POWDER injection molding, RAPID prototyping, MARAGING steel, SINTERING, INJECTION molding of metals, PRODUCTION engineering, MANUFACTURING processes, MATERIALS, INDUSTRIAL engineering, RESEARCH methodology, and METALLURGICAL research

In this research work, attempts have been made to design, develop and evaluate the performance of mould inserts for injection moulding by using a powder-sintering process. Maraging steel powder, sintering aid and binder are materials used in this proposed development process. Attempts have been made to perform in-depth studies and to apply the powder-sintering process, to eventually produce the final sintered components. In addition, an analysis of the dimensional accuracy of the respective stereolithography master models and an analysis of the sintered specimens during various stages of powder-sintering process have been carried out. The intelligent manufacturing systems (IMS) test part with minor modifications has been used in the evaluation of dimensional accuracy, tolerances, distortion and volumetric variations. The main reason for using this unique geometry is the suitability of its design for injection-moulding processes and tooling. [ABSTRACT FROM AUTHOR]

SURFACE roughness, SINTERING, ALGORITHMS, INDUSTRIAL efficiency, PROBLEM solving, and PRODUCTION (Economic theory)

In the present work an attempt has been made to achieve minimum average part surface roughness (best overall surface quality), minimum build time and support structure for stereolithography (SL) and selective laser sintering (SLS) processed parts by determining optimum part deposition orientation. A conventional optimisation algorithm based on a trust region method (available with MATLAB-7 optimisation tool box) has been used to solve the multi-objective optimisation problem. It is observed that the problem is highly multi-modal in nature and a suitable initial guess, which is used as an input to execute the optimisation module, is important to achieve a global optimum. A simple methodology has been proposed to find out the initial guess so that global minimum is obtained. Finally the surface roughness simulation is carried out with optimum part deposition orientation to have an idea of surface roughness variation over the entire part's surface before depositing the part. Case studies are presented to demonstrate the capabilities of the developed system. The major achievements of this work are consideration of multiple objectives for the two rapid prototyping processes, successful use of conventional optimisation algorithm available with MATLAB to handle multiple objectives and development of graphical user interface-based system. [ABSTRACT FROM AUTHOR]

POLYMERIC composites, RAPID prototyping, RAPID tooling, SINTERING, LASERS, and HUAZHONG University of Science & Technology (Beijing, China)

Rapid prototyping (RP) and tooling (RT) are the technologies for quickly fabricating functional components and tooling inserts directly from CAD data by selectively adding material layer by layer. In this paper, multiphase polymeric materials for RP and RT technologies and their applications, which are developed by the Rapid Manufacturing (RM) Center of Huazhong University of Science and Technology (HUST) in China, were introduced. Selective laser sintering (SLS) is a powder-based RP process. Multi-types of multiphase polymer materials for SLS process were successfully developed in the RM center, and the SLS components were formed from these materials by using the commercial SLS machines HRPS series for various applications. High impact polystyrene (HIPS)/wax blend SLS parts were used as lost patterns for the investment casting process to make complex metal parts rapidly; nylon-12/organically modified rectorite and nylon-12/nanosilica composite powders were used to fabricate functional parts, which showed higher thermal and mechanical properties than neat nylon-12 SLS parts. As a RT application, Fe/epoxy composite tooling inserts were rapidly fabricated by SLS and post-processing. Stereolithography (SLA) uses photocurable resins to rapidly manufacture components with high accuracy and mechanical properties. A freeradical and cationic mixed-type radiation curable composite resin was also successfully developed, and SLA parts without obvious distortion were built on the SLA machines HRPL series from this hybrid resin, successfully and efficiently. [ABSTRACT FROM AUTHOR]

RAPID prototyping, INTERNET, COMPUTER systems, PROTOTYPES, and SINTERING

The part quality and cost are greatly affected by process parameters during rapid prototyping (RP). This paper proposes a Virtual Rapid Prototyping System (VRPS) and describes its functions, characteristics and realization method. Moreover, aimed at the Selective Laser Sintering (SLS) technology, an Internet-based virtual rapid prototyping system named VRPS-I is implemented using Java and Virtual Reality Modeling Language (VRML). The system resembles the physical fabrication system of SLS. With the aid of this system, not only can the visual rapid prototyping process be dynamically previewed, but the forming process and some part-quality-related parameters can also be predicted and evaluated. Therefore, the reasonable rapid prototyping parameters can be predetermined according to the simulated results without any physical RP machine. Hence, it can help optimize the prototyping process, improve part quality, enhance fabrication efficiency, and lower the model making cost significantly. [ABSTRACT FROM AUTHOR]

