Mixed Model Scheduling

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A Discussion On...
Mixed Model Scheduling
Developed by The Office of Continuous
Improvement North Berwick
Developed 3/98 Rev. F, 10/98
S.W.Hall, Manager, OCI-NB 426-4138
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The following is an animated slide presentation
on the subject of Mixed Model Scheduling as
developed by the Office of Continuous - North
Berwick. It presents some interesting points to
consider and a methodology in achieving single
piece flow production in the face of mixed and
changing product schedules, variable process
times, and part and setup times which exceed cell
takt time. Any questions or comments, please call
me at 8-426-4138. Start the slide show and it
will automatically run through the
presentation. Enjoy.
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An Easy Question
In theory
theory
How often can takt time be adjusted?
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A More Difficult Question
In practice
practice
How often should takt time be adjusted?
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ACE Silver Requirement
(Setup/pieces in engine set)process time lt takt
time
Is this time remaining for setup or
running more production? Should we do
anything with this time?
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Can we make cell takt time?
No ?
Yes ?
Above are the usual responses, so why the
question marks? Lets see...
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Understanding Mixed Model Scheduling
Lets consider an example
1,440 minute day (3 shifts) with no lost time. 24
pieces required per day. Takt time, then 60
mins per piece. Therefore, there are 24 takt time
beats in a day. Each beat is 60 minutes
long. We have 1 part number in our cell. And the
cell is empty...
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If we think of our scenario as a matrix (takt
time beats across work centers) and
we represent our part with a colored block...
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Lets follow this part through the cell for a
bit...
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Continuing on...
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Our part proceeds through the cell to its
completion.
6th work center
4th work center
1st work center
2nd work center
5th work center
3rd work center
Youve noticed that every moment available in a
takt time block was not used, however, we did not
proceed until the start of the next available
takt time block Living to the takt time beat is
a very important aspect of Mixed Model Scheduling.
1 2 3 4
Takt Time Block
5 6 7
So far, so good! One part number, one part. Lets
modify our example a bit...
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Understanding Mixed Model Scheduling
Modified example
Same time as before. Same daily requirement. We
now have 2 part numbers in our cell. The cell is
empty...
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Lets see what happens when another part number
is entered into the cell...
1st work center
The first part enters the cell at the 1st work
center, at the first takt time block.
6th work center
4th work center
5th work center
2nd work center
3rd work center
1 2 3 4
Once processed, it is moved to the 2nd
work center, and the next part number enters the
first work center.
5 6 7
Notice, the second part requires the 3rd work
center as well, which is not available until the
6th takt time block...
Notice too, the first part is finished at the
end of the 7th takt time beat - the second part
doesnt finish until the end of the 10th.
8 9
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Understanding Mixed Model Scheduling
Time to review
The cell has to produce to the takt time beat. We
used a matrix to represent takt time intervals or
blocks. We processed one part number, one part
through the cell. Then, we introduced a 2nd part
number, a 2nd part and processed the first and
second parts through the cell. In each case we
started with a cell which was empty.
Lets look at a little more detail...
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What this overlooks is that each work center
has a takt time of its own.
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One part number is processed using a certain
sequence of work centers,
while another part number uses another sequence
of work centers. Thus, each work centers
schedule may differ.
X
X
X
X
X
X
X
X

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This opens up a lot of opportunity, even if we
have parts with long process times, we can still
meet takt through proper scheduling.
1st work center
6th work center
4th work center
2nd work center
5th work center
3rd work center
1 2 3 4
5 6 7
In our simple two part example, the parts
progressed through the cell quite easily with no
other parts to be concerned with. How do we
arrange a multiple part mix?
8 9
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Understanding Mixed Model Scheduling
Modify yet again
Three shift day with considerable lost time. 178
parts due for the week. We now have 22 part
numbers in our cell. Five part families. The cell
is still empty...
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Mixed Model scheduling part families
Based on Time Observation, and using a Process
Matrix, group parts into families according to
similar processes and/or similar flow.
Assign color codes for each family of parts.

For the example that follows cell takt time 30
MIN...
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Following the matrix concept discussed earlier -
takt time blocks across the work centers in the
cell, a mixed model schedule takes shape like the
diagram below...
Schedule the first part, continue it through the
matrix.
Proceed with the next part in the same manner.
Continue scheduling each part as above...
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Continue to build the model one part after
another, keeping in mind periods of time where
everyone in the cell is away from producrion
Key point - every takt time block in the last
work center, must have a part scheduled. This is
how we meet cell takt time!
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Monday Tuesday
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Monday Tuesday
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Understanding Mixed Model Scheduling
Wrap up
Cells can meet takt time even when some parts
have long process times. Work centers typically
do not have 100 of the cells schedule. Schedule
the work according to the takt time beat, not the
process. Repeat the model week-after-week to
allow for the practice of standard work. Strive
to continue to reduce setup time to seconds. The
cell will never be empty again!
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Understanding Mixed Model Scheduling
Whats next?
Establishing Standard Work In Process...
Stay Tuned
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