Method and apparatus for disassembly of a spot-welded structure

A method and apparatus for removing spot welds from a sheet metal structure is shown. A fluid powered hand punch has a handpiece and an L-shaped extension forming a punch die. An elongated rod extends from a fluid piston within the handpiece to a punch bit, allowing the punch to be conveniently positioned over spot welds in diverse structures. An extension of the handpiece body guides and stabilizes the rod. Spot welds are removed by positioning the punch bit over the weld and entirely punching it out. A tapered punch bit engaging the metal along a partial perimeter of its front face is also shown.

BACKGROUND OF THE INVENTION 
The present invention relates to a method and apparatus for disassembly of 
sheet metal structures which have been spot welded together, and to a 
novel hand tool for performing such method in the auto body industry. 
Spot welding is a widely used assembly technique for all manner of 
structures in which different sheets of metal must be fastened to each 
other. Examples of such structures are appliance cabinets, chassis for 
electronic parts, airplanes and perhaps most ubiquitously, automobile 
bodies. Spot welding is not only inexpensive and fast, but has the 
esthetic advantage of not involving fastener heads or other elements 
protruding above the surface of the sheet metal being fastened. In an 
automobile, numerous curved, stamped sheets of metal, such as those 
comprising fenders, rocker panels, reinforcements for the perimeter of the 
trunk, and other such pieces are spot welded into the final assembly at 
the factory. When an automobile is involved in a collision, or because of 
rust or deterioration requires replacement of such assemblies, the spot 
welded sheet must be separated from the undamaged portions of the vehicle 
and a new contoured sheet assembly must be installed. However, because the 
damaged assembly is spot welded, certain problems arise in disassembling 
the structure. With a simple bolted structure, it is common to burn off 
the bolt heads with an acetylene torch or to unscrew the bolts, allowing 
the sheets to simply separate. However, with the spot welded structure, 
the prevalent methods of disassembly are either tedious, or require force 
which may be destructive of other portions of the car. 
One existing method is to painstakingly drill out each spot weld. Drilling 
out spot welds is accomplished by drilling first a small pilot hole 
through the middle of each spot weld and then using a circular piloted bit 
to entirely remove the weld from the exterior sheet. This operation must 
be done for each spot weld, to separate the portions of metal fused to the 
exterior sheet, after which the two sheets will simply separate. The 
protruding welds remaining on the lower sheet must then be ground flat. 
This process of removing welds, while resulting in a neat work product, is 
extremely tedious. 
A second method of disassembling spot welded structures is to separate the 
two sheets at some point, and then to drive a dull chisel with a sharpened 
notch along the seam between the sheets so as to pry the sheets apart 
while severing the fused portions. Such a chisel, the use of which is now 
common together with a pneumatic handle assembly in auto body shops, is 
shown in U.S. Pat. No. 3,191,909 issued June 29, 1965 to N. M. Reischl. 
The use of a pneumatic chisel or parting tool in this manner, while 
effective, entails the use of force which may bend, rip or alter the 
underlying contour of the otherwise undamaged metal pieces, especially 
when used on the thinner gauge steels now common in the auto industry. 
Furthermore, such a parting tool and pneumatic hammer together form a 
rather bulky assembly, and may be serviceable only in situations where the 
spot welded seam is very exposed, without other structures or contours of 
the workpiece obstructing the area of work for a large distance on all 
sides. 
