CA1129502A - Method and apparatus for conducting smut-free stud welding - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A method and apparatus for welding studs to a work-piece are provided. When the studs are welding to workpieces using a drawn-arc, studs welding technique, sometimes a coating of smut is deposited on the workpiece around the welded end of the stud. This coating detracts from the appearance of the stud and workpiece. Further, if the workpiece is to be covered with a coating material, the coating of smut must first be removed, resulting in an extra operation. It has been found that the coating of smut will not be deposited if, during the stud welding cycle, gas is directed toward the weld area in a swirling manner around the end of stud where the weld occurs.

Description

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This invention relates to a method and apparatus for welding a stud to a workpiece without a coating of smut deposited thereon, by directing gas through a spark shield around the weld area. ;
The broad concept of supplying gas through a spark shield or ferrule around a stud to be welded to a workpiece is ~ -known in the art. This can be found in the following patents: ' -~ 2,727,123; 2,790,066; 3,096,~29; 3,'363~084; 3,736,401, and \~ 3,790,740~ ~n the prior patents, the equipment has usùally ~10 been used to appl~ an inert atmosphere around an ~aluminum stud "
during weIding or to supply air around a stud to aid in weIding through galvanized sheet steeIO ~'' When studs are weIded to workpieces by a drawn-arc, stud welding technique, it is common for a coating of smut to ~' be deposited on the workpiece around the welded end of the stud.
For example, this usuall~ occurs with trim studs'~hich-are weIded to automobile bodies for the subsequent-attachment of -~
clips and trim strips. After the'studs are welded and before ~ ' the clips and trlm are appliedj the body receives a protective `' ' 20 coating, such as"a pr~mer, and subsequent~de~orative coatings. ~`
~f the coating of smut around the welded stud is not remoyed from the workpiece or automobile body,- the'protective coatings will not adhere~properly and wi;ll separate~ from the surface.
A'method and apparatus-for welding studs *o workpiecés ''' without coa~ings of smut being deposited on the workpieces haye ' been discovered. `~n accordance ~ith the'inyention, a spark ;
shieId is utilized around the stud and ths chuck in which it is `~
held, with the'spark shield having a plurality of passages therein which are aligned wi'th an area of the ~arkpiece around ;
3Q the location where'the'stud ls-~to be wel'ded. 'A suitab-le~gas, such as air, is directed t~rough the passages' toward the area ' ''~

during the welding cycle~` The air then swi'rls around the area ;

