A review of flow forming processes and mechanisms

After years of purely academic interest and niche applications, today the flow forming process is increasing demand in aerospace, automotive and defense industries. This review surveys academic paper of last fifty years, in order to evaluate the current state-of-the-art for academic and practitioner. Theoretical and experimental approaches are collected and compared by evaluating their prediction models. As a result, several knowledge gaps are identified, for example stress and strain tensors evolutions are not determined for workpiece, due to high computational cost and uncertainty about the correct finite elements approach to adopt. Similarly although, the final microstructure is often evaluated for specific cases, study of its evolution during plastic deformation has not been reported. Residual stress and final material proprieties, such as corrosion behavior, have been not studied numerically or experimentally. Tool path impact and alternative geometries are not deeply explored. Particular attention is given to process experimental optimization and characterization through Design of Experiment, which is still limited to a few papers and sometimes not well developed. The results of this review will help define a research agenda for future developments

Systematic process selection for cold forging

This paper presents a hybrid model for determining feasible cold forging methods for individual components that is extendable to other manufacturing areas. An initial screening of candidate processes could potentially be followed by a systematic comparison of their capabilities through fuzzy sets and the product’s functional requirements. A comparative complexity evaluation between the component and a Near Net Shape (NNS) approximation formed product allows evaluation of the further effort necessary to produce the final component. The model supports the possibility of redesign by means of an iterative procedure in order to assess different cold forging processes with different designs. After presentation of the methodology the paper end with a case study application that ranks feasible combinations of process for a given design. This illustrates both the strengths and limitations of the proposed approach

Near net shape manufacturing of metal : a review of approaches and their evolutions

In the last thirty years the concept of manufacturability has been applied to many different processes in numerous industries. This has resulted in the emergence of several different "Design for Manufacturing" methodologies which have in common the aim of reducing productions costs through the application of general manufacturing rules. Near net shape technologies have expanded these concepts, targeting mainly primary shaping process, such as casting or forging. The desired outcomes of manufacturability analysis for near-net-shape (NNS) processes are cost and lead/time reduction through minimization of process steps (in particular cutting and finishing operations) and raw material saving. Product quality improvement, variability reduction and component design functionality enhancement are also achievable through NNS optimization. Process parameters, product design and material selection are the changing variables in a manufacturing chain that interact in complex, non-linear ways. Consequently modeling and simulation play important roles in the investigation of alternative approaches. However defining the manufacturing capability of different processes is also a “moving target” because the various NNS technologies are constantly improving and evolving so there is challenge in accurately reflecting their requirements and capabilities. In the last decade, for example, CAD, CNC technologies and innovation in materials have impacted enormously on the development of NNS technologies. This paper reviews the different methods reported for NNS manufacturability assessment and examines how they can make an impact on cost, quality and process variability in the context of a specific production volume. The discussion identifies a lack of structured approaches, poor connection with process optimization methodologies and a lack of empirical models as gaps in the reported approaches

A methodology for assessing the feasibility of producing components by flow forming

This paper describes a methodology for assessing the applicability of the flow forming process for the manufacture of specific components. The process starts by filtering potential candidates for flow forming from a component collection (e.g. company catalogue) and then carries out a detailed assessment of quantitative, technological and economic feasibility before determining a viable process plan. The process described uses analytical relationships and empirical criteria drawn from the literature.. A process time model (based on an analogy with CNC turning) is used to develop a hybrid cost model in order to evaluate economic feasibility. The paper concluded with a brief summary of the results of applying the process to an industrial case study

Flow forming : a review of research methodologies, prediction models and their applications

After years of largely academic interest and niche applications, a new generation of high duty CNC machines is enabling the flow forming process find increasing application in aerospace, automotive and defense industries. The versatility of digital control has made it economically viable to deliver weight and cost savings for small to medium batch sizes while simultaneously improving quality and material proprieties. To better understand the capabilities of flow forming this review surveys the reported research over last fifty years and summarizes both theoretical models and experimental investigations. Where possible the contributions of different researchers are described and assessed in terms of the accuracy of their predictive capabilities. In some cases practice has preceded the development of theory for example: the ratio of circumferential to axial contact is widely used as a defect prediction parameter, even if the process' failure mechanism is still not fully understood. In other areas, such as forming forces and powers, the literature provides a clear rational based on experimentally validated analytical models. In addition to summarizing current knowledge the review also identifies gaps in current literature where more research is required. For example: the evolution of stress/strain tensors during a flow forming process has not been reported due to the high computational cost and a lack of consensus on the most appropriate finite elements modeling approach to adopt. Similarly while the final microstructure of a formed part is often evaluated models of its development (during the series of plastic deformations created by a flow forming process) have not been reported. Likewise residual stress and final material proprieties, such as corrosion behaviour, have been not studied numerically or experimentally. It is also noted that the impact of tool paths (e.g. their geometry and topology) has not been deeply explored. Lastly the authors note, the surprising observation, that only a few researchers have reported the experimental optimization and characterization of flow forming process parameters using a 'Design of Experiments' methodology

What Are Lightness Illusions and Why Do We See Them?

Lightness illusions are fundamental to human perception, and yet why we see them is still the focus of much research. Here we address the question by modelling not human physiology or perception directly as is typically the case but our natural visual world and the need for robust behaviour. Artificial neural networks were trained to predict the reflectance of surfaces in a synthetic ecology consisting of 3-D “dead-leaves” scenes under non-uniform illumination. The networks learned to solve this task accurately and robustly given only ambiguous sense data. In addition—and as a direct consequence of their experience—the networks also made systematic “errors” in their behaviour commensurate with human illusions, which includes brightness contrast and assimilation—although assimilation (specifically White's illusion) only emerged when the virtual ecology included 3-D, as opposed to 2-D scenes. Subtle variations in these illusions, also found in human perception, were observed, such as the asymmetry of brightness contrast. These data suggest that “illusions” arise in humans because (i) natural stimuli are ambiguous, and (ii) this ambiguity is resolved empirically by encoding the statistical relationship between images and scenes in past visual experience. Since resolving stimulus ambiguity is a challenge faced by all visual systems, a corollary of these findings is that human illusions must be experienced by all visual animals regardless of their particular neural machinery. The data also provide a more formal definition of illusion: the condition in which the true source of a stimulus differs from what is its most likely (and thus perceived) source. As such, illusions are not fundamentally different from non-illusory percepts, all being direct manifestations of the statistical relationship between images and scenes

Research directions in hydroforming technology

This paper both summarizes and explores the literature published between 1995 and 2015 on enhancing and extending hydroforming technology. Many different research areas have been proposed, all of which try to enhance the well-established manufacturing process by either improving formability or reducing costs. Each of the technological variations are first described and then their uses, benefits, drawbacks and applications are discussed and summarized

A state of the art review of hydroforming technology : its applications, research areas, history and future in manufacturing

Hydroforming is a relatively new metal forming process with many advantages over traditional cold forming processes including the ability to create more complicated components with fewer operations. For certain geometries, hydroforming technology permits the creation of parts that are lighter weight, have stiffer properties, are cheaper to produce and can be manufactured from fewer blanks which produces less material waste. This paper provides a detailed survey of the hydroforming literature of both established and emerging processes in a single taxonomy. Recently reported innovations in hydroforming processes (which are incorporated in the taxonomy) are also detailed and classified in terms of “technology readiness level”. The paper concludes with a discussion on the future of hydroforming including the current state of the art techniques, the research directions, and the process advantages to make predictions about emerging hydroforming technologies