Tool design for the production of a collimator on a 3-axes vertical milling centre
The continuous quest for modernization and industrialization has brought a great challenge upon the third world countries such as Zambia in that these countries have to keep on importing production machinery whose spares cannot be obtained locally but from outside. This problem has been compounded by these countries' lack of funds to acquire machinery that could produce the much-needed spares. However, the high cost of initial investment of Computer Numeric Control (CNC) machines is a huge obstacle to many companies. It is, therefore, imperative that avenues of adapting these machines to perform a variety of operations than what they were initially designed for are sought and thereby make the investment much more cost effective. A cobalt refinery plant at Chambishi Metals Pic running at normal capacity consumes about one collimator in every three to four weeks. The cost of replacement of each collimator is approximately US$3800 from Mitutoyo and Fowyer in America. Chambishi Metals Pic notes that it is spending thousands of dollars in importing the component and is looking for means to have local manufacturers to produce it locally since this would be cheaper and readily available. However, local companies have so far failed to achieve the required tolerances using conventional machining and have very little or no capacity in ordering CNC machine tools.The collimator assembly is a water-cooled frontal electrode, used on the plasma arc torch. This torch is used in the reheating of the alloy prior to atomizing. A collimator is an assembly made up of two separate components whose metallurgical composition is 90 to 99 percent copper. In order to accommodate plasma gas flow, process thermodynamics and to prevent coolant leakages, collimator components are normally produced by precision machining, a process that is best performed on CNC lathe machine tools. It is for this reason that it was identified as a test piece for production. In 2001, Mwanza S. M.,University of Zambia, successfully adapted a Supermax 65A, 3-axes CNC Vertical Milling Centre (VMC) to include turning operations'. Later, in 2002, Daka B., University of Zambia, looked at turning tools that could produce various profiles using the adaptations made on the same machine tool. After having done the modifications, it was imperative that a specific commercial product was produced to test the applicability of the adaptations. In addition, this was to answer and reduce on queries and shortcomings that were unanswered in the previous two studies. These included improvement in dimensional tolerances and surface texture of the products, use of CAD/CAM software and DNC to accommodate complex products. Thus, this research started by designing the production process and production tools which involved coming up with turning, threading and boring tools and also the workpiece and tool holding mechanisms. The designed production process, tools and fixtures were further used in the configuration of the 3-axes CNC VMC machine tool. Since no software capable of generating NC part programs for turning and compatible with VMC machine tools exists, it was imperative that less time consuming methodologies of generating such programs were developed. Thus, Mastercam Lathe V9, an advanced CAD/CAM software, was modified to generate turning NC part programs to run on the VMC machine tool with the application of a unique remote operation of direct numeric control (DNC). Hence, with these techniques, the coilimator assembly was produced and examined for dimensional accuracy and surface finish. An analysis of generated forces was also done to avoid overloading the machine tool. After costing, the total cost of producing one collimator came out to be ZMK 9,9 75,686.00. The produced collimator assembly was inspected and tested on a plasma arc torch-testing rig found at Chambihsi Metals Pic, Ultra-modern Smelter Plant, and it was found to conform to ISO 9001 standards.
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