Precision Sheet Metal Parts Processing Basic Process Knowledge Popularization and Detailed Explanation
Precision sheet metal processing refers to the fabrication of various three-dimensional structural components from thin metal plates (conventional thickness: 0.5‑12mm) through a series of processes including cutting, forming, joining, and surface treatment. Compared with ordinary sheet metal, precision sheet metal features higher requirements for dimensional accuracy, appearance, flatness and assembly fit, with a conventional tolerance of ±0.05~±0.2mm. It is widely applied in equipment enclosures, server chassis, automation jigs and fixtures, medical equipment, new energy, communication cabinets and other parts.
Complete Standard Process Flow: Raw Material Cutting & Blanking → Cutting Processing → Deburring → Bending Forming → Rivet Pressing & Riveting → Welding → Correction & Polishing → Surface Treatment → Full Dimensional Inspection → Packaging & Delivery
Blanking is the first procedure of sheet metal processing, which separates plates according to the drawing profile. Different processes are applicable to different production batches and pattern complexities.
1.1 Fiber Laser Cutting (Mainstream for Precision Sheet Metal)
It melts and blows away metals with high-energy laser beams to realize cutting.
• Advantages: Capable of processing arbitrary complex special-shaped contours and holes with high dimensional accuracy; applicable to carbon steel, stainless steel and aluminum plates; suitable for prototype production and mass production of all scales.
• Notes: Slag and burrs will be generated on the cutting edge, which must be removed in subsequent procedures; special process parameters are required for high-reflectivity aluminum plates.
It adopts die stamping for forming.
• Advantages: High efficiency for mass production, suitable for regular holes such as round and square holes.
• Limitations: Unable to process complex special shapes; dies are subject to wear and tear.
It is only used for linear shearing of simple plates with low cost, serving as rough blanking and unavailable for special-shaped processing.
Mainly used for rough processing of thick plates with low accuracy, generally not applied to precision sheet metal parts.
Burrs, slag and sharp edges will appear on the cutting surface after laser cutting and stamping, which is an indispensable procedure for precision sheet metal. Burrs may cause assembly scratches, seal damage, coating peeling, and interfere with bending dimensional accuracy.
Common treatment methods:
• Brush Deburring Machine: Automatic batch processing for mass production;
• Vibration Grinding: Batch chamfering and edge rounding for small parts;
• Sand Blasting: Realize deburring and matte surface pretreatment simultaneously;
• Manual Polishing: Supplementary treatment for small-batch complex workpieces.
High-end products require edge rounding of R0.2‑R0.5 to eliminate sharp corners.
It bends flat unfolded plates into 3D structures via CNC bending machines and matched bending dies, serving as the core forming process of sheet metal.
3.1 Bending K-Factor (Bending Compensation)
During plate bending, the outer layer is stretched while the inner layer is compressed. The unfolding compensation value (K-factor) varies with material and plate thickness, which directly determines the unfolded drawing size and acts as the core calculation parameter for sheet metal processing.
High-elastic materials such as stainless steel and aluminum alloy will spring back after bending. Pre-angle compensation via dies is required to avoid angular dimension deviation.
3.3 Minimum Bending Inner Radius
The plate bending inner radius shall not be smaller than the plate thickness; excessively small radius will cause cracks on the outer plate surface.
A sufficient distance shall be reserved between holes and bending edges; too short a distance will stretch round holes into ellipses during bending.
Precision bending dimensional tolerance: ±0.1~±0.2mm
4. Rivet Pressing & Riveting Process
Since thin plates are inconvenient for tapping, rivet pressing is widely adopted. Rivet nuts, studs and screws are extruded and pressed into plates by rivet pressing machines.
• Advantages: Welding-free, neat appearance and convenient assembly;
• Limitations: The plate thickness shall meet the minimum requirement; insufficient thickness will cause rivet bulging and thread falling off.
Other riveting types: Blind riveting, used for splicing and fixing two plates.