A second specialized tool for disassembly of sheet metal structures 
operates with a rotary driver and essentially works in the manner of a 
sardine can opener. Such a device is shown in U.S. Pat. No. 3,688,383 
issued Sept. 5, 1972 to A. M. Martin. It is not known whether the tool 
shown in that patent has been made or marketed; however that tool also 
involves parting the welds by force, essentially pulling them apart along 
a narrow band immediately surrounding the line of spot welds. In addition 
to exerting tearing force along the spot welds, that tool requires 
substantial clearance for insertion of the tool along the length of the 
seam, and also would appear to work only for the removal of a well exposed 
piece from another, substantially thicker, piece. As such, there are 
numerous portions of an automobile body, such as curved pieces, or pieces 
having vertical corners rising quite near to the spot weld, or pieces 
having spot welds situated at the base of a shallow channel or trench, as 
in the perimeter of a trunk compartment of an automobile, where none of 
the above specialized tools would work, and where the laborious drilling 
out of individual spot welds by hand would be the only practicable method, 
if any, of disassembly or of nondestructive disassembly. Finally a 
clamp-like structure having a pneumatically driven end mill has recently 
appeared on the market for removing spot welds. This device has the end 
mill and drive motor affixed to one arm of a C-shaped clamp, so as to be 
moved down toward the opposing arm of the clamp. As the clamp is closed, 
the mill cuts through one of a pair of spot welded sheets. That device is 
a logical extension of the usual art of drilling out welds, but is bulky, 
requires adjustment to suit the gauge of metal involved, is subject to bit 
wear, and may "skitter" on curved seams, or if incorrectly aligned. 
BRIEF DESCRIPTION OF THE INVENTION 
The present invention overcomes the disadvantages of the prior methods and 
devices by providing a method and device for disassembling spot welded 
structures by punching out the spot welds. A fluid actuated hand tool is 
configured with a narrow extension of the body extending between a fluid 
powered piston and a punch bit, so as to be able to reach normally 
inaccessible spot welded seams in an automobile body and conveniently 
punch out the fused spot welds along the edges of the sheet assemblies. 
The punch device has a hand piece with machined fluid cylinder formed 
therein and a piston with a long nosepiece or rod, to which a punching 
element is mounted. An L-shaped member extends from one end of the hand 
piece along one side thereof, defining, together with the hand piece, a 
work-receiving throat, with the horizontal portion of the L defining an 
anvil including a punch die aperture. The piston nosepiece or rod is 
guided by the central narrow extension of the hand piece and, in one 
embodiment, is adapted to threadedly receive replaceable punch tools, 
which are preferably of a shearing, rather than straight punching, profile 
to minimize power requirements of the tool. A tool steel die plate is 
mounted on the anvil and the entire anvil structure extends only a small 
amount radially beyond the edges of, or axially below the surface of, the 
die aperture, so that the punch may conveniently be positioned over spot 
welds within a fraction of an inch of obstructions. A trigger may be 
provided in the hand piece.

DESCRIPTION OF THE INVENTION 
Turning now to FIG. 1 there is shown a perspective view of a fluid actuated 
punch for use in removing spot welds according to the present invention. 
As shown, the punch 1 comprises a hand piece portion 2 and an L shaped 
portion 3 extending from one end of the hand piece. The hand piece has a 
fluid inlet 4 which is preferably an inlet for hydraulic fluid having a 
substantial pressure in the range of 2 to 10,000 PSI (125-700 
atmospheres). As shown, the device is a hand tool of a size to be gripped 
in the palm of one hand, with a hydraulically actuated piston for driving 
the punch. The small size of the device dictates the relatively high 
hydraulic fluid pressure required to operate it. As shown in FIG. 1, a 
preferred embodiment of the device incorporates a trigger handle 5 which 
is actuable by the hand holding the device, and which controls the 
provision of pressurized fluid to the piston within, by bearing against a 
button valve located under the handle. It is not necessary that the valve 
directly control the hydraulic fluid, but may rather control a pneumatic 
source, or even an electrical contact, which regulates a remote device 
which provides, in turn, the surges of hydraulic fluid under pressure for 
powering the punch. The L shaped extension 3 has a horizontal portion 6 
projecting outwardly therefrom so as to define a throat for receiving a 
workpiece. The inner face of the horizontal portion 6 is an anvil 7 or 
flat surface having an aperture 8 therein, through which the punch tool 9 
passes for punching sheet metal. As shown, the hand piece 2 is of a 
substantially cylindrical shape having a longitudinal axis. The body of 
the handpiece between the piston and the anvil includes an extension 
portion 12 of the hand piece with an exterior profile inwardly offset from 
that of the hand piece and with a bore therein for accommodating and 
guiding the punch tool. In a preferred embodiment, the punch tool itself 
is a small hardened steel element, preferably configured for shearing 
rather than straight punching action, and adapted to replaceably mount in 
the piston element (not shown). The efficiency of a punch mechanism, and 
the longevity of the punch bits, critically depend on the alignment of the 
punch bit with the die hole, so that the bit does not either strike into 
the die plate, or strike the metal at a distance too far removed from the 
edge of the die aperture to allow efficient cutting action. Accordingly, 
the extension portion 12 serves a function of stabilizing the punch bit 
assembly to provide such stability and tool longevity; the guide extension 
comprises a thin wall, approximately 1/10" (1.5 mm) thick, chosen as the 
minimal diameter housing necessary to accomplish this result, so as to 
provide the maximum clearance around the sides of the throat for 
positioning the device in proximity to sheet metal assemblies of diverse 
shapes. 
