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In automotive body manufacturing, there are two processes are often applied, Nominal Build and Functional Build. The Nominal Build process requires all individual stamping components meet their nominal dimensions with specified tolerances. While, the Functional Build process emphasizes more on the tolerances of the entire assembly as opposed to those of the individual stamped parts. The common goal of both processes is to build the body assemblies that meet the specified tolerances. Although there is strict tolerance specified for individual stamping parts the finished stampings frequently are released to assembly process with certain levels of dimensioning deviations, or they are within the specified tolerances but require heavy clamping during assembly. It is of high interest to predict the dimensional deviations in the stamping sub-assembly or body-in-white assembly process.

A common occurrence in computer aided design is the need to make changes to an existing CAD model to compensate for shape changes which occur during a manufacturing process. For instance, finite element analysis of die forming or die tryout results may indicate that a stamped panel springs back after the press line operation so that the final shape is different from nominal shape. Springback may be corrected by redesigning the die face so that the stamped panel springs back to the nominal shape. When done manually, this redesign process is often time consuming and expensive. This article presents a computer program, FESHAPE, that reshapes the CAD or finite element mesh models automatically. The method is based on the technique of volume morphing pioneered by Sederberg and Parry [Sederberg 1986] and refined in [Sarraga 2004]. Volume morphing reshapes regions of surfaces or meshes by reshaping volumes containing those regions.

Springback is a major concern in stamping of advanced high strength steels (AHSS). The existing computer simulation technology has difficulty predicting this phenomenon accurately even though it is well developed for formability simulations. Great efforts made in recent years to improve springback predictions have achieved noticeable progress in the computational capability and accuracy. In this work, springback simulation studies are conducted using FEA software LS-DYNA®. Various parametric sensitivity studies are carried out and key variables affecting the springback prediction accuracy are identified. Recently developed simulation technologies in LS-DYNA® are implemented including dynamic effect minimization, smooth tool contact and newly developed nonlinear isotropic/kinematic hardening material models. Case studies on lab-scale and full-scale industrial parts are provided and the predicted springback results are compared to the experimental data.

Since 1997, General Motors Body Manufacturing Engineering - Die Engineering Services (BME-DES) has been working jointly with our software vendor to develop and implement a parallel version of stamping simulation software for mass production analysis applications. The evolution of this technology and the insight gained through the implementation of DMP/MPP technology as well as performance benchmarks are discussed in this publication.

In this paper, the factors that affect the accuracy of springback prediction are discussed. Springback predictions of aluminum and high strength steel panels are compared with measurement data. The effect of springback can be reduced or eliminated through process control and die face compensation. The first method involves finding the root causes of springback and eliminating them through process modification. The second method is a direct way to eliminate the springback effect. For large springback with twisting, an incremental compensation is required and the final deviation can be controlled by setting tight convergent tolerance. Stamping production environment can introduce many variables which deviate from engineering condition. The paper shows that material property change within the same grade will cause significant springback variation. This means that the process control is one of the key factors that we have to pay attention to solve springback issue.

A demonstration of the preform anneal process was conducted to form a one-piece aluminum door inner. In preform annealing, the aluminum panel is partially formed, annealed at 350°C to eliminate the cold work (strain hardening) from the first step, and then formed to the final shape using the same die. This process has the ability to form more complex parts than conventional aluminum stamping. Preform annealing uses non-age hardenable aluminum alloys of the 5xxx series and is suitable for a wide range of interior body panels. A rear door inner panel for a mid-size sports utility vehicle (SUV) was used in this study. This door inner was successfully created in one piece out of AA5182-O sheet with only slight design modifications to the original steel product geometry. The design of the door inner panel was conducted based on finite element analysis and predictions were verified with physical parts using thickness measurements and mechanical testing.

The analysis of localized necking is strongly dependent on the yield function. Numerous yield criteria have been advanced to characterize the plastic deformation of sheet materials. Among them Hill's 1948 and the fourth form of 1979 yield criteria are the most commonly used yield criterion. A new and user-friendly yield criterion was proposed by Hill in 1993, which uses five independent and easily-obtainable material parameters. The present investigation compares these three yield criteria in forming limit predictions based on the M-K approach. The M-K analysis based on Hill's 1993 yield criterion yields forming limit predictions for aluminum in good agreement with experimental data. All three yield criteria are found to provide acceptable predictions for aluminum killed steel.