CA1171143A

CA1171143A - Electrical welding device

Info

Publication number: CA1171143A
Application number: CA000372480A
Authority: CA
Inventors: Yoichiro Tabata; Shigeo Ueguri; Hirotsugu Komura; Toshio Ito
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1980-03-19
Filing date: 1981-03-06
Publication date: 1984-07-17
Also published as: DE3108917A1; DE3108917C2; GB2076235A; JPS56134069A; FR2478931B1; FR2478931A1; GB2076235B

Abstract

ABSTRACT OF THE DISCLOSURE
An electrical welding device which requires no high frequency insulation and an eletrical discharge gap for main-taining the arc discharge is made large. A main power source supplies an arc discharge current through an electrical conductor to the welding electrode. A high frequency electric power source applies a high-frequency high voltage between the electrode and the material to be welded to generate a high frequency discharge for arc ignition in the electric discharge gap. A high frequency magnetic choke element, which is preferably a plurality of stacked annular ferrite discs, surrounds a predetermined part of the electrical conductor. A high-frequency bypass capacitor is utilized to ground the electrical conductor between the magnetic choke element and the main power source.

Description

~ ~ 7~43 DEVIC~ WITH HIGH FR~QUBNCY, CONTACTLESS TYPE ARC GEN~RATING MECHANISM

BACKGROUND OF THE INVENTION
The present invention relates to welding devices such -as a MIG welding machine, a TIG welding machine, an arc fusing type cut~er, a fusing type cutter or an electric dlscharge machine in which a materiaI is processed using an arc discharge, specifically, a machine of this type in which a high frequency electric source is employed to generate arcs contactlessly.
By way of example, a MIG welding machine will be de-scribed. In general, in a MIG welding machine, a wire-shaped electrode ~hereinafter~referred to as "a wire electrode" when applicable) is fused by the heat of electrical arcing or Joule heating into molten metal drops which are transferred onto a base material.
In a conventional MIG welding machine, the generation of an arc is carried out by bringing the wire eleckrode inko contact wlth the base material momenkarily to cause a short-circuit currenk which heats and melts the wlre electrode. The molten metal is scattered in khe ~form'of particles. The molken ; ;
mekal particles khus~scaktered may adhere to~the surface of the base material. I this happens, lt is necessary kO remove the molten mekal particles from khe base ma~erial surface which operation decreases the overall work efflciency of khe weld~ing :

1 procedure.
This difficulty may be eliminated by utilîzing with the MIG welding machine a contactless type arc generating mechanism using a high frequency electric sourse such as is employed in a TIG welding machine~
BRIEF DESCRIPTION OF T~E ~RAWINGS
.
In the accompanying drawings:
Fig. l is an e~planatory diagram showing the arrange-ment of a MIG weldin~ machine to which an arc generating high frequency electric sourse employed in a TIG welding machine is appliedi Fig. 2 is an explanatory diagram showing a ~irst embodi-ment of the inventîon;
Fig. 3 is an explanatory diagram showing a second embodiment of the invention;
Fig. 4 is a perspective view showing an example of a high frequen~y magnetic element which forms an essential part of the welding device o~ the invention; and Fig. 5 is a graphical representation indicating high frequency magnetîc element thickness with resistivity.
Fig. l shows the arrangement of a MIG welding machine so modified. In Fig. l, re~erence numeral l designates a base mater-ial, 2 a torch, 3 a~welding power sou~ce, 4a and 4b current supply-ing wires extending from the welding power source 3, and 5 a high frequency source composed of a series circuit including an oscil-lating coil 51, discharge gaps 52 and 53 and a high Ereq~ency oscillating capacitor 54. The high frequency source 5 oscillates, for instance, at 3 UHz when a high voltage is applied across term-inals 55 by a high voltage source (not shown). A coupling coil 4l is formed by the current feeding wire 4;and it is coupled to the .:

