RF cables are a critical medium for high-frequency signal transmission, and their molding process directly impacts their electrical performance and mechanical reliability. The molding process must balance material properties, structural design, and manufacturing precision to ensure signal integrity and adaptability to complex application environments.
Material selection and pretreatment are fundamental to molding. RF cables typically consist of an inner conductor (such as copper wire or silver-plated copper wire), an insulation layer (such as polytetrafluoroethylene (PTFE) or polyethylene (PE), a shielding layer (braided copper mesh or aluminum foil), and an outer jacket (such as PVC or polyurethane). The insulation material must have a low dielectric constant and loss tangent to minimize signal attenuation, while the shielding layer must have high coverage to suppress electromagnetic interference. During the pretreatment stage, the conductor must be cleaned and annealed to relieve stress and improve ductility, ensuring dimensional stability during subsequent molding.
Extrusion and insulation molding are key steps. The insulation layer is applied to the conductor surface using a precision extruder. Nitrogen assist or high-temperature molds are used to control the expansion coefficient of materials such as PTFE to prevent bubbles and eccentricity. For multi-layer structures, insulation and shielding are laminated layer by layer through multiple extrusion processes, with thickness uniformity monitored in real time using an online capacitance tester.
The integration of the braid and shield directly impacts anti-interference capabilities. The shielding layer is typically braided using a high-speed braiding machine, wrapping copper or tinned copper wire at a specific angle (e.g., 45°-60°). The density must exceed 90% to create a Faraday cage effect. Some high-end cables are further enhanced by the longitudinal wrapping of aluminum-plastic composite tape. This step requires strict tension control to prevent conductor displacement or insulation damage.
Outer sheath molding and post-processing complete the final protection. The sheath material is melted at high temperature in an extruder and then applied to the shielding layer. It then passes through a cooling water tank to quickly set and maintain roundness. Special applications (such as aerospace) may require an additional radiation cross-linking process to improve temperature and abrasion resistance. The finished cable undergoes high-frequency testing (such as VSWR vector network analysis) and mechanical performance verification (such as flex life testing) to ensure compliance with industry standards.
The RF cable forming process lies at the intersection of materials science, mechanical control, and electromagnetic theory. Its level of sophistication directly determines the reliability of communication systems. With the development of 5G and satellite communications, the demand for ultra-low-loss, highly flexible cables will continue to drive process innovation.