In the electrical switchgear industry, there is a conclusion that has been repeatedly validated: More than 70% of the cabinet’s quality is determined by sheet-metal fabrication. Whether the surface is smooth, the dimensions are precise, the structure is robust, and the protective features are reliable—these most straightforward quality indicators all stem from every step of the sheet-metal workshop’s production process.

Many people assume that sheet metal fabrication is nothing more than “cutting and bending,” with little technical sophistication. In reality, from material selection to coating, the precision and process control at every stage directly affect the electrical cabinet’s final quality, its service life, and even the operational safety of the power distribution system. This article will examine the complete sheet‑metal fabrication process to explain how it determines the quality of the cabinet body.

I. Panel Selection: The Starting Point of Quality

It all starts with the sheet metal. For high-voltage switchgear such as KYN28, XGN, and HXGN, the mainstream choice is Aluminum-zinc coated steel sheet 。

Advantages of Aluzinc Steel Sheets ：

Corrosion resistance: The surface coating (55% aluminum + 43.4% zinc + 1.6% silicon) forms a dense protective film, providing salt-spray resistance that far exceeds that of conventional cold-rolled steel with a paint finish.

Thermal Conductivity: Aluminum’s high thermal conductivity facilitates heat dissipation within the enclosure.

Self-healing capability: The coating on the cut edges can repair itself, slowing down rusting.

Optional no‑spray finish: In certain application scenarios, the surface may remain uncoated, preserving its natural color.

The Cost of Low-Quality Board Material Using ordinary cold‑rolled sheet steel in place of aluminum‑zinc‑coated sheet steel may not reveal any differences in the short term, but after two to three years, rust will appear along the cabinet edges. Such corrosion not only compromises the appearance but also degrades grounding continuity and can allow debris to fall into live parts, potentially causing a short circuit. Moreover, reducing the material thickness—e.g., from 2.0 mm to 1.2 mm—results in insufficient cabinet rigidity, leading to deformation under lifting loads or short‑circuit electromagnetic forces, which in turn prevents the doors from closing properly and causes handcart insertion to become jammed.

Key Points for Incoming Inspection of Sheet Materials : Verification of material certification, actual thickness measurement (using calipers at multiple points), and surface quality inspection (for scratches, rust spots, and coating uniformity).

II. CNC Cutting and Punching: Precision Determines Fit

1. Laser Cutting vs. Punch Press Material Preparation

Modern sheet metal workshops are generally equipped with CNC laser cutting machine or CNC turret punch press Laser cutting achieves an accuracy of ±0.1 mm, with narrow kerfs and a small heat-affected zone, making it well suited for machining irregularly shaped holes and producing prototype parts. Press‑brake punching, on the other hand, is ideal for high‑volume production of standard holes.

Consequences of Loss of Precision Control : A positional deviation of no more than 0.5 mm for the mounting‑hole centers is a fundamental requirement. Excessive deviation can prevent bolt holes from aligning during subsequent cabinet assembly; forcing assembly may warp the frame, leading to a cascade of issues—such as doors failing to close tightly (resulting in loss of protection rating), handcart guide rails becoming misaligned (causing sticking or even misalignment of contact points), and connection bolts being unable to pass through when cabinets are joined.

2. Burr Control

After blanking or cutting, the edges of the cut will retain Burrs . Burrs must be removed by grinding or chamfering. Sheets with burrs not only scratch operators, but more critically: burrs that act as conductors can trigger— Partial discharge , prolonged operation may lead to insulation degradation or even breakdown.

High-quality logo The cut edge is smooth, free of burrs and slag, and feels non-abrasive to the touch.

III. Bending Forming: The Foundation of Stiffness and Sealing

1. Bending accuracy

The accuracy of a CNC press brake directly affects the cabinet’s geometric dimensions. A bending angle tolerance of ±0.5° and an edge‑length tolerance of ±0.3 mm are standard requirements. Insufficient precision can lead to: columns that are not plumb (resulting in cabinet distortion and excessive diagonal deviations), door panels that do not seal tightly against the cabinet (compromising protection ratings and electromagnetic shielding), and excessively large gaps between cabinets when they are joined, making busbar bridging difficult.

2. Multi-bend forming process

Why do high-quality switchgear cabinets such as the KYN28 exhibit excellent rigidity and strong resistance to deformation? The key lies in… Multi-bend — The edges of the steel plate are bent two to three times to form a complex “U‑shaped” or “C‑shaped” cross‑section, enabling a large section modulus and bending stiffness with a relatively thin material thickness. From a materials mechanics perspective, this is equivalent to increasing the moment of inertia, thereby reducing deformation of the cabinet under short‑circuit electromagnetic forces or lifting stresses.

3. Rebound Control

During bending, steel plates exhibit elastic springback. Advanced manufacturing processes account for this in advance. Cornering angle or adopt Bottom-press bending Compensate for springback to ensure accurate angles in the finished product. Inexperienced small manufacturers often overlook springback, resulting in excessively large bending angles and overall misalignment after cabinet assembly.

