19-11-2012, 05:22 PM
Finite-Element Simulation of Electron Beam Machining (EBM) Process
[attachment=40243]
INTRODUCTION
Electron beam is generated in an electron beam gun. The
construction and working principle of the electron beam gun
would be discussed in the next section. Electron beam gun
provides high velocity electrons over a very small spot size.
Electron Beam Machining is required to be carried out in
vacuum. Otherwise the electrons would interact with the air
molecules, thus they would lose their energy and cutting
ability. Thus the workpiece to be machined is located under
the electron beam and is kept under vacuum. The highenergy
focused electron beam is made to impinge on the
workpiece with a spot size of 10 – 100 μm. The kinetic
energy of the high velocity electrons is converted to heat
energy as the electrons strike the work material. Electron
Beam Machining Process shows in Fig.1.
Due to high power density instant melting and
vaporization starts and “melt – vaporization” front gradually
progresses, as shown in Fig. 2. Finally the molten material, if
any at the top of the front, is expelled from the cutting zone
by the high vapor pressure at the lower part. Unlike in
Electron Beam Machining, the gun in EBM is used in pulsed
mode. Holes can be drilled in thin sheets using a single
pulse. For thicker plates, multiple pulses would be required.
Electron beam can also be maneuvered using the
electromagnetic deflection coils for drilling holes of any
shape.
ELECTRON BEAM PROCESS CAPABILITY
EBM can provide holes of diameter in the range of 100
μm to 2 mm with a depth upto 15 mm, i.e., with a l/d ratio of
around 10. Fig.5. schematically represents a typical hole
drilled by electron beam. The hole can be tapered along the
depth or barrel shaped. By focusing the beam below the
surface a reverse taper can also be obtained. Typically as
shown in Fig. 5, there would be an edge rounding at the
entry point along with presence of recast layer. Generally
burr formation does not occur in EBM.
A wide range of materials such as steel, stainless steel,
Ti and Ni super-alloys, aluminum as well as plastics,
ceramics, leathers can be machined successfully using
electron beam. As the mechanism of material removal is
thermal in nature as for example in electro-discharge
machining, there would be thermal damages associated with
EBM. However, the heat-affected zone is rather narrow due
to shorter pulse duration in EBM. Typically the heataffected
zone is around 20 to 30 μm.
TECHNOLOGICAL AND MECHANICAL CHARACTERIZATION
For a characterization of the technological and
mechanical properties of electron beam silicon-glass bonds a
series of methods may be used. Among those are their
resistance against a chemical attack in the form of etching,
the helium- leak-test for the detection of gas leaks, the
bursting pressure test for the determination of the strength of
hermetically tight joints, the micro-Chevron test for the
control of the fracture mechanics of the brittle-elastic
components and also the tensile test for the determination of
the maximally transmissible force.
CONCLUSIONS
Besides their high rating in macro-range industrial
manufacturing processes, beam joining methods are also
increasingly gaining in importance in the micro-system
technology (MST). While the industry is already using the
electron beam for joining, surface modifications or for
structuring with different process variations, micro-range
electron beam joining is still in the laboratory stage.
A more elaborate mathematical model than the one
existing before was developed for calculation of melting rate
in single-wire arc machining. Additionally a mathematical
model for calculation of melting rate in twin-wire arc
machining not known from the literature before was
developed. On the basis of variation of validity of the
mathematical models developed for single-wire and twinwire
arc machining it can be stated that the models are quite
a true representation of the experimental results and that they
are applicable to practical cases as well as to further research
work.
[attachment=40243]
INTRODUCTION
Electron beam is generated in an electron beam gun. The
construction and working principle of the electron beam gun
would be discussed in the next section. Electron beam gun
provides high velocity electrons over a very small spot size.
Electron Beam Machining is required to be carried out in
vacuum. Otherwise the electrons would interact with the air
molecules, thus they would lose their energy and cutting
ability. Thus the workpiece to be machined is located under
the electron beam and is kept under vacuum. The highenergy
focused electron beam is made to impinge on the
workpiece with a spot size of 10 – 100 μm. The kinetic
energy of the high velocity electrons is converted to heat
energy as the electrons strike the work material. Electron
Beam Machining Process shows in Fig.1.
Due to high power density instant melting and
vaporization starts and “melt – vaporization” front gradually
progresses, as shown in Fig. 2. Finally the molten material, if
any at the top of the front, is expelled from the cutting zone
by the high vapor pressure at the lower part. Unlike in
Electron Beam Machining, the gun in EBM is used in pulsed
mode. Holes can be drilled in thin sheets using a single
pulse. For thicker plates, multiple pulses would be required.
Electron beam can also be maneuvered using the
electromagnetic deflection coils for drilling holes of any
shape.
ELECTRON BEAM PROCESS CAPABILITY
EBM can provide holes of diameter in the range of 100
μm to 2 mm with a depth upto 15 mm, i.e., with a l/d ratio of
around 10. Fig.5. schematically represents a typical hole
drilled by electron beam. The hole can be tapered along the
depth or barrel shaped. By focusing the beam below the
surface a reverse taper can also be obtained. Typically as
shown in Fig. 5, there would be an edge rounding at the
entry point along with presence of recast layer. Generally
burr formation does not occur in EBM.
A wide range of materials such as steel, stainless steel,
Ti and Ni super-alloys, aluminum as well as plastics,
ceramics, leathers can be machined successfully using
electron beam. As the mechanism of material removal is
thermal in nature as for example in electro-discharge
machining, there would be thermal damages associated with
EBM. However, the heat-affected zone is rather narrow due
to shorter pulse duration in EBM. Typically the heataffected
zone is around 20 to 30 μm.
TECHNOLOGICAL AND MECHANICAL CHARACTERIZATION
For a characterization of the technological and
mechanical properties of electron beam silicon-glass bonds a
series of methods may be used. Among those are their
resistance against a chemical attack in the form of etching,
the helium- leak-test for the detection of gas leaks, the
bursting pressure test for the determination of the strength of
hermetically tight joints, the micro-Chevron test for the
control of the fracture mechanics of the brittle-elastic
components and also the tensile test for the determination of
the maximally transmissible force.
CONCLUSIONS
Besides their high rating in macro-range industrial
manufacturing processes, beam joining methods are also
increasingly gaining in importance in the micro-system
technology (MST). While the industry is already using the
electron beam for joining, surface modifications or for
structuring with different process variations, micro-range
electron beam joining is still in the laboratory stage.
A more elaborate mathematical model than the one
existing before was developed for calculation of melting rate
in single-wire arc machining. Additionally a mathematical
model for calculation of melting rate in twin-wire arc
machining not known from the literature before was
developed. On the basis of variation of validity of the
mathematical models developed for single-wire and twinwire
arc machining it can be stated that the models are quite
a true representation of the experimental results and that they
are applicable to practical cases as well as to further research
work.