FORM 2
THE PATENT ACT, 1970,
(39 OF 1970)
&
THE PATENTS RULE, 2003
COMPLETE SPECIFICATION
(SEE SECTION 10; RULE 13)
"IMPROVEMENT IN WELDING GUN TO AVOID SPOT BURR"
MAHINDRA & MAHINDRA LIMITED
A COMPANY REGISTERED UNDER THE
PROVISIONS OF COMPANIES ACT, 1956
HAVING ADDRESS AT R & D CENTER,
AUTOMOTIVE SECTOR,
89, M.I.D.C., SATPUR,
NASHIK-422 007,
MAHARASHTRA, INDIA.
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE NATURE OF THE INVENTION AND MANNER IN WHICH IT IS TO BE PERFORMED

FIELD OF THE INVENTION:-
The present invention is related to welding techniques in manufacturing industry. More particularly, the present invention is related to the improvements in spot welding gun to eliminate the spot burr during the welding process.
BACKGROUND OF THE INVENTION:-
In spot welding operation followed in body shop of automotive industry, two sheet metals are weld together with resistance welding. In resistance welding the current is kept very high which results in melting of two metals due to resistance. During this welding process if small gap or dust on the panel surface creates splashes which results in spot burr, this spot burr stick in spotting area which may cause injury during further operation of vehicle.
Efforts have been made to eliminate such burr spots during the spot welding process. Prior art document No. CN101373879A discloses a welding procedure for welding conductive copperplate connectors and a plurality of copper wires or weaved copper wires, a special fixture thereof and a resistance welding electrode which is also used as a holding fixture. A fluted structure corresponding to the heaves of the strip-shaped connectors is arranged on one plane surface of the adopted special fixture; the fluted structure corresponding to the heaves of the strip-shaped connectors is arranged on one plane surface of the adopted resistance welding electrode which is also used as the holding fixture. By adopting the welding procedure, the special fixture thereof and the resistance welding electrode, the firm connectors can be obtained through welding, and the energy consumption is low, the melting area of the connectors is sufficient and the conductive area requirement can be satisfied.
However, this prior art is aimed at welding a bunch of strands of a copper wire. The drawback of this prior art is this fixture cannot be applicable for spot welding the metals body parts of a vehicle in manufacturing processes.

OBJECT OF THE PRESENT INVENTION:-
The main object of the present invention is to provide an improved method and apparatus to avoid spot burr in spot welding process.
Another object of the invention is to provide an apparatus for spot welding wherein the welding electrode has a copper plate to eliminate the spot burr.
Another object of the present invention is to control the heat in the weld area to by providing suitable means of cooling therein.
Another objective of the present invention is to provide an improved apparatus with copper plate for spot welding wherein the said copper plate incorporate water cooling system.
Still another object of the present invention is to avoid surface undulations and/or deep spot at the weld area.
STATEMENT OF INVENTION:-
Accordingly the invention provides an improvement in welding gun to avoid spot burr comprises a fixed arm (2), a moving arm (3),with the electrodes (4) attached to the said fixed and moving arm;) a copper plate (7) pivotally mounted to the copper plate mounting fixture (5) on the said moveable (3) arm by means of a mounting bars (6) and brackets (8) with fasteners; a water circulation passage (11) .having an inlet (10) for cold water and an out let (13) for hot water, provided in the said copper plate throughout surface area.

BRIEF DESCRIPTION OF THE FIGURES:-
Figure 1 show the simple impulse spot welding cycle followed in the spot welding process.
Figure 2 shows the improvement done in spot welding gun to eliminate the spot burr in accordance with the present invention.
Figure 2A is front view of the improved welding gun according invention showing fixed and moveable arms provided with electrodes with a copper plate pivotally mounted.
Figure 3 shows the exploded view of the copper plate and its mounting arrangement on the moveable arm of the gun in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION:-
Welding is a process of joining two similar or dissimilar metals by application of heat. The types of welding are Arc welding, Gas welding, Resistance Spot welding, MIG (Metal inert gas) welding, TIG (Tungsten inert gas) welding.
Resistance spot welding is the process for joining two or more sheet metal parts together at a point. The weld is made by holding the parts together under pressure and passing an electric current through the metal at the pressure point. The current passing through the point melts the metal forming a molten nugget. The molten metal solidifies, forming a solid nugget at the spot.
In spot welding process, when current flows through a conductor it experiences resistance due to which heat is generated
H = I2 RT
Heat: Heat generated (Joules)

