A welded assembly joins two or more fabricated metal parts into one structure through a fusion or resistance weld, creating a continuous metallurgical bond rather than a mechanical connection at discrete fastener points. The components themselves start as laser-cut, formed, and punched pieces, then get fixtured, aligned, and welded to hold a finished dimensional tolerance. Whether a joint runs clean depends on three decisions made on the print: which welding process suits the material and thickness, which joint geometry gives the arc access, and how the weld sequence is planned so the part does not pull out of tolerance as it cools.

This guide covers the working knowledge a designer or buyer needs to specify a welded sheet-metal assembly: process selection by material and gauge, the AWS codes that actually govern sheet-metal and structural welds, weld-symbol basics for an unambiguous drawing, minimum material thickness per process, distortion control, and the tradeoff between a welded joint and a fastened one. The standards cited below carry working links to the publishing bodies.

Welding Processes for Sheet-Metal Assemblies

Four processes cover the large majority of sheet-metal weldments: MIG (GMAW), TIG (GTAW), resistance spot welding, and stud welding. Each sets a practical floor on material thickness, a level of heat input that drives distortion, and a relative cost per joint. The choice follows from material, gauge, joint count, and whether the weld is structural, leak-tight, or cosmetic.

MIG / GMAW (Gas Metal Arc Welding)

MIG welding feeds a consumable wire electrode through a torch under a shielding-gas cover, depositing filler continuously. It is the production workhorse for carbon and stainless steel assemblies: fast, easy to automate, and tolerant of less-than-perfect fit-up. The continuous arc puts more heat into thin stock than TIG, so on light gauge it is usually run in short-circuit or pulsed-spray transfer to limit burn-through and distortion. A common filler for mild steel, ER70S-6, is classified to a 70 ksi (480 MPa) minimum tensile strength under AWS A5.18, the filler-metal specification for carbon-steel GMAW electrodes. Atlas runs MIG for structural frames, brackets, and multi-part weldments where throughput and consistent fillet quality matter.

TIG / GTAW (Gas Tungsten Arc Welding)

TIG uses a non-consumable tungsten electrode and an inert shielding gas (argon, or argon-helium), with filler added by hand. It gives the operator the finest control over heat input of any arc process, which is why it owns thin-gauge stainless, aluminum, and any joint where appearance and corrosion resistance in the heat-affected zone are critical. It produces almost no spatter and the cleanest bead, at a much lower deposition rate than MIG. For aluminum, TIG is run on AC to break up the tenacious surface oxide. Atlas uses TIG for medical, dental, and food-grade stainless enclosures and for aluminum assemblies where the weld is visible or sealed.

Resistance Spot Welding

Spot welding clamps two overlapping sheets between copper electrodes and passes a high current through the joint; resistance at the interface melts a small nugget that fuses the sheets. It needs no filler and no shielding gas, makes a joint in a fraction of a second, and is highly repeatable, which is why it dominates panel and enclosure work with many identical joints. It is best suited to similar materials of comparable thickness in a lap configuration. Atlas uses spot welding for enclosure panels and bracketry where dozens of identical joins are required.

Stud Welding (Including Capacitor-Discharge)

Stud welding fuses a threaded stud, pin, or boss to a sheet in a single pulse, giving a fastener point on a panel with no hole, no back-side access, and no marking on the show face. Capacitor-discharge (CD) stud welding discharges stored energy in a few milliseconds, so the heat-affected zone stays tiny: it can attach studs to sheet as thin as roughly 0.020 in (0.5 mm, about 24 ga) without burn-through on the opposite face, which is why it is the go-to for cosmetic enclosure panels. Drawn-arc stud welding handles heavier studs into thicker base material. Both are governed for steel and stainless studs by AWS D1.1 Clause 7 (stud welding provisions within the Structural Welding Code).

Process Selection by Material and Thickness

Which AWS Code Governs the Weld

The single most common point of confusion on a welding spec is which American Welding Society code actually applies. The answer is driven by material type, the role of the joint (structural versus nonstructural), and thickness. Calling out the right code on the print tells the fabricator which procedure qualification, welder qualification, and inspection rules govern the part.

For nonstructural sheet metal, the controlling document is AWS D9.1, the Sheet Metal Welding Code. It covers arc and braze welding of sheet up to and including 0.2391 in (6.07 mm, roughly 3/16 in) for nonstructural applications such as enclosures, HVAC, and architectural sheet metal, and explicitly does not apply where pressure exceeds 5 psi. The moment the same sheet carries a design stress, it moves to a structural code. (AWS D9.1M/D9.1:2018)

There is a deliberate overlap between D1.1 and D1.3 in the 1/8 in to 3/16 in band. Sheet and cold-formed members in that range fall under D1.3; plate, pipe, and rolled shapes under D1.1. Where a welded steel frame ties into a building structure, the building code and the American Institute of Steel Construction (AISC 360, Specification for Structural Steel Buildings) reference D1.1 for the weld requirements, so the same fillet may answer to both the AISC design rules and the AWS fabrication code.

Material Selection and Weldability

Material choice sets the process, the filler, the shielding gas, and any pre- or post-weld treatment before the first arc is struck. Carbon steel, stainless, and aluminum cover most sheet-metal weldments, and each behaves differently under heat.

