Title page for ETD etd-04092008-110148


Type of Document Dissertation
Author Jiang, Jing
Author's Email Address jjiang3@lsu.edu
URN etd-04092008-110148
Title Replication of Metal-Based Microscale Structures by Compression Molding: A Combined Experimental and Finite Element Analysis Study
Degree Doctor of Philosophy (Ph.D.)
Department Mechanical Engineering
Advisory Committee
Advisor Name Title
Glenn Sinclair Committee Co-Chair
Wen Jin Meng Committee Co-Chair
Dorel Moldovan Committee Member
Suresh Moorthy Committee Member
Yitshak Ram Committee Member
Luis Lehner Dean's Representative
Keywords
  • replication
  • compression molding
  • finite element analysis
Date of Defense 2008-03-14
Availability unrestricted
Abstract
Fabrication of microscale Ta mold inserts by micro-electrical-discharge-machining (ģEDM) is reported. Morphology, chemistry, and structure of the near-surface region of as-machined Ta blanks have been characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. A TaC surface layer forms on as-machined Ta surfaces. This altered surface layer was removed by electro-chemical-polishing. Further modification of Ta insert surfaces was accomplished by deposition of a conformal Ti-containing hydrogenated carbon coating. We demonstrate successful replication of high-aspect-ratio microscale structures (HARMS) in Al and Cu by compression molding with such surface-engineered Ta mold inserts. In addition, a hybrid microfabrication technique, combining micropattern definition with LIGA (Lithographie, Galvanoformung, Abformung) fabricated Ni microstructures with parallel micropattern generation with µEDM, was used to fabricate micropattern with some geometrical complexity on elemental Ta and 304 stainless steel.

Also, the results of instrumented micromolding of Al are studied. Measured molding response was rationalized with companion high-temperature tensile testing of Al using a simple mechanics model of the micromolding process. The present results suggest that stresses on the mold insert during micromolding are determined primarily by the flow stress of the molded metal at the molding temperature and the frictional traction on the sides of the insert. The influence of strain rate was also considered.

In addition, the elasto-plastic response of an Al block indented by a periodic array of long smooth strip punches made of a relatively rigid material is studied through finite element analysis (FEA). First, elastic test problems, for which analytical solution exist, are carried out to calibrate the FEA mesh. Results demonstrate that satisfactory accuracy is achieved for key, peak, contact stresses near the edge-of-contact region and interior stresses. Second, indentation response is tracked with FEA into the elasto-plastic regime. Results show that the yield region within the indented material approaches a self-similar state as indentation progresses.

Finally, Al molded by Si inserts at room temperature is studied through experiment and FEA.

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