Chapter 4 Section (9) Control of Distortion and Increasing Welding Accuracy

Accurately size parts, joint preparation, and fit up to minimize the amount of weld metal required.
Implement backstepping or skip welding techniques.
Direct welding progress outward from a central point.
Balance welds on either side of a center line, central point, or the neutral axis of a section.
Weld joints before fillets to permit large contractions to occur first.
Utilize intermittent fillet welds rather than continuous fillet welds when permitted by design.
Sequence welds so each joint maintains the maximum freedom of movement for the longest possible period.
Divide the weldment into subassemblies to limit cumulative shrinkage and distortion.

Counteract plate edge curvature through planned weld placement.
Arrange components to prevent the accumulation of tolerance errors from purchased shapes such as beams, channels, plates, and bars.
Prepare components accurately to prevent the stacking of fit up tolerances where high accuracy is required.
Sequence operations so location points requiring high precision are assembled and welded last.
Account for weld metal shrinkage in the design.
Incorporate latitude in assembly dimensions, such as designing extra material allowance for final machining to size.

Preheating: Promotes uniform heating and cooling to minimize shrinkage stress.
Pinning: Stretches the weld metal to decrease final shrinkage.
Restraint: Restricts shrinkage through external restraint or self-weight via clamping, rigid tacking, maintaining a minimum or zero root opening to reduce transverse shrinkage, and allowing cooling between weld passes.
Mechanical control: Mitigates distortion using presetting for angular distortion recovery, temporary stiffeners, strong backs, special jigs or fixtures, and artificial cooling.