Casting defects · analysis

Foundry rejection analysis

A rejection total tells you the month was worse. Analysis tells you which pattern, which defect and which shift to spend Monday morning on, and whether the last change you made actually worked.

By Versatile Equipments Pvt Ltd · equipment manufacturer & calibration provider · updated 2026-09-07

Rank before you act

The first question is not what caused the rejections, it is which ones are worth this week. In most plants a small number of defect types account for a large share of what is scrapped, so a simple ranking - a Pareto - usually makes the choice obvious and says plainly which problems can wait.

Ranking has a second use that is easy to miss. If the ranked list keeps reshuffling from month to month without any process change to explain it, the likely problem is the naming rather than the process. That is a signal to fix the register before drawing conclusions from it.

Slice it the ways that carry a decision

A single ranked list is a start, but causes tend to appear when two things are crossed against each other. Useful cuts include:

• Defect by pattern. A defect concentrated on one pattern points at method or tooling rather than the whole line.
• Defect by shift. A skew toward one shift points at practice, sand control or manning rather than the pattern.
• Defect by heat. Rejections clustered in particular heats point at melt condition or pouring rather than the mould.
• Defect by cavity. The cleanest comparison available, because the impressions share everything else. See cavity-wise analysis.
• Defect by date. Useful for finding the day something changed, which is often the fastest route to the cause.

The point of crossing two dimensions is that a total conceals what a cut reveals. A pattern with an ordinary overall rejection figure can still be carrying one impression that fails constantly.

From the ranked list to a cause

Once the leading defect is known and trusted, the investigation follows the defect family rather than the count. Gas defects such as blowholes and pinholes lead to venting, moisture and melt condition. Shrinkage leads to feeding, gating and chills. Sand inclusion leads to mould strength, friability and closing practice. Misruns and cold shuts lead to fluidity, pouring temperature and speed.

Where the leading defects belong to sand-driven families, reading the register against the sand lab record for the same hours is usually the quickest way to a cause. That comparison is set out in sand properties and casting defects.

Check that the fix held

The step most often skipped is the last one. An action is agreed, someone changes the venting or the moisture target, and the matter is treated as closed. Whether the defect actually fell afterwards is rarely checked, partly because checking it means comparing two periods of a register nobody fully believes.

With dated and consistently named entries the check is straightforward: look at the weeks either side of the change, for that defect on that pattern. Over time the plant accumulates a short list of actions that are known to have worked on its own castings, which is worth more than any general advice.

Evidence for the audit

Plants working to IATF 16949 or ISO 9001 have to show traceable evidence of nonconformance and of the action taken. Where the register already holds photographs, timestamps, the person who classified the defect, any correction and the disposition, most of that evidence exists as a by-product of ordinary work rather than as something assembled the week before the audit. Calibration records for the instruments behind the numbers sit alongside it - see calibration intervals and IATF 16949.

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