Sheet metal fabrication is the process of transforming flat metal sheets into finished components and assemblies through a sequence of cutting, bending, forming, joining, and finishing operations. The typical process flow: design → laser cutting/punching → deburring → bending (press brake) → welding (if assembly) → surface treatment (powder coating/painting/plating) → final inspection → packaging. Sheet metal is the backbone of countless industries — enclosures, chassis, brackets, panels, cabinets, ductwork, and structural components for electronics, automotive, HVAC, medical equipment, construction, and industrial machinery.
China's sheet metal fabrication industry is vast and deeply export-oriented. The Pearl River Delta (Guangdong) and Yangtze River Delta (Jiangsu/Zhejiang/Shanghai) alone host tens of thousands of sheet metal shops ranging from one-man workshops with a manual press brake to 500-employee factories with automated panel bender lines, robotic welding cells, and full finishing lines. For overseas buyers, the challenge is finding the right tier of supplier for your quality and volume needs.
| Operation | Typical Capability | Precision (General) | Precision (High-End) |
|---|---|---|---|
| Laser cutting (thickness) | 0.5–25 mm (steel), 0.5–16 mm (SS), 0.5–12 mm (Al) | ±0.2 mm | ±0.05 mm |
| Press brake bending | Length up to 6 m, thickness up to 12 mm | ±0.3° angle, ±0.2 mm position | ±0.1° angle, ±0.1 mm |
| Welding | TIG, MIG/MAG, spot, laser, robotic | Class C (visual acceptable) | Class B (non-destructive test) |
| Punching (turret punch) | Thickness up to 6 mm, tool up to ∅ 114 mm | ±0.10 mm | ±0.05 mm |
| Threaded inserts | M2–M12, clinch nuts, PEM, rivet nuts | ±0.05 mm position | ±0.03 mm |
| Surface treatment | Powder coating, painting, zinc plating, anodizing | 60–120 μm coating | 60–100 μm, ΔE ≤ 1.0 |
The largest concentration of sheet metal shops in China. Over 5,000 shops range from small (3–5 press brakes) to large (100+ employees, full finishing lines). Specialty: consumer electronics enclosures (server cases, power supply chassis, telecom cabinets, LED lighting housings). Extremely competitive on small-to-mid-size parts. Quick prototyping: 24–72 hour turnaround. Prices for standard enclosures: ¥30–80/kg ($4.50–12.00/kg). High labor mobility — the best welders and press brake operators cycle between shops frequently.
Premium sheet metal hub serving international automotive, medical, and electronics OEMs. Many shops are ISO 9001, IATF 16949, or ISO 13485 certified. Japanese-style 5S factory management, robotic welding, and automated bending cells (e.g., Amada HG series or Salvagnini panel benders). Prices: ¥80–200/kg ($12–30/kg) but with traceability, documented quality systems, and serious QC. Good for high-volume, high-precision work.
Large structural sheet metal hub for heavy equipment, steel structures, and agricultural/construction machinery. Thick-gauge plate (3–12 mm) bending and welding is core competency. Low overhead costs drive prices down: ¥20–50/kg ($3–7.50/kg). Quality: functional but cosmetic finish can be rough. Excellent for heavy industrial parts where appearance is secondary to strength.
The prototyping trap: We often see overseas buyers pay a premium for quick prototyping at a Shenzhen shop, then move to mass production at the same shop — only to find that mass production quality doesn't match the prototype. Reason: prototype was made by the owner/factory manager personally (the best worker), but mass production runs through the general workforce. Solution: when evaluating a sheet metal shop for volume production, don't just approve the prototype — also audit a random batch of 20 parts from their ongoing production line. If you can't visit, request photos of 10 random parts from a production run, showing the same features as your prototype.
This is the single biggest source of dimensional error in sheet metal sourcing. The K-Factor (ratio of neutral bend axis to material thickness) determines how much the flat pattern length needs to be before bending. Different materials, thicknesses, and bend radii have different K-Factors. Chinese shops may use a default K-Factor (typically 0.33) that doesn't match your material. If the unfolded flat pattern is wrong, everything is wrong: holes won't align, edges won't meet. Mitigation: ask the supplier which K-Factor they use for your material and confirm via a test bend on a 100 mm sample piece. Measure the resulting flange — if it's off by more than 0.3 mm, recalculate.
