Rapid Prototyping Process Research Articles

Serpens: A Highly Compliant Low-Cost ROS-Based Snake Robot with Series Elastic Actuators, Stereoscopic Vision and a Screw-Less Assembly Mechanism

Snake robot locomotion in a cluttered environment where the snake robot utilises a sensory-perceptual system to perceive the surrounding operational environment for means of propulsion is defined as perception-driven obstacle-aided locomotion (POAL). From a control point of view, achieving POAL with traditional rigidly-actuated robots is challenging because of the complex interaction between the snake robot and the immediate environment. To simplify the control complexity, compliant motion and fine torque control on each joint is essential. Accordingly, intrinsically elastic joints have become progressively prominent over the last years for a variety robotic applications. Commonly, elastic joints are considered to outperform rigid actuation in terms of peak dynamics, robustness, and energy efficiency. Even though a few examples of elastic snake robots exist, they are generally expensive to manufacture and tailored to custom-made hardware/software components that are not openly available off-the-shelf. In this work, Serpens, a newly-designed low-cost, open-source and highly-compliant multi-purpose modular snake robot with series elastic actuator (SEA) is presented. Serpens features precision torque control and stereoscopic vision. Only low-cost commercial-off-the-shelf (COTS) components are adopted. The robot modules can be 3D-printed by using Fused Deposition Modelling (FDM) manufacturing technology, thus making the rapid-prototyping process very economical and fast. A screw-less assembly mechanism allows for connecting the modules and reconfigure the robot in a very reliable and robust manner. The concept of modularity is also applied to the system architecture on both the software and hardware sides. Each module is independent, being controlled by a self-reliant controller board. The software architecture is based on the Robot Operating System (ROS). This paper describes the design of Serpens and presents preliminary simulation and experimental results, which illustrate its performance.

Influence of Powder Deposition on Powder Bed and Specimen Properties.

Three-dimensional printing used to be a rapid prototyping process, but nowadays it is establishing as an additive manufacturing (AM) process. One of these AM techniques is selective laser sintering (SLS), which most often involves partial melting of the particles and therefore belongs to the category of powder bed fusion processes. Much progress has been made in this field by research on process parameters like laser power, hatch distance, and scanning speed while still lacking a fundamental understanding of the powder deposition and its influence on parts. A critical issue for economic manufacturing is the building time of parts with good mechanical properties, which can be reduced by lower surface roughness due to less or missing post processing. Therefore, the influence of three blade shapes on powder bed surface roughness has been evaluated for PA12 powder with three different grain size distributions by using advanced X-ray micro computed tomography (XMT) and a confocal laser scanning microscope (LSM). Along with those methods, new techniques for powder characterization were tested and compared. Lowest roughness has been achieved with a flat blade, based on a higher compression due to a larger contact zone between blade and powder bed. Furthermore, an anisotropic effect of the mechanical properties resulting from different building directions has been detected which can be explained by varying amounts of solid contact paths through the powder bed depending on powder application direction. In addition, an optimal combination of process parameters with an even compression of the powder bed leads to low surface roughness, complementing the advantages of additive manufacturing.

Economical rapid-prototyping of aspherical lenses

We present a rapid-prototyping process to fabricate aspherical lens arrays based on surface deformation due to thermal expansion of PDMS. Using laser-structuring and molding in combination with an FEM-based shape optimization, we were able to design, fabricate and characterize different micro-lens arrays. This fabrication process can be used for almost any kind of arbitrary lens shape, which allows for a large design freedom for micro lenses.

Selection of optical system parameters and methods for software development of technical vision complex for three-dimensional printing