P

~ 3 71 1~3 1 oscillatiny coil 51 $o that, for ins.tance~ a high vol-~age of 5 KV
is induced across the coupliny coil 41. A high ~requency bypass capacitor 6 is proviaed for the protection of the wel~ing power source 3. A wire electro~e 8 ~.hereinafter referred to merely as "a wire 8" when applicable) ~s wound on a reel 7~ A wire supply-ing unit ~ is made up of ~ driving motor 91, a drive roller 92 driven by the driving motor gl, and a wire depressing roller 93 adapted to press the wtre 8 against the drive roller 92. The wire supplying unit 9 is controlled by a control device ~not shown) to feed the wire 8 to the torch 2 at a rate corresponding to the particular welding conditions~ In Fig. 1, reference charac~er 8a de~ignates the end portion of the wire electrode which protrudes from the torch 2 IThe end portion will hereinafter be referred to as "electrode 8b" when applicable). The wire 8 is inserted through a guide pipe (not shown~, which is juxtaposed with the current feeding wire 4a, and into the torch 2 where electrical con-tact is made with the wire 8.
' The operation of the MIG welding machine thus constructed will be described. .In starting an initial arc, the high frequency '..
electric source 5 is operated so that the output high fre~uency voltage of the high frequency electric source 5 causes a high fre-quency discharge between the electrode 8a and the base material 1, In response to the occurrence of the high frequency discharge, current is supplled from the welding power source 3 to'generate and maintain an arc 10. The wire 8 from the reel is fed.by the wire supplying unit 9. The electrode 8b is fused by the arc 10 thus generated and the base material :1 is welded along 'the welding line with the molten metal drops 8b :formed from the elec*rode. 8 As was described above, a contactless type arc generat~ :~
ing mechanism using R high frequency electric source, which is ~,~," , 1 employed in a TIG welaing machine, can be applied to a MIG welding machine. Elowever, as the high fre~uency voltage is applied direc-tly to the wire 8, ;t ~s necessary to electrically insulate ~he wire supplying unit g and the reel 7, that is, to provide a high frequency insuLation treatment for these members so that they can sufficiently withstand t~R ~igh voltage of h~gh frequency.
U~RY OF THE INVE~TION
Accordingly, an object of the inventlon lS to prevent the application of a high frequency voltage to a welding device with a contactless type arc generating mechanism using a high frequency electric source and also to prevent application there-~f to the power source of the welding device.
Another object of the invention is to provide a welding device with a high frequency, eontactless type arc generating meeh-.
anism in which the applicakion of a particular high frequency in-sulation treatment is unnecessary and~high frequency insulation is effected with a mechanism simple in eonstruction and low in manu-facturing cost.
A further object o~ the inventlon is to provide a deviee

2~ with a high frequency, contaetless type arc generatiny mechanism in which the arrangement of high requency insulation means is aehieved readily and the size of the device is made small.
~ still further object of the invention is to provide a welding device with a high frequency, contactless type are gener- ~;
ating mechanism in which h~gh frequency insulation is~effected and an eleetric diseharge gap for maintainlng arc discharge can . :~
be made large. :

~ -. ' .

- s ~

A particular object of the invention is to provide a welding device with a high frequency, contactless type arc generating mechanism in which the wire supplying unit, etc.
are protected from a high frequency voltage.
The foregoing objects and other objects of the inven-tion have been achieved by the provision of a welding device with a high frequency, contactless type arc generating mechanism which, according to the invention, includes an electrode which confronts a material to be processed therewith through an arc .
discharge gap, a high frequency:electric source for applying an :
: arc generating high frequency voltage:between the electrode and the materiaI, a main power sour~ce for supplying a processing current, a high frequency:magnetic choke element surr~unding a predetermined part of an electrical conductor which extends between~the h~igh freqùency electr1~c source~and means for pre-: venting the unwanted appl1cation of the output high frequencyvoltage of the high requency~electric:source, and a high fre-.
quency bypass capacitor coupled to the side of the means ifor : ~ preventing the unwanted application of the high frequency voltage.
20: The nature, principle and:utility of the invention , : :
will become more apparent from the following detailed descrip~
tion when read in conjunction with~the~accompanying~drawings~
in.which like parts~ are~desi~gna.ted by 11ke re~ference numerals ~ ~ :
: or characters. :

~: :
~ 5 - ~
:

:
:
.. : . .. . . . . . .. . . . .. . .. ........... .
:
-.

