Development of a novel differential velocity sideways extrusion process for forming curved profiles with fine grains and high strength

The aim of this study is to develop a novel process, differential velocity sideways extrusion (DVSE), for forming curved profiles with fine grains and high strength. In this new forming-bending-refining process, billets are used as the work-piece material to directly form curved profiles with certain cross-sections in order to increase the manufacturing efficiency and decrease the bending defects in conventional bending process. The DVSE process has been studied in this thesis by using forming experiments, microstructure characterisation experiments, finite element (FE) modelling and theoretical modelling. A tool set enabling sideways extrusion to be performed using opposing punches moving with different velocities was designed and manufactured. Plasticine was used as a model work-piece material and a series of compression tests were undertaken, to determine its constitutive properties and gain an estimate of work-piece die friction for use in process simulation. Feasibility studies for the DVSE process were carried out through a series of designed experimental programmes on plasticine, in which punch/extrusion velocity ratio, extrusion ratio and die land length were process parameters. Ultimately, trial tests using AA1050 at room temperature and AZ31 at elevated temperatures were conducted. Effects of extrusion velocity ratio, extrusion ratio, die land length, forming temperature and strain rate on profile curvature were studied. The microstructure evolution of the formed curved AA1050 bar by DVSE at room temperature was studied through EBSD. The evolution of grain structure and texture of formed curved AZ31 bars at different DVSE process conditions (temperature and strain rate) was investigated through optical microscopy and EBSD, and the optimum temperature and strain rate condition for obtaining fine equiaxed and homogeneous microstructure was identified. The different grain refinement mechanisms of AA1050 and AZ31 during the DVSE process were revealed. Micro-hardness of formed curved AA1050 and AZ31 bars was examined. Process mechanics of DVSE were modelled using FE modelling and upper bound theorem. The extent of work-piece flow velocity gradient across the die exit orifice, which causes curvature, was identified. A dead zone of roughly triangular shape, which exists on the chamber wall opposite the die exit orifice, was determined. The effective strain of the formed curved profiles was studied to confirm the rise of severe plastic deformation (SPD). The effective strain rate in the intersection regions of the channels was investigated to identify the source of severe plastic deformation. An analytical upper-bound-based model has been developed with the consideration of the determined dead zone. The extrusion force and curvature predicted by the analytical method agreed reasonably well with results from experiments and FE modelling. Discussions were made about the correlations between experimental and modelling approaches and results. The relationships between mechanical properties (yield strength, ultimate tensile strength, and elongation to failure) and microstructures (grain size, micro-texture) of formed curved profiles were correlated. From the experimental and modelling work, it has been demonstrated that the DVSE process proposed in this thesis is an effective way to efficiently form curved aluminium and magnesium profiles with controlled curvature and improved properties.Open Acces

Upper bound analysis of differential velocity sideways extrusion process for curved profiles using a fan-shaped flow line model

An analytical model for predicting the shapes of rectangular bars with variable curvatures along their lengths through a novel forming method, differential velocity sideways extrusion (DVSE), previously proposed by the authors, has been developed on the basis of the upper bound method. A new flow line function was presented to describe its deformation field. The plastic deformation zone (PDZ) was assumed to be fan-shaped, where the trajectory of the material flow within the PDZ had an elliptic shape. The proposed continuous flow line function was validated using finite element simulations. The flow patterns, extrusion pressure, curvature, and effective strain predicted by the analytical solutions agreed well with modelling results. Compared to the classical discontinuous simple shear model of channel angular extrusion (CAE) with a 90° die, the new approach was shown to predict the effective strain more closely

Utilizing RepRap Style 3D Printers for the Manufacturing of Composite Heat Exchangers

The low cost 3D printing market is currently dominated by the application of RepRap (self-replicating rapid-prototyper) variants. Presented in this document are practical utilizations of RepRap technology. Developed are innovative processes to manufacture composite materials systems for thermal management solutions. First, a laser polymer welder system is validated by quantifying maximum peak load and weld width of linear low density polyethylene (LLDPE) lap welds as a function of linear energy density. The development of practical engineering data, in this application, is critical to producing mechanically durable welds. Developed laser and printer parameter sets allow for manufacturing of LLDPE multi-layered heat exchangers Second, newly introduced metal-polymer composite materials (e.g. copper-PLA, bronze-PLA, iron-PLA and stainless steel-PLA) were shown to influence the thermal conductivity (W/m·K) of the composite matrix. Increased volume percentage of metallic constituent was shown to increase thermal conductivity. Air void fraction, a resultant of the manufacturing process, reduced the bulk composite 3D printed component. No significant effects were realized dependent upon the metallic constituent morphology (i.e. flake-like vs. spherical). Third, development and fabrication of a large format multi-head RepRap 3D printer displays the ability of large-scale manufacturing potential. Energy efficiencies are realized upon utilization of all hot-ends (i.e. the embodied energy of each printer movement (X, Y and Z)) and are simultaneously shown at each hot-end. Furthermore, multi-head format printers are proven to develop composite components. Utilizing a novel weaving and layering method 1000-series aluminum wire is embedded into a polyethylene terephthalate glycol modified (PETG) matrix. Parametric customized gcode commands allow for innovative manufacturing. In total, laser parameter development, material characterization, custom machine fabrication and printing process development are quantified. The three presented projects demonstrate the engineering advancement of RepRap technology in application to thermal management solutions and composite material development

