THE PATENT ACT, 1970,
(39 OF 1970)
&
THE PATENTS RULE, 2003
COMPLETE SPECIFICATION
(SEE SECTION 10; RULE 13)
"METHOD FOR AUTO-SELECTION OF THIRD SET OF SPOT WELD PARAMETERS IN MANUAL SPOT WELDING"
MAHINDRA & MAHlNDRA 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,
NASH1K - 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 INVENTION:-
The present invention is related to sheet metal body manufacturing process followed in the press shop. More particularly, the present invention is related to a method for auto selection of third set of spot weld parameters in manual spot welding process in non-linear path.
OBJECT OF INVENTION:-
It is object invention to provide a method for auto-selection of third set of spot weld parameters in manual spot welding where only two set of spot weld parameters possible by manual setting.
It is also object of invention to set automatically third parameter when welding gun on the spot where third set of weld parameter necessary.
STATEMENT OF INVENTION:-
Accordingly the invention provides a method for auto-selection of third set of spot weld parameters in manual spot welding comprises:
a. a frame having exactly same profile of seal channel is mounted
overhead facing at distant and parallel to the said seal channel to be
weld;
b. a monorail fixed below and proximate to the said frame;
c. a spring balancer fastened by bolt means to fabricated MS flat movably
mounted in the said monorail; a proximate sensor is inserted in hole
made in the said fabricated MS flat at spring balancer centre point;
d. a portable manual spot welding gun is mounted on spring balancer;
the arrangement is such that at particular joint, the spring balancer is exactly above the location of joint of welding job fixed in the jig so while doing manual spot welding there is always a fixed relationship between location of spot weld gun shank and overhead position of spring

balancer the said center point so that the relationship between location of spot weld & corresponding position of balancer centre point utilized for providing trigger by the said sensor for auto-selection third set. of spot welding parameters.
BRIEF DESCRIPTION OF FIGURES:-
Figure 1 shows portable manual spot welding gun and a thumb operated toggle
switch.
Figure 2 shows an illustrated in example of door sub assembly with three thickness
combinations to be welded as per the present invention.
Figure 3 shows portable manual spot welding gun is mounted on spring balancer.
Figure 4 shows the details of door inner assembly & the frame mounted overhead.
Figure 5 shows the spot welds taken as per the auto-selection of third set of spot
weld parameters in manual spot welding of the present invention.
DESCRIPTION OF THE PRESENT INVENTION:-
In automobile sheet metal body manufacturing operations, manual spot welding is done using portable spot welding equipment which is also called as Spot welding gun. The portable spot welding guns are widely used for resistance welding of sheet metal parts in automobile industry. As per the vehicle body design, two or three sheet-metal parts (13, 14, 15) with same or different sheet metal thickness combinations with base sheet metal part are joined together with base panel (11) using spot welding process.
The weld time, Weld current and force between spot weld electrodes are main parameters for good quality spot welding joint formation. Incorrect set of parameters result in poor spot weld joint quality with defects like spot burr, low strength, indentation, spot dent, pin hole, etc. For joining different sheet-metal thickness combinations, the different sets of spot welding parameters are required. Higher

thickness combinations require higher current, weld time for formation of welded joint and vice versa.
As mentioned above, the different combinations of sheet metal thickness demand different sets of spot welding parameters. If in some body sub assembly like door, the vehicle design consists of different thickness combinations, then operator has to manually select correct spot welding parameters as per sheet metal combinations at . spot welding joints. On portable manual spot welding gun, a thumb operated toggle switch (marked with red circle in Fig. 1) is provided to select correct set of spot weld parameters as per thickness combination. Two sets of parameters can be selected and used for spot welding to take care of two sets of sheet metal thickness combinations. Each position of toggle switch delivers separate set of spot welding parameters.
On few body sub assemblies, there are three sets of thickness combinations of sheet
metal. Spot welding on such sub assemblies demand more than two sets of spot
welding parameters.
For example, In given case as shown in Figure 1,
Base Panel (11): Door inner panel: Thickness: 0.8 mm
Part B (13): Hinge Reinforcement: Thickness: 1.8 mm
Part C (14): Door striker: 1.4 mm
Part D (15): Door seal channel: Thickness: 0.7 mm
There are three thickness combinations;
Base Panel+ Hinge reinforcement: 0.8 mm +1.8 mm
Base Panel+ Door striker: 0.8 mm + 1.4 mm
Base Panel+ Door Seal Channel: 0.8 mm + 0.7 mm
There are following options to cater such requirements,
i) One portable spot welding equipment has provision of selection of two sets of parameters available using toggle switch. To make available third set of parameters, one more equipment (additional spot welding gun) will have to be added. But it has following drawbacks, but this leads to increase in capital cost due to additional equipments, Space constraints, this option is not viable. Also it will result in extra movement for operator

