Papers by Author: Joost R. Duflou

Abstract: Titanium alloys combine strength, low weight, and corrosion resistance, making them vital in high-performance industries; yet machining generates substantial chips that is difficult to recycle via conventional remelting due to contamination and high energy requirements, reducing material sustainability. Solid-state recycling methods, like Shear Assisted Processing and Extrusion (ShAPE), provide a promising alternative by consolidating chips below the melting point while preserving alloy chemistry. This study assesses the environmental performance of ShAPE across a system boundary spanning degreasing through consolidation and extrusion. Impacts were quantified using Cumulative Energy Demand (CED), Global Warming Potential, Environmental Footprint, Average Dissipation Rate (ADR), and Lost Potential Value (LPV), with ADR and LPV applied for the first time to solid-state recycling of scrap from discrete manufacturing. Scenario analyses addressed variations in torque, argon consumption, and electricity mix. Energy demand and CO₂-eq for the ShAPE process were estimated at 279.51-567.75 MJ and 17.22-32.35 kg per kg of wire, respectively, with sensitivity analysis showing that variations in torque constitute the dominant determinant of these environmental outcomes. While energy demand is comparable to, or moderately lower than, that of traditional wire fabrication only under low-and baseline-torque conditions, ShAPE substantially reduces the resource dissipation and lost material values, with its overall environmental impacts further decreasing by 45.45% when powered with greener electricity. These results highlight ShAPE as a viable route for circular titanium production, preserving material value & reducing dependence on primary extraction.

Abstract: This study investigates a hybrid manufacturing route combining heat-assisted Single Point Incremental Sheet Forming (SPIF) with Tungsten Inert Gas welding (TIG)-based material deposition for the local reinforcement of Mg–Zn–Zr (ZK61) alloy thin sheets. Flat and curved substrates extracted from SPIF-formed geometries were used to examine the influence of substrate thickness, forming temperature, and geometry on TIG deposition morphology and thermal distortion. The results indicate that heat input and substrate thickness strongly affect deposition morphology and dimensional stability, while SPIF sheet forming temperature influences the repeatability of the deposition process. In addition, deposition behavior exhibited limited sensitivity to substrate curvature for single depositions, whereas successive depositions resulted in increased thermal distortion due to cumulative residual stresses. Overall, this work identifies key process sensitivities and constraints associated with TIG deposition on SPIF-formed magnesium alloy sheets, providing a basis for the development of hybrid forming-deposition process chains for localized reinforcement applications.

Abstract: This paper discusses the thickness distributions calculated from surface strain measurements using stereo Digital Image Correlations (DIC) for parts produced with Single Point Incremental Forming (SPIF). The research is carried out on six benchmark cones and pyramids with each convex, straight and concave walls. The accuracy of the thickness calculations, under the assumption of material incompressibility and using the formula for the Green-Lagrange strains, is compared to the thickness distributions measured with a fringe projection scanner. The thickness estimations based on the measured strains proved to be representative for the measured thickness distributions with a mean error of 0.0182 mm, which corresponds to a relative error of 1.47 % of the mean measured thickness. However, errors of up to 0.1688 mm were found in areas of high wall angles and curvatures, corresponding to a relative maximal error of 13.69 % of the mean measured thickness. Hence, the DIC measurements are well suited for characterizing the thickness. Using the thicknesses calculated from the DIC measurements to find the minimal thickness as an indicator of part failure, is possible with relative errors that have an average overestimation of 2.87% of the minimal measured thickness.

Abstract: While Incremental Sheet Forming (ISF) is approaching accuracy levels suitable for industrial take-up for specific applications, limited forming angles are still a great concern, leaving many applications out of reach. In this paper a two sided strategy for multistep incremental forming is presented, aiming at increased uniform wall thickness. By sequentially forming steeper wall angles, alternating passes between front and back side of the sheet, wall angles up to 105.5° were successfully reached in AA3103 with a blank thickness of 1.5mm. A resulting minimal thickness of 0.4mm and thickness range of 0.2mm was achieved for the 105.5°part.

