Laser techniques for welding polythermalese coated magnet wire to stainless steel and gold plated nickel terminal

Martin, L. J.

Shackleton, J. R.

English

NASA Technical Reports Server

tf 653 J U ~ V  65 
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J 
17 November 1965 
RE-ORDER NO. &3Z4 
FR 65-10-257 
LASW WELDING OF COATED MAGNET W I E  
J. R. Shackleton and L. J.  Martin 
Hughes Aircraf t  Company 
FINAL REPORT 
P,o.# cu-326020 
The Jet  Propulsion Laboratory 
California Inst i tute  of  Technology 
4.800 Oak Grove Drive 
Pasadena, California 
Thls work WBQ p e r f o m d  for the Jet Propulsion Labomtaip, 
California Institute of Technology, sponsored by the 
tion under National Aeronautics d Space Admrnurtra 
Contract NU7-100. 
. .  
b 
TABU OF CONTENTS 
I 
I1 
I11 
IV 
V 
VI 
VI1 
Tables 
INTRODUCTION 
SUMMARY 
EXPERIMENTAL APPARATUS 
A. The Welding Machine 
B. The Assembly Fixture 
C. The Testing Machine 
TEST SPECIMENS 
PROCEDURE FOR MAKING THE 
STRENGTH TESTING 
DATA 
ELDS 
Page No. 
4 
4 
4 
7 
10 
10 
T-3 6 
T-40 
W-3 6 
W-40 
#36 Copper Wire t o  S ta in less  S t e e l  Terminals 
#40 Copper Wire t o  S ta in less  S t e e l  Terminals 
#36 Copper Wire t o  ,020 Nickel Wire 
#40 Copper W i x  t o  .020 Nickel Wire 
Appendix 1 Pic tures  of Welds 
Appendix 2 Preliminary Study of Results 
11 
13 
15 
17 
a1-1 
A2-1 
Y 
I. INTRODUCTION 
The object ive of t h i s  program i s  t o  demonstrate t he  c a p a b i l i t i e s  
of Laser microwelding f o r  terminating coated magnet wire. 
This r epor t  descr ibes  the  equipment and technique used t o  perform 
Laser welds of #36 and #40 ltpolythermalezetV coated magnet wire t o  
s t a i n l e s s  steel  and gold plated n icke l  terminals  without using 
conventional methods f o r  s t r ipp ing  t h e  coated magnet wire. 
11. SUMMARY 
The following remarks summarize the  f indings of t h i s  program: 
1. Good high s t rength welds were nade between the  desired 
terminal mater ia ls .  
2. Low s t rength  welds could be detected v i s u a l l y  by the  
necking down of t he  wire adjacent t o  the  weld. 
3.  One off-center shot  was necessary t o  vaporize insu la t ion ;  
a second on-center shot fused the  metals together.  
4, A l l  of the  ItTt1 weld breaks occurred i n  the  heat  a f f e c t  
zone, ind ica t ing  good fusion. 
5, Necking down of the  wire is undoubtedly caused by va r i a t ions  
i n  hea t  input  i n t o  the weld, excessive heat  causing excessive 
fusion and necking down. I n  both types of welds there  was a 
more severe dropoff on the  extreme value cha r t  on #40 wire 
than f o r  #36, indicat ing t h a t  with f i n e r  wire more prec ise  
Laser cont ro l  is necessary, 
Consis tent ly  nigh strsngth welds can be obtained by ( a )  
r e j e c t i n g  welds showing a neckdown of t he  wire ar;d r e w l d i n g  
o r  (b) a very prec ise ly  control led Laser so t h a t  excess 
fus ion  and necking down do not  occur. 
6. 
III. EXPERIMENTAL APPARATUS 
The apparatus used on this.program consisted of: 
1. A Hughes Model 202 Laser Microwelder (Figure 1) 
2. A holding f ix tu re  t o  support the  p a r t s  of the  specimen 
during the  welding operation (Figure 2 )  
1 
3 
I -  
* 
i 
3 .  A Dillon Model M Testing Machine equipped with a va r i ab le  
p u l l  r a t e  mechanism and Hunter Spring Company Model L1000-M 
0 - 1000 gm reading range ind ica tor  head (Figure 3 ) .  
A ,  The Welding Machine 
The Laser Microwelder was a Hughes Ai rc ra f t  Company Model 
202. This u n i t  was 
s p e c i f i c a l l y  prepared t o  perform the microwelding operation 
f o r  laboratory s tudies .  Basical ly ,  any Laser un i t  cons i s t s  
of three elements -- the power supply, the  Laser i t se l f ,  
and the  spec ia l  op t ics  required t o  adapt the  Laser u n i t  t o  
the  s p e c i f i c  function. A mechanical contrivance is, of 
course, necessary t o  hold th ings  together.  I n  t h i s  i n s t ru -  
ment a l i  of these items are in tegra ted  i n t o  the  u n i t  shown, 
complete with a s e r i e s  of in te r locks ,  a l l  necessary cont ro ls ,  
a microposit ioning tab le  and a work l i g h t .  
