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Machininability
of
Metalic Matrix Composites |
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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. |
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Machining
Operations |
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Drilling |
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Milling |
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Turning |
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Drilling
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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.
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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
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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.
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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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