Search Results

This paper gives a short summary of a new approximate method to include bending stiffness into an implicit membrane FEM formulation for axisymmetric multi-stage drawing problems. It compares analyses of round cup drawing processes using pure membrane elements with those employing the new formulation. The sensitivity of the maximum required forming force, the draw-in of the sheet rim, and the true strain distributions to small changes in a variety of modeling, material, and process parameters is investigated for both the membrane and bending formulations. Those parameters that influence the accuracy of the numerical solution most significantly are identified, and recommendations for the optimum choice of parameters are made.

Shrink flanging is a major sheet forming operation to produce convex flanges in structural sheet metal components. Flanges are used for appearance, rigidity, hidden joints, and strengthening of the edge of sheet parts such as automobile front fender and complex panels formed by stretch/draw forming. Wrinkling around the flange edge is the major defect in shrink flanging operation. There has been a lack of reliable mathematical modeling to predict the strains and wrinkles in shrink flanging operations. A trial-and-error approach has been usually practiced in tooling and process designs. In this paper, a wrinkling criterion in shrink flange is proposed based on a simplification from a general criterion for a doubly curved anisotropic shell. The mathematical model for strain analysis in shrink flanging is established based on Wang and Wenner's strain model for stretch flange. Shrink flanging experiments were conducted to validate the theories.

In sheet metal forming, drawbeads are often used to control uneven material flow which may cause defects such as wrinkles, fractures, surface distortion and springback. Appropriate setting and adjusting the drawbead force is one of the most important parameters in sheet forming process control. However, drawbead design and drawbead force adjustment still rely on trial-and-error procedures. This paper summarizes the guidelines in drawbead design, evaluates a number of mathematical models in estimating drawbead forces, and investigates the effects of sheet thickness, material properties, drawbead geometry and penetration on the drawbead force.

Predominant failure modes in the forming of sheet metal parts are wrinkling and tearing. Wrinkling may occur at the flange as well as in other areas of the drawn part and is generated by excessive compressive stresses that cause the sheet to buckle locally. Fracture occurs in a drawn material which is under excessive tensile stresses. For a given part and blank geometries, the major factors affecting the occurrence of defects in sheet metal parts are the blank holder force (BHF) and the blank holder pressure (BHP). These variables can be controlled to delay or completely eliminate wrinkling and fracture. Modern mechanical presses are equipped with hydraulic cushions and various advanced multi-point pressure control systems. Thus, the BHP can be adjusted over the periphery of the blank holder as a function of location and time (or press stroke).

Plane strain bending (e.g. bending about a straight line) is a major sheet forming operation and it is practiced as brake bending (air bending, U-die, V-die and wiping-die bending). Precise prediction of springback is the key to the design of the bending dies and to the control of the process and press brake to obtain close tolerances in bent parts. In this paper, reliable mathematical models for press brake bending are presented. These models can predict springback, bendability, strain and stress distributions, and the maximum loads on the punch and die. The elasto-plastic bending model incorporates the true (nonlinear) strain distribution across the sheet thickness, Swift's strain hardening law, Hill's 1979 nonquadratic yield criterion for normal anisotropic materials, and plane strain deformation mode.

Computer graphics and computer-aided engineering can be used effectively in both structured and unstructured classes: however, the infrastructure is more critical for unstructured classes. Open-ended design projects can require diverse types of software and hardware, and it is difficult for the faculty in charge to be an expert on the software for all of the projects which might be proposed. This paper identifies some of the types of hardware and software required to support open-ended projects. The need for support staffing is also discussed.

The Advanced Design Methods Laboratory (ADML) was established in the Department of Mechanical Engineering at Ohio State in 1977. This lab has the goal of integrating computer and interactive graphics into the teaching and research programs of the department. Currently, every Mechanical Engineering student at Ohio State uses computer graphics in junior-level courses in mechanical design; the ADML is involved in 12 courses at both the undergraduate and graduate levels. Increased application of the ADML is also occurring in research, with projects using computer and interactive graphics in the areas of machine element design, truck braking, V-belt transmissions, auto safety, pedestrian safety and linkage synthesis.