It i s  shown i n  Figure 1 (64-01-243). 
The power supply uses a capaci tor  discharge design. This 
power supply is capable o f . s t o r i n g  1200 joules ,  
f o r  the  power supply a r e  conveniently located on a panel a t  
the  r e a r  of t he  work surface.  
are located on the  l e f t  (hidden), and the  charging vol tage 
cont ro l  and indicator  a r e  on the  r i g h t  of the  Laser head. 
The cont ro ls  
The s torage capaci tor  switches 
The Laser head, the  metal cyl inder  above the  work t ab le ,  
c a r r i e s  s igh t ing  and focusing op t i c s  and a shut te r .  The 
u n i t  i s  designed so  t h a t  s igh t ing  i s  done through the  
ruby c r y s t a l ;  both surfaces of t he  ruby c r y s t a l  were made 
p a r t i a l l y  transmitt ing.  This design was used because it 
permits pos i t ion ing  and depth of focus while a t  the  same 
time minimizing supplementary hardware t h a t  would compli- 
ca t e  experimental programs. This design r e s u l t s  i n  some 
of the Laser  l i g h t  being t ransmit ted backward toward the  
eyepiece. 
prevent t he  operator from being in jured  by the  Laser f l a sh .  
The s h u t t e r  is  i n  the in te r lock  system so  t h a t  the  Laser 
cannot be f i r e d  unless the  s h u t t e r  is  closed, 
The shut te r  i s  a s a f e t y  device ineorasrat.ed t o  
The output power from the  Laser i s  r a t ed  a t  one jou le  
minimum with 750 joules of exc i t a t ion ,  
The e n t i r e  volume i n  which the  Laser beam is exposed i s  
enclosed by a blue t i n t e d  s a f e t y  sh i e ld  which p ro tec t s  t he  
eyes of the  operator from high intensi ty  reflections,  
sh i e lds  are hinged t o  allow acces8 t o  the  work area and are 
a l so  i n  the  inter lock system. 
These 
2 
3 
r i  
I -  
An aux i l i a ry  cooling system was incorporated and at tached 
t o  the cooling f i t t i n g  on the Laser head. 
system cons is t s  of a supply of dry  nitrogen (nominally 
40 cg f t / h r )  and a heat exchanger t o  cool t he  gas t o  
-150 C. 
t he  r e p e t i t i o n  r a t e  o f  welding. 
This coo l ing '  
This cooling system was required t o  increase 
B. The Assembly Fixture 
The holding f i x t u r e  is shown, disassembled, i n  Figure 2 
(65-11-053). 
a ted  board held together by bo l t s .  
elongated openings through which the Laser beam i s  focused 
and f i r e d .  
pads which press  the  pieces ,  t o  be welded, together.  The 
botton b a r d  has two s e r i e s  of fou r  shaiiow grooves mi i lea  
i n  i t s  surface.  These grooves receive and o r i e n t  the  n i cke l  
wire o r  s t a i n l e s s  s t e e l  tee terminals.  The f i n e  copper wire 
specimens a re  l a i d  across the  n icke l  or  s t a i n l e s s  s t e e l  
terminals, and t h e  top board is faGtened i n  place.  Before 
f i n a l  t ightening of the assembly bo l t s ,  t h e  f i n e  w i r e  i s  
pul led t a u t .  
It i s  constructed of two pieces  of perfor-  
The top board has 
The grey s t r i p s  on t h i s  board a re  sponge rubber 
C. The Testing Machine 
The t e s t i n g  machine used t o  perform the  p u l l  s t rength  t e s t s  
i s  shown i n  Figure 3 (65-11-052) . 
Dillon Model M Universal Testing Machine (1) modified by 
mounting a Hunter Spring Model L-1OOOM force gage (2 )  on 
the  ind ica t ing  head. 
jaws from a Hunter Spring Company Model TJH Testing Machine. 
This lower jaw i s  always used t o  g r ip  the  copper wire. 
upper specimen f i t t i n g  has been spec ia l ly  made t o  hold the  
gold plated n i c k e l  w i ~ o  nr the stainless steel tem,inal st 
an angle of 45' with respect  t o  t he  d i r ec t ion  of head t r ave l .  
The base machine i s  
The lower jaws are  automatic gripping 
The 
The head t r a v e l  rate used i n  these  tests was one inch per 
mknute . 
