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Article
Publication date: 15 August 2016

William Walker Wroe, Jessica Gladstone, Tim Phillips, Scott Fish, Joseph Beaman and Austin McElroy

This paper aims to establish a method to verify in real time the quality of a part being built using Selective Laser Sintering (SLS).

Abstract

Purpose

This paper aims to establish a method to verify in real time the quality of a part being built using Selective Laser Sintering (SLS).

Design/methodology/approach

A SLS build of 30 Nylon 12 tensile bars was done while using an infrared camera to record the thermal history of each bar. The thermal history was then compared to the ultimate tensile strength (UTS) of each bar. In addition, an attempt was made to identify where the fracture of each bar occurred based on its thermal history.

Findings

Several analysis techniques were used to compare the thermal history of each bar to its UTS. The strongest correlation found was 0.746. In addition, multiple strategies for predicting the break location where used, with the most successful making a correct prediction on 46 per cent of the bars.

Originality/value

This paper studies the feasibility of in-situ build verification, a technique that if successful would greatly help the further adoption of SLS as a method of manufacturing.

Details

Rapid Prototyping Journal, vol. 22 no. 5
Type: Research Article
ISSN: 1355-2546

Keywords

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Article
Publication date: 20 September 2021

Jared Allison, John Pearce, Joseph Beaman and Carolyn Seepersad

Additive manufacturing (AM) of thermoplastic polymers for powder bed fusion processes typically requires each layer to be fused before the next can be deposited. The…

Abstract

Purpose

Additive manufacturing (AM) of thermoplastic polymers for powder bed fusion processes typically requires each layer to be fused before the next can be deposited. The purpose of this paper is to present a volumetric AM method in the form of deeply penetrating radio frequency (RF) radiation to improve the speed of the process and the mechanical properties of the polymer parts.

Design/methodology/approach

The focus of this study was to demonstrate the volumetric fusion of composite mixtures containing polyamide (nylon) 12 and graphite powders using RF radiation as the sole energy source to establish the feasibility of a volumetric AM process for thermoplastic polymers. Impedance spectroscopy was used to measure the dielectric properties of the mixtures as a function of increasing graphite content and identify the percolation limit. The mixtures were then tested in a parallel plate electrode chamber connected to an RF generator to measure the heating effectiveness of different graphite concentrations. During the experiments, the surface temperature of the doped mixtures was monitored.

Findings

Nylon 12 mixtures containing between 10% and 60% graphite by weight were created, and the loss tangent reached a maximum of 35%. Selective RF heating was shown through the formation of fused composite parts within the powder beds.

Originality/value

The feasibility of a novel volumetric AM process for thermoplastic polymers was demonstrated in this study, in which RF radiation was used to achieve fusion in graphite-doped nylon powders.

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Article
Publication date: 1 March 1995

Mukesh Agarwala, David Bourell, Joseph Beaman, Harris Marcus and Joel Barlow

Considers efforts to date to produce parts by direct selective laser sintering (SLS) of metals, including post processing to improve structural integrity and/or to induce…

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Abstract

Considers efforts to date to produce parts by direct selective laser sintering (SLS) of metals, including post processing to improve structural integrity and/or to induce a transformation. Provides a brief overview of the basic principles of SLS machine operation, and discusses materials issues affecting direct SLS of metals and the resultant properties and microstructures of the parts. Reviews results of past efforts on SLS of metal systems such as Cu‐Sn, Cu‐Solder (Pb‐Sn), Ni‐Sn, pre‐alloyed bronze (Cu‐Sn). Finally discusses more recent efforts on SLS of bronze‐nickel powder mixtures in greater detail.

Details

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

Keywords

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Article
Publication date: 1 March 2003

Alan J. Dutson, Kristin L. Wood, Joseph J. Beaman, Richard H. Crawford and David L. Bourell

Functional testing of rapid prototypes (RP) represents an exciting area of research in solid freeform fabrication. One approach to functional testing is to use similitude…

Abstract

Functional testing of rapid prototypes (RP) represents an exciting area of research in solid freeform fabrication. One approach to functional testing is to use similitude techniques to correlate the behavior of an RP model and a product. Previous research at UT, Austin has resulted in the development of an empirical similitude technique for correlating the behavior of parts with different material properties. Advances in the empirical similitude technique are presented in this paper. Sources of coupling between material properties and geometric shape that produce distortions in the current empirical similitude technique are outlined. A modified approach that corrects such distortions is presented. Numerical examples are used to illustrate both the current and the advanced empirical similitude methods.

