spares retrieval system
See how a Kellogg’s plant in Mexico achieved a seamless changeover by making SMED part of a kaizen exercise.
With today’s rapidly increasing diversity and smaller batch sizes, using set-up time reduction to improve cash flow and profitability is becoming critical to the survival of manufacturers. The basic concept of SMED is to reduce machine set-up time, which directly results in smaller batch sizes for parts, allowing the manufacturer to produce only what is demanded by the customer.
DOWNLOAD the white paper The economic significance of effective equipment maintenance for a real-life example of an award-winning improvement strategy developed for a large bottling company.
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