An Integrated Stack-Up Analysis Tool

The development of a product requires the definition of its architecture and of its physical and functional elements that have to be assembled together to realize the new product. Functional elements are the set of operations and transformations necessary to reach the product performance while physical elements are related to parts, components and subassemblies and are established from the product concept or defined in the detailed design of the product. Functional elements are associated to one or more physical elements and together define the product architecture. [Ulrich and Eppinger 2008]. The design of the product architecture and of each physical elements is very critical in the development of a new product since a worst design will impact also on the product manufacturing and changes and stops in that phase requires higher costs for the companies. Therefore, accurately design the product, its physical elements and how to assembly them in the architecture, it’s a critical activity for the company. The product model including its architecture and physical elements, is realized in computer aided design (CAD) systems but also other systems (i.e. Computer Aided Technologies, CAX) are used to define engineering, manufacturing or testing data. In many companies, all the data generating by the CAD systems together with others product data (e.g. the bill of material - BOM) are integrated and available in PDM systems that store data and information about the product and its elements. They can be simple repository of information and the users manually search and access to the information required or can provide workflows and other tools to manage the product data. [Grieves 2006]. In the design of each physical element of a product, geometrical and dimensional values are established and for each value, the tolerance limits are forecasted and fixed. Tolerance limit are the upper and lower variation that a dimensional value can assume guarantying, however, a correct assembly of all the elements in the whole product. The tolerance limits depends from the type of materials or from the machines used to realize the product. Changes in a tolerance value have effect in the whole assembly generating a chain of changes. Therefore, the need to correctly define the tolerance limits is very high to guarantee yet in the design a correct assembly. The stack-up analysis is the technique used to evaluate the tolerance chain created joining the physical elements and it is used to verify if there are problems to realize the final assembly and therefore, if the elements could be joined in the desired product architecture. The geometrical and dimensional information are available on the product engineering drawings or in the model based definition (MBD) dataset of the product. The engineering drawings provide a 2D vision of the product with dimensional and geometrical information. MBD datasets have been developed to integrate in the 3D model the information available in the engineering drawings providing a complete file with both information. 400 DESIGN SUPPORT TOOLS The paper aims to describe the case of an Italian aerospace company, Avio S.p.A., and the stack-up tool realized to improve the whole tolerance analysis process. The company has met some problems in the management of the stack-up analysis due to the use of IT tools that have led to human errors in the calculus and further time for reaching the results. Based on ten-month activities of a team of university researchers and company engineers, a new stack-up tool has been developed, it is integrated in the company CAD (Siemens Nx) and PDM (Teamcenter Engineering) systems and it is currently used by the company designers. It has solved the company problems in the stack-up analysis providing a solution for the calculus of the stack-up analysis both from engineering drawings and MBD datasets. In the next section of the paper, some remarks from the literature in the tolerance analysis field are described to guide the comprehsion of the concepts used in the paper. A further section treats the research design and provides the scenario in which has been developed the stack-up tool that is described in a successive section where technological choices and functionalities that have guided the tool development are discussed and an example of application of the tool enriches the view in the research results. A final section concludes the paper providing discussion and insights.