Turning now to FIG. 2 there is shown a side view of the fluid actuated 
punch of the present invention, showing the side profile of the 
workpiece-receiving throat defined by the hand piece 2, the extension 12, 
and the L shaped member 3. As shown, the central axis 20, along which the 
punch bit moves, extends quite close to the leading edge of the die plate 
7. Also, the exterior edge of the extension 12 lies along an axis also 
quite close to the central axis 20. This results in a relatively thin wall 
around the central bore (not shown) which accommodates and guides the tool 
bit and the structure attached to it; the choice of such a minimal 
exterior contour is done to permit the maximum amount of clearance of the 
hand tool, as a whole, in relation to possibly abutting sheet metal 
assemblies which it may be required to punch. Die plate 7 is formed of 
tool steel, tempered and hardened so that it is hard enough to use for the 
die aperture, yet tough and resistant to cracking and chipping. In the 
embodiments shown die plate 7 is approximately 3/32 inch in thickness and 
preferably is attached to the anvil formed by the horizontal portion of 
the L shaped extension with a weld having a low melting point, such as a 
braze or silver solder. The weld serves to efficiently convey the forces 
exerted on the die plate to the underlying casting, and is chosen to have 
a low melting point so as not to adversely affect the hardness and 
toughness of the plate 7, and to permit replacement or interchange of the 
plate. To aid in the alignment of plate 7, a groove 70 is rabbeted 
therein. Groove 70 slides over a corresponding raised ridge or boss 25 of 
the handle, thereby aligning the plate along a line through the axis of 
the punch. Because the plate 7 is welded to the underlying casting, no 
bolt or fastener holes need be drilled in the casting of the L shaped 
member. For this reason the underlying casting or support region of the L 
may be made quite thin, and still be strong; in addition the cumbersome 
die jigs of the prior art are eliminated, resulting in the increased 
maneuverability required of the hand tool. As shown, a clearance, below 
the sheet being punched, of less than approximately 1/4 inch is all the 
tool requires; this is in sharp contrast to existing punches which have a 
reinforced casting of substantial depth on the die plate side. Further 
contributing to the compactness of construction is the shape of punch tool 
9. The preferred contour of the punch bit will be discussed below in 
relation to FIG. 4; at this point it suffices to say that the bit is 
configured with advance portions which engage the sheet metal for shearing 
along a portion of the hole perimeter, rather than punching through the 
entire hole at once. The punch bit thus requires less force than if the 
bit were configured for straight punching rather than shearing action. 
FIG. 3 shows an end view, from the anvil end, of the fluid powered punch of 
the embodiment of FIGS. 1 and 2. As shown, the horizontal portion 6 of the 
L-shaped extension is of a narrow cross section extending in a narrow 
angular range on one side of the axis of the punch. The portion 6 extends 
only so far as is necessary to define the die aperture 8, and is gently 
radiussed so as to allow placement of the punch aperture within 
approximately 1/8" of an obstructing surface oriented parallel to the 
punch axis for approximately 270 degrees of arc around the aperture. By 
contrast, the handpiece 2 extends approximately 1/2-3/4 inches (1-2 cm) 
out from the axis in all directions. Trigger 5 is shown mounted on 
handpiece 2 on a side opposing the L-shaped member 3; however the location 
of trigger 5 is a matter of choice. 
