WIP (work in progress) is the cut work waiting between operations on a sewing line. A little WIP keeps every operator busy; too much hides problems, damages garments and slows the whole order.
Reading WIP
WIP tells you where the line is out of balance:
- WIP piles up before an operation → that operation is a bottleneck.
- An operator has no WIP → the operation before is too slow, or bundles are not moving.
Formula: WIP at an operation = Pieces completed by the previous operation − Pieces completed by this operation
Example: side seam has finished 700 pieces since the style started; bottom hem has finished 520. There are 180 pieces of WIP waiting at bottom hem.
How much WIP is right?
A common rule is one to two hours of the line's output in total, spread evenly - enough to absorb small stoppages without hiding problems. For a line making 100 pieces per hour, 100-200 pieces across the line is usually enough.
Controlling WIP
- Balance the line so no operation is much slower than the pitch time.
- Set a WIP limit per operation - an operation should not produce far more than the next one can handle.
- Move operators to the bottleneck when WIP starts to grow.
- Feed cut work at the line's actual output rate, not faster.
Tip: Record production by operation every hour. WIP is simply the difference between neighbouring operations, so hourly data shows a bottleneck while you can still fix it.