Fabricate 2020

Fabricate 2020 is the fourth title in the FABRICATE series on the theme of digital fabrication and published in conjunction with a triennial conference (London, April 2020). The book features cutting-edge built projects and work-in-progress from both academia and practice. It brings together pioneers in design and making from across the fields of architecture, construction, engineering, manufacturing, materials technology and computation. Fabricate 2020 includes 32 illustrated articles punctuated by four conversations between world-leading experts from design to engineering, discussing themes such as drawing-to-production, behavioural composites, robotic assembly, and digital craft

Centrifugal assembly of bijel ropes via helical microfluidics

Bicontinuous interfacially jammed emulsion gels (bijels) are soft materials that retain a liquid bicontinuous network stabilized by an interfacially jammed layer of nanoparticles. In this thesis, we investigated a microfluidic twisting method to fabricate micro-ropes of nano-structured bijel fibers. This method shows how weak microfibers with tensile strengths of a few kPa can be reinforced by 4 orders of magnitude by means of microfluidic twisting. Microfluidic twisting allows to produce continuous bijel fiber ropes of controllable architecture. Modelling the fluid flow field reveals the rope geometry dependence on a subtle force balance composed of rotational and translational shear stresses. However, the direction of the centrifugal force determines whether microropes undergo undulation during microfluidic twisting. The undulation of ropes can be avoided by decreasing the density of the fiber casting mixture, or upon increasing the density of the co-flowing liquid, enabling a controlled and continuous collection of uniform microropes. We envision microfluidic twisting to enable the fabrication of new composite materials with applications in flexible electronics, micro robotics, actuators, and tissue engineering. Furthermore, the knowledge gained from this thesis will facilitate future studies of microfiber twisting, as well as the assembly of particles, emulsion droplets or biological cells via microfluidic twisting

Inflatable pillow system as a glass substitute in terms of building envelope

Thesis (Master)--İzmir Institute of Technology, Architecture, İzmir, 2003Includes bibliographical references (leaves: 169-171)Text in English; Abstract: Turkish and Englishxiii, 174 leavesIn the line with the increasing energy demand, there have been many investigations related with the conservation of energy used in buildings. The systems and materials used in buildings have an important role in consumption of energy. Transparent materials and the systems occupies transparent materials contributes this consumption in positive and negative way due to their design and properties. Nevertheless, the transparent materials used in buildings as glazing have importance in order to increase comfort, decrease cost and environmental harm.This study aims to investigate a contemporary construction system; ETFE foil pillow system, which is also known as, Inflatable Pillow System made of ETFE Foil. In the scope of the study, pneumatic pillow system investigated in detail and its performance evaluated due to environmental control criteria, which can be compared with other conventional glass glazing products. The study also involves cost analysis and brief knowledge about contemporary cases that have been completely or partially constructed with this system. The increase in the amount of transparent surfaces in contemporary buildings, pointed out that the conventional glazing system are no more appropriate. Therefore, in specific cases, usage of conventional glass glazing systems results as a cost increase and loss of comfort. The alternatives of the conventional glazing systems don.t have appropriate performance or don.t meet the need of the consumer. Inflatable ETFE foil pillows have better optical properties than glass glazing systems. Generally, thermal properties of this system equal to the advanced double-glazing. Light and heat transmission values vary by changing the foil type and number of layer. Low sound reduction index can be an obstacle or a chance for designers that should be given attention in design phase. The pillow system that relatively provides fire and earthquake protection is also lightweight and flexible. Thus, includes many criteria that are expected in contemporary constructions. The inflatable pillow system made of ETFE foil can be considered as a safe construction method due to mechanical properties of the system and the membrane material that is used as pillows. System reduces operational and maintenance cost for the building. Considerable amount of expenses for lighting and heating can also be reduced by the usage of the pillow system. The lightweight nature of the pillow system affects the construction of the whole building, which also results as a cost reduction.Pillow system is commonly used for greenhouses and botanical gardens and also used for sports and leisure halls as well as institutions ands museums. Addition to its usage as a skylight or façade cover, pillow system can be used as a total envelope that covers the whole construction underneath.As a result, this study investigates ETFE foil pillows and their environmental control properties against conventional glass glazing systems. The results are evaluated in the line with the information gained. The advantages and disadvantages of the system as a glazing are given in detail. Although it.s not expected that ETFE pillow system totally be replaced with the conventional glass glazing system, it constitutes an alternative glazing system in specific cases.Keywords: pillow system, pneumatic membrane, glazing, ETFE foil, glass, fluoropolymer, environmental control criteria

Polymers and Their Application in 3D Printing

Dear Colleagues, Fused filament fabrication, also known as 3D printing, is extensively used to produce prototypes for applications in, e.g., the aerospace, medical, and automotive industries. In this process, a thermoplastic polymer is fed into a liquefier that extrudes a filament while moving in successive X–Y planes along the Z direction to fabricate a 3D part in a layer-by-layer process. Due to the progressive advances of this process in industry, the application of polymeric (or even composite) materials have received much attention. Researchers and industries now engage in 3D printing by implementing numerous polymeric materials in their domain. In this Special Issue, we will present a collection of recent and novel works regarding the application of polymers in 3D printing