Preparation of Coated Microtools for Electrochemical Machining Applications

PREPARATION OF COATED MICROTOOLS FOR ELECTROCHEMICAL MACHINING APPLICATIONS Ajaya K. Swain, M.S. University of Nebraska, 2010 Advisor: K.P. Rajurkar Coated tools have improved the performance of both traditional and nontraditional machining processes and have resulted in higher material removal, better surface finish, and increased wear resistance. However, a study on the performance of coated tools in micromachining has not yet been adequately conducted. One possible reason is the difficulties associated with the preparation of coated microtools. Besides the technical requirement, economic and environmental aspects of the material and the coating technique used also play a significant role in coating microtools. This, in fact, restricts the range of coating materials and the type of coating process. Handling is another major issue in case of microtools purely because of their miniature size. This research focuses on the preparation of coated microtools for pulse electrochemical machining by electrodeposition. The motivation of this research is derived from the fact that although there were reports of improved machining by using insulating coatings on ECM tools, particularly in ECM drilling operations, not much literature was found relating to use of metallic coating materials in other ECM process types. An ideal ECM tool should be good thermal and electrical conductor, corrosion resistant, electrochemically stable, and stiff enough to withstand electrolyte pressure. Tungsten has almost all the properties desired in an ECM tool material except being electrochemically unstable. Tungsten can be oxidized during machining resulting in poor machining quality. Electrochemical stability of a tungsten ECM tool can be improved by electroplating it with nickel which has superior electrochemical resistance. Moreover, a tungsten tool can be coated in situ reducing the tool handling and breakage frequency. The tungsten microtool was electroplated with nickel with direct and pulse current. The effect of the various input parameters on the coating characteristics was studied and performance of the coated microtool was evaluated in pulse ECM. The coated tool removed more material (about 28%) than the uncoated tool under similar conditions and was more electrochemical stable. It was concluded that nickel coated tungsten microtool can improve the pulse ECM performance.

A METHODOLOGY TO EVALUATE OBSOLETE INVENTORY IN HEALTH CARE

Many organizations are currently facing inventory management problems such as distributing inventory on-time and maintain the correct inventory levels to satisfy the customer or end users. Organizations understand the need for maintaining the accurate inventory levels but sometimes fall short leading a wide performance gap in maintaining inventory accurately. The inventory inaccuracy can consume much of the investment on purchasing inventory and many times leads to excessive inventory. The research objective of thesis is to provide a decision making criteria to the management for closing or maintaining the warehouse based on basic purchasing and holding cost information. The specific objectives provide information regarding the impact of inventory carrying cost, obsolete inventory, inventory turns. The methodology section explains about the carrying cost ratio that would help inventory managers to adopt best practices to avoid obsolete inventory and also reduce excessive inventory levels. The research model was helpful in providing a decision making criteria based on the performance metric developed. This research model and performance metric had been validated by analysis of warehouse data and results indicated a shift from two-echelon inventory supply chain to a one-echelon or Just In Time (JIT) based inventory supply chain. The recommendations from the case study were used by a health care organization to reorganize the supply chain resulting in the reduction of excessive inventory.