1.Wall thickness deformation.
If the copper mould tube is in the extrusion deformation, the deformation amount is selected to be small, then the inner surface of the copper tube cannot produce enough plastic deformation, resulting in the copper tube not being filmed. However, if the amount of deformation is larger, the extrusion resistance will increase, which makes it easier to straighten the formed tube wall. Therefore, the selection of the deformation amount of the copper mould tube is the key.
2. Eliminate the internal stress of copper tube forming.
The Causes of internal stress: In the extrusion deformation of a copper tube with a large wall thickness, the deformation of the inner and outer surfaces is different. The metal on the outer surface is stretched very long, and the inner surface deforms less or unchanged so that there is large internal stress in the tube.