Non-Uniform Offsetting and its Applications in Laser Path Planning of Sterolithography Machine

Laser path planning is an important step in solid freeform fabrication processes such as Stereolithography (SLA). An important consideration in the laser path planning is to compensate the shape of laser beam. Currently the compensation is divided into two steps, Z-compensation and X-Y compensation, and the shape of laser beam is assumed to be uniform for the whole platform. In this research, we present a sampling based non-uniform offsetting method which accounts for the different shapes of laser beam at various locations. We discuss the related steps and algorithms. We demonstrate its effectiveness by using various test cases. Besides improving the accuracy of SLA machine, non-uniform offsetting can also be applied to address other accuracy issues caused by thermal and structural variationsMechanical Engineerin

Design of bifurcation junctions in artificial vascular vessels additively manufactured for skin tissue engineering

Construction of an artificial vascular network ready for its additive manufacturing is an important task in tissue engineering. This paper presents a set of simple mathematical algorithms for the computer-aided design of complex three dimensional vascular networks. Firstly various existing mathematical methods from the literature are reviewed and simplified for the convenience of applications in tissue engineering. This leads to a complete and step by step method for the construction of an artificial vascular network. Secondly a systematic parametric study is presented to illustrate how the various parameters in the vascular junction model affect the key factors that have to be controlled when designing the bifurcation junctions of a vascular network. These results are presented as a set of simple design rules and a design map which serve as a convenient guide for tissue engineering researchers when constructing artificial vascular networks

Inductive machine learning of optimal modular structures: Estimating solutions using support vector machines

Structural optimization is usually handled by iterative methods requiring repeated samples of a physics-based model, but this process can be computationally demanding. Given a set of previously optimized structures of the same topology, this paper uses inductive learning to replace this optimization process entirely by deriving a function that directly maps any given load to an optimal geometry. A support vector machine is trained to determine the optimal geometry of individual modules of a space frame structure given a specified load condition. Structures produced by learning are compared against those found by a standard gradient descent optimization, both as individual modules and then as a composite structure. The primary motivation for this is speed, and results show the process is highly efficient for cases in which similar optimizations must be performed repeatedly. The function learned by the algorithm can approximate the result of optimization very closely after sufficient training, and has also been found effective at generalizing the underlying optima to produce structures that perform better than those found by standard iterative methods

Characterization of a soft pneumatic actuator using fe modelling

Actuators are devices that provides controlled changes regarding their displacement and position. They can be triggered by different inputs, one of them being fluids. Pneumatic actuators are commonly used in different areas. Rigid pneumatic actuators present multiple disadvantages, in size, weight, etc. limiting the application in other areas like soft robotic and biomechanics. On the other hand, soft actuators possess big advantages in comparison with the rigid ones. The materials used give them an advantage in geometry, cost, etc. Yet, the development of this new technology is not fully understood due to the material properties in the manufacturing process. 3D printing is seen as one of the most feasible manufacturing processes for this new technology. However, the information regarding the topic is limited. This study will focus into the characterization of 3D printed soft pneumatic actuator using as material silicone, especially in how the properties change when 3D printed with different printing orientations. Simulations were run using ANSYS and the results showed that the bellow printed at 90° has a higher resistance in the pressure applied and the 45° has a bigger deformation with a lower pressure

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

Triangulation of 3D Surfaces Recovered from STL Grids

In the present paper, an algorithm for the discretization of parametric 3D surfaces has been extended to the family of discrete surfaces represented by stereolithography (STL) grids. The STL file format, developed for the rapid prototyping industry, is an attractive alternative to surface representation in solid modeling. Initially, a boundary representation is constructed from the STL file using feature recognition. Then a smooth surface is recovered over the original STL grid using an interpolating subdivision procedure. Finally, the reconstructed surface is subjected to the triangulation accomplished using the advancing front technique operating directly on the surface. The capability of the proposed methodology is illustrated on an example.

