Rapid manufacturing- state of the art, analysis and future perspectives

Layer based manufacturing system often referred to as Rapid Prototyping (RP) have been in existence for 22 years, in the past 5 years Rapid Manufacturing (RM) has emerged from these RP systems to produce functional and structural customer focused end use components and products. This keynote paper will review the current range of technologies for metallic systems, it will also evaluate the operating principles, features, potential and limitations of current commercially available systems. Rapid Manufacture is increasingly being used for high value difficult to manufacture components with a new set of design rules required to fully exploit the RM systems inherent characteristics. A case studies approach will be used to show the benefits and pitfalls this new design freedom can provide designers

Multi-objective Optimisation in Additive Manufacturing

Additive Manufacturing (AM) has demonstrated great potential to advance product design and manufacturing, and has showed higher flexibility than conventional manufacturing techniques for the production of small volume, complex and customised components. In an economy focused on the need to develop customised and hi-tech products, there is increasing interest in establishing AM technologies as a more efficient production approach for high value products such as aerospace and biomedical products. Nevertheless, the use of AM processes, for even small to medium volume production faces a number of issues in the current state of the technology. AM production is normally used for making parts with complex geometry which implicates the assessment of numerous processing options or choices; the wrong choice of process parameters can result in poor surface quality, onerous manufacturing time and energy waste, and thus increased production costs and resources. A few commonly used AM processes require the presence of cellular support structures for the production of overhanging parts. Depending on the object complexity their removal can be impossible or very time (and resources) consuming. Currently, there is a lack of tools to advise the AM operator on the optimal choice of process parameters. This prevents the diffusion of AM as an efficient production process for enterprises, and as affordable access to democratic product development for individual users. Research in literature has focused mainly on the optimisation of single criteria for AM production. An integrated predictive modelling and optimisation technique has not yet been well established for identifying an efficient process set up for complicated products which often involve critical building requirements. For instance, there are no robust methods for the optimal design of complex cellular support structures, and most of the software commercially available today does not provide adequate guidance on how to optimally orientate the part into the machine bed, or which particular combination of cellular structures need to be used as support. The choice of wrong support and orientation can degenerate into structure collapse during an AM process such as Selective Laser Melting (SLM), due to the high thermal stress in the junctions between fillets of different cells. Another issue of AM production is the limited parts’ surface quality typically generated by the discrete deposition and fusion of material. This research has focused on the formation of surface morphology of AM parts. Analysis of SLM parts showed that roughness measured was different from that predicted through a classic model based on pure geometrical consideration on the stair step profile. Experiments also revealed the presence of partially bonded particles on the surface; an explanation of this phenomenon has been proposed. Results have been integrated into a novel mathematical model for the prediction of surface roughness of SLM parts. The model formulated correctly describes the observed trend of the experimental data, and thus provides an accurate prediction of surface roughness. This thesis aims to deliver an effective computational methodology for the multi- objective optimisation of the main building conditions that affect process efficiency of AM production. For this purpose, mathematical models have been formulated for the determination of parts’ surface quality, manufacturing time and energy consumption, and for the design of optimal cellular support structures. All the predictive models have been used to evaluate multiple performance and costs objectives; all the objectives are typically contrasting; and all greatly affected by the part’s build orientation. A multi-objective optimisation technique has been developed to visualise and identify optimal trade-offs between all the contrastive objectives for the most efficient AM production. Hence, this thesis has delivered a decision support system to assist the operator in the "process planning" stage, in order to achieve optimal efficiency and sustainability in AM production through maximum material, time and energy savings.EADS Airbus, Great Western Researc

Tool manufacturing by metal casting in sand moulds produced by additive manufacturing processes

