Steel fabrication begins with one fundamental operation: separating metal from sheet or plate. The method you choose determines edge quality, heat-affected zone, material loss, speed, and ultimately production cost. In a shipyard or heavy fabrication environment, this decision is made thousands of times a day across machines costing anywhere from ₹5 lakh to ₹5 crore.
Oxyfuel (Flame) Cutting
Oxyfuel cutting is the original thermal cutting process and remains the most cost-effective method for thick mild steel. A preheat flame (typically acetylene, propane, or LPG) raises the steel to its ignition temperature (~870°C), then a high-pressure pure oxygen jet causes rapid oxidation — effectively burning through the metal. The process is a chemical reaction, not simple melting.
Best For
Mild steel 6mm–300mm thick. Structural plates, ship frames, pressure vessel components.
Limitations
Cannot cut stainless steel, aluminium, or copper alloys. Larger heat-affected zone than plasma or laser.
Cost Profile
Lowest capital cost. Gas consumption is the primary operating expense. Ideal for yards with existing gas infrastructure.
Modern CNC oxyfuel machines (multi-torch gantry systems) can run 8–16 torches simultaneously, cutting complex hull plate shapes from full 12m × 3m sheets. Preheat gas consumption optimization is where the real efficiency gains lie — modern proportional valve control can reduce gas use by 20–30% versus older systems.
Plasma Arc Cutting
Plasma cutting creates a superheated, electrically conductive gas jet (plasma) by forcing gas through an electric arc at temperatures reaching 20,000–25,000°C — over three times the surface temperature of the sun. The plasma melts the metal while the high-velocity gas jet expels the molten material. Unlike oxyfuel, plasma can cut any electrically conductive material.
Best For
Mild steel, stainless steel, aluminium, and other conductors. Optimal range 3mm–80mm. High-definition plasma extends precision to 0.5mm tolerance.
Speed Advantage
On 6–25mm mild steel, plasma cuts 3–5× faster than oxyfuel. A key advantage in high-volume shipyard production.
Consumable Management
Nozzle, electrode, and shield cup wear are the primary operating cost. Proper gas pressure and pierce height control extend consumable life 3–5×.
High-Definition (HD) plasma systems (Hypertherm XPR, Lincoln Electric Spirit II) use precision torch design and real-time arc voltage control to achieve edge squareness within 1–3° and surface roughness (Ra) of 3–6 µm on mild steel — approaching laser quality at a fraction of the capital cost. In shipyards, HD plasma is the workhorse for 6–50mm ship plate.
Laser Cutting
Laser cutting focuses an amplified light beam (typically CO₂ or fiber laser) to a spot of 0.1–0.3mm diameter, creating extremely high power density that vaporizes or melts metal with minimal heat-affected zone. Fiber lasers (1070nm wavelength) have largely replaced CO₂ (10,600nm) for metal cutting due to higher wall-plug efficiency and superior performance on thin sheets.
Precision Leader
Tolerances of ±0.05–0.1mm. Edge roughness Ra < 2µm. Ideal for complex bracket profiles, pipe flanges, and precision fitment parts.
Material Range
Mild steel up to 30mm, stainless up to 25mm, aluminium up to 20mm, copper up to 12mm. Fiber lasers cut highly reflective metals that damage CO₂ optics.
Capital Intensive
High-power fiber laser systems cost ₹50L–₹3Cr. Running cost per cut is often lower than plasma on thin material due to speed and consumable-free operation.
Abrasive Waterjet Cutting
Waterjet cutting uses an ultra-high-pressure water stream (typically 3,000–6,000 bar / 40,000–90,000 PSI) focused through a precision orifice. For metal cutting, garnet abrasive (80 mesh) is entrained into the jet, creating an erosion process rather than a thermal one. The cut is entirely cold — no heat-affected zone, no metallurgical changes, no warping.
Cold Process
Zero heat-affected zone. Critical for hardened steels, titanium, composites, and materials that cannot tolerate thermal stress.
Any Material
Cuts steel, glass, stone, rubber, composites, ceramics — anything that cannot be cut thermally. 5-axis waterjet handles complex 3D geometry.
Speed Limitation
Significantly slower than plasma and laser on metal. Best suited for specialty cuts, thick sections, and materials requiring no heat input.
Other Methods: EDM, Shearing, Sawing, Air Carbon Arc
EDM (Electrical Discharge Machining) cuts hardened tool steel and exotic alloys with extreme precision using controlled spark erosion — used in precision tooling, not production plate cutting. Guillotine shearing is the fastest method for straight cuts on thin sheet (< 12mm) but leaves a slightly deformed edge. Bandsaw and circular saw cutting are used for bar stock and structural sections. Air carbon arc gouging removes weld defects and cuts thick sections when other methods are impractical on-site.
Comparison & Selection Guide
| Area | Industry 4.0 | Industry 5.0 |
|---|---|---|
| Method | Best Thickness Range | Edge Quality / HAZ / Typical Use |
| Oxyfuel | 6mm – 300mm (mild steel only) | Moderate edge, large HAZ. Heavy structural plates, ship frames |
| Plasma (Standard) | 1mm – 80mm (all conductors) | Good edge, medium HAZ. High-speed production cuts on ship plate |
| HD Plasma | 1mm – 50mm (all conductors) | Very good edge, small HAZ. Near-laser quality at lower capital cost |
| Fiber Laser | 0.5mm – 30mm (most metals) | Excellent edge, minimal HAZ. Precision brackets, flanges, fitment parts |
| Waterjet | Up to 200mm (any material) | Excellent edge, zero HAZ. Hardened steel, titanium, composites |
In a shipyard setting, the answer is almost never one method — it's a complement. Oxyfuel for heavy frames and keels, HD plasma for the majority of hull plate, laser for precision structural brackets, and waterjet for specialty stainless or coated plate that cannot tolerate heat. The key is matching the process to the part, not to what machine the yard already owns.