Development of device to prevent high voltage arcing in electron beam weldin

Hanchey, K. K.

Kubik, J. S.

Mahan, J. C.

English

NASA Technical Reports Server

Oct. 21, 1969 JAMES E. WEBB 3,474,220 
ADM IN ISTRAT E O N A L  AERONAUTICS 
AN A STRATION 
D E V l @ B  FOR PREVENTING H I G H  -VOLTAGE'XRCING I N  ELECTRON BEAM WELDING '', 
Fi l ed  May 17, 19@f 2 Sheets-Shee t 1 
FIG. 2 
KARL K. HANCHEY, 
JAMES C. MAHAN, 
JAMES S. KUBIK, 
lNVENTORS 
https://ntrs.nasa.gov/search.jsp?R=19710010011 2020-03-17T02:44:36+00:00Z
Oct. 21, 1969 JAMES E. WEBB 3,474,2 20 
ADMINISTRATOR OF THE N A T I O N A L  AERONAUTICS 
AND SPACE ADMINISTRATION 
DEVICE FOR PREVENTING HIGH VOLTAGE ARCING IN 
ELECTRON BEAM WELDING 
Filed May 17, 1967 2 Sheets-Sheet 2 
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JAMES C MAHAN, 
JAMES S. KUBIK, 
INVENTORS 
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3,474,220 United States Patent 0 ce patented Oct. 21, 1969 
1 
3,474,220 
ING IN ELECTRON BEAM WELDING 
James E. Webb, Administrator of the National Aero- 
nautics and Space Administration, with respect to an 
invention of Karl K. Hanchey, Utica, Mich., James C. 
Mahan, Athens, Ala., and James S. Kubik, Utica, Mich. 
DEVICE FOR PREVENTING HIGH VOLTAGE ARC- 
Filed May 17, 1967, Ser. No. 640,447 
Int. C1. B23k 9/00 
U.S, C1.219-121 2 Claims 
ABSTRACT OF THE DISCLQSW 
A device for preventing high voltage arcing in electron 
beam welding wherein an arc suppressor plate is mounted 
on an electron gun from which the electron welding beam 
emits, the welding operation being performed within an 
evacuated chamber. A metallic tube has the suppressor 
plate attached to one end thereof and the other end of 
the tube is attached to the electron gun. The electron weld- 
ing beam passes from the electron gun, through the 
metallic tube and through an opening in the suppressor 
plate before striking the work. The suppressor plate is 
positioned very close to the work and attracts and col- 
iects arc producing plasma rising from the work during 
welding. 
The invention described herein was made in the per- 
formance of work under a NASA contract and is subject 
to the provisions of Section 305 of the National Aeronau- 
tics and Space Act of 1958, Public Law 85-568 (72 Stat. 
435; 42 U.S.C. 2457). 
This invention relates generally to electron beam weld- 
h g  and particularly to a device for eliminating one of 
the major problems connected with electron beam weld- 
ing, that of high voltage arcing. 
While electron beam welding is well known and com- 
monly practiced in the welding field, its potentialities for 
certain applications are just beginning to be realized, and 
it is the object of much study, experimentation, and de- 
velopment. 
Electron beam welding is conducted within an evacu- 
ated region, such as a vacuum cha,mber, and basically in- 
volves the acceleration of a stream of electrons from 
an electron gun to a workpiece. This manner of welding 
offers several very important advantages including a high 
purity, which is essential to welding reactive metals, and 
produces very high heat concentration at the area to be 
welded, permitting sound weldment of a high depth to 
width ratio. These and other attributes of electron beam 
welding causes this type of welding to be of particular 
interest and use in the aerospace field in the construction 
of missiles, rockets, and aircraft. 
Heretofore, one of the most serious problems asso- 
ciated with electron beam welding has been the occurrence 
of intermittent disturbances of the electron beam due to 
high voltage discharges, com4monly referred to as arcing. 
Although the problem of arcing has been encountered by 
most practitioners of electron beam welding, its exact 
cause or causes are not completely understood, It is gen- 
erally believed, however, that the escaping gases and 
metallic vapor emitted from the workpiece during weld- 
ing form what might be called a conductive cloud that 
