Emerald | Rapid Prototyping Journal

Distortion Modeling of SL Parts by Classical lamination Theory

Morteza Vatani, Farshad Barazandeh, Abdolreza Rahimi, Amir Sanati Nezhad — 2012-04-20 00:00:00.0

Abstract

Purpose - In Stereolithography (SL), the total exposure absorbed by photopolymer is variable and is a function of height. This phenomenon causes heterogeneous properties and develops residual stresses during process. Consequently a pronounced deformation occurs especially when small and more intricate objects are fabricated. The objective of this paper is to predict this deformation when miniature and complicated parts are fabricated.Design/methodology/approach - In this paper classical lamination theory is employed to model mechanical properties of layers, layers shrinkage and residual stress growth during SL process. Distortion is predicted based on the developed model. Findings - Results show that final distortion is proportional to part thickness and it increases exponentially as parts thickness or layers thickness decrease.Practical implications - To verify the results, several test pieces were built with SLA 5000 machine and SOMOS 11120 resins. Their distortions were measured with video measuring machine (VMM-3020D machine). The estimation agrees very well with the experimental results (less than 10% error).Originality/value - This study considers the heterogeneous properties of SL parts during fabrication process; an item which was ignored in previous researches. This theoretical and experimental study provides useful information about estimation of deformation of SL parts after building. This information help SL machine user to select the best parameters when fabrication miniature and intricate features especially for biomechanics parts.

Design, Fabrication, and Evaluation of Negative Stiffness Elements Using SLS

Lia Kashdan, Carolyn Seepersad, Michael Haberman, Preston Wilson — 2012-04-20 00:00:00.0

Abstract

Purpose - Recent research has shown that constrained bistable structures can display negative stiffness behavior and provide extremal vibrational and acoustical absorptive capacity. These bistable structures are therefore compelling candidates for constructing new meta-materials for noise reduction, anechoic coatings, and backing materials for broadband imaging transducers. To date, demonstrations of these capabilities have been primarily theoretical because the geometry of bistable elements is difficult to construct and refine with conventional manufacturing methods and materials. The objective of this research is to leverage the geometric design freedoms provided by selective laser sintering (SLS) technology to design and construct constrained bistable structures with negative stiffness behavior.Design/methodology/approach - A meso-scale negative stiffness system is designed and fabricated with SLS technology. The system includes a bistable structure in the form of a pre-compressed/pre-buckled beam. The dynamic transmissibility of the system is measured, and its behavior is compared to the predictions of analytical models. Findings - Experimental results demonstrate that pre-compression and pre-buckling can be used to induce negative stiffness behavior and thereby increase the damping and shift the resonant frequency of an unconstrained beam. Originality/value - The results support the usefulness of SLS and other additive manufacturing technologies for acoustic and dynamic applications. Specifically, the demonstrated advantages of SLS include the ability to rapidly redesign, functionally prototype, and tune physical models for acoustic and dynamic experimentation. Of significant importance is the ability of SLS to enable consolidation of parts that are traditionally separate, thereby reducing vibrational noise in these systems. In this specific application, SLS enables a proof-of-concept comparison of the theoretical and experimental behavior of a meso-scale negative stiffness system. The demonstrated acoustical and vibrational absorptive capacity of these systems is expected to lead to designs for new structures and materials that offer significantly improved energy absorbing capabilities over a broad range of tunable frequencies without compromising structural stiffness.

