Reels and Sheets Waiting: WIP in a Packaging Plant

Every reel, stack of boards and pallet of finished boxes standing between two stages of your plant is money you have already spent and not yet been paid for — and in corrugated, it is money that is quietly degrading while it waits. Cut the average time a board spends between the corrugator and the conversion line from three days to one, and on a 250-tonne plant you free up several lakh in working capital and remove a warp-and-damp risk at the same time. This page shows how to see that waiting and put a rupee number on it.

Walk your plant at 11 a.m. and count what is standing still: reels staged at the corrugator, boards stacked waiting for the printer-slotter, die-cut blanks waiting for stitching, finished bundles waiting for the truck. Each pile feels like "work in progress" — normal, necessary, the sign of a busy plant. Most of it is neither necessary nor free. It is working capital frozen in a shape you cannot invoice, aging in a climate that does it no favours.

Key points

• WIP is cash you have spent and can't bill. Paper bought, partly converted, labour and power already applied — but not yet a sellable, despatched box.
• In corrugated it is also a quality clock. Boards warp, absorb moisture and lose compression strength the longer they wait, especially through the monsoon. Waiting is not neutral storage; it is slow spoilage.
• Little's Law makes it measurable. Average WIP = throughput × average time-in-plant. Halve the waiting time and you halve the WIP — no extra sales needed.
• The carrying cost is real money. Working-capital interest, space, handling, damage and obsolescence on held stock typically run well into double-digit percentages a year.
• A camera counts piles and clocks dwell time — how many pallets are waiting and for how long — but it does not weigh them or read grade. The kilograms stay a weighbridge job.

Why waiting is worse in corrugated than in most plants

In a machine shop, a part waiting between operations is just idle capital. In a corrugated plant, a board waiting between the corrugator and conversion is idle capital that is changing. Freshly corrugated board is warm and holds moisture; stacked too long, too high or in a damp godown, it warps, the flutes relax, and the box you make from it fails the customer's box-compression spec. So WIP in packaging carries two costs at once: the financing cost of any held inventory, and a spoilage cost that is specific to paper and board.

This is why "we'll run it tomorrow" is more expensive than it looks. The board you corrugate today and convert Thursday is not the same board — it has lost some of what you paid for. Reducing waiting time is therefore both a working-capital play and a quality play, and the two reinforce each other. It is the same bottleneck logic that makes shipments slip; see why your shipments slip and how to see the bottleneck in time.

How to see WIP without a WMS

You do not need a warehouse management system to get started. You need to count the same waiting points at the same time each day and watch the trend. The three that matter in most corrugated and packaging plants:

1. Reels before the corrugator. Some staging is sensible — you want the next reel ready. Beyond that, reels standing for days are capital and damage risk (crushed outer wraps, core losses).
2. Boards between corrugator and conversion. This is the big one. It is the hand-off that warps, and the queue that hides your real lead time.
3. Finished boxes awaiting despatch. Boxes made ahead of the truck are the most expensive WIP of all — fully converted, fully costed, occupying the most space, and exposed to the most handling damage.

For each point, log a simple count once or twice a shift. Within two weeks you have a profile: where WIP concentrates, which shift builds it, and whether it is growing. That profile is worth more than a precise one-off valuation, because it tells you where to act. The general discipline of reading output and queues in real time is covered in production line monitoring with cameras.

Putting a rupee number on the waiting

Use Little's Law to size the WIP, then apply a carrying cost. Illustrative; plug in your own.

Three honest notes. First, ₹45/kg blends paper near ₹38/kg with partial conversion added — a finished-box pallet is worth more per kg, a staged raw reel less, so weight the value by where the WIP sits. Second, 18% is a stand-in for the all-in carrying cost (working-capital interest, space, handling, damage, obsolescence); yours may be higher if you borrow on a cash-credit limit. Third, and most important, this table only counts the financing cost — it does not count the warp-and-reject cost of board that waited too long, which in a bad monsoon can dwarf the interest. The real prize is usually quality, not interest.

What halving the waiting actually takes

You reduce WIP by smoothing flow, not by working harder:

• Balance the two stages. If the corrugator out-runs conversion, boards pile up by design. Match the pace, or schedule the corrugator to feed conversion just ahead of need.
• Smaller, more frequent lots. Big batches feel efficient and create the biggest queues. Shorter runs that match the conversion line's pace cut the waiting stack sharply.
• Despatch discipline. Boxes should be made close to the truck, not to a comfortable schedule. Finished-goods WIP is the easiest to attack and the most expensive to hold.
• A dry, disciplined board float. If some float is unavoidable, protect it — off the floor, capped height, out of the damp — so waiting costs you interest but not rejects.

Each of these shows up as a shorter dwell time at the waiting points you are already counting, so you can see the improvement in the same daily log that found the problem.

What a camera can — and cannot — do here

This is the honest boundary. A general floor camera is genuinely good at WIP, because WIP is a visible, countable, time-stamped thing: it can see how many pallets of boards are standing between the corrugator and conversion, and — because it watches all day — how long they have been there before they move. Dwell time, which is the hard number to get by hand, is exactly what continuous video measures. It also sees the upstream cause: a conversion line that stopped and let the board stack build.

What it cannot do is weigh those pallets or read board grade and moisture. It gives you counts and dwell times, not kilograms and GSM. So the rupee valuation still needs your weighbridge and costing; the camera supplies the time and location that tell you which pile to attack. The same honesty applies across plant types — see how it plays out in injection-moulding units, where WIP is totes of mouldings between the press and assembly.

That slice is exactly what Mama does. It watches the morning's footage — your cameras or ones we install — and sends the owner a short WhatsApp note: machines that stood idle, changeovers that ran long, and pallets and reels that have been waiting too long between stages. It will not weigh the board or read its grade, and we would rather tell you that up front than have you discover it later. Pair it with your weighbridge and you have both halves: the kilograms from your scales, the waiting from video.

Send us a short video walk-through of your plant and we will send back where the hours and the WIP are piling up, a camera plan and a proposal. Read this alongside conversion cost per kg and corrugated box wastage — waiting, wastage and conversion cost are the three places a thin box-making margin quietly leaks.

The bottom line

Reels and sheets waiting are not a sign of a busy plant; they are a sign of an unbalanced one, and in corrugated they age while they wait. Count the three waiting points daily, size the WIP with Little's Law, and remember the interest is the small half of the cost — the warp and the reject is the big half. Shorten the waiting and you free cash and cut rejects in the same move.

By the Mama Editorial Team. Figures are illustrative; build your WIP valuation from your own throughput, value-per-kg by stage and carrying rate before acting.