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The purpose of this paper is to develop a methodology to achieve successful infiltration of indirect selective laser sintered steel components with ferrous alloys and thereby to produce fully ferrous components with desirable properties while preserving part geometry.

The approach is to generate a “green” part by selective laser sintering (SLS) of ferrous powder mixed with a transient binder in a commercial polymer machine. This part is post‐processed to burn off the transient binder (brown part) and to infiltrate the porous structure with a lower melting point ferrous metal. A critical consideration is loss of part structural integrity by over‐melting after infiltration as a result of chemical diffusion of alloying elements, principally carbon. A predictive model defining the degree of success of infiltration based on chemical equilibrium may be used to select the temperature for infiltration.

The infiltration temperature should be set such that the equilibrium solid fraction of the final infiltrated part is at least equal to or greater than the brown part solid fraction.

Infiltration temperature must be carefully controlled to prevent melting of the brown part. Effect of alloying elements other than carbon on equilibrium solid fraction is not considered while constructing the predictive model.

This approach can be used to obtain fully ferrous parts with complex geometry and desirable properties using a low‐cost polymer SLS machine.

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.

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.

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.

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

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.

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.

This paper focuses on recent advances in direct freeform fabrication of high performance components via selective laser sintering (SLS). The application, known as SLS/HIP, is a low cost manufacturing technique that combines the strengths of selective laser sintering and hot isostatic pressing (HIP) to rapidly produce low volume or “one of a kind” high performance metal components. Direct selective laser sintering is a rapid manufacturing technique that can produce high density metal parts of complex geometry with an integral, gas impermeable skin. These parts can then be directly post‐processed by containerless HIP. The advantages of in situ encapsulation include elimination of a secondary container material and associated container‐powder interaction, reduced pre‐processing time, a short HIP cycle and reduction in post‐processing steps compared to HIP of canned parts. SLS/HIP is currently being developed under a DARPA/ONR program for INCONEL® 625 superalloy and Ti‐6Al‐4V, the demonstration components being the F‐14 turbine engine vane and the AIM‐9 missile guidance section housing base respectively.

This paper aims to present a new fabrication method for fuel cell current collectors. Demonstration of its usefulness and discussion of its impact on current collector design and performance are also given.

The selective laser sintering (SLS) technique is used to create green parts followed by a high temperature curing process and pressureless infiltration treatment to meet basic part design requirements.

A material system and process satisfying both manufacturing constraints and product property requirements can be used for fabrication of current collectors via SLS. Relative particle size and composition of the constituents play an important role in successful manufacture of the plates. Strategies to improve electrical conductivity are also discussed.

A new manufacturing method has been developed for the construction of fuel cell current collectors that could generate opportunities for performance enhancement and fuel cell application by eliminating the constraints imposed by traditional fabrication processes.

The purpose of this paper is to report selected optical properties of laser sintered polyamide 12 blank plates under different monochromatic and white light conditions and to apply these properties in production of laser sintered lithophanes.

A UNICO 1201E spectrophotometer was used to measure the transmittance of laser sintered polyamide 12 plates as a function of plate thickness. Monochromatic light-emitting diodes were used to assess the wavelength dependence on the transmission and contrast as captured by a SONY DSC-W55 camera.

The transmittance decreased with increasing plate thickness which varied significantly depending on the monochromatic wavelength. Highest transmission was observed using green light (525 nm) and poorest transmission was measured for yellow light (589 nm).

There is a limit to the amount of contrast obtained in polyamide lithophanes because the thickness of the plates is limited to less than about 5 mm. Greater thickness results in discernible topology on the lithophane which impairs the quality of the image.

Light transmittance of polyamide 12 plates under different lighting conditions is reported and applied to optically defined laser sintered lithophanes.

The purpose of this paper is to produce electrically conductive, fluid impermeable graphite bipolar plates for a direct methanol fuel cell, using indirect selective laser sintering (SLS) and suitable post processing techniques.

Bipolar plates are made by the indirect SLS of graphite powder and phenolic resin mixture. The phenolic resin binder is then burnt off at a high temperature in a vacuum furnace to produce a 100 per cent carbon part. This brown part is then infiltrated using a low‐viscosity (∼5‐10  cps) cyanoacrylate to seal up the open pores, rendering the plates fluid impermeable.

It has been found that the electrical conductivity increases significantly (> 220 S/cm) with a corresponding increase in pyrolyzing temperature which correlates well with literature on the carbonization of phenol formaldehyde resins. The cyanoacrylate infiltrated parts tested under fluid pressure demonstrated no leakage through the plate, indicating full closure of open porosity.

This work demonstrates the capability of the SLS process to produce working bipolar plates with complex flow field designs that can be tested to verify its efficacy in a working fuel cell, thereby saving time and cost in machining natural graphite.