Download Research of Electromagnetic Effects on the Compound Arc Beam in

PIERS Proceedings, Beijing, China, March 23–27, 2009
964
Research of Electromagnetic Effects on the Compound Arc Beam in
the Hybrid Plasma-laser Manufacturing Process
Ying-Ping Qian1 , Hai-Ou Zhang2 , Gui-Lan Wang3 , and Guangchao Han4
1
2
School of Mechanical Engineering, Hubei University of Technology, 430068, China
School of Mechanical Engineering, Huazhong University of Science and Technology, 430074, China
3
School of Material, Huazhong University of Science and Technology, Wuhan 430074, China
4
China University of Geosiences, China
Abstract— In this paper, the mechanism of electromagnetic influence on the compound arc
column is analyzed theoreticly, and the influence rule of electromagnetic on the compound arc
beam is studied experimentally. The experimental results show that the compound arc column
can absorb electromagnetic waves, and electromagnetic waves can compress the compound arc
column. The compound arc column can maintain the same patterns only when the magnetic
compressure and the expansive power outward are balance.
1. THE PRINCIPLE OF HYBRID PLASMA-LASER DEPOSITION MANUFACTURE
(PLDM)
The principle of PLDM technology is shown in Fig. 1. The shape, dimension and function of the
conception model are gained by means of concept design, and then workout a CAD model with the
help of shaping software. According to the requirement of the component’s dimensional accuracy,
the CAD model is dealt with slices and transferred into an STL document. In accordance with the
shape of every layer, the control system draws up to route, generates the CNC code to control the
movement of the NC machine [1–4]. On the one side of the plasma arc, the laser beam is focused on
the plasma arc into the molten pool through adjusting the optical path for light transmitting and
focusing. The deposition and shaping are then carried out under the control of the parameters such
as movement of sending powder system, plasma arc-stream, shielding gas flow, sending powder gas
flow, electric current according to the precious design. The high-temperature alloy powder is sent
to the pool to melt and solidify into a compact metal layer rapidly then continues repeating the
lamination until the entire three-dimensional component’s layers are formed.
Figure 1: Schematic representation of the PLDM process.
Progress In Electromagnetics Research Symposium, Beijing, China, March 23–27, 2009
965
2. THE CHARACTER OF THE COMPOUND ARC BEAM
The compound arc column is most plasma arc beam. Plasma is a kind of ionization gas which
composes of a great deal of free electron and ion and behave whole electricity neuter, which is
the fourth state except solid, liquid and gas. Simply speaking, plasma is a kind of high ionization
gas. And high ionization means that the density of the electrification particle is enough high
and the interaction of the positive and negative charged particle is quite strong. Commonly, the
generation of the plasma is a complicated process which relate to many classical gas discharge
theory, experiments, the atom microcosmic process and exterior effect. In addition, the producing
way of the plasma sometimes close connects the plasma’s restriction and application. The mainly
mechanism of the plasma production include ionization caused by heating, gas discharge and the
laser induction.
3. THE MAGNETISM SHRINK EFFECT OF THE COMPOUND ARC BEAM
In the compound arc beam, the plasma take up the finity area and keep the column, this is called
the linear plasma column as Fig. 2. The angle magnetic field which circle itself will produce when
mightiness electric current pass the plasma along the axis direction. The magnetic field interacts
with the rapidly moving particle, which makes the plasma pressure increasing and the column radial
decreasing. Appearancely, the plasma beam can reach balance till the plasma pressure is equal to
the magnetism pressure [5].
Figure 2: The balance of the linear plasma.
The balance factor of the linear shrinkage plasma is following:
<P >+
2 >
B2
< Bzi
B2
= ze + θe
2µ0
2µ0
2µ0
(1)
Thereinto:
1
<P > =
πa2
2
< Bzi
> =
1
πa2
Za
P (r)2πrdr
(2)
Bz2 (r)2πrdr
(3)
0
Za
0
In the formula, µ0 is the magnetic conductivity in vacuum, Bzi and Bze parting denote the
inside and outside magnetic field intensityof plasma along the axial direction, Bθe denotes the
outside angle magnetic field intensity of plasma, P denotes the plasma pressure. The left of the
formula (1) denotes the inner pressure and the average magnetic field intensity of the plasma
beam. The right of the formula (1) denotes the external column axial direction and angle direction
magnetism pressure. The balance condition shows, when the inside and outside plasma beam total
magnetism pressure are equal, the plasma beam will reach balance.
When electric current flow through the parallel conducting wire, they will attract for each
other. If regards the voltaic arc beam as numberless conducting wire with electric currents, and
every conducting wire will receive a larenz force which produced by magnetism caused by electric
current. Direction of Larenz force will attract for each other and towards the center of arc column,
which like as a hank wire will become tighter more and more when electric current pass through,
and the arc column diameter will decrease because of the self-magnetic compression.
The element force balance equation of arc column is following:
dP
+ jz · BΦ = 0
dr
(4)
PIERS Proceedings, Beijing, China, March 23–27, 2009
966
Thereinto P is the barometric pressure, jz is axial direction electric current, BΦ is the arc column
self-magenetic field strength, and it always point to the tangential direction, and jz · BΦ delegate
the Lorenz power, the physical significance of the force balance equation formula (4) is that the
Lorenz power in the arc column will be balanced by the pressure gradient. Because of the Lorenz
power is centripetal, the result that the arc column center pressure is inevitable greater than the
other place’s pressure can be gained easily from the formula (4).
