Key Engineering Materials Vols. 622-623

Abstract: Superficial coatings are widely used in industrial applications in order to improve the superficial properties of metallic components. In particular, in the aeronautic field, all the components are coated in order to prevent both corrosion and wear. In this field, heat treatable aluminum alloys, in age hardened condition, are used; consequently, superficial coatings must be carried out through “cold” processes, i.e. coating processes in which the component to be coated remains at low temperatures, below 100°C. Cold gas dynamic spray technique (CGDS) is a process of deposition that consists in the realization of surface coatings with high-velocity metal particles sprayed on the substrate at temperature significantly lower than the melting one of the substrate itself and at relatively low temperatures if compared to other spray techniques. When processing conditions are optimized, the process can produce near fully dense coatings. This technique could be particularly useful in the coating of rolled sheets, needing of successive cold plastic deformations. One of the cold plastic processes is incremental forming, a high flexible process for rapid manufacturing of complex sheet metal part shapes; it presents the potential to be easy to automate and particularly attractive for small batches and customized parts. In this process, a simple tool describes a path that allows to locally deform the sheet clamped along its periphery. The aim of this paper is to study the evolution and behaviour of aluminum coating deposed by CGDS on AA 2024-T3 sheets carried out by an incremental forming process. This evaluation is carried out by characterizing the cold sprayed coating after the forming process for different wall angles of simples geometries.

Abstract: It is well known that Incremental Sheet Forming has two main drawbacks, i.e. accuracy and slowness. The former has been studied and partially solved by several researchers while the latter did not receive convincing answers. Thus, the idea of several research groups is that the process applicability is suggested only for rapid manufacturing or small batch production. The lack of knowledge is certainly caused by the available machines, like milling or Amino, which are typically used for incremental forming operations. In the present research the attention was focalized on the above limit: an experimental campaign was performed in order to evaluate the process feasibility at very high speed. To do that a lathe machine has been used instead of the conventional milling one, increasing the process speed up to two order of magnitude. An aluminum alloy, widely used in the mechanical fields, has been chosen as sample material and an experimental investigation has been aimed at determining the influence of tool speed on the material behavior.

Abstract: The Incremental Profile Forming process (IPF) is a new method to manufacture tubes and profiles with variable cross-section design along the centre-line of the profile. The innovative process design enables the combination of high workpiece complexity and high process flexibility. For this reason, a machine concept was developed and finally a prototype realized. The new machine consists of eight numerically controlled axes, which allow the processing of thinwalled tubes and profiles with a maximum diameter of 80 mm. The design of the machine combined with the control system leads to a forming technology with a high degree of flexibility, which is an advantage of the process. Depending on the final workpiece shape the forming process proceeds in several steps and can therefore be considered as an incremental forming process. Furthermore, the tool concept supports both a kinematical and a form-closed forming process.

Abstract: The idea of incrementally forming sheet metal with a single point tool, called ‘dieless forming’, was patented by Leszak [1] well before it was technically feasible. There have been many studies, which have lead to the present situation [2-9]. The new processes are attractive because manufacturing sheet metal can be accomplished by any facility having a three-axis cnc mill. Sheet metal spif is an innovative, flexible sheet metal-forming technology that uses principles of layered manufacturing. It transforms the complicated geometry information into a series of parameter of two-dimensional layers and then the plastic deformation is carried out layer-by-layer through the computer numerically controlled. The basic principle of spif (Fig. 1) is that the forming tool moves around the outline of the part along the predefined tool path and extrudes the sheet metal point by point so that the local plastic deformations occur incrementally [8, 10]. The forming tool paths have a great effect on the surface quality, forming time and dimensional accuracy. Although the movement mode of the forming tool is similar to one of the cutters in the cnc milling machine, the forming process based on the plastic deformation and milling process is totally different, so the requirements for the tool paths are different. As a result, there are some specific characteristics which should be considered in forming tool path generation. The goal of this paper is to evaluate the possibility of producing low-cost polymer sheet components by means of spif. Three different thermoplastic materials were incrementally formed on a conventional cnc milling machine. Experiments are conducted to determine the formability, failure modes and significant process parameters. Even though considerable amount of research work has been done in the field, these aspects are not completely defined and only limited number of materials has been tested.

