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Precision
Turning
Precision machining and micromachining
aims the production of advanced components with high dimensional
accuracy and acceptable surface integrity. Fiber reinforced
composites are widely employed in various fields of engineering,
such as aircraft, automobile, robots and machines due to their good
properties.
This work aims the better understanding of the machinability of PA
66 polyamide without and with 30% glass fiber reinforcing, when
precision turning at different feed rates, cutting speeds and using
various tools materials.
The
performance of PCD, CVD diamond coated, K15-KF and K15 carbide
cutting tools and the influence of feed rate and cutting speed on
cutting forces,
surface roughness
and micro-chip formation were investigated for polyamide composites,
whereas, performance P25 and K15 carbide cutting tools were
investigated for AISI D2, AISI 4140 and AISI
1045 steels. The findings for polyamide composites indicated that the
radial force component presented highest values, followed by the
cutting and feed forces. The PCD tool gave the lowest force values
associated with best surface finish, followed by the ISO grade K15
uncoated carbide tool
without
chip breaker.
Continuous coiled micro-chips were produced, irrespectively of the
cutting parameters and tool material employed. The addition of 30%
glass fiber reinforcing significantly affected the performance of
the tooling used in comparison with the material without
reinforcing. The results for steels indicated that, in general, the
turning force components increased as feed rate is elevated
and the specific cutting force decreases strongly with feed rate
when cutting AISI D2 steel, however, for the machining of AISI 4140
and AISI 1045 steels the specific cutting force decreases
slightly or remains unaltered as feed rate is elevated.
Finally, the surface roughness produced by the two cutting tools was
significantly affected by feed rate within the range tested. Best
surface finish was obtained when turning the AISI D2 steel followed
by AISI 4140 steel.
Figure
1
- Effect of feed rate on cutting force
when
machining PA66-GF30 composite at vc = 70 m/min and ap=150
mm
with CVDD, PCD, K15 and K15-KF tools.
Figure 2 - Effect of feed rate on cutting force when machining AISI
D2; AISI 4140 and AISI 1045 steels at vc = 100 m/min and
ap = 100
mm
using uncoated (K15) cemented carbide tool.
Micro-milling
The demand for
miniaturized devices with high aspect ratios and superior surfaces
has been rapidly increasing in aerospace, automotive, biomedical,
optical, military and micro-electronics packaging industries. There
is a growing need for fast, direct, and mass manufacturing of
miniaturized functional products from metals, polymers, composites
and ceramics. In the present work, the machining of micro surfaces
on aluminum alloy is made, using conventional machines and
commercially available miniature tools. With the aid of CAD
(Computer Aided Design) software, several micro surfaces were
designed to test their machinability on a conventional CNC (Computer
Numerically Controlled) machining centre using sub millimeter tools.
In order to perform a comprehensive study on the quality of the
machined surfaces (roughness, accuracy and burrs), machining
parameters such as feed rate were varied. Also, a variety of
machining strategies was performed in order to study the quality of
the machined surfaces. Hence, the thesis’ main goal is to determine
up to which extent conventional machines and micro tools can be used
to achieve quality micro surfaces. In Fig. 3 one can see the
photograph of a micro-milled surface on aluminium stock using a 0.8
mm diameter end mill.
Figure 3 - Photograph of micro-milled aluminium surface using a 0,8
mmm end mill compared to a0,5 mm pencil lead
After the design of the different surfaces using 3D modelling
software, the experimental work took place. Several cases of study
were conducted for each designed surface, varying the feed rate and
machining strategy. The analysis of the finished surface consisted
in measuring its roughness with a profilometer and measuring the
minimum wall thickness achieved without burrs. |