IV. Welding and Assembly: Balancing Strength and Aesthetics

1. Welding Process

The load-bearing parts of the cabinet are made of Spot welding or Carbon dioxide gas-shielded welding . Solder joints shall be uniform, with adequate penetration and free of cold solder joints. After soldering, the surfaces must be ground smooth to ensure they do not interfere with subsequent painting or component mounting.

The Hazards of Welding Defects : Cold solder joints may crack during transportation-induced vibration, leading to loosening of the cabinet; if weld beads and spatter are not removed, they can reduce creepage and clearance distances (particularly hazardous in high-voltage switchgear); and welding distortion compromises dimensional accuracy.

2. Riveting and Bolted Joints

Modern modular cabinets increasingly adopt Riveting and Bolted connection , to prevent thermal deformation during welding. The rivet nuts are pre‑installed on the sheet metal, and later the components are fastened together with bolts. The tightening torque must comply with the specified standard—insufficient torque can cause loosening and abnormal noises, while excessive torque may crush the sheet metal or strip the threads.

Key Points of Quality Control : The rivet nut must be perpendicular to the sheet metal and free of looseness (a loose nut will rotate, preventing proper tightening of the bolt); after fastening, apply a scribe mark to facilitate subsequent inspection for loosening.

V. Surface Treatment: The Final Line of Defense Against Corrosion

1. Pre‑coating treatment — the foundation of adhesion and corrosion protection

Must be performed before spraying. Degreasing, derusting, and phosphating or Silanization Treatment. Inadequately cleaned oil and rust can result in poor coating adhesion, leading to widespread delamination within a short period.

Common Process Routes ：

Electrostatic powder coating after acid pickling and phosphating: a conventional process with well-established technology.

Silanization + Electrostatic Powder Coating: environmentally friendly, zero heavy-metal emissions, and superior adhesion.

Consequences of Inadequate Pre-treatment The sprayed coating may appear aesthetically pleasing, but when tested for adhesion using the cross‑hatch method, large areas peel off; in outdoor conditions, it begins to blister and rust within just a few months.

2. Electrostatic powder coating

Adopt Electrostatic powder coating The process involves uniformly adsorbing powder onto the workpiece surface under the influence of an electrostatic field, followed by high-temperature baking to achieve leveling and curing. The coating thickness is controlled within… 60~80μm . Insufficient thickness results in poor corrosion resistance; excessive thickness can lead to brittleness and cracking.

Key indicators ：

Adhesion: Cross-cut test ≤ Grade 1

Impact strength: 50 kg·cm, no cracks upon impact.

Salt Spray Test: No red rust for ≥500 hours (higher requirements apply to outdoor cabinets).

Color difference and gloss: visually free of color variation, with uniform gloss.

3. Color‑coated galvalume steel, uncoated and ready for painting

Aluzinc sheet itself exhibits excellent corrosion resistance; in certain applications, such as interior partitions, it can be left unpainted to retain its natural color, offering both environmental benefits and cost savings.

VI. The Direct Impact of Sheet Metal Quality on Cabinet Performance

VII. How to assess the quality of sheet metal fabrication?

During on-site inspections or acceptance tests, you may focus on the following details:

View the board material : Inquire about the material and examine the surface of the sheet—aluzinc-coated steel exhibits a distinctive metallic sheen and crystalline texture, whereas ordinary cold-rolled steel appears dull and lusterless.

Touch the edge : Gently sweep the cut edges and edges of the board with your hand—smoothness and the absence of burrs are essential requirements.

Look at the gap : Visually inspect the gap between the door panel and the cabinet body—ensure it is uniform and no greater than 1.5 mm.

Shaking cabinet body : Push and shake the cabinet frame with both hands—stable, no wobbling, no unusual noises.

Look at the coating. : Observe under illumination for any exposed substrate, sagging, orange‑peel texture, or particulates; lightly scratch concealed areas with a fingernail—no powder should easily come off.

Check the process The radius of the arc at the bend shall be uniform and consistent, with no cracks.

A great cabinet starts with sheet metal.

An electrical cabinet is not merely a simple metal box; it is a critical piece of equipment that ensures the safe and reliable operation of the power system. Sheet-metal fabrication determines the cabinet’s… Strength, precision, and corrosion resistance —These seemingly fundamental attributes ultimately translate into the reliability, safety, and service life of the distribution system.

A manufacturer that does not prioritize sheet-metal quality cannot deliver high‑quality electrical cabinets. Hunan Electrical Appliance Co., Ltd. As a leading manufacturer of high-voltage switchgear, we firmly believe that “the base material determines the quality.” From the moment sheet metal arrives at our warehouse, we rigorously control every step of the sheet-metal fabrication process, ensuring that each cabinet can stand the test of time.

Welcome to our factory for a site visit and see firsthand how our sheet-metal workshop crafts high-quality cabinets.