Selection of micromilling conditions for improved productivity and part quality
Bulgurcu, Gözde (2017) Selection of micromilling conditions for improved productivity and part quality. [Thesis]
Micromilling process has a rising demand in recent years where the production industry is becoming more competitive with the advancing technology. In hi-tech industries such as aerospace, biomedical, electronics, the increasing demand for high precise micro products with complex geometries create necessity to improve micro machining processes for more accurate, repeatable, and efficient production. Micro end milling process is relatively a new developing research area. It varies from conventional milling with its unique cutting dynamics due to the geometrical size reduction. In terms of the both micro tool and the workpiece, size reduction brings new difficulties to the process. The ratio of hone radius to uncut chip thickness creates a great difference between micro and conventional milling processes and precludes the application of conventional milling models to micromilling process. By the nature of the micromilling and its industries of usage, high accuracy and surface quality is expected in micro products. This makes the surface roughness and burr formation critical for micromilling process. On the other hand, since micro tools with very small radii are more fragile than conventional milling tools, workpiece-tool contact and cutting forces have also a remarkable importance. Due to the same reason, tool costs and tool life are another significant point. All of these conditions make pre analysis and the parameter selection of micro end milling process essential for micromilling. The main aim of this research is to determine micromilling parameters and conditions for improved productivity and part quality by considering multiple constraints and objectives at a time, unlike the previous studies on micro end milling process optimization which are limited and focus to optimize one objective at a time. The objectives in this study are the production time and production cost. Production time involves the actual cutting time, which involves the calculation of material removal rate (MRR), tool idling and changing time and time spent without any cutting. In production cost, tool costs, which is related with the tool life, machine idling costs, labour and overhead costs are included. Production time and cost are minimized respecting certain values of cutting forces, burr size and surface quality constraints. The effects of parameters; cutting speed, feed rate, and depth of cut on these objectives and constraints were investigated. For the first time, parameter selection in micro end milling process is done through multi-objective optimization using Particle Swarm Optimization method. Optimal process parameters are proposed for minimum process cost and minimum process time.
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