Introduction: Welding Is Where Steel Components Are Made or Broken
Of all the processes involved in manufacturing steel components, welding carries the highest consequences for getting it wrong. A machined dimension that is out of tolerance can be reworked. A laser cut profile that is slightly off can be recut. A weld that is incomplete, porous, cracked, or incorrectly sized cannot be invisible — and in a structural or pressure application, it cannot be acceptable.
Nathan Engineering, as a steel components manufacturer in India with certified welding capability across multiple processes, uses this guide to explain the most important welding processes for steel components — when each is the right choice, what joint design principles apply, what quality controls are required, and what buyers should verify when evaluating a potential welding supplier.
Process 1: MIG Welding (GMAW — Gas Metal Arc Welding)
What MIG welding is and how it works
MIG (Metal Inert Gas) welding, formally known as Gas Metal Arc Welding (GMAW), uses a continuously fed wire electrode that melts in an electric arc between the wire and the workpiece. The arc and weld pool are shielded from atmospheric contamination by a shielding gas — typically a mixture of argon and carbon dioxide (CO2) for mild steel, or pure argon for stainless steel and aluminium.
MIG welding is a semi-automatic process in most industrial applications — the welder controls torch position, travel speed, and angle while the machine automatically feeds wire and maintains the arc. Robotic MIG welding automates all of these variables for high-volume production.
When MIG welding is the right choice for steel components
- Structural steel fabrication — frames, chassis, machine bases, and any assembly where weld deposition rate matters more than cosmetic appearance
- Medium to heavy gauge steel — material thicknesses from 2 mm to 25 mm and above
- High-volume welded assemblies — MIG welding’s faster deposition rate and semi-automatic operation make it more productive than TIG for most structural applications
- Carbon steel and low alloy steel — MIG’s productivity advantage is most pronounced on carbon steel, where the process is well-optimised
MIG welding limitations
MIG welding produces more spatter than TIG welding (small particles of molten metal ejected from the weld pool), requires post-weld spatter removal for appearance-critical surfaces, and produces wider heat-affected zones (HAZ) than TIG. For thin material (below 2 mm), stainless steel, and cosmetic-quality welds, TIG welding is typically preferred.
Nathan Engineering’s MIG welding capability
Nathan Engineering’s welding team operates MIG welding for structural carbon steel assemblies — machine frames, guarding panels, welded enclosures, brackets, and equipment structures. Shielding gas mixtures are selected for the base material: Ar/CO2 blends for carbon steel, pure argon for stainless steel MIG welding where TIG is not specified.
Process 2: TIG Welding (GTAW — Gas Tungsten Arc Welding)
What TIG welding is and how it works
TIG (Tungsten Inert Gas) welding uses a non-consumable tungsten electrode to create the arc, with filler metal added separately by hand as a rod. The weld pool and electrode are shielded by pure argon or argon/helium gas. The welder controls all variables — arc length, filler addition rate, travel speed — requiring significantly more skill than MIG welding.
TIG welding produces the highest quality welds of any arc welding process: low spatter, clean appearance, narrow HAZ, and superior control over weld bead geometry. It is the preferred process for stainless steel, aluminium, titanium, and any application where weld quality is paramount.
When TIG welding is the right choice
- Stainless steel components — TIG welding’s low heat input minimises sensitisation of the heat-affected zone, preserving the corrosion resistance of the stainless alloy. Nathan Engineering uses ER308L filler for SS304 and ER316L filler for SS316 as standard.
- Thin material (0.5 mm to 3 mm) — TIG’s precise arc control enables welding of very thin gauges without burn-through
- Cosmetic-quality welds — TIG produces smooth, consistent bead profiles that require minimal post-weld finishing
- Pressure-containing welds — piping, pressure vessels, and hydraulic assemblies where weld quality directly affects safety
- Root pass in multi-pass welds — TIG is frequently used for the root pass on structural welds (to ensure full root penetration) with MIG or SMAW for subsequent fill and cap passes
Back-purging for stainless steel TIG welding
When welding stainless steel tube, pipe, or closed sections, the back face of the weld (the side not directly accessible to the torch) can be oxidised and sensitised by atmospheric oxygen during welding. Back-purging — flooding the internal space with argon before and during welding — prevents this oxidation and ensures that the internal weld surface has the same corrosion resistance as the external surface.
Nathan Engineering implements back-purging for all stainless steel tube and pipe welds where the internal surface quality is specified — a practice that distinguishes technically correct stainless welding from cosmetically acceptable but metallurgically compromised welds.
