A tool and process to be used in the explosive joining of tubes is disclosed. The tool consists of an initiator, a tool form, and a ribbon explosive. The assembled tool is a compact, storable, and safe device suitable for explosive joining of small, lightweight tubes down to 0.20 inch in diameter. The invention is inserted into either another tube or a tube plate. A shim or standoff between the two surfaces to be welded is necessary. Initiation of the explosive inside the tube results in a high velocity, angular collision between the mating surfaces. This collision creates surface melts and collision bonding wherein electron-sharing linkups are formed

Bailey, James W.

Bement, Laurence J.

English

NASA Technical Reports Server

ed States Patent [191 p i ]  Patent Number: 4,708,280 
~ e m e m t  et an. ~451 Date of Patent: NOV. 24, 6987 
TOOL AND PROCESS FOR MINIATURE 4,003,513 1/1977 Chadwick ........................... 228/107 
EXPLOSIVE JOINING OF TUBES 4,028,789 6/1977 Loch ................................... 228/107 
4.117.966 10/1978 Green et al. ......................... 228/2.5 
Inventors: 
Assignee: 
Appl. No.: 
Filed: 
Laurence J. Bement, Newport News; 
James W. Bailey, Tabb, both of Va. 
The United States of America as 
represented by the Administrator, 
National Aeronautics & Space 
Administration, Washington, D.C. 
904,812 
Sep. 8, 1986 
Related U.S. Application Data 
Continuation-in-part of Ser. No. 790,597, Oct. 23, 1985. 
Int. Cl.4 .............................................. B23K 20/08 
228/109 
Field of Search ................. 228/107, 2.5, 108, 109 
us. a. ..................................... 22m07; 2 2 ~ 2 . 5 ;  
References Cited 
U.S. PATENT DOCUMENTS 
2,367,206 1/1945 Davis .................................. 228/107 
2,779,279 1/1957 Maiwurm .. 
3,025,596 3/1962 Ward et al. 
3,724,062 4/1973 Cantrell et al. 
3,774,291 11/1973 Snyder et al. ....................... 228/107 
3,790,060 2/1974 Feiss ..................................... 228/2.5 
3,848,794 11/1974 Howell ............... 
3,910,478 10/1975 Howell et al. ...................... 228/107 
3,987,529 10/1976 Nakagawa et al. ................. 228/107 
4,272,005 6/1981 Jackson et al. ..................... 228/107 
4,347,790 9/1982 Lizen .................................... 228/2.5 
FOREIGN PATENT DOCUMENTS 
20096 9/1964 Japan ................................... 228/107 
OTHER PUBLICATIONS 
NASA Technical Memorandum 84649, “Practical 
Small-Scale Explosive Seam Welding”, Apr., 1983. 
Primary Examiner-Nicholas P. Godici 
Assistant Examiner-Samuel M. Heinrich 
Attorney, Agent, or Firm-George F. Helfrich; John R. 
Manning 
1571 ABSTRACT 
The invention is a tool and process to be used in explo- 
sive joining of tubes. The tool consists of an initiator 81, 
a tool form 82 and a ribbon explosive 25. The assembled 
tool 80 is a compact, storable and safe device suitable 
for explosive joining of small, lightweight tubes down 
to 0.20 inch in diameter. The invention is inserted into a 
tube 51 to be welded which tube has itself been inserted 
into either another tube 52 or a tube plate. A shim or  
standoff between the two surfaces to be welded is nec- 
essary. Initiation of the explosive inside the tube results 
in a high velocity, angular collision between the mating 
surfaces. This collision creates surface melts and colli- 
sion bonding wherein electron-sharing linkups are 
formed. 
5 Claims, 8 Drawing Figures 
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1 
TQOL AND PROCESS FOR MINIATURE 
EXPLOSIVE JOINING QF TUBES 
ORIGIN O F  THE INVENTION 
The invention described herein was made in the per- 
formance of work under a NASA Contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act pf 1958, Public Law 85-568 
(72 Stat. 435; 42 USC 2457). 
This application is a continuation-in-part of applica- 
tion Ser. No. 790,597, filed Oct. 23, 1985. 
TECHNICAL FIELD O F  THE INVENTION 
The invention is related to the welding, joining and 
fabricating technology field. 
BACKGROUND O F  THE INVENTION 
This invention relates to joining tools and processes 
and more particularly to tools and processes for explo- 
sive joining of tubes. 
