Oral literature in South Africa: 20 years on

I offer a retrospective on the field of orality and performance studies in South Africa from the perspective of 2016, assessing what has been achieved, what may have happened inadvertently or worryingly, what some of the significant implications have been, what remain challenges, and how we may think of, or rethink, orality and performance studies in a present and future that are changing at almost inconceivable pace.DHE

Computer Aided Modelling of Rubber Pad Forming Process

Rubber pad forming (RPF) is a novel method for sheet metal forming that has been increasingly used for: automotive, energy, electronic and aeronautic applications. Compared with the conventional forming processes, this method only requires one rigid die, according to the shape of the part, and the other tool is replaced by a rubber pad. This method can greatly improve the formability of the blank because the contact surface between the rigid die and the rubber pad is flexible. By this way the rubber pad forming enables the production of sheet metal parts with complex contours and bends. Furthermore, the rubber pad forming process is characterized by a low cost of the die because only one rigid die is required. The conventional way to develop rubber pad forming processes of metallic components requires a burdensome trial-and-error process for setting-up the technology, whose success chiefly depends on operator’s skill and experience. In the aeronautical field, where the parts are produced in small series, a too lengthy and costly development phase cannot be accepted. Moreover, the small number of components does not justify large investments in tooling. For these reasons, it is necessary that, during the conceptual design, possible technological troubles are preliminarily faced by means of numerical simulation. In this study, the rubber forming process of an aluminum alloy aeronautic component has been explored with numerical simulations and the significant parameters associated with this process have been investigated. Several effects, depending on: stamping strategy, component geometry and rubber pad characterization have been taken into account. The process analysis has been carried out thanks to an extensive use of a commercially finite element (FE) package useful for an appropriate set-up of the process model. These investigations have shown the effectiveness of simulations in process design and highlighted the critical parameters which require necessary adjustments before physical tests

Multi Shape Sheet Hydroforming Tooling design

In order to value the process of variables influence in sheet metal hydroforming, a special hydroforming cell has been developed. Generally, sheet hydroforming is obtained using appropriate press tooling. This option requires large investments completely dedicated to this technology of production. As an alternative, conventional hydraulic presses can be used for sheet hydroforming in combination with special hydraulic tooling named “hydroforming cells”. A special “hydroforming cell” concept has been developed to perform experimental analysis for different shapes using the same tooling set up. CAE tools had a strategic role just to develop the best layout and to find the optimum solutions for the process variables. FEA has been used to define the distribution of the blank holder variable forces: a solution which implies the use of twelve independent actuators have been implemented. The position and the load path of each one of them has been chosen for each formed shape, in accordance with the FEA results. Customized actuators have been used to solve interferences between mechanical parts of the hydroforming cell. For this specific aspects the virtual 3D design was necessary for the appropriate decisions. The developed process system is very effective so that is possible to set up experimental campaigns for sheet hydroformed components

Sheet Metal Hydroforming Process Review Through Shape Factors Analysis and Numerical Simulation

Hydroforming is a forming technology for semi-finished goods like: tubes and sheets that aims to obtain high strength parts and to manufacture complex geometries in one step. Even the material straining caused by fluid pressure leads to a uniform rise in yield strength in the used materials, resulting in a lower need necessary for high wall thicknesses [9]. Nowadays the need of improving the quality and the reliability of products and of decreasing their cost represent general market requests in any field. In particular, in the automotive industry, the main aim is the reduction of CO2 emissions and energy consumptions through the increase of the lightness of cars. In order to satisfy such targets, the attention has been recently focused on many new methods; some of them are aimed to the forming of certain lightweight metals and alloys, while other techniques are directed to a more economic components production than conventional forming methods [10]. Hydroforming allows to overcome some of the limitations of conventional deep drawing, increasing the drawing ratio and minimizing the thickness reduction of the formed parts. Some of the advantages introduced by hydroforming are: a greater flexibility and a remarkable reduction of tooling costs [11]. The basic parts of the tool for a hydroforming process include a punch, a blank holder and a fluid chamber. The draw ratio achievable in hydroforming is quite high (values of about 3,2 are reported in literature) [12], very little thinning occurs and asymmetrical shapes can be drawn. Different studies have been conducted to design a possible classification valid for Tube Hydro Forming (THF), starting from the analysis of the shape of the formed part [13]. Though this paper only relates to Sheet metal Hydro Forming (SHF) , it refers back to the above consideration about THF. The aim of this paper is to define a “shape factors” set and to direct the designer towards a proper goal in his development of the process for metal components produced through the application of sheet hydroforming. Finite Element Analysis (FEA) has been extensively used in order to investigate and define each shape factor with a proper comparison to the macro feasibility of the chosen component geometry. In other studies, these shape factors have been also used to track the process performances through their variation thanks to the usage of the numerical simulation which has been later validated with an appropriate experimental campaign. In this paper, these parameters have been applied to a geometrical complex shape in order to investigate its own feasibility only analyzing its CAD model and to evaluate different modifications on the geometry to reach its own feasibility

