Guidelines for dimensional accuracy and machining allowances of 3D printed metal parts

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Insinööritieteiden korkeakoulu | Master's thesis
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Master's Programme in Mechanical Engineering (MEC)
In this research, characteristics of 3D printed metal parts are investigated. Main objectives are to find dimensional accuracy and define machining allowances for 3D printed metal parts. To achieve this goal internal threads were manufactured, and their quality was examined. Method of this study was to examine quality of M5 and M8, internal threads. For this purpose, preholes were printed in flat plates in 5 different printing inclinations to build plate. Aluminium and maraging steels were main materials used in this research. Printing-machine’s recoater angle was varied to observe its effect in determining part’s dimensional accuracy. Printed parts were examined in as-built condition and after heat treatment. Physical properties measured during experimentation were surface roughness, flatness, hardness, porosity near surface, hole size and drilling forces. Thread strength was measured using thread stripping forces and thread profile was analyzed with optical microscope. In results, effect of printing inclination on material properties was investigated. Comparison of different recoater angles and heat treatments were done separately. Results revealed that printing inclination and recoater angle do not affect material properties significantly and that threads are equally strong in all directions. Machining allowances, due to material surface defects, are recommended to be 0.2 mm for aluminium and 0.1 mm for maraging steel components. Making a pre-hole during printing reduces drilling forces up to 80%. To avoid off-centering effects during drilling, pre-hole size is recommended to be 1 mm smaller than nominal diameter. Funding for this project was provided by Aalto University, Department of Mechanical Engineering, “FIN3D” research project. Equipment from laboratories of Production Engineering and Material Science of Mechanical Engineering, Aalto University, were utilized in the research. EOS Finland provided metal printed parts and valuable information.
Niemi, Esko
Thesis advisor
Niemi, Esko
additive manufacturing, machining allowances, metal printing, dimensional accuracy, drilling and tapping, internal threads
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