Influence of resin infiltrants on mechanical and thermal performance in plaster binder jetting additive manufacturing

Abstract

Plaster Binder Jetting (BJ) is one of the major Additive Manufacturing (AM) technologies which has been in use since the 1990s. It has many advantages such as the ability to print in full color CMY(K), no support structures, and is relatively faster and less expensive when compared to other AM technologies. Since there is no phase transformation (e.g. powder to molten pool in powder bed fusion, directed energy deposition), BJ does not require support structures and enables higher packing density in the build volume. However, relatively lower mechanical strength when compared to other AM processes has mostly limited it to non-functional applications such as prototyping. This paper investigates novel methods to improve the mechanical and temperature performance of plaster BJ additive manufactured parts via improved infiltration processes and incorporation of infiltrants with higher strength. Potential applications include functional end use products, including tooling, jigs and fixtures for higher temperature applications. Three 2-part epoxy resin systems were evaluated as infiltrants in comparison to epoxy and cyanoacrylate (CA) resins recommended by the original equipment manufacturer (OEM). Multiple impregnation methods including hot and wet vacuum were evaluated on their infiltration effectiveness. The best impregnation method was then used to prepare tensile, flexural and compressive samples for additional evaluation of each resin. Statistical analysis was conducted to analyze and compare the data. Both resins and infiltrated samples were individually evaluated using Differential Scanning Calorimetry (DSC) to determine glass transition temperatures and other thermal events. Infiltrated specimens of the best performing resins were evaluated for Heat Deflection Temperature (HDT) performance utilizing Dynamic Mechanical Analysis (DMA). It was found that infiltration is anisotropic, with the higher penetration depth from the sides (between layers) than top and bottom (across layers). Vacuum impregnation resulted in the highest infiltration depth by fully impregnating the 25 mm cubic samples. The best performing epoxy showed a 10% increase in mechanical strength over the OEM epoxy at 76% reduction in cost. The OEM cyanoacrylate had the lowest mechanical strength across all tests. DSC analysis revealed that the plaster and gypsum base material will start to dehydrate above 100 °C and will ultimately limit the parts’ high temperature capabilities. The OEM epoxy showed the highest HDT.