https://popups.uliege.be/esaform21/index.php?id=76 Coordinator: Dr. Javad Hazrati Co-organiser: Dr Lander Galdos Description: In material forming, relative motion of the tool and workpiece during production makes friction and wear phenomena (tribology) of the utmost importance. On that account, accurate prediction of friction and wear is necessary for designing zero-defect manufacturing processes. The tribological performance in forming processes is influenced by several parameters at the micro- and macro levels (local contact conditions: surface texture, contact pressure, temperature and lubrication). Thus, for optimum process design, improving formability, enhancing tool life and finally control of tribology, a better understanding of tribology and an accurate prediction of friction/wear in forming processes are necessary. In this mini-symposium, different aspects of tribology in cold/hot forming of (sheet/bulk) metals, polymers and composites will be discussed. The topics that will be covered in this mini-symposium in particular are: modeling friction and wear; tribological characterization methods; surface engineering and control of friction/wear in cold/hot material forming. Mini Symposia fr Wed, 03 Mar 2021 09:26:18 +0100 Tue, 24 Aug 2021 12:05:31 +0200 https://popups.uliege.be/esaform21/index.php?id=76 0 https://popups.uliege.be/esaform21/index.php?id=426 In the last few years many efforts have been carried out in order to better understand what the real contact between material and tools is. Based on the better understanding new friction models have been developed which have allowed process designers to improve numerical results in terms of component viability and geometrical accuracy. The new models define the coefficient of friction depending on different process parameters such as the contact pressure, the sliding velocity, the material strain, and the tool temperature. Many examples of the improvements achieved, both at laboratory scale and at industrial scale, can be found in the recent literature. However, in each of the examples found in the literature, different ranges of the variables affecting the coefficient of friction are covered depending on the component analysed and the material used to produce such component. The present work statistically analyses the contact pressure and sliding velocity ranges achieved during numerical simulation (FEM) of sheet metal forming processes. Nineteen different industrial components representing a high variety of shapes have been studied to cover a wide range of casuistic. The contact pressure and sliding velocity corresponding to typical areas of the tooling have been analysed though numerical simulation in each case. This study identifies the ranges of contact-pressure and sliding velocities occurring in sheet metal forming aimed to set the characterization range for future friction studies. Fri, 19 Mar 2021 19:10:22 +0100 https://popups.uliege.be/esaform21/index.php?id=426 https://popups.uliege.be/esaform21/index.php?id=1920 Pure titanium and titanium alloys were difficult to be forged and press-forged because of their easiness in galling to die and punch surfaces during metal forming. β-SiC coated SiC dies were developed to perform a galling free cold forging of pure titanium wire up to the higher reduction of thickness than 50%. Since the thickness of this SiC coating was 4 mm, various cavities and micro-punches were formed into coating by micro-machining. The pure titanium and β-phase titanium alloy wires were employed as a work for cold and warm forging to investigate the effect of flow stress on the forging behavior up to the reduction of thickness by 70% under the controlled holding temperature. The contact interface of β-SiC coating to the work was precisely analyzed to describe the in situ solid lubricating process on the interface. The free carbon agglomerates isolated at the center of contact interface from the carbon supersaturated β-SiC coating, and, worked as a solid lubricant to prevent the β-SiC coating punch and die from galling during forging under high reduction of thickness. Tue, 23 Mar 2021 10:36:24 +0100 https://popups.uliege.be/esaform21/index.php?id=1920 https://popups.uliege.be/esaform21/index.php?id=1977 Determination of flow stress and friction in cold forging is of paramount importance. In this work, an inverse procedure is developed for predicting the Coulomb’s coefficient of friction and strain-dependent flow stress simultaneously based on the measurement of bulge and forging load. It is also established that in cold forging Coulomb’s coefficient of friction can be approximated as half the friction factor in Tresca (or constant friction) model. In the inverse procedure, forging load is estimated analytically but bulging is estimated by developing an empirical relation. The efficacy of the inverse procedure is ascertained by the data obtained from finite element method simulations. Finite element method was implemented in ABAQUS and validated with the results available in literature. In most of the cases, inverse procedure provides less than 5% error in the estimates of friction and flow stress. A sensitivity analysis is also carried out to study the effect of measurement error. It is observed that error in the estimation of friction is proportional to error in the measurement of bulge. The novelty of the method lies in the quickness and simplicity of the method. Tue, 23 Mar 2021 12:17:42 +0100 https://popups.uliege.be/esaform21/index.php?id=1977 https://popups.uliege.be/esaform21/index.php?id=2075 Like in many other production technologies, a broad process window for metal forming is desired. The goal is always a stable process chain. One of the key aspects for metal forming are stable tribological conditions. Instabilities can be caused by, amongst others, different material batches, change in temperature during the production process, different lubricant amounts and different stroke rates. At the beginning of a production run, the tribological stability suffers from transient temperature effects caused by plastic and frictional work and a viscosity drop of the lubricant. To control the tribology, different strategies are suitable: changing the oil type, the oil amount, the blank holder force or the stroke rate. Within the EU-project ASPECT, control strategies on blank holder forces are developed as well as lubricants with improved stability on their behaviour as a function of temperature. This paper will focus on the latter. In preliminary ball on plate test the friction and wear of lubricant formulations were investigated and compared to a Reference lubricant. Followed by strip drawing and forming