• Low-carbon steel (1008, 1010, 1018). The most forgiving to weld. Carbon below about 0.20 percent welds without preheat and with low cracking risk; weldability falls as carbon (and the resulting heat-affected-zone hardness) climbs. The default for frames, brackets, and housings. Needs a finish or coating for corrosion resistance.
• Austenitic stainless (304, 316). Readily weldable with no pre- or post-weld heat treatment, but its low thermal conductivity concentrates heat and it distorts more than carbon steel for the same input. Control heat input to preserve corrosion resistance in the HAZ; TIG is preferred for thin and cosmetic work.
• Ferritic stainless (430, 409). Weldable but prone to grain growth and embrittlement at temperature; limit heat input and keep passes small.
• Aluminum (3003, 5052, 6061). High thermal conductivity pulls heat away from the joint and a tenacious oxide layer (melting far above the base metal) must be removed before welding to avoid porosity. AC TIG with argon is the standard. 3003 and 5052 weld readily; 6061-T6 loses strength in the HAZ and may need post-weld consideration.
• Galvanized steel. Weldable, but the zinc coating vaporizes and produces fumes; it needs ventilation and often local removal of the coating at the joint, then re-coating after.

Weld Symbol Basics for an Unambiguous Drawing

A welded assembly is only as clear as its weld callouts. The American Welding Society standardizes those callouts in AWS A2.4, Standard Symbols for Welding, Brazing, and Nondestructive Examination. A weld symbol is built on a reference line with an arrow pointing at the joint. The core conventions:

• Arrow side vs. other side. A symbol below the reference line means weld the arrow side of the joint; above the line means the other side. Symbols on both sides call for welds on both.
• Weld-type symbol. A small graphic sets the weld type, fillet (a triangle), groove (square, V, bevel, U, J), plug/slot, spot, seam, or stud. A2.4 defines a distinct symbol for each.
• Size and length. The number to the left of a fillet symbol is the leg size; numbers to the right give length and pitch for intermittent welds (for example, length-pitch like 2-6 means 2 in welds on 6 in centers).
• Supplementary symbols. A circle at the arrow-line junction means weld all around; a flag means a field weld; a tail carries the process or specification reference.

Specifying weld type, size, length, and side per A2.4 removes the guesswork that drives quoting variance and rework. An incomplete callout forces the fabricator to assume, and assumptions are where cost and scrap come from.

Joint Design and Distortion Control

Five basic joint types cover sheet-metal weldments: butt, lap, tee, corner, and edge. Lap and corner joints dominate sheet work because they self-locate and give the torch good access. Joint design should call out weld type, size, and welding position, and should leave room for the arc: a tight inside corner the torch cannot reach is a weld that will be slow, ugly, or impossible.

The defining problem of welding thin material is distortion. Welding puts localized heat into the part; the metal expands, then shrinks as it cools, and uneven shrinkage warps the assembly out of tolerance. Thin sheet has little stiffness to resist that pull, so distortion control is a design and process concern from the start, not a cleanup step. Proven controls:

• Minimum weld size. Specify the smallest fillet that carries the load. Oversized welds add heat, shrinkage, and cost for no structural gain.
• Balanced sequencing. Alternate welds across the neutral axis and skip around the part so shrinkage forces cancel rather than accumulate on one side.
• Tack and fixture. Tack welds and rigid fixtures hold alignment against shrinkage; for multi-part assemblies, fixturing also controls cumulative tolerance stack-up.
• Lower, pulsed heat input. Pulsed MIG or pulsed TIG deliver peak energy in short bursts, cutting average heat input and shrinking the heat-affected zone. Intermittent (stitch) welds, where strength allows, cut total heat further.
• Self-locating features. Tab-and-slot details locate parts to each other, reducing fixturing time and improving repeatability.

The heat-affected zone (HAZ), the band of base metal altered by welding heat but not melted, is where distortion, grain growth, and any loss of corrosion resistance or strength show up. Lower, more concentrated heat input keeps the HAZ small. (CWB Group, Heat-Affected Zone)

Quality Control and Inspection

Weld quality is verified through a tiered set of methods, from a visual check on every weld to nondestructive and destructive testing where the application demands it. A welding program qualified to AWS codes carries documented Welding Procedure Specifications (WPS) and welder qualification records (WQTR) that prove each weld was made to a tested procedure by a qualified welder. At Atlas, those records live inside the quality management system of its ISO 9001:2015 certified Minneapolis facility.

Welded Joint vs. Fastened Joint

Welding is not automatically the right joining method. A weld gives the strongest, most rigid, inherently leak-tight joint with no added hardware weight, but it is permanent, it inputs heat that distorts thin parts, and it cannot be serviced without cutting. Mechanical fastening trades some strength and seal for reversibility and field assembly; adhesive bonding spreads load over an area and joins without heat. The right call depends on load, serviceability, seal requirements, and volume.

Applications

Welded sheet-metal assemblies appear wherever parts must be permanently joined for structural integrity, environmental sealing, or a held dimensional relationship. Common categories at Atlas:

• Electronics and telecom. Server chassis, communication housings, and electronic enclosures needing EMI shielding, ESD grounding, and environmental protection.
• Medical and food service. Stainless assemblies with leak-tight, crevice-free TIG welds for sanitary and corrosion-critical use.
• Industrial and high-performance computing. Equipment frames, machine guards, control-panel enclosures, and server-rack structures that take vibration, thermal cycling, and load.

Welded Assemblies at Atlas Manufacturing

Atlas Manufacturing runs MIG, TIG, robotic, resistance spot, and capacitor-discharge stud welding out of facilities in Minneapolis, Minnesota and Chippewa Falls, Wisconsin, serving engineers and procurement teams across telecom, medical, industrial, and OEM markets. Welding is supported in-house by laser cutting, forming, punching, hardware insertion, powder coating, and final assembly, so a multi-part weldment is built, finished, and inspected under one roof rather than coordinated across suppliers.

The practical value to a design team is catching the weld problems before fixturing: confirming the process suits the gauge, that the joints give the torch access, that the right AWS code is called out, and that the weld sequence is planned for distortion. Send a print and the welding group will flag process, access, and distortion issues up front. Contact Atlas Manufacturing to discuss a welded assembly.

Frequently Asked Questions