Projection welding

A welding method and apparatus in which a hollow positioning guide pin (7) is installed upon an electrode (8) to project through an aperture in a plate (1), whereupon a flanged elongate or slender part (4) is inserted in the guide pin, and as another electrode (15) presses the flange, the guide pin is withdrawn from the aperture.

FIELD OF THE INVENTION 
This invention is concerned with welding attachment or jointing of elements 
between welding electrodes, and in particular the fixing or mounting by 
so-called `projection welding` of an elongate or slender part, such as a 
flanged bolt or other fastener, to a mounting plate, for example of steel, 
as used in automobile construction. As such, the invention is effectively 
utilized where a slender part is inserted in an aperture in a steel plate 
part or the like after it has been supported upon an electrode. 
By way of background information, a related phenomenon will now be 
described with reference to FIGS. 5 through 8 of the corresponding 
diagrammatic and schematic drawings, depicting a background related art 
example. 
A metal (eg steel) plate part 1 is formed with an aperture 2, through which 
is passed an elongate or slender part 4 having a flange or head 3 (such as 
the bolt shown, or another fastener). The flange 3 and the metal plate 1 
are then welded together in localised weld regions 5, by the compression 
and heat melting or fusion of circumferentially-spaced contact projections 
6 formed on the underside of the flange 3 (see FIG. 7), when an electric 
current is passed therethrough. 
FIG. 5 shows the `normal` or desired case, where the plate aperture 2 is 
concentric with the bolt 4, but FIG. 6 shows an `abnormal` or undesirable 
case, where the bolt 4 is eccentrically positioned, deviating to one side 
of the aperture 2. 
To prevent such eccentricity of FIG. 6, a construction shown in FIG. 7 has 
been proposed--in which a hollow guide pin 7 is slidably inserted within a 
guide hole 9 in a fixed electrode 8, with the bottom plate 10 of the guide 
pin 7 disposed in a spring chamber 11, and abutting a coil spring, 
effectively biassing the guide pin 7 upwards. 
The bottom plate 10 is greater than the diameter of the guide pin 7 and its 
larger diameter portion 12 abuts the upper surface 13 of the spring 
chamber 11, thereby limiting the upward travel of the guide pin 7. 
The compression of a coil spring 14 disposed in the spring chamber 11 helps 
to effect this abutment and in this condition the upper end of the guide 
pin 7 projects above the upper surface of the fixed electrode 8 by an 
amount corresponding to the thickness of the metal plate 1. 
Although the lateral clearance c between the aperture 2 and the guide pin 7 
is designed to be as small as possible to improve accuracy, it is depicted 
as a larger clearance in FIGS. 7 and 8 for clarity of illustration. 
Further, the difference in the inner diameter between the bolt 4 and the 
guide pin 7 is also designed to be as small as possible to improve 
accuracy 
In FIG. 7, the metal plate 1 is placed on the fixed electrode 8, with the 
guide pin 7 passed through the aperture 2 and with the bolt 4 inserted in 
the guide pin 7. A movable (upper) electrode 15 will then be lowered and 
an electric current passed therethrough to complete projection welding. 
When the welding is completed in the manner just described, the 
circumferentially-spaced welded regions 5 are formed by melting the 
projections 6 and their localised contact regions with the metal plate 1 
as they are pressed together At the inner peripheral regions of the 
aperture 2 adjacent the welded regions 5, bulges 16 deviating toward the 
center are formed. 
Therefore, when it is desired to withdraw the integrated (i.e. by welding) 
article shown in FIG. 5 from the fixed electrode 8, upon completion of 
welding, it cannot be smoothly detached, since either the bulges 16 are in 
contact with the outer peripheral surface of the guide pin 7 or since the 
clearance c is very small and has been effectively reduced by the bulges 
16. 
If it is possible to raise the article precisely axially of the guide pin 
7, then it may be detached, even if the clearance c is very small. 
However, in practice it is very difficult for an operator to raise it 
precisely axially. 
If it should be raised at all obliquely, the inner peripheral surface of 
the aperture 2 interferes with the outer peripheral surface of the guide 
pin, making it difficult to withdraw the article. 
The bulges 16 in FIG. 8 are also depicted exaggerated in size, for ease of 
understanding. Actually, the clearance is extremely small and sometimes 
the bulges 16 are hardly discernable by the naked eye. 
SUMMARY OF THE INVENTION 
The present invention addresses the problems described above and in one of 
its aspects provides a welding method characterized in that a hollow 
positioning guide pin 7 is installed upon an electrode 8 to project 
through an aperture in a plate 1, whereupon a flanged elongate or slender 
part 4 is inserted in the guide pin, and as another electrode 15 presses 
the flange, the guide pin is withdrawn from the aperture. 
Another aspect of the invention provides a welding apparatus characterized 
in that a hollow positioning guide pin 7 is installed upon an electrode 8 
to project through an aperture 2 in a plate 1, the guide pin having a 
closed end 10 and the inside length of the pin being less than the length 
of an elongate or slender part to be inserted therein, to achieve guide 
pin displacement with pin travel. 
A further aspect of the invention provides a welding apparatus 
characterized in that a hollow positioning guide pin 7 is installed upon 
an electrode to 8 to project through an aperture 2 in a plate 1, the guide 
pin being connected to a traction mechanism 19,25 for movement ahead of 
the travel of an elongate or slender part inserted therein. 