PIEZOELECTRIC ceramics, LASERS, SINTERING, PIEZOELECTRICITY, CERAMICS, and RAPID prototyping

This article presents a new lost mold rapid prototyping method which combines selective laser sintering (SLS) and gelcasting techniques for fabricating piezoelectric ceramics. SLS was used to fabricate sacrificial molds of the desired structure of the ceramic part. Then aqueous PZT (lead zirconate titanate) suspension was cast in the mold and solidified in situ through formation of a three-dimensional network gel. Because the polymer mold can be easily removed at the initial stage of sintering and the gelcast PZT body has a high green strength, the desired geometry of the PZT part can be completely retained after sintering of the ceramics. Complex-shaped PZT parts were successfully fabricated after using concentrated PZT suspension with low viscosity. Densities and electrical properties, such as the d[sub 33], the relative permittivity ε, the dielectric loss tgδ and the electromechanical coupling factor K[sub p] of the gelcast PZT parts were also compared with those of the die-pressed PZT samples. The results indicated that the gelforming process did not deteriorate the electrical properties of the samples, if proper dispersant was selected in developing concentrated ceramic slurry. [ABSTRACT FROM AUTHOR]

SINTERING, METAL powders, RAPID prototyping, MANUFACTURING processes, ARTIFICIAL neural networks, and BACK propagation

As one of the promising Rapid Prototyping (RP) processes, the Direct Metal Laser Sintering (DMLS) technique is capable of building prototype parts by depositing and melting metal powders layer by layer. Metal powder can be melted directly to build functional prototype tools. During fabrication, four important resulting properties of interest to the users are: the processing time, mechanical properties, geometric accuracy and surface roughness. By adjusting an identified set of process parameters, these properties can be properly controlled. The process parameters involve: the laser scan speed, laser power, hatch density, layer thickness and scan path. But the relationships between these parameters and their resulting properties are quite complicated. In many cases, the effects of different parameters on the resulting properties contradict one another. In this paper, an intelligent system to assist the RP user to choose the optimal parameter settings based on different user requirements is presented. For the accurate prediction of the resulting properties of the laser-sintered metal parts, a method based on the feed-forward neural network (NN) with backpropagation (BP) learning algorithm is described. Through experiments, some input-output data pairs have been identified. After continuous training by using the data pairs, this NN constructs a good mapping relationship between the process parameters and their resulting properties. The system developed can determine the most suitable parameter settings containing the process parameters and predict resulting properties from the database built based on different process requirements automatically. It is very useful to RP users for saving material cost and reducing processing time. [ABSTRACT FROM AUTHOR]

RAPID tooling, INJECTION molding of metals, SINTERING, RAPID prototyping, MANUFACTURING processes, and INDUSTRIAL engineering

With the continuing development of Rapid Prototyping technologies, there has been a move into areas of Rapid Tooling. This takes advantage of the shorter lead times and lower costs associated with the production of tooling, particularly for injection moulding. This paper analyses the effectiveness of using direct metal laser sintering to produce injection-moulding tools, in terms of the force required to eject a part from a tool. Different levels of finishing were applied to test tools, and the results show that in some cases the forces required to eject parts from direct metal laser sintered tools were comparable with those from machined tools. [ABSTRACT FROM AUTHOR]

POLYAMIDES, MECHANICAL behavior of materials, MATHEMATICAL optimization, RAPID prototyping, SINTERING, and RESPONSE surfaces (Statistics)

Selective laser sintering (SLS) is one of the widely used rapid prototyping (RP) processes. The main challenge of this process is to choose the correct working parameters to attain the desired shape, size, and strength of different products. Therefore, this article pertains to an experimental study carried out to understand mechanical properties of selective laser sintered polyamide parts. Experiments were established based on face-centered central composite design (CCD) of response surface methodology (RSM). The effect of various process parameters on different properties (i.e., ultimate tensile strength, % elongation, yield strength, and Young's modulus) was analyzed. Analysis of variance was employed to check the adequacy of the developed models. Furthermore, the optimal combination of these process parameters has been evaluated. Considering ultimate tensile strength, % elongation, yield strength, and Young's modulus simultaneously, the optimum values of different process parameters have been obtained as: laser power, 32 W; scan spacing, 0.17 mm; bed temp, 178°C; and scan count, 2. [ABSTRACT FROM AUTHOR]

