I. Tolerance Specifications by Process

1. Laser Cutting
Standard contours and heat dissipation vents: ±0.1mm;
Charging gun openings, display screen windows, and module mounting holes: ±0.05mm to ±0.1mm (These are the most critical areas, directly affecting assembly and IP protection ratings).
2. CNC Bending
Bending dimension tolerance: ±0.2mm; bending angle: ±0.5° to ±1°;
For tall cabinets (height > 1.2m), flatness and perpendicularity tolerances are relaxed, with primary control focused on the flange where the sealing gasket is installed.
3. Cabinet Assembly (Post-welding/assembly)
- Flatness of module mounting reference surface: 0.2mm/m
- Diagonal error of the unit: ≤1.5mm (for cabinets around 1m tall); ≤2mm for large floor-standing DC charging piles
- Assembly gaps: Casing seams must be uniform, generally controlled within 0.5mm to ensure IP54/IP65 water and dust resistance.

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> For standard structural dimensions that do not affect appearance or sealing, the GB/T1804-m standard applies, allowing tolerances to be relaxed to ±0.5mm–1mm to help control manufacturing costs.

II. Key Challenges in Precision Control (Distinct from Battery Packs)

1. Large, Thin-Walled Panels Prone to Distortion: Charging pile cabinets feature thin walls and large overall dimensions, making the sheet metal itself prone to warping; welding-induced deformation—rather than bending springback—poses the greatest risk.
2. Waterproof Sealing Surfaces Are Critical: Poor flatness in the gasket mounting channel leads to localized gaps, causing failure during rain-exposure tests; this is the top priority for precision control in charging piles.
3. Alignment of Holes and Modules: Positional accuracy for mounting holes (for internal power modules and main control boards) must be guaranteed; otherwise, forced assembly strains the casing, leading to loose screws and seal failure after prolonged vibration. 4. For long-term outdoor use, the flatness of the sheet metal prior to coating directly affects the final appearance; any slight deformation becomes visually exaggerated after the powder coating process.

III. Process Strategies to Ensure Sheet Metal Precision for Charging Piles

 1. Design and Flat-Pattern Development

- Differentiated tolerance allocation: Tighten tolerances for sealing surfaces, charging gun ports, and module mounting holes; relax tolerances for non-mating housing surfaces, outer contours, and ventilation holes to reduce costs.
- Structural reinforcement: Add stiffening ribs to large door panels and side panels to enhance rigidity and minimize warping; position welds away from sealing surfaces.
- Spring-back compensation: Cold-rolled steel exhibits minimal spring-back, whereas aluminum alloy housings require compensation for bending spring-back.

 2. Blanking and Bending

- Level raw materials to eliminate internal stress and prevent large sheets from warping after blanking;
- Establish a unified datum and perform first-article inspection on bending angles and dimensions; use segmented bending to avoid sealing flanges and minimize cumulative tolerance errors.

3. Welding (Core Focus: Deformation Control)

- Prioritize spot welding and robotic intermittent welding; minimize continuous full-seam welding to reduce heat input; employ a symmetrical skip-welding sequence;
- Use rigid clamping fixtures during welding to prevent warping; perform post-weld shaping to correct the flatness of sealing surfaces;
- Whenever possible, use bolted assembly instead of long weld seams to reduce welding deformation (a common practice for wall-mounted AC charging piles).

 4. Inspection Plan

- Individual components: Calipers, height gauges, and angle gauges;
- Cabinet assembly: Measure diagonals and check sealing surface flatness using optical flats or dial indicators; perform batch sampling for critical hole locations;
- Unlike battery packs, full-part CMM scanning is not required; a combination of first-article inspection and batch sampling is generally sufficient and more cost-effective. ## IV. Charging Pile vs. Battery Pack (Distinction in a Nutshell)

- Battery Pack: High-voltage housing + liquid-cooling sealing + vehicle integration; requires high precision for the entire assembly, strict control over welding deformation, spring-back, and tolerance chain accumulation, plus 100% inspection using CMM (Coordinate Measuring Machines).
- Charging Pile: Outdoor IP protection + internal module assembly; precision is required only for sealing surfaces, cutouts, and mounting datums, while other dimensions allow for looser tolerances, resulting in a more cost-effective design.

V. Common Failure Points

Cabinet distortion after welding → Poor seal fitment, failure of IP rain-ingress test;
Misalignment of charging gun cutout → Charging gun cannot be inserted, uneven gaps;
Positional deviation of mounting holes → Forced assembly (stressing the housing), leading to loosening after vibration.