Thesis (D. Tech. ( Mechanical Engineering )) - Central University of technology, Free State, 2012In this study an alternative indirect Rapid Tooling process is proposed. It essentially consists of producing sand moulds by Additive Manufacturing (AM) processes followed by casting of tools in the moulds. Various features of this tool making method have been investigated. A process chain for the proposed tool manufacturing method was conceptually developed. This process chain referred to as Rapid Casting for Tooling (RCT) is made up of five steps including Computer Aided Design (CAD) modeling, casting simulation, AM of moulds, metal casting and finishing operations. A validation stage is also provided to determine the suitability of the tool geometry and material for RCT. The theoretical assessment of the RCT process chain indicated that it has potential benefits such as short manufacturing time, low manufacturing cost and good quality of tools in terms of surface finish and dimensional accuracy. Focusing on the step of AM of the sand moulds, the selection of available AM processes between the Laser Sintering (LS) using an EOSINT S 700 machine and Three Dimensional Printing using a Z-Corporation Spectrum 550 printer was addressed by means of the Analytic Hierarchy Process (AHP). The criteria considered at this stage were manufacturing time, manufacturing cost, surface finish and dimensional accuracy. LS was found to be the most suitable for RCT compared to Three Dimensional Printing. The overall preferences for these two alternatives were respectively calculated at 73% and 27%. LS was then used as the default AM process of sand moulds in the present research work. A practical implementation of RCT to the manufacturing of foundry tooling used a case study provided by a local foundry. It consisted of the production of a sand casting pattern in cast iron for a high pressure moulding machine. The investigation confirmed the feasibility of RCT for producing foundry tools. In addition it demonstrated the crucial role of casting simulation in the prevention of casting defects and the prediction of tool properties. The challenges of RCT were found to be exogenous mainly related to workmanship. An assessment of RCT manufacturing time and cost was conducted using the case study above mentioned as well as an additional one dealing with the manufacturing of an aluminium die for the production of lost wax patterns. Durations and prices of RCT steps were carefully recorded and aggregated. The results indicated that the AM of moulds was the rate determining and cost driving step of RCT if procurement of technology was considered to be a sunk cost. Overall RCT was found to be faster but more expensive than machining and investment casting. Modern surface analyses and scanning techniques were used to assess the quality of RCT tools in terms of surface finish and dimensional accuracy. The best surface finish obtained for the cast dies had Ra and Rz respectively equal to 3.23 μm and 11.38 μm. In terms of dimensional accuracy, 82% of cast die points coincided with die Computer Aided Design (CAD) data which is within the typical tolerances of sand cast products. The investigation also showed that mould coating contributed slightly to the improvement of the cast tool surface finish. Finally this study also found that the additive manufacturing of the sand mould was the chief factor responsible for the loss of dimensional accuracy. Because of the above, it was concluded that light machining will always be required to improve the surface finish and the dimensional accuracy of cast tools. Durability was the last characteristic of RCT tools to be assessed. This property was empirically inferred from the mechanical properties and metallographic analysis of castings. Merit of durability figures of 0.048 to 0.152 were obtained for the cast tools. It was found that tools obtained from Direct Croning (DC) moulds have merit of durability figures three times higher than the tools produced from Z-Cast moulds thus a better resistance to abrasion wear of the former tools compared to the latter

Effects of electroplating on the mechanical properties of stereolithography and laser sintered parts

This paper provides a quantitative and qualitative assessment of the effects of electroplating on polymer parts made by stereolithography and laser sintering. A series of test samples were coated with copper and nickel with varying thickness. Thicker coatings (120μm) were reproduced with a repeatability that should not adversely affect the tolerances with which such parts may be produced given the tolerances of the initial rapid prototyping processes themselves. Thinner coatings (20μm) resulted in a smother surface finish than thicker coatings for stereolithography parts, however the converse was true for laser-sintered parts. Composite theory was used to predict that thicker coating would lead to higher Young’s modulus in parts and this was shown to be true in physical tests although the practical values were lower than the predicted values especially for thicker coatings. Physical tests also confirmed that thicker coatings increased UTS and impact energy but had a minimal effect on the ductility of parts

Advances in Three Dimensional Printing - state of the art and future perspectives

Published ArticleThis paper surveys the current state and capabilities of Three Dimensional Printing (3DP). Based on its technical background - the ink jet printing as known from the printer and plotter industry - a classification structure has been developed and proposed. Different printing techniques and process concepts, together with their advantages and limitations are described and analysed. A large variety of manufacturing applications such as rapid pattern making and rapid tooling using the 3DP process directly or as core technology, as well as further implications in design and engineering analysis, medicine, and architecture are presented and evaluated. Some research issues are also discussed. An attempt, based on the state of the art, to show weaknesses and opportunities, and to draw conclusions about the future of this important process wraps up this paper

Analysis of the Accuracy and the Surface Roughness of FDM/FFF Technology and Optimisation of Process Parameters

The work deals with the influence of process parameters on the quality and accuracy of parts produced by FDM (Fused Deposition Modelling)/FFF (Fused filament fabrication) technologies. The experiments were carried out on the 3D Ultimaker printer, PLA (Polylactid Acid) thermoplastics were used as the test materials. The practical part is divided into 3 experiments. First, the optimum temperature was set. In the next part, the parameters of retraction rate, retraction length and crossing speed were determined. In the last part, the impact of 13 parameters on the printing time, material consumption, surface quality and accuracy were determined. In this part of the experiment, the effect of the factors on the quality indicators was determined using the DoE Taguchi methodology. Subsequently, the influential parameters were determined by Paret\u27s rule. The results showed how layer height and print speed are the most important factor for the print time. The parameters-percent filling, number of walls, and the height of the layer were marked as essential parameters affecting the material\u27s consumption. The surface roughness and dimensional accuracy are most influenced by the height of the layer