for using additional equipment. It will increase the cycle time & drop productivity.
ii) Manually operated thumb switch with three toggle selection can be provided. But it will be difficult for operator to remember the combination to be used at particular joint. Wrong selection of spot weld parameters will result in weld joint with low strength and will cause failure of joint. So this option cannot be implemented.
iii) Additional third manually operated button on pendant attached to loom can used to select third set of parameters. But it does have possibility of wrong selection by operator. The pendant which is mounted on loom is 5-6 walking steps away from operator. So time required for walking towards pendant for selection of third set of parameters first and then again to bring switch to normal from third set for next cycle also will increase activity time per job. Thus it will.reduce productivity due to extra operator movements for operating the switch. Thus this option is also not viable.
In order to provide third set of weld parameters for manual spot welding in non linear path & auto-selection to avoid mistakes from operator or also without addition of new equipments and without decrease in productivity, following innovative ideas is implemented.
(i) As illustrated in example of door sub assembly, there are three thickness combinations (13,14,15) of sheet metal parts with base part (15) at various locations. Combination-13 is welded by operator by selection Programme-1 on manual toggle switch (10) installed on body of portable spot welding gun (8). For combination 14, operator uses second set of spot weld parameters by shifting position of toggle switch. For combination 15, third set of lower parameters is required considering that part thickness at combination 15 is less than earlier two combinations. As operator does not have third set of parameters, he has to weld on combination 15 with parameters set for combination of 13 or 14 with selecting position of toggle switch. Due to high welding parameters set for higher thickness at earlier two combinations, the

heat produced at joint will be more than required. It results in defect of spot burr on joint. Spot burr cause cut on rubber parts fitted on door in subsequent operations or cause injury to operator figure in paint shop, (ii) As shown in figure 3, portable manual spot welding gun (8) is mounted on spring balancer (5). The spring balancer is a device mounted on overhead monorail. Fabricated bracket with MS flat is fastened to balancer by inserting it in bolt which is used to mount balancer on overhead monorail.
Spot welding gun is attached to hook on spring balancers. Spring balancer gives zero gravity effect while upward & downwards movement of spot welding gun. Zero gravity effect results in effortless handling of spot welding gun by an operator. Proximity sensor is mounted in hole on fabricated bracket.
(iii) The spring balancer moves on overhead rails (3) & (4). When operator (9) does spot welding at particular joint, the spring balancer is exactly above the location of joint (As shown by dotted red line in figure 3). Thus while doing manual spot welding; there is always a fixed relationship between location of spot weld gun shank (12) and overhead position of spring balancer center point. In this innovation the relationship between location of spot weld & corresponding position of balancer is utilized for providing trigger for auto-selection third set of spot welding parameters.
(iv) Figure 5 shows the details of door inner assembly & the frame (1) mounted overhead. The profile of frame is the same as the top side profile of door inner panel on which seal channel (part 15) is assembled and to be welded. One electric proximity sensor (2) is mounted on center of gun balancer. (5) This sensor travels as per the gun movement while doing spot welding from one position to another. As balancer has fixed relationship with respect to location of spot, the position of sensor also has fixed relationship with position of spot weld on part. (If A=B, B=C, then A=C).

(v) As shown in the figure the seal channel profile on door frame. One frame having exactly same profile of seal channel is mounted overhead. The frame has width of 180 mm. The width is decided considering slight movement of balancer & sensor due to jerks while gun travel from one location to next location.
(vi) Operator starts spot welding operation from Part B (13) with selection of Programmed with position "A" of toggle switch then he moves gun on Part D: Door seal channel 15).
(vii) Then he goes for spot welding of part C.
Referring to figure 5, Spot weld „I' is taken with weld parameters with position 1 on thumb switch on Part 13, spot weld 'ii,iii,iv,v,vi' are taken on seal channel (part 15), When spot welding gun tip enters on part 15, the sensor mounted on gun balancer travels below overhead frame & senses its metal surface. After sensing frame, sensor gets "ON" gives trigger to controller for auto-selection of third set of parameters. After completing spot welding on Part D, when gun moves to Part C the sensor mover out from area of overhead frames & gets OFF. Operator will now select Second position of thumb switch to select other set of parameter for spot „vii". Thus using the overhead frame with profile same as that of part on which we need third set of parameter, sensor on balancer & input of sensor to controller for auto switching of parameter. Thus, the auto selection of third set of spot weld parameter in manual spot welding in non linear path is achieved.

WE CLAIM:-
1. A method for auto-selection of third set of spot weld parameters in manual spot welding comprises:
a. a frame having exactly same profile of seal channel is mounted
overhead facing at distant and parallel to the said seal channel to be
weld;
b. a monorail fixed beow and proximate to the said frame;
c. a spring balancer fastened by bolt means to fabricated MS flat movably
mounted in the said monorail; a proximaty sensor is inserted in hole
made in the said fabricated MS flat at spring balancer centre point;
d. a portable manual spot welding gun is mounted on spring balancer;
the arrangement is such that at particular joint, the spring balancer is
exactly above the location of joint of welding job fixed in the jig so while
doing manual spot welding there is always a fixed relationship between
location of spot weld gun shank and overhead position of spring
balancer the said center point so that the relationship between location
of spot weld & corresponding position of balancer centre point utilized
for providing trigger by the said sensor for auto-selection third set of
spot welding parameters.