Welding
Also: welding services, weld fabrication, weldments, fabrication welding, arc welding, fusion welding, welded assemblies, metal joining, certified welding
Welding fuses metal parts into one assembly: MIG for speed, TIG for precision, spot for sheet, laser for low heat. AWS D1.1 and D17.1 set the rules.
2,941 welding and fabrication companies in the Noramark directory
Welding melts the edges of two parts, usually with filler metal, so they solidify as one. The arc processes do most job-shop work: MIG (GMAW) feeds wire continuously and is the fast, economical choice for steel, stainless and aluminum fabrication; TIG (GTAW) uses a tungsten electrode and hand-fed filler for the cleanest, most controlled welds on thin sections, stainless, aluminum, titanium and nickel alloys; stick (SMAW) and flux-cored (FCAW) cover thick plate and field work. Resistance spot welding joins sheet without filler at a fraction of a second per spot, and laser welding puts a narrow, deep, low-distortion seam where fit-up is good.
Choose by material, thickness, quantity and what the weld must look like. Steel brackets and frames are MIG welded; a stainless sanitary tube or an aluminum enclosure that will be anodized is TIG welded; a thin stainless sheet-metal seam that must be cosmetic is laser welded; a thousand steel sheet assemblies are spot or robot welded. The codes that govern the work are AWS D1.1 for structural steel, D1.2 for aluminum, D1.6 for stainless, D1.3 for sheet steel, D17.1 for aerospace fusion welding, and ASME Section IX for pressure work; each requires a written procedure (WPS) qualified by test (PQR) and welders qualified to it.
The drawing speaks through weld symbols (AWS A2.4): the arrow points at the joint, the symbol below the line describes the arrow side, and the size, length and pitch ride on the symbol. Heat is the enemy of accuracy. A weld shrinks as it cools and pulls the assembly toward it, so weldments are fixtured, welded in a balanced sequence, and either stress relieved or machined afterwards when a dimension must hold ±0.25 mm (±0.010") or better. Inspection is visual at minimum, with dye penetrant, magnetic particle, ultrasonic or radiographic testing when the code or the drawing calls for it.
At a glance
| Typical tolerances | As-welded assemblies ±1.5 mm (±1/16") over 300 mm (12") standard, ±0.8 mm (±1/32") with fixturing and a planned sequence; angles ±1° standard, ±0.5° fixtured. Flatness after welding 1-3 mm per m without straightening. ±0.25 mm (±0.010") or better only on features machined after welding. Weld size per the symbol, typically +1.5 mm (+1/16"), -0. |
|---|---|
| Size limits | From 0.3 mm (0.012") foil by micro TIG and laser to unlimited plate thickness with multi-pass arc welding. Job shops weld assemblies up to 3 x 6 m (10 x 20 ft) on tables and larger on the floor, with cranes of 5-20 tons; positioners and rotators turn heavy weldments to the flat position. Sheet below 0.8 mm (0.030") is TIG, spot or laser work, not MIG. |
| Surface finish | MIG leaves a convex ripple bead with some spatter; TIG leaves a smooth, evenly rippled bead with none; laser leaves a narrow flush seam. Welds are left as welded, ground flush, or blended for cosmetics, each at a cost. Stainless shows heat tint that is pickled or passivated off; aluminum welds anodize darker than the base metal; powder coat covers welds well. |
| Lead time | Simple weldments in 3-10 business days; fabricated assemblies with machining and finishing in 2-5 weeks. Add 1-2 weeks when a new procedure must be qualified for coded work. |
Typical of U.S. job shops; confirm with the shop for your part.
Materials
Carbon and low-alloy steels (A36, 1018, A572, 4130) weld with ordinary care; 4140 and 4340 need preheat, controlled interpass and post-weld tempering. Austenitic stainless (304, 316, 2205 duplex) welds well with matching filler; the free-machining grades 303, 416 and 12L14 crack because of sulfur and lead. 5052, 5083 and 6061 aluminum weld with 4043 or 5356 filler, with 6061 losing about 40% of its T6 strength in the heat-affected zone; 7075 and 2024 are not fusion welded for structure. Titanium and the nickel alloys (625, 718, C-276) weld well under full inert shielding. Copper needs preheat because it conducts the heat away; brass gives off zinc fumes. Gray cast iron is brazed or welded with nickel rod and preheat, and only for repair.