The investigation of a method to generate conformal lattice structures for additive manufacturing

Additive manufacturing (AM) allows a geometric complexity in products not seen in conventional manufacturing. This geometric freedom facilitates the design and fabrication of conformal hierarchical structures. Entire parts or regions of a part can be populated with lattice structure, designed to exhibit properties that differ from the solid material used in fabrication. Current computer aided design (CAD) software used to design products is not suitable for the generation of lattice structure models. Although conceptually simple, the memory requirements to store a virtual CAD model of a lattice structure are prohibitively high. Conventional CAD software defines geometry through boundary representation (B-rep); shapes are described by the connectivity of faces, edges and vertices. While useful for representing accurate models of complex shape, the sheer quantity of individual surfaces required to represent each of the relatively simple individual struts that comprise a lattice structure ensure that memory limitations are soon reached. Additionally, the conventional data flow from CAD to manufactured part is arduous, involving several conversions between file formats. As well as a lengthy process, each conversion risks the generation of geometric errors that must be fixed before manufacture. A method was developed to specifically generate large arrays of lattice structures, based on a general voxel modelling method identified in the literature review. The method is much less sensitive to geometric complexity than conventional methods and thus facilitates the design of considerably more complex structures. The ability to grade structure designs across regions of a part (termed functional grading ) was also investigated, as well as a method to retain connectivity between boundary struts of a conformal structure. In addition, the method streamlines the data flow from design to manufacture: earlier steps of the data conversion process are bypassed entirely. The effect of the modelling method on surface roughness of parts produced was investigated, as voxel models define boundaries with discrete, stepped blocks. It was concluded that the effect of this stepping on surface roughness was minimal. This thesis concludes with suggestions for further work to improve the efficiency, capability and usability of the conformal structure method developed in this work

Build orientation optimization of car hoodvent with additive manufacturing

Additive manufacturing is a widely used process consisting in the building of a three-dimensional (3D) object from a model projected on a computer, adding the material layer-by-layer. This technology allows the printing of complex shape objects and is being increasingly adopted by the aircraft industry, medical implants, jewelry, footwear, automotive, fashion products, among others. The build orientation optimization of 3D models has a great influence on costs and surface quality when printing three-dimensional objects. In this work, three build orientation optimization problems are studied: single objective problem, bi-objective problem and many-objective problem. To this end, three quality measures are applied: the support area, the build time and the surface roughness, for the Car Hoodvent model. First, a single-objective optimization problem is presented and solved by the genetic algorithm, obtaining optimal solutions for each objective function. Then, the study of the bi-objective optimization problem is carried out for each pair of two objectives and some representative trade-off solutions are identified. Finally, the study of the many objective optimization problem, considering the three measures optimized simultaneously, is presented with some more optimal solutions found. The bi-objective and many-objective problems are solved by a multi-objective genetic algorithm. For a better analysis and comparison of the solutions found, the Pareto fronts are used, enabling a better visualization of the solutions between the objectives. This study aims to assist the decision-maker in choosing the best part print orientation angles according to his/her preferences. The optimal solutions found confirmed the effectiveness of the proposed approach.info:eu-repo/semantics/publishedVersio

Improving additive manufacturing performance by build orientation optimization

Additive manufacturing (AM) is an emerging type of production technology to create three-dimensional objects layer-by-layer directly from a 3D CAD model. AM is being extensively used in several areas by engineers and designers. Build orientation is a critical issue in AM since it is associated with the part accuracy, the number of supports required and the processing time to produce the object. This paper presents an optimization approach to solve the part build orientation problem taking into account some characteristics or measures that can affect the accuracy of the part, namely the volumetric error, the support area, the staircase effect, the build time, the surface roughness and the surface quality. A global optimization method, the Electromagnetism-like algorithm, is used to solve the part build orientation problem.The authors are grateful to the anonymous referees for their fruitfulcomments and suggestions. This work has been supported and developed under the FIBR3Dproject - Hybrid processes based on additive manufacturing of composites with long or shortfibers reinforced thermoplastic matrix (POCI-01-0145-FEDER-016414), supported by theLisbon Regional Operational Programme 2020, under the PORTUGAL 2020 PartnershipAgreement, through the European Regional Development Fund (ERDF). This work hasbeen also supported by national funds through FCT - Funda ̧c ̃ao para a Ciˆencia e Tecnologiawithin the Project Scope: UID/CEC/00319/201