intermittently provides a conductive path from the high 
voltage components of the welding apparatus to ground. 
The combination of gases, electrons, and ions emitted 
from the area of beam i,mpingment is commonly referred 
to as plasma and the emission of this plasma from the 
workpiece during welding is referred to as “secondary 
emission.” It has been noted that the arcing problem is 
particularly severe when welding thick aluminum alloys 
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that generate relatively large amounts of metallic vapor 
and gases during welding. 
The effect of high voltage arcing on the quality of the 
weld depends on the severity and duration of the arcing. 
A “spike” defect usually appears in the weld at the point 
where arcing occurs, and if the arcing is of sufficient dura- 
tion to cause the high voltage circuit to open, the electron 
beam is extinguished leaving a hole completely through 
the weldment. 
Accordingly, it is an object of this invention to provide 
a means for suppressing secondary emission and thus pre- 
venting high voltage arcing in electron beam welding. 
Another object is to provide in electron beam welding 
a device for preventing weld defects caused by high volt- 
age arcing. 
A further object is to provide a device for electron beam 
welding of reactive metals while preventing weld defects 
caused by high voltage arcing. 
Other objects, uses, and advantages of the present in- 
vention will become apparent as the description pro- 
ceeds. 
Although, as indicated previously, the precise cause or 
causes of arcing in electron beam welding are not thor- 
oughly understood, a means of eliminating this problem 
has been found in accordance with the present invention. 
Briefly described, the invention comprises an electron 
beam welding device including a vacuum chamber 
equipped with an electron gun that carries a metallic arc 
suppressor element positioned between the electron gun 
and the work to be welded. Typically, the suppressor ele- 
ment comprises a metallic plate having an opening there- 
through to per.mit passage of an electron beam passing 
from the electron gun to the work, the suppressor plate 
being very close to the point where the electron beam 
strikes the work. The electrons which are emitted sec- 
ondarily from the work are attracted by the metallic sup- 
pressor plate thus preventing the formation of the arc pro- 
ducing conductive cloud within the vacuum chamber. 
In describing the invention in detail, reference will be 
made to the accompanying drawing in which: 
FIGURE 1 is a front elevational view, partially broken 
away, of a vacuum chamber of an electron beam weld- 
ing apparatus. 
FIGURE 2 is a fragmentary cross sectional view taken 
along line 2-2 of FIGURE 1. 
FlGURE 3 is an enlarged cross sectional view taken 
along line 3-3 of FIGURE 1. 
FIGURE 4 is a cross sectional view taken along line 
4-4 of FIGURE 3. 
Referring now to FIGURE 1, there is shown a vacuum 
chamber 11 of an electron beam welding apparatus with 
an access door 13 cut away to reveal the interior of the 
vacuum chamber. The chamber 11 contains an electron 
gun 15 movably suspended approximately along the 
vertical axis of the chamber by a bracket 17 on a track 
system 19 installed in the upper region of the vacuum 
chamber 11. Attached to the electron gun 15 is a second- 
ary emission suppressor 16, the details and purpose of 
which will be provided hereinafter. The bracket 17 is con- 
nected to a travel block 21 through which a screw 23 
is threaded and which carriers rollers 25 that roll on a 
track 27 upon rotation of the screw 23. The screw 23 is 
actuated by a motor 29 through a gear train including 
gears 31 and 33. Wires 35 lead from the electron gun 15 
to an appropriate high voltage power source (not shown). 
The details of the electron gun and track system 19 form 
no part of the present invention and will not be described 
in further detail. 
Mounted on the bottom of the chamber 11 are spaced 
