Abstract: For a certain series of automotive flange produced by the company, the coaxiality requirement between the internal spline and the rabbet is ≤0.05 mm. After finish turning of the inner hole and rabbet, the surface electrophoresis treatment is required. Due to the narrow width of the rabbet, local protection of the flange rabbet position cannot be achieved during the electrophoresis process, it is necessitates finish machining of the rabbet after electrophoresis. The design and manufacture of the finish turning fixture for the rabbet, as well as the selection of the positioning datum, have long been difficult points in production. To resolve this problem, a floating self-adjusting expansion sleeve fixture was designed, and optimization design for the mandrel—the core component of the fixture. Practical machining verification shows that after using this fixture, the pass rate of flange rabbet machining reaches 100%, it meets the mass production requirements of the product and provides a reference for the machining of similar products.