Details

Rapid Prototyping Journal, vol. 9 no. 1
Type: Research Article
ISSN: 1355-2546

Keywords

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Article
Publication date: 1 June 1995

Mukesh Agarwala, David Bourell, Joseph Beaman, Harris Marcus and Joel Barlow

Gives a brief overview of post‐processing of selective laser sintered (SLS) metal parts to improve structural integrity and/or to induce a material transformation…

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Abstract

Gives a brief overview of post‐processing of selective laser sintered (SLS) metal parts to improve structural integrity and/or to induce a material transformation. Presents results which show the effect of post‐processing liquid phase sintering temperature and time on material properties. Describes the hot isostatic pressing process, and discusses its application to SLS metal parts. Results gained from using this process show that it is suitable for achieving almost full‐density parts.

Details

Rapid Prototyping Journal, vol. 1 no. 2
Type: Research Article
ISSN: 1355-2546

Keywords

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Article
Publication date: 30 September 2013

Mengqi Yuan, Timothy T Diller, David Bourell and Joseph Beaman

The purpose of this paper is to acquire thermal conductivities of both fresh and preheated polyamide 12 powder under various conditions to provide a basis for effective…

Abstract

Purpose

The purpose of this paper is to acquire thermal conductivities of both fresh and preheated polyamide 12 powder under various conditions to provide a basis for effective and accurate control during the laser sintering (LS) process.

Design/methodology/approach

A Hot Disk® TPS 500 thermal measurement system using a transient plane source (TPS) technology was employed for thermal conductivity measurements. Polyamide 12 powder was packed at different densities, and different carrier gases were used. Tests were also performed on fully dense laser sintered polyamide 12 to establish a baseline.

Findings

Polyamide 12 powder thermal conductivity varies with packing density and temperature, which is approximately one-third bulk form thermal conductivity. Inter-particle bonding is the primary factor influencing polyamide 12 thermal conductivity.

Research limitations/implications

Limited ranges of density were tested, and the carrier gas needed carefully control to prevent powder oxidation. Thermal properties obtained were not tested in the LS process.

Originality/value

This experimental result could be used to enhance thermal control during the LS process.

Details

Rapid Prototyping Journal, vol. 19 no. 6
Type: Research Article
ISSN: 1355-2546

Keywords

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Article
Publication date: 1 September 1996

Joel W. Barlow, Joseph J. Beaman and Badrinarayan Balasubramanian

Presents the mechanical properties of a new mould‐making material, proposed for producing rapidly prototyped injection mould inserts for plastics by selective laser…

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1227

Abstract

Presents the mechanical properties of a new mould‐making material, proposed for producing rapidly prototyped injection mould inserts for plastics by selective laser sintering. Explains that although the strength of this material is far below that of the tool steel usually used to fabricate moulds, design calculations indicate that it can still be used for mould insert production. Points out that the thermal conductivity of this material is lower than that for steel but higher than that for plastic melts. Indicates from the calculations that proper choices of conduction length and cycle time can minimize differences, relative to steel moulds, in the operational behaviour of moulds made of the new material. Discusses the longevity of example moulds.

Details

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

Keywords

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Article
Publication date: 19 January 2015

Timothy T Diller, Mengqi Yuan, David L. Bourell and Joseph J. Beaman

The purpose of this paper is to analyze the bulk energy transport processes in the build chamber environment before and during laser sintering (LS) to provide a basis for…

Abstract

Purpose

The purpose of this paper is to analyze the bulk energy transport processes in the build chamber environment before and during laser sintering (LS) to provide a basis for effective and accurate thermal control for the LS process. This leads to improved mechanical properties and geometrical tolerances for LS products and may be applied to optimize operation cycle times for the LS process.

