Variable fused deposition modelling - concept design and tool path generation

Current Fused Deposition Modelling (FDM) techniques use fixed diameter nozzles to deposit a filament of plastic layer by layer. The consequence is that the same small nozzle, essential for fine details, is also used to fill in relatively large volumes. In practice a Pareto-optimal nozzle diameter is chosen that attempts to maximise resolution while minimising build time. This paper introduces a concept for adapting an additive manufacturing system, which exploits a variable diameter nozzle for the fused deposition of polymers. The variable nozzle allows the print resolution and the build speed to become independent variables which may be optimised. The paper discusses a concept design for the variable diameter nozzle to be fitted to a RapMan 3D printer and the software used to generate the tool paths for the extrusion head. The methodology involves the use of existing software solutions to gather basic data from STL files and generate the tool paths. A method for integrating the data and the deposition system is proposed. The challenges and possibilities of the technology are discussed as well as future research

Using the Finite Element Method to Determine the Temperature Distributions in Hot-wire Cutting.

Hot-wire cutting is a common material removal process used to shape and sculpt plastic foam materials, such as expanded polystyrene (EPS). Due to the low cost and sculpt-ability of plastic foams they are popular materials for large sized (> 1 m³) prototypes and bespoke visual artefacts. Recent developments in robotic foam sculpting machines have greatly increased the ability of hot-tools to sculpt complex geometrical surfaces bringing the subject into the realm of subtractive rapid prototyping/manufacturing. Nevertheless foam cut objects are not being exploited to their full potential due to the common perception that hot-wires are a low accuracy cutting tool. If greater accuracy for hot-wires can be obtained, it could provide a low cost method of producing high value functional engineering parts. Polystyrene patterns for lost foam casting are one such possibility. A nonlinear transient thermal finite element model was developed with the purpose of predicting the kerf width of hot-wire cut foams. Accurate predictions of the kerfwidth during cutting will allow the tool paths to be corrected off-line at the tool definition stage of the CAM process. Finite element analysis software (ANSYS) was used to simulate the hot-wire plastic foam cutting. The material property models were compiled from experimental data and commonly accepted values found in literature. The simulations showed good agreement with the experimental data and thus the model is thought to be reliable. The simulations provide an effective method of predicting kerf widths, under steady state cutting conditions. Limitations and further developments to the model are described

A Review of State-of-the-Art Large Sized Foam Cutting Rapid Prototyping and Manufacturing Technologies.

Purpose – Current additive rapid prototyping (RP) technologies fail to efficiently produce objects greater than 0.5?m3 due to restrictions in build size, build time and cost. A need exists to develop RP and manufacturing technologies capable of producing large objects in a rapid manner directly from computer-aided design data. Foam cutting RP is a relatively new technology capable of producing large complex objects using inexpensive materials. The purpose of this paper is to describe nine such technologies that have been developed or are currently being developed at institutions around the world. The relative merits of each system are discussed. Recommendations are given with the aim of enhancing the performance of existing and future foam cutting RP systems. Design/methodology/approach – The review is based on an extensive literature review covering academic publications, company documents and web site information. Findings – The paper provides insights into the different machine configurations and cutting strategies. The most successful machines and cutting strategies are identified. Research limitations/implications – Most of the foam cutting RP systems described have not been developed to the commercial level, thus a benchmark study directly comparing the nine systems was not possible. Originality/value – This paper provides the first overview of foam cutting RP technology, a field which is over a decade old. The information contained in this paper will help improve future developments in foam cutting RP systems

Electrospinning predictions using artificial neural networks

Electrospinning is a relatively simple method of producing nanofibres. Currently there is no method to predict the characteristics of electrospun fibres produced from a wide range of polymer/solvent combinations and concentrations without first measuring a number of solution properties. This paper shows how artificial neural networks can be trained to make electrospinning predictions using only commonly available prior knowledge of the polymer and solvent. Firstly, a probabilistic neural network was trained to predict the classification of three possibilities: no fibres (electrospraying); beaded fibres; and smooth fibres with > 80% correct predictions. Secondly, a generalised neural network was trained to predict fibre diameter with an average absolute percentage error of 22.3% for the validation data. These predictive tools can be used to reduce the parameter space before scoping exercises

Research Towards High Speed Freeforming

Additive manufacturing (AM) methods are currently utilised for the manufacture of prototypes and low volume, high cost parts. This is because in most cases the high material costs and low volumetric deposition rates of AM parts result in higher per part cost than traditional manufacturing methods. This paper brings together recent research aimed at improving the economics of AM, in particular Extrusion Freeforming (EF). A new class of machine is described called High Speed Additive Manufacturing (HSAM) in which software, hardware and materials advances are aggregated. HSAM could be cost competitive with injection moulding for medium sized medium quantity parts. A general outline for a HSAM machine and supply chain is provided along with future required research

Design of conformal cooling layers with self-supporting lattices for additively manufactured tooling

Additively manufactured (AM) conformal cooling channels are currently the state of the art for high performing tooling with reduced cycle times. This paper introduces the concept of conformal cooling layers which challenges the status quo in providing higher heat transfer rates that also provide less variation in tooling temperatures. The cooling layers are filled with self-supporting repeatable unit cells that form a lattice throughout the cooling layers. The lattices increase fluid vorticity which improves convective heat transfer. Mechanical testing of the lattices shows that the design of the unit cell significantly varies the compression characteristics. A virtual case study of the injection moulding of a plastic enclosure is used to compare the performance of conformal cooling layers with that of conventional (drilled) cooling channels and conformal (AM) cooling channels. The results show the conformal layers reduce cooling time by 26.34% over conventional cooling channels

Design and evaluation of additively manufactured parts with three dimensional continuous fibre reinforcement.

