Machining Quality Analysis of an Engine Cylinder Head Using Finite Element Methods

Structural analysis is routinely used to design parts but less frequently used to design manufacturing processes. Structural analysis should be used in process design for many parts because loads experienced during manufacture exceed service loads. Application of these analyses has been limited due to lack of validation results for realistically complex parts against extensive sets of data. This paper describes structural analysis results for the manufacture of an aluminum engine cylinder head. Three specific error sources are modeled using finite element analysis (FEA): (1) cylinder head deckface distortion due to clamping forces, (2) deckface (or part) distortion due to a pressing in of seats and guides, and (3) seat and guide distortion due to clamping forces. A compliant fixture and contact-based boundary conditions are used for the clamping analysis using ABAQUS/Standard for the FEA modeling. The valve seat and guide insertion is modeled as a shrink-fit operation using the contact-pair approach, which greatly simplifies the numerical problem with satisfactory precision. The roundness and concentricity are computed for a variety of press-fit interference conditions covering the range of variation expected within the tolerance bands of the powder metal inserts and the pre-bored holes. Computed results from all studies agree well with direct CMM measurements and laboratory validation data.