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With the availability of advanced machine designs and controls, tube hydroforming has become an economic alternative to various stamping processes. The technology is relatively new so that there is no large “knowledge base” to assist the product and process designers. This paper reviews the fundamentals of tube hydroforming technology and discusses how various parameters, such as tube material properties, pre-form geometry, lubrication and process control affect product design and quality. In addition, relations between process variables and achievable part geometry are discussed. Finally, using examples, the status of the current technology and critical issues for future development are reviewed.

The practical and proven use of computers in forming technology include: CAD/CAM for die making; transfer of geometric data from the customer's CAD/CAM system to that of the supplier and vice versa; application of artificial intelligence and expert systems for part and process design; simulation of metal flow to eliminate forging defects; prediction and optimization of process variables; and analysis of stresses in dies as well as prevention of premature die failure. Intelligent use of this information can lead to significant gains in product quality and productivity. This paper presents three examples of application of process simulation to forming : rolling, ring rolling and forging.

Deep drawing and ironing are the major processes used today in manufacturing of most beverage cans from aluminum. The same technology is utilized in manufacturing of steel cans for the food industry. The practical aspects of this technology are well known and gained through extensive experimentation and production know-how. The fundamental aspects of the processes, however, are relatively less known, especially regarding the temperature developed during deformation and the effect of deformation speed upon temperatures and lubrication. Thus, it is expected that process simulations using FEM techniques would provide additional detailed information that could be utilized to improve the process conditions. This paper illustrates the application of process modeling to deep drawing and ironing operations. The predictions agree well with the experimental results.

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.

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).

The capabilities of the servo press for varying the ram speed during stroke and for adjusting the stroke length are well known. Various companies installed servo presses for blanking. Some of the considerations may include increase in productivity and flexibility in adjusting the ram stroke, noise reduction and improvement of edge quality of blanked edge. The objectives of this study are to determine the effect of ram (blanking) speed upon the edge quality, and the effect of multiple step blanking using several punch motions, during one blanking stroke.

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.

Springback affects the dimensional accuracy and final shape of stamped parts. Accurate prediction of springback is necessary to design dies that produce the desired part geometry and tolerances. Springback occurs after stamping and ejection of the part because the state of the stresses and strains in the deformed material has changed. To accurately predict springback through finite element analysis, the material model should be well defined for accurate simulation and prediction of stresses and strains after unloading. Despite the development of several advanced material models that comprehensively describe the Bauschinger effect, transient behavior, permanent softening of the blank material, and unloading elastic modulus degradation, the prediction of springback is still not satisfactory for production parts. Dies are often recut several times, after the first tryouts, to compensate for springback and achieve the required part geometry.

Recent studies in sheet metal forming, conducted at universities world wide, emphasize the development of computer aided techniques for process simulation. To be practical and acceptable in a production environment, these codes must be easy to use and allow relatively quick solutions. Often, it is not necessary to make exact predictions but rather to establish the influence of process variables upon part quality, tool stresses, material flow, and material thickness variation. In cooperation with its industrial partners, the ERC for Net Shape Manufacturing of the Ohio State University has applied a number of computer codes for analysis and design of sheet metal forming operations. This paper gives a few selected examples taken from automotive applications and illustrates practical uses of computer simulations to improve productivity and reduce tool development and manufacturing costs.