Subject of Research.The paper presents the study of methods for control of rapid prototyping processes with the use of technical vision hardware and software system. Product monitoring is a crucial function of any manufacturing process. It becomes more important when the monitoring is performed during the the product manufacturing. Three-dimensional printing technology requires this kind of monitoring system in order to improve the visual and durable qualities of the product, optimize the material costs and the speed of manufacturing. Method. The parameters of the optical system for capturing images in the printing process are defined in theory. Optical systems are selected providing the necessary image quality. The analysis of the camera placement configuration has been carried out to match optimally the task. The analysis was based on overall dimensions of the 3D printer, its working area and free space in the printer case. The ways for solution of software part problems were analyzed. Main Results. A mathematical apparatus was developed for calculation of the optical system parameters of a technical vision complex. Different variants of optical systems were selected for efficiency verification of the hardware and software system. Different methods for development of programs and algorithms for data processing from video cameras were considered. Practical Relevance. The development of the hardware and software system that controls the rapid prototyping process has a significant benefit in expanding the possibilities of automating rapid prototyping processes. The results of the work can be useful in quality control of the product during its manufacturing, in disclosure of deviations from the virtual three-dimensional model, in development of recommendations for control commands update in order to improve the quality and increase the speed of product manufacturing.

Mechanical behavior of calcium sulfate scaffold prototypes built by solid free-form fabrication

PurposeThis paper aims to investigate the mechanical behavior of three-dimensional (3D) calcium sulfate porous structures created by a powder-based 3D printer. The effects of the binder-jetting and powder-spreading orientations on the microstructure of the specimens are studied. A micromechanical finite element model is also examined to predict the properties of the porous structures under the load.Design/methodology/approachThe authors printed cylindrical porous and solid samples based on a predefined designed model to study the mechanical behavior of the prototypes. They investigated the effect of three main build bed orientations (x, y and z) on the mechanical behavior of solid and porous specimens fabricated in each direction then evaluated the micromechanical finite-element model for each direction. The strut fractures were analyzed by scanning electron microscopy, micro-computed tomography and the von Mises stress distribution.FindingsResults showed that the orientation of powder spreading and binder jetting substantially influenced the mechanical behavior of the 3D-printed prototypes. The samples that were fabricated parallel to the applied load had higher compressive strength compared with those printed perpendicular to the load. The results of the finite element analysis agreed with the results of the experimental mechanical testing.Research limitations/implicationsThe mechanical behavior was studied for the material and the 3D-printing machine used in this research. If one were to use another material formulation or machine, the printing parameters would have to be set accordingly.Practical implicationsThis work aimed to re-tune the control factors of an existing rapid prototyping process for the given machine. The authors achieved these goals without major changes in the already developed hardware and software architecture.Originality/valueThe results can be used as guidelines to set the printing parameters and a model to predict the mechanical properties of 3D-printed objects for the development of patient- and site-specific scaffolds.

Classification of materials for selective laser melting by laser-induced breakdown spectroscopy

In the present work, we introduce a possibility to improve the rapid prototyping process of selective laser melting (SLM) using laser-induced breakdown spectroscopy (LIBS) which provides a material analysis. SLM uses many disparate materials for manufacturing of parts. The elemental composition of raw materials and constructed parts is obtained from a characteristic spectrum, which is a result of LIBS measurement. We compared a high-end LIBS instrumentation with a low-cost one; the latter could be easily implemented to a SLM device. The measured data were processed using multivariate data analysis algorithms. First, the principal component analysis was employed for a visualization and dimensionality reduction. Second, the reduced data set was classified using support vector machines. Moreover, we have suggested a procedure for an automatized classification of materials and parts during the SLM process without any supervision of a spectroscopy-specialist.

Properties and microstructure of elements made by electron beam rapid prototyping process with wire

In the paper the results of research on rapid prototyping using electron beam and deposit-ed material in the form of wire are presented. Electron beam rapid prototyping with wire is an efficient method for manufacturing complex shapes from metal alloys such as alloy steels, nickel alloys or titanium. This technology is used primarily in the aviation industry, especially in the military as it is designed rather for a unit production or small series production. As part of the work, technological conditions of the process for which it is possible to deposit test pieces in the form of rectangular prism were determined. Test elements were made using a stainless steel wire grade G 18 8 Mn. Metallographic examinations and selected mechanical properties were investigated. The deposited material is characterized by austenitic with ferrite delta, cell-dendritic microstructure. There are large dendritic grains which are extended towards the heat dissipation – towards the substrate. The hardness in the deposited material is in the range of 192 to 273 HV0.05 depending on the number of layers. In the area of mixing with the substrate, the hardness reaches the value of 355 HV0.05.

