Emerald | Rapid Prototyping Journal | Table of Contents

Prototype production and experimental analysis for circular and profiled conformal cooling channels in aluminium filled epoxy injection mould tools

Fri, 07 Jun 2013 00:00:00 +0100

Abstract

Purpose – The purpose of this paper is to present a technique of fabricating profiled conformal cooling channels (PCCC) in an aluminium filled epoxy mould using rapid prototyping (RP) and rapid tooling (RT) techniques and to compare the cooling times for the moulds with circular and profiled channels experimentally. The cooling channels in injection mould tools have a circular cross section. In a PCCC, the cross sectional shape is so designed that the flat face surface of the channel facing the cavity follows the profile of the cavity. These types of channels can be manufactured through RP and RT techniques. Design/methodology/approach – A part to be moulded was designed and modelled. Two moulds were then designed with the part cavity, one having a circular channel and the second with a profiled channel, both having the same cross sectional area for coolant flow. The channel patterns were designed with supports according to their position regarding height and distance from the cavity as designed earlier. Both channels have the same distance from the cavity wall. RP patterns were produced for both channels and part using the Thermojet 3D printer. The cooling channel and the moulded part patterns were then assembled as designed in the moulds. Moulding frames were fabricated with aluminium plates and the pattern was placed in the frames. Epoxy was poured on the pattern and then cured. The moulded part and the channel patterns embedded inside epoxy were melted out during the final curing cycle, leaving behind the circular- and profiled-cooling channels in the moulds. For the cooling time measurement, injection moulding was done with moulds with circular and profiled channels. Moulded part temperature will be recorded by embedding thermocouples within the mould cavities. Findings – A technique for the manufacture of cooling channels of different profiles in epoxy moulds was presented. Experimental analysis for temperature measurement for the moulded part with injection moulding process showed that PCCC mould has less cooling time then mould with circular channels. Research limitations/implications – The technique presented is based on the metal-filled epoxy materials used in RT and was obtained using a specific test part. Epoxy tooling can be a useful alternative of metallic mould to produce injection mould tools. A limitation for the epoxy moulds is that they have a limited life as compared with metallic moulds. Originality/value – This is a new technique of manufacturing moulds with cooling channels using RP/RT techniques. Moulds with different channel cross sections can be manufactured using this technique.

Novel polymeric support materials for jetting based additive manufacturing processes

literatinetwork@emeraldinsight.com (M. Fahad, P. Dickens, M. Gilbert) — Fri, 07 Jun 2013 00:00:00 +0100

Abstract

Purpose – Jetting-based additive manufacturing processes are gaining attention due to their high speed of operation, accuracy and resolution. Support material plays an important role in the additive manufacturing of parts by using processes that utilise jetting (inkjet) technology. This research aims to present novel support material compositions consisting of methylcellulose (MC) and propylene glycol or butylene glycol. These compositions form gels which are easy to remove and provide the advantage of reusability. Design/methodology/approach – MC was mixed in propylene glycol or butylene glycol in different concentrations and examined for gel formation on heating and subsequent cooling. The viscosity and surface tension of these compositions were measured at temperatures suitable for jetting. Gel strength was characterised using texture analysis. Findings – The viscosity and surface tension values at elevated temperatures (i.e. 800°C) show the suitability of these compositions for jetting-based additive manufacturing processes. Due to their softness, these gels can be removed easily and their low melting points (i.e. near 500°C) allow their reusability as support materials. Practical implications – This paper provides a novel approach of using polymer gels as support materials for additive manufacturing processes. These gels are easy to prepare and enhance the sustainability due to their reusability. Originality/value – Although, MC in water have shown to form gels and these aqueous gels have been used in many applications such as medicine and food industries, the compositions presented in this paper are unique. Such combinations of MC and non-aqueous solvents (i.e. propylene glycol and butylene glycol) have not been discussed before and provide an early step towards a new application area (i.e. additive manufacturing) for these gels.

