Lean Problem Solving

By Ron Pereira Published on July 8th, 2007

I was over on iSixSigma and saw this question from Chris on their forum.

I have a process that involves 3 seperate work cells. The first cell has an avg. cycle time of 2 hours and so does the third cell. My problem is that the second cell has a test procedure that takes about 6 hours.

I want to set up in/out locations for product in each cell and then shift resources to constraint areas when in/out locations are full. My eventual goal is to put out 20 units per day. How do I determine the size of my in/out boxes for the second and third cells?


I wanted to take some time tonight to comment on this sharing my two cents.  First, I am not sure I really understand all the facts as well as I need to but will make some assumptions.  If I am wrong in my assumptions my advice needs to be taken with a grain of salt.

Takt Time

The first thing Chris needs to understand is what the takt time is for this product.  Using some major assumptions regarding the time available I calculate (assuming customer demand of 20 pieces per day as Chris stated) takt time to be ~ 24 minutes per piece (1440 seconds per piece).  Here are the “time available” assumptions I used to calculate this.

  • Hours per Shift: 9
  • Break Minutes per Shift: 60
  • Shifts per Day: 1
  • Days per Week: 5
  • Days per Month: 20

So, using these assumptions Chris and his friends need to produce a “widget” every 24 minutes.  If they run two shifts we double this and make takt time 48 minutes/piece.

Houston, we have a problem

If I am understanding Chris correctly cells 1 and 3 complete a widget every 2 hours and cell 2 completes a widget every 6 hours.  Since takt time is 24 minutes (1 shift) or 48 minutes (2 shifts) we obviously have some issues here since all three cells have cycle times greater than takt time.  So true flow is impossible until we are able to get our cycle times under takt time.

In/Out Locations

Chris speaks about in/out locations for “product” so I am assuming he means he wants to store some WIP.  In the lean world we typically refer to these locations as WIP supermarkets.  I would like to recommend Chris worry less about how to store more inventory on the line and instead think about how he can get all 3 cells completing a part under takt time.

How to Do This

It is impossible for me to offer much more advice than this since I don’t even know what the product is.  But there is one thing we can be sure of when working to reduce cycle times.  We must attack waste like it broke into our house and wants to hurt our kids.  This waste doesn’t discriminate and will pummel any manufacturer of any product.  So get nasty and kill it like the sick dog it is.

Call Gemba Research

I am not a consultant and have a day job where I work to solve these types of problems for my own company.  So short of the free advice on this blog and possibly email I can only help so much.  But if I can offer a shameless plug for a friend of the blog I would recommend Chris consider ringing the nice folks over at Gemba Research to see if they could be of any assistance.  In my book they are the best of the best.

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