Specific Controls And Key Points For Sheet Metal Processing

Quality control standards for sheet metal processing cover multiple dimensions, including dimensional accuracy, surface quality, and structural strength. These standards must be implemented in conjunction with industry regulations and company standards. The following are specific control standards and key points:

I. General Dimensional Accuracy Standards

1. Linear Dimension Tolerances

Plate thickness ≤ 2mm: ±0.15mm (e.g., the dimensional tolerance of a 1mm steel plate cut is ≤0.15mm);

Plate thickness 2-4mm: ±0.2mm;

Plate thickness > 4mm: ±0.3mm (based on the "medium accuracy" level in GB/T 1804-2000, "General Tolerances - Tolerances for Linear and Angular Dimensions Not Indicated with Tolerances").

2. Bending Angle Tolerances

90° bend: ±1° (e.g., the workpiece angle must be controlled between 89° and 91°);

Special angles (e.g., 135°, 60°): ±1.5° (refer to ISO 2768-1, "Tolerance Standards").

3. Hole Position Accuracy

Hole Center Distance: ±0.2mm (applicable to holes with a diameter ≤10mm);

Hole-to-Edge Distance: ±0.3mm (to prevent hole deformation during bending).

II. Surface Quality Control Standards

1. Appearance Defects

Prohibited Items:

Cracks (visible cracks are prohibited at bends and weld areas);

Severe Scratches (scratches >0.1mm deep or >5mm long require repair);

Indentations (indentations on the stamped part surface ≤0.05mm deep).

Permitted Range:

Minor Scratches (<0.05mm deep, <2mm long, ≤3 scratches per square meter);

Oxidation Spots (minor oxidation is permitted on stainless steel surfaces, requiring a salt spray test for ≥24 hours).

2. Surface Treatment Standards

Spraying:

Coating Thickness: 60-80μm (tested with a thickness gauge, deviation ≤±5μm);

Adhesion: Tested according to GB/T 9286-1998, cross-cut method meets Level 0 (no coating peeling).

Electroplating:

Galvanized Layer Thickness: 8-12μm (corrosion protection requirement for steel parts);

Chromate Passivation: Uniform blue-white zinc passivation film, free of missing plating or blackening.

III. Structural Strength and Functional Standards

1. Welding Quality

Weld Seam Requirements:

Weld seam height ≥ 70% of the plate thickness (e.g., for 2mm steel plate welding, weld height ≥ 1.4mm);

Porosity: ≤ 3 pores with a diameter ≤ 0.5mm per 100mm of weld, with spacing ≥ 20mm;

Cold Welds and Weld Leaks: Strictly Prohibited (affects structural strength).

Inspection Methods:

Visual inspection of weld flatness;

Ultrasonic testing (for welds thicker than 5mm).

2. Bending Strength

After bending, the part must show no metal lattice tearing (observed under a 10x magnifying glass).

When the flange height is ≥ 3 times the plate thickness, a tensile test is required (e.g., a 5mm flange on a 1mm steel plate requires a tensile strength of ≥ 200MPa).

3. Assembly Functionality

Threaded hole go/no-go gauge inspection: The go gauge can be screwed in smoothly, and the no-go gauge has been screwed in ≤ 2 threads.