Giuseppina Ambrogio

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.

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.

Some considerations on force trends in Incremental Forming of different materials

Today, incremental Forming challenges are mainly related to formability limits and precision. High achievable strain levels, together with the possibility to form complex shapes without need for dedicated dies, probably represent the main process advantages. However the attention on material formability is always very relevant. Taking into account both the formability and the process accuracy, the knowledge of the forces generated between the punch and the clamped sheet supplies strategic information to the analyst. In fact, the force level is not only relevant for the equipment deflection but also influences the precision. In fact, in previous publications the authors demonstrated that there is a strict correlation between the force trend and the material failure approaching. In this paper, a broader analysis on AA1050‐O, AA3003‐O and DC04 drawing steel is carried out, highlighting the force trends depending on the process parameters and the relationship with formability limits.

Heuristic techniques to optimize neural network architecture in manufacturing applications

Abstract Nowadays application of neural networks in the manufacturing field is widely assessed even if this type of problem is typically characterized by an insufficient availability of data for a robust network training. Satisfactory results can be found in the literature, in both forming and machining operations, regarding the use of a neural network as a predictive tool. Nevertheless, the research of the optimal network configuration is still based on trial-and-error approaches, rather than on the application of specific techniques . As a consequence, the best method to determine the optimal neural network configuration is still a lack of knowledge in the literature overview. According to that, a comparative analysis is proposed in this work. More in detail four different approaches have been used to increase the generalization abilities of a neural network. These methods are based, respectively, on the use of genetic algorithms, Taguchi, tabu search and decision trees. The parameters taken into account in this work are the training algorithm, the number of hidden layers, the number of neurons and the activation function of each hidden layer. These techniques have been firstly tested on three different datasets, generated through numerical simulations in the Deform2D environment, in an attempt to map the input–output relationship for an extrusion, a rolling and a shearing process. Subsequently, the same approach has been validated on a fourth dataset derived from the literature review for a complex industrial process to widely generalize and asses the proposed methodology in the whole manufacturing field. Four tests were carried out for each dataset modifying the original data with a random noise with zero mean and standard deviation of one, two and five per cent. The results show that the use of a suitable technique for determining the architecture of a neural network can generate a significant performance improvement compared to a trial-and-error approach.

Enhancing Incremental Sheet Forming Performance Using High Speed

Flexible sheet metal forming processes represent one of the most relevant industrial issues of the scientific research. Incremental Sheet Forming is one of the most promising answers for many production scenarios. In particular, it becomes competitive when the production lot size decreases and the production variability increases. The process is basically set up on numerically controlled machines: a blank is clamped at its border and progressively deformed by a punch that moves according to a proper tool path program, reproducing the final part shape. Thus, the manufacturing time is directly dependent on the tool path length. Up to now, this aspect is one of the reasons why a systematic industrial application is not permitted. To overcome this drawback, an experimental investigation was planned in order to evaluate how the process is affected changing the cycle time. More in detail, an extended experimental investigation on the influence of process speed (i.e. tool rotation speed, tool feed) and other process parameters was executed taking into account a relatively simple 3D component. An accurate analysis of the obtained parts was performed, with particular attention to the thinning distribution that, of course, influences the material failure. Finally, the surface quality was also measured as an output variable.

White and Dark Layer Analysis Using Response Surface Methodology

This paper presents a study of the influence of cutting conditions on the finished surface obtained after an hard turning process, in particular a case study is presented where AISI 52100 bearing steel is machined under different cutting conditions. An analysis carried out using Surface Response Methodology has been developed in order to study the influence of the main cutting parameters such as cutting speed, feed rate and workpiece initial hardness on white (WL) and dark layer (DL) thickness. The whole experimental campaign has been performed using a chamfered PCBN tool inserts without any cutting fluid. Results show an evident influence of cutting speed and feed rate on both white and dark layer thickness while less relevant is the contribute given from the workpiece hardness on defining WL and DL depth. Finally, a model to find the optimal process conditions to minimize white and dark layer thickness is developed.