In previous airplane programs, Boeing identified interferences and misalignments between airplane parts as the two largest causes of engineering changes. Boeing is currently designing the 777 with a state-of-the-art solid modeling system. While the system is capable of detecting interferences and misalignments between ideally-sized and ideally-located solid models, it cannot model the effects of variation in the size, shape and location of parts and tools. This paper presents an initial, novel framework for modeling these variations called Indexed Pre-Assembly with Variation (IPAV).
The main points made in this paper are:
• Variations in both parts and tools should be modeled in exactly the same way.
• Mating features of parts and tools can be represented in the solid models with local index-point coordinate systems.
• Linking the mating index-point coordinate systems enables the positioning of the solid models in an assembly.
• The order in which the index-point coordinate systems are linked corresponds to the planned assembly sequence.
• The effects of size, shape and location variations on an assembly can be modeled by manipulating the index-point coordinate systems within the individual solid models.
The academic literature on tolerancing and existing software tools for tolerance analysis are reviewed. A survey of Boeing engineers is presented which led to the development of the Indexed Pre-Assembly with Variation method. A case study involving an actual assembly problem at Boeing is analyzed with IPAV. The paper also discusses the benefits of simulating variation at the design stage and proposes an implementation plan to integrate IPAV into a generic airplane development schedule. Lastly, the applicability of IPAV to other industries is evaluated and areas for further research are identified.