Turning now to FIG. 4 there is shown a section through the hand piece and 
piston. As shown, hand piece 2 comprises a fluid inlet 4 to a central 
chamber 32. The chamber is a cylindrical bore and accommodates therein a 
piston 33 of a diameter corresponding to the chamber. Piston 33 is 
attached to a spring 34 the other end of which is anchored via a set screw 
35 to the inner cylinder wall at the inlet end of the chamber. Access to 
the screw 35 is via a threaded bore horizontally directed to the opposing 
side wall of the chamber, which in turn is closed with a plug (neither 
shown). The piston end of the spring is preferably bolted to the piston by 
a similar screw or bolt 36. As shown piston 33 has a first end 
substantially of the same diameter as the inner diameter of central 
chamber 32. This end acts as a hydraulic piston and serves, under the 
influence of fluid pressure, to advance the tool bit. Extending downward 
from piston 33 is a nosepiece 37 which extends approximately 2 inches (5 
cm) from the face of the piston. The nosepiece 37 is in the form of a thin 
rod, which advantageously may be of a length between approximately 1/2" 
and 4" without departing from the scope of the present invention. The tip 
of nosepiece 37 preferably has a central bore threaded therein for 
receiving punch bits. Nosepiece 37 projects through extension guide bore 
38 formed in the housing at region 12, thereby stabilizing and enhancing 
the accuracy of the punch bit holding member. Also shown in FIG. 4 is the 
punch bit 9, which, as shown, has a V-shaped notch at the front cutting 
edge thereof, a slightly tapered body extending back toward its other end, 
a first cylindrical shank, and finally a second narrower cylindrical 
portion which is threaded for mounting in the threaded bore of the 
nosepiece. The taper of the bit assures that it will not bind in the 
punched hole, so that a mild spring 34 may be of sufficient strength to 
retract the cutting face of the bit within, and almost up to the face of 
the hole, after a punching operation. A slight motion of the handpiece 
then suffices to entirely disengage the bit from the punched hole. In this 
manner use of the bulky spring-loaded die jigs and ejector mechanisms of 
the prior art is avoided. Sealing ring 39 is shown surrounding the piston 
so as to prevent leakage of fluid from the chamber past the piston. Ring 
39 may be replaced by any conventional hydraulic sealing ring assembly, 
which may include one or more wipers and seals, in one or more grooves of 
the piston. 
FIG. 4 shows in detail the manner in which the casting walls around the 
above-described bores and chambers are minimized so as to provide a hand 
tool capable of punching spot welds from contoured sheet assemblies. In 
particular, the wall 321 defining the central chamber is thin, so that a 
maximum possible diameter piston 33 may be used while still maintaining 
sufficiently small dimensions to allow the device to be held in one hand. 
Similarly, the wall 381 defining the extension guide bore is, except on 
the side of the tool having the L shaped or goose neck extension, even 
thinner. The purpose of the L-extension is to define a work-receiving 
throat removed from, and offset clear of, the side of the piston, so that 
the handpiece radius of approximately 3/4" will not pose a lower limit to 
the range of accessible punching locations. This extension portion serves 
to maintain the nose portion of the piston in axial alignment, and, except 
for slight deflections upon initial punching impact, receives little, if 
any, force. Finally, the anvil nose portion 71 is also quite thin, and the 
punch die hole situated very near to the edges thereof, both of which 
features serve to permit the device to be used on spot welded seams, even 
those having a vertically-rising surface abutting the welds, or welds 
located on curved surfaces. The nose has an aperture 711 formed therein 
coaxial with the bit. This entire anvil portion of the handpiece may be 
forged, and the die plate 7 dispensed with. However, preferably, die plate 
7 is used. The die plate 7 is preferably rabbeted 712, and receives a 
corresponding boss milled on the casting, for ease of alignment when 
replaced. 
