Meaning
Cold tube-drawing operations employ a rigid internal styling tool to control the inner diameter and wall thickness of the metallic tube during the reduction process. This specific method of fabrication, known as fixed mandrel drawing, involves securing a mandrel on a long rod inside the die while the tube is pulled over it. This technique provides high dimensional control on the inside surface of the tube, unlike sink drawing which only controls the outside diameter.
It requires high drawing forces to overcome the friction on both the inner and outer surfaces of the tube, making proper lubrication vital to prevent metal-on-metal contact. The process is used to produce high-precision instrumentation tubing.
Tooling Setup
Mechanical components must be precisely aligned to prevent concentricity errors or wall thickness variations. In fixed mandrel drawing, the operator secures the mandrel rod to the back support of the draw bench and adjusts the axial position of the mandrel tip within the die throat. The die dictates the outer diameter of the tube, while the mandrel tip establishes the inner diameter.
Incorrect positioning of the mandrel will cause the tube to break or create uneven walls.
Process Limitations
Friction restricts the maximum length of tubing that can be drawn using this method. Because the mandrel rod must be longer than the starting tube, fixed mandrel drawing is limited by the physical length of the draw bench.
Dimensional Precision
Production runs for high-performance alloy tubing demand tight tolerances that are difficult to achieve through simple die-sinking. Utilizing fixed mandrel drawing ensures that the inner diameter maintains a consistent dimension with minimal variation across the entire length of the tube batch. This level of precision is necessary for fittings used in hydraulic and gas distribution systems.
High quality control is maintained by verifying the wall thickness at both ends of each drawn tube.