Process Design for hydroformed tailored blank through CAE techniques

Ecological awareness and economic analysis force industry to decrease the weight of transportation vehicles and to achieve a higher product quality with a reduction of production costs. Lightweight constructions made out of Tailored Blanks (TBs) and advanced manufacturing technologies, like sheet metal Hydromechanical Deep Drawing (HDD), help to reach these goals. From this point of view, HDD techniques have been largely accepted by the industry for the production of components characterized by: complex shapes, good surface quality and small residual stress. In this work, starting from previous studies of the same authors about hydroformed components with a redrawing area, an original approach based on Thickness Percentage Reduction (TPR) distribution has been implemented to design a particular TBs for HDD applications. Numerical and experimental results about the studied test case have been allowed the verification of their correlation as well as the necessary reliability of the implemented process simulation methodology

Feasibility Evaluation of Sheet Metal Hydroformed ComponentsThrough Shape Factors Application

Sheet hydroforming has gained increasing interest in the automotive and aerospace industries because of its many advantages such as higher forming potentiality, good quality of the formed parts which may have complex geometry. The main advantage is that the uniform pressure can be transferred to any part of the formed blank at the same time [1]. In this paper, a “shape factors” set has been defined with the proper goal to understand if it can be used to help engineers to define “process rules” for the studied non conventional technology [2]. A specific prediction model, obtained thanks to a numerical factorial fractional plane, has been used in order to preview the process responses vs each defined shape factor. These shape factors have been used to track the process performances through their variation thanks to the usage of the numerical simulation that has been validated with an appropriate experimental campaign executed thanks to the usage of a specific equipment properly designed

Design for Manufacturing for energy absorbing systems

In the typical scenario of a helicopter crash, impact with the ground is preceded by a substantially vertical drop, with the result that a seated occupant of a helicopter experiences high spinal loads and pelvic deceleration during such crash due to the sudden arresting of vertical downward motion. It has long been recognized that spinal injuries to occupants of helicopters in such crash scenario can be minimized by seat arrangements which limit the deceleration to which the seated occupant is subjected, relative to the helicopter, to a predetermined maximum, by allowing downward movement of the seated occupant relative to the helicopter, at the time of impact with the ground, under a restraining force which, over a limited range of such movement, is limited to a predetermined maximum. In practice, significant benefits, in the way of reduced injuries and reduced seriousness of injuries, can be afforded in this way in such crash situations even where the extent of such controlled vertical movement permitted by the crashworthy seat arrangement is quite limited. Important increase of accident safety is reached with the installation of crashworthy shock absorbers on the main landing gear, but this solution is mostly feasible on military helicopters with long fixed landing gear. Seats can then give high contribution to survivability. Commonly, an energy absorber is a constant load device, if one excludes an initial elastic part of the load-stroke curve. On helicopter seats, this behavior is obtained by plastic deformation of a metal component or scraping of material. In the present work the authors have studied three absorption systems, which differ in relation to their shape, their working conditions and their constructive materials. All the combinations have been analyzed for applications in VIP helicopter seats