What drives the cost
- Weld length, size and number of passes: inches of weld is the unit of work
- Process: TIG runs three to five times slower than MIG per inch
- Material: aluminum, titanium, stainless and nickel alloys need cleaning, shielding and slower travel
- Fit-up and fixturing: gaps and mismatch cost more than the weld
- Distortion control and post-weld machining or straightening
- Certification and inspection: coded procedures, certified welders, NDT, documentation
- Cosmetics: grinding, blending and polishing of welds
When to use it
- Frames, brackets, enclosures, tanks, skids, guards and structures from cut plate, sheet and tube
- Assemblies too large, too complex or too low in volume to cast or forge
- Joining machined details to fabricated bodies, or repairing and building up worn parts
- Leak-tight and pressure-retaining joints under a code
- Any metal-to-metal joint that must carry full structural load
When not to
- Hardened or pre-hardened parts: the weld zone anneals or cracks
- Free-machining grades (303, 416, 12L14) and the high-strength aluminum alloys 7075 and 2024
- Dissimilar pairs such as aluminum to steel, which need fasteners, adhesives or explosion-bonded transitions
- Dimensions that must hold ±0.25 mm (±0.010") without machining afterwards
- Very high volumes of a simple part, where casting, forging or stamping avoids the joint
Design tips
- Put weld symbols on the drawing (AWS A2.4) with size, length and pitch, and mark which welds are structural, which seal, and which cosmetic.
- Size fillets to the load, not the plate: a 5 mm (3/16") fillet is usually enough on 6 mm plate, and overwelding costs money and distortion.
- Give the welder access: a MIG gun needs about 20 mm (3/4") of clearance and a 45° approach.
- Balance welds about the neutral axis and use intermittent welds where a continuous one is not needed, to limit distortion.
- Leave machining stock on datum faces and bores and machine after welding when a tolerance is tighter than ±0.8 mm (±1/32").
- Keep joint thicknesses within about 3:1 of each other, or bevel the thick member.
- Name the code (D1.1, D1.2, D17.1, ASME IX), the inspection level and whether certified welders and a WPS are required.
- Sequence finishing: weld, then stress relieve, then machine, then plate or anodize.
Welding by material
Frequently asked questions
- MIG or TIG welding: which should I choose?
- MIG for steel and thicker aluminum where speed and cost matter and the bead can be as welded or ground; TIG for thin sections, stainless, aluminum, titanium and nickel alloys, and wherever the weld must be clean, small and cosmetic. Many assemblies use both: MIG for the structure, TIG for the visible or precise joints.
- What is AWS D1.1?
- The American Welding Society Structural Welding Code for steel: it sets joint designs, procedure and welder qualification, workmanship and inspection for welded steel structures. D1.2 covers aluminum, D1.6 stainless, D1.3 sheet steel and D17.1 aerospace fusion welding. Calling out a code on the drawing tells the shop what qualification and inspection to price.
- Can aluminum be welded?
- Yes: 5052, 5083, 6061 and 6063 weld routinely by TIG and MIG with 4043 or 5356 filler, after the oxide is cleaned off. 6061-T6 loses about 40% of its strength in the heat-affected zone unless the assembly is re-heat-treated. 7075 and 2024 are not fusion welded for structural parts.
- How do you reduce welding distortion?
- Less heat and balanced heat: smaller welds, intermittent welds, faster processes such as pulsed MIG or laser, welding in a sequence that alternates sides, rigid fixtures, and pre-setting parts against the expected pull. Where a dimension still must hold, stress relieve and machine after welding.
- What do weld symbols mean on a drawing?
- An arrow points to the joint; the reference line carries a symbol for the weld type (fillet, groove, plug, spot), with the size to its left and the length and pitch to its right. A symbol below the line is on the arrow side, above the line on the other side, and a flag means field weld. AWS A2.4 is the standard.
