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Article

G. Zak, M. Haberer, C.B. Park and B. Benhabib

As a way of enhancing the mechanical properties of photopolymer‐based parts produced by layered manufacturing (LM) techniques, the use of short glass‐fibre reinforcements…

Abstract

As a way of enhancing the mechanical properties of photopolymer‐based parts produced by layered manufacturing (LM) techniques, the use of short glass‐fibre reinforcements has been recently explored in the literature. This paper proposes a novel methodology that utilizes a modified rule‐of‐mixtures model for the prediction of the mechanical properties of such layered composites. The prediction process employs empirical data on (i) the fibre‐matrix interface, (ii) the fibres’ geometrical arrangement within the specimens (i.e. fibre‐orientation distribution), and (iii) the fibre‐length distribution. The effects of the fibre‐orientation and fibre‐length distributions are accounted for in the prediction model by the fibre‐length‐correction and orientation‐efficiency factors. Comparison of extensive experimental results and model‐based predictions of mechanical properties of layered composites demonstrated the effectiveness of the proposed estimation methodology.

Details

Rapid Prototyping Journal, vol. 6 no. 2
Type: Research Article
ISSN: 1355-2546

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Article

Shih-Hsuan Chiu, Sigit Tri Wicaksono, Kun-Ting Chen, Chiu-Yen Chen and Sheng-Hong Pong

The purpose of this paper is to evaluate the mechanical properties of photopolymer/CB (carbon black) nanocomposite when applied in a visible-light rapid prototyping (RP…

Abstract

Purpose

The purpose of this paper is to evaluate the mechanical properties of photopolymer/CB (carbon black) nanocomposite when applied in a visible-light rapid prototyping (RP) machine.

Design/methodology/approach

The mechanical properties of the samples such as hardness and tensile strength along with thermal stability were analyzed. The curing time behavior of the photopolymer/CB nanocomposites was tested by using a rigid-body pendulum rheometer. The shrinkage property and dimensional stability were also analyzed using the technique according to ASTM D2566 and ASTM D1204, respectively.

Findings

The results showed that the prototype fabricated from pristine photopolymer tended to exhibit poor mechanical properties and low thermal stability. However, after adding the photopolymer with various concentrations of nano-CB and dispersant in appropriate composition, the photopolymer/CB nanocomposite prototype not only reduced its curing time but also enhanced its mechanical properties, thermal stability and dimensional stability.

Practical implications

The presented results can be used in a visible-light RP machine.

Originality/value

The mechanical and thermal properties of photopolymer are improved with nano-CB additives for a RP system.

Details

Rapid Prototyping Journal, vol. 21 no. 3
Type: Research Article
ISSN: 1355-2546

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Article

Timothy J. Horn, Ola L.A. Harrysson, Harvey A. West II, Jeffrey P. Little and Denis J. Marcellin-Little

The aim of this study is to describe an improved experimental substrate for the mechanical testing of patient-specific implants fabricated using direct metal additive…

Abstract

Purpose

The aim of this study is to describe an improved experimental substrate for the mechanical testing of patient-specific implants fabricated using direct metal additive manufacturing processes. This method reduces variability and sample size requirements and addresses the importance of geometry at the bone/implant interface.

Design/methodology/approach

Short-fiber glass/resin materials for cortical bone and polyurethane foam materials for cancellous bone were evaluated using standard tensile coupons. A method for fabricating bone analogs with patient-specific geometries using rapid tooling is presented. Bone analogs of a canine radius were fabricated and compared to cadaveric specimens in several biomechanical tests as validation.

Findings

The analog materials exhibit a tensile modulus that falls within the range of expected values for cortical and cancellous bone. The tensile properties of the cortical bone analog vary with fiber loading. The canine radius models exhibited similar mechanical properties to the cadaveric specimens with a reduced variability.

Research limitations/implications

Additional replications involving different bone geometries, types of bone and/or implants are required for a full validation. Further, the materials used here are only intended to mimic the mechanical properties of bone on a macro scale within a relatively narrow range. These analog models have not been shown to address the complex microscopic or viscoelastic behavior of bone in the present study.

Originality/value

Scientific data on the formulation and fabrication of bone analogs are absent from the literature. The literature also lacks an experimental platform that matches patient-specific implant/bone geometries at the bone implant interface.

Details

Rapid Prototyping Journal, vol. 20 no. 1
Type: Research Article
ISSN: 1355-2546

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Article

V. Yevko, C.B. Park, G. Zak, T.W. Coyle and B. Benhabib

Current commercial rapid prototyping systems can be used for fabricating layered models for subsequent creation of fully‐dense metal parts using investment casting. Due to…

Abstract

Current commercial rapid prototyping systems can be used for fabricating layered models for subsequent creation of fully‐dense metal parts using investment casting. Due to increased demand for shortened product development cycles however, there exists a demand to rapidly fabricate functional fully‐dense metal parts without hard tooling. A possible solution to this problem is direct layered rapid manufacturing of such parts, for example, via laser‐beam fusion of the metal powder. The rapid manufacturing process discussed herein is based on this approach. It involves selective laser‐beam scanning of a predeposited metal‐powder layer, forming fully‐dense claddings as the basic building block of individual layers. This paper specifically addresses only one of the fundamental issues of the rapid manufacturing process under investigation at the University of Toronto, namely the fabrication of single claddings. Our theoretical investigation of the influence of the process parameters on cladding’s geometrical properties employed thermal modeling and computer process simulation. Numerous experiments, involving fabrication of single claddings, were also carried out with varying process parameters. Comparisons of the process simulations and experimental results showed good agreement in terms of overall trends.

