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Abstract
High Speed Machining (HSM) has become a higWy growing technology in the industrial world in the last two decades. This is attributed to the fact that HSM leads to an increase in productivity, workpieces efficiency, product quality, and a decrease in production costs. This has led to the increasing application of HSM in the plastics industry to machine and finish dies and molds, the automobile industry in the machining of gray cast iron and high silicon aluminum alloys, and the aerospace industry to machine large thin-wall aluminum structures.
One of the major problems facing the industrial world is distortion of manufactured parts, which is a deviation from the normal shape of a part due to the mechanical and thermal effects. This problem places a constraint on the achievable dimensional, geometrical, and surface texture characteristics of manufactured parts. That’s why there is a need to characterize this distortion and identify the machining conditions that will maintain stability of finished products. Those working conditions are related to the tooling systems, machined materials and the machine tools. This is the main objective of the present work; that is to consider the working conditions that maintain the stability of finished products machined by HSM.
Due to the importance of cooperation between the industrial world and the academic research, this work studies the distortion problem of the gray cast iron (GG25) brake disk during its manufacturing process. The braking system of most modern cars is based on gray cast iron brake disks. The brake disks are subjected to thermal stresses arising from high temperatures that may induce a number of unfavorable conditions such as wear, surface cracks and permanent distortions. These conditions cause ronout which is feedback to the driver as juddering through the brake pedal. This is a multi-million dollar per year warranty problem for all car and aircraft manufacturers.
Many experiments were carried out in this work to study the brake disk quality characteristics when cut with the HSM technology using ceramic tools. The experiments are performed on 64 Work samples of Gray cast iron (GG25). All cutting experiments are performed on Emag VSC400 CNC vertical turning center machine. A full factorial design of experiment was developed to organize the experiments and to investigate the effect of cutting conditions such as; cutting speed, feed rate, and depth of cut on the product quality characteristics such as; surface roughness, axial runout, flatness error, and thickness variation. It has been concluded that the cutting speed is the most significant parameter affecting the product quality characteristics and the best product quality characteristics are produced at cutting speed higher than 1000 mImin, feed rate higher than 0.5 mmlrev, and shallow depths of cut. A regression analysis was adopted to formulate the relation between the investigated parameters and each of the product quality characteristics.
Fmally, a two-dimensional finite element model for high speed machining of gray cast iron (GG25) was also developed to predict the temperature, stresses, strain distributions, and chip shapes. The main advantage of this method is that it allows studying the cutting process in
greater dcLiil than possible in practical experiments. The dependence of temperature on cutting speed is more pronounced for an increase from 800-1 100 m/min. The increase of cuttin~’ ~pe,’d will increase the temperature. However, for cutting speeds larger than 1000 m/min. which define the starting range of high speed machining of cast iron, the temperature decreases.