Because the arc column is pillar symmetrical, the relationship of magnetic density and electric
current can be get by the Ampere’s law as following:
I
X
B · dl = µ0
I
(5)
l
P
Thereinto, µ0 is vacuum magnetic permeability,
I is the the electric current algebraic sum
included in the closed circuit l. If make l as a circle with radius r, then the B and dl have the
same direction, and |B| = BΦ , and they remain the constants in the circle, so the formula (5) can
be predigested as the following:
Z
µ0 r
BΦ =
jz dr
(6)
r 0
To get the formula (2)–(4) substitude the formula (2)–(6):
µ Z r
¶
jz
dP = −µ0
jz rdr dr
r 0
(7)
To get the pressure p integrate from arc column edge to the interior, the edge pressure of the
arc column should be the environmental pressure P0 , so:
Z r Z r
jz
P (r) − P0 = −µ0
jz rdr
(8)
r∗ r 0
That is:
Z
∆P (r) = −µ0
r
r∗
jz
r
Z
r
0
jz rdr
(9)
Thereinto, ∆P (r) = P (r)−P0 means the pressure increasing generated along the radial direction
r because of the self magnetic compression. The formula (9) shows the relationship of the one
dimention arc column self magnetism compression, appending pressure, the arc column diameter
and the electric current. If the electric current density distributing form can be got, the relationship
of the appending pressure of self magnetism compress and the electric current of arc beam can be
gained too. Supposing the electric current density in the arc column is constant, ViZ.:
jz =
I
= const
πr∗2
∆P (r) =
µ0 I 2 ³
1−
4π πr∗2
(10)
The formula (9) simplified as following:
r2
r∗2
´
Supposing the arc column electric current density distributed like the parabola:
µ
¶
r2
jz = jm 1 − 2
r∗
(11)
(12)
The formula (9) simplified as following:
5 µ0 I 2
∆P (r) =
3 4π πr∗2
In the arc column axis:
∆P (r) =
µ
¶
12 r2 9 r4 2 r6
1−
+
−
5 r∗2 5 r∗4 5 r∗6
(13)
5 µ0 I 2
= ∆Pmax
3 4π πr∗2
(14)
Progress In Electromagnetics Research Symposium, Beijing, China, March 23–27, 2009
967
Above several expressions show that the self magnetism compress appending pressure and arc
current’s square have the direct ratio arelationship, and inverse proportion to the arc radius square,
the appending pressure in the arc axes are will become higher with the electric current density
distribute more steeper.
4. THE EXPERIMENT OF LASER INFLUENCE ON THE APPEARANCE OF THE
COMPOUND ARC COLUMN
The appearance of plasma arc beam changed with the laser average power under the condition that
the repeat frequency is 50 Hz and the pulse width is 1.0 ms is shown as Fig. 3. The relationship
between plasma arc characteristic and laser average power is shown as Fig. 4. It is clear that the
plasma arc is becoming smaller when the laser average power is increasing, which means that the
laser has the compression effect on the plasma arc. The reason is that the increase of the laser
average power makes the energy absorbed by the plasma arc increase, improves ionization and
magnetic effect compression, and then results in the reduction of the plasma arc diameter.
(a) The appearance of the single plasma arc beam
(Left: the original arc image. Right: the image figure)
(b) The hybrid arc beam appearance under the condition of average power 4 W
(Left: the original image. Right: the image figure)
(c) The hybrid arc beam appearance under the condition of average power 39 W
(Left: the original arc image. Right: the image figure)
PIERS Proceedings, Beijing, China, March 23–27, 2009
968
(d) The hybrid arc beam appearance under the condition average power 91 W
(Left: the original arc image. Right: the image figure)
(e) The hybrid arc beam appearance under the condition of average power 160 W
(Left: the original arc image. Right: the image figure)
(f) The hybrid arc beam appearance under the condition of average power 254 W
(Left: the original arc image. Right: the image figure)
Plasma arc diameter (mm)
Figure 3: The hybrid arc beam appearance under the condition of different laser average power (laser
repetition frequency: 50 Hz, laser pulse width: 1.0 ms).
Average power (W)
Figure 4: The relationship between laser average power and plasma arc diameter.
Progress In Electromagnetics Research Symposium, Beijing, China, March 23–27, 2009
969
5. CONCLUSION
(1). Self magnetism compress appending pressure and arc current’s square have the direct ratio
arelationship, and inverse proportion to the arc radius square, the appending pressure in the
arc axes are will become higher with the electric current density distribute more steeper.
(2). Only when the magnetic compression strength and the compound arc column outward expansion power are balance, the arc column can maintain a certain form of the same shape.
(3). The plasma arc is becoming smaller when the laser average power is increasing.
ACKNOWLEDGMENT
The authors gratefully acknowledge the contribution of the National Nature Science Foundation
of China under project No. 50075032 and the Hubei Province Educational Foundation of China
under project No. q200714003 and the Hubei Province Nature Science Foundation of China under
project No. 2007ABA185.
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