5. Sheet Metal Welding Process
Welding is used for splicing multiple plates. The biggest difficulty in welding is thermal deformation; concentrated heat will cause warping and dimensional offset, so tooling fixtures are required to control deformation for high-precision products.
|
Welding Process |
Applicable Materials |
Characteristics |
Application Scenarios |
|
CO2 Shielded Welding |
Carbon Steel |
High efficiency, large weld seam, relatively large deformation |
Ordinary equipment frames |
|
TIG Argon Arc Welding |
Stainless Steel, Aluminum Alloy |
Beautiful weld seam, relatively small deformation |
Precision stainless steel sheet metal parts |
|
Resistance Spot Welding |
Various thin plates |
Small welding spot, no filler metal, fast speed |
Mass thin plate lap joint |
|
Laser Welding |
Carbon Steel, Stainless Steel, Aluminum |
Ultra-low heat input, minimal deformation, fine weld seam |
High-end precision sheet metal and appearance parts; high cost |
Post-welding procedures: Grind weld scars and smooth weld seams to ensure flat surface for subsequent spraying and oxidation treatment.
Cutting, bending and welding all cause plate warping and deformation. Leveling machines and tooling fixtures are used to correct workpieces and control flatness. It is impossible to achieve zero deformation for thin plates after welding, so the tolerance on drawings shall be reasonably set based on process characteristics.
7. Common Raw Materials for Precision Sheet Metal
7.1 SPCC Cold Rolled Steel Plate
Ordinary carbon steel with excellent bending and welding performance; prone to rust, so powder coating or painting is mandatory for rust prevention.
7.2 SGCC Hot-Dip Galvanized Plate
Comes with a built-in anti-rust galvanized layer, widely used for cabinet enclosures; high welding temperature will burn off local zinc layers, so supplementary protection is required for welding positions.
• 304: General-purpose stainless steel with good rust resistance and large springback, high bending difficulty;
• 316: Stronger acid and alkali corrosion resistance, suitable for outdoor and chemical equipment parts.
7.4 Aluminum Alloy Plate AL5052 / AL6061
• AL5052: Excellent bending performance, suitable for bent sheet metal parts;
• AL6061: High hardness, commonly used for tooling enclosures, prone to cracking during bending.
Aluminum alloy parts are generally treated with anodization.
8. Mainstream Surface Treatment Processes
1. Powder Coating: The most common process in the sheet metal industry. Electrostatic spraying with wear-resistant and scratch-resistant thick paint films, rich color options and high cost performance, preferred for equipment and cabinet enclosures.
2. Liquid Painting: Thin paint film, suitable for special colors and small-batch production.
3. Anodization (Aluminum Alloy Only): Conductive, available in natural and colored finishes; hard anodization provides high wear resistance.
4. Electroplating (Zinc Plating, Nickel Plating): Anti-rust treatment for carbon steel parts.
5. Stainless Steel Brushing: Decorative surface treatment to remove processing traces.
6. Sand Blasting: Form matte surface and improve coating adhesion.
9. Basic Tolerance Knowledge of Precision Sheet Metal
• Ordinary Sheet Metal: ±0.5mm
• Conventional Precision Sheet Metal: ±0.1 ~ ±0.2mm
• Ultra-High Precision Sheet Metal: ±0.05mm (sharp cost increase)
Process Tip: The tolerance of bending and welding areas will deteriorate. The flatness of welded thin plate parts cannot reach the level of machined parts, so overly strict tolerances beyond process capability shall be avoided on design drawings.
10. Common Sheet Metal Defects and Causes
1. Sharp Cutting Edges & Burrs: Missing deburring procedure after cutting;
2. Bending Angle Deviation: Uncompensated material springback;
3. Welding Warping & Deformation: Concentrated welding heat and no tooling positioning;
4. Bending Cracking: Excessively small bending inner radius or unreasonable plate rolling texture direction;
5. Loose & Bulging Rivets: Insufficient plate thickness or incorrect rivet pressing parameters;
6. Coating Peeling: Unclean workpiece surface with residual oil stains and oxide scales.
11. Basic Design Process Key Points for Sheet Metal
1. The bending inner radius shall not be smaller than the plate thickness to avoid outer surface cracking;
2. Reserve a safe distance between holes and bending edges to prevent hole deformation caused by bending stretching;
3. Minimize large weld seams for thin-plate structures to reduce welding deformation;
4. Adopt laser cutting + laser welding for appearance parts to reduce polishing workload;
5. Reserve avoidance space for rivet pressing positions to prevent interference with bending edges;
6. Set drawing tolerances in line with sheet metal process capabilities, and avoid excessive precision requirements that increase costs blindly.
Server chassis, industrial equipment enclosures, automation jigs and fixtures, medical device shells, new energy parts, communication cabinet and instrument enclosures.
|（注：部分内容可能由 AI 生成）
