Key takeaways
- In a tray with fixed positions, a missing part becomes an empty spot anyone can see.
- Counting becomes multiplication. For example, 24 parts per tray and 10 trays per box means 240 parts per box.
- With a label and barcode on the box, the receiver knows the quantity without opening it.
- Inventory counts and audits check boxes and trays, not loose parts.
Trays speed up inventory counts because they turn counting into a quick visual check. Every part has a fixed position, so a missing part shows up as an empty spot, and the quantity per box always comes from the same simple multiplication. This kind of visual control in production works at receiving, in line feeding, at shipping, and when counting parts for inventory. Below, we explain why shortages are usually found late, how the count adds up by tray and by box, and what changes in audits.
Why part shortages are found late
When parts arrive in bulk, nobody knows exactly how many are in the box without counting them one by one. Because counting everything takes time, checks are often done by weight, by sampling, or simply by trusting the packing slip. The discrepancy stays hidden until someone needs the last part.
That's when assembly stops. The shortage was there at receiving, but it only became visible once it turned into line downtime. By then, the cost includes the downtime, the search for the part, the rush replacement, and often a dispute with the supplier over where the part went missing.
The problem is rarely a lack of attention. It's the lack of a simple way to see the quantity. A tray with fixed positions solves exactly that, and the logic is the same as in the process and automation trays used to organize the line.
How fixed positions change visual control in production
In a custom thermoformed tray, each cavity holds one part. A full tray has a regular pattern, and any empty position breaks it. The human eye spots an absence much faster than it counts what's there, so the check takes a glance, with no need to handle the parts.
The effect gets stronger when the cavity also orients the part. A flipped or swapped part stands out as much as an empty position. Combining fixed positions with poka-yoke tray design lets a single check answer two questions at once: is everything there, and is everything the right way around?
A few features make the tray easier to read. Position numbers can be molded into the edge, as on the tray in the photo, which helps locate a missing part in trays with many cavities. Tray color-coding can show part status, for example green for released and red for review, using a color scheme defined by the customer.
Where visual checks help: receiving, line feeding, and shipping
At receiving, whoever opens the box checks whether the trays are full without removing the parts. A discrepancy gets recorded on arrival, while it's still easy to trace where it came from. In line feeding, operators see how many parts are left in the tray and know when to call for the next one, which helps the line keep pace and lowers the risk of running out of parts mid-shift.
At shipping, a full tray doubles as the outbound check. The packer spots an empty position right away, before closing the box. This applies both to in-plant logistics trays, which circulate between departments of the same plant, and to trays that travel from supplier to customer and come back empty.
How inventory part counts add up by tray and by box
With a fixed quantity per tray, counting becomes multiplication. For example, with 24 parts per tray and 10 trays per box, each full box holds 240 parts. The person taking inventory counts boxes and checks that the trays are full, without counting all 240 parts one by one.
The layout is set during design. Our engineering team starts from the part and the container you already use, whether that's a KLT bin (small load carrier), a rack, or your customer's standard packaging, and calculates how many parts fit per tray and how many trays fit per box. That calculation accounts for part protection, stacking, and, when possible, a number that makes the math easier, such as a multiple of the production lot or of line consumption.
With trays in repeated use, the quantity per box stays the same every cycle, which simplifies planning. Returnable trays are often sized specifically for the standard container used in that loop, and the count follows from that sizing.
Labels, barcodes, and what changes in audits
Because the quantity per box is fixed, it can go on the label with confidence. The box ships with a label and barcode, and the receiver knows the count before opening it. Scanning the barcode logs the receipt in the system, and a visual check of the trays confirms that the contents match the label.
In an audit, the nature of the work changes. Instead of counting loose parts, the auditor checks sealed boxes by their labels and opens a sample of them to verify that the trays are full. Traceability also improves, because every box has a known quantity and an ID, and a discrepancy can be traced to the point where it happened.
How to specify a tray for counting and checks
To propose a layout, we need to understand the part, the box, and the point in the process where shortages usually show up. With that information, our engineering team presents an initial tray proposal with the quantity per tray and per box already calculated.
- A drawing, 3D CAD file, or physical sample of the part.
- The box, rack, or standard packaging the tray will work in.
- The production lot size and line consumption, if you have a preferred quantity per box.
- Where shortages show up today: at receiving, in line feeding, or at shipping.
- Whether the tray stays inside the plant or travels on to the customer.
If the same tray will also feed a robot, tell us from the start, because the layout then has to account for pocket pitch, the topic of our article on matrix trays for robots. You can send your part and box details when you request a quote.
The numbers 24, 10, and 240 are an example layout. The quantity per tray and per box is calculated for each part and each box.
Frequently asked questions
Yes. Visual checks work with small parts. A tray for small parts usually has many cavities, and the regular pattern still shows the empty position. In trays with many positions, position numbers molded into the edge and tray color help locate a missing part faster.
No. Visual checks are done by the operator, just by looking at the tray, with no camera or system required. If your line already uses a vision system, a tray with fixed positions also makes it easier for the camera to read, but that's an added benefit, not a requirement.
The part's geometry and the box size determine how many cavities fit, and the result isn't always a round number. What matters is that the quantity is fixed. When there's some flexibility, our engineering team looks for a layout that makes the math easier, such as a multiple of the lot size or of line consumption.
Counting by the box works when each part has its own cavity. A tray can hold different parts in defined positions, as in a kit, and the quantity of each item per box stays fixed. For models of very different sizes, a separate tray for each one is sometimes the better option.
