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Weld distortion: a cost that appears on no line of the sheet

Heat moves steel, and the money spent straightening it is scattered across four categories where nobody can see it. How to gather it into one number, and why fixturing beats straightening once volume is involved.

Updated

Welding puts heat into one place and lets it cool. The metal contracts unevenly, so the assembly is no longer the shape it was before welding.

Every fabricator knows this. What almost nobody does is **measure what it costs** — because the cost does not appear on any line of the sheet.

The money is scattered across four places

WhereAppears asWhy it is invisible
LaborStraightening time, fixturing timeMerged into general fabrication labor
ReworkCutting apart and rewelding to positionRecorded as rework with no cause noted
ConsumablesWire and gas for the reweldingAbsorbed into the job total
ScrapAssemblies too far out to saveRare, so treated as an exception rather than a pattern

No line is named distortion, so the cost is genuinely invisible — and nobody improves what they cannot see.

Gathering it into one number

No new fields required. Just **record the cause** whenever you enter something from the table above:

  1. Enter straightening time as straightening, not as general finishing.
  2. When entering rework, note whether the cause was a weld defect or a dimensional error.
  3. After a few jobs, add up the lines with a distortion cause.
The total is usually larger than people expect, and that is the point of the exercise. If it turns out small, you can stop worrying about it with evidence. If it turns out large, you have just found the most valuable improvement in the shop — and until now nobody knew it existed.

Why fixturing beats straightening at volume

There are two ways to deal with distortion, and the cost sheet distinguishes them sharply:

  • Prevent it — a fixture holds the assembly during welding, and the weld sequence is planned so heat is distributed. Cost is **one-time** (the fixture) plus a little fit-up time per unit.
  • Correct it — weld first, straighten after. Cost **repeats on every unit** and does not fall with volume.

This is exactly the trade the machinery guide describes: a one-time cost bought in exchange for a recurring one. At sufficient volume prevention always wins; for a one-off it may not.

And it is directly measurable here: cost the assembly twice — once as it runs now, once with a fixture and no straightening — and compare. That is a complete improvement case with a number on both sides, not an opinion.

Where this guide stops

This is about **measuring and recording** the cost of distortion. It does not tell you which weld sequence distorts least, how to fixture a given assembly, or what heat input is appropriate — those depend on your material, thickness, joint design and equipment, and you know them far better than any general document.

What is hard to do alone is the rest: keeping both options side by side with their numbers, keeping the history of who changed which figure and why, and having someone else in the trade confirm or challenge it with their own.

Related guides

Weld distortion: a cost that appears on no line of the sheet | costdown.org