Post-weld treatment for TIG-welded stainless steel
Even correctly performed TIG welds on stainless steel produce heat tint (the blue, gold, and brown discolouration visible around the weld) caused by oxidation of the chromium oxide passive layer during welding. This heat tint reduces corrosion resistance in the affected area and must be removed by:
- Pickling — acid treatment (nitric/hydrofluoric acid paste or bath) that removes heat tint and restores the passive layer. Required for food, pharmaceutical, and marine-grade stainless assemblies.
- Electrochemical cleaning — a lower-hazard alternative to acid pickling that uses electrochemical action to remove heat tint. Nathan Engineering uses this method for field repairs and for assemblies where acid pickling is impractical.
- Mechanical brushing — stainless steel wire brushing (dedicated brushes that have never touched carbon steel) removes surface tint but does not fully restore the passive layer. Followed by passivation for critical applications.
Process 3: Spot Welding (Resistance Spot Welding)
What spot welding is and how it works
Spot welding (resistance spot welding, RSW) joins overlapping sheets of metal by passing a high-amperage, low-voltage electrical current through the joint via copper electrodes pressed against both sides of the stack. The electrical resistance of the metal generates localised heat at the interface between the sheets, melting a small nugget of metal that fuses the sheets together when the current ceases and the electrodes maintain pressure during cooling.
Spot welding is a rapid, clean, and highly repeatable process with no filler metal, no shielding gas, and minimal heat distortion. A single spot weld on 1 mm mild steel can be completed in under one second. Robotic spot welding systems produce hundreds of welds per minute in automotive body-in-white manufacturing.
When spot welding is the right choice for steel components
- Sheet metal assemblies — spot welding is ideal for joining overlapping flanges in sheet metal enclosures, panels, and formed assemblies where weld appearance is not critical on the visible face
- High-volume production — spot welding’s cycle time advantage over MIG or TIG is most pronounced in high-volume production where robotic systems fully exploit its speed
- Thin gauge material (0.5 mm to 3 mm) — spot welding is particularly well suited to thin gauge sheets where MIG or TIG would produce heat distortion
- CRCA, galvanised, and zinc-coated steel — spot welding works well on coated steels where MIG or TIG would burn through the coating and produce spatter contamination
Spot weld quality parameters
A spot weld’s quality is determined by the nugget diameter, penetration, and freedom from cracks or voids. These parameters are set by the combination of current, weld time, electrode force, and electrode face geometry. Nathan Engineering’s spot welding processes are set up using peel testing and cross-section inspection of sample welds to verify nugget formation before production begins.
Process 4: Projection Welding
What projection welding is
Projection welding is a resistance welding process similar to spot welding, but the current concentration is achieved by a raised projection (embossed feature) on one of the workpieces rather than by the electrode tip geometry. The projection collapses as it heats and fuses, creating a weld nugget at a precisely defined location.
Applications for steel components
Projection welding is used for attaching nuts, studs, and fasteners to sheet metal components — the weld projection is formed on the fastener, which is then resistance welded to the sheet at a precisely located position. PEM weld nuts, weld studs, and weld bolts in steel components are almost always attached by projection welding. Nathan Engineering uses projection welding for installing weld nuts in sheet metal enclosures and brackets across its fabrication range.
Process 5: Submerged Arc Welding (SAW) for Heavy Steel
When SAW is used
Submerged Arc Welding (SAW) is used for heavy structural steel — thick plate (above 12 mm), large structural sections, and pressure vessel manufacture. The arc is submerged beneath a blanket of granular flux that shields the weld from the atmosphere and recovers into slag post-weld. SAW produces high deposition rates and excellent weld quality for straight, flat, or rotational weld joints.
Nathan Engineering coordinates SAW for heavy fabricated components where MIG or TIG cannot achieve the required deposition rate or penetration. For most of Nathan Engineering’s typical component range (material below 12 mm), SAW is not required — MIG is the standard structural process.
Weld Joint Design: The Foundation of Weld Quality
Why joint design matters as much as welding process
The strongest welding process in the world cannot overcome a poorly designed joint. Joint design determines accessibility for the torch, weld cross-section area, stress distribution in service, and the amount of weld metal required. Nathan Engineering’s fabrication engineers review joint design as part of every new component DFM review — identifying joints that cannot be welded as drawn, joints that will be under-strength, and opportunities to reduce weld volume (and therefore cost and distortion) through better joint design.