tests. Finally, the concept is proven in trials on a demonstrator line, which is close to serial production. Tue, 23 Mar 2021 12:41:17 +0100 https://popups.uliege.be/esaform21/index.php?id=2075 https://popups.uliege.be/esaform21/index.php?id=2081 The final quality of sheet and tube metal formed components strongly depends of the tribology and friction conditions between the tools and the material to be formed. Furthermore, it has been recently demonstrated that friction is the numerical input parameter that has the biggest effect in the numerical models used for feasibility studies and process design. Industrial dedicated software packages have introduced friction laws which are dependent on sliding velocity, contact pressure and sometimes strain suffered by the sheet and currently, temperature dependency is being implemented as it has also major effect on friction. This last dependency on temperature is attributed to the viscosity change of the lubricant with temperature. In this work, three lubricant having different viscosity have been characterized using the tube sliding test. The final aim of the study is to obtain friction laws that are contact pressure and sliding velocity dependent for their use in tube hydroforming modelling. The tests, performed at various contact pressures and velocities, demonstrate that viscosity has a major effect on friction. As shown in the literature, the friction coefficient is also varying with the contact pressure and sliding velocity.Abs Tue, 23 Mar 2021 12:44:01 +0100 https://popups.uliege.be/esaform21/index.php?id=2081 https://popups.uliege.be/esaform21/index.php?id=2129 The measurement of thermoelectric current is a new and effective method for inline wear detection in sheet metal forming. The measuring principle is based on the Seebeck effect, whose characteristic value, the Seebeck coefficient depends on the material composition. In the previous research of the authors, a boundary value of the thermoelectric value that separates the mild and severe wear was identified. Due to the large deviation of the Seebeck coefficient of the material used in sheet metal forming, it is worth discussing the influence of the Seebeck coefficient of the sheet metal material on the effectiveness and boundary value of the thermoelectric current for wear detection. In this paper, the measuring principle is first illustrated using an equation based on thermoelectricity. The Seebeck coefficients of the tools and sheet metals are then determined by a specifically designed device. At the same time, the wear tests for different materials are used to determine the boundary values for different tribological systems. Finally, the obtained Seebeck coefficient and boundary values are compared. From the results it can be concluded that the value of the measured Seebeck coefficients have a discernible effect on the boundary values, which provides a useful insight for inline wear diagnosis for practical applications. Tue, 23 Mar 2021 13:01:48 +0100 https://popups.uliege.be/esaform21/index.php?id=2129 https://popups.uliege.be/esaform21/index.php?id=2137 Titanium forming processes are often limited by severe adhesive wear as a result of poor friction conditions. This can be partially remedied with careful selection of lubricant, billet preparation and tool coating, but the optimal combination of these factors is not known. A full factorial ring compression experiment, with grade 2 commercially pure titanium rings deformed at 300 °C, was conducted to study the effect of each of these factors over three levels. The change in internal diameter was compared to a set of calibration curves generated by an FEA simulation of the process in order to determine the friction coefficient during each trial. A robust statistical analysis methodology was used to isolate and evaluate the effect of varying each factor. The choice of lubricant was found to be the most statistically significant factor by a considerable margin, followed by the method of billet preparation, with tool coating found to be insignificant. Of the lubricants tested, the graphite-based lubricant resulted in the lowest friction, followed by the WS2- and MoS2-based lubricants. Sandblasted billet surfaces resulted in similar friction to as-machined surfaces, whereas those subjected to micro-arc oxidation performed notably worse. For reducing friction during warm forming of titanium, a graphite-based lubricant is therefore recommended, with tool coating and billet surface preparation unlikely to provide significant further improvement. Tue, 23 Mar 2021 13:09:22 +0100 https://popups.uliege.be/esaform21/index.php?id=2137 https://popups.uliege.be/esaform21/index.php?id=3732 High process stability is needed in sheet metal forming industry. This can be achieved by predicting and controlling the transient process and temperature variation, especially at start of production. In this connection, the temperature induced friction changing plays a significant role because it leads to product failures. The handling of the transient friction effects is currently done reactively, based on the individual experience of the machine operators. In future, those transient effects need to be controlled. This paper shows initially an analysis of the temperature induced friction increase in a well-known and proven flat strip drawing test. Different tribological systems were tested at tool temperatures between 20 and 80 °C. The temperature increase results in a higher friction of up to 77 %. Several influences on friction increase will be presented. These friction influences were verified afterwards with a heated forming demonstrator under laboratory conditions. Mon, 29 Mar 2021 14:22:14 +0200 https://popups.uliege.be/esaform21/index.php?id=3732 https://popups.uliege.be/esaform21/index.php?id=3981 This experimental work focuses on the evaluation of deformation mechanisms due to sliding between carbon fiber tows with a flat tool in dry and lubricated with liquid resin conditions. The experiments were carried out on manually woven and single tows. The effect of angle between tow axes and sliding direction was also studied. The topography of the tows in contact with a sliding transparent glass plate was measured with a 3D optical microscope before and after sliding. These measurements revealed a decrease of roughness with sliding in all tested conditions, a contraction of lubricated single tows in perpendicular to sliding orientation, and high residual displacements in lubricated woven tows in 0°/90° orientation and dry single tows in perpendicular to sliding orientation. Tue, 30 Mar 2021 09:35:00 +0200 https://popups.uliege.be/esaform21/index.php?id=3981