IV. TEST SPECIMENS 
The t e s t  specimens were made by forming a weld a t  the  90' 
in te rsec t ion  of the  copper wire and the  terminal specimen, 
The specimen terminals were 303 stainless steel tees  with 
4 
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Figure 3 
6 
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a cross  sec t ion  of ,025 inch a t  the  poin t  of weld and 3/4 
inch lengths  of .020 gold p la ted  n i cke l  w i r e .  The copper 
w i r e  was #36 and #40 w i r e .  
terminals  and w i r e  s i ze s  produce four series of specimens 
designated T36, T40, ~ 3 6  and W40. All specimen mater ia l s  
and p a r t s  were supplied by the  Je t  Propulsion Laboratories,  
Inc. 
inch length of copper wire t o  be gripped i n  the  t e s t i n g  
machine . 
' 
The combinations of these 
After  welding, the  copper was cu t  o f f ,  leaving a 3/4 
V. PROCEDURE FOR MAKING THE WELDS 
A t  the  present  s tage of the development of the  Laser welding 
process and Laser microwelding equipment, the  procedure is  
not amenable t o  the  development of r igorous weld schedules. 
Today, the  accomplishment of  Laser microweids i s  l a rge ly  
dependent on operator skill. 
machine, t he  operator can est imate  the  general  power l e v e l  
f o r  t h e  t r i a l  welds. From the  way the  machine performs on 
the  t r i a l  welds, adjustments a re  made -til sa t i s f ac to ry  
welds a re  made. I n  no case on t h i s  program was it neces- 
s a ry  t o  exceed f o u r  t r i a l  welds t o  ad jus t  the  machine f o r  
a new wire-terminal combination. 
From experience with the  
The c r i t e r i o n  f o r  the proper s e t t i n g  of weld energy is  the  
degree of melt. In su f f i c i en t  energy produces "dry*' o r  semi- 
dry welds. 
excessive necking down of t h e  copper wire and a la rge  amount 
of metal evaporation, r e su l t i ng  i n  a l a rge  p i t  a t  t he  poin t  
of fus ion  r a the r  than a nice flow. 
Too much energy produces more than adequate melt, 
The cont ro ls  ava i lab le  f o r  machine adjustment are:  
1. Energy storage capacitance var iab le  from 200 t o  1400 
mizrcfarads. 
2. Capacitor charging voltage var iab le  from 0 - 1350 v o l t s .  
3 .  Coolant flow ra t e .  
The primary controls  a r e  capacitance and voltage.  
e s t a b l i s h  t h e  luminous energy ava i lab le  t o  pump the ruby. 
Although the  capacitance inf luences the  luminous pulse time, 
t he  cont ro l  i s  not adequate t o  study pulse duration e f f e c t s .  
The s torage capacitance control is bes t  considered as just 
an energy storage range switch. 
These 
7 
i .  
The vol tage cont ro l  i s  the  continuous cont ro l  on the  amount 
of energy s tored  i n  the  capaci tor  bank. 
The coolant flow r a t e  a f f ec t s  the  operating temperature of 
t he  ruby. 
operating temperature, t h i s  control  has a profound e f f e c t  
on energy output and pulse r e p e t i t i o n  r a t e .  
cooling, it would be necessary t o  wai t  a t  l e a s t  f i v e  minutes 
between f l a shes  i n  order t o  achieve r epea tab i l i t y .  
adequate cooling, t h e  r a t e  may be increased t o  two f l a shes  
per  minute' (with t h i s  machine which has an upper limit on 
r e p e t i t i v e  r a t e  se t  by capacitor charging time). 
Since Laser act ion i s  s t rongly  dependent on 
Without adequate 
With 
Laser welding i s  accomplished by focusing the  f l a s h  of t h e  
Laser a t  the  point  a t  which it is  desired t o  hea t  the  work. 
It was found advantageous t o  form the  weld i n  two separate  
Laser f lashes .  The f i r s t  f l a s h ,  focused adjacent t o  the 
eventual weld, accomplished the  s t r ipp ing  o f  the in su la t ion  
from the  w i r e .  The second f l a s h ,  focused a t  the point  of 
weld, caused ac tua l  metal flow, The s i t e  p ic ture  used i n  
making these two flashes is shown i n  Figure 4. 
noted i n  Figure 4 t h a t  an e f f o r t  was made t o  loca te  the  weld 
toward the  top edge of the terminal. 
precaution aga ins t  burning off  the  wire when the weld was 
made. The reasoning was t h a t  i f  a %urn-offtt d id  occur 
there  would be enough wire mater ia l  l e f t  t o  be welded without 
having t o  disassemble the holding f i x t u r e .  
It will be 
This was done a s  a 
I n  ac tua l  p rac t i ce ,  
there  were very f e w  "burn-offsft and when they did occur t h e  
holding fixture d id  not  hold the  loose end i n  contact with 
,- 
\ 
t h e  terminal,  such t h a t  disassembly was required.  