Abstract: Despite years of supporting research, commercial use of the Single Point Incremental Forming process remains very limited. The promised flexibility and lack of specific tooling is contradicted by its highly complex deformation mechanics, resulting in a process that is easy to implement but where workpiece accuracy is very difficult to control. This paper looks at geometry compensation as a viable control strategy to increase the accuracy of produced workpieces. The input geometry of the process can be compensated using knowledge about the deformations occurring during production. The deviations between the nominal CAD geometry and the actual produced geometry can be calculated in a variety of different ways, thus directly influencing the compensation. Two different alignment methods and three deviation calculation methods are explained in detail. Six combined deviation calculation methods are used to generate compensated inputs, which are experimentally produced and compared to the uncompensated part. All different methods are able to noticeably improve the accuracy, with the production alignment and closest point deviation calculation achieving the best results

Abstract: Pallets and forklifts equipped with Radio-Frequency Identification (RFID) technology can be a suitable option for bridging the information gap between cutting and bending stages in sheet metal production. However, a decision on how tagged pallets can be assigned to their content needs to be made. In this paper, a reactive and a proactive approach for the near-automatic identification of parts on pallets after cutting are discussed and their performance is evaluated through a series of simulations. In both approaches, the nesting information along with the measured net weight of the pallets are used to determine the parts on top of each pallet. The influence of the alternative solutions problem on the performance is investigated for both approaches. It is concluded that the actual decision on the approach selection depends on the time that is required for each recalculation and each pre-allocation. Those times are workshop dependent and, therefore, a decision should be made for each workshop specifically.

Abstract: Bump bending or step bending is a forming technique that allows making large radius bends in a sheet metal part by means of a series of bends performed close to each other. The bump bending process has been studied by means of both an experimental campaign and finite element analysis. High-strength steel Weldox 1300 and a punch of radius 30 mm have been used. The finite element calculations have been performed with Abaqus using the solid formulation and Implicit/Explicit solvers. The results of the finite element analysis have been validated experimentally by monitoring the bending process using a camera system aligned with the bending line. Experiments were performed on a press-brake with a capacity of 50 metric tons. Deflections of a sheet during and after bending have been measured using the images recorded by the camera. In order to investigate the influence of a new bend on a previously formed bend, experiments have been performed with different distances between two consecutive bends. Based on the experiments, the size of the affected zone for the bend has been measured. The dependence of the distance between two consecutive bends on the resulting global bending angle has been studied. Moreover the influence of the bump distance on the springback has been investigated.

Abstract: Various solid state or ‘meltless’ recycling techniques have recently been developed for light metal scrap in form of chips. Main objective of all approaches is to bypass the need for remelting in order to reduce the overall required energy, and to avoid the material losses that occur during this step. Within this paper, the use of Spark Plasma Sintering (SPS) is proposed as a novel solid state recycling/welding technique for sheet metal scrap. Aluminium 5182 alloy scrap, derived from sheet metal, was successfully consolidated into a fully dense billet via SPS. The use of pulsed electric current heating, in temperatures well below the alloy melting point, combined with mechanical pressure, enchased the densification process resulting into a void-less material. The recycled SPS sample was fully densified and microstructural investigation has been performed in order to confirm effective oxide film breakage. The results illustrate the effectiveness of SPS in aluminium scrap consolidation, also in form of sheet scrap, providing additional means in solid state recycling. The involved mechanisms that contribute to oxide film fracture and scrap consolidation in SPS are being discussed.Keywords: Aluminium, recycling, spark plasma sintering (SPS)

Abstract: Large radius air bending has a different loading diagram than conventional bending, which affects the material behavior during the bending process. In order to establish a correct loading diagram, the position of the contact points between the plate and the punch is determinant. The position of the contact points is depending on the evolution of the bending process and the influence of the material is unknown. In this work, the determination of the position of the contact points in large radius air bending has been studied by means of both an experimental campaign and finite element analysis. Experiments were performed on a press-brake with a capacity of 50 metric tons. High-strength steel Weldox 1300 and aluminum alloy AlMg₃, and punches of radii 30, 35 and 40 mm have been used. During the bending process, the punch movement has been monitored and the bending angle has been measured by means of images recorded by a camera system. Based on the obtained results, the relation between the bending angle and the position of the contact points is discussed.

Abstract: The aim of this study is to establish general guidelines for minimizing the number of tests required to determine optimum process parameters in terms of formability for laser assisted single point incremental forming (LASPIF). An automotive aluminium alloy (AA5182-O) is selected and the room temperature failure angle of this material is determined experimentally. The straining behaviour as well as sheet thinning of the test part (at its maximum forming angle) is studied using an experimentally validated finite element model. From the thinning rate of the sheet metal and the shape of the contact zone between tool and sheet it is concluded that continuous straining of the sheet on the wall region of the contact area is responsible for extra thinning and failure. Based on the size and position of the contact zone, different laser tool positioning strategies have been used to achieve the highest forming angle. It is concluded that due to an elongated shape of the contact zone in steep wall angle parts and considering a small deviation of the forming robot, the selection of a large spot diameter is necessary in terms of maximum obtainable wall angle. It has been observed that the maximum forming angle is still achievable using a large forward offset. It is concluded that the partial stress-relief annealing of the deformed geometry during the approach of the forming tool, is responsible for this formability enhancement.