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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.

The influence of elevated temperature forming on local mechanical properties of AZ31B magnesium (Mg) sheet material was investigated. The Mg sheet was formed into a closure component with high temperature gas pressure at 485°C. Miniature tensile testing specimens were cut from selected areas of the component where different levels of thinning occurred. The specimens were strained in tension to fracture using a miniature tensile stage. The two-dimensional strain distribution in the necking region along with true stress-true strain curves were computed using a digital image correlation technique to assess the influence of the forming-induced thinning on tensile strength and percent elongation at fracture.

Two alternative finite element formulations are described which consider the influence of normal stress components on sheet deformations in Quick Plastic Forming [1]. The new formulations, single field bricks and multi-field shells, were implemented in the forming simulation program PAM-STAMP [2] using a non-linear viscoelastic constitutive relation [3,4]. Simulations of two industrial components indicate that both new elements simulate local necking more accurately than the standard shells which ignore normal stresses. The multi-field shells require slightly more calculation time than the standard shells and significantly less than equivalent brick models.

The component being formed experiences some type of prestrain that may have an effect on its fatigue strength. This study investigated the forming effects on material fatigue strength of dual phase sheet steel (DP600) subjected to various uniaxial prestrains. In the as-received condition, DP600 specimens were tested for tensile properties to determine the prestraining level based on the uniform elongation corresponding to the maximum strength of DP600 on the stress-strain curve. Three different levels of prestrain at 90%, 70% and 50% of the uniform elongation were applied to uniaxial prestrain specimens for tensile tests and fatigue tests. Fatigue tests were conducted with strain controlled to obtain fatigue properties and compare them with the as-received DP600. The fatigue test results were presented with strain amplitude and Neuber's factor.

Tensile measurements and fracture surface analysis of low carbon heat-treated boron steel are reported. Tensile coupons were quasi-statically deformed to fracture in a miniature tensile testing stage with custom data acquisition software. Strain contours were computed via a digital image correlation method that allowed placement of a digital strain gage in the necking region. True stress-true strain data corresponding to the standard tensile testing method are presented for comparison with previous measurements. Fracture surfaces were examined using scanning electron microscopy and the deformation mechanisms were identified.

Laminated steel has been increasingly applied in automotive products for vibration and noise reduction. One of the major challenges the laminated steel poses is how to simulate forming processes and predict formability severity with acceptable correlation in production environment, which is caused by the fact that a thin polymer core possesses mechanical properties with significant difference in comparison with that of steel skins. In this study a cantilever beam test is conducted for investigating flexural behavior of the laminated steel and a finite element modeling technique is proposed for forming simulation of the laminated steel. Two production panels are analyzed for formability prediction and the results are compared with those from the try-out for validation. This procedure demonstrates that the prediction and try-out are in good agreement for both panels.

As a virtual manufacturing press line, line die forming simulation provides a full range math-based engineering tool for stamping die developments of automotive structure and closure panels. Much beyond draw-die-only formability analysis that has been widely used in stamping simulation community during the last decade, the line die formability analysis allows incorporating more manufacturing requirements and resolving more potential failures before die construction and press tryout. Representing the most difficult level in formability analysis, conducting line die formability analysis of automotive body side outers exemplifies the greatest technological challenge to stamping CAE community. This paper discusses some critical issues in line die analysis of the body side outers, describes technical challenges in applications, and finally demonstrates the impact of line die forming simulation on the die development.

Durability requirements for exhaust materials have resulted in the increased use of stainless steels throughout the exhaust system. The conversion of carbon steel exhaust flanges to stainless steel has occurred on many vehicles. Ferritic stainless steels are commonly used for exhaust flanges. Flange construction methods include stamped sheet steel, thick plate flanges and powder metal designs. Flange material selection criteria may include strength, oxidation resistance, weldability and cold temperature impact resistance. Flange geometry considerations include desired stiffness criteria, flange rotation, gasket/sealing technique and vehicle packaging. Both the material selection and flange geometry are considered in terms of meeting the desired durability and cost. The cyclic oxidation performance of the material is a key consideration when selecting flange materials.

Two thread forming processes, rolling and cutting, were studied for their effects on fatigue in cast aluminum 319-T7. Material was excised from cylinder blocks and tested in rotating-bending fatigue in the form of unnotched and notched specimens. The notched specimens were prepared by either rolling or cutting to replicate threads in production-intent parts. Cut threads exhibited conventional notch behavior for notch sensitive materials. In contrast, plastic deformation induced by rolling created residual compressive stresses in the notch root and significantly improved fatigue strength to the point that most of the rolled specimens broke outside the notch. Fractographic and metallographic investigation showed that cracks at the root of rolled notches were deflected upon initiation. This lengthened their incubation period, which effectively increased fatigue resistance.

This paper will describe an investigation of the formability of high strength steel (HSS) laser welded blanks (LWBs). Anticipated combinations of thickness and steel grades, including high strength low alloy (HSLA) and dual phase (DP) steels were selected. The blanks were characterized through chemical analysis and mechanical testing, as well as microstructural analysis of the weld. Samples were strained in a limiting dome height tester. Weld line movement, dome height and strain at failure were then measured. Data from these tests resulted in development of forming limit diagrams, and allowed correlation of weld line movement to forming conditions. In part, the results showed that the presence of the weld has a negative influence on formability, and that balancing the load carrying capacity of each side of the blank results in minimum weld line movement in the blanks.