Yet another aspect of the invention provides a welding method adapted for 
attaching an elongate element to a plate 1 with an aperture 2 to receive a 
shank 4 of that elongate element and a surface for localised contact 
welding 5 with a flange 3 of that elongate element, the method comprising 
the steps of locating a hollow guide tube 7 in alignment with the plate 
aperture, to receive the shank of the elongate element, inserting the 
shank through the plate aperture into the guide tube, and passing welding 
current between the abutting flange and plate through respective contact 
electrodes 8,15 and withdrawing that guide tube upon initiating of fusion 
welding contact between the flange of the elongate element and the plate 
surface. 
A still further aspect of the invention provides a welding apparatus 
adapted for contact fusion welding together a flanged shank element 3,4 
and an apertured or perforated plate element 1, the apparatus comprising a 
hollow support electrode 8, incorporating a movable guide tube 7, to 
support a plate, and a spaced electrode to contact a flanged shank element 
to be fitted within an aperture 2 in the plate, the guide tube being 
adapted for alignment with a plate aperture and thereafter to receive the 
shank, whereby to align it with the plate aperture, the electrodes being 
relatively movable, to compress the flange and plate into fusion welding 
contact upon the passage of an electric current therebetween, and upon 
that relative electrode movement the movable guide being withdrawn 
progressively from the shank, to facilitate subsequent removal of the 
welded shank flange and plate from the support electrode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
For succinctness of explanation, in the embodiments shown in FIGS. 1 
through 4, the corresponding members to those previously described in the 
background art example of FIG. 8 are denoted by the same reference 
characters, but their description will not be repeated 
Further, in the embodiment figures, the clearance between the bolt and the 
guide pin is shown enlarged 
Firstly, referring to an embodiment shown in FIGS. 1 and 2, the guide pin 7 
has a bottom plate 10. Its inside length (the length of the through hole) 
is less than the length of the bolt 4, the difference being approximately 
equal to the thickness of the metal plate part 1, i.e. to (the initial 
flange 3 to plate 1 separation) `1` in FIG. 1. In addition, the `fixed` 
(support) electrode 8 is force-fitted in a base block 17. 
In the condition depicted in FIG. 1, when the movable electrode 15 is 
lowered, the guide pin 7 is depressed by the bolt 4 and the coil spring 14 
is displaced towards the lower region in the spring chamber 11 while being 
compressed, whereby the guide pin 7 is withdrawn from the plate aperture 
2. 
In this embodiment, at the same time as the movable electrode 15 begins to 
press the flange 3, the guide pin 7 is withdrawn from the aperture 2. 
Since the projections 6 are in contact with the metal plate part 1 until 
this withdrawal is completed, there is no danger of the metal plate part 1 
deviating towards eccentricity as shown in FIG. 6. 
Moreover, instead of using the coil spring 1 of FIG. 1, air pressure may be 
fed from a supply passage 18 (shown in broken lines). 
In the embodiment shown in FIG. 3, it is arranged that the guide pin 7 is 
pulled down by the force of an air cylinder 19. The piston rod 20 of the 
air cylinder is threadedly driven into a thick bottom plate 10, with a nut 
21 applied thereto to prevent loosening. The fixed electrode 8 is mounted 
on a strong support block 23 fixed to a stationary member 22. In this 
embodiment, at the same time as the movable electrode presses the flange 
3, the guide pin 7 can be pulled down by the air cylinder 19, or it can be 
pulled down after the flange 3 is pressed (or after welding is completed). 
In the embodiment shown in FIG. 4 the metal plate part 1 is mounted on a 
support block 24, so that, when the whole of the fixed electrode 8 is 
pulled down by an air cylinder 25, the guide pin 7 is withdrawn from the 
aperture 2. This arrangement is of the so-called `traction mechanism` 
type. The support block 24 is an annular member surrounding the fixed 
electrode 8 and firmly fixed to the stationary member 22 through bracket 
22. When the hitherto `fixed` electrode 8 is lowered, the large diameter 
portion 12 is in intimate contact with the upper surface 13 of the spring 
chamber In this embodiment, the guide pin 7 is withdrawn after the flange 
3 is welded to the metal plate part 1. Though not shown, an arrangement 
may be used in which, with the fixed electrode of FIG. 4 maintained 
stationary, the support block 24 is raised. 
In addition, the air cylinder in each embodiment has an air hose connected 
thereto, but not illustrated. 
In the welding method of the present invention, the guide pin is withdrawn 
from the plate aperture, either at the same time as, or after, the movable 
electrode presses the flange of an elongate or slender part. Therefore, 
when the operator withdraws the assembly of the metal plate part and 
slender part from the guide pin, the problem described in the prior art 
example can be completely solved, since the fit relationship between the 
plate aperture and the guide pin has disappeared. 
Further, the arrangement in which the closed-ended guide pin is depressed 
by a slender part whose length is greater than the inside length of the 
guide pin, enables retraction of the guide pin from the plate aperture by 
utilizing the displacement of the movable electrode. 
Further, the arrangement in which the fixed electrode is displaced relative 
to the slender part upon completion of welding makes forcible withdrawal 
possible.