3D roughness profile model in fused deposition modelling

Fri, 07 Jun 2013 00:00:00 +0100

Abstract

Purpose – The paper aims to predict the surface roughness of fused deposition modelling prototypes. Since average roughness is not comprehensive, this study aims to extend the characterization to all the roughness parameters obtainable by a profilometric analysis. Design/methodology/approach – A theoretical model of the 3D profile is supplied as a function of process parameters and part shape. A suitable geometry was designed and prototyped for validation. Data were measured by a profilometer and complemented by microscopic analysis. A methodology based on the proposed model was applied to optimise prototype fabrication in two practical cases. Findings – The proposed profile is effective in describing the micro-geometrical surface of fused deposition modelling prototypes. The third dimension enables the calculation of amplitude, spatial and hybrid roughness parameters. Research limitations/implications – Because of mathematical assumptions and technological aspects, the validity of the model presents limitations related to the deposition angle. Practical implications – The method is an effective tool in the process planning stage: it enables knowing in advance how to assure part specifications delivering a set of technical choices. Two practical applications point out the usability in the product development and process parameters optimisation. Originality/value – This work fulfils an identified need to predict a complete surface characterization of fused deposition modelling technology.

Regulating complex geometries using layered depth-normal images for rapid prototyping and manufacturing

literatinetwork@emeraldinsight.com (Yong Chen, Charlie C.L. Wang) — Fri, 07 Jun 2013 00:00:00 +0100

Abstract

Purpose – Most layer-based rapid prototyping systems use polygonal models as input. In addition, the input polygonal models need to be manifold and water-tight; otherwise the built objects may have defects or the building process may fail in some cases. This paper aims to present a regulation method of an arbitrarily complex polygonal model for rapid prototyping and manufacturing applications. Design/methodology/approach – The method is based on a semi-implicit representation of a solid model named the layered depth-normal images (LDNI), which sparsely encodes the shape boundary of a polygonal model in three orthogonal directions. In the method, input polygonal models or parametric equations are first converted into LDNI models. A regulation operator based on the computed LDNI models is presented. A volume tiling technique is developed for very complex geometries and high accuracy requirements. From the processed LDNI model, an adaptive contouring method is presented to construct a cell representation that includes both uniform and octree cells. Finally, two-manifold and water-tight polygonal mesh surfaces are constructed from the cell representation. Findings – The LDNI-based mesh regulation operation can be robust due to its simplicity. The accuracy of the generated regulated models can be controlled by setting LDNI pixel width. Parallel computing techniques can be employed to accelerate the computation in the LDNI-based method. Experimental results on various CAD models demonstrate the effectiveness and efficiency of our approach for complex geometries. Research limitations/implications – The input polygonal model is assumed to be closed in our method. The regulated polygonal model based on our method may have a big file size. Originality/value – A novel mesh regulation method is presented in this paper. The method is suitable for rapid prototyping and manufacturing applications by achieving a balance between simplicity, robustness, accuracy, speed and scalability. This research contributes to the additive manufacturing development by providing a digital data preparation method and related tools.

Efficient three dimensional modelling of additive manufactured textiles

literatinetwork@emeraldinsight.com (Guy A. Bingham, Richard Hague) — Fri, 07 Jun 2013 00:00:00 +0100

Abstract

Purpose – The purpose of this paper is to investigate, develop and validate a three-dimensional modelling strategy for the efficient generation of conformal textile data suitable for additive manufacture. Design/methodology/approach – A series of additive manufactured (AM) textiles samples were modelled using currently available computer-aided design software to understand the limitations associated with the generation of conformal data. Results of the initial three-dimensional modelling processes informed the exploration and development of a new dedicated efficient modelling strategy that was tested to understand its capabilities. Findings – The research demonstrates the dramatically improved capabilities of the developed three-dimensional modelling strategy, over existing approaches by accurately mapping complex geometries described as STL data to a mapping mesh without distortion and correctly matching the orientation and surface normal. Originality/value – To date the generation of data for AM textiles has been seen as a manual and time-consuming process. The research presents a new dedicated methodology for the efficient generation of complex and conformal AM textile data that will underpin further research in this area.

