A prototype software tool was developed at the NASA Glenn Research Center to integrate manufacturing process modeling and probabilistic structural analysis. Two manufacturing processes were considered: a powdered-metal forging process and annular deformation resistance welding (ADRW). Interface modules were developed that automatically transfer IGES files or convert CDB files from ANSYS computer-aided design (ANSYS, Inc., Canonsburg, PA) models to the DEFORM manufacturing process simulation code (Scientific Forming Technologies Corporation, Columbus, OH). Other modules handle such tasks as setting up probabilistic input data. These modules utilize graphical user interfaces to specify input parameters that are subsequently transferred to NESTEM, a NASA-sponsored probabilistic finite-element analysis code. Although the prototype represents a work in progress, some example problems have already been solved.
Present-day structural analysis performs either a deterministic or probabilistic calculation based on either a fixed set of mechanical properties and process parameters or the same properties and parameters with assumed distributions, respectively. The distribution characteristics of these variations are not necessarily reflective of the actual variation that may arise in practice. Probably the single most important factor influencing these variations comes from the manufacturing processes. For example, processes such as welding, casting, and forging can cause large variations in the resulting mechanical properties because of the operational variations in these processes, as well as variations in the materials themselves. Therefore, having a quantitative understanding of these processes and integrating the resulting information into a probabilistic calculation environment could lead to a much more realistic prediction of the structural response of a mechanical component in service. Specifically, this could lead to a more realistic assessment of the sensitivities of the mechanical properties and response, and of how they are affected by variations in the manufacturing process.
Resistance heating is used for many different manufacturing processes, including the welding of two parts. However, joining parts by this process has been restricted primarily to the flat-sheet components used in automotive and aerospace applications. In welding tubular products, a conventional welding process may burn holes unless very precise control is in place. Also, round parts may need to be fixtured or turned during the joining process, increasing cost and time substantially.
ADRW takes advantage of the resistance heating process used in resistance spot welding, but it uses an annular electrode to handle tubular products. By using resistance heating, it raises the temperature of the joining surfaces locally to a high fraction of the homologous temperature. It also allows substantially high pressure to be applied at the joining so that the two joining surfaces can slide past each other, creating a solid-state bond instead of the fusion nugget in spot welding that signifies melting and solidification. Even though this is a recently developed welding process, it has been used successfully to join tubes to solids: various sizes of sheet metals and tubes made of mild steel, stainless steel, and some nickel-based super-alloys. The process has been shown to create leak-tight joints with superior strength at a much more rapid pace than with conventional welding methods.
Two separate interfaces, Forgprob and Probdraw, were developed at Glenn to connect the forging code DEFORM and ADRW process modeling with NESTEM. These interfaces enable users to quantify the influences of uncertainties in the variables associated with these two manufacturing processes. This quantified information is very critical for designers. Although designers traditionally account for these effects via factors of safety, the outcome of such factors remains unquantified. Probdraw is illustrated in the figure. The architecture of the two interfaces is basically the same.
Probabilistic analysis of deformation resistance annular welding (Probdraw).
Last updated: October 11, 2006
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