A Case Study on the Correlation Between Functional and Manufacturing Specifications for a Large Injection Moulded Part

Large parts produced by injection moulding are usually subjected to large deformations that may be reduced during assembly. The single parts manufacturing specification should refer to the as produced (free) state. On the other hand, the functional specification, derived from the assembly functional specification should address the “as assembled” state. Geometrical inspection, based on the functional specification requires dedicated fixtures to simulate the “as assembled” state. This contribution suggests a procedure, based on FEM simulation, to correlate the geometric specification at the “as assembled” state with the “as produced” (free) state, applied to an industrial case study. The result of the procedure are free state tolerance limits, e.g., manufacturing specification, that allows conformity of the part to the functional specification once assembled. The part may be inspected based on the manufacturing specification fixtureless during mass production. The result of the case study shows a significant reduction in position and orientation error due to the assembly process as it was expected.