High temperature material properties of IN738LC processed by selective laser melting (SLM) technology

Fri, 07 Jun 2013 00:00:00 +0100

Abstract

Purpose – Selective laser melting (SLM) is being investigated by Alstom and IWF due to its flexibility, cost- and lead-time reduction potential for reconditioning of hot gas path components used in today's heavy-duty gas turbines. This paper aims to address this issue. Design/methodology/approach – Tensile tests as well as relaxation and creep tests were carried out to assess SLM processed IN738LC for use in high temperature applications. To evaluate potential anisotropic material behaviour resulting from the layer-wise build up process, all specimens were built in two directions: parallel and perpendicular to the build direction, respectively. Furthermore, extensive metallurgical investigations were made to analyse the chemical homogeneity as well as the correlation between microstructure and high temperature properties of SLM processed IN738LC. Findings – Tensile tests showed that strength properties superior to cast IN738LC can be achieved by processing this material by SLM alternatively. Due to differences in grain size, grain orientation as well as ?'size and morphology the relaxation behaviour of SLM specimens is inferior compared to cast material. However, creep tests have shown that values within the lower scatter band of cast material can still be achieved along the build direction. Originality/value – Very limited knowledge exists regarding the processing of ?'precipitation-strengthened nickel-base superalloys by SLM and the resulting high temperature material properties. Layered manufacturing and any lack-of-fusion porosity influences them as well as high temperature gradients, occurring during the process. This article presents the latest insights from material testing of selective laser molten IN738LC at elevated temperatures.

Fatigue analysis of FDM materials

literatinetwork@emeraldinsight.com (John Lee, Adam Huang) — Fri, 07 Jun 2013 00:00:00 +0100

Abstract

Purpose – The purpose of this paper is to determine the effects of fatigue on fused deposition modeling rapid prototyped acrylonitrile butadiene styrene (ABS) materials. Design/methodology/approach – FDM dog bones based on UNI EN ISO 527-1 (1997) were tested at 100, 80, 60, and 40 per cent nominal values of the ultimate stress for nine different print orientations. The samples were cyclically stressed in a tensile tester at 25.4?mm/min (extension) and relaxed at 12.7?mm/min. Findings – Although FDM ABS has a tensile strength that is relatively close to that of the bulk material, up to 80 percent, its ability to absorb energy before fracture has a tremendous amount of room for improvement. FDM ABSplus (P430) material properties are noticeably more isotropic than the predecessor, ABS (P400). The ABSplus fractures in the order of thousands of cycles at 40 percent of ultimate stress load, while the ABS exhibits the similar cycle limits at 60 percent of its ultimate stress load. Practical implications – FDM ABS parts are limited in fatigue characteristics even though they exhibit similar ultimate stress limits as with bulk materials, warranting further research in improving FDM parts expected to experience cyclical loads. Originality/value – This paper adds knowledge to the limited fatigue data in literature for FDM ABS. It investigated the load cyclic data of fused deposition modeled ABS through analyzing its cycle-by-cycle strain energy, providing another means of identifying the fatigue characteristics of materials.

Weibull growth modeling of laser-sintered nylon 12

Fri, 07 Jun 2013 00:00:00 +0100

Abstract

Purpose – This paper seeks to present the results of an experiment to investigate the effect of six part orientation (XY, XZ, YX, YZ, ZY, ZX) and a wide range of energy densities on ultimate tensile strength (UTS) and elongation of laser-sintered nylon 12 (PA-12) test specimens. Design/methodology/approach – ASTM Type 1 specimens were built on a DTM Sinterstation 2500+ and tensile tested on an Instron 5569?A. The resulting data were fit to non-linear regression models based on the well-known Weibull growth model to predict each response based on the total energy density used in each trial. Findings – The resulting regression models provide excellent fits with low sum of squared errors and normally distributed residuals. The resulting material properties are highly affected by the energy density and the build orientation. However, once sufficient energy density is applied, properties tend to converge to consistent values. To achieve maximum UTS of approximately 52?MPa, it is recommended that values of energy density above 0.25?W-s per mm3 be used. To achieve maximum elongation of approximately 15-16 percent, it is recommended that values of energy density above 0.40?W-s per mm3 be used when building parts in the XY, XZ, YX, YZ orientations. Parts built in the ZX orientation exhibit lower elongation values at or below 12 percent for even high values of energy density. Originality/value – This paper extends previous work of Starr, Gornet and Usher on the relationship between material properties, part orientation and energy density by proposing the use of the Weibull growth model. Recommendations are provided to assist users in the selection of correct energy density to achieve desirable mechanical properties in each specified orientation.

Editorial

literatinetwork@emeraldinsight.com (Ian Campbell) — Thu, 01 Jan 1970 01:00:00 +0100