The Welded Frame That Bent (Distortion)
We welded a steel frame (article 145). The welds (all around) heated the frame. After welding, the frame bent (it warped, not flat). The problem: the welding heat distorted the metal (the weld shrank, pulling the frame). We either added a stress relief (an oven, article 145) or welded in a sequence (skip, to balance the heat). We welded in a sequence (weld the left, then the right, to balance). The frame was flat. The mistake was welding all at once (the heat distorted it).
Welding distortion — control the heat (and the sequence). This article covers the methods.
Why Welding Distorts
A weld (the molten metal) heats the local area. The metal expands (hot), then contracts (cool). The contraction (shrinkage) pulls the part (it bends). A long weld (on one side) pulls that side (the part bends toward the weld).
Step 1: The Sequence (Skip Weld)
Don’t weld all at once (one long weld). Weld in a sequence (weld a short segment, then move to the other side, to balance). The heat is distributed (not concentrated on one side). The part stays flat. For a long beam, weld the top (100 mm), then the bottom (100 mm), then repeat (skip).
The distortion rule: Weld in a sequence (balance the heat). The frame that bent had one long weld (all on one side). Weld short segments (left, right, repeat). The heat is balanced. The part stays flat.
Step 2: The Tack Welds
Tack the part first (small welds, to hold it). Check it’s square (and flat). Then weld (the tacks hold it, it doesn’t move). A part that’s not tacked (free to move) warps (the weld pulls it).
Step 3: The Pre-Weld Setup (Clamps)
Clamp the part (to a fixture) before welding. The clamps hold it (it can’t warp). After welding (and cooling), unclamp. The part stays flat (the clamps held it). Without clamps, the part warps (it’s free to move).
Step 4: The Stress Relief (Oven, Article 145)
For a precision frame (a machine base, article 145), stress-relieve it (an oven, article 145). The oven heats the frame (relieves the stress). The frame stays flat (no warping later). For a general frame, the sequence (skip weld) is enough.
| Method | Effect |
|---|---|
| Skip weld (sequence) | Balanced heat (no warp) |
| Tack first | Holds the part (square) |
| Clamp (fixture) | Can’t warp (held) |
| Oven (stress relief, article 145) | Relieves stress (precision) |
A Distortion Checklist
- Is the part tacked? (Square?)
- Is it clamped? (Fixture?)
- Is the sequence balanced? (Skip weld?)
- Is the heat concentrated? (One side?)
- Does it warp? (After cool?)
- Is it stress-relieved? (Oven? Article 145?)
- Is it machined after? (Article 145?)
- Is it flat? (Straight edge?)
- Is the weld right? (Penetration?)
- Is the cost right? (Oven?)
The Bottom Line
Welding distortion is controlled by the sequence. The frame that bent had one long weld. Weld in a sequence (skip). Tack and clamp. Stress-relieve (for precision, article 145). The frame that stayed flat wasn’t the best welder — it used a sequence.
