Introduction to SMED: A Neglected Method in Lean Construction

18 Aug 2016

SMED, short for Single-Minute Exchange of Dies, refers to a method in the Lean Production System that is used for quick, simplified and efficient production set-up and changeover from one product/process to another, which often constitute the major causes of production downtime (non-productive time/stoppages)¹. It is one of the foundational blocks of a continuous, improved production flow. The phrase "single minute" does not mean that all changeovers and setups should take only one minute, but that they should take less than 10 minutes (in other words, "single digit minute")². The “Dies” refer to specialized tools used in manufacturing industries to cut or shape material mostly using a press, which need to be modified and re-setup when a production model is changed. Changing dies could stop processes for an extended amount of time.

Car racing is often used as a metaphor for SMED, with process setups/changeover as pit stops. In fact, many of the pit stop tricks are used in SMED, from prepositioning everything you need to using quick attach and release tools (see the following video).

The video contrasts a Formula 1 racing pit stop at the Indianapolis 500 in 1950 with one in 2013 in Melbourne, Australia. The time the car was stopped reduced from 67 to 3 seconds. The 1950 pit stop used 4 people for 67 seconds, which sums up to 4 minutes and 28 seconds of labor. If we include the external setup — before the car arrives — and the cleanup afterwards, the 2013 pit stop used 17 people for 44 seconds, or 12 minutes and 28 seconds of labor. In terms of labor costs, the 2013 pit stop was therefore more “costly.” In a race, however, cutting the car stoppage time by a factor of 22 is something invaluable ².

Main Steps

SMED has applications in construction too and needs to be thought through in a different way. The problem to be addressed is how can one reduce the set-up to complete a particular task. Therefore, construction practitioners need to understand the core of SMED with its techniques in Lean production and adopt them to their work contexts.

Good questions to ask are⁴:

What can we do before we get to the workplace that will make work at the point of assembly safer, faster, cheaper, etc.?
What can we do while subsequent teams are at the workplace?
How can we reduce the time we spend at the workplace?

As an introduction to the topic, we will just give the main steps to SMED, which are^5,6,7:

1) Observe the current methodology:
Current procedures generally are recorded on video tape of all the setup/ changeover process. Get an activity or process where the changeovers/setups take a long time and the variability is high. Be sure to capture both “human” elements (elements where the operator is doing something) and “equipment” elements (elements where the equipment is doing something). A simple table can be created to investigate the setup/ changeover process (describing activities, activity durations, activity reparations, activity types - Internal or External):

Figure 1. An exemplary setup preparation sheet - setup activities, activity durations, repetitions and activity types (Internal or External) recorded.

2) Separate the Internal and External activities:
internal activities are those that can only be performed when the process is stopped (i.e. setting-up the supporting legs of a mobile crane), while external activities can be done while the process is on-going (i.e. getting the equipment ready for the lifting operation -slings etc can be done before the machine is shut down). The key question here is “Do I have to shut the machine/process down to perform this activity?”. Some prime candidates for external activities are retrival (parts, tools, materials etc), inspection, cleaning and quality checks. Using post-its to discuss with your team whether activities are internal or external can help.

Figure 2. Decide on Internal(I) and External(E) activities with your team using Post-Its

3) Converting the Internal activities to External activities:
For construction, this conversion can be achieved by preparing staff, activity, tool and information planning. Some things to consider are: positioning, on-site tool/equipment configuration, small prefabrications/ tweaks (e.g. prefabricated blocks of competents coming on-site with hooking protrusions), modularization, tool tweaking, increasing on-site process transparency and information flow etc. The question is: If there was a way to make this element external, what would it be? How could we do it?

4) Stream line the process of changeover/setup:
For each iteration of the above process, a substantial improvement in set-up times should be expected, so it may take several iterations. In this step, the remaining internal set-up items are reviewed with an eye towards streamlining and simplifying. Eliminating motion, waiting, adjustments, creating parallel operations, standardizing hardware are typical in this step. The question: How can this element be completed in less time? How can we simplify this element?

5) Continuous training:
After the successful first iteration of SMED application the prime requirement becomes training of all the team members.

A SMED Case from Construction

A SMED implementation for quick setup preparation in construction came from the Manchester Smart Motorways site in the UK8. The project’s Lean Construction team streamlined their chamber installation for underground utilities, a critical task in their project, by studying the installation process setup and externalising some internal activities. The team mainly studied and re-configured the longitudinal site layout and material interface, removed site obstructions with better coordination and preparation, prepositioned components and re-designed a HIAB truck with a trailer to carry and install materials simultaneously for quick attach (see images below)⁸:

Figure 3. Improved material lay-down on an ideal model

Figure 4. Modified HIAB

The benefits obtained from those simple looking modifications are certainly not minor, especially when the repetitive nature and importance of those tasks to the project are considered. The SMED process led to:

Increased productivity from 1.5 chambers in 2 days to 2 per day (167% productivity increase)
Significant increase in the percentage of value adding activities, improved process flow and waste reduction

Conclusion

Although described as an essential method in Lean, systematic SMED studies in construction have received little attention. This may be in part due to the misinterpretation that it is an exclusively manufacturing concept. This blog post aims at increasing the practitioners’ awareness of the topic and prompting them to give some thought to SMED opportunities in their work environments. Construction operations could also be improved through learning from many sophisticated SMED examples from other industries. The key here is to recognize the opportunities for SMED and asking the right questions. The author would like to see more SMED stories from construction. In future posts, some practical details of SMED applications and construction SMED cases could be discussed in more detail.