Demand is increasing for highly reliable, remote, 
metal joining processes for hazardous or inaccessible 
operations such as nuclear reactor repairs or  assembly 
of structures in space. Prior art methods, such as me- 
chanical fasteners, swaging fusion welding, soldering 
and adhesives have been inadequate due to  constraints 
to hand operations, excessive downtime of the mecha- 
nism, inaccessibility of the parts to be joined, insuffi- 
cient strength, resistance to environments (particularly 
high temperatures) and other constraints. Only explo- 
sive joining offers the characteristics to meet the above 
requirements. This type of joining produces metallurgi- 
cal bonds which are impossible to achieve by any other 
processes. The explosive joining process produces a 
high velocity, angular collision between the metal sur- 
faces which causes interactomic, electron-sharing link- 
ups to be formed. However, previous methods of explo- 
sive joining have had limited suitability due to the ne- 
cessity of using relatively large amounts of explosive 
which results in a lack of ability to precisely locate the 
joint and probable damage to lightweight structures 
such as small tubes and thin tube plates. 
Accordingly, it is an object of the present invention 
to  provide a means of explosive joining which mini- 
mizes the amount of explosive required. 
Another object of the present invention is to provide 
a means of explosive joining which allows precise loca- 
tion of the joint. 
Yet another object of the present invention is to pro- 
vide a means of explosive joining which reduces damag- 
ing pressure waves, noise nuisance and damage to sur- 
rounding structures. 
A further object of the present invention is to provide 
a tool capable of holding an explosive joining means in 
contact with the internal surface of a tube to be joined. 
Still another object of the present invention is to 
provide a method of explosive joining which uses safe, 
prepackaged joining devices which are storable and 
which can be mechanized for use without human 
contact. 
STATEMENT OF T H E  INVENTION 
According to the present invention, the foregoing 
and additional objects are attained by providing a tool 
and process for explosive joining of tubes 0.20 inches in 
diameter and larger. The tool consists of an element, 
shaped to match the cross-section of the tube to be 
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welded, made of a rigid material which can be either 
machined or molded. This material can be wood, plastic 
or paper or for a reusable tool can be metal such as steel. 
One or more bands of ribbon explosive are wrapped 
around the tool to form the joining charge. The external 
circumference of the tool is shaped so as to hold the 
ribbon explosive in contact with the inner surface of a 
tube to be welded. The tool also holds an initiation 
charge (explosive-filled tube or blasting cap). Proper 
standoff between the tubes to be joined is achieved by 
either shims or by machining of the contact surfaces. 
The tool assembly is then inserted within the tube to be 
joined and fired to complete the joint. 
BRIEF DESCRIPTION OF THE DRAWINGS 
A more complete appreciation of the present inven- 
tion and many of the attendant advantages thereof will 
be readily apparent as the same becomes better under- 
stood by reference to the following descriptions when 
considered in connection with the accompanying draw- 
ings wherein: 
FIG. 1 is a longitudinal cross-sectional of a joined 
tube and outer surface showing an unfired tool of the 
present invention in the joining position. 
FIG. 2 is a cross-sectional view of an explosive join- 
ing of two metal plates exaggerating the joint depths 
and impact angles for illustration purposes; 
FIG. 3 is a cross-sectional view of two metal plates 
(or tubes) depicting shims used to achieve the required 
standoff necessary to set the proper impact angle; 
FIG. 4 is a cross-sectional view of two metal plates 
(or tubes) using a machined groove in the base plate to 
achieve the required standoff distance; 
FIG. 5 is a perspective view of a tube with ring shims 
ready for insertion in an outer tube; 
FIG. 6 is a perspective view of a machined tube with 
circumferential grooving ready for insertion into the 
outer tube; 
FIG. 7 is a drawing of a photographed section of part 
of an actual joined sample in which circumferential 
grooving was machined into the outer tube; and 
FIG. 8 is a perspective view of the joining tool in 
various stages of assembly. 
. 
DETAILED DESCRIPTION OF T H E  
INVENTION 
Referring now to the drawings wherein like elements 
are referred to by the same reference numeral through- 
out the several views and more particularly to FIG. 1, 
an explosively bonded joint, designated generally by the 
numeral 10, is shown in cross-section with the outer 
surface of inner tube I1 and outer surface 12 bonded 
together. An unfired tool 13 of the present invention is 
shown in the welding position. 
The physical mechanism of the tool 13 and process 
can be best understood by reference to FIG.  2, wherein 
a sectional view depicts the operation of the explosive 
joint 10 with the surface interaction depth 23 and im- 
pact angle 24 between plates 21 and 22 exaggerated for 
illustrative purposes. Explosive charge 25 is a high en- 
ergy low-yield sheathed miniature ribbon explosive, 
such as cyclotrimethylene-trinitramine (RDX), which 
generates several million pounds of pressure per square 
inch on top of plate 21. This over pressure creates ve- 
locities 26 in plate 21 of several thousand feet per sec- 
ond. On impact with plate 22, this kinetic energy is 
converted into skin-deep (approximately 0.001 inch) 
4,708,2 80 
3 
melts, which are stripped from the surface and squeezed 
out in jet action 27 by the closing angle 24. 
