Monday, August 30, 2010

A Step-By-Step Process for a Changeover Workshop (Part 1)

Changeovers take time. Different models need different dies, different fixtures, and different settings. Usually, all of these have to be changed. During the changeover process, I’m making nothing. I am very tempted to make more than I need when I have everything set and ready to run.  I may only need 100, but I will go ahead an make 500 or 1,000 units, because at least the machine was productive, and I can put the extra pieces on the shelf, ready for when they are needed.
Then they sit on the shelf.  I didn’t need them when I made them. I t can turn out that now that I have made them, I won’t need them for a long time.  Depending on what “they” are they can get dirty or damaged just from sitting.  The can rust or otherwise deteriorate.  In any case, I’d better keep track of them, because I need to know where I put them when I need them.  So someone will have to keep (or enter into the system) an accurate record of how may I stored and where I put them.
When I need some again, I need to remember to look up how many I have already and where I put them.  Sometimes we go ahead and make a fresh batch because we forget that days, weeks, even months ago, we made some of these.
It would be better if we could make the changeover so short that the easiest thing to do is to make exactly the number we need when we need them.  What if we could change from one product to another on a piece of equipment in less than ten minutes?  That would make a big difference, but it can seem like wishful thinking, because now it takes us over an hour and sometimes longer.  We can’t even predict how long it will take.  It depends on how things go.
SMED stands for Single Minute Exchange of Dies.  Single minute really means single digits. SMED means changing dies (or whatever has to change) in less than ten minutes. Our aim is to do this consistently.
If we have a machine that is idle most of the time anyway, the need to get it down to SMED is not as great.  The ideal machine for a SMED or quick change workshop is a machine that gets heavy use, and now takes an hour or so to change over if things go reasonably well.
Our first step is to pick a machine or set of machines that take around an hour to change over.  Then, we form a team.  The team should have eight to twelve people: An operator who runs the machine; a person who does the changeover (this may be the same as the operator); a supervisor from the area; depending on the equipment, a tool-maker, a maintenance person, a manufacturing engineer, an industrial  engineer; and it is often useful to have one or more people who are completely na├»ve about the process, who can ask, “Why do you do that?” without fear of looking foolish.
We start by giving the team a brief orientation about our approach to shortening the changeover time.  Our goal is to shorted the time that the machine is actually not producing, often referred to as the “internal” time. We want to identify all the activity that takes place during the time the equipment is not running.  One of our early steps will be to make some of the “internal” activity “external.”  By this we mean that some of the things we do while the equipment is stopped can be done before we actually shut down the machine.  Others can be done after the machine is up and running again.  The latter include cleaning up and putting away tools and tooling.
We summarize our effort by using the analogy of a pit stop in an auto race.  We want to get the car back into the race as quickly as possible.  We do this by having everything at hand.  Fuel can be added quickly.  Tires are ready and can be changed out very quickly.  The car gets back in the race, and then the tires that have been removed are put away, along with any tools that were used.
In our case we want to get our equipment back into production as quickly as possible.  The team will carefully observe a changeover to see how we do it now.  Then we will begin to make changes that make the changeover quicker.
These are the techniques for observing the changeover, recording data as we observe the work. 
1.     A verbal written record of every action of the people doing the changeover
2.     A spaghetti diagram of the changeover operators’ movements.
3.     A measurement of the distant walked, either using a pedometer or counting the operators’ steps.
4.     A written capture of ideas for improving the changeover, as these come to mind.
Sometimes the team is tempted to make a video of the entire changeover process.  Video can be a very useful tool, but at the initial stages of a workshop I would argue strongly against using video. 
The techniques listed above make it possible to move much more quickly to implementing changes that get results.  When an hour or more of video is recorded, the next step almost inevitably becomes watching the video and extracting data from it.  The techniques we will detail here extract and summarize important data as we go.

In the next posting we will go into detail about using the four techniques listed.

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