- Fillet-weld capacity follows effective throat, not visual leg size alone.
- Provide access for torch, fixture, cleaning and inspection.
- Control distortion with minimum necessary weld, balance and sequence.
- Define dimensional tolerance, weld quality and NDT separately.
Values in this guide are practical starting points for RFQ, DFM and prototype validation. They do not replace load calculations, regulations, material certificates, qualified procedures or approved production drawings.
Specify the Required Joint, Not “Fully Weld” Everywhere
For an equal-leg 45° fillet, effective throat a≈0.707z, where z is leg size. Capacity depends on throat, effective length, load direction and parent material—not visual bead size alone. Continuous weld may be necessary for sealing, water exclusion or crevice control. Intermittent weld may suit some static joints, but fatigue, corrosion and cleaning requirements must be checked separately.
Provide Torch, Sight and Inspection Access
Provide access for torch angle, shielding gas, slag removal/grinding and visual inspection. Closed boxes need a weld-before-closing sequence. Do not specify an inaccessible internal weld. Where a critical butt joint requires full penetration, define groove, root gap, backing or procedure-qualification requirements.
Make the Assembly Self-locating Where Practical
Use datum faces, stops, tabs and slots to aid fixturing, but tabs do not replace weld-capacity design. Constrain accurately only where needed and leave sensible clearance elsewhere to avoid over-constraint. Clamp near joints and datums without blocking weld access or forcing the assembly into an artificial shape.
Manage Distortion Through Sequence
Reduce distortion by minimizing unnecessary weld metal, balancing welds, back-step or skip sequencing, progressing from restrained to free areas, controlling gaps and heat input, and allowing cooling. Long welds on thin sheet are especially distortion-prone; consider plug/spot welds, mechanical joints or formed stiffness. Preset counter-distortion must come from trials, not arbitrary angles.
Separate Dimensional and Weld-quality Acceptance
Inspect overall length, hole pattern, squareness and mounting-face flatness from functional datums. Specify weld imperfection quality separately. ISO 5817 provides B/C/D levels, with B most stringent, but these workmanship levels do not replace structural fitness calculations. ISO 13920 provides four general tolerance classes for weldments; the drawing must state the selected class rather than assume one.
Critical Work Needs Procedure and Inspection Planning
Define process, material group, filler, WPS/WPQR, welder qualification and traceability where required. Visual testing is the baseline. PT/MT detect suitable surface-breaking flaws; UT/RT address selected internal flaws. Method, coverage and acceptance level must follow joint geometry, thickness and risk—not a vague “100% NDT” note.
REFERENCES
ISO 2553:2019 (welding symbols), ISO 5817:2023 (quality levels for imperfections in fusion-welded joints), ISO 13920:2023 (general tolerances for welded constructions), and ISO 17635:2025 (general rules for nondestructive testing of welds).