parallel tracks 39 that support a carriage bed 41 through 
rollers 43. Movement of the carriage bed over the tracks 
39 is effected by a oog wheel 45 meshed with a rack 
3,474,220 
3 
47 connected to andkxtending the length of the carriage 
bed 41. A shaft 49 is joined to the cog wheel and is 
rotated by a motor (not shown) mounted beneath the 
vacuum chamber 11. 
Bearing on the carriage bed 41 is a frame unit 53 includ- 
ing a series of spaced parallel cross beams or bars 55. 
At each end of each cross beam 55 is connected, as by 
welding, a bracket 57 that has a vertical portion 59 and 
an inwardly directed horizontal portion 61. Clamps 63 are 
located between the brackets 57, being pivotally connected 
to pins 65 extending between and through the brackets 57. 
Clamping pressure of the clamps 63 is exerted by screws 
67 supported by and threaded through bars 69 extending 
between the brackets 57. The ends of the screws 67 bear 
on plates 71 welded to the respective clamps 63. 
The frame unit 53, comprising the cross beams 55, 
brackets 57 and clamps 63, is secured to the carriage bed 
41 by clamp bolts 73 mounted in plates 75 welded to the 
respective cross beams 55. The bolts 73 threadedly en- 
gage movable nuts 77 that slide within slots 79 in the car- 
riage bed 41. 
A workpiece support 81 rests on the cross beams 55, 
being retained in position by stops 83 removably clamped 
to the beams 55 and abutting the opposite edges of the 
workpiece support 81. In order to provide for a slot 85 
in the workpiece support to  coincide with the joint to  be 
welded, the workpiece support comprises two separable 
plates 87 that are adjustably spaced apart by bolts 89 
threaded in opposed projections 91 at the ends of the 
plates 87. 
The work to be welded is arranged on the workpiece 
support 81 and comprises metallic components 93 set 
up  for a square butt joint weld along a meeting line 95, 
with clamps 63 holding the components 93 in position. 
As shown in FIGURES 3 and 4, the secondary emission 
suppressor 16 comprises a suppressor element in the form 
of a circular plate 97 attached to the electron gun 15 
by a triangular mounting plate 99 having a slotted clamp 
101 at each corner thereof so that each clamp engages 
a disk 193 which constitutes the lower element of the 
electron gun 15, the clamps 101 being actuated by screws 
105. Welded to and extending between mounting plates 
99 and the suppressor plate 97 is a metallic tube 107, 
the latter being aligned with a hole 109 in the mounting 
plate 99 and a hole 111 in the disk 103. 
The suppressor plate 97 is a relatively thick metallic 
element with a concave recess 113 around a hole 115 in 
the center of the plate. The hole 115 is aligned with 
the holes 109 and 111 in the mounting plate 99 and disk 
103, respectively, and thus is aligned with the electron 
welding beam produced by the electron gun 15. The Sup- 
pressor plate 97 has a slight integral sleeve 117 that fits 
over the tube 107. 
In the electron beam welding operation, the work, such 
as metalic components 93, are arranged as described 
above within the vacuum chamber 11 and the electron 
gun 15 is focused on the meeting line 95. After the 
vacuum chamber is closed and evacuated, an electron 
beam produced by the electron gun 15 is passed from the 
gun through the tube 107 and the hole 115 in the sup- 
pressor plate 97 and then strikes and penetrates the work 
at the meeting line 95, the high heat concentration result- 
ing in a melting and fusion of the abutting edges of the 
components 93. Directly below the meeting line 95 aligned 
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recesses 96 are formed in the cross beams 55. The work 65 
is removed by the carriage bed at a predetermined and 
constant rate beneath the electron gun 15 until the full 
length of the joint to be welded has intersected the elec- 
tron beam. The near surface of the suppressor plate 97 
is spaced from the work by a small amount, preferably 70 