Details

Rapid Prototyping Journal, vol. 4 no. 4
Type: Research Article
ISSN: 1355-2546

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Article

G. Zak, A.Y.F. Chan, C.B. Park and B. Benhabib

Refers to how the mechanical properties of polymer‐based composite objects produced via rapid layered fabrication methods can be improved significantly using short…

Abstract

Refers to how the mechanical properties of polymer‐based composite objects produced via rapid layered fabrication methods can be improved significantly using short discontinuous fibres as reinforcements. Notes in this context, that the viscosity of the uncured fibre‐photopolymer composite liquids affects the raw‐material handling, the layer formation and the draining operations. Assesses the effects of aspect ratio, surface coating and volume fraction of short glass fibres on the viscosity of the fibre‐photopolymer composite liquids. Based on extensive experimentation and analysis, concludes that the shear viscosity of the composite liquids increases with increasing fibre‐volume fraction, showing that this effect is more pronounced at low shear rates than at high shear rates. Reveals, similarly, that the aspect ratio of the dispersed fibres has a stronger effect on the increase of viscosity at low shear rates and that the surface coating of the dispersed fibres also affects the viscosity of the composite liquids.

Details

Rapid Prototyping Journal, vol. 2 no. 3
Type: Research Article
ISSN: 1355-2546

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Article

José F. Rodríguez, James P. Thomas and John E. Renaud

Analytical/Computational models for the fused deposition (FD) material stiffness and strength as a function of mesostructural parameters are developed. Effective elastic…

Abstract

Analytical/Computational models for the fused deposition (FD) material stiffness and strength as a function of mesostructural parameters are developed. Effective elastic moduli are obtained using the strength of materials approach and an elasticity approach based on the asymptotic theory of homogenization. Theoretical predictions for unidirectional FD‐acrylonitrile butadiene styrene materials are validated with experimentally determined values of moduli and strength. For moduli predictions, the results were found to be satisfactory with difference between experimental and theoretical values of less than 10 percent in most cases.

Details

Rapid Prototyping Journal, vol. 9 no. 4
Type: Research Article
ISSN: 1355-2546

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Article

William Owen, Elizabeth Croft and Beno Benhabib

Recent research has considered robotic machining as a dextrous alternative to traditional CNC machine tools for complex sculptured surfaces. One challenge in using robotic…

Abstract

Purpose

Recent research has considered robotic machining as a dextrous alternative to traditional CNC machine tools for complex sculptured surfaces. One challenge in using robotic machining is that the stiffness is lower than traditional machine tools, due to the cantilever design of the links and low‐torsional stiffness of the actuators. This paper seeks to examine this limitation, using optimization algorithms to determine the best trajectories for the manipulators such that the stiffness is maximized.

Design/methodology/approach

The issue of low stiffness is addressed with an integrated off‐line planner and real‐time re‐planner. The available manipulator stiffness is maximized during off‐line planning through a trajectory resolution method that exploits the nullspace of the robot machining system. In response to unmodeled disturbances, a real‐time trajectory re‐planner utilizes a time‐scaling method to reduce the tool speed, thereby reducing the demand on the actuator torques, increasing the robot's dynamic stiffness capabilities. During real‐time re‐planning, priorities are assigned to conflicting performance criteria such as stiffness, collision avoidance, and joint limits.

Findings

The algorithms developed were able to generate trajectories with stiffer configurations, which resulted in a reduction in the actuator torques. The real‐time re‐planner successfully allowed the process plan to continue when disturbances were encountered.

Research limitations/implications

Simulations are presented to demonstrate the effectiveness of the approach.

Practical implications

Addressing the limitation of stiffness in serial‐link manipulators will enable robots to become more suitable for machining tasks. The real‐time re‐planning approach will allow robots to become more autonomous during the execution of a given task.

Originality/value

An integrated off‐line and real‐time planning approach has been applied to robotic machining.