Turning now to FIG. 5 there is shown an enlarged detail of a preferred 
punch bit 9 used in the practice of the present invention. As shown, the 
punch bit 9 is a replaceable bit, having threads 91 at one end thereof, a 
cylindrical shank, 90, and a body 92 tapering outwardly towards the 
cutting end of the bit. The cutting end has a V shaped cross section 94 so 
as to engage the work piece at opposing beveled edges 93, thereby 
instituting a shearing, rather than a straight punching action, only along 
a partial perimeter of the hole to be punched, at a given instant, thus 
requiring less punching force than otherwise. Other configurations of the 
cutting face known in the art for producing a progressive shearing action 
are also suited to this punch. The taper along portion 92 assures that 
after the punch has penetrated the sheet metal, the edges of the punch do 
not engage the metal or jam in the hole. 
The fluid powered punch for the use in accordance with the present 
invention may, as discussed above, incorporate a trigger for turning on 
and off the pressurized fluid, in a manner well known in the art. It is 
envisaged that, as adapted for use in an auto body shop, the punch may be 
operated from an auxiliary hydraulic step-up unit, similar in operation to 
an automotive power brake unit, in which a source of pressurized air at 
approximately 100 PSI is used to drive a single-displacement piston pump 
to produce the necessary hydraulic fluid pressure at several thousands of 
PSI. Alternatively the tool may be attached to an electrically-driven 
hydraulic pump to attain the necessary operating pressures. In either of 
these two cases the trigger assembly would be operative to open or close a 
valve for the auxiliary air source, or to close an electrical contact for 
actuating the auxiliary fluid power device. Alternatively, the trigger 
could directly open a fluid pressure valve. 
The construction details of an illustrative embodiment of the punch tool 
configured for removing spot welds having been discussed in detail in 
relation to FIGS. 1-5, the operation of the tool and several illustrative 
examples of its use in effecting the method of the present invention will 
now be discussed in relation to FIGS. 6, 7 and 8 below. 
FIG. 6 shows the logical sequence of steps of the method, according to the 
present invention, for separating spot welded structures. As shown, the 
method comprises the steps of locating the spot welds joining a piece to 
the structure; placing the punch over each such spot weld and entirely 
punching out the fused metal; and separating the structures when all welds 
have been thus removed. While simple in approach, punching as a technique 
for removing spot welds has not been done before because spot welding is 
used precisely for structures unsuitable for conventional punches, which, 
as a rule, have a die block or narrow sheet-receiving die portion which 
will not accommodate a typical assembled spot welded structure. 
FIG. 7 shows one example of such a configuration, and the use of the tool 
of the present invention for removing spot welds. As shown, a first piece 
72 having a U-shaped channel 74 is spot-welded along the bottom of channel 
74 to a second, L-shaped, piece of metal 73. The U-shaped channel 74 has 
vertically-rising sides 75a, 75b which would clearly prevent access to a 
conventional punch. As shown in FIG. 7, the punch 1 according to the 
present invention can conveniently punch the spot welds from the bottom of 
channel 74 because the nosepiece 37, in sharp contrast to the punch bit 
holder or die block assembly of the prior art, can fit into a narrow 
channel. 
This feature is more clearly indicated in FIG. 8, in which a typical 
automotive roof panel 80 is shown, having a rain channel 84 with a 
vertical roof face 85b and a vertical channel face 85a. The face 85b may 
rise vertically several inches or more (over 5 cm) and the channel 84 may 
be as narrow as 5/16 inch (8 mm) or less. Roof panel 80 is joined to body 
member 86 which in turn holds window frame 87 surrounding a sheet of glass 
88. The plane defined by sheet 88 may be within 1/4" of the vertical plane 
passing through the line of spot welds in the bottom of channel 84. In 
such a situation the window would entirely prevent use of a tool extending 
1/4" beyond the punch axis, so that the handle could not be oriented 
downward. The vertical roof face 85b poses a similar restraint on the 
tool. As shown, the tool of the present invention, having extension 
portion 12 housing the nosepiece 37, is not obstructed by such an assembly 
of welded sheet metal structures and accordingly is operative to remove 
the spot welds and separate the sheets.