Sheet Metal laser cutting versus shearing quality trade-offs for edge finish requirements
Content Menu
● What Really Happens at the Edge During Shearing
● Laser Edge Formation – Why It Looks and Behaves Differently
● Side-by-Side Numbers from Real Production Parts
● Metallurgical Damage Comparison
● Material-by-Material Guidance
● Tricks to Make Shearing Tolerable When You’re Stuck With It
Introduction
Edge condition drives more hidden costs in sheet metal fabrication than most people realize until the parts reach forming, welding, or paint. A bracket that looks fine on the layout table can turn into a nightmare the moment the press brake operator sees rollover and burr catching on the die, or when the robot welder burns through a hardened shear zone and spatters everywhere.
I’ve spent years quoting jobs where the customer starts with “just shear it, it’s cheaper,” then six months later they’re back asking why their powder coat is peeling at the edges or why half the parts crack on the first bend. The conversation almost always ends with the same question: how good does the edge actually need to be for this specific part, material, and finishing process?
Laser cutting and mechanical shearing (guillotine, right-angle shear, turret punch, or single-station press) remain the two dominant ways to separate a blank or a finished part from the sheet. Both have their place in 2025, even with 30 kW fibers now common and servo-electric punches getting faster. The difference shows up clearest when you put the edges side by side under a 20× scope or run them through a hole-expansion test.
What Really Happens at the Edge During Shearing
When you shear sheet metal you’re not cutting—you’re controlled fracturing. The blade or punch pushes the material until it yields, then tears. Four zones form every single time:
- Rollover – the plastic deformation at the entrance
- Burnish – the smooth rubbed zone where the tool actually shears
- Fracture – the rough torn area
- Burr – the extruded lip at the die side
On 2 mm CR4 mild steel with 0.16 mm clearance (8 %), you typically get about 0.6–0.8 mm of burnish and the rest fracture plus a 0.1–0.25 mm burr. Drop the clearance to 0.06 mm and the burnish can reach 70–80 % of thickness, but tonnage goes through the roof and the punch starts chipping after a few thousand hits.
Aluminum is worse. On 5754-H22 the burnish rarely exceeds 20 % because the material has low shear strength and tears early. Stainless 1.4301 (304) work-hardens so fast that the burnished land looks polished but the fracture zone is full of micro-voids that open up later in flanging.
I still remember a run of 1.2 mm 304 refrigerator side panels. The shop sheared them on a guillotine with brand-new blades. Burr averaged 0.12 mm. After roll-forming, every burr faced inward and scratched the plastic inner liners during door slam tests. They added a nylon brushing station that cost €180,000 and still left visible witness lines.
Laser Edge Formation – Why It Looks and Behaves Differently
A modern fiber laser removes material by vaporization in a kerf 0.20–0.35 mm wide. With high-pressure nitrogen (18–25 bar) you get almost no oxide, very little recast, and essentially zero burr on everything up to 6–8 mm thick.
Typical roughness numbers I measure on the floor with a Mitutoyo SJ-410:
- 2 mm S235, 12 kW fiber, nitrogen → Ra 1.6–2.8 µm, Rz 10–18 µm, no dross
- Same material, oxygen assist → Ra 4–7 µm, noticeable striations, occasional adherent dross
- 1.5 mm AlMg3, nitrogen → Ra 2.0–3.5 µm, clean bottom edge
- 3 mm 1.4404 (316L), nitrogen → Ra 2.5–4.0 µm, faint vertical striations that polish out easily
The heat-affected zone on fiber is tiny—usually 30–70 µm—and hardness increase is modest (30–60 HV). That matters a lot on DP780 or CP800 where sheared edges can hit 450–500 HV in the work-hardened layer and kill hole expansion ratio.
A Tier-1 supplier I work with switched B-pillar inner reinforcements from turret-punched + laser trimmed to full laser blanking. Hole expansion went from 28–35 % (sheared) to 85–110 % (laser) and they eliminated two robotic deburring cells.
