Expansion hobbing fixture for large-diameter hole

The utility model discloses an expansion hobbing fixture for a large-diameter hole. The expansion hobbing fixture for the large-diameter hole comprises a support block and a gland, wherein the support block is used for supporting a workpiece, and the gland is matched with the support block to clamp the workpiece. The expansion hobbing fixture for the large-diameter hole further comprises a draw bar shaft, the draw bar shaft is used for clamping the gland and for conducting centralized positioning, an expansion sleeve and a centralized positioning plate are coaxially arranged on the draw bar shaft, the centralized positioning plate is matched with the expansion sleeve in conical surfaces, and a disc spring for clamping the expansion sleeve is further arranged on the draw bar shaft. When the draw bar shaft of the expansion hobbing fixture is tensioned, the draw bar shaft clamps the expansion sleeve through the disc spring, the expansion sleeve expands along a conical surface of the centralized positioning plate to clamp the workpiece, and thus centralized positioning of the workpiece is guaranteed. After the workpiced is centralizedly positioned, the draw bar shaft is pulled further, then the draw bar shaft can clamp the gland in order to clamp the workpiece, therefore, the expansion hobbing fixture can be used for centralizedly positioning and clamping a hobbing workpiece with the large-diameter hole rapidly.