between % and 34 inch. The welding operation is ob- 
served through windows 119 located in the walls and 
door of the vacuum chamber 11. 
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tive in preventing high voltage arcing between the high 
voltage components and any portion of the gun or vacuum 
chamber that it at ground potential. The suppressor plate 
97 is maintained at ground potential and attracts and 
collects the secondary emission, thus preventing the for- 
mation of arc producing conductive clouds within the 
vacuum chamber. 
Obviously, numerous modifications and variations of 
the present invention are possible in the light of the above 
teachings. The secondary emission suppressor is suscep- 
tible of various configurations and structures. For ex- 
ample, the suppressor element oould take the form of an 
integral annular flange on the end of the tube 107. Thus 
it is to be understood that within the scope of the ap- 
pended claims the invention may be practiced otherwise 
than specifically described herein. 
1 
What is claimed is: 
1. In an electron beam welding apparatus comprising a 
vacuum chamber enclosing an electron gun and adapted 
to enclose a work to be welded, and having means includ- 
ing said electron gun for producing an electron welding 
beam within said vacuum chamber and impinging said 
beam on a work to  be welded within said vacuum cham- 
ber: 
(a)  the exit end of said electron gun having an opening 
therein which is adapted to pass an electron beam; 
(b) a secondary emission suppressor carried by said 
electron gun; 
(c) said suppressor comprising a metallic tube having 
one end attached to and contiguous with said exit end 
of said gun; 
(d) the opening through said tube being in alignment 
with said opening in said exit end of said gun; 
(e) a metallic suppressor plate joined to  and covering 
the end of said tube opposite said exit end of said 
gun ; 
( f )  said plate having an aperture therethrough in align- 
ment with said opening in said exit end of said gun 
whereby said opening through said tube and said 
aperture in said plate are aligned with the path of the 
electron beam produced by said gun; 
(g) means within said vacuum chamber for moving a 
workpiece relative to  said gun; 
(h)  said gun being movably mounted for positioning 
within said chamber; 
(i) said metallic tube extending from said gun a dis- 
tance sufficient to position the nearest surface of said 
suppressor plate to within %I inches of a workpiece 
mounted in said chamber. 
2. The invention as defined in claim 1 wherein said 
tube is attached to said exit end of said gun by a connect- 
ing plate detachably clamped to said gun, said connecting 
plate having an aperture therethrough aligned with said 
aperture in said suppressor plate, said tube completely en- 
closing the path of said welding beam between said con- 
necting plate and said suppressor plate. 
References Cited 
2,899,556 
3,132,198 
3,174,026 
3,291,959 
3,315,157 
3,327,090 
2,793,281 
3,187,216 
3,219,792 
3,322,930 
3,351,731 
3,406,273 
UNITED STATES PATENTS 
8/1959 Schopper et al. _ _ _ _ _ _  219-121 
311965 Bowers et al. _ _ _ _ _ _ _ _  219-121 
12/1966 Schleich et al. _ _ _ _ _ _  219-121 
411967 Watanabe et  al. _ _ _ _ _ _  219-121 
6/1967 Greene _ _ _ _ _ _ _ _ _ _ _ _ _  219-121 
5/1957 Steigerwald _ _ _ _ _ _ _ _ _  219-121 
611965 Sciaky _ _ _ _ _ _ _ _ _ _ _ _ _  219-121 
1111965 Pederson _ _ _ _ _ _ _ _ _ _ _  219-121 
511967 Sciaky _ _ _ _ _ _ _ _ _ _ _ _ _  219-121 
1111967 Tanaka _ _ _ _ _ _ _ _ _ _ _ _ _  219-121 
1011968 Holland _ _ _ _ _ _ _ _ _ _ _ _  219-121 
5/1964 Du Bois et al. _ _ _ _ _ _  219-121 1 
._._ 
With this arrangement it has been found that during TRUHE, Primary Examiner 
welding the secondary emission suppressor is quite effec- 75 W. DEXTER BROOKS, Assistant Examiner 


Device for preventing high voltage arcing in electron beam welding Patent

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