Generally, the amount of explosive required is af- 
fected by plate material and thickness, and by the stand- 
off distance between plates. Referring to FIG. 3, a plate 
standoff 31 or  separation is required to achieve the high 
velocity, angular collision necessary to effect the bond. 
This standoff 31 can be achieved by shimming 32, fix- 
turing or machining. Any convenient shim may be used 
including masking tape. Alternately, a notch may be 
machined in either or both plates. The plates can be 
configured to present a parallel interface, or referring to 
FIG. 4, for maximum efficiency an inverted “V” 41 
may be machined in one or both plates 21 and 22 pro- 
viding an approximate five degree sloping surface 42. 
FIG. 5 depicts the shim 32 configured to provide 
proper standoff between inner tube 51 and outer tube 
52. Minimum standoff, approximately 0.010 inch, is 
required to achieve the required velocity to effect the 
joint. Maximum standoff, approximately 0.025 inch, is 
established to minimize material deformation and bend- 
ing energy losses. 
Similarly, FIG. 6 shows a machining application to 
the tube surface. Tube 51 is-machined to provide an 
inverted “V” circumferentially inscribed around the 
tube. The surface of inverted “V” 61 angles at approxi- 
mately a five degree slope 62 shown in exaggerated 
scale for purposes of illustration. The tube wall is main- 
tained a constant thickness throughout the “V” section. 
Referring to FIG. 7, a cross-sectional drawing of a 
photographed test sample shows the completed joint. 
Inner tube 51 is bonded to outer tube 52 at the inverted 
“V” 61 location which had been previously machined 
into the outer surface of inner tube 52. 
Referring to FIG. 8, a depiction of the joining tool, is 
shown generally by the numeral 80. Three components 
make up the completed joining tool, the initiator 81 
which can also be an electrically initiated blasting cap, 
the tool form 82, and the low-yield sheathed miniature 
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ribbon explosive 25. Initiator 81 is made up of an 0.090 40 
inch diameter, one-inch long, 0.005 inch wall tube with 
an 0.500 inch long packed explosive column that is 
located 0.300 inch from one end of the tube; a tube of 
S-grains/foot mild detonating cord is inserted and 
bonded into the 0.300 inch deep cavity. Tool form 82 is 45 
center bored so that initiator 81 may be inserted into the 
end of the tool form. A slot 84 located at the ribbon 
explosive holding point 85 receives the end of initiator 
81 such that the initiator is held in contact with the 
ribbon explosive 25. Tool form 82 also has a slight re- 50 
cess at the ribbon explosive holding point 85 so that the 
ribbon explosive 25 may be pressed flush with the tool 
surface. Insertion of the initiator 81 into tool form 82, 
and wrapping of ribbon explosive 25 around the tool 
form, and and completes the explosive joining tool 80. 55 
As packaged in this configuration, the joining tool 80 is 
storable with a shelf life of around five years. The size 
of the smallest completed tool is slightly smaller in 
diameter than an ordinary pencil (0.200 inch) and the 
length including the initiator can be made any conve- 60 
nient dimension. The ribbon explosive is a secondary 
explosive which requires an explosion to initiate the 
ribbon. Impacts, electrical shocks, heat and fire will not 
cuase the ribbon to explode. Further, the completed 
tool contains the least amount of explosive which can be 65 
used to effect a reliable joint. Compared to prior art the 
present invention uses less than ten percent of the explo- 
sive required for center loaded devices (cylindrical 
4 
explosive plugs). For example, an 0.625 inch diameter 
tube using the center load method uses approximately 
ninety grains of explosive to form a continuous, sealed 
joint and achieve parent metal strength. This present 
invention requires only 6.5 grains to achieve the same 
function. Also, this tool is adaptable to various tube 
configurations by changing the shape of the tool form. 
These changes will allow joining of curved tube sec- 
tions and of other shaped tubes such as square or triang- 
ular at any point in a tube length. 
