TIG. MIG.
Laser. Resistance.
Know the standard.
Welding standards cover process qualification, operator certification, joint design, and inspection. This guide navigates the major standards and common processes used in manufacturing.
Standards by industry.
Structural steel
American Welding Society structural steel code. Buildings, bridges, structures. Covers welder qualification, inspection, acceptance criteria.
Structural aluminum
Aluminum structural welding — similar scope to D1.1 but for aluminum. Common for shipbuilding, aerospace ground structures.
Pressure vessels
ASME Boiler and Pressure Vessel Code, Section IX. Welding qualification for pressure vessels, boilers, piping. Rigorous documented procedures.
Aerospace fusion
Fusion welding for aerospace applications. More stringent than AWS D1.1, includes titanium, Inconel, special procedures.
Aerospace quality
Aerospace quality management (not specifically welding). Requires qualified welding processes under the QMS.
Aerospace process
National Aerospace and Defense Contractors Accreditation Program. NADCAP welding audit — stringent process qualification for aerospace manufacturers.
Common processes.
| Process | Best for | Quality | Speed | Notes |
|---|---|---|---|---|
| TIG (GTAW) | Thin material, aerospace, precision | Excellent | Slow | Manual or automated, requires skill |
| MIG (GMAW) | Thick material, production | Good | Fast | Semi-automatic, common for production |
| Stick (SMAW) | Field welding, heavy structural | Good | Medium | No shielding gas required, portable |
| Flux-Cored (FCAW) | Thick material outdoor | Good | Fast | Self-shielded, outdoor capable |
| Resistance (spot) | Sheet metal assembly | Good consistent | Very fast | Standard for automotive body |
| Resistance (seam) | Leak-tight sheet assemblies | Good | Fast | Continuous seam, fuel tanks |
| Laser welding | Precision, thin material | Excellent | Fast | Specialty process, costly |
| Electron beam | Precision, thick material, exotic | Excellent | Medium | Vacuum process, specialty |
| Friction welding | Dissimilar metals, no HAZ | Excellent | Fast | Specialty, inertia or linear |
| Ultrasonic | Thin metal, plastic | Good | Very fast | No heat input, specialty |
Weld joint types.
Common joints
- • Butt joint — two plates edge-to-edge, strongest joint type
- • Lap joint — one plate overlapping another, common for sheet metal
- • T-joint — perpendicular plates, used in structural welding
- • Corner joint — two plates at corner, common for enclosures
- • Edge joint — parallel plates welded on edge (rare)
Edge prep
- • Square edge — no prep, for thin material (<3mm)
- • Single V-groove — for medium thickness (3-20mm)
- • Double V-groove — for thicker material (15mm+)
- • Bevel groove — unilateral preparation, for T-joints
- • J-groove, U-groove — reduces filler material, for thick material
Fit-up requirements
- • Root gap typically 1-3mm for grooved joints
- • Land (flat at root) 1-3mm for proper penetration
- • Bevel angle typically 30-37.5° each side for V-groove
- • Alignment within 10% of thickness for butt joints
- • Tacks for alignment before final welding
Filler materials
- • ER70S-6 — general steel MIG/TIG filler
- • ER308L — 304 stainless welding
- • ER316L — 316L stainless welding
- • ER4043 — general aluminum MIG/TIG
- • ER5356 — higher strength aluminum
- • Inconel 625 filler — for Inconel or dissimilar welds
Welder and procedure qualification.
Welding Procedure Specification (WPS): Written document specifying the welding process, material, filler, position, preheating, current, voltage, travel speed, shielding gas, post-weld treatment. Must be developed for each unique welding situation. PWHT (post-weld heat treatment) often part of WPS.
Procedure Qualification Record (PQR): Testing of sample welds made per WPS to verify the procedure produces acceptable welds. Tests: tensile, bend, hardness, macro-etch. When passed, procedure is qualified for production. WPS may be used for qualified material/thickness/position range.
Welder Performance Qualification (WPQ): Individual welders qualify on specific processes, materials, positions. Welder qualification is specific — not every welder can weld every process/material. Typically 6-month validity with periodic requalification.
Traceability for critical welds: Aerospace and nuclear welds require: WPS/PQR documentation, welder ID on each weld, witnessed inspection, documentation retention. Non-destructive examination (NDE) for critical welds: radiographic (X-ray), ultrasonic, dye penetrant, magnetic particle. Testing per applicable code.
Our capability: We maintain qualified welders for common processes (TIG, MIG, spot welding) on common materials (carbon steel, stainless, aluminum). For aerospace NADCAP welding, we partner with NADCAP-qualified shops. For pressure vessel ASME IX welding, we coordinate with qualified suppliers. Our documented capability: AWS D1.1-compliant structural welding, AWS D1.2-compliant aluminum welding.
FAQ
TIG vs MIG — when to specify?
TIG: higher quality, slower, good for thin material and specialty alloys (titanium, Inconel, aluminum), aerospace applications. Requires more operator skill. MIG: faster, good for production, thicker materials (3mm+), standard shop capability. Generally cheaper than TIG. For prototype and aerospace: specify TIG. For production structural and general industrial: MIG acceptable.
When is stress relief required?
Post-weld heat treatment (PWHT) or stress relief required for: pressure vessels (ASME IX specifies), critical fatigue-loaded parts, thick sections (>25mm typical), high-restraint welding (where weld shrinkage is restricted), materials prone to stress cracking. Benefits: reduces residual stress, reduces distortion, reduces stress corrosion cracking susceptibility. Consult applicable code for specific requirements.
Distortion and warpage?
Welding causes shrinkage and distortion. Minimize by: (1) Pre-welding jigs holding parts in position, (2) Symmetric weld sequences to balance heat input, (3) Tack welding at multiple points before continuous welding, (4) Minimal filler material (narrow gap welding), (5) Low heat input processes where appropriate, (6) Pre-bending parts to compensate for expected distortion. For precision assemblies, post-weld machining brings dimensions to specification.
Dissimilar metal welding?
Combining different metals possible but challenging. Common: austenitic stainless to carbon steel (with stainless filler), Inconel to stainless (Inconel filler), copper to steel (brazing preferred). Problems: thermal expansion mismatch, intermetallic formation, corrosion acceleration. For critical dissimilar welding, specify process, filler, and testing requirements.
Weld defects — what to watch for?
Common defects: (1) Porosity — gas trapped in weld, often from contamination. (2) Lack of fusion — weld didn't bond properly to base metal. (3) Slag inclusions — (SMAW) slag trapped in weld. (4) Cracks — hot cracks from improper filler, cold cracks from hydrogen. (5) Undercutting — base metal eroded at weld edge. Inspection: visual first, then NDE (penetrant, radiographic, ultrasonic) for critical welds.
Documentation package for welded assemblies?
Standard welded assembly documentation: welder IDs per weld, WPS/PQR reference, inspection reports (visual + NDE as required), weld maps showing location of each weld, material traceability, post-weld processing records. For aerospace or pressure vessel: additional procedures per applicable code. Our welded assemblies include complete documentation package.
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