A.N. Bramley

Asymmetric single point incremental forming of sheet metal

The use of computers in manufacturing has enabled the development of several new sheet metal forming processes, which are based upon older technologies. This paper describes modifications that have been made to traditional forming methods such as conventional spinning and shear forming, forming processes in which deformation is localized. Recent advances have enabled this localized deformation to be accurately controlled and studied. Current developments have been focused on forming asymmetric parts using CNC technology, without the need for costly dies. Asymmetric Incremental Sheet Forming has the potential to revolutionize sheet metal forming, making it accessible to all levels of manufacturing. This paper describes the genesis and current state-of-the-art of Asymmetric Incremental Sheet Forming.

Enhancing technology and skills in small and medium-sized manufacturing firms: problems and prospects

DR. PETER SCOTT IS CURRENTLY A researcher at the University of Cardiff, Wales, Dr. Bryn Jones, Professor Alan Bramley and Dr. Brian Bolton are all with the University of Bath, England. This paper discusses the results of, and issues arising from, an interdisciplinary study of technology management expertise in a sample of smalland medium-sized manufacturing establishments in South-west England. Many mature companies suffer from an unrecognised deficiency in high-level technological skills. Although examples of good practice are identified and enabling factors discussed, the stimuli to improvement both within, and external to, the firm are weak overall. Changes in the practices of SMEs themselves, and of external agencies, will be necessary to facilitate progress.

UBET and TEUBA: fast methods for forging simulation and preform design

Abstract This paper describes the evolution of research led by the author into rapid approximate numerical techniques for analysing forging and extrusion-type processes. It describes how the original work of Prof. Kudo with his unit deforming regions has been adapted to develop the simulation tool known as the upper bound elemental technique. Its use for load, flow, strain and tool pressure prediction together with preform design is described. A more recent formulation, the tetrahedral upper bound analysis is presented which enables a more realistic flow simulation to be achieved. It also embodies the characteristic of fast simulation and can be used in 3D and for preform design.

A Finite Element Simulation of the Electrochemical Machining Process

Summary The paper describes a computer package based on the FEM (Finite Element Method), which simulates the Electrochemical Machining (ECM) process. The FEM is used to determine the two-dimensional potential and flux distributions in the electrolyte, in order to estimate surface erosion for a finite time-step. Algorithms have been developed which automatically change the FE mesh, to simulate moving boundaries for tool movement and workpiece erosion. The complex flux distributions produced in the electrolyte have yielded considerable insight into the erosion process for the tool shapes used in practice.

A Novel Method for the Rapid Production of Inexpensive Dies and Moulds with Surfaces Made by Incremental Sheet Forming

Abstract The choice of processing routes for parts is often strongly influenced by high tooling costs that can only be justified when large batches are required. This paper describes a novel system for producing inexpensive dies and moulds. The system exploits the recently developed ‘incremental sheet forming’ process to produce a die surface, which is then supported by a reinforcement and used as a conventional die or mould. A demonstrator die pair has been designed, constructed and tested, and the results show that even with a temporary reinforcement such as sand, the dies retain geometric accuracy. The use of this system allows more widespread application of incremental sheet forming than has been envisaged to date, as it expands the potential process applicability beyond prototypes and small batches by allowing manufacture, validation, and adjustment of dies and moulds for conventional mass production processes.

Upper-bound analysis for the automation of open-die forging

Abstract The automation of open-die forging systems can be attractive for small batch manufacture of medium-size parts where they can compete against a number of machining processes. The introduction of new manufacturing systems and the associated work-in-progress minimization technique prompts a consideration of the use of open-die forging for incremental profiling and shaping processes. In order to develop an automated open-die forging process it is essential to be able to predict the shape changes occurring at each step. Therefore a general computerized methodology is proposed for small batch manufacture via a theoretical model, producing rapid predictions of metal flow for continuing incremental deformation. This paper reviews the open-die forging process in this context as a part of a computer-controlled robotics flexible forging system for the economic production of small-batch quantities. The metal flow in open-die forging is analyzed through a number of upper-bound solutions and the basis of an on-line analytical modeling system, together with experimental correlation and a planning system, is presented to produce bar profile features.

The use of forging simulation tools

Abstract The paper reviews briefly the origins of plasticity theory and its application to the forging process; including the demise of some procedures. The paper then focuses on the use of numerical modelling/simulation tools and their application and future potential for the forging industry. This includes the results of research by the authors and others into the usability aspects of these techniques. Some of the limitations of current commercial software are discussed, thus, suggesting a future research agenda.

Parametric sensitivity analyses for FEA of hot steel forging

Abstract This paper reports a system for quantifying and comparing the sensitivity of a thermomechanical finite element analysis (FEA) of forging to variations in different input parameters. The results of applying the method to analyses of simple upsetting, impression-die forging and backward extrusion of hot steel are also described. The number of parameters in a thermomechanical FEA of forging make it impractical to investigate all of them, so the investigations were restricted to the parameters that define the flow stress of the forged steel and heat transfer and friction at the die–workpiece interface. Theoretical forging investigations of the kind described should be compared with the results of physical forging trials. This comparison would indicate whether or not more work characterising parameters for FEA of forging were justified.

Non-conventional cold extrusion

Abstract In recent years new extrusion processes have been developed for non axisymmetric shapes and with a variety of tool geometry, among them radial extrusion, rotary forming, non-axisymmetric extrusion etc. In this paper two “non-conventional” cold extrusion processes are investigated; radial extrusion using a circular punch and backward extrusion with the punch of square cross section. Experiments have been conducted in order to determine the basic process parameters. Furthermore, an Upper Bound solution for load prediction in radial extrusion have been developed which shows relatively good agreement with the experiment.

Sensitivity of finite element analysis of forging to input parameters

Abstract Attaining high quality input data for the finite element analysis (FEA) of forging can be difficult and expensive. The object of this study was to examine the sensitivity of the results of an FEA of forging to key input parameters. The case examined was a closed-die forging operation. Six input parameters, four used to define the plastic flow stress of the workpiece and two to define the conditions at the die–workpiece boundary, were varied. Results of full-factorial experiments, with each of the variable parameters assigned nine different values, were collated and analysed. Each response was then subjected to a regression analysis to establish linearity. In this way it was possible to assess the accuracy required of input data relative to the output requirements of the analysis. In the constitutive equation used for flow stress, the constant coefficient and temperature sensitivity term had a greater influence on the FEA results than that the strain-rate sensitivity and strain-hardening terms. At the die–workpiece interface, friction was more important than the cooling effect of the die. None of the parameters examined affected shape and strain predictions significantly. Results may well differ for the analysis of other shapes, metals and types of forging process. To gain a general picture of how accurately the input parameters for the FEA of forging need to be specified, the same investigation should be applied to other shapes and processes.