-. . , ~ J 71 ~3 1 DESCRIPTION OF TH~ PREFERRED EMBODI~ENTS
The inventîon w~ll be described with reference to pre-ferred embodiments thereo~
Fi~. 2 shows the arrangement of a first preferred e~bodiment of the invention whlch is applied to a MI~ welding machine. In Fig. 2, those components which have ~een previously described with reference to Fig. 1 are therefore similarly numbered and their detailed descriptions w~ll be omitted.
In Fig. 2, a welding power source 3 includes a main power source 31 for supplying Welding current and an auxiliary .'' ~ ' '. ,.

', ~ ' ;
.

~ ~ ' ' ' ' -- :

::

: : : :
: 6 ', ' :: ~

:

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3 3 ~ 3 power source 32 for supplying a voltage higher than that of the main power source 31 to maintain a welding arc. The main power source 31 is connected through a cable 4b to a material to be welded, i.e. a base material 1, and ~hrough a cable 4a to an electrode 8a which confronts the base material 1 through an arc discharge gap. On the other hand, the auxiliary power source 32 is connected through a current limiting resistor 33 and a current feeding wire 4c to a torch 2, and is connected to a high frequency electric source~S through a coupling coil 41 which is inserted in series in the wire 4c.~ A high;frequency magnetic element~in the form o a cylinder made of a high frequency mag-netic material (hereinafter reerred to as~ a choke ll when appli-cable) has a hole 12 formed therein through which the wire 4a and a wire 8 pass. ~The c~hoke ll forms~a hlgh frequency reactor.
In Fig. Z, r~eference numeral 12 designates~;a high frequency~
shield, 6a a hlgh frequency bypass capacltor which~grounds the current feeding wire 4a ~etween the choke ll and the main power source 31,~and 6b~a high frequency bypass~capacitor which grounds ~ the wire~ 8 between~the choke 11 and a wire supplying unit 9.
When the ~high frequency electric~source 5 is operated in the welding machine~ thus arranged, a high frequency discharge lS caused between~the~electrode 8a and the base materlal l.~ As~
a result, first ~an~arc;~is~generated~by~the;auxiliary~power~source~
a~ter which~welding~c~urrent from~th~e~main power source 31~forms~
and maint-lns an~arc~lO with whlch ~ weldlng~operatlon ls~carrled : : : :`~ ~ :`

,: ,. . . . . .. . . . . .. . . . . . ...
, ' . ~. : .~ .
: .

.~
'` `

l ~ 71 ~3 out as in a conventional welding machine.
The provision of the auxiliary power source 32 is advantageous in that, as the discharge gap for main~aining the arc 10 can be made large, the arc 10 can'be readily maintained.
On the other hand, the high-frequency high voltage which is applied through the torch 2, the current feeding wire 4a and the wire 8 to the main power source 31 and the wire -supplying unit 9 is signlficantly decre,ased by the action of the choke ll and the bypass capacitors 6a and 6b. Therefore, it is unnecessary to apply a ;special~hlgh~frequency insulation treatment to these components. ' ~ ~
Fig. 3;shows a second preferr~ed embodiment of the in-vention,which, as~ln;the~flrst~embodiment in Fig. ~2,~is applied ~ to ~a MIG welding~machlne;.~ ~In Fig~ 3, those components whi~h have been~previously~descrlbed with reference ~o Fl~g. 2 are ~ ' ~; therefore similarly~numbered and thelr~ deta~iled descrlptions w~ill;be omitte~d. ~
As ~is apparent from comparing Fig. 3 with Pig. 2, the ~welding machine~in~Fig. 3~is constructed by modifying the weld-20' ~ln~g~machIne ln~ Fig.~2,as follows. The~auxlllary power sou~rce ; ~ 32~is eliminated~but~the maIn power source~31 for supplying the~
~weld~in~g~current i~s~utiliæed.~ The~high~-~frequency high voltage~
s~applied directly'~to~the~torch~2 by ~the~hi~gh -frequency~electric~
sourcé~ 15.~ In~addition,~two~chokes~ ather than one~are~pro~
~5 ~ vided~in~the~circuit~

- ~ .
~ , : : ~ ~ : ::: :

