Vapor Smoothing Process Research Articles

Effect of Hot Vapor Smoothing Process on Surface Hardness of Fused Deposition Modeling Parts

Fused deposition modeling (FDM) has a staircase effect (as inherent process characteristics), which results in rough surface of the final components (usually of polymer-based materials such as acrylonitrile butadiene styrene [ABS]). This is one of the major limitations of this process, which hinders the use of this technique in precision industrial applications such as assembly parts and investment casting. Hot vapor smoothing (HVS) is one of the commercial techniques available for the improvement of surface finish of the FDM-based components. However, the reflow of the material by application of HVS may affect the surface hardness, tensile strength, and other mechanical properties of ABS parts. In the present study, surface hardness of ABS components has been improved through the HVS process by using acetone as smoothening media. Parts with different shapes and at different densities of FDM system were prepared at 0° orientation. Design of experimentation has been employed for optimization of input process parameters (namely geometry of the components/appliance, density of components/appliance, and acetone exposure time) in response to surface hardness of the parts. The scanning electron microscopic-based characterization of the components was carried out for justification of the surface hardness data.

Enhancing dimensional accuracy of FDM based biomedical implant replicas by statistically controlled vapor smoothing process

The aim of the present study is to highlight the benefits of vapor smoothing on ABS replicas prepared by fused deposition modeling (FDM) for rapid casting of biomedical implants. The FDM process induced stair steps on circular and sloping surfaces, which increased part dimensions when measured and led to oversized parts (contrary to reduced part dimensions in linear surfaces).The process originally developed for surface finishing employs the technique of plastic reflowing of heated material, in contrast to material removal in traditional finishing processes. Measurements performed on CMM helped in evaluating the dimensional tolerances of replicas which emerged to be within limits for three cycles of vapor smoothing (each of 20 s). Similar parameter settings yielded the best surface finish, which supported the assumption of layer resettlement of the semi-liquid ABS material. The statistical analysis strongly indicated the vapor smoothing process to be statistically controlled.

Preparation of Polyimide Ablator Coatings Using an Improved Solvent Vapor Smoothing Process

We completed the development of a method for preparing smooth vapor-deposited polyimide ablators up to 160 m thick for NIF target capsules. The process consists of two steps. The first step is vacuum chemical vapor deposition of monomer species, pyromellitic dianhydride and 4,4′-oxidianiline, onto the surface of a spherical shell mandrel where they may react to form polyamic acid. In the second step dimethyl sulfoxide (DMSO) vapor exposure in a gas-levitation smoothing apparatus swells and fluidizes the outer surface. Roughness in the outer fluid layer is reduced by surface-tension-driven flow. The shells are cured in the final smoothing step by heating to 300°C, converting the polyamic acid to polyimide. Recent experiments using X-ray radiography have allowed us to determine the depth of solvent penetration and the solvent concentration over a range of solvent exposure conditions. We found that the rate of penetration is a function of the solvent partial pressure in the flowing vapor stream. The concentration of solvent in the swollen layer is ∼0.43 g/cm3 and is independent of exposure conditions. Using the penetration information we were able to improve the smoothing process by increasing the solvent partial pressure. The optimized vapor smoothing process allowed us to consistently meet the surface smoothness specifications of NIF capsules.