A computer assisted development technique for Quick Plastic Forming parts [1] is described, based on the simulation program PAM-STAMP [2]. The technique allows thickness changes during forming to be accurately considered in the development process without physical trials. Process pressure cycles, which provide for maximal material formability, can be determined with a single simulation. The paper describes new program features, which reduce modeling effort and increase simulation accuracy. Various validation examples and industrial case studies are also presented, demonstrating current capabilities.

Sheet metal forming processes change the material properties due to work hardening (or softening) in the thickness direction as well as throughout the entire part. At the same time, uneven thickness distribution, mostly thinning, occurs as the result of forming. This is true for all commonly used sheet metal forming processes including stamping (deep drawing), tube hydroforming, sheet hydroforming and super plastic forming. The effects from forming can sometimes strongly influence the structural performance. Though the CAE analysts have been trying to consider forming effect in their models for performance simulations, there was no easy way to do it consistently and reliably. Some analysts have been trying to modify the initial gage or yield strength to compensate for the property change due to forming. Replace the model with the formed panel is not feasible due to the mesh density difference.

Free expansion of straight tubes is the simplest test to evaluate tube properties for hydroforming applications and to provide basic understanding of the mechanics of tube hydroforming. A circular cylindrical tube is sealed at both ends and fluid, usually water, is pumped into the tube to increase its internal pressure to bulge and burst the tube. Previous numerical simulations of the free expansion tube test were limited to modeling the midsection of the tube under various assumptions of deformation path. The simulation results obtained deviated from the experimental results under all simulation conditions considered. A new model is developed in this paper in which the whole tube is simulated instead of considering only its mid-section. Judged by the pressure-expansion relations, the model accurately predicted free expansion hydroforming tests results.

Corner filling is a benchmark experiment in tube hydroforming. It was designed to gain knowledge pertinent of this new fabrication process. The corner filling benchmark has been widely used in the automotive and steel industries. Common sense as well as physical tests suggests that friction is an important parameter that affects the deformation of the tube and the bursting of the tubes. However, numerical simulations have yet to verify this fact. In this paper, the stress/strain states in the tube were computed using a finite element model. The dependence of bursting on friction for corner filling was estimated by using the forming limit diagram and a tensile-based failure criterion.

A series of tests were performed to determine the influence of curvature on the forming limits of 1008 AK steel. Rectangular blanks cut from three thicknesses of the material from 0.69 mm to 1.04 mm were securely clamped at opposite edges and stretched over wedge shaped punches of different radii. A series of punches were used with radii that varied from 0.508 mm to 12.7 mm to produce bending effects that range from severe to mild. Measurements show that the neck forms on the convex surface when the strain on the concave side of the sheet reaches a value consistent with the forming limit in plane-strain for in-plane deformation.

Forming of sheet metal structures induces pre-strains, thickness variations, and residual stresses. Pre-strains in the formed structures introduce work hardening effects and change material fatigue properties such as stress-life or strain-life. In the past, crashworthiness and durability analyses have been carried out using uniform sheet thickness and stress- and strain-free initial conditions. In this paper, crashworthiness and durability analyses of hydroformed front rails, stamped engine rails and shock towers on a full vehicle and a Body-In-White structure are performed considering the residual forming effects. The forming effects on the crash performance and fatigue life are evaluated.

Automotive manufacturers have intensified their efforts to increase vehicle fuel economy by reducing weight without sacrificing vehicle size and comfort. Vehicle areas that offer the potential to reduce weight include chassis structural components. A cradle or a subframe is a chassis structural component that is utilized to support the engine/powertrain in front wheel drive vehicles. Traditionally, engine cradles have been manufactured by using stamped steel weldments. Recently, automotive designers are considering alternative processes, i.e., hydro-forming, as well as fabricating engine cradles using lightweight materials. The objective of this paper is to describe the development of an aluminum engine cradle for a General Motors's midsize vehicle. The design criteria and structural performance requirements for this cradle are presented along with an overview of the manufacturing processes used to produce this lightweight structural part.

Over the past 20 years, polyvinyl chloride (PVC) has almost replaced metal in stationary glass reveal moldings with dramatic part cost savings on cars and trucks world-wide. The process of assembly is generally simple and convenient but to replace a reveal molding can be difficult. Many times, in order to replace the molding, it may also be necessary to replace or reseal the glass. In short, PVC reveal moldings, relatively inexpensive parts, are very expensive to service. Outside of general assembly and processing issues, there are 5 variables that may cause a failure in the performance of a stationary glass reveal molding. They are as follows: material degradation, crystallization, plasticizer loss, material properties, and molded-in stress. Because of modern standard PVC formulations and the material requirements of most automotive companies, material degradation, crystallization and plasticizer loss do not commonly cause failure. Material properties and molded-in stress do.