The final broad class of machines has in common the property that thermal processing plays a strong role during the RP process. This thermal processing role is crucial because of (1) the generation of thermal stresses in the part as it is being formed, and (2) the attainment of the desired physical properties of the part. Designing the equipment used to effect the thermal control is often one of the most challenging aspects of these processes.

In FDM, it has already been noted that control of the extrudate temperature is critical. In addition, however, the control of the temperature in the atmosphere around the part has been found to be important in controlling part distortion. Similarly, in laser sintering, the control of the environment and the powder is crucial to control of residual stress and distortion. This control is particularly challenging because the powder bed must be held at an elevated temperature so as to further reduce the generation of stress. In the processes that laminate sheet such as hot roll with LOM and hot press with SAHP, the design of these laminators so as to minimize the introduction of stress has been a major focus of machine design efforts. In SDM, minimizing the stress introduced when a new layer of material is applied is an important consideration. In the LENS process and other similar processes, no studies of residual stress have yet been conducted; however, it is possible that such stresses will be strongly dependent on processing parameters.

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Published: March 1997; WTEC Hyper-Librarian