Side-by-Side Numbers from Real Production Parts
Here’s data I pulled from three different shops running both processes on the same materials last quarter:
| Material / Thickness | Process | Burr Height (max) | Ra (µm) | Burnish Depth | Dimensional Tol. | Cycle Time (typical 500×300 mm blank) |
|---|---|---|---|---|---|---|
| DX51D+Z 1.5 mm | Guillotine shear | 0.18 mm | 6–14 | 35–45 % | ±0.20 mm | 3–4 s |
| Same | 12 kW fiber N₂ | <0.005 mm | 1.8–3.2 | 100 % | ±0.05 mm | 18–22 s |
| S355MC 4 mm | Turret punch | 0.35 mm | 12–22 | 25–30 % | ±0.25 mm | 12 s |
| Same | 15 kW fiber O₂ | 0.05 mm (dross) | 6–10 | 100 % | ±0.08 mm | 28 s |
| 304 2 mm | Turret punch | 0.22 mm | 8–16 | 30–40 % | ±0.18 mm | 15 s |
| Same | 10 kW fiber N₂ | <0.01 mm | 2.2–4.0 | 100 % | ±0.06 mm | 24 s |
Laser wins every quality metric, but shearing is still 5–8× faster on simple rectangles.
Metallurgical Damage Comparison
Shearing introduces massive plastic strain at the edge—equivalent strain often exceeds 1.0 in the burnished zone. That strain-hardened layer becomes a crack initiation site in AHSS. Multiple studies on DP600 and DP1000 show fatigue life drops 40–70 % on sheared edges versus laser-cut.
Fiber laser HAZ is narrow and the thermal cycle is so fast that you rarely see martensite formation in quench-hardenable steels unless you deliberately slow the speed. In press-hardening steels (22MnB5), laser blanking before hot stamping is now standard at most European OEMs because sheared edges cause die galling and quench cracks.
Cost Realities in 2025
A new 12 kW fiber with automation is still €800k–€1.2M. A 400-ton servo-hydraulic CNC guillotine or a 30-ton thick-turret punch with 58 stations costs €250k–€450k.
Consumables flip the equation:
- Shearing: punch and die sharpening/replacement every 100k–400k hits depending on material
- Laser: nozzles €15 each, 10–20 per shift; assist gas €0.02–€0.05 per meter cut
Break-even on a typical job-shop part mix is now around 1,500–3,000 pieces per year. Below that shear, above that laser. For high-volume straight blanks feeding transfer presses (washer tubs, deep-drawn automotive panels) shearing still rules because you’re at 600–1,200 parts per hour.
Material-by-Material Guidance
Mild steel <2.5 mm, hidden edges, e-coat → shear is fine if you control clearance and deburr Galvanized or pre-painted → laser only; shearing cracks the coating AHSS DP600 and above → laser mandatory for stretch-flange edges Stainless visible or food contact → laser (customers reject shear marks even after brushing) Aluminum 5xxx/6xxx → laser; shearing gives terrible burr and cracks Thick plate >10 mm → laser or plasma; shearing tonnage becomes absurd
Tricks to Make Shearing Tolerable When You’re Stuck With It
- Run 3–5 % clearance instead of 8–10 % (needs sharper tools and more tonnage)
- Use rake angle 1.5–2.5° on guillotine blades to spread force
- PVD-coated punches last 3–5× longer in stainless
- Polyurethane stripper plates suppress burr on thin material
- Fineblanking for small high-precision parts (100 % burnish, but slow and expensive presses)
Even with all those tricks you won’t match a decent laser edge.
Conclusion
By 2025 the decision is simpler than it was ten years ago. If the edge is structural, visible, heavily formed, coated before cutting, or made of anything stronger than S355, laser is the default choice. The machines are fast enough and cheap enough that the old “laser is only for prototypes” argument no longer holds.
Shearing still owns straight blanks at 50,000+ pieces per year where cycle time and capital amortization dominate. Most contract manufacturers now run both: coil-fed shears and punches for volume rectangles, high-power fibers for everything complex or quality-critical.
Measure your actual downstream cost—deburring labor, forming scrap, weld rework, coating defects, field failures—and the right process usually becomes obvious.