Wonsik Lee

Evaluation of feedstock for powder injection molding

Methods to evaluate powder injection molding feedstock without performing the complete processing were developed to reduce the development-to-commercialization cycle time for feedstock. The mixing homogeneity of the powder and binder, rheological properties, mechanical property and shape retainability during debinding were characterized to evaluate the feedstock. The validity of using these parameters was investigated through comparison with various feedstocks. Based on these results, the evaluation methods developed in this work have potential to aid in the selection of proper feedstock without undergoing the subsequent processing.

Manufacture of μ-PIM gear mold by electroforming of Fe–Ni and Fe–Ni–W alloys

The micro gear mold for powder injection molding was made by electroforming process of Fe–Ni and Fe–Ni–W alloys using UV-lithography process. Kinetics and activation energies in electroplating of both alloys were investigated to determine the best process conditions. Fe content within electrodeposited Fe–Ni alloys increased with the increase of rotating disk speed and the decrease of temperature and it is considered from the calculated activation energy of iron content that the rate determining step is controlled by mass transfer. Iron content in Fe–Ni electrodeposit varied from 58.33% to 70.45% by increasing current density from 2 to 6 A/dm2. Also, iron content in Fe–Ni–W electrodeposit increased from 59.32% to 70.15%, nickel content decreased from 27.86% to 17.07% and the content of tungsten was almost consistent in the range of 12.78%–12.82% although the current density increases from 1.5 to 5 A/dm2. For the electroforming of micro gear mold, SU–8 mandrel with 550 μm in diameter and 400 μm in height was prepared by UV-lithography processing. Subsequently, Fe–36Ni and Fe–20Ni–13W alloys micro gear molds were electroformed successfully. Surface hardness values of the electroformed micro molds were measured to be HV490 and HV645, respectively.

Recovery of Nitric acid and Copper from Plating Waste of Automobile Wheel

It has been known that there are large amount of nitric acid and valuable metals, copper in the plating waste solution of automobile wheel. As nitric acid and valuable metals are high price and toxic, they should be recovered for economics and environment. Plating waste was extracted with TBP diluted with kerosene. The concentration of nitric acid in aqueous phase was analyzed by titration method by NaOH solution (0.1∼1.0N) and the amount of metals by ICP-MS and ICP-AES. The concentration of copper in plating waste were 76,850 mg/L. The concentration of nitric acid in plating waste was 1.02 M. After three step extraction was performed with 50% TBP, each organic phase was stripped three times with distilled water to obtain 48.1% of nitric acid. Purity of final nitric acid was over 99.9% by ICP analysis. After recovery of nitric acid, copper was extracted with various solvent extractors like PC 88A, D2EPHA, LIX 84 and ISE 106. Among these extractors, 92% of copper was recovered by ISE 106 after 1st extraction and 30% H2SO4 stripping. Copper ion was reduced with N2H4 to make metal powders, respectively. Key word : Tributylphosphate, Plating waste, Nitric acid, Solvent extraction, Metal powder

FABRICATION OF MICRO GEARS BY MICRO-POWDER INJECTION–COMPRESSION MOLDING

Micro-spur gears were fabricated by powder injection–compression molding and micro-two-step gears were produced through stacking and sintering of the green parts. Shrinkage of micro-gears by sintering was larger in teeth and with increase of compression pressure, shrinkage was decreased due to increase of density in green parts. Surface roughness of sintered body was reduced to a few hundreds of nanometers by ultrasonic micro-polishing. The joining of green bodies by stacking and sintering was achieved using the pressurized sintering and insert of feedstock powders between both green bodies.

Surface modification of cast inconel 740 superalloy by heat-assisted friction stir processing

Cast In740 Ni-based alloy with large grains generally show remarkable high temperature strength. However, this alloy is still have insufficient surface microstructure-dependent properties. In this study, for improvement of surface properties, surface modification of a cast In740 Ni-based superalloy was successfully performed by friction stir processing using a conventional two-horsepower milling machine and by additional heating to facilitate plastic flow of the hard alloy. Without using a high-power heavy stirring machine, a notable reduction in grain size of 2.9 μm was achieved and a corresponding 30% increase in Vickers hardness was observed. The microstructure in the stir zone was analyzed in terms of the grain size and precipitate distribution. The result of the potential dynamic polarization test and in-situ acoustic emission monitoring show that electrochemical corrosion resistance was improved by this surface modification process.

Research Trend of Additive Manufacturing Technology − A=B+C+D+E, add Innovative Concept to Current Additive Manufacturing Technology: Four Conceptual Factors for Building Additive Manufacturing Technology −

Additive manufacturing (AM) is defined as the manufacture of three-dimensional tangible products by additively consolidating two-dimensional patterns layer by layer. In this review, we introduce four fundamental conceptual pillars that support AM technology: the bottom-up manufacturing factor, computer-aided manufacturing factor, distributed manufacturing factor, and eliminated manufacturing factor. All the conceptual factors work together; however, business strategy and technology optimization will vary according to the main factor that we emphasize. In parallel to the manufacturing paradigm shift toward mass personalization, manufacturing industrial ecology evolves to achieve competitiveness in economics of scope. AM technology is indeed a potent candidate manufacturing technology for satisfying volatile and customized markets. From the viewpoint of the innovation technology adoption cycle, various pros and cons of AM technology themselves prove that it is an innovative technology, in particular a disruptive innovation in manufacturing technology, as powder technology was when ingot metallurgy was dominant. Chasms related to the AM technology adoption cycle and efforts to cross the chasms are considered.

GRAPHITE REINFORCED Fe–Al–X COMPOSITES FOR SLIDE BEARING APPLICATIONS

The Fe–Al–X(Cu, Ni, Ti) composites reinforced with graphite particles were fabricated employing the powder metallurgy process for slide bearing applications. In all samples, graphite particles of 6 wt.% were added. Elemental powders were mixed to specific compositions with a powder lubricant, and then the mixed powders were compacted at 500 MPa. The green compacts were heated to 450°C to remove the lubricant and sintered at 1200°C for 1 h. The sintering was conducted in vacuum. The sintering of binary Fe–Al–graphite system showed low density and growth in dimension. Complex addition of Cu, Ni and Ti improved the sinterability of green compacts due to occurrence of partial liquid phases. Hardness of sintered samples strongly depended on dimensional change during sintering. The samples of high hardness showed better wear resistance properties.

Variation of Tensile Strength by Addition of Y 2 O 3 and Effect of Aging Treatment in Ni Base Alloy Fabricated by MA Method

Ni-20Cr-20Fe-5Nb alloy with or without was manufactured by mechanical alloying process and consolidated by spark plasma sintering (SPS). The grain size of the alloy with was smaller than that of alloy without which results from the effect of suppressing grain growth. The tensile strength at room temperature was increased by the addition of but decreased abruptly at temperature above . It seems to result from the change of deformation mechanism due to fine grain size, that is, grain boundary sliding is predominant at above while internal dislocation movement is predominant at below . After conventional heat treatment process of solution treatment and aging, a small amount of phase was formed in Ni-20Cr-20Fe-5Nb alloy while a large amount of was formed in Inconel 718 in the previous report. This is due to exhaustion of Nb content by the formation of NbC during consolidation.