OPERATION OF THE INVENTION 
The assembly and operation of the joining tool 80 is 
accomplished by the following steps: (1) Bond mild 
detonating fuse to initiator 81 using a non-reactive, 
non-solvent, non-vaporizing adhesive. In the present 
embodiment, a 3M adhesive “scotch cast” was used; (2) 
Wrap double-backed tape around tool form 82 at loca- 
tion for attaching ribbon explosive 25; (3) Cut ribbon 
explosive 25 to length to wrap around tool form 82 over 
the double-backed tape; (4) Install ribbon 25 on double- 
backed tape; (5) Insert initiator 81 into tool form 82 by 
inserting through slot and centerline hole in tool form 
82; (6) Trim ends of ribbon explosive 25 with razor 
blade to produce a tight fit with the tool form 82; (7) 
Press ribbon explosive 25 into tool form 82 to achieve a 
flush surface with the initiator 81 explosive load cen- 
tered on the ribbon explosive 25; (8) Use 0.75X0.002 
inch teflon tape to wrap around ribbon explosive 25 and 
tool form 82 or approximately 0.020 inch wall thickness 
heat shrink tubing to increase the diameter of the assem- 
bled tool to provide a snug fit to the inside diameter of 
the tube 51 to be joined; (9) Use 0.5 X0.002 inch teflon 
tape to wrap around the tool form 82 on both sides of 
ribbon explosive 25 to bring these areas up to the inside 
diameter of the steel tube 51 as well as cover the ex- 
posed portions of the initiator 81; (10) Insert the tube 51 
to be joined to the desired depth into the outer tube 52. 
Tube 51 must cover the machined area in tube 52 or  
shimming may be used; (1 1)  Insert the assembled tool 80 
into tube 51 and assure that the centerline of the ribbon 
explosive 25 is directly opposite the peak in the inverted 
“V” 41 or centered between the shims; (12) Secure 
assembled tool 80 in position using any convenient 
means such as taping; (13) Initiate mild detonating fuse 
81 by using of blasting cap or initiate blasting cap; and 
(14) Remove debris from tube by brush or other conve- 
nient means. 
Although specific embodiments of the invention have 
been described herein, they are to  be considered as 
exemplary of the novel features thereof and are not 
exhaustive. There are many variations and modifica- 
tions of these specific examples which will be readily 
apparent to those skilled in the art in light of the above 
teachings without departing from the scope of the ap- 
pended claims. It is therefore understood that this in- 
vention may be practiced otherwise than as specifically 
described herein. 
What is claimed as new and desired to be secured by 
Letters Patent of the United States is: 
1. A joining tool for miniaturized explosive welding 
of an inner surface to an outer surface comprising: 
an elongated tool form; 
a low-yield sheathed miniature ribbon explosive; and 
an initiator; 
said tool form having a recessed ribbon explosive 
holding point for receiving the low-yield ribbon 
explosive and an initiator end suitable for receiving 
5 
4,708,280 
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a detonating means, and shaped so as to maintain wherein the tool form is bored axially to accept said 
contact between the ribbon explosive and a surface initiator and said recessed ribbon explosive holding 
to be welded; point is slotted axially so that mating of the initiator 
said low-yield sheathed miniature ribbon explosive detonation means to the complete width of the low- 
being disposed so as to match the area of said sur- 5 yield sheathed ribbon explosive can be effected. 
face and the external dimension formed by the 5. A process for miniature explosive welding of an 
recessed ribbon explosive holding point and being inner surface to an outer surface which minimizes use of 
uniformly distributed in said ribbon explosive hold- explosives and reduces damaging pressure waves and 
ing point whereby thin concentrations causing the noise, comprising: 
explosion to fizzle and thick concentrations causing 10 shaping a tool form to match the interior of an inner 
excessive pressure to be developed are avoided; surface to be welded while maintaining a loose fit; 
said initiator being inserted into said tool form and circumscribing said tool form with a recessed ribbon 
received at said recessed ribbon explosive holding explosive holding point; 
point such that the initiator detonating means ex- forming a low-yield sheathed miniature ribbon explo- 
tends across the complete width of said low-yield 15 sive around the outer circumference of said ribbon 
sheathed miniature ribbon explosive, whereby the explosive holding point; 
complete cross-section of the ribbon explosive is mating said explosive ribbon to a detonating means so 
detonated simultaneously, allowing minimum pres- that the detonation area extends across the com- 
sure to be attained and thereby causing the explo- plete width of the explosive ribbon; 
sion to be self-sustaining. forming the above tool assembly into an integral unit; 
2. A jointing tool for miniaturized explosive welding providing stand off means between the inner surface 
of an inner surface to an outer surface as in claim 1 and the outer surface to be welded; 
wherein the recessed ribbon explosive holding point is positioning the inner surface to  be welded inside an 
an annular recess around said tool form. outer surface; 
inserting said tool assembly into said inner surface to 
of an inner surface to an outer surface as in claim 1 be welded and positioning the tool assembly so as 
wherein the low-yield sheathed miniature ribbon explo- to center the explosives over the stand off means; 
sive is a miniature ribbon of miniature lead-sheathed and 
cyclotrimethelenetrinitramine. initiating the low-yield ribbon explosive with the 
detonating means to effect a joint. 
of an inner surface to an outer surface as in claim E 
. 
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3. A joining tool for miniaturized explosive welding 25 
4. A joining tool for miniaturized explosive welding 30 * * * * *  
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Tool and process for miniature explosive joining of tubes

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