Simulation of the axial joint pressing process

When designing the axial joint pressing process, a relevant issue is the process parameters which directly influence the nature of the deformation of the housing, and, ultimately, on the formation of an all-in-one connection of a ball stud with a joint housing. These parameters are press force, punch displacement and matrix geometry. The quality of the all-in-one connection depends on a correct selection of the indicated parameters. If the axial joint insert is compressed evenly, the connection will be considered to be the most rational, that is the load will be distributed uniformly over the entire insert surface from the spherical surfaces of the ball stud and the deformed housing. In this way, the press must provide necessary force and displacement; the matrix geometry must provide the required shape of the deformed part of the housing. The all-in-one connection quality is evaluated by a number of operational characteristics of finished products, whose values must be located in intervals acceptable from the customer's point of view. Such characteristics include the following: ball stud rocking resistance torque, breakaway torque at ball stud rocking, axial spring travel and axial stiffness of the joint. In order to determine the specified parameters without many experiments on physical objects, a computer simulation model of the axial joint pressing process based on the finite element method was developed. Required press force, punch displacement and matrix geometry are determined by a computer simulation of the pressing process based on the finite element method. The accomplished experimental research led to the conclusion about acceptable repeatability of the results of the developed mathematical model and experimental data.

A New Method of Producing Bend Angle by Applying Sheet Forging to V-Bending Process

In actual manufacturing, some empirical method such as the bottoming technique is generally used in order to adjust the bend angles of products. In this study, a new method for controlling the bend angle in the V-bending process was attempted by applying sheet metal forging. In the experiments, three punches with lumps at the punch tip were used. These lumps were pushed into a bent section at the final stage of bending and were able to stretch the inside plane of the bent section. In both cases examined (using punches with one or two lumps at the tip), the bend angle decreased with an increase in punch displacement. This result shows new possibilities for controlling the bend angle by introducing plastic deformation to the bent section.

The Effect of Sheet and Material Properties on Springback in Air Bending

Angle control in air bending is achieved either by exploiting direct angle measurement (adaptive forming) or by controlling punch displacement. In general, the desired angle is supplied as input to CNC press brakes and the choice of punch stroke relies on either analytical or empirical models. Process geometry and material properties affect the outcome, therefore, full knowledge of these values is critical. Since a major source of inaccuracies is due to errors in material description (sheet thickness is critical as well), material data (or, more generally, sheet behavior information) collection in process is advisable. In air bending, process control can be improved by studying the total load as a function of punch displacement. This approach becomes more and more interesting since devices for load measurement are now available on the market. The aim of this work is to analyze some experimental load measures, collected in actual working conditions, to evaluate the accuracy of such technique and its potential for in process applications. Several sheet materials (ferrous and non-ferrous alloys) are studied through both bending and tensile tests; the resulting material properties (tensile and bending) are evaluated and compared. After data treatment of punch force signal, the ability of predicting punch displacement needed to reach a defined bending angle (after springback) is discussed.

Enhanced Semi-Analytical Process Simulation of Air Bending

The air bending process is one of the most widely used process for the manufacturing of sheet metal bending parts made of thin as well as of thick sheet metal. Although the air bending process offers a very high production potential due to its great flexibility, it is associated with certain problems which can negatively influence the shape and dimensional accuracy of the bending parts. Examples for such negative influences are the springback of the material, the batch variations, or the deflections of the bending machine and tools. These differences have to be considered either in the determination of the process parameters or they have to be compensated later on in the manufacturing process itself. A well established approach to calculate process data for forming processes is the use of a process simulation. At the Institute of Forming Technology and Lightweight Construction (IUL) a simulation software called Sheet Metal Bending Simulation (SMBS) has been developed and successfully been tested for the field of sheet metal bending, based on semi-analytical approaches. Although it already provides very satisfactory results in general, disturbances such as material and batch variations as well as the deflections of C-frame, machine table, and press brake ram can still negatively affect the prediction of the punch displacement necessary to achieve a certain bend angle. While material and batch variations cannot properly be considered in a process simulation at present, the afore mentioned influences offer a promising potential for improvements. Therefore, in order to further improve the accuracy of predicted quantities such as punch displacement and bending angle, a new module describing the elastic machine behaviour of press brakes has been developed and successfully been integrated in the process simulation SMBS. Experimental investigations have been carried out on a conventional CNC press brake to verify the efficiency of the newly implemented approach.

The Influence of Residual Stress on Micromachine Stiction

Adhesion plays an important role in microelectromechanical systems (MEMS). It is a major concern in MEMS reliability and oftentimes excessive adhesion forces lead to permanent adherence of MEMS surfaces resulting in microdevice failure. The role of residual stresses in the adhesive contact between a pre-stressed membrane and a rigid flat-ended cylindrical punch is studied. Breaking the contact can be achieved under either fixed-load or fixed-grips configuration. The influence of the residual stress on the pull-off force, punch displacement, and contact area at pull-off is studied. It is shown that residual stresses have significant influence on interfacial contact behavior in MEMS and, hence, should be taken into consideration in formulating the adhesion contact mechanics.

The Effects of Tooling Imperfections on the Initiation of Wrinkling in Finite Element Modeling of a Deep Drawing Process

A brief review of the literature on wrinkling in deep drawing processes is presented. It is noted that, while there is a large body of literature related to thin sheet, only one study related to thick sheet or plate has been identified. Finite element based models are used to investigate the effect of initial tooling imperfections on the initiation of wrinkling in deep drawing of thick sheet. Two sorts of tooling imperfections, punch displacement and blank tilting, are considered. The simulation results are compared qualitatively to the experimental forming operation. It is confirmed that tooling imperfections, in particular blank tilting, are an important type of imperfection governing the wrinkling behavior of the blank in deep drawing process.

The Effects of Tooling Imperfections on the Initiation of Wrinkling in Finite Element Modeling of a Deep Drawing Process

A brief review of the literature on wrinkling in deep drawing processes is presented. It is noted that, while there is a large body of literature related to thin sheet, only one study related to thick sheet or plate has been identified. Finite element based models are used to investigate the effect of initial tooling imperfections on the initiation of wrinkling in deep drawing of thick sheet. Two sorts of tooling imperfections, punch displacement and blank tilting, are considered. The simulation results are compared qualitatively to the experimental forming operation. It is confirmed that tooling imperfections, in particular blank tilting, are an important type of imperfection governing the wrinkling behavior of the blank in deep drawing process.