A sample arrives and is approved; the production delivery is subtly different. It is common enough to be worth understanding, because the response depends entirely on why – and two of the four reasons are legitimate.
Reason one: process variation, which is legitimate
Everything manufactured varies within a tolerance. Thickness, colour, weight – all of it moves slightly between runs. If the difference is inside the tolerance you specified, it is not a defect and there is no complaint to make.
Which is why the tolerance has to be in the specification. Without one, there is no basis for the conversation in either direction.
Reason two: different production conditions, also legitimate
A sample is often made on a different machine, at a different time, from a different resin lot. Colour matching in particular varies between lots more than buyers expect. Within reason this is normal manufacturing.
What is not normal is a large difference with no notice. A supplier who knows a lot has shifted should say so before shipping.
Reason three: the sample was not representative
Some samples are made carefully – selected, hand-finished, or produced under tighter control than routine output. This is the one to watch for, and it is why you should ask explicitly whether the sample is from production.
A supplier who says “yes, that is a production sample” can be held to it. One who is vague is telling you something.
Reason four: the specification changed
Sometimes the production item is different because something in the specification changed – a resin substitution, a tooling change, a different process. Legitimate to do, unacceptable to do silently.
Insist on notification and re-approval. It belongs in the contract, and it is one of the clauses worth writing in rather than assuming.
How to protect yourself
Keep the approved sample. Specify tolerances. Ask whether the sample is from production. And make re-approval after any change a stated condition of the order rather than a request.
At goods-in, check against the sample and the specification rather than against memory. The checking routine is described in how to check corrugated sheet quality.
How much variation is normal
Ask for the tolerance rather than assuming one. On thickness for extruded sheet, a few percent either side of nominal is common; on a moulded dimension, less. Colour is the loosest of the three and the one that generates the most complaints per millimetre of actual difference.
If the supplier will not state a tolerance, that is the answer – there is nothing to hold them to, and nothing to argue from.
What to do when it happens
Measure before calling. A caliper and a set of scales turn a disagreement into facts, and sometimes the difference is smaller than it looked or inside a tolerance you had forgotten you agreed.
Then ask which of the four reasons it is. A supplier who says “different resin lot, we should have told you” is a supplier you can work with. One who says “it is the same” when it measurably is not is a different problem.
The clause that prevents it recurring
Notification and re-approval before any change to resin, tooling or process. One sentence, in the order terms, and it converts a recurring annoyance into a conversation that happens before shipping rather than after.
What we can do
We supply PP corrugated sheet and send production samples with tolerances stated, and we notify before any specification change. Tell us what you need to hold us to and we will put it in writing.