How Is Sheet Metal Cut? Five Methods Used in Corten Steel Fabrication
Jan 24, 2024
Leave a message
Why the Cutting Method Matters
How a sheet of metal is cut decides the edge quality, dimensional accuracy and corrosion behavior of the finished part. For corten steel products such as screens, planters, fire pits and decorative panels, the cut edge is also where the protective patina starts to form, so the cutting process deserves as much attention as the steel grade itself.
Weathering steel grades such as ASTM A588, ASTM A242 and ASTM A606 Type 4 are commonly supplied as sheet and plate. The fabricator cuts the material to shape before bending, welding and forming. Each cutting method leaves a different edge profile, heat-affected zone and tolerance, which is why the same design can behave differently depending on how it is cut.
Shearing
Shearing is the fastest and most economical method for straight cuts. A shear blade presses the sheet against a fixed bed and cuts along a straight line, which is why it is used to square sheet edges before roll forming. In coated-panel production, shearing before roll forming, or profile shearing as the panel leaves the forming machine, wipes the zinc-aluminum coating onto the fresh cut edge. This edge protection provides continuous corrosion resistance at the cut, which is a key reason coated metal panels survive decades outdoors. Shearing suits straight blanks and simple rectangles; it cannot cut internal holes or curved profiles.
Laser Cutting
CNC fiber laser cutting melts the metal with a focused beam and removes it with assist gas. It produces a narrow kerf, a smooth edge and tight tolerances, typically around plus or minus 0.1 mm on sheet up to a few millimeters thick. Laser cutting is the standard method for intricate corten steel screens, planters with decorative cut-outs, letters and sculpture components, because it holds fine detail without mechanical tooling and leaves a clean surface for patina development.
Plasma Cutting
Plasma cutting uses an ionized gas arc to sever the metal and is the workhorse for thicker plate, commonly from 6 mm to 25 mm and beyond. It is faster than laser on heavy material but leaves a slightly tapered edge and a wider heat-affected zone. For corten steel structural elements such as table frames and heavy fire bowls, plasma cutting is a practical balance of speed and cost; edges are usually ground or brushed before finishing.
Waterjet Cutting
Abrasive waterjet cutting blasts a high-pressure stream of water mixed with garnet abrasive through the material. Because it is a cold process, there is no heat-affected zone, no hardening and no discoloration at the cut edge. Waterjet is chosen when the edge metallurgy must remain unchanged, for example on thick weathering steel plates where the patina is a visible design feature and heat tint would be difficult to remove.
Comparison Table
| Method | Typical thickness | Edge quality | Accuracy | Best for |
|---|---|---|---|---|
| Shearing | Up to about 6 mm | Straight, slight burr | Moderate | Straight blanks, roll forming |
| Laser cutting | 0.5-20 mm | Clean, narrow kerf | High, about ±0.1 mm | Intricate decorative parts |
| Plasma cutting | 6-25 mm and thicker | Slight taper, wider heat zone | Good | Thick plate and frames |
| Waterjet cutting | Up to 100 mm | Excellent, no heat zone | Very high | Edge-critical plates |
Cut Edge Treatment After Cutting
After any cutting process, deburr the edges and remove cutting oil or residue before the steel enters service. On corten steel, a clean and grease-free edge oxidizes evenly, while oil-contaminated edges stay bright and can look patchy against the surrounding patina. For coated metal panels, confirm with the fabricator that the edge protection, such as the zinc-aluminum wipe described above, is intact before installation.
Frequently Asked Questions
Which cutting method is best for corten steel? For decorative panels and planters, laser cutting gives the best detail and edge quality. For heavy structural plate, plasma or waterjet is more practical. Shearing remains the lowest-cost option for straight cuts and production blanks.
Does laser cutting harden the edge of weathering steel? The laser creates a small heat-affected zone at the cut edge. On the sheet thicknesses used for corten products the effect is minor and normally removed by deburring. Waterjet is the alternative when zero heat input is required.
Can corten steel be cut with a saw or grinder on site? Yes, for small adjustments. Use a metal-cutting blade, keep the cut cool, and clean the edge afterwards so the patina forms evenly. Avoid leaving bare edges exposed to standing water.
Why do the cut edges of coated panels not rust? In roll-forming lines, the shear wipes the zinc-aluminum coating over the fresh cut edge and seals it. This edge protection is a major reason coated metal panels keep their corrosion resistance after cutting.
How accurate is sheet metal cutting? CNC laser cutting holds about plus or minus 0.1 mm on thin sheet. Plasma is less precise on complex contours, and shearing is accurate for straight cuts but limited to them. Always confirm the drawing tolerance with the fabricator.
Does the cutting method change the steel grade? No. Cutting shapes the part but does not change the metallurgy of the base sheet, so the certified properties of ASTM A588, ASTM A242 and ASTM A606 Type 4 material remain valid after cutting.