Reducing Downtime with SMED

As we explained in our previous Lean Maintenance column about waste or Muda reduction, waiting for something or inappropriate work (work that doesn’t add value) are considered to be waste in the Lean environment.

In Japan, Shigeo Shingo observed that there were some organizations that were spending as much time changing over for products as they were running the products. He decided that he should work towards a Single Minute Exchange of Dies (SMED), which really meant a changeover in nine minutes or less.

In the world of maintenance, the same principles as applied by Shingo can be applied to change-outs of pieces of equipment. As with all Lean initiatives, the focus is first placed on those pieces of equipment that have the greatest effect on production — red line or critical equipment. It follows then, that the longest changeovers on the critical equipment are the first to look at.

When you take a look at the cost of downtime in the auto industry at thousands of dollars per minute, the savings become significant. Similarly in the steel and paper industries where the downtime cost is only in the hundreds of dollars per minute — but change-outs often take between 12 and 24 hours — minutes or hours make a big impact

Once the change-out to be analyzed has been identified, the first questions you ask are Why are we doing this change-out ? Why do we do it in the frequency that we do? Is it really necessary? Is there a technology or combination of technologies that would allow us to extend the time between change-outs?

At one paper mill, the staff was able to extend the frequency of 12-hour roll changes from the traditional time frame of every six months to 18 months — and even two years — by installing on-line vibration monitoring and an oil analysis program. This was applied to seven rolls, reducing the return on investment (ROI) on the monitoring equipment to less than a year.

If it has been decided that the change-out must take place, you need to get a realistic idea of how long it takes to do that job. At this point the involvement of those doing the work is crucial. The purpose of the exercise needs to be explained and staff co-operation gained, which in some instances might include communication with a trade union.

If the culture allows, the best way of carrying out the analysis is by making a video recording of the change-out, if not then the good-old pen, paper and stopwatch will do. The obvious advantage of video is that you can go back over the work time and time again.

The next stage is to split the change-out into discreet tasks or elements. If you have a good Standard Task Procedure, this can be used before the change-out. If not, it will have to be done after the change-out has been observed.

A note of each element should be made (here’s a tip: write them on sticky Post-It notes) and after the change-out has been observed, a time should be allocated to each element. You then need to separate them into Internal Elements — those that can only be done during the change-out, and External Elements — those that could be done before or after the change-out while the equipment is running.

For example, fittings are moved from the old to the new equipment, couplings are swapped, bearings are greased, the old equipment is cleaned, and the new equipment is not brought into the area until the old is removed.

Also, any waiting time that is observed needs to analyzed. Are parts being moved? Is an operator required? Could something else be done?

The goal now is to move as many of the external elements out of the change-out and eliminate the waiting. This is done by ensuring that rigging, tools, etc., are available at the worksite, neatly laid out in the order they will be used — even to the extent that they may be colour-coded.

Replacement equipment should be complete, as typically the downtime incurred making them complete far exceeds the cost of spare fittings or couplings, etc. Any equipment, parts or labour should be on site at the appropriate time, with no waiting.

If you have noted the elements on the Post-Its, they can now be placed in a column titled ‘External.’

When you have moved all the External elements, it is time to analyze the Internal elements by asking these questions: What exactly are we doing? Why are we doing it? Why are we doing it now? Who is doing it? Where are we doing it?

The idea is that you will be able to streamline the process by: combining rigging to eliminate changing it over, combining tasks, installing quick disconnects wherever possible, installing quick-release pins, using power tools, or making sure guards are easily removable, and so on. You might even find that it is cost-effective to have toolboxes dedicated to the change-out.

Note : Safety should never be compromised in any part of the exercise.

As you round out the analysis, it is worthwhile to take a look at the external elements with a view to streamlining, by asking the same questions as for the internal elements.

The next stage of the process is to decide which of the ideas you are going to adopt, based on cost effectiveness, how quickly it can be implemented, its effect on other elements, etc. Once this is done, you will need to test the ideas and develop a new Standard Task Procedure, making sure that all the elements observed in the change-out have been accounted for in the new procedure.

This procedure is then rolled out and used at the next change-out, with any modifications required being entered in the Standard Task Procedure. Many of the ideas that you come up with will be able to be incorporated very easily into similar change-outs, increasing the product of the maintenance department — equipment availability.

A byproduct of these analyses is a solution for another problem facing maintenance groups — the diminishing skilled and experienced workforce — as, at the end of the exercise, you will have a set of procedures that will encompass the knowledge of the existing workforce in a format that any newcomer could follow.

Cliff Williams is engineering and maintenance manager at Multipak Ltd., Mississauga, Ont., and a consultant with TMS Total Maintenance Solutions of Markham, Ont. He can be reached at williamsc@sprint.ca.