HV Transformer Expandable Coil Winding Mandrel is indispensable professional equipment for high-precision transformer coil winding and forming. Designed with flexible outer diameter expansion function, this mandrel supports both motor-driven automatic expansion and manual fine expansion modes to meet diverse production demands. It features a wide adjustable diameter range and effortless coil stripping and demoulding processes, delivering strong compatibility with all types of horizontal and vertical transformer winding machines. Adopting a scientific and optimized structural design, the mandrel undergoes high-precision machining to ensure stable overall performance and long service life. The complete structure includes a sturdy cage frame, sliding sleeve assembly, strip plate assembly, base strips, extended strips, transmission parts and right-angle baffles. Its innovative structural design enables smooth diameter adjustment and fully protects finished coils, achieving zero damage during demoulding and winding processes. Strict quality control guarantees that the diameter deviation of any position is within 2mm and the overall cylindricity error is below 2mm, ensuring high coaxiality and winding uniformity. Matched with professional transformer winding equipment, this expandable mandrel can deliver stable, efficient and high-precision winding performance, making it ideal core equipment for industrial transformer manufacturing factories.