Single point incremental forming of polymers

AbstractThe aim of the present paper is to evaluate the possibility of producing low-cost, small-batch, polymer sheet components by means of single point incremental forming (SPIF) at room temperature. During the research work, five different thermoplastic materials were incrementally formed into cones with an increasing wall angle on a conventional CNC milling machine. In designed experiments, significant process parameters were found, and influential material properties were identified. The experimental results confirm that SPIF of commercial polymer sheets at room temperature has potential for the manufacture of complex parts with very high depths

Microstructural characterization and simulation of damage for geared sheet components

The evolution of damage in geared components manufactured from steel sheets was investigated, to analyse the influence of damage caused by the sheet-bulk-metal forming. Due to the inhomogeneous and multi-axial deformation in the investigated parts, different aspects such as the location-dependent shape and size of voids are analysed by means of various microscopic methods. In particular, a method to characterize the state of damage evolution, i. e. void nucleation, growth and coalescence using scanning electron microscopy (SEM) is applied. The investigations reveal a strong dependence of the void area fraction, shape of voids and thus damage evolution on the loading mode. The microstructural analysis is complemented with FEM simulations using material models which consider the characteristics of the void evolution. © Published under licence by IOP Publishing Ltd

Influence of axial workpiece position in the coil for the electromagnetic pulse joining

Magnetic Pulse Welding (MPW) enables the fabrication of joints via the harnessing of Lorentz forces, which result from discharging a current pulse through a coil. In the process an outer piece (flyer) is accelerated onto an inner piece (parent), and welding is achieved using propagating impact fronts. The working length of the experimental setup allows for various shapes of the deformation front, and each configuration has its own advantages and drawbacks. The objective of this work is to show how the working length of tubular MPW specimens affects the front propagation as well as to indicate ways to optimize the front propagations, which are vital to the welding result. It is shown that for steel-aluminum joints, three different front regimes exist, which are related to geometrical factors. These results may be used to avoid seemingly favorable but nevertheless suboptimal conditions for flyer movement, which reduce the weld quality and the energy efficiency of the process. Additionally, the methodology presented here may allow for faster process optimization without the need for time-consuming metallographic analyses

Closed-loop control of product properties in metal forming

Metal forming processes operate in conditions of uncertainty due to parameter variation and imperfect understanding. This uncertainty leads to a degradation of product properties from customer specifications, which can be reduced by the use of closed-loop control. A framework of analysis is presented for understanding closed-loop control in metal forming, allowing an assessment of current and future developments in actuators, sensors and models. This leads to a survey of current and emerging applications across a broad spectrum of metal forming processes, and a discussion of likely developments.Engineering and Physical Sciences Research Council (Grant ID: EP/K018108/1)This is the final version of the article. It first appeared from Elsevier via https://doi.org/10.1016/j.cirp.2016.06.00

A semi-empirical approach for residual stresses in electric discharge machining (EDM)

High residual stresses are developed on the surfaces of electric discharge machined parts. In this study, layer removal method is used to measure the residual stress profile as a function of depth beneath the surface caused by die sinking type EDM. Cracking and its consequences on residual stresses are also studied on samples machined at long pulse durations. A modified empirical equation is developed for scaling residual stresses in machined surfaces with respect to operating conditions. In this model, a unit amplitude shape function representing change in curvature with respect to removal depth is proposed. The proposed form is found to be a special form of a Gauss Distribution. It is the sum of two Gaussian peaks, with the same amplitude and pulse width but opposite center location. The form can be represented by three constant coefficients. These coefficients depend on the released energy by a power function. © 2005 Elsevier Ltd. All rights reserved.This research was supported by the Middle East Technical University Research Fund. The authors are thankful to Mr M. Halkacı of Mechanical Engineering Department, Konya Selcuk University, Konya, Turkey, for his help in the preparation of samples and Mr O. Elkoca of Research and Development Center, Eregli Iron and Steel Works Co., Zonguldak, Turkey, for the Scanning Electron Micrograph

Void nucleation, growth and closure in cold forging: An uncoupled modelling approach

Forward rod extrusion experiments with high extrusions strains show a decrease of void area during forming. Most of the established damage modelling approaches have been developed without that knowledge and do not adequately cover the effect of void closure. Furthermore, many so called coupled models focus on the effect of ductile damage on the plastic flow of the material which results in more complex and numerically expensive models. But the effect of voids on plastic flow is insignificant for many cold forging applications, as shown in recent experiments. Thus, an uncoupled model is proposed that covers the effects of void nucleation, growth and closure. The proposed model is calibrated using void area fractions measured in forward rod extrusion experiments. A validation for various load paths shows good accordance with experimental data for void closure conditions under low triaxiality as well as for void evolution under higher triaxialities

Microstructure analysis of aluminum extrusion: Prediction of microstructure on AA6060 alloy

An experimental\u2013numerical procedure for predicting the recrystallized structure in aluminumextrusion is presented here, altogether with its validation. The whole plan is carried out in three steps: in the first step, the evolution of microstructure of an AA6060 alloy during deformationwas studied by means of small-scale laboratory test, the processing parameters being chosen in order to reproduce the typical industrial conditions. In the second step, the analysis of microstructure evolution after the heat treatment (550 ◦C for 30 min and 180 ◦C for 10 h)was analyzed, the obtained informations being used in order to fit a recrystallization model to be implemented inside the Deform FEM code environment. Finally, in the third step, the obtained informations are applied to extrusion tests presented in another papers by the authors (Schikorra, M., Donati, L., Tomesani, L., Tekkaya, A.E. 2007a. Microstructure analysis of aluminum extrusion: grain size distribution in AA6060, AA6082 and AA7075 alloys, J. Mech. Sci. Technol. 21, 1445\u20131451); the simulation results are compared and discussed with the experimental grain size distribution analyzed on the extruded rest

Residual stress state and hardness depth in electric discharge machining: De-ionized water as dielectric liquid

Procedures and results of experimental work to measure residual stresses and hardness depth in electric discharge machined surfaces are presented. Layer removal method is used to express the residual stress profile as a function of depth caused by a die sinking type EDM. Thin stressed layers are removed from machined samples by electrochemical machining. Corresponding deformations due to stress relaxation are recorded for each removal to determine the stress profile from elasticity theory. The relational dependence of the machining parameters with residual stresses is obtained and a semi-empirical model is proposed for plastic mold steel for de-ionized water as dielectric liquid. These stresses are found to be increasing rapidly with respect to depth, attaining to its maximum value, around the yield strength, and then fall rapidly to compressive residual stresses in the core of the material since the stresses within plastically deformed layers are equilibrated with elastic stresses. Copyright © 2005 Taylor & Francis Inc.This research was supported by the Middle East Technical University Research Fund. The authors are thankful to Mr. M. Halkac of Mechanical Engineering Department, Konya Selcuk University, Konya, Turkey, for his help in the preparation of samples