Keeping an eye on Sales - Association of Independent Corrugated ...

Folding—R<strong>an</strong>domness Controlled
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Figure 2. Conceptual plot of the number of unsellable boxes compared to the average
m<strong>an</strong>ufacturer’s gap value.
is often the enemy of consistent
quality <strong>an</strong>d the result is m<strong>an</strong>y out
of spec boxes that could be easily
avoided.
Real Examples
Shown in Figure 3(a) is data from
a typical RSC medium-weight
liner single-wall order where the
distribution of the m<strong>an</strong>ufacturer’s
gap is not widely varied. As the
order was originally run, 83 boxes
out of the 8319 boxes fell outside
the 1/4” – 1/2” gap toler<strong>an</strong>ce, a
defect rate of 1.00%. The average
gap in the run is found to be around
0.42”. Figure 3(b) shows how the
result would have been different
with only 29 defects if the average
m<strong>an</strong>ufacturer’s gap was kept close
to 3/8”, a defect rate of 0.35%.
Figure 3. An 8319 RSC box medium-weight
single-wall order (a) as it actually was run with
1.00% defect rate (b) with average gap kept
close to 3/8” target with 0.35% defect rate.
Next, Figure 4(a) shows data from
a RSC light-weight liner single-wall
order with small box depth where
the resulting m<strong>an</strong>ufacturer’s gap
was not well controlled. As the
order was originally run, a shocking
1344 boxes out of the 4805 boxes
r<strong>an</strong> fell outside the 1/4” – 1/2” gap
toler<strong>an</strong>ce, a defect rate of 28.0%.
The average gap in the run is found
to be around 0.29”. If necessary
ch<strong>an</strong>ges were made to move this
average gap up closer to the target
of 3/8”, Figure 4(b) shows how only
308 defects would have resulted at a
defect rate of 6.4%.
Figure 4. A 4805 box RSC light-weight liner
single-wall order with small box depth (a) as it
actually was run with 28.0% defect rate (b) with
average gap kept close to 3/8” target with 6.4%
defect rate.
Finally, Figure 5 investigates <strong>an</strong>
order where the board stock warp
ch<strong>an</strong>ged midway through the order.
As originally r<strong>an</strong>, the 8283 box
order ended up with 1127 defective
boxes, a defect rate of 13.6%.
This was primarily because of a
distinct increase in the size of the
m<strong>an</strong>ufacturer’s gap that occurred
1580 boxes into the order. The
increase was due to a ch<strong>an</strong>ge in
the warp of the incoming board
stock. Figure 5(b) shows how if the
average gap was then reduced to
stay in line with the 3/8” target, the
order could have been completed
with a defect rate of 4.18%.
Figure 5. A 8283 box order with warp ch<strong>an</strong>ge
mid order (a) as it actually was run with 13.6%
defect rate (b) with average gap kept close to
3/8” target throughout run with 4.18% defect
rate.
Solving the Problem
Practically
Controlling r<strong>an</strong>domness is not a
new concept: m<strong>an</strong>y processes are
variable <strong>an</strong>d m<strong>an</strong>y industries use
SPC control to m<strong>an</strong>age variability
<strong>an</strong>d use data to decide on target
shifts. However, controlling
r<strong>an</strong>domness is a new concept
to most box makers because
they never had access to tools to
measure variability. However, that
has ch<strong>an</strong>ged with the introduction
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bOXSCORE
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