With the trend of miniaturization and high performance of electronic equipment, the electromagnetic shielding performance of switch housing has become the key to ensure the stable operation of equipment. CNC (computer numerical control) processing technology, with its advantages of high precision and high flexibility, can improve the electromagnetic shielding effectiveness through multiple dimensions such as material selection, structural design and process parameter optimization.
The core of electromagnetic shielding performance lies in the conductivity of the material. In CNC processing, aluminum alloy (such as 6061-T6) and stainless steel (such as 304) are commonly used materials. Aluminum alloy has low density and is easy to process, but its conductivity is inferior to stainless steel; stainless steel has excellent conductivity, but it is more difficult to cut. By optimizing the tool path (such as spiral cutting) and coolant parameters, the difficulty of stainless steel processing can be reduced while retaining its high conductivity advantage. In addition, surface plating (such as nickel and copper) can further improve the shielding effectiveness, which needs to be achieved through electroplating after CNC processing.
CNC processing can realize complex three-dimensional structures, providing flexibility for electromagnetic shielding design. For example, the shielding effect of low-frequency magnetic fields can be improved by increasing the thickness of the shell wall (recommended ≥1.5mm); the use of a honeycomb or wavy inner wall structure can extend the electromagnetic wave reflection path and enhance the high-frequency shielding capability. In addition, a "maze-like" structure needs to be designed at the shell joints to prevent straight gaps from becoming electromagnetic leakage channels.
The surface roughness after CNC processing (Ra≤0.8μm) directly affects the conductivity. Polishing or sandblasting can reduce the surface roughness and reduce electromagnetic wave scattering. For complex curved surfaces, chemical nickel plating can be used to fill tiny pits to form a uniform conductive layer. Experiments show that the shielding effectiveness can be improved by 10-15dB after surface treatment.
Tool selection is crucial to shielding performance. Carbide tools (such as K20) are suitable for aluminum alloy processing, while ceramic tools (such as SiAlON) are suitable for stainless steel. Cutting parameters need to match material properties: high-speed cutting (Vc=300-500m/min) is recommended for aluminum alloy, while stainless steel needs to reduce cutting speed (Vc=80-120m/min) and increase feed rate (fn=0.1-0.2mm/r) to reduce material phase change caused by cutting heat.
Switch housings often need to have functional openings such as key holes and heat dissipation holes. CNC processing can achieve the "electromagnetic window" effect through micro-hole array design (such as diameter ≤0.5mm, spacing ≤1mm), which can weaken electromagnetic wave penetration while ensuring ventilation. For necessary large openings, metal grids (such as copper mesh, aperture ≤0.3mm) or conductive foam filling can be added to ensure shielding continuity.
CNC processing requires reserved grounding structures (such as threaded holes and buckles) to ensure reliable connection between the housing and the PCB ground wire. The grounding resistance should be ≤0.1Ω, which can be achieved by increasing the contact area (such as bump design) or filling the gap with conductive glue. In addition, the inner wall of the housing can be coated with conductive paint to further reduce the grounding impedance.
Combined with electromagnetic simulation software (such as HFSS, CST), the shielding effectiveness of the housing can be predicted before CNC processing. By adjusting structural parameters (such as wall thickness, opening ratio) and material properties, the design scheme can be quickly iterated. For example, in a case, the shielding effectiveness of the switch housing was improved from 40dB to 60dB through simulation optimization, meeting the EN 55022 Class B standard.
CNC process optimization requires collaboration from the entire process of materials, structure, process to design. Through scientific material selection, precision processing and simulation verification, the electromagnetic shielding performance of the switch housing can be significantly improved, providing reliable electromagnetic protection for electronic equipment. In the future, with the popularization of technologies such as 5G and the Internet of Things, the application of CNC processing in the field of electromagnetic shielding will be more extensive.