Low-Cost Microfabrication for MEMS Switches and Varactors

This paper presents a low-cost microfabrication technique for manufacturing radio frequency microelectromechanical system (RF MEMS) switches and varactors without intensive clean-room environments. The fabrication process entails only laser microstructuring technique, non-clean-room microlithography, and standard wet-bench and hot-film emboss of SU-8 and ADEX polymers. MEMS movable structures were fabricated out of 14- $\mu \text{m}$ -thick aluminum foils and suspended above coplanar-waveguide transmission lines, which were implemented on top of FR4 substrates via 5- $\mu \text{m}$ -thick SU-8 dielectric anchors. Both MEMS structures and an FR4 substrate were integrated using micropatterned polymers, developed by using dry-film ADEX and SU-8 polymers, for a composite assembly. An average fabrication yield of higher than 60% was achieved, calculated from 10 fabrication attempts. The RF measurement results show that the RF MEMS devices fabricated by using the novel microfabrication process have good figures of merit, at much lower overall fabrication costs, as compared to the devices fabricated by conventional clean-room process, enabling it as a very good microfabrication process for cost-effective rapid prototyping of MEMS.

Use of a three-dimensional printed polylactide-coglycolide/tricalcium phosphate composite scaffold incorporating magnesium powder to enhance bone defect repair in rabbits

BackgroundThe repair of large bone defects remains challenging for orthopaedic surgeons. Bone grafting remains the method of choice; such grafts fill spaces and enhance bone repair. Therapeutic agents also aid bone healing. The objective of this study is to develop a composite bioactive scaffold composed of polylactide-coglycolide (PLGA) and tricalcium phosphate (TCP) (the basic carrier) incorporating osteogenic, bioactive magnesium metal powder (Mg). MethodPorous PLGA/TCP scaffolds incorporating Mg were fabricated using a low-temperature rapid-prototyping process. We term the PLGA/TCP/Mg porous scaffold (hereafter, PPS). PLGA/TCP lacking Mg served as the control material when evaluating the efficacy of PPS. A total of 36 New Zealand white rabbits were randomly divided into blank, PLGA/TCP (P/T) and PPS group, with 12 rabbits in each group. We established bone defects 15 mm in length in rabbit radii to evaluate the in vivo osteogenic potential of the bioactive scaffold in terms of the direct controlled release of osteogenic Mg ion during in vivo scaffold degradation. Radiographs of the operated radii were taken immediately after implantation and then at 2, 4, 8 and 12 weeks. Micro-computed tomography of new bone formation and remaining scaffold and histological analysis were performed at 4, 8, 12 weeks after operation. ResultsX-ray imaging performed at weeks 4, 8 and 12 post-surgery revealed more newly formed bone within defects implanted with PPS and PLGA/TCP scaffolds than blank group (p < 0.05). And micro-computed tomography performed at weeks 4 and 8 after surgery revealed more newly formed bone within defects implanted with PPS scaffolds than PLGA/TCP scaffolds (p < 0.05). Histologically, the PPS group had more newly mineralized bone than controls (p < 0.05). The increases in new bone areas (total implant regions) in the PPS and PLGA/TCP groups were 19.42% and 5.67% at week 4 and 48.23% and 28.93% at week 8, respectively. The percentages of remaining scaffold material in total implant regions in the PPS and PLGA/TCP groups were 53.30% and 7.65% at week 8 and 20.52% and 2.70% at week 12, respectively. ConclusionOur new PPS composite scaffold may be an excellent orthopaedic substitute; it exhibits good biocompatibility and may potentially have clinical utility. Translational potential of this articleMagnesium and beta-tricalcium phosphate had osteoinduction. It is significant to print a novel bone composite scaffold with osteoinduction to repair segmental bone defects. This study evaluated efficacy of PPS in the rabbit radius segmental bone defect model. The results showed that the novel scaffold with good biocompatibility may be an excellent graft and potentially have clinical utility.