Additive manufacturing (AM) provides many benefits such as reduced manufacturing lead times, streamlined supply chains, part consolidation, structural optimisation and improved buy-to-fly ratios. Barriers to adoption include high material and processing costs, low build rates, isotropic material properties, and variable processing conditions. Currently AM polymer parts are far less expensive to manufacture than AM metal parts, therefore improving the properties of polymer parts is highly desirable. This paper introduces a design methodology used to integrate continuous reinforcement into AM polymer parts with the aim of improving their mechanical properties. The method is validated with the design and testing of three case studies, a pulley housing, hook and universal joint used to demonstrate the applicability of the method for tensile, bending and torsion loading types respectively. Physical testing showed that it was possible to improve the strength of parts by over 4000%, elongation to failure by over 2000% and stiffness by approximately 200%. In addition a method of integrating condition monitoring capabilities into the parts was demonstrated. An analysis of the specific strength of the parts suggests that the reinforced parts are comparable to aluminium alloys, suggesting that in some cases AM polymer composite parts could supplant more costly metal parts

Tensile and fatigue failure of 3D printed parts with continuous fibre reinforcement

This paper introduces a design methodology used to integrate continuous fibre reinforcement into AM polymer parts with the aim of improving their mechanical properties. Tensile and low cycle fatigue testing of reinforced parts is carried out for a range of load conditions and strain rates Physical testing showed that it was possible to improve the strength of parts by 400% and cycles to failure by 42,800% with the addition of 4% carbon by weight. Logarithmic load/cycle relationships were found also samples showed significant variability in the number of cycles to failure. No correlation between the density of the polylactic acid (PLA) infill and the tensile strength or low cycle fatigue life. Access holes used to thread the fibre into the reinforcement channels were identified as stress concentrators initiating cracks in the PLA and separation of the reinforcement from the PLA part

Plastic Foam Cutting Mechanics for Rapid Prototyping and Manufacturing Purposes

Development of foam cutting machines for rapid prototyping and manufacturing purposes began shortly after the first additive manufacturing machines became commercialised in the late 1980s. Increased computer power, the development and adoption of CAD/CAM software and rising demand for customisation has caused the rapid prototyping industry to grow swiftly in recent decades. While conventional rapid prototyping technologies are continuing to improve in speed and accuracy the ability to produce large (> 1m³) prototypes, moulds or parts it is still expensive, time consuming and often impossible. Foam cutting rapid prototyping and manufacturing machines are ideally suited to fulfil this niche because of their high speed, large working volumes and inexpensive working materials. Few foam cutting rapid prototyping machines have been commercialised to-date leaving significant opportunities for research and development in this area. Thermal plastic foam cutting is the material removal process most commonly used in foam cutting rapid prototyping to shape or sculpt the plastic foam into desired shapes and sizes. The process is achieved by introducing a heat source (generally a wire or ribbon) which alters the physical properties of the plastic foam and allows low cutting forces to be achieved. In thermal plastic foam cutting the heat source is generated via Joule (electrical) heating. This study investigates the plastic foam cutting process using experimental cutting trials and finite element analysis. The first part of this thesis presents an introduction to conventional foam cutting machines and rapid prototyping machines. It is suggested that a market opportunity lies out of reach of both of these groups of machines. By combining attributes from each, foam cutting rapid prototyping machines can be developed to fill the gap. The second part of this thesis introduces the state-of-the-art in foam cutting rapid prototyping and investigates previous research into plastic foam cutting mechanics. The third part of this thesis describes cutting trials used to determine important factors which influence plastic foam cutting. Collectively over 800 individual cutting tests were made. The cutting trials included two main material sets, expanded polystyrene and extruded polystyrene, three different wire diameters, two hot-ribbon configurations and a wide range of feed rates and power inputs. For each cut the cutting force, wire temperature and kerf width was measured as well as observations of the surface texture. The data was then analysed and empirical relationships were identified. An excel spreadsheet is established which allows the calculation of important outcomes, such as kerf width, based on chosen inputs. Quantitative measurements of the surface roughness and form, of cuts made with hot-tools, will not be addressed in this thesis. This body of work is currently under investigation by a colleague within the FAST group. The fourth part of this thesis describes the formation of a nonlinear transient two-dimensional heat transfer finite element model, which is developed for plastic foam cutting simulations. The conclusion is that the cutting trials contributed to a better understanding of plastic foam cutting mechanics. A new parameter was identified called the mass specific effective heat input, which is a function of the foam material and the cutting tool, it allows the prediction of cutting conditions with given cutting parameters and hence provides the necessary relationships needed for adaptive automated foam sculpting. Simulation results were validated by comparison with experimental data and provide a strong base for further developments including optimisation processes with adaptive control for kerf width (cut error) minimization. This study has added considerably to the pool of knowledge for foam cutting with a hot-tool. In general, much of the work reported herein has not been previously published. This work provides the most advanced study of foam sculpting work available to date

30th International Conference on Condition Monitoring and Diagnostic Engineering Management (COMADEM 2017)

Proceedings of COMADEM 201