Can Six Sigma be applied to Maintenance Efficiency (wrench time)?

EP Editorial Staff | December 1, 2001

We know there are two principal inputs to the maintenance cost equation: Reduce or eliminate the need to do maintenance (reliability of equipment), and improve the effectiveness of the resources needed to accomplish maintenance (people, parts, and outside services).

Leadership and crafts both want greater productivity in the execution of work. Leadership definitely wants to reduce waste and the dollars associated with it. Crafts want to utilize their time and skills effectively to accomplish equipment tasks professionally. Eliminating wasted time is good for business and good for general morale.

Typical wrench time ranges from 25 to 35 percent while benchmark levels range from 50 to 60 percent. What time-wasting issues make up this gap? From past Viewpoint articles you know that I see things through Six Sigma glasses. Using Six Sigma methodology, we can discover the set of circumstances that represent the gaps. Fundamental to Six Sigma thinking is that: Y (wrench time) = f (x1, x2, x3, x4, &).

What are some of the xs? How about stores delays, equipment preparation, work permitting, travel time, incomplete or wrong diagnosis, inadequate tools, waiting on the cherry picker, bad or wrong spare parts, inadequate work plans, and more.

The trained Black Belt or Green Belt will summon the disciplined Six Sigma roadmap: Measure Analyze Improve Control (MAIC). A team of cross-functional stakeholders will drive the effort to eliminate these daunting wastes. Some key MAIC tools include:

  • Map the as-is process with operations and maintenance stakeholders. (There is an as-is process whether it is controlled or uncontrolled.)
  • Define the inputs that make up the existing process. Are they controlled or uncontrolled?
  • What outputs are really important to the process (in addition to wrench time)?
  • Measure the defects and the current pro-cess capability (sigma, defects per million opportunities).
  • Analyze the failure modes of key inputs.
  • Mitigate the failure modes.
  • Improve the process by mapping the should-be process.
  • Install mistake-proofing tools at key steps (a.k.a. poka-yoke).
  • Validate the improvements and measure the new process capability (sigma, defects per million opportunities).
  • Establish measures and controls to ensure sigma capability is improving and sustained. Yes, statistical process control (SPC) can be used for work processes.

Of the bullets above, measuring becomes a key element of the effort to improve. How is the current process performing? Where are the wastes? How often do these wastes occur (frequency, or MTBF)? How severe are the waste events (time wasted, or MTTR)?

To answer these questions, a data collection method needs to be designed and deployed. Work sampling is one method. Another approach is to “follow the babies,” as we say in Six Sigma; maintenance events (work orders) are literally followed from start to finish. It sounds simple, almost juvenile; but the team will be amazed by what it learns about how the current process works and what comprises the defects (wastes).

Once the measuring phase has been completed, a cadre of immediate quick fixes and opportunities (greater analysis required) will emerge. The opportunities likely will point to broken supporting processes (job plans, work permits, tool crib, outside services coordination).

None of these are simple processes with easy fixes. They likely will require a new, more detailed set of work-process improvement projects.

One of the truisms of Six Sigma is “you don’t know what you don’t know.” Once you have data (now you know), it becomes very apparent that the interactions of maintenance activities are quite complex. If your wrench time is estimated in the 35 percent range, then your maintenance work process is broken.

What supporting processes are broken? You know that the brokenness is impacting the margin on the products you produce, and therefore can be classified a business driver for your company.

Go find out by measuring and converting to estimated dollars wasted (cost of poor quality in Six Sigma terminology). Then begin a structured MAIC path to uncover the defects, mitigate the failure modes, and install the should-be processes to control and sustain to benchmark wrench time. MT




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