L. Filice

Analysis of Material Formability in Incremental Forming

Abstract Incremental forming is an innovative sheet metal forming technology in which a blank is plastically deformed through the progressive action of a small-size punch, whose movement is governed by a CNC machine. In this way the tool locally deforms the material through an almost pure stretching deformation mechanics. The paper is focused on material formability in incremental forming. Several tests were developed, aimed to the achievement of different straining conditions in the material and consequently to the determination of Forming Limit Diagrams for progressive forming operations. The features and the application of such FLD are discussed in the paper.

Influence of mechanical properties of the sheet material on formability in single point incremental forming

Abstract New trends in sheet metal forming are rapidly developing and several new forming processes have been proposed to accomplish the goals of flexibility and cost reduction. Among them single point incremental forming operations, in which the final shape of the component is obtained by the relative movement of a simple and small punch with respect to the blank, appear quite promising. In the paper, material formability issues in incremental forming were studied. Some relevant correlations among material formability and other mechanical properties of the material were analysed. The FLD 0 value, i.e. the major strain at fracture in plane strain conditions, was determined for different materials and the influence of the main material parameters on formability was accurately investigated through a statistical analysis.

On-line control of single point incremental forming operations through punch force monitoring

Abstract Among the innovative sheet metal forming processes, Single Point Incremental Forming (SPIF) represents the simplest and the cheapest one. Despite its relevant advantages, up to now no specific CAE tools for SPIF were developed and the tool trajectory is generally defined utilizing CAD/CAM software developed for machining applications. In the paper an innovative monitoring and control approach, aimed to define and in-process update the most relevant process parameters during an industrial SPIF operation, is proposed. The strategy utilizes as monitoring variable the punch force trend: a set of preliminary tests demonstrated, in fact, its suitability as “spy variable” of the process mechanics and, in particular, of excessive sheet thinning and material failure approaching.

A simple approach for reducing profile diverting in a single point incremental forming process

Abstract Incremental forming applications are currently increasing in industry, especially for the production of small batches or single components. In fact, sufficient know-how is now available for the manufacture of simple products. However, further efforts are required to reduce the drawbacks of typical incremental forming processes, which compromise important advantages in terms of costs and flexibility. First of all the duration of the process, usually a few minutes, influences this kind of process, even if the operations are carried out on highspeed digitally controlled units. A tendency to produce inaccurate parts can reduce industrial interest with respect to incremental forming. Different approaches could be proposed to reduce this drawback, and a feasible and easily implemented strategy is the design of modified trajectories able to take into account both springback effects and stiffness reduction owing to specific clamping equipment. In this paper, such a strategy is pursued by integrating an on-line measuring system, composed of a digital inspector and a computer numerically controlled (CNC) open program. The geometry obtained is sampled in particular steps and an appropriate routine modifies the coordinates of the future punch path. This procedure of automatic control has been developed using an effective finite element (FE) code. An experimental design illustrates the potential use of the suggested methodology.

Influence of Laser Surface Modification on Bonding Strength of Al/Mg Adhesive Joints

Key properties of magnesium alloys, such as the high strength-to-density ratio, are driving the production of lightweight structural components in the automotive and aeronautical industries. Many efforts have been carried out on various aspects of processing and fabrication, but the joining of Mg alloys to dissimilar materials is a subject which attracted much research interest in the last decades. In the present work a preliminary investigation on the strength of Al/Mg (AA6082/AZ31B) single-lap epoxy bonded joints was carried out. To this aim, Mg and Al substrates were laser irradiated using a pulsed ytterbium fiber laser. For comparison, and in order to estimate the beneficial action of the laser surface treatment, single lap joints with grit-blasted substrates were prepared and tested. The interaction between laser treated surfaces and two different epoxy adhesives was also analyzed. Finally, the results and discussion were supported by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) executed on treated and post-failure sample surfaces.

On the Finite Element Simulation of Thermal Phenomena in Machining Processes

Machining processes are frequently investigated by numerical simulations. Usually 2D analyses are carried out in order to reduce CPU times, considering orthogonal cutting conditions. In this way, the computational time sharply reduces and many process variables may be calculated (i.e. forces, chip morphology, shear angle, contact length). On the other hand, the analysis of thermal aspects involved in machining, for instance the temperature distribution reached in tool, still represents an open problem. Finite element codes are able to simulate a very short process time that is not sufficient to reach steady state conditions. Several approaches have been proposed to overcome this problem: in the paper some of them are applied and critically discussed.

DEPENDENCE OF MACHINING SIMULATION EFFECTIVENESS ON MATERIAL AND FRICTION MODELLING

Numerical simulation of cutting processes is still a very difficult matter, although some relevant geometrical simplifications and high-performance codes are used. A large number of technical papers have been focused on the predictive capability of the codes: nevertheless the prediction quality is not very satisfactory if the problem is analyzed in a wide sense. In this paper the simple orthogonal cutting process of a plain-carbon steel is investigated taking into account different process conditions (cutting speed and feed rate). Furthermore, four material constitutive equations and three friction models were implemented and a sensitivity analysis was carried out comparing the numerical predictions and the experimental evidences. The results of this wide analysis are described in the paper.

Process Mechanics Analysis in Single Point Incremental Forming

The request of highly differentiated products and the need of process flexibility have brought the researchers to focus the attention on innovative sheet forming processes. Industrial application of conventional processes is, in fact, economically convenient just for large scale productions; furthermore conventional processes do not allow to fully satisfy the mentioned demand of flexibility. In this contest, single point incremental forming (SPIF) is an innovative and flexible answer to market requests. The process is characterized by a peculiar process mechanics, being the sheet plastically deformed only through a localised stretching mechanism. Some recent experimental studies have shown that SPIF permits a relevant increase of formability limits, just as a consequence of the peculiar deformation mechanics. The research here addressed is focused on the theoretical investigation of process mechanics; the aim was to achieve a deeper understanding of basic phenomena involved in SPIF which justify the above...

Sheet Thinning Prediction in Single Point Incremental Forming

Incremental forming processes are characterized by a well known and particular feature: any deformation across the sheet plane determines sheet thinning, since the blank is fully clamped by means of a proper equipment. As a consequence, the availability of effective and reliable CAE tools capable to supply an accurate prediction of sheet thinning as a function of process parameters, represents a strong requirement for a wider practical application of incremental forming. The already available theoretical models (i.e. the sine law) do not provide, on the other hand, satisfactory results. Therefore in the paper a couple of numerical analysis strategies was applied to simulate simple incremental forming processes, as well as a proper experimental equipment was developed to verify the accuracy of the numerical predictions.

Optimal design of tube hydroforming processes: a fuzzy-logic-based approach

Abstract In recent years, tube hydroforming has become an economic and industrially suitable alternative to various traditional stamping processes, in particular for small batch production. In the present paper, an artificial intelligence system based on fuzzy logic was implemented for tube hydroforming process design. The aim was to achieve a process design procedure able to prevent forming defects and guarantee the achievement of the desired final shape of the component. In particular, the process design concerns the internal pressure history and the axial feeding. The fuzzy system is able to provide optimal trajectories for both the controlled parameters, producing a defect-free final part.