Abstract: Sheet metal spinning is one of the forming processes based on gradual shaping of metal blank into an axisymetric part by a roller according to a mandrel. Very significant feature of spinning is ability to produce components with high mechanical properties and high quality of surface layers. The paper brings the results of major true strains analysis of mild steel parts produced by CNC multi-pass conventional metal spinning. The influence of the spindle speed, feed rate, workpiece geometry and planar anisotropy of the blank on the strain distribution of formed part is studied by method of grain size measurement. The design of experiment using the Taguchi approach and analysis of variance (ANOVA) is applied to find optimal process parameters.

Abstract: Incremental Sheet Forming processes have been characterized by their limited forming speed and accompanying lengthy production time. ISF has therefore been considered a process category suitable for small batch sizes or discrete part production only. The potential for greatly increasing the forming speed of incremental forming processes is studied here by means of axisymmetric incremental forming on a lathe. As an aluminium alloy commonly used in automotive applications, AA5182-O, is of interest for incremental forming at increased speed. In this paper the influence of an increasing feed rate on forming forces, temperature and formability is analyzed.

Abstract: Flexible and economic production of composite structures which include functional layersrequires new manufacturing techniques. Joining by plastic deformation is a powerful technique whichis widely used in production processes to create metal composites [1]. The use of plastic deformationin joining processes offers improved accuracy, reliability and environmental safety [2]. The presentstudy deals with modeling of the bonding and debonding behavior in metallic composite structures.Therefore, a general cohesive zone element formulation in the framework of zero-thickness interfaceelements is developed. This enables the accurate and efficient modeling of the interface based on aninterfacial traction-separation law. The paper is concluded by a detailed description of the processsimulation and a comparison of its results with experimental data.

Abstract: In recent years, multi-component injection molding has largely developed in the industries. During the manufacturing process, the critical challenge is in achieving an optimum adhesion between the two materials. This study examines the influence of curing kinetics on the interfacial adhesion strength between a silicone rubber and nylon 66 using a rotational rheometer. The evolution of adhesion strength of assembly during the curing behaviour of silicone rubber was measured by tensile test at different curing temperature and different curing time. The results showed a significant increase in adhesion was obtained while either the curing temperature or the curing time increased. In this study, the rheological property of silicone rubber fluid has been also determined by the rotational rheometer. In addition, the kinetics of the curing reaction of silicone rubber has been studied by differential scanning calorimeter.

Abstract: The present investigation aims at studying post-welding forming operations of friction stir welded AA1050 aluminium thin sheets. A preliminary investigation has allowed to define the rotational and welding speed values leading to friction stir welded joints with high mechanical properties. Then, formability and elastic springback were evaluated using the hemispherical punch and bending tests, respectively. A microstructural investigation has allowed to relate the mechanical properties of joints to microstructure. Finally, the friction stir welded assemblies were subjected to air bending and stamping experiments in order to evaluate their attitude to undergo to sheet metal forming operations.

Abstract: Composite sheet of Twin Roll Cast (TRC) AZ31-Mg alloy and industrial pure Al-1050 was fabricated as Al/Mg/Al with a hot roll bonding process. As the diffusion zone at the interface between the layers plays a crucial role in the formation of bonding strength and formability of clad sheets. It is important to describe the processes of inter-diffusion layer generation in order to assess the abilities of the laminate composites for further processing. Thus, the aim of this study was to investigate the development of the bonding strength, microstructure and mechanical properties of the bonding interface directly after roll bonding and additionally post-annealing processes. Microstructure characterization techniques such as optical and scanning electron microscopy including energy dispersive X-ray analysis (EDX) were applied to investigate the bonding area. No inter-metallic phases were present directly after the roll bonding process. The creation and growth of Al₂Mg₃ and Al₁₂Mg₁₇ phases were apparent after annealing at temperatures of 250 to 400 °C at different times ranging from five to 120 minutes. The results prove that the growth rate of inter-metallic phases increases considerably with an increase in the annealing temperature. The micro-hardness of the interface-area was also investigated. It was observed that the two inter-metallic phases were significantly harder than the substrate Mg and Al. In order to examine the influence of the inter-metallic phases on the resulting bonding strength after the annealing process, the shear bonding strength test has been conducted for different samples that were annealed at different heat treatment conditions. The results indicate that the optimum annealing temperature is 200 °C leading to a maximum bonding strength. Moreover, the mechanical properties of the composite after roll bonding and post annealing were determined by means of room temperature tensile test. The fracture mechanism after tensile test was also discussed.Keywords: Roll bonding, Al/Mg hot roll bonding, Twin roll cast AZ31, bonding strength