N. Alberti

Springback Evaluation in Fully 3-D Sheet Metal Forming Processes

Abstract In the modern manufacturing industries the knowledge and proper control of the sheet metal springback after forming is a fundamental aspect in the achievement of near net shape stamped parts. In this paper an effective springback prediction in some fully three-dimensional stamping processes is carried out. Such a prediction is based on a combined approach in which an explicit finite element code has been employed to simulate the forming phase while a traditional implicit procedure has been used to analyse the springback phase. The results obtained have been compared with a set of experimental tests and an excellent correlation between the predicted and experimental data has been found.

Sheet Metal Forming of Titanium Blanks Using Flexible Media

Abstract Sheet metal forming processes using flexible media are increasingly utilized in the industrial practice due to the relatively low tooling cost. In the present investigation, a rubber forming process is applied to the manufacturing cycle of a titanium alloy component for acoustic tweeters. The proposed process allows a reduction in manufacturing costs and production time since it permits the elimination of some joining operations. The FEM analysis has permitted the definition of the optimal process parameters and tooling geometry. Accordingly, several components have been produced; the achieved quality level is comparable with the one obtained utilizing the conventional technology and consistent with the FEM predictions.

Interdependence Between Tool Fracture and Wear

Wear and fracture are the main causes of tool scrapping. However fracture plays a major role for increasing values of the hardness and brittleness of tool materials or when low-cobalt tungsten carbides are used or in interrupted cutting conditions where it is the most relevant factor for tool scrapping. In order to obtain the optimal values of the cutting speed both these factors should be considered. The hypothesis of stochastic independence among them simplifies the mathematical formulation of the optimization problem; but experimental investigations do not agree with this assumption and, as a matter of fact, the probability density function of tool fracture results to be dependent on the wear conditions. In the paper some experimental results will be reported; these results are then applied to the evaluation of the optimal cutting speed and tool replacement policy.

Central bursting defects in drawing and extrusion: numerical and ultrasonic evaluation

Abstract A new approach for the prediction of central bursting defects in extrusion and drawing is proposed: a finite element analysis of the processes has been carried out, and the obtained results have been elaborated by means of a post-processor, which, employing a proper ductile fracture criterion, is able to suggest if and where the central burst occur. An ultrasonic control system able to detect the insurgence of defects with a resolution of 0.2 mm. has been setup in order to verify the predictive capability of the model. The experimental results show a good agreement with the numerical predictions confirming the effectiveness of the proposed approach, whose industrial application appears very suitable.

Prediction of Ductile Fractures in Metal-Forming Processes: an Approach Based on the Damage Mechanics

The Authors propose a new approach for the prediction of ductile fractures in bulk metal forming processes: the approach is based on a numerical analysis able to take into account damage occurrence and evolution in constitutive equations. The model supplies the distribution of the void volume fraction in the workpiece during the deformation path: consequently, the comparison to a critical value, determined by means of a simple tension test, allows to predict the growth of defects. The proposed approach has been applied to the drawing process: the numerical results have been compared with a set of experimental tests showing a good predictive capability of the model.

The Effects of the Fracture, Chipping and Wear of Cemented Carbide Tools on the Determination of the Optimum Metal-Cutting Conditions

A computer program has been prepared to optimize machining conditions when the stochastic tool-life has a probability density function resulting from fracture, chipping and wear. The optimization has been performed under the assumption that the fracture and the chipping probability density functions are indipendent from the cutting velocity. This hypotesis is well confirmed by several interrupted cutting tests showing two different probability distributions for fracture and chipping both having parameters which remain constant when cutting velocity is varied.

Knowledge-Based Systems and F.E. Simulations in Metal-Forming Processes Design An integrated Approach

Summary The automatic computer aided planning and design of cold forming processes includes several phases, among which the most important are the optimal choice of the forming operations sequence and, for each operation, the determination of the more suitable operating parameters. With this aim the Authors propose an integrated approach based on the preliminary choice of some feasible forming sequences, carried out by means of a knowledge-based system, and on the subsequent determination of the optimal one employing a finite element simulation of the process.

Optimum Tool Replacement Policies with Running-in of the Cutting-Edge

Summary The influence of the preliminary running-in of the cutting-edge to reduce the risk of unforeseen tool failures has been studied with reference to different tool replacement strategies. Models are developed to select the optimal tool replacement policy using the minimum production cost criterion.

A New Numerical Method for Axisymmetrical Forming Processes

Summary In this paper a numerical method for the analysis of axisymmetrical forming processes is proposed. This method represents the last development of a previous one which allows to solve forming problems in plane strain condition. The proposed model is baaed on the finite element discretization and on the linearization of the yield surface which leads to solve a LP problem. Two different examples of application, concerning the upsetting of a cylinder and of a hollow disk are reported.

A Numerical Method for the Analysis of Plane-Strain Forming Processes with Unilateral Constraints

The Authors propose a numerical model for the solution of plane-strain forming processes, based on the linearization of the yield surface. This allows to employ the linear programming technique for the solution of the variational problem derived from the application of the upper-bound theorem. Such a model permits to take into account the unilateral constraints in a very simple way. Therefore it is well suited to solve a large class of problems, such as sheet forming, in which the unilateral constraints are often present.