Abstract
Overconstrained assemblies such as aircraft sub-assemblies present a challenge to production planners, as variations in parts and processes can make it difficult to achieve all assembly Key Characteristics (KCs) simultaneously. Despite assigning tight tolerances to sub-component manufacture, part variation propagation necessitates expensive and time-consuming variation management processes such as shimming in order to ensure the final assembly is within specification. This paper presents for the first time a variation propagation model for overconstrained assemblies, and develops a novel modelling method to connect variations with production costs. This facilitates a novel process optimisation method based on variation propagation, with the ability to analyse the trade-offs between the cost and achievable variation limits of the entire manufacturing chain in order to minimise the overall manufacturing cost. An overconstrained wing spar assembly is used as a case study to validate the methodology.
Highlights
In the highly competitive aerospace industry, cost reduction whilst ensuring high quality standards, has become an important method of gaining an edge in the market [1]
This paper presents for the first time a variation propagation model for overconstrained assemblies, and develops a novel modelling method to connect variations with production costs
This paper presents a methodology for holistic process optimisation based on a variation propagation model
Summary
In the highly competitive aerospace industry, cost reduction whilst ensuring high quality standards, has become an important method of gaining an edge in the market [1]. Overconstraint is beneficial in assemblies in order to withstand external forces when in operation, and is ensured by having more locators than needed to provide location [2] In both cases, overconstrained assemblies present a difficult task to design engineers and process planners, as variations in sub-components make it problematic to assemble a final product that meets specification. This paper will develop this research further by relating the variation level at KC features to the cost of assembly in order to determine the most appropriate variation management process that will reduce the overall cost of production. The cost impact of variation management processes has been only scarcely investigated [7] This paper addresses these gaps in the literature, and proposes a methodology that relates cost and variation for an entire production chain, from part fabrication to final assembly.
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