Factor analysis of selective laser melting process parameters and geometrical characteristics of synthesized single tracks

Igor Yadroitsev, Ina Yadroitsava, Philippe Bertrand, Igor Smurov — 2012-04-20 00:00:00.0

Abstract

Purpose - Properties of the parts manufactured by selective laser melting (SLM) depend strongly on the each single laser-melted track and each single layer, as well as the strength of the connections between them. The purpose of this paper to establish links between the principal SLM parameters (laser power density, scanning speed, layer thickness), properties of the powder and geometrical characteristics of single tracks. This study will provide a theoretical and technical basis for production of parts from metal powders.Design/methodology/approach - This paper discusses the SLM parameters affecting on geometrical characteristics of the synthesized single tracks. Granulomorphometric characteristics of powders were studied in detail. A Greco-Latin square design was used to control geometrical characteristics of the tracks. Analysis of variance (ANOVA) permitted to establish a statistically significant influence of the SLM process parameters on geometry of the single laser-melted track.Findings - The behavior of individual tracks and their geometric characteristics depend on the process parameters, physical-chemical and granulomorphometrical properties of the powder. Each powder shows peculiar behavior in the process of single track formation. For stainless steel grade 904L powders with different particle size it was found that the most influencing parameter is the laser power (the following values were applied: 25, 37.5, 50 W), and then, in order of decreasing importance, are the powder layer thickness (60, 90, 120 µm), the scanning speed (0.05, 0.10, 0.15 m/s), and, finally, the particle size.Practical implications - Originality/value - The proposed hierarchy of the process parameters is a new systematic study presented by the authors, developed for selective laser melting. Obtained data can be used in surface structuring and micro-manufacturing characterized by a small number of layers within a part and, thus, sensible to the geometric dimensions and shape of the individual tracks.

Patient specific reconstruction with 3D modeling and DMLS additive manufacturing

2012-04-20 00:00:00.0

Abstract

Purpose - Purpose - To develop a workflow for 3D modeling and additive manufacturing (AM) of patient specific medical implants. The comprehensive workflow consists of four steps: medical imaging, 3D modeling, additive manufacturing and clinical application. Implants are used to reconstruct bone damage or defects caused by trauma or disease. Traditionally, implants have been manually bent and shaped either preoperatively or intraoperatively with the help of anatomic solid models. The proposed workflow obviates the manual procedure and may result to more accurate and cost effective implants Design/methodology/approach - Approach - A patient specific implant was digitally designed to reconstruct a facial bone defect. Several test pieces were additive manufactured from stainless steel and titanium by direct metal laser sintering technology. An additive manufactured titanium EOS Titanium Ti64 ELI reconstruction plate was successfully implanted onto patient’s injured orbital wall Findings - Findings - This method enables exact fitting of implants to surrounding tissues. Creating implants before surgery improves accuracy, may reduce operation time and decrease patient morbidity hence improving quality of surgery. By using AM methods it is possible to manufacture a volumetric net structure, which also allows cells and tissues to grow through it to and from surrounding tissues. The net is created from surface and its thickness and hole size are adjustable. The implant can be designed so that its mass is low and therefore sensitivity to hot and cold temperatures is reduced.Originality/value - Originality – This paper describes a novel technique to create patient specific reconstruction implants for facial bony defects.

FDM MODELS AND FEA IN DYSPLASTIC HIP

Ratnadurai Dhakshyani, Nukman Yusoff, Abu Osman Noor Azuan — 2012-04-20 00:00:00.0

Abstract

Purpose - The use of FDM models and finite element analysis related to dysplastic hip orthopaedic surgery.Design/methodology/approach - Study involved the use of Mimics and Abaqus softwares. Mimics was used to process the CT scan patient data to STL format before producing FDM models which were for before and after surgery. FEA was done to study the two different type of implant biomaterials used in dysplastic hip surgery.Findings - The use of FDM pre models for preplanning of dysplastic hip surgery by orthopaedic surgeons and viewing of the surgery outcome via FDM post models. Different implant biomaterials used gave different results in reduction of stresses that were achieved. Originality/value - This is original work involving patients in hospital which got ethical approval and funded by the university grant due to new research of this kind in the university.