Details

Industrial Robot: An International Journal, vol. 35 no. 1
Type: Research Article
ISSN: 0143-991X

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Article

S. Rooks and T. Sack

To accommodate increasing levels of device integration at the chip level, circuit line densities in electronic packages are continually increasing. Greater circuit line…

Abstract

To accommodate increasing levels of device integration at the chip level, circuit line densities in electronic packages are continually increasing. Greater circuit line density, in turn, necessitates a corresponding increase in package‐to‐board interconnection density, with I/O counts expected to reach over 600 by 1995. In conjunction with the upward trend in I/O counts are a complementary upward trend in clock speed and an opposing downward trend in package sizes driven by the need to provide more functionality in less space, particularly in notebooks and PCMCIA cards. To satisfy the requirements of increased I/O counts and clock speed, and reduced package sizes, various package‐to‐board interconnection technologies are being developed, such as flip chip attach (FCA) using C4 joints. However, FCA interconnections have a disadvantage of being very difficult, if not impossible, to visually inspect. Though automatic test equipment (ATE) can determine whether the package is functional, it cannot determine the quality and reliability of FCA interconnections. Of the possible inspection techniques available to assess the quality of FCA interconnections — differential laser thermal analysis, acoustic microscopy and cross‐sectional X‐ray radiography — only cross‐sectional X‐ray radiography is capable of accurate, automated inspection of production volumes. This paper will first examine the requirements for inspecting FCA joints and will then describe the various inspection alternatives, outlining their advantages and disadvantages. Having described the potential advantage of one particular cross‐sectional X‐ray technique, digital tomosynthesis, the paper will conclude with some cross‐sectional images of FCA and SMT joints taken by a digital tomosynthesis system being developed for the inspection of FCA joints.

Details

Circuit World, vol. 21 no. 3
Type: Research Article
ISSN: 0305-6120

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Article

Mario Andrei Garzon Oviedo, Antonio Barrientos, Jaime Del Cerro, Andrés Alacid, Efstathios Fotiadis, Gonzalo R. Rodríguez-Canosa and Bang-Chen Wang

This paper aims to present a system that is fully capable of addressing the issue of detection, tracking and following pedestrians, which is a very challenging task…

Abstract

Purpose

This paper aims to present a system that is fully capable of addressing the issue of detection, tracking and following pedestrians, which is a very challenging task, especially when it is considered for using in large outdoors infrastructures. Three modules, detection, tracking and following, are integrated and tested over long distances in semi-structured scenarios, where static or dynamic obstacles, including other pedestrians, can be found.

Design/methodology/approach

The detection is based on the probabilistic fusion of a laser scanner and a camera. The tracking module pairs observations with previously detected targets by using Kalman Filters and a Mahalanobis-distance. The following module allows to safely pursue the target by using a well-defined navigation scheme.

Findings

The system can track pedestrians from static position to 3.46 m/s (running). It handles occlusions, crossings or miss-detections, keeping track of the position even if the pedestrian is only detected in 55/per cent of the observations. Moreover, it autonomously selects and follows a target at a maximum speed of 1.46 m/s.

Originality/value

The main novelty of this study is the integration of the three algorithms in a fully operational system, tested in real outdoor scenarios. Furthermore, the addition of labelling to the detection algorithm allows using the full range of a single sensor while preserving the high performance of a combined detection. False-positives’ rate is reduced by handling the uncertainty level when pairing observations. The inclusion of pedestrian speed in the model speeds up and simplifies tracking process. Finally, the most suitable target is automatically selected by a scoring system.

Details

Industrial Robot: An International Journal, vol. 42 no. 5
Type: Research Article
ISSN: 0143-991X

Keywords

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Article

Henrique Guilherme da Silva, João Carlos Espíndola Ferreira, Vikas Kumar and Jose Arturo Garza-Reyes

The purpose of this research was to develop new sustainability indicators consistent with the sand mould casting industry, through benchmarking of cleaner production (CP)…

Abstract

Purpose

The purpose of this research was to develop new sustainability indicators consistent with the sand mould casting industry, through benchmarking of cleaner production (CP), in order to identify the levels of practice and performance of companies of the casting sector. In addition, a lean manufacturing checklist was specified in order to verify the presence of lean manufacturing techniques employed to eliminate waste towards CP. No previous work was found in the literature that attempts to assess practices and performance of companies performing sand mould casting (a significantly polluting manufacturing process) in the context of CP and lean manufacturing.

Design/methodology/approach

For the application of this benchmarking, nine companies from the sand mould casting sector were studied, where the profile of each company was analysed through eight variables and 47 indicators. Data was obtained through face-to-face visits and questionnaire application in the companies, and the data was analysed both quantitatively and qualitatively.

Findings

The results obtained were the diagnosis of companies' practices and performance resulting from their position in the benchmarking charts, as well as the identification of the areas in which companies should implement improvements aiming at achieving CP.

Research limitations/implications

This research was developed specifically for sand mould casting companies, and each process has its own characteristics

Practical implications

14 companies were invited to participate in this survey, but nine companies agreed to participate. Unfortunately, there were companies that declined to participate in the survey.

Originality/value

It is important to diagnose casting companies regarding CP practices, performance and deployment potential. Thus, important negative issues in the company can be identified, and with this information, they can develop actions focussed on cases that need more attention. In addition, this work contributes to evaluate the relationship and efficiency of improvement actions developed by companies in the context of both lean manufacturing and CP, aiming to reduce or eliminate the environmental impact. The improvement of practices and performance of a company regarding CP is considered to be beneficial to supply chain management in the context of sustainability, as the other participating companies are likely to seek ways to reduce environmental impact, and the diagnostics provided by this work may also be used by those companies.

Details

Management of Environmental Quality: An International Journal, vol. 31 no. 5
Type: Research Article
ISSN: 1477-7835

Keywords

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