Selection and Validation of Mathematical Models of Power Converters using Rapid Modeling and Control Prototyping Methods

This paper presents a methodology based on two interrelated rapid prototyping processes in order to find the best correspondence between theoretical, simulated, and experimental results of a power converter controlled by a digital PWM. The method supplements rapid control prototyping (RCP) with effective math tools to quickly select and validate models of a controlled system. We show stability analysis of the classical and two modified buck converter models controlled by zero average dynamics (ZAD) and fixed-point induction control (FPIC). The methodology consists of obtaining the mathematical representation of power converters with the controllers and the Lyapunov Exponents (LEs). Besides, the theoretical results are compared with the simulated and experimental results by means of one- and two-parameter bifurcation diagrams. The responses of the three models are compared by changing the parameter K_s of the ZAD and the parameter N of the FPIC. The results show that the stability zones, periodic orbits, periodic bands, and chaos are obtained for the three models, finding more similarities between theoretical, simulated, and experimental tests with the third model of the buck converter with ZAD and FPIC as it considers more parameters related to the losses in different elements of the system. Additionally, the intervals of the chaos are obtained by using the LEs and validated by numerical and experimental tests

Angle defines attachment: Switching the biological response to titanium interfaces by modifying the inclination angle during selective laser melting

Developing patient-specific biomedical implants for clinical application requires the integration of material science, manufacturing engineering, and biology. As selective laser melted (SLM) metallic additive manufactured implants become common, a key, but overlooked design parameter is its inclination angle. In this study, we have fabricated Ti6Al4V implants at three different inclination angles (0, 45 and 90 degrees) reporting the relationship between cell attachment, surface topography and surface chemistry at each angle. During the SLM process, we show that as the inclination angles increase, there is a corresponding increase in the number of partially melted particles adhering to the surface, greatly affecting the surface topography, morphology, roughness, chemistry, and wettability of the implant. In order to validate the approach, the effect of surface properties on cell fate was determined. In each case, the overall viability of Chinese hamster ovarian cells (CHO) was found to be statistically indistinguishable; however, the number of spindle cells and their dimension were found to increase significantly at higher inclination angles. This work demonstrates a novel approach for combining SLM technology in manufacturing metallic biomedical implants and provides a novel insight in case of switching cell‑titanium interface by modifying one process parameter, inclination angle, during rapid prototyping process.

Rapid Prototyping and Its Role in Supporting Architectural Design Process

Model making is a crucial part of the design development for evaluating the form, fit and functionality of a design before a notable investment is performed. The emergence of novel technologies and their increasing uptake are helping to redefine the architecture and the architects’ master builder role, by altering the way architects think and make things. Different methods and strategies are available to utilize for production of artefacts that are considered not only to be new communication and representation tools but also being utilized for testing and evaluation during design processes. Rapid prototyping processes are forming a language between different phases of the design and considered as a feedback mechanism informing each other. This paper presents experimental research products of two rapid prototyping technologies, focusing on how each technology can effectively be used in the delivery of design intent. Prototyping machines were used in testing the accuracy of the geometry of the design, in terms of protecting the design intent within the production process of each model. In order to verify the results of the experiment, researchers conducted semi-structured interviews with the experts in the built environment and a preliminary decision-making matrix was generated, aiming to provide guidance to the architectural designers on how to effectively use current rapid prototyping technologies within design processes. Keywords: Rapid Prototyping, Model Making, Complex Surfaces

The use of rapid prototyping in the joining of fractured historical silver object

PurposeThis paper aims to present a proposal for the restoration of a silver crown by means of fitting pieces produced by the process of 3D modelling and rapid prototyping. It also analyses the benefits of this procedure in restoration of objects weakened by corrosive processes.Design/methodology/approachElemental chemical analysis was carried out in the alloy used in the manufacture of the crown and the constructive and corrosive processes present were studied. Three fitting pieces were modelled and prototyped in wax casting by the stereolithography apparatus system aiming to restore the part and protect the original metal against impacts and external tensions which could speed up some deterioration processes.FindingsThe procedure presented in this paper has shown that formal and dimensional accuracy, only achieved by means of 3D technologies, made the restoration and mechanical stability of the crown possible without the use of adhesives or welding.Originality/valueThe proposed procedure is a new restoration alternative which causes minimal impact to the object and abides by the main standards for modern conservation. It is made with metal which is compatible with the original piece, retractable and easily identifiable.

