Various flat cable forming methods have their applicable scope and advantages and disadvantages. The forming method used in production depends on the processing performance of the insulation material. Some specifications of flat cables can be formed using two methods, such as UL2651, which can be formed using both direct extrusion and lamination; while some flat cables can only be formed using one method, such as UL2468 and UL2877, which can only be formed using direct extrusion, and UL2902, which can only be formed using bonding. The forming methods for various UL specifications of flat cables are clearly specified in UL documents.
To produce qualified flat cables, in addition to selecting the appropriate processing method based on the processing performance of the insulation, many specific process issues (some unique to flat cable forming, and some encountered in ordinary cable production) must be resolved during forming. Otherwise, although the product may have a similar appearance, it will be unusable if its electrical performance does not meet the requirements. Problems frequently encountered in production include center distance exceeding requirements, severe conductor eccentricity, low insulation resistance, and short flat cable length. Plastics have a relatively large coefficient of linear expansion; for soft polyvinyl chloride, it is 7.0~25X10-5/℃. As ambient temperature changes, the center-to-center distance must also change. However, once the flat cable forming mold is filled with the required amount of clay, it cannot adapt to temperature variations. For ease of operation and to reduce mold costs, flat cables must be formed in an environment with minimal temperature fluctuations; the workshop temperature should be controlled between 15 and 25°C.
The dimensional accuracy of flat cables is largely guaranteed by the mold's accuracy. The mold's dimensional tolerances, surface roughness, and geometric tolerances are all very high, resulting in high mold costs and poor versatility. When designing the mold, in addition to ensuring the accuracy of the finished product, the ease of clay filling and installation must also be considered.
