Core Summary:
The expanding mandrel is the core tooling that ensures tightness between coil turns and roundness. It solves the industry pain point of the mandrel "getting stuck" and being impossible to remove after winding.
Technical Details of the Three Types:
Cylindrical Vertical-Horizontal Dual-Purpose Expanding Mandrel:
Principle: Uses a wedge structure or hydraulic/mechanical expansion mechanism. Diameter can shrink 20-40mm during contraction for easy demolding.
Advanced Knowledge: In precision machining, some mandrels utilize the thermal expansion/contraction principle (e.g., beryllium copper mandrels). After cryogenic treatment, they shrink for insertion and expand at room temperature to achieve tight fit with extremely high precision.
Block Expanding Mandrel:
Structure: Composed of 6-12 independent curved segments.
Characteristics: Through radial expansion, it provides uniform clamping force and supports the inner corners of rectangular or elliptical coils well. Its tolerance control is extremely strict — diameter deviation across the full working length can be controlled within 1.5mm, effectively preventing "polygonal effect" in coils.
Oval Expanding Mandrel:
Challenge: The changing curvature of the oval shape makes it difficult to distribute clamping force evenly.
Application: Typically used for dry-type transformers or special traction transformers. Requires stress compensation calculation for the major and minor axes during design.