A designable surface via the micro-molding process

A rapid prototyping process was presented to fabricate a nylon honeycomb microstructure coated with parylene C. The surface structure was designed to obtain a hydrophobic surface using the volume of fluid (VOF) model. With the micro-molding technique, the contact angle of the polymer surface could be designed and fabricated by changing the different microstructure surface die-steel mold inserts. For the honeycomb (20 μm width and 60 μm depth) microcavity side wall, an average micro-molding filling percentage of 95% could be achieved by using a three-section constant-pressure molding process. The solid surface wettability is governed by both the geometrical microstructures and the surface energy. A 2 μm parylene C layer was deposited on the nylon honeycomb microsurface to reduce the surface energy. To design honeycomb structures with different microcavity densities, the contact angle of these artificial surfaces could change from 91° to 130°. From a comparison of the contact angle measurements with the different models, the honeycomb-structured microsurface could be described by the Cassie–Baxter model. The errors between the VOF simulation and the measured data were <10%. The drag reduction performance of the honeycomb microplates was investigated in a water tunnel with a high Reynolds number (from 0.5×106 to 4.6×106). As a result, the honeycomb microplates showed a maximum drag reduction rate of 36±0.6% in comparison with the bare plates in such turbulent flow. Benefiting from the replaceable mold insert, more designable microstructure polymer surfaces can be manufactured by this rapid prototyping technique.

Development of three-dimensional brain arteriovenous malformation model for patient communication and young neurosurgeon education

Purpose: Rapid prototyping technology is used to fabricate three-dimensional (3D) brain arteriovenous malformation (AVM) models and facilitate presurgical patient communication and medical education for young surgeons.Methods: Two intracranial AVM cases were selected for this study. Using 3D CT angiography or 3D rotational angiography images, the brain AVM models were reconstructed on personal computer and the rapid prototyping process was completed using a 3D printer. The size and morphology of the models were compared to brain digital subtraction arteriography of the same patients. 3D brain AVM models were used for preoperative patient communication and young neurosurgeon education.Results: Two brain AVM models were successfully produced. By neurosurgeons’ evaluation, the printed models have high fidelity with the actual brain AVM structures of the patients. The patient responded positively toward the brain AVM model specific to himself. Twenty surgical residents from residency programs tested the brain AVM models and provided positive feedback on their usefulness as educational tool and resemblance to real brain AVM structures.Conclusions: Patient-specific 3D printed models of brain AVM can be constructed with high fidelity. 3D printed brain AVM models are proved to be helpful in preoperative patient consultation, surgical planning and resident training.

Investigation on the Effect of Support Structure Space in Determining Optimal Part Orientation Using a Generic Algorithm

Prominence on support structure in limiting the build time of additive manufacturing (AM) or rapid prototyping (RP) processes got the least allure from researchers. Likewise, the support structure space (3S) was not utilised yet to prolong the investigation in this arena. Build time reduction leads to faster production and lower fabrication cost of the part. This paper proposes a critical thinking approach that limits build time to a lesser value, for part building in RP processes using a generic algorithm. The support structure (2S) volume is one of the dominant factors in reducing the build time. The proposed algorithm replaces the 2S volume by the 3S volume to find the best part deposition orientation. Construction of the bounding box, computation of the 3S volume and orientation of the part are discussed in the development phase of the algorithm. The verification and validation of sample-fabricated parts on FDM system have been done by comparing the outcomes obtained against the numerically estimated values.

Three-dimensional brain arteriovenous malformation models for clinical use and resident training

Background:To fabricate three-dimensional (3D) models of brain arteriovenous malformation (bAVM) and report our experience with customized 3D printed models of patients with bAVM as an educational and clinical tool for patients, doctors, and surgical residents.Methods:Using computerized tomography angiography (CTA) or digital subtraction angiography (DSA) images, the rapid prototyping process was completed with specialized software and “in-house” 3D printing service. Intraoperative validation of model fidelity was performed by comparing to DSA images of the same patient during the endovascular treatment process. 3D bAVM models were used for preoperative patient education and consultation, surgical planning, and resident training.Results:3D printed bAVM models were successful made. By neurosurgeons’ evaluation, the printed models precisely replicated the actual bAVM structure of the same patients (n = 7, 97% concordance, range 95%–99% with average of < 2 mm variation). The use of 3D models was associated shorter time for preoperative patient education and consultation, higher acceptable of the procedure for patients and relatives, shorter time between obtaining intraoperative DSA data and the start of endovascular treatment. Thirty surgical residents from residency programs tested the bAVM models and provided feedback on their resemblance to real bAVM structures and the usefulness of printed solid model as an educational tool.Conclusions:Patient-specific 3D printed models of bAVM can be constructed with high fidelity. 3D printed bAVM models were proven to be helpful in preoperative patient consultation, surgical planning, and resident training.

