High green density metal parts by vibrational compaction of dry powder in three dimensional printing process

The material properties and dimensional accuracy of metal tooling produced by the Three Dimensional Printing process can be enhanced by increasing the green density of the 3D printed part. Green density is the ratio of metal powder volume to the external volume of the printed part, and is a measure of how tightly packed the powder particles in the printed part are. The central goal of this thesis was to increase the green density of metal parts from the current level of 58% to levels greater than 75%. Two approaches were taken for increasing green density. The first was to utilize bimodal mixtures of metal powders which could be packed to significantly higher densities than the monomodal powders which had been previously used. Three bimodal powder mixtures, with tap densities near 80%, were studied. The second approach was to develop a new powder layering device which could pack these bimodal powders to the tap density during layer creation. New understandings about the relationship between the stresses applied to the powder layer and the resulting packing density changes were required to design this device. Shear cell and unconfined compression tests were performed to characterize the metal powder stress / strain behavior. Particulate stress / strain models, such as the Mohr-Coulomb failure law and the Jenike yield locus theory, were used to interpret the packing behavior of the metal powders under various stress conditions.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

1996

Author dc:creator

• Gregorski, Steven Joseph

Advisor dc:contributor.advisor

• Emanuel M. Sachs.

• Mechanical Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/8179

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/8179