Design/methodology/approach

Computational models with two levels of complexity were built to explore the heat transfer mechanisms in the LS process. In a one-dimensional model (1D), the powder performed as a semi-infinite solid and heater flux to the powder surface was modeled with a heater control law. A two-dimensional (2D) fluid/solid finite element model of the build chamber and powder bins provided insight into the thermal processes in the build chamber.

Findings

Numerical 1D simulations were verified with measurements from sensors embedded in the build chamber powder bed. Using a 2D model, computed powder surface temperatures during the warm up and build phases were verified with an infrared camera. Convective currents in the build chamber and non-uniformities in the distribution of temperature over the radiant heater surface were found to be substantial contributors to non-uniformities in the powder bed surface temperature.

Research limitations/implications

Limited heat sources were analyzed. No three-dimensional model was built. Assumptions to decrease the part bed temperature difference were not tested.

Originality/value

These simulation and experimental results may be used to enhance thermal control and operation efficiency during the LS process and to improve LS product mechanical properties.

Details

Rapid Prototyping Journal, vol. 21 no. 1
Type: Research Article
ISSN: 1355-2546

Keywords

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Article
Publication date: 28 March 2008

K.M. Fan, W.L. Cheung and I. Gibson

This paper aims to study the effects of solid additives and compounding processes on the selective laser sintering (SLS) behavior of composite powders.

Abstract

Purpose

This paper aims to study the effects of solid additives and compounding processes on the selective laser sintering (SLS) behavior of composite powders.

Design/methodology/approach

Composite powders were prepared from TrueForm™ acrylic‐styrene co‐polymer and SiO2 powder. Dry mixing and melt extrusion were used as the blending processes to produce the composite powders. Some SiO2 powder was ground and treated with silane coupling agent before blending to study the effects of particle size and surface treatment of the filler, respectively. The temperature of the powder bed was monitored using an infrared thermometer. The fusion behaviors of the powders were investigated in situ using an optical microscope and the sintered specimens were examined by scanning electron microscopy.

Findings

For a given volume fraction of the filler, reducing its particle size will hinder fusion between the polymer particles and weaken the sintered specimens. Surface treatment of the filler by silane coupling agent had little effect on the morphology of the sintered specimens; however, it slightly improved their strength. The blending method plays an important role in the sintering behavior of the composite powders. Although melt blending improved the polymer‐to‐polymer contact between the composite powder particles, the high‐resultant viscosity of the material adversely affected the densification of the powder bed, leading to a highly porous structure of the sintered specimens.

Research limitations/implications

The sintering experiments were conducted in ambient conditions using a laser engraving machine instead of a commercial SLS machine with atmospheric control. The temperature gradient within the powder bed was expected to be higher than that in normal SLS processes.

Practical implications

The SLS behavior of a composite powder not only depends on its composition but also on the powder preparation method or powder morphology.

Originality/value

This paper provides some useful information for future development of composite powders for SLS applications.

Details

Rapid Prototyping Journal, vol. 14 no. 2
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 20 April 2015

Brian N. Turner and Scott A Gold

The purpose of this paper is to critically review the literature related to dimensional accuracy and surface roughness for fused deposition modeling and similar…

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7951

Abstract

Purpose

The purpose of this paper is to critically review the literature related to dimensional accuracy and surface roughness for fused deposition modeling and similar extrusion-based additive manufacturing or rapid prototyping processes.

Design/methodology/approach

A systematic review of the literature was carried out by focusing on the relationship between process and product design parameters and the dimensional and surface properties of finished parts. Methods for evaluating these performance parameters are also reviewed.

Findings

Fused deposition modeling® and related processes are the most widely used polymer rapid prototyping processes. For many applications, resolution, dimensional accuracy and surface roughness are among the most important properties in final parts. The influence of feedstock properties and system design on dimensional accuracy and resolution is reviewed. Thermal warping and shrinkage are often major sources of dimensional error in finished parts. This phenomenon is explored along with various approaches for evaluating dimensional accuracy. Product design parameters, in particular, slice height, strongly impact surface roughness. A geometric model for surface roughness is also reviewed.

Originality/value

This represents the first review of extrusion AM processes focusing on dimensional accuracy and surface roughness. Understanding and improving relationships between materials, design parameters and the ultimate properties of finished parts will be key to improving extrusion AM processes and expanding their applications.

Details

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

Keywords

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