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and does not impinge directly on thè workpiece area aligned with the end of the stud and between which the pilot arc and a main welding arc are drawn. Also, if the air is directed at the workpiece at,too sharp of an angle, turbulence will result.
Direct impingement or turbulence will tend to extinguish the pilot arc and the main weIding arc will not be imposed between the end of the stud and the workpiece~ The end of the spark ,"~- shield ~can also have'a plurali~y of notches or passages through `` which small molten beads or ~eld metal~ known as splatte:r, can .
'10 escape, ~t is, therefore, principal object of the:invention to weId studs- to workpieces wi:thout a coating of contaminants :~
being deposited on the workpieces: around the:studs~
Another object:of the in,vention is to proyide a method and apparatus for welding studs'to wbrkpieces:and to preyent a coating of smut from being deposited on the workpieces during the wel'ding cycle. `
A.further object of the invention IS~ to ~eld trim studs to automobile bodies' and to sub.sffquently~coat:the bodies 20 with protective'materi-al without ~aYing to; first remove coatings ~:
of smut around the'studs. ' -Many other objects: and advantages of the'inyention , will ~e`apparent from the.f.ollo~ing detalled discripti:on of a .: ;,. . ~-.. , preferred embodiment.thereof, reference being made to t~e accom~ ' `.
panying dra~ings, in ~hich: , ,','~
Fig.- 1 is an oyerall vie~,: partly in eleyation and partly in perspecti.ve,: of apparatus for ~eIding studs in açcordance wi'th the'inyention; -' Fig. 2:is a greatly enlarged view:in eleyation~ wit~ '~
parts in section, of a weIding foot and spark shield of the apparatus of Fig, l? ; "
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Fig. 3 is a front view in~je~evation of the welding foot and spark shield of Fig. 2;
Fig. 4 is a fragment~ary view of the spark shield and chuck taken generally along the line 4-4 of Fig. 5; and ~' Fig. 5 is a view in transverse-cross section taken generally along the line 5-5 of Fig. 2.
Refe-rring to the drawings, and particularly to Fig~ 1, ' a stud welding tool 10 according to the'invention is used to `~ weld a stud to a workpiece by means of a~drawn-arc welding technique.' The basic tool is known in the art and includes means-for retracting stud from the'~orkpiece, means for holding -the'stud in a retracted:position ;for a predetermined period~ and means for moving or plunging the'stud toward and against the -workpiece at the end of the predetermined period. 'As the stud is retracted from the't~orkpiece,' a pilot arc is drawn bett~een the'end of the'stud and the wQrkpiece and the'main welding arc is subsequently imposed on the pilot arc, t~Lth the main t~elding arc then being maintained u til the'stud is-plunged~back against -the workpiece.' The'tool can be'of the type s~own in U.S.
Patent 3,525',8'46, for example, and preferably-utilizes a capaci~ ' tive power source,' as shbwn in U.~'. Patent 3,136,880~ for example.
A powe'r an~ control unit'12 supplies pot~er for the ~ --pilot and the ma~n weIding arcs-and fox a solenoid coil in a tool body 14, the'coil re-tracting the'stud against the force Qf a plunge'spring whèn en'ergized. 'A chuck- leg 16 extends into the coil and also extends- for~a'rdly of the tool body 14 ~here it is-suitakly aonnected to a chuck 18 (Figs. 3'and 41~ ~n this;
instance~ a trim stud 20 has a head 22 uhich is held by the ~huck 18 and a stem 24 ~hich'extends~foxwa'rdly, with the stud~'' 30 backed up by~ an adjustable stop 19 during the'welding cy~le. ' ~ ''' ~he studs can be fed into the front of the chuck by hand. 'They also can be transported by air through a tube- from a remote ;
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supply source into a chamber in the chuck leg 16 behi~nd the chuck 18. The studs can then be pushed into the chuck from the chamber by a plunger and backed up by the plunger during the welding cycle. The plunger can be connected to a piston in an ~' air cylinder in th:e'chuck leg to ~hich air is supplied from a remote source. 'This type of loading arrangement is shown in U,S. Patents 3,525`,846 and 3,'489',878 and does not consti:tute~
~ part of the instant inyenti:on. ' '. A pair of supporting legs 26 extend forwardly of the i' tool body 14 and support:a ~elding foot 28~ 'The welding foot has an opening 30 around the'chuck'leg 16 wi'th an inwardly- ~' extending flange 32~:'An air supply passage'34 is fo'rmed in the foot and communicates wi`th'th;e opening 30. The'foot has a : ~' fitting 36 connected with: a tube 38 through which air is supplied from a control module 40 CFig, 1~. Clean shop air can be supplied ; .
to the module 40, ~i'th'this air usually being at a pressure of about 80 psi. 'T~è module'40. has-a ~alYe ~hich is~-controlled through the:unit:22 and supplies' air to the:~eIding foot.28 .
