11-08-2012, 12:56 PM
Finite-element analysis and simulation of machining
Finite-element analysis.pdf (Size: 184.38 KB / Downloads: 62)
Introduction
Machining is a term covering a large collection of
manufacturing processes designed to remove material
from a workpiece. The primary machining processes
are: turning, shaping, milling, drilling, sawing, abrasive
machining, and broaching. Some advanced machining
methods used today are: electric discharge machining
(EDMs), laser cutting, chemical milling, high-pressure
water cutting, electrochemical machining, etc.
Turning is the machining process used to generate
external, cylindrical forms by removing material by a
cutting tool. Boring is internal turning to generate
internal shapes. Shaping processes remove material
from surfaces through the use of a single-point tool
supported by a ram that reciprocates the tool in a linear
motion against the workpiece. Milling is a process for
generating surfaces by removing a predetermined
amount of material from the workpiece.
Material removal and cutting processes in general
This section deals with the investigation of metal
cutting processes in general. These processes are dependent
on the workpiece parameters (material type, crystallography,
temperature, pre-deformation), cutting
tool parameters (tool design geometry, material), and
cutting parameters (speed, feed, depth of cut, environment).
Some studies have been done that include the
influence of only a few specific topics, other, more
advanced studies, have been conducted to understand
the complex physical behavior underlying the specific
machining process.
Computational models for specific machining
processes
Listed references are sorted into the following categories:
turning, milling, drilling, sawing, grinding,
broaching, and advanced machining; in the last category
subjects such as EDM, laser cutting, electrochemical
machining, flame cutting, high-pressure water
cutting, ultrasonic machining, nanoscale cutting etc. are
included.
The machining of composites, especially of metal
matrix composites, causes particular problems such as
greater tool wear; also the hardness of the ceramic
fibres and particles is too high. Usually polycrystalline
diamond-tipped tools are necessary for the successful
machining of metal–matrix composite.
Physical understanding of microcutting is necessary
for developing and improving the process of ultraprecision
metal cutting technology. FEMs have also been
used to simulate nanoscale cutting. The purpose of
these studies was to clarify the chip removal of
nanoscale cutting and to reexamine the cutting process
in general.
Thermal aspects in machining
High temperatures in machining are the cause of
unsatisfactory tool life and limitations on cutting speed.
Various numerical and experimental techniques are
available to study the flow of cutting heat and the
temperature distribution within both the workpiece and
the tool. The role of temperature becomes more important
with increasing cutting speed and the usage of
more advanced ceramic materials. The thermal model
of a machine tool should account for the following
heat-transfer situations: heat conduction, heat conduction
across contact zones, radiation, forced convection
along rotated element surfaces, free convection along
external surfaces, and convection along the body surfaces
that is caused by rotating parts. The finite-element
model should preferably be in 3D.
Residual stresses in machining
The machining process evokes a residual stress in the
surface layer. The main cause of a residual stress is the
phase transformation of the surface material. Distortions
and residual stresses are unwanted results from
abusive machining conditions. The residual stresses on
the machining surface is an important factor in determining
the performance and fatigue strength of
components.