Six Core Processes in Sheet Metal Fabrication

Six Core Processes in Sheet Metal Fabrication
Sheet metal fabrication is a cold-forming process for metal sheets ranging from 0.2 mm to 6 mm in thickness. Unlike machining (subtractive manufacturing), which relies primarily on material removal, sheet metal fabrication focuses on “deformation forming” with minimal material removal. Performed entirely at room temperature, this process ensures low material waste and stable structural integrity, making it the preferred manufacturing method for enclosures, cabinets, automation equipment housings, and structural components for new energy systems. A high-quality sheet metal part must pass through six essential stages:
Stage 1: Drawing Analysis and Process Planning (DFM). Upon receiving the technical drawings, a “Design for Manufacturing” (DFM) analysis is conducted. This includes verifying flat-pattern dimensions, ensuring appropriate bend radii (typically R ≥ 1.5t; radii that are too small can lead to cracking), and confirming sufficient spacing between holes and bend lines (ideally ≥ 1.5 times the material thickness to prevent circular holes from deforming into ellipses during the bending process). This stage also involves nesting—optimizing the layout of parts on the raw material sheet to achieve a material utilization rate of over 80%.
Stage 2: Precision Blanking. The current industry standard involves a combination of fiber laser cutting and CNC punching. Laser cutting is ideal for complex, irregular contours, offering a positioning accuracy of ±0.03 mm, a kerf width of 0.1–0.2 mm, and smooth edges that rarely require secondary finishing. CNC punching, by contrast, is more efficient for high-volume production of circular holes, square holes, and louvers. For plates thicker than 6 mm, plasma cutting may be used to control costs, though this requires a more relaxed tolerance for precision.
Stage 3: Bending. This is the critical step that transforms a flat sheet into a three-dimensional component. The width of the V-groove in the bottom die is typically set to 6–8 times the material thickness; a groove that is too narrow can damage the sheet, while one that is too wide can lead to inaccurate bend angles. For long workpieces, deflection compensation (crowning) is applied to prevent the “bowing” effect—where the ends are accurate, but the center dips. Because metal naturally exhibits “springback” after bending, a 90° bend often requires over-bending to an angle of 88°–89°. Since materials like stainless steel exhibit greater springback than cold-rolled steel, compensation parameters must be carefully calibrated based on the specific material type and thickness. The sequence of operations must be strictly followed: deburring, riveting, and tapping must be completed before bending. If bending is performed before riveting, the pressure applied during the riveting process can pull on the bent edges, leading to dimensional inaccuracies.
Step 4: Joining and Welding. For thin-gauge sheet metal and stainless steel, TIG (argon arc) welding is preferred, as it produces clean, aesthetically pleasing seams with a minimal heat-affected zone. For thicker plates and carbon steel structural components, gas-shielded welding offers higher efficiency, while spot welding is commonly used for overlapping parts in batch production. To control deformation, three methods are employed: using rigid fixtures, applying symmetric segmented welding (for long seams, welding in 100–150mm segments with cooling intervals), and, when necessary, performing low-temperature annealing post-welding to relieve internal stress.
Step 5: Pretreatment and Surface Finishing. Pretreatment is critical to the longevity of the coating. This process includes degreasing, acid pickling to remove oxide scale, and phosphating to create a 3–5μm conversion layer—a layer that must be carefully controlled, as one that is too thick compromises adhesion, while one that is too thin fails to provide adequate rust protection. This is followed by electrostatic powder coating, typically applied at a thickness of 60–120μm, with a curing process at 180–200°C for 15–20 minutes.
Step 6: Inspection and Delivery. Mass production may only commence after a First Article Inspection (FAI) has been signed off. The process includes routine in-process inspections, and a final Outgoing Quality Control (OQC) report is generated upon completion. For precision components, a Coordinate Measuring Machine (CMM) is used to verify geometric and positional tolerances. Proper packaging—utilizing EPE foam interlayers, corner protectors, and moisture/rust-proofing measures—is essential to prevent transit damage, such as scratches, which is the most frequent cause of delivery-related disputes.
For clients, the primary value of custom sheet metal fabrication lies in the elimination of the need for dedicated molds. This allows for single-piece prototyping, small-batch production of diverse parts, and standardized mass production—offering a significant cost advantage, particularly during the R&D and product iteration phases.