The procedure of forming the  weld toward one edge of t he  
terminal produced b u t t  type welds t o  the  non-functional end 
of t he  wire which appeared t o  be very sa t i s f ac to ry .  
-. me cut  o f f  end of weid Tj6-22 (Appendix P ia te  i) appears 
on the s ide  of the  terminal. 
cons is ten t ly  were not successful.  
E f fo r t s  t o  produce t h i s  weld 
I n  a few cases,  it was necessary t o  use more than two b u r s t s  
t o  perform a weld. 
t h e  welds with the  #40 wire. 
caused by problems i n  the holding f i x t u r e .  The sponge rubber 
pads ( p a r t i c u l a r l y  one of t he  pads) were not able  t o  hold the  
wire t a u t .  
These cases were dominantly i n  forming 
These exceptional cases were 
Microexplosions, caused by the  evaporation of some of the 
metal, physical ly  moved the  wire away from the  point  of weld, 
8 
F O H M  7 0 3  HUGHES A I R C R A F T  CO. 
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By %hasingI' the wire with the welder sometimes a weld could 
be accomplished; other  times no weld could be made. This 5 
d i f f i c u l t y  is  believed t o  be due t o  the  design of the  holding 
fixture and not  a t t r i b u t a b l e  t o  the Laser. Weld #T36-6 on 
Appended P l a t e  1 shows evidence of where the wire has been 
moved during the welding operation and subsequently welded 
i n  the new posi t ion.  
VI* STRENGTH TESTING 
The specimens were mounted i n  the  t e s t i n g  machine such t h a t  
the mor& r i g i d  element ( the tee or  the  nickel  wire) was held 
a t  a 45 angle with respect t o  the  d i r e c t i o n  of head t rave l .  
The head t r a v e l  r a t e  was one inch per minute. 
VII. DATA 
The data  accumulated on t h i s  program a r e  presented i n  t h e  
following fou r  tables, Some comments on the data appear in 
Appendix 2. 
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Appendix 1 
The following e i g h t  p l a t e s  a r e  photographs of t h e  experimental welds 
performed i n  work against  P.O.# cu-326020. 
The welds were made between #36 and #40 polythermaleze coated copper 
w i r e  and gold p la ted  .020 nickel wire and 303 s t a i n l e s s  s teel  tee 
terminals. 
Each series of welds is coded a s  follows: 
1. T-36 #36 copper wire t o  303 SS tee terminals 
2, T-40 #40 c q p r  wire t o  303 SS t e e  terminals 
3.  W-36 #36 copper wire to nicke l  wire ' 
4. W-40 #40 copper wire t o  n icke l  wire 
Within the series each weld i s  s e r i a l  numbered t o  allow l a t e r  correla- 
t i o n  between weld appearance and p u l l  strength.  
PLATE 1 
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PLATE 2 
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PLATE 3 
PLATE 4 
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Appendix 2 
Preliminary Study of Results 
Inspection of t he  data  was performed by the construction of t he  
histograms (s t rength  value observed versus t h e  number of t i m e s  
observed) shown i n  Figure A2-1.  Since none of these histograms 
resembles a normal d i s t r i b u t i o n  and two of them, the T34 s e r i e s  
and the  T40 series, show the  skewness typ ica l  of data  t h a t  should 
be handled by Itextreme-valuett s t a t i s t i c s  (1) ( t h i s  is a l s o  j u s t i -  
f i e d  on t h e o r e t i c a l  grounds) t h i s  method of ana lys i s  was applied 
t o  a l l  four  series of t e s t s .  
shown graphical ly  i n  Figures A2 - A 5 .  
show a main sequence ( a l so  v i s ib l e  i n  the  histograms) and then a 
f e w  s t ragglers .  
The r e s u l t s  of t h i s  ana lys i s  a r e  
I n  most cases, these graphs 
Further manipulation of the  data i s  s t a t i s t i c a l l y  i l l eg i t ima te ;  
however, it i s  believed t h a t  careful  ana lys i s  of p l a t e s  1 through 
8 f o r  inspectable  inadequacies of the weld combined with more 
ca re fu l  handling of the  test  specimens t o  e l iminate  handling damage 
w i l l  remove the  s t r agg le r s  t h a t  appear i n  the  d i s t r i b u t i o n  histograms, 
If t h i s  proves true, then the  d i s t r ibu t ion  of weld s t rengths  w i l l  be 
g r e a t l y  improved. 
l i n e  i n  Figure A2-2 where 98% of the  welds would show a s t rength  
g rea t e r  than 35 gm and a mean s t rength of about 90 gm, 
The new d i s t r ibu t ion  i s  suggested by the  dot ted  
(1) Gumbel, E, J,, Probabi l i ty  Tables f o r  the Analysis of Extreme- 
Value Data, N . B b S . ,  App. Math Series 22 
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Laser welding of coated magnet wire Final report

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