Quality checks before dispatch: stage inspection and PDI

In a multi-stage process each operation builds on the last. If the only serious check happens at the end, four problems follow.

• Rework runs backwards. A part with an early defect has to be undone through every later stage, or scrapped along with all the work added to it. Grinding off paint to repair a weld costs more than repairing the weld before painting.
• The cause is hard to find. The final inspector can see that a part is wrong, but often can't tell which stage made it wrong, or whether that stage is still producing the same fault right now.
• Later operations hide earlier problems. Paint covers weld porosity and surface damage. Assembly hides dimensions that can no longer be reached with a gauge.
• Problems surface at the worst moment. When every issue appears at the end, it appears when the delivery date is closest and there is least time to fix it properly. That is when the pressure to pass a borderline part is highest.

Stage-wise inspection, also called in-process inspection, places a quality check after each operation that can introduce a defect, using criteria specific to that operation. The question at each checkpoint is narrow: did this stage do its job correctly?

A narrow question is quicker to answer and easier to act on. If a bend angle is out after the press brake, the operator can correct the setup before the rest of the batch is bent, and the parts already bent are the only ones affected.

Many shops check the first piece of a new job, or the first piece after a setup change, before running the rest of the batch. A wrong setup caught on the first part costs one part. The same mistake caught at the end of the run costs the whole run.

A check that isn't recorded can't be used later, when someone asks what happened to an order. At minimum, record:

• The production order or work order the parts belong to.
• The stage and, where it matters, the machine.
• The result: passed, rejected, or held for a decision.
• Who checked it and when.
• Remarks on anything found, including what was done about it.
• The drawing or inspection sheet the check was made against, including its revision.

The right checks depend on the part, the drawing and the customer's requirements. As a general example, this is how checkpoints often look in sheet-metal and fabrication work:

Quality that runs through production is less about adding inspectors and more about deciding who checks what, and what happens when a check fails.

• Operators can own first-line checks. Simple checks with a gauge or template, such as a bend angle or a hole position, are often done by the operator at the machine, immediately.
• Inspectors verify what matters most. Critical dimensions, welds and anything the customer specifies usually warrant an independent check by quality.
• Some checks gate the work, others are recorded. A failed weld check should stop the assembly going to paint. A cosmetic note might only need recording. Decide this per check, in advance.
• Held parts need a visible status. A part waiting for a decision on rework, use-as-is or scrap should be impossible to miss, not sitting in a corner with a chalk mark.

In many shops, production status lives on job cards, a whiteboard or a spreadsheet, while inspection results live in a quality register. Each record may be accurate on its own, but the connection between them depends on someone matching them by hand.

That gap creates predictable problems. A stage is marked finished while its inspection hasn't happened. A part moves on because the next stage didn't know it was waiting for quality. When a customer asks about an order, its production and quality history have to be pieced together from different places.

1. 1.A production order is planned into work orders, each with its sequence of stages.
2. 2.When a stage finishes, the work order shows that it is waiting for its quality check, so nobody has to remember.
3. 3.The inspection result is recorded against that work order, at that stage.
4. 4.The next stage can't start until the previous one is complete, so parts don't move ahead of inspection.
5. 5.PDI is recorded against the order before release, and the order leaves with its production and quality history together.

Pre-dispatch inspection is the final inspection of finished goods before they leave the factory. Stage inspection asks whether each operation did its job. PDI asks a different question: is this order, as a whole, what the customer ordered, and is it ready to ship?

A typical PDI covers quantity against the order, critical dimensions and features against the current drawing (often on a sample), finish and visible damage, marking and labelling, packing, and the documents that travel with the shipment where the customer requires them. It is also where customer-specific requirements are usually confirmed, because it is the last time the complete order is in one place. What is pre-dispatch inspection (PDI)? covers the PDI process itself in more depth, including sampling and how to record it.

Every check is only as good as the criteria behind it. If an inspector measures against an old drawing, a part made to the old revision passes and a part made correctly to the new revision fails. The same goes for operators: a stage can be done perfectly and still be wrong because the work instruction was out of date.

That is why drawings, SOPs, work instructions and inspection checklists need to be under the same revision control, and why the operator and the inspector at a stage should be looking at the same current revision. We cover this in detail in document and revision control on the shop floor.

Software doesn't inspect parts. People do. What a system can do is make the process hold: checks happen in the right order, results are recorded where the work happens, and every record stays attached to the order it belongs to.

Budve SmartFlow is a production and quality management system Reinstate Labs built for a manufacturing unit. Production orders are planned into work orders that move through the shop's manufacturing processes: bending; pressing, which covers blanking, forming, pearling and restricting; welding, carried out in five stages; and painting. PDI and dispatch follow.

Quality management runs as a stage-wise workflow within production rather than in a separate register, and stage blocking keeps a stage closed until the previous one is complete. Production IDs, batch and lot tracking and a QR and barcode workflow capability help identify work on the floor. On the dashboard, quality check is one of the work-order statuses alongside in progress, on hold and completed, so work waiting for inspection is visible. Drawings, SOPs, work instructions and quality documents are managed in the same system under revision control.

You don't need to change everything at once. A practical order:

1. 1.List your stages and, for each one, what can go wrong there. That list is the basis of your stage checks.
2. 2.Write the criteria for each check, and tie each one to a specific drawing or document revision.
3. 3.Decide which checks must pass before work moves on, and which are only recorded.
4. 4.Record checks at the stage when the work happens, not at the end of the shift from memory.
5. 5.Turn PDI into a recorded step against the order with its own checklist, not a signature on a delivery note.
6. 6.Once stage results are recorded consistently, look at where rejections and rework actually start, and work on those stages first.

PDI is the final gate, not the main filter. Defects are cheapest to deal with at the stage that creates them, so quality checks belong at each stage, recorded against the order and made against the current documents. When production and quality share one record, PDI becomes a confirmation rather than a discovery.

If you are working out how this would fit your own process, see how we approach production and quality systems for manufacturers, and our workflow automation service for the rules, such as stage blocking, that keep checks in sequence.