: ~
, :, , '', ~ :171~3 In Fig. 3, reference character lla designates a choke coupled to the current -feeding wire 4b, and 6c designates a high frequency bypass capacitor connected between the wires 4a and 4b which extend between the welding power source 31 and the choke 11 and between the welding power source 31 and the choke lla, respectively.
In the welding machine thus constructed, the ignition of the arc is effected and maintained by the current which is -supplied from the welding power source 31 in response to the -~ high frequency discharge caused by the-high frequency electric source 5. While the arc is maintained, the welding operation is carried out.
The welding power source 31 is protected from the high-frequency high voltage by the chokesll and lla and the bypass capacitor 6c. The wlre supplylng unit 9 and a reel 7 is pro-tected by the choke 11 and the bypass capacitor 6b. Generally, stoppers can be provided at various points or in a distributed form in the circuit.
One example of the choke, which is one o the spe-cific features of the lnvention, will be described with refer-ence to Fig. 4.
As shown in Fig. 4, the stopper is fabricated by piling a plurality of annular discs one on another to a length L. Each disc has an outside~ diameter~of D, an inside diameter d, and a thickness of Q

g . ~ :

.. . . . . .. . . . . . . . . ... .

~ 3 The impedance of the high frequency reactor which is formed by the choke ll is represented by the following expres-sion:

2n~0~r~ logd (1) where ~0 is the free-space magnetic permeability (4~ x 10 7 H/m), ~r is the relative permeability of the magnetic material, and is the angular frequency (1.88 x 107 rad/sec corresponding to a frequency of 3 MHz of the electric source 5).
Assuming, for lnstance ~hat the output frequency of the high frequency electric source 5 is 3 MHz, the output vol-tage is 5 KV, the required impedance Z of the high frequency reactor is 2 KQ, and the dimensions of the choke ~re D = 40 mm, d = 5 mm and L = 500~mm, for these values, the relation be-tween the thickness Q and the~resistlvlty p of a ferrite used is as shown in a characteristic diagram in Fig. 5. For example, if the~ferrite's relatl~e permeability ~ is 760, then the thick-ness Q is 50 mm. The inside diameter _ is set to 5 mm so that the hol~low bare copper wire which is employed as the current feeding wire 4a can pass therethrough.
The material of the high;frequency reactor is pre- , ferably a ferrite magnetic materlal~having ~a hlgh resistlvity.
The configuration of the high frequency react~or is determined in accordance with~the relevant~dimensionsof the welding machine and cable wi~h whlch lt is us~ed~and~from~the permisslble~manu-:; ~ :' : : ~ . :

"" . . . . .. . . , ... . . . . . . .. .. ~ . . .

~ 17~ l3 facturing cost. The maximum allowances in dimension of the high frequency reactor are 40 mm in outside diameter, 15 mm in inside diameter and 0.5 m in length. Because of the inherent characteristics of the high frequency electric source 5, it is 5 preferable that the impedance Z of the choke 11 at a frequency of 3 MHz be at least 2 K~.
Due to the above-described~limitations and in view o-f equation ~1), the relative permeability ~r should be at least 110~. However, since the relatlve permeability ~r of -ferrite - lO material is typically not more -than about 5000, the ratio of the outslde diameter of the high frequency reactor to the inside diameter must be at least 1.2 as may be determined from expres-sion (1).
~he choke ll has an eddy current effect and a skin effect. Accordingly, as the frequency is increased, the rela-. tive permeability ~r is decreased. Thus, it is desirable to fabricate the choke 11 by piling a plurality of ferrite discs one one another as shown in Fig. 4 which are electrically in-sulated from one another.
Decrease of the relative permeability ~r due to the eddy curr0nt effect and the skin effect will be described. A
skin depth ~ is represented by the following expression (2):
~ = ~ (2}

where p is the ferrite's resistivity, f is the frequency of the j~ 25 ~applied current, ~0 is the free space permeability~ and ur is , '.
.. . . . . . . .. .. ....
.
~`