Investigation of the effect of relative humidity on additive manufactured polymers by depth-sensing indentation

Additive manufacturing methods have been developed from rapid prototyping techniques and are now being considered as alternatives to conventional techniques of manufacturing. Stereolithography is one of the main additive methods and is considered highly accurate and consistent. Polymers are used as stereolithography materials and exhibit features such as high strength-to-weight ratio, corrosion resistance, ease of manufacturing and good thermal and electrical resistance properties. However, they are sensitive to environmental factors such as temperature, moisture and UV light, with moisture being identified as one of the most important factors that affect their properties. Moisture generally has an adverse effect on the mechanical properties of polymers. Investigation of the effects of moisture on polymers can be carried out using a number of experimental techniques; however, the benefits of the depth sensing indentation method over bulk tests include its ability to characterise various mechanical properties in a single test from only a small volume of material and the investigation of spatial variation in mechanical properties near the surface. The aim of this research was to investigate the effects of varying relative humidity on the indentation behaviour of stereolithography polymers and to develop a modelling methodology that can predict this behaviour under various humidities. It was achieved by a combination of experimental and numerical methods. Depth sensing indentation experiments were carried out at 33.5 %, 53.8 %, 75.3 % and 84.5 % RH (relative humidity) and 22.5 °C temperature to investigate the effects of varying humidity on the micron scale properties of the stereolithography resin, Accura 60. In order to minimise the effects of creep on the calculated properties, appropriate loading and unloading rates with suitable dwell period were selected and indentation data was analysed using the Oliver and Pharr method (1992). A humidity control unit fitted to the machine was used to condition the samples and regulate humidity during testing. Samples were also preconditioned at 33.5 %, 53.8 %, 75.3 % and 84.5 % RH using saturated salt solutions and were tested at 33.5 % RH using humidity control unit. It was seen that properties such as indentation depth increased and contact iv hardness and contact modulus decreased with increasing RH. The samples conditioned and tested using the humidity control unit at high RH showed a greater effect of moisture than the preconditioned samples tested at 33.5 % RH. This was because the samples preconditioned at high RH exhibited surface desorption of moisture when tested at ambient RH, resulting in some recovery of the mechanical properties. In order to investigate these further, tests were performed periodically on saturated samples after drying. Ten days drying of samples conditioned for five days at 84.5 % RH provided significant, though not complete, recovery in the mechanical properties. These tests confirmed that Accura 60 is highly hygroscopic and its mechanical properties are a function of RH and removal of moisture leads to a significant recovery of the original mechanical properties

Optimized normal and distance matching for heterogeneous object modeling

This paper presents a new optimization methodology of material blending for heterogeneous object modeling by matching the material governing features for designing a heterogeneous object. The proposed method establishes point-to-point correspondence represented by a set of connecting lines between two material directrices. To blend the material features between the directrices, a heuristic optimization method developed with the objective is to maximize the sum of the inner products of the unit normals at the end points of the connecting lines and minimize the sum of the lengths of connecting lines. The geometric features with material information are matched to generate non-self-intersecting and non-twisted connecting surfaces. By subdividing the connecting lines into equal number of segments, a series of intermediate piecewise curves are generated to represent the material metamorphosis between the governing material features. Alternatively, a dynamic programming approach developed in our earlier work is presented for comparison purposes. Result and computational efficiency of the proposed heuristic method is also compared with earlier techniques in the literature. Computer interface implementation and illustrative examples are also presented in this paper

Advanced Applications of Rapid Prototyping Technology in Modern Engineering

Rapid prototyping (RP) technology has been widely known and appreciated due to its flexible and customized manufacturing capabilities. The widely studied RP techniques include stereolithography apparatus (SLA), selective laser sintering (SLS), three-dimensional printing (3DP), fused deposition modeling (FDM), 3D plotting, solid ground curing (SGC), multiphase jet solidification (MJS), laminated object manufacturing (LOM). Different techniques are associated with different materials and/or processing principles and thus are devoted to specific applications. RP technology has no longer been only for prototype building rather has been extended for real industrial manufacturing solutions. Today, the RP technology has contributed to almost all engineering areas that include mechanical, materials, industrial, aerospace, electrical and most recently biomedical engineering. This book aims to present the advanced development of RP technologies in various engineering areas as the solutions to the real world engineering problems

A CAE approach for the stress analysis of gear models by 3D digital photoelasticity

The use of numerical and experimental methods to determine the stress field of mechanical components is well known. In particular, 3D photoelasticity can be considered the only experimental technique for the complete stress state evaluation of 3D components. The advent of rapid prototyping techniques has allowed the manufacturing of complex models in a matter of hours by using birifrangent materials. The present paper is focused on the description of a Computer Aided Engineering (CAE) approach which combines Finite Element (FE) simulations and automatic photoelastic investigations for the stress analysis of face gear drives, made by stereolithography. Computer Aided Design (CAD) geometries, used to manufacture the stereolithographic models, are directly used to perform FE analyses, thus allowing the stress analysis process to become simpler and easier. The substantial agreement observed between experimental and numerical results proved the potentialities of the adopted approach and the usefulness of FE simulations to optimize photoelastic analyses through cost- and time-effective experiments even for complex 3D shapes