Three-dimensional multi-material Electromagnetic Band-gap Structure: design, fabrication and property studies

Kun Sun, Dichen Li, Haihua Wu, Minjie Wang, Xiaoyong Tian — 2012-04-20 00:00:00.0

Abstract

Purpose - The purpose of this paper is to bring up the concept of multi-material Electromagnetic Band-gap Structure (EBGs) and develop a method for its fabrication. Meanwhile, its microwave properties was studied compared with the traditional EBGs consisting of two kinds of material. Design/methodology/approach - Stereolithography (SL) and gel casting were used to fabricate 3D multi-material EBGs. Resin mold was designed and fabricated based on SL process, slurries loaded with 55vol% Al2O3 and 55vol% TiO2 respectively were prepared, and using gel casting, multilayer EBGs with diamond structure were fabricated. T/R method was used to obtain the characteristic parameter S21 of the EBGs; meanwhile, characters of their band structure were studied based on plane wave expansion method.Findings - The fabricated EBGs with a TiO2-resin-air structure showed a band gap from 11.7GHz to 16.0GHz along <1, 1, 0> direction; the EBGs with a TiO2-resin-Al2O3 structure showed a band gap from 11.4GHz to 11.9GHz along <1, 1, 0> direction. Both of them agreed well with the simulation result. Also, through the study of multi-material EBGs' microwave properties, it could be seen this structure was a good approach to adjust the band gap.Originality/value - With the concept of multi-material EBG structure brought up, multilayer 3D EBGs were designed and fabricated based on SL combined with gel casting. It could be seen multi-material EBGs was a good approach to adjust the band gap. Also, the fact that testing result matching with the simulation validates that the feasibility of the process.

Preliminary fabrication of thin-wall structure of Ti6Al4V for dental restoration by Electron Beam Melting

2012-04-20 00:00:00.0

Abstract

Purpose - Purpose: This experiment investigated the potential application of electron beam melting, as layered manufacturing process, to fabricate dental coping of metal-ceramic crown restoration using Ti6Al4V powder.Design/methodology/approach - Design/methodology/approach: This experiment was conducted in two steps: shrinkage study to determine scale up factor for shrinkage compensation and parameter selection study, based on thickness, hardness, and surface roughness, to select process parameter of electron beam melting. Findings - Findings: Promising result of fabricating metal coping of Ti6Al4V via electron beam melting was shown. Ti6Al4V coping was successfully fabricated with average thickness of 0.52 mm required for dental coping. Total average hardness of 333.35 HV that is comparable to casted Ti6Al4V with considerably high roughness RSm of 382 µm.Originality/value - Originality/value: This paper presents a novel application of electron beam melting to fabricate metal coping for metal-ceramic crown restoration.

Effect of Selective Laser Melting Layout on the Quality of Stainless Steel Parts

Sasan Dadbakhsh, Liang Hao, Neil Sewell — 2012-04-20 00:00:00.0

Abstract

Purpose - Selective laser melting (SLM) is increasingly used for the manufacture of end-use metal tools and parts, requiring the careful identification of a range of appropriate process parameters and conditions to achieve desirable properties and quality. Process conditions such as the relation between layout of parts and internal gas flow within the SLM platform can influence the consolidation of metal powers and therefore the quality and properties of the final parts. This research investigates the effect of part layout on quality and mechanical properties of cylindrical 316L stainless steel parts manufactured by SLM. Design/methodology/approach - The cylindrical 316L stainless steel parts were manufactured in two directions, one perpendicular to the gas flow direction and one parallel to it. The investigation first focuses on visual inspection and porosity measurements to compare the quality factors such as delamination and porosity of the parts. A mechanical test procedure including tensile, compressive, and shear-punch is used to assess the mechanical properties of the SLM specimens. Cross sectional analyses are carried out to better understand of material response under mechanical tests. Findings - The results show that the part layout and gas flow condition have a negligible influence on porosity formation, however they notably affect the thermal stress and bonding strength between particles which consequently influences the mechanical properties of final parts. The manufacturing of parts perpendicular to gas flow seems to be more advantageous rather than parallel to gas flow.Originality/value - This is the first work investigating the effects of the SLM layout on the quality and mechanical properties of stainless steel specimens. The results can be used in quality control purposes and for quality improvement of SLM parts.