Every metal returns slightly toward its original shape after bending — this is springback. For a 90° bend in 1.5 mm mild steel, springback is roughly 1–3°. For stainless steel (which work-hardens faster), it's 3–7°. Chinese press brake operators compensate by over-bending by the expected springback angle. But this compensation is based on experience and trial — different batches of steel from different mills (with slightly different yield strength) produce different springback. If you have critical closed-loop dimensions on bent parts (e.g., enclosure frame where corners must meet), specify a bend angle check after the first 5 parts and adjust the program before full production.
MIG welding on thin sheet (< 1.5 mm) causes significant heat distortion — the metal warps around the weld seam. Specifying a TIG weld (lower heat input) helps but costs 2–3× more because it's slower. Better solution: use resistance spot welding (for lap joints) or tab-and-slot design (self-locating interlocking tabs) to reduce weld length. For cosmetic seam welding on thin enclosures, specify "stitch weld at 30 mm intervals, 15 mm weld length" instead of continuous seam — this reduces total heat input by 50% while maintaining adequate joint strength.
| Cost Component | % of Total | Notes |
|---|---|---|
| Material | 30–50% | Steel sheet cost. Thickness, grade, and coating (galvanized, pre-painted) drive this. SPCC/DC01 = base, SECC/SGCC = +8–15%, SUS304 = +150–200% |
| Laser cutting | 10–20% | ¥3–20/m ($0.45–3.00/m) depending on thickness. Small holes are expensive (piercing time + per-hole rate) |
| Bending | 10–25% | ¥5–30 per bend ($0.75–4.50/bend). Complex parts with 8+ bends = significant cost. Simple 4-bend box = cheap |
| Welding / assembly | 5–20% | ¥30–80/hour for welders ($4.50–12.00/hr). Robotic welding amortized over long production runs reduces per-unit cost |
| Surface treatment | 10–20% | Powder coating ¥15–40/m² ($2.25–6.00). Zinc plating ¥5–15/kg. Anodizing ¥10–30/kg. Finishing is often underestimated in RFQ |
| Deburring + cleaning | 3–8% | Manual deburring of all cut edges and holes. For small batches, this can be 10–15% of cost |
Typical range: ¥20–200/kg ($3–30/kg) finished part, heavily dependent on complexity, thickness, and finishing requirements.
For outdoor sheet metal enclosures, the standard recommendation: 1.5–2.0 mm SECC (electro-galvanized steel) with epoxy powder coating (100–120 μm, RAL 7035 or 9006). SECC provides good corrosion protection at the cut edges (because electro-galvanizing offers uniform coating on both sides). SGCC (hot-dip galvanized) is cheaper but has thicker zinc on the surface and thinner on cut edges, making laser-cut edges more susceptible to red rust. For coastal environments (salt spray), consider 304 stainless steel with pickling/passivation.
For tab-and-slot assembly of 1.0–2.0 mm sheet metal: slot width = tab thickness + 0.1 mm (snug fit) to 0.3 mm (assembly clearance). Tighter clearance gives a more secure connection but requires full welding. For EMS-type enclosures: 0.2 mm clearance is standard. Tab length: 6–12 mm depending on plate thickness. Corner cutout radius: at least 1.5× material thickness to avoid stress cracking. Following these ratios avoids the dimension stack troubleshooting that often adds 2–3 days to production.
For interior/unseen parts: standard mill finish (no treatment) or simple oiling for temporary rust protection. For visible parts: powder coating is the most cost-effective standard finish. For bracket-type parts: zinc plating (blue/white/yellow passivation) at ¥5–15/kg. For stainless steel parts: #400 brushed finish (Ra 0.4–0.8 μm) is standard, with optional pickling to remove weld discoloration. Always confirm the finish spec on your drawing — "standard" means different things to different shops.
Best practice: send the supplier TWO files — (1) the assembled 3D model (STEP or IGES format) showing the finished part/bending sequence, and (2) a flat pattern DXF or DWG for their CAM programming. Some Chinese shops prefer to unfold the 3D model themselves using SolidWorks or Inventor — but their unfolding may use a different K-Factor than yours, causing mismatch. If you provide both files and specify the K-Factor, you eliminate the most common source of flat pattern errors. Include a dimensioned 2D PDF as a cross-check reference.
Yes — for laser-cut and press-brake bent parts, there is generally zero tooling cost (unlike stamping which requires dies). The only tooling charges for sheet metal fabrication are usually: (1) bending punch/die selection (¥50–200 for specialized tool inserts for unique profiles), (2) welding jigs for repeatable assembly positioning (¥500–2,000 for a simple fixture), (3) inspection gauges for high-volume runs (¥200–1,000). For simple brackets and enclosures fabricated in quantities < 500 pcs, tooling is typically free.