The second tie tensioner motion pattern pulls one tarp tensioner motion pattern to move for release. When the tension hook moves to the end of the limiter block, the hook rotation opens under the elastic force of the torsion spring, so that the hook portion of the hook leaves the shoulder of the second moving mode, thus losing the support of the limiter block. Disengaging the first-motion mode and the second-motion mode, the second-motion mode continues to move and the first-motion mold is stationary, thereby extracting the mandrel from the workpiece and realizing the secondary mold release. With the above scheme, the secondary mold release is more stable and reliable, and at the same time the structure is very simple, easy to manufacture, install and maintain.