Optimization of surface roughness by MOORA method in EDM by electrode prepared via selective laser sintering process

Electrical discharge machining (EDM) is a non-traditional machining process widely used in the machining of difficult to machine materials. The EDM process is extensively use in aerospace, biomedical, die and mold making industries. In this present work, EDM of AISI 1040 stainless steel work piece has been performed by using three different types of tool electrodes like AiSiMg electrode prepared via selective laser sintering (SLS) process along with conventional copper and brass tool electrodes and EDM 30 oil as dielectric fluid. The SLS process is a rapid prototyping (RP) process also called as additive manufacturing (AM) process, which can be used to produce complex shape tool electrode from metallic powder by melting and sintering with the help of laser power. The EDM is performed by varying different process parameters like discharge current (Ip) and pulse-on-time (Ton). The surface roughness parameters like average roughness (Ra), maximum height of the profile (Rt) and average height of the profile (Rz) are measured by the use of surface roughness measurement machine. To reduce the number of experiments, design of experiment (DOE) approach like Taguchi’s L9 orthogonal array has been use. The surface properties of the EDM specimen are optimized by MOORA method and the best parametric setting is reported for the EDM process. Type of tool is found to be the most significant parameters followed by discharge current and pulse-on-time. The AlSiMg RP electrode gave best surface finish followed by brass and copper. With increase in discharge current and pulse-on-time, the surface roughness value of the EDM machined surface increased. So, it preferable to use lower setting of discharge current and pulse-on-time along with AlSiMg RP electrode to get better surface finish EDM machined specimens.

Experimental Investigation using Taguchi Method to Optimize Process Parameters of Fused Deposition Modeling for ABS and Nylon Materials

The term Rapid Prototyping (RP) is utilized as a part of a large portions of the ventures to clarify prepare for quickly making a framework or part before conclusive arrival of that item. Fused deposition modelling (FDM) is an extrusion based RP process which works on layer-by layer additive manufacturing principle. This paper aims at identifying the impact of process parameters of FDM PRAMAAN MINI on properties such as ultimate tensile strength and dimensional accuracy of ABS and Nylon materials. The parameters are model orientation, layer thickness, and shell thickness. The specimens prepared by using taguchi’s L9 orthogonal array to reduce the number of experiments and it give different combinations of different parameters and their levels for each experiment. The results indicate the effect of orientation angle and shell thickness on ultimate tensile strength and moderately affect the dimensional accuracy with maximum manufacturing

Instrumented Incremental Sheet Testing for material behavior extraction under very large strain: Information richness of continuous force measurement

Incremental forming is a rapid prototyping process which uses a forming tool to form a sheet metal according to a predetermined trajectory. In this paper, a micro incremental deformation test (Micro InDef test) derived from the principle of single point incremental sheet forming is developed and proposed. A complex mechanical loading is applied and has a strong potential for the identification of inelastic behavior using inverse method.In a first part, this paper addresses the parameters identification and validation procedures of the ductile damage behavior of ultra-thin sheet metal under very large strain during this instrumented Micro InDef test. An inverse finite element method based on the comparison between numerical and experimental axial forming forces of the incremental deformation test is employed to extract a coupled ductile damaged plastic model.In the last part, the objective is to prove the reliability of ductile damage parameters identification using forming force. The richness of data contained in forming force is quantified and compared to the one from tensile test. Firstly the verification of the estimated parameter's reliability is done via a simple analysis based on the forming force sensitivity to material parameters and secondly by calculating elastoplastic and elastoplastic with ductile damage.