I: Current flowing
R : Resistance to flow of current
T : Time for which the current flows
Heat generated is proportional to resistance, welding gun is of copper based alloys and hence less resistance. Sheet Metal is of Mild steel and hence offers high resistance and hence heat is generated. The heat zone area is then pressed to make the tight spot.
In spot welding operation followed in body shop of automotive industry, two sheet metals are weld together with resistance welding. In resistance welding the currant is kept very high which results in melting of two metals due to resistance. During this welding process if small gap or dust on the panel surface creates splashes which results in spot burr, this spot burr stick in spotting area which may cause injury during further operation of vehicle..
In regular standard practice followed in the industry, copper plate between panel and gun electrode are generally used to avoid the spot damage and spot burr on panel concern.
But due to design constraint of panel and assembly criticality of automotive body in some areas provision of fix type copper plate is not possible. In such cases the concern of spot burr and spot twist remains as it is on skin panel.
In some vehicles of SUV category for example Quanto and Xylo, in window area on vertical flange there is no seal in TCF line which gives requirement of spot welding on flange without spot burr and spot twist. Similar is the requirement in back door area in Quanto vehicle body.
Therefore, an idea of providing guide mounted on arm of portable spot welding gun was thought off. Referring to Figure 2, improved apparatus (1) to avoid spot burr comprises of fixed arm (2), moving arm (3), electrodes (4) attached to the

fixed and moving arm and a copper plate mounting fixture (5). The copper plate mounting fixture (5) further comprises of a copper plate (7), mounting bars (6), and brackets (8). The said copper plate mounting fixture (5) is mounted on the moveable arm (3) of the welding gun with the help of brackets (8) and nut and bolts (9).
Referring to Figure 3, the copper plate (7) is pivotally attached to the mounting bars (6). The said copper plate (7) is provided with a water circulation passage (11) throughout its surface area. The size of the copper plate is optimized as 30 x 50 x 12 mm to take care of the angle and joint thickness (reference thickness) and flange width of the body panel to be welded during the process. The said circulation area is selected in relation to the area of the spot (12) to be given during the process. The said copper plate is provided with water circulation system for cooling the heated copper plate and thereby removing the heat at the spot area to be welded. The water circulation system comprises of water inlet (10) and water outlet (13) and is seamlessly connected to the water source (15). The water inlet (10) tube gets accommodated in the water inlet (17) of the copper plate and forms a leak proof connection passage. Similarly the water outlet (10) gets accommodated within the water outlet groove (18) of the copper plate (7) and forms the leak proof passage. A water circulation channel provided in the copper plate with the input of cold water in & Hot water flowing out from the output of the channel. The copper plate (7) is configured for the free movement to match with the face of the panel as required for different angles and profiles of the body panels to be welded. The free movement of the copper plate is achieved through pivot (20) through which the said copper plate is attached to the mounting bars (6) of the arrangement.
The technical advantages achieved through this improvement are as under,
- The concern for spot burr and deep spot was eliminated.
- The aesthetic of the vehicle reported for welding purposed was improved.

- The complete arrangement is very simple to mount on the movable arm of the welding gun and is cost effective.
- For cooling purpose, no separate cooling facility is required. The cooling circuit of the gun can be comfortably used for cooling the copper plate without any major modifications in the system.

WE CLAIM:-
1. An improvement in welding gun to avoid spot burr comprises a fixed arm (2), a moving arm (3),with the electrodes (4) attached to the said fixed and moving arm;) a copper plate (7) pivotally mounted to the copper plate mounting fixture (5) on the said moveable (3) arm by means of a mounting bars (6) and brackets (8) with fasteners; a water circulation passage (11) having an inlet (10) for cold water and an out let (13) for hot water, provided in the said copper plate throughout surface area.
2. The welding gun as claimed in claim 1 wherein the said the copper plate (7) is configured for the free movement to match with the face of the panel as required for different angles and profiles of the body panels to be welded.
3. The welding gun as claimed in claims 1 and 2 wherein the said copper plate supported to a pivot.(20) for fixing to the said mounting bar (6) for free movement of said copper plate.
4. The welding gun as claimed in claims 1 to 3 wherein the size of the copper plate is optimized as 30 x 50 x 12 mm to take care of the angle and joint thickness (reference thickness) and flange width of the body panel to be welded during the process.
5. The welding gun as claimed in claims 1 to 4 wherein the said circulation surface area is selected in relation to the area of the spot (12) to be given during the process.
6. The welding gun as claimed in claims 1 to 4 wherein the said circulation surface area is selected in relation to the area of the spot (12) to be given during the process for cooling the heated copper plate and thereby removing the heat at the spot area to be welded.

7. The welding gun as claimed in claims 1 to 5 wherein the said water inlet (10) tube gets accommodated in the water inlet (17) of the copper plate and forms a leak proof connection passage the said water outlet (10) gets accommodated within the water outlet groove (18) of the copper plate (7) and forms the leak proof passage.