Table 2 Mechanical properties of the rubber specimens
Related Figures (7)
Table 1 Process parameters and levels A single layer of 10 mm by 10 mm squares was fabricated at different combinations of process parameters. An optical microscope was used to inspect the sample morphology. The best- known combination of the process parameters was subsequently determined, and three specimens were additively manufactured for mechanical test and equilibrium swelling test. The mechanical test was conducted under the ASTM D412 standard with the rate of grip separation of 500450 mm/min. The equilibrium swelling test was conducted using toluene and crosslink densities of the samples were calculated by using the Flory-Rehner equation. In both tests, the specimens were layer thickness that is controlled by a vertical displacement of the platform. The surface of the latex is selectively irradiated by a laser beam to form a semi-solid layer. Figure 1 Diagram of the in-house developed SLA machine Figure 3 Surface morphology of the samples with the layer thickness of 200 um Figure 3 and Figure 4 illustrate the surface morphology of each sample observed under ar optical microscope, with 200-um and 300- um thickness, respectively. The figures clearly assure that the appearance of the surface can possibly be used as an index to assess the quality of the samples. As the NR is naturally an unsaturated polymer, the material is highly vulnerable to ar excess heat due to its thermal degradation mechanism. As a result, the samples became somewha tacky when the laser energy density was too high. The degradation of the rubber can be observec by the shiny surfaces and also the physical condition of a tacky surface shown through the micrographs. On the other hand, when the laser energy density is scarce, sufficient heat is no transferred into the layer of the NR latex. If this is the case, the 3D part cannot be formed, sinc« the solidified line after the laser exposure is rather flimsy to connect to the neighboring line. Figure 4 Surface morphology of the samples with the layer thickness of 300 pm Subsequently, NR samples with a cellular structure were fabricated using the in-house developed SLA machine to demonstrate the potential of the technology with the best known set of process parameters. Seven layers of the latex were formed into a 3D part shown in Figure 5. The fabricated sample with the cellular features reveals that the latex mixture and SLA process developed in this work is capable of producing a customized components with tailored cellular sizes and stiffness gradient.
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