~ 171~3 relative permeability. It is assumed that ~e represents an effective permeability when ~ cannot be neglected. Then, as lS apparent from Fig. 5, the permeability decreasing ratio ~ ~ ) can be expressed as a function of the ratio r = Q/~ of the thickness Q of the ferrite to ~. For instance, if r = 3, then (~ ~ ) is 0.52 and in this case ~e is 0.52 ~O~r Accord-ingly, in order to prevent a decrease of ~e (i.e. making ~e equal to ~O~r)~ it can be understood from Pig. 5 that the fer-rite cannot be used effectively without setting r to 1 or less.
In general9 the relative permeability ~r of commercial-ly available ferrite materials is substantially in reverse pro-portion to the resistivity p. In one particular ferrite materi-al which can be used with the invention, p is 100 Q-cm with ~r = llO0 and p = lO0 Q-cm. Insertmg these in the -following expression (3), then the maximum thickness Q of the ferrite for making r equal to 1 or less must be lO mm or less.
Q /
1 ~ 2 ~4~fp-~o~r -While the invention has been described with reference to preerred embodiments thereof as relate to a MIG welding machine, it should be noted t~at the invention is not limited - thereto or thereby.~ That lS, the te~hnical concept of the in-vention can be app~lied;to an arc dlscharge mach;ne in which a high frequency electric source~is employed to generate arcs contactlessly, such as a TIG weldlng machine, an arc fusing type cutter or an electric discharge machine with the same advantageous effects.

.. . - .. . . , ~ . . . .. . . .. . .. . . .. .

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A welding device with a high frequency, contactless type arc gererating mechanism which comprises:
a single electrode disposed confronting an electrically conductive material to be processed therewith through an electric discharge gap;
a main power source for supplying an arc discharge cur-rent between said electrode and said material;
an electrical conductor for coupling said main power source to said electrode;.
a high frequency electric source for applying a high frequency high voltage between said electrode and said material to generate a high frequency discharge for arc ignition in said electric discharge gap;
a high frequency magnetic choke element surrounding a predetermined part of said electrical conductor between said main power source and said electrode, said high frequency magnetic choke element comprising a plurality of stacked ferrite discs in the form of a cylinder, each of said ferrite discs having a central hole, said electrical conductor passing through said hole; and a high-frequency bypass capacitor connected in parallel with said main power source and having one terminal connected to said electrical conductor between said magnetic choke element and .
said main power source.

2. The device as claimed in claim 1 in which said high-frequency bypass capacitor has a second terminal coupled directly to a ground terminal of said main power source.

3. The device as claimed in claim 1 further comprising a second high. frequency magnetic choke element mounted on a second electrical conductor connecting said main power source to said material to he processed and wherein a second terminal of said capacitor is coupled to said second electrical conductor between said main power source and said second electrical conductor.

4. The device as claimed in claim 1 in which said high frequency magnetic choke element comprises a plurality of stacked discs in the form of a cylinder, each of said discs having a central hole and having an outside diameter at least 1.2 times the inside diameter thereof and a thickness of at most 10 mm.

5. The device as claimed in claim l in which said electrode comprises a welding electrode and said material to be processed is a material to be welded.

6. A device with a high frequency, contactless type arc igniting mechanism which comprises:
an electrode disposed confronting an electrically con-ductive material to be processed therewith through an electric dis-charge gap;
a main power source for supplying an arc discharge cur-rent between said electrode and said material;
a first electrical conductor connecting a first terminal of said main power source to said electrode and a second electrical conductor connecting a second terminal of said main power source to said material;
a high frequency electric source for applying a high-frequency high voltage between said electrode and said material to generate a high frequency discharge for arc ignition in said electric discharge gap;

Claim 6 cont.

a current limiting resistor;
an auxiliary power source for applying a voltage higher than that of said main power source between said electrode and said material through said current limiting resistor, to maintain an arc in said electric discharge gap;
a coupling coil for superposing said high frequency high voltage from said high frequency electric source on a current supplying wire extending from said auxiliary power source to said electrode;
a high frequency magnetic choke element surrounding a predetermined part of said first electrical conductor for blocking transmission of said high frequency high voltage to said main power source, said high frequency magnetic choke element comprising a plurality of s-tacked ferrite discs in the form of a cylinder, each of said ferrite discs having a central hole; said first elec-trical conductor passing through said hole; and a high frequency bypass capacitor connected in parallel with said main power source.

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