Professor Tien-Chien Jen


Thermal Manufacturing and Machining Group

Research


Electrostatic Force-Assisted Cold Gas Dynamic Spraying Process


        Nanoparticles with diameters between 1 and 100 nm are naturally the source materials or "building blocks" of nanocrystalline solids and coatings. A direct fabrication technique for nanostructured coatings and bulk materials involve the deposition or the compaction of nanoparticles to form coatings or bulk parts without coarsening the nanoscale structure. Since the unique properties are very often limited to the finest grain sizes, methods must be found to stabilize the grain size (i.e. without coarsening) while attaining theoretical density and completing particulate bonding.
       
       
One of the greatest challenges for nanostructured coatings and bulk materials is the fast turn-around and high throughput. The fundamental gateway for this is cost-effective nanoparticle production and nanostructure deposition and compaction. Although there are quite a wide variety of techniques for the fabrication of nanostructured coatings and bulk materials, the most current techniques are often limited to the laboratory scale and are high-temperature-related fabrication process which will cause most of the nanoparticle material oxidizing and coarsening so that the nanostructure coatings and bulk materials with required properties cannot be obtained. Therefore, developing innovative techniques without grain coarsening, melting temperature limitation, and contamination or oxidation for fabricating nanostructured coating and bulk materials inexpensively and quickly is an important area that requires substantial research. The main objective of this proposal is to develop a cost-effective low temperature nanostructure deposition and compaction technology to fulfill this challenge.

        Dr. Jen's group is developing an innovative, highly efficient, and low-cost technique of low temperature Electrostatic-force-assisted Cold Gas Dynamic Spray (ECGDS) with mini-arc source nanoparticle production for the fabrication of nanostructured coatings and bulk materials. This project is supported by the National Science Foundation, UW System Applied Research Grant, and Research Growth Initiative Grant.


          ECGDS and ECGDS Research Team

Decentralized Solar and Bio Combined Sustainable Energy System

        The objective of this research is to develop a decentralized Bio Solar Combined Sustainable Energy System  for transportation engine and micro turbine fuel application (Biomass from waste & solar-to-Hydrogen enriched Biogas) and fuel cell hydrogen application (Biomass & solar-to-Hydrogen). The intention is to promote the utilization of eco-friendly bio and solar energy resources at a massive scale and to the maximal extent in view of reducing greenhouse gas emission and building up recycling-oriented society through the effort of intensive research into the bio and solar combined sustainable energy system.


Graphite Coating Metal Bipolar Plate for PEM Fuel Cell

        In fuel cell technology, one of the most important, heavy and expensive part in fuel cell is the bipolar plate (fluid field plate) manufacture. The bipolar plate is one of the key components of proton exchange membrane (PEM) fuel cells. The development of materials suitable for use as bipolar plates is technically challenging due to the need to maintain high electrical conductivity in both oxidizing and reducing environments, exhibit chemical compatibility with the aqueous environment and the polymer electrolyte, provide mechanical integrity, and separate/distribute anodic and cathodic reactant gas streams. 

          Thin metallic bipolar plates have the advantage of significantly higher power densities than carbon fiber (and carbon-polymer) bipolar plates. However, inadequate corrosion resistance for metallic bipolar plates can lead to high electrical resistance and/or contaminate the proton exchange membrane. Excessive plate corrosion and the formation of metallic cations can alter fuel cell operation and performance in a number of different ways, by reducing the membrane's ionic conductivity, or even impairing tightness or obstructing channels. Therefore, an effective, low-cost approach is needed to fabricate corrosion resistant coatings on thin metallic bipolar plates.

        In this research, Dr. Jen’s research group is developing advanced CGDS (Cold Gas dynamic Spraying) technology to the submicron and nano-particles size. Theoretically, there are many challenging issues have to be addressed, in particular, it is necessary to understand the gas mixture with particles two-phase flow in supersonic nozzle and its effects on particle bonding on the surface of substrate and the microstructure of coating formed by cold gas dynamic spray.

    This research is supported by NSF, UW System Applied Research Grant and International Thermal Systems, LLC.


Environmentally Benign Machining Process

        In many machining processes, a metalworking fluid serves many system functions such as lubrication, thermal sink, corrosion inhibitor, chip control and washing. These fluids could adversely affect the health of the personnel in the machine room.  Metal chips (solid waste) in used cutting fluid are a source of pollution and must be disposed of in an appropriate manner. Contaminants retained in the scrap usually means that the scrap cannot be recycled for application similar to the original application. The cost for recovery for these contaminated materials consists nearly 30% of the total operational cost of the machining processes.

        The main objective of this research is to demonstrate the feasibility of running the machining operation completely dry, thus not only completely eliminate the usage of the metalworking fluid, but also eliminate the solid waste (chips, swarfs and scraped parts). All these can then be fully recycled. However, in any materials removal process, most of the input energy is converted into heat in the cutting zone. The generated heat is then transferred to the tool and workpiece, and carried away by the machining fluid and the chips.  The absence of the metalworking fluid reduces the amount of heat carried away, resulting in an increase in tool and workpiece temperatures. Elevated temperature can significantly shorten the tool life. Excessive heat accumulated in the tool and workpiece can contribute to thermal distortion and poor dimensional control of the workpiece. The innovative concept behind this proposed research is to demonstrate that internally-cooled machining tool can perform at the same level as conventional externally cooled machining tool and thus eliminate the use of metalworking fluids.

 

        In this research, heat pipe technology is employed as a method of removing heat from the cutting zone in two major machining processes, namely drilling and milling processes to demonstrate its feasibility. A three-dimensional model for a heat pipe under rotation is currently under developing, and a solution will be obtained numerically. These results will then be coupled with the transient temperature model to predict the too temperature in the vicinity of the cutting tip. Experiments will be performed under actual drilling and milling conditions.  This research is supported by NSF, EPA, UW System Applied Research Grant and Lamb Technicon.


Experimental and Numerical Studies in Grind-Hardening

          In any grinding processes, the heat generated in the grinding process causes the workpiece and wheel temperatures to rise. The high temperatures could cause various forms of thermal damages, such as workpiece burns. In the past, almost all of researchers tried to eliminate the grinding heat in grinding zone to avoid the grinding burns. In this paper, however, a novel technology named grind-hardening is introduced.  Due to the significant heat generated during the grinding process, the surface temperature of the workpiece, which rose by the grinding heat, is higher than the austenitizing temperature. This is then followed by rapid cooling to achieve the purpose of surface hardening. Simply speaking, this technology utilizes the dissipated heat in grinding zone to harden the surface layer of the workpiece.  It is worth noting that this technology has the potential to be fully integrated the surface hardening processes into the production line, and thus reducing manufacturing processes and increasing productivity.

 

        Dr. Jen’s research group is currently studying the effect of cooling, cutting speed, depth of cut, and other relevant parameters on the grind-hardening process both numerically and experimentally.

 
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