during the:weld cycle~ 'The ~alve'can haye a time'de~Iay so as to 20: kèep the air on continuously unles's~no weId is'~:made`for a `
predetermined period of time-,' such'as two'seconds~
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A spark sh~i'eld:42:is located in the'foot opening 300 '~
and extends for~ardly ther'eof~ 'The'spark shield 42:'is posit~oned so that the stem:24 ~f the s.tud 20. prot:rudes' sl~ightly beyond.:the e~d o~ the sp~ark'shi:el'd, as shown in Fig~ 1 J before the stud is ~i~
pressed against:thè ~brkpiece~'`'The'shield 42~has a generally ' cylindrical body 44 with'a rear:flange 46 ~hIch'abuts: the:flange :
32 of the ~oot 28. 'An annular groove`48 is formed in the body 44 a`djacent to the flange'46 and communicates wi'th the air 3Q passage 34 In thè'foot 28~ 'The ~ody 44 hàs an outer cyllndrical portion. 50 and a sh-oulder 52 adjacent:the'annular groove:48~ wi:th `-' ~ ,.
a sealing ring 54 located on the:oute.r cyl~ndrical portion 50 .
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: -4 lI29~i2 adjacent the shoulder 52. The ring 54 has a annular groove 56 containing an O-ring 58 which seals off the spark shield 42 and the foot opening 30. A front plate 59 abuts the ring 50 to retain the spark shield 42 in the foot 28. A plurality of longitudinally-extending air passages 60 extend from the annular groove '48 past the shoulder 52:and the outer cylindrical portion 50 and terminate 'at a fon~ard shoulder 62 at the forward end of ,:
the`spark shieId 42. 'The longitudinal:Ly-extending passages 60 ':~
) are enclosed by a sleeve 64 which :extends fr'om the cylindrical "'10portion 50 of the body 44 to the forward shoulder 62, being -.
assem~led ~ith a force`fit~ 'At th-e fon~ard end :of the spark shield body -44 a plurality of rectangularly shaped, radially , ;-extending notches -66 are forme-d ~hich communicate: with the outer ,~.,' surface of t~e body 44 and ~i`th a fon~=ard~ inner surface 68.
The 'shieId 42 preferably is made of copper ànd the surface 68 is highly polished to minimize :the :adherence of s~latter thereto.
.. A larger diame-ter inner surface`70 is locàted to;;:the~:~ear of th-e `forward inner sur.face''68 and is offse-t by.a~.:shuulder-72.
~ plurallty of gas or air passages:74.are ;located in .
20 a fon~ard end portion of th:e'spark`shieId hody 44~ There'is one' -~
of the passages ~74 for eaah of the 'longitudinally-extending ~, passages 60, Eac~ of the passa~ges';74 has an outer end-76 communi- ~
cating wi`th one ~of the passages':'60`and an inner end 78 terminating :' at the'inner surface:`68 of the 'sp~ark `shield. The passages: 74 are positioned so~ as'.to direct :st~reams of gas or air to~ard the ~orkpiece around the: Iocati:on at ~hich'the end of the `stud stem ' .' 24 is to be ~elded~ 'The s~re`ams of air thus apparently fo'rm a , .
s~rling action àround the ~el`d arear which action preY~nts the deposi~tion of 'smut during the ~eIding cycle. ~f the 'streams ~ere 30 directed directly~ at the location.at ~hich'the 'stud is to be .:
welded, the streams of air ~ould extInguish the pilot :arc and thus ~also prevent the main we`lding arc from being imposed thereon. ~' :
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This can also occur if the air is directed toward the ~orkpiece at too sharp of an angle so as to become turbulent.
Each of the passages 74 is approximately tangential ' to the inner surface 68 of the spark shieId and forms an angle of 25 to 35 degrees, and preferably 30 degrees, to a radius of the spark shieId. Each of the passages -74 also is located at an angle'up to about 20 degrees, and preferably 18 degrees, to a plane perpendicular to the'axis of the spark shield 42 or to the surface 'of the workpiece. '~lr passages in the`end of the spark '10 shield in place of the notches, and forming a 0 degree angle ~ith respect to the wo'rkpiece'surface, have bee'n found to be ;
effective.` 'The problem wi'th this design is that the arc is blo~n out if the spark shieId is tilted slightly. With thè shop air at'80 psi, from 1 to lO of the pàssage~ 74 are'employed and preferabl~ e~ght of themj ~lth di'ameters from 0.020 to 0.060 in., and preferabl~ 0.040 in '~ith the inner ~surface 68 ha~ing a di'ameter of 7~16 in.,'the`inner ends 78 of the'passa~ges 74 terminate from 0-~IOO to 0.180 in., and preferably 0.125 in., ` ' "
-from the for~ard end of the'spark shieId body 44. `~n any case, the position of the'passa~ges sh-ould be`such`that they -direct the air streams beyond th-e end of the 'chuck 18j and at sufficiently ' '~
narrow angles tQ the'~orkpiece'so as not to cause 'turbulence. Of course,` it ~1'11 be understood that the'an-gles~ lengths, and di`ameters of the air passages' 74 ~i'll'vary ~ccording to the stud ' size~ sp~ark shieId si~ze,' and air pres'sure, by ~ay of example. ;' ''' ~he important effect is~ to obtain a s~irling~ non~turbulent ;
action around the we:Ld arqa to preyent the deposi-tion of smut ' ~ithout extinguishing the arcs~

