Improvement of a variable-length work support for a drill fixture

Abstract

    In the production of intake manifolds for engines, the workpieces are formed by aluminum casting process and finished by machining and drilling. For drilling process, the fixture must secure the workpieces with clamps and variable-length work supports to accommodate the slight variations in the size of the cast workpieces. If the work supports are not completely locked, the workpieces may move along the compression forces from the clamps causing the deviation of the hole position. The objectives of this study are to improve the variable-length work support to withstand the clamping force without movement. The hole must not deviate by more than 0.5 mm from the design position. Moreover, the new work support can function in automated operation thus generating a consistent locking force and reducing the overall operation time. The study began with the principles and theories on position locking using friction force on inclined surfaces. Followed by the design, production and test of the new work support. Finally, the new work support was installed onto the drilling machine for production testing. The design of the new variable-length work support has resulted in an equation relating the compressive force resistance and the locking force required by the support. This allows for the variable adjustment based on usage conditions in future designs. When the hydraulic pressure of 40 bars is supplied, there is no workpiece movement under the compressive force of the clamps. The average deviation of the hole center is 0.145 mm from the design position with the standard deviation of 0.056 mm. Lastly, the new work support with a hydraulic system can perform automated operation. The production of intake manifolds using the new variable-length work support has increased the production rate by 33.33%. The investment in this improvement has a payback period of 4 months.