Investigation on Mechanical Properties, Geometric Accuracy and Surface Roughness Improvement for Fused Deposition Modeling

Abstract

Fused deposition modeling (FDM) process is one of rapid prototyping (RP) technology widely adopted by the industries for producing low cost complex geometrical parts. This prototype making process involves environmental friendly thermoplastic material in form of a filament to melt and deposit materials layer by layer with admirable accuracy and part strength. Materials are deposited through nozzles in a desired pattern onto a worktable that moves in Z direction (depth) whereas nozzle head moves on plane of worktable in X and Y direction. The bonding between the adjoining layers is caused due to thermally driven diffusion bonding. After one layer is deposited, the work table moves down by amount of layer thickness and next layer is added. Simplicity of operation together with the ability to fabricate complex parts resulted in its wide spread applications not only for prototyping but also for making functional parts. However, FDM process has its own demerits related with highly anisotropic mechanical properties, geometric accuracy, surface quality etc. Hence, it is absolutely necessary to investigate role of controllable factors for improvement of part quality. In this direction, present study focuses on the improvement of part build methodology by properly controlling the process parameters. The thesis deals investigation of with various part quality such as mechanical properties (tensile and flexural strength), improvement in geometric accuracy, minimization of surface roughness and build cost of FDM processed ABS P430 parts. The understanding generated in this work not only explains the complex build mechanism but also present in detail the influence of process parameters such as part orientation and raster angle on responses with the help of experimental results, scanning electron microscopy and multi response optimization using analytical hierarchy process. For experimental investigation three different part orientation (along X, Y and Z axis ) and four different raster angles (0°, 30°, 60°, 90°) are considered for building of components and tested for mechanical strength (tensile and flexural) and surface roughness. For geometric accuracy and surface quality measurement, parts with different primitives and doubly curved/ freeform surfaces are considered which are built at seven different part orientation (0°, 15°, 30°, 45°, 60°, 75°, 90°) about Y axis and part orientation along X, Y and Z axis are considered for freeform surfaces. Geometric error of the built part with respect to the CAD geometry is measured for all the parts. For FDM parts, model material, support material consumption along with build time cumulatively represents the build cost. For each of the part orientation and raster angle, the volume of model and support material consumption, build time are measured and compared. Next, all the parts are chemically treated with cold vapor of dimethylketone and tensile strength, flexural strength, surface roughness and geometric accuracy are measured and compared with those without any post treatment. Rapture surfaces under tensile and flexural loading are also studied by SEM to understand the failure mode of the specimen under different loading conditions. Later, the FDM process parameters that affected the studied responses were identified and optimized by multi-response optimization using analytic hierarchy process for maximum achievable tensile and flexural strength, with improved geometric accuracy, surface finish and lower the build time. The methods adopted in this study are quite general and can be used for other related or allied processes, and believed to be beneficial for industries like aerospace, automobile, home appliances, etc. for identifying the process capability and further improvement in FDM process.