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Claims (3)

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

1. Apparatus for welding a trim stud to a vehicle body with the area of the vehicle body around the trim stud being main-tained substantially free of smut, said apparatus comprising a weld-ing tool having a chuck extending therefrom for holding the trim stud, means for establishing a welding arc between the stud and the vehicle body, and means for moving the stud toward and away from the vehicle body, a spark shield, a welding foot supporting one end portion of said spark shield in a position around said chuck with said spark shield having an inner surface spaced from said chuck and an outer surface, said spark shield having a plurality of fluid passages extending therethrough from the outer surface toward the inner surface and spaced uniformly around the periphery of said spark shield, said passages being positioned at common angles to radii of said spark shield as viewed in generally transverse cross section through said shield, and positioned at common angles to a plane perpendicular to the axis of said spark shield as viewed in generally longitudinal cross section through said shield, there being less than ten of said passages, and each of said passages having an opening at the inner end spaced closer to the end of said spark shield which is opposite said one end portion than an opening at the outer surface to direct fluid beyond the end of said chuck and toward the vehicle body, a plurality of radially-extending notches in the end of the spark shield opposite said one end portion, and a source of fluid under pressure communicating with the outer openings of said passages for supplying fluid through said passages and toward the area of the vehicle body around the trim stud during a welding operation.

2. In a method of welding a trim stud to a surface of a kept substantially free of smut, said method comprising holding a trim stud against a surface of a vehicle body, withdrawing the stud from the surface of the vehicle body, establishing a welding arc between the end of the trim stud and the surface of the vehicle body, moving the stud back toward the surface of the vehicle body, and di-recting a plurality of streams of fluid toward the surface of the vehicle body at angles to the surface of the vehicle body around but not at the location of the weld during the entire welding cycle to cause the streams to move in a slow swirling pattern around the weld location on the vehicle body.

3. Apparatus for welding a trim stud to a vehicle body with the weld area of the vehicle body around the welded stud being main-tained substantially free of smut, said apparatus comprising a weld-ing tool having a chuck extending therefrom, a welding foot, a spark shield having one end portion mounted in said welding foot, means ex-tending from said tool and supporting said welding foot with an inner surface of said spark shield positioned around said chuck, a plural-ity of fluid passages formed in a second end portion of said spark shield and extending from an outer surface thereof toward the inner surface, said passages being positioned at common angles to radii of said spark shield, said passages being positioned at common angles to a plane perpendicular to the axis of said spark shield and being positioned to direct fluid beyond the end of said chuck and toward the area of the vehicle body around the stud, a plurality of notches in the end of said second portion of said spark shield, a sleeve positioned around said spark shield, and means for supplying fluid through said passages during a welding operation, said fluid supply means comprising passage means extending longitudinally of said spark shield and said sleeve, said longitudinal passage means being formed between the outer surface of said spark shield and an inner surface of said sleeve, said longitudinal passage means extending around the entire periphery of the spark shield and communicating with the fluid passages at the outer surface of said spark shield, and an additional passage formed in said welding foot and communi-cating with said longitudinal passage means.