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Machininability of Metalic Matrix Composites

Machining metal matrix composites have been successfully applied in the aeronautic and aerospace industries. Metal Matrix Composites (MMC's) are a relatively a new class of materials characterized by lighter weight and higher wear resistance. In the 80's, metal matrix composites reached to the automobile industry (brake rotors and several components for internal combustion engines) and nowadays its use is extremeely important. Machining MMC's is estremelly difficult due to the highly abrasive nature of the reinforcement ceramic. The structural aluminium matrix sheet, reinforced with large fibres, was developed and in the last few years, research has been specially focused on the aluminium matrix composites with discontinuous reinforcements - short fibres, particles and whiskers of SiC and Al2O3.

Machining Operations

Drilling 
Milling

Turning

Drilling

The evolution of the cutting force, tool wear and surface finish, measured when drilling the metal matrix composite A356/20/SiCp-T6, is presented. The experimental work was developed through the continuous measurement of the torque with an appropriate piezoelectric dynamometer and the results were used to derive the cutting power and the specific cutting pressure. The tool wear type was identified and its evolution with cutting time was measured for different sets of cutting conditions, using polycrystalline diamond drills. The holes surface roughness was evaluated and very good results, exceeding standard values for drilling.

Using the experimental results, a numerical search of optimal drilling conditions was performed. Since there are contradictory objectives, such as maximization of tool life and minimization of tool wear, the concept of the Pareto optimum solution is considered in the optimization procedure. An evolution strategy is adopted to obtain the optimal solution for cutting speed, feed rate and tool life prediction with industrial interest.

 

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Turning

This work presents an experimental study of the evolution of the cutting forces, tool wear and surface roughness during the turning of the particulate metal matrix composite A356/20/SiCp-T6. The experimental work was developed through the continuous measurement of the cutting forces with an appropriate piezoelectric dynamometer. The wear type was identified and its evolution with cutting time was measured. Inserts with polycrystalline diamond (PCD) were tested. The surface roughness was evaluated with a profilometer in workpiece.

A hybrid technique based on an evolutionary search over the experimental design space is considered. Optimal turning cutting conditions are searched using a genetic algorithm based on an elitist strategy. The chromosomes composed by random keys represent cutting conditions defined according to a temporal scale.

 

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MACTRIB - Department of Mechanical Engineering , University of Aveiro

Campus UniversitŠrio de Santiago, 3810-193 AVEIRO, PORTUGAL

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