Common joint types and their applications
- Butt joint — two pieces joined edge to edge. Strongest joint type when full penetration is achieved. Requires edge preparation (bevelling) for material above 6 mm. Used for structural seams, pressure-containing joints.
- Fillet joint (T-joint, lap joint) — the most common joint in sheet metal fabrication. Weld fills the corner between two surfaces. Easier to access than butt joints. Weld size must be specified (throat dimension) to carry the required load.
- Corner joint — two pieces meeting at an angle (typically 90°). Common in enclosures and frames. Can be welded from inside (fillet) or outside (edge weld) depending on access and appearance requirements.
- Edge joint — the edges of two sheets meeting flush. Used for thin sheet assemblies where a fillet joint would be inaccessible.
Weld distortion control — the biggest fabrication challenge
All welding generates distortion. The weld metal contracts as it cools, pulling the surrounding base metal toward the weld. In a symmetrical assembly, this effect is balanced. In an asymmetrical assembly — which most fabricated components are — the distortion is unbalanced and produces bowing, twisting, and angular errors.
Nathan Engineering controls weld distortion through:
- Fixture welding — holding components in purpose-built steel fixtures during welding that constrain distortion to acceptable levels
- Balanced welding sequence — distributing weld heat symmetrically around the component’s neutral axis where possible
- Backstep welding technique — short weld segments applied in a reverse direction to the overall progression, balancing thermal input
- Pre-set (pre-distortion) — deliberately setting the joint at an angle that the weld pull will correct to the desired final geometry
- Post-weld straightening — controlled pressing or spot-heating to correct residual distortion within acceptable limits
Welding Quality Control at Nathan Engineering
Welder qualification
Nathan Engineering’s welders are qualified to weld specific material types, thicknesses, and joint configurations in accordance with the applicable welding standard (IS 9606 for Indian standard, or AWS D1.1 for structural steel work to US standards). Welder qualification records are maintained and renewed on the required schedule.
Weld procedure qualification
For critical welds, a Welding Procedure Specification (WPS) is prepared and qualified by producing test welds that are destructively tested to verify mechanical properties. Nathan Engineering’s WPSs cover MIG welding of carbon steel in common thicknesses and joint configurations, and TIG welding of SS304 and SS316 for the joints most commonly produced.
Weld inspection methods
- Visual inspection (VT) — 100% visual inspection of all welds for surface defects: cracks, undercut, overlap, incomplete fusion, and excessive spatter. The primary inspection method for most structural welds.
- Dimensional inspection — weld size (throat, leg length) measured against drawing specification using weld gauges.
- Dye penetrant testing (PT) — liquid penetrant applied to weld surface reveals surface-breaking defects (cracks, pores) not visible to the naked eye. Used for pressure-containing welds and safety-critical joints.
- Magnetic particle testing (MT) — detects surface and near-surface defects in ferromagnetic steel. More sensitive than dye penetrant for magnetic materials.
- Radiographic testing (RT) / X-ray — reveals internal defects including porosity, lack of fusion, and cracks. Used for pressure vessel and safety-critical structural welds where internal quality must be verified.
Frequently Asked Questions
Q: Do Nathan Engineering’s welders hold formal qualifications? Yes. Nathan Engineering maintains welder qualification records aligned with IS 9606 for steel welding. Customer-specific welder qualification requirements (AWS D1.1, EN 9606) can be discussed at the enquiry stage.
Q: Can you weld dissimilar metals — for example, stainless steel to mild steel? Yes. Dissimilar metal welding (stainless to carbon steel) requires careful filler metal selection — typically ER309L, which bridges the metallurgical gap between austenitic stainless and carbon steel. Nathan Engineering’s welding team is experienced in dissimilar metal joints.
Q: Can you provide weld inspection certificates with deliveries? Yes. Nathan Engineering provides visual inspection records for all welded assemblies. Dye penetrant or magnetic particle test reports can be provided for joints requiring NDT, at cost.
Q: What is the thinnest material you can TIG weld? Nathan Engineering’s TIG welders routinely weld stainless steel from 0.8 mm thickness. With specialist micro-TIG equipment, 0.5 mm is achievable for specific applications. Discuss thin-gauge requirements at the RFQ stage.
Contact Nathan Engineering for Welded Steel Components
- Email: nathan@nathanengineering.co.in
- Phone: +91 93601 75927
- Website: www.nathanengineering.in
- Location: Bangalore, Karnataka, India
Submit your drawings with weld specification, material grade, and volume for a detailed quotation within 24–48 hours. Welding process recommendation included at no charge.
