Automatic sizing device and method for expanding diameter and plugging head of hydraulic cold-drawing machine

The invention discloses an automatic sizing device and method for expanding diameter and plugging head of a hydraulic cold-drawing machine, and belongs to the technical field of pipes. The method comprises the following steps: 1, mounting a blank pipe on the cold-drawing machine; 2, starting a pushing oil cylinder, and allowing the pushing oil cylinder to push the blank pipe to move along a die through a pushing beam; 3, using a displacement sensor to monitor the displacement of the pushing oil cylinder in real time, and using a pressure sensor monitor the pressure of the pushing oil cylinderin real time; step 4, taking the suddenly and sharply increased pressure firstly detected by the pressure sensor as a pressure signal pickup point; fifthly, taking the displacement detected by the displacement sensor at the pressure signal pickup point as a distance measurement starting point, when the pushing oil cylinder moves to a set value from the distance measurement starting point, the pushing oil cylinder stops ad