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The ability to evaluate and determine the best part building orientation for different rapid prototyping (RP) processes is important for building a satisfactory part/prototype within the limits of manufacturing time and building cost. It is also an essential step towards the identification of the most suitable RP process with a given RP application. This paper discusses the selection of building direction for four RP processes, namely stereolithography (SL), selective laser sintering (SLS), fusion deposition modelling (FDM) and laminated object manufacturing (LOM). Main differences in the four processes are first examined with emphasis on the effects of these differences with regard to the building inaccuracy, the surface finish, the manufacturing time and cost. An optimal orientation algorithm is demonstrated on a part considered for processing with one of the four RP processes. The influence of the process characteristics on the selection of appropriate orientation with different RP processes is illustrated in the example. [ABSTRACT FROM AUTHOR]

A new rapid tooling technique named Rapid Pattern Based Powder Sintering (RPBPS) has been developed. It comprises the steps of first building a pattern made of polymer materials using a rapid prototyping machine based on a 3-D CAD model. The pattern is positioned on a substrate in a box or frame, then a mixture of metal (ceramic or polymer) powder and binder is cast around the pattern. Next, there is a step of removing the pattern and separating the substrate to obtain a green compact that has the desired cavity. Then the green compact will be sintered and/or infiltrated to form a tool or part. The new technique has the advantages of using a variety of materials, rapidity, making complex geometry parts and low cost, compared with several existing rapid tooling techniques. Many key technical problems in RPBPS are related to the binder. In order to select a suitable binder, the heat deformation resistance and heat stabilization of some polymer materials are discussed in depth. [ABSTRACT FROM AUTHOR]

Selective laser sintering (SLS) is one of the most successful rapid tooling processes. Shrinkage and beam offset are the two most important control parameters in this process. First, the SLS process and procedure of calibration are described. Second, based on the property of shrinkage and beam offset, a basic formula of shrinkage and beam offset is derived. Finally, the procedure of applying shrinkage (scaling factor) and beam offset is described. [ABSTRACT FROM AUTHOR]

The prospect of including colour in models using rapid prototyping systems significantly increases the range of potential applications. It is considered that prototypes displaying physical properties suitable for functional use that can also be coloured would lead to domestic use of the technology. The selective laser sintering (SLS) process, whilst not the easiest method for introduction of colour, provides those physical attributes. A mechanism developed for use inside an SLS machine is described along with some preliminary experiments and observations. [ABSTRACT FROM AUTHOR]

Selective laser sintering (SLS) is a solid freeform fabrication process whereby a part is built layerwise by scanning a powder bed. The processability of metal powder varies depending on the state of the powder prior to SLS. A powder thermal pre-treatment was developed which involved degassing the powder at an elevated temperature in a vacuum. Without powder thermal pre-treatment, the powder may flow poorly and may "ball" or form molten clumps during the laser exposure rather than wetting into the present and previous layer. These effects result in SLS parts with poor surface finish, mechanical properties and density. The purpose of this study was to identify for titanium alloy powder the mechanisms responsible for the improvements obtained after powder thermal pre-treatment and to optimize the thermal excursion. [ABSTRACT FROM AUTHOR]

The ability of portable inspection arms for inspection and redesign of body in white assembly tooling is evaluated. Issues of data exchange between the systems used including the accuracy and usability of the data are discussed. Data generated are used to directly produce modified location blocks using selective laser sintering. This offers a rapid route for tooling modifications and has proved to be a robust solution despite initial doubts. Other uses of inspection arms are also discussed. [ABSTRACT FROM AUTHOR]

LASER research, RAPID prototyping, STAINLESS steel, POROSITY, and SINTERING

Direct Metal Laser Re-Melting is a variant of the Selective Laser Sintering process, a Rapid Prototyping (RP) technology. This tool-less manufacturing technology has the potential of producing complex, high quality components from single-phase metal powders in short time scales. This is made possible by the production of consecutive two-dimensional layers. Unfortunately, finished components manufactured by this technique have their integrity and material properties dictated by the porosity within the laser re-melted structure. In order to maintain structural integrity comparable to conventionally produced components, metal components produced by the rapid prototyping method should exhibit a porosity of the order of maximum of ∼2% with corresponding bulk material properties. To achieve these objectives, process and laser parameters require optimisation for maximum densities to be attained. This paper reports on the development of a scanning strategy that produces stainless steel (316L) laser re-melted components which exhibit porosities of <1%, while maintaining the concept of rapid prototyping. [ABSTRACT FROM AUTHOR]

A non-contact infrared temperature sensor was used to monitor the temperature–time relation of a point on the powder bed during laser sintering. The results were translated into a temperature–distance relation of the monitored spot with respect to its distance from the laser beam. The effect of particle size of polycarbonate (PC) powder on the temperature–distance relation was studied. The maximum temperature attained at the monitored spot was found to increase with decreasing size of the PC particles. The phenomenon was probably caused by the higher packing density of the smaller particles, and more laser energy was absorbed near the powder bed surface. The temperature–distance relations of some common additives such as graphite, quartz, silica and talc were also studied, and graphite was found to give the highest temperature distribution. PC/graphite composite powders were blended and sintered under similar conditions. The surface temperature of the powder bed increased greatly with the addition of a small amount (up to 2 per cent) of graphite powder. The result was attributed to the higher absorptance of CO2 laser energy by the graphite powder. [ABSTRACT FROM AUTHOR]

SINTERING, METALLURGY, POLYMERS, MANUFACTURING processes, and RESEARCH

Selective inhibition of sintering (SIS) is a layered fabrication process which is capable of rapidly producing accurate functional parts out of polymers and metals using a relatively inexpensive machine. This article presents a brief overview of the research and development aimed at establishing the feasibility and the potential of the process. [ABSTRACT FROM AUTHOR]