MICROFABRICATION, CERAMIC materials, SINTERING, SHELL molding (Founding), LASER fusion, POROSITY, and RAPID prototyping

Through studying the porosity of the ceramic parts fabricated with slurry-based rapid prototyping process of ceramic laser fusion and ceramic laser sintering, the feasibility of directly fabricating ceramic shell mold was investigated in this paper. Although the total porosity of the fusion part was low, microcracks led to low strength, which was hardly enhanced by post-treatment of infiltration. On the other hand, by adjusting the slurry formulation and varying the laser scanning energy, the open porosity of the sintered part was over 90 vol.% of the total porosity. High open porosity resulted in good permeability, which is one of the important characteristics of the ceramic shell mold for investment casting. To verify the feasibility of producing casting part with ceramic shell molds fabricated by the processes of ceramic laser fusion and ceramic laser sintering, the casting process was conducted to obtain the casting parts. [ABSTRACT FROM AUTHOR]

SINTERING, SINTER (Metallurgy), LASER beams, RAPID prototyping, PROTOTYPES, MANUFACTURING processes, and POWER transmission

This paper presents a linear drive system that implements the high-accuracy reciprocating motion of the dynamic focus module in selective laser sintering (SLS) rapid prototyping manufacturing. The linear drive system consists of a moving-coil type PM linear DC motor (LDM), a DSP-based digital controller, a pulse-width modulated servo amplifier, and a linear optical encoder. The special configuration and dynamic model of the LDM are presented, the transfer function of the control system is derived, and a PID feedback controller including a low-pass filter with the derivative term and a model-based feedforward controller are designed. The present experiment proves that the tracking performance of the control system is satisfactory. The experimental results show that the linear drive system has fast dynamic response and acceptable tracking error in the driving dynamic focus module of SLS machines. [ABSTRACT FROM AUTHOR]

COPPER alloys, SINTERING, RAPID prototyping, METAL powders, LASERS in metallurgy, and ENERGY level densities

Direct laser sintering of a multicomponent Cu based metal powder was successfully processed through the mechanism of liquid phase sintering with partial melting of the powder. The effects of processing parameters such as laser power, scan speed, scan line spacing and layer thickness on the densification and microstructural evolution of the laser sintered powder were investigated. It was found that with increasing laser power or decreasing scan speed, the density of the sintered parts increased and the microstructures became denser. However, the combination of higher laser powers (>400 W) and higher scan speeds (≥0·06 ms-1) gave rise to 'balling' effect. A successive transition from discontinuous scan tracks to coherently joined ones occurs with decreasing scan line spacing. Lowering the thickness of the powder layer promises an improvement in bonding coherence between sintered layers. A single factor termed 'energy density by volume' is defined to evaluate the combined effect of various processing parameters on the density of laser sintered powder. With increasing the energy density by volume up to ∼0·16 kJ mm-3, the densification rate is relatively high. However, with intensifying the energy density over ∼0·23 kJ mm-3, the mechanism of particle bonding may change into full melting/solidification, leading to a decrease in the sintered density. [ABSTRACT FROM AUTHOR]

RAPID prototyping, SINTERING, TOOL-steel, MICROSTRUCTURE, and POWDER metallurgy

In the present work, the densification and microstructure of M2 high speed steel powder processed by direct laser sintering method was studied. Test specimens were produced using a 200 W continuous wave CO2 laser beam at different scan rates ranging from 50 to 175 mm s-1. The building process was performed under argon and nitrogen atmospheres in order to evaluate the role of sintering atmosphere. It was found that the sintered density strongly depends on the laser scan rate and thus on the duration time of the laser beam on the surface of the powder particles. Generally, with a decrease in the scan rate higher densification was obtained. However, formation of large cracks and delamination of the sintered layers is feasible at low scan rates. The results also demonstrated that sintering under argon atmosphere yields better densification compared to a nitrogen atmosphere, in particular at higher scan rates. The microstructure of laser sintered parts consisted of large and elongated pores parallel to the building direction. The metal matrix structure was found to be heterogeneous, i.e.carbon rich austenite was formed due to carbon segregation. This structure consisted of fine cellulars or dendrites of martensite and retained austenite. This article describes the influence of manufacturing parameters on the densification of laser sintered M2 high speed steel powder. The microstructural features of the processed parts are also addressed. MST/6144 [ABSTRACT FROM AUTHOR]