FIELD OF INVENTION
The present invention relates to a device for lap joining of Thin Sheets by spot welding techniques for manufacturing test samples to carryout weldability studies. More particularly the present invention relates to developing an apparatus in the form of a fixture whereby two thin sheets or the like may be disposed in fixed relationship to one another to permit lap welding of the sheets together by spot welding method to produce necessary test samples to carryout weldability studies as per code requirements. Use of the fixture eliminates all the deficiencies of the prior art and ensure speedy completion with assured quality.
BACKGROUND OF INVENTION
Resistance welding is used as the one of the major welding processes for lap joining of thin sheet materials in many sectors of industry. Manufacturers provide details about the properties of the sheet materials and the limits about the set parameters to be used in forming and joining of them including weldability and parameters for welding. The data sheet will be provided by the manufacturer by conducting number of trials to arrive the weldability of a specific sheet material. The weldability of the sheet material calls for number of welding trials and test methods to adhere to the standards which

need to be preferred. Weldability calls for various tests such as Peel test, Lobe test, Shear Tensile test, Cross tensile test, etc. as per the code of construction. To conduct all these tests it is necessary to properly position the sheets and align the sheets to have a lap joint with a predetermined distance apart to permit precision welding and to accomplish the welding in a most expedient manner.It is also desirable to provide a welding apparatus for disposing two sheets in a predetermined position with respect to one another so that they may be welded.
In accordance with the present invention a novel fixture is provided whereby two separate sheets may be located in aposition to each other to provide means whereby the two sheets may be spot welded together as lap joint for preparing welded samples for various tests like Peel test, Lobe test, Shear Tensile test, Cross tensile test, etc.
Prior Art
WO2007001947A2 2007-01-04 AUTOGENOUSLY WELDED METALLIC
CELLULAR STRUCTURES AND METHODS FOR FORMING SUCH STRUCTURES
(en)
Abstract: An autogenously welded structure is provided that includes a first face sheet, a plurality of individual stiffener elements, and a second face sheet. The stiffener elements each have a first edge disposed against the first face sheet and an opposed second edge. Each stiffener element has a central portion extending between the opposed edges. The central portion is disposed at an angle to the first face sheet. The

stiffener elements include at least some stiffener elements that are disposed at an angle to at least some of the other stiffener elements. The second face sheet is disposed against the second edges of the stiffener elements and the first and second face sheets are autogenously welded to the edges of the stiffener elements. This patent is not related to our invention.
DE102009006585A1 2010-08-05 Guidance device for spot welding electrode hand drills (en)
Abstract: A device for finishing spot welding electrodes comprises a milling head that is
suited for said finishing of spot welding electrodes. The device furthermore comprises a
guide device for guiding the milling head relative to at least one spot welding electrode
or relative to at least one spot welding electrode shaft.
This patent is not related to our invention. The above patent is for making spot welding
electrodes.
WO2010086117A1 2010-08-05 GUIDE DEVICE FOR HAND-HELD SPOT WELDING ELECTRODE MILLING CUTTER (en)
Abstract: A device for finishing spot welding electrodes (14) comprises a milling head (11) that is suited for said finishing of spot welding electrodes. The device furthermore comprises a guide device (13) for guiding the milling head (11) relative to at least one spot welding electrode (14) or relative to at least one spot welding electrode shaft. This patent is not related to our invention. The above patent is for making spot welding electrodes.

DE202009015607U1 2010-04-29 Milling fixture for spot welding electrodes (en)
Abstract: Milling fixture with a blade socket (8; 108) for the training or re-establishment of a rotationally symmetric working on section (48c, 48d) or two spot welding electrodes (48; 148), those in each case in the proximity of the working on section (48c, 48d) a circular cylinder section (48a) exhibits, in the fact characterized that for at least a first spot welding electrode (48) a positioning fixture (4) is intended, at least into which the spot welding electrode (48) is in sections importable, whereby the circular cylinder section (48a) of the spot welding electrode (48) of the positioning fixture (4) is fixable, and whereby the milling fixture as mobiles hand attachment with a speed adjusted electric motor (2) for the drive of the blade socket (8; 108) is trained. This patent is not related to our invention. The above patent is for making spot welding electrodes.
US20050230374A1 2005-10-20 Multi-architecture flexible assembly structure and method (en)
Abstract: A multi-architecture flexible assembly structure includes transfer devices, and programmable loading structures, work fixtures, and unloading structures for assembling components into selected different styles of finished assemblies. This patent is not related to our invention. The above patent is for making assemblies pertaining to automotive components.

US5602341A 1997-02-11 Test fixture for spot welds (en)
Abstract:A fixture for testing the strength of a resistance spot weld connecting two test strips comprises two identical clamping frames, each having releasable clamps for gripping and holding one of the test strips. A pull bar is mounted on each clamping frame in any one of several selected angular positions. The pull bars are aligned with one another and then grasped by a pulling mechanism to apply a separating force on the two strips. The arrangement is such that the line of the separating force passes through the weld.
This patent is not related to our invention. The above patent is for making a fixture for testing of the spot welds.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a device for lap joining of Thin Sheets by spot welding techniques for manufacturing test samples to carryout weldability studies, which is capable of eliminating the disadvantages of prior art.
Another object of the invention is to propose a device for lap joining of Thin Sheets by spot welding techniques for manufacturing test samples to carryout weldability studies, which is able to hold two sheets of materials together in a predetermined location till they are welded.

A further object of the invention is to propose a device for lap joining of Thin Sheets by spot welding techniques for manufacturing test samples to carryout weldability studies, which is capable of providing a rugged yet simple welding fixture for holding two sheets of materials together in a predetermined location to carry out resistance spot welds to achieve dimensional accuracy and repetitiveness to ensure reliable weldability test results.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Fig.1 - Shows the spot welding of thin sheet for making specimen for tensile and
lobe test according to prior art.
Fig.2 - Shows spot welding method adopted for making cross tensile test
specimen according to prior art.
Fig.3 - Shows one side of the composite fixture for carrying out spot welding trial
for tensile, lobe tests etc. according to the invention.
Fig.4 - Shows other side of the composite fixture for welding two sheets together
for cross tensile test according to invention.
Fig.5 - Shows the welding fixture with electrode mounted therein and the plates
in a predetermined location for commencing welding with the two sheets
according to invention.

Fig.6 - Shows the welding fixture with electrode mounted therein and the plates
in a predetermined location for commencing welding of two sheets for
cross tensile specimen according to invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Various other objects and advantages of the present invention will be readily apparent from the following detailed description which when considered in connection with the accompanying drawings forming a part thereof and in which the sheet material to be welded are placed in between the top and bottom electrodes of the conventional resistance welding machines manually. Fig.1 shows the spot welding of thin sheet for tensile and lobe test specimens. Fig.2 show the conventional spot welding method adopted for cross tensile test specimens.
For each trial the sheets are to be placed in between the two spot welding electrodes without airgap and the spot should be made on the specific position as per the code / standard. For weldability tests on one sheet it is required to be done min. 112 lap joints for various testing such as tensile, lobe, hold time sensitivity, etc. and also for cross tensile tests. In conventional method of placing of samples and performing welding it may take a) it takes minimum amount of time to keep the sample in position without airgap

b) spot trial may not be in the predefined position of sample as per standard. For example the spot has to be made at a dimension of 25 mm from the end of two thin sheet on which lap spot to be made.
c) Placing the sample to carry out welding at proper position will lead to more fit up time while considering the number of joints to be made is more than 100 to meet the requirement of standard.
In view of this it was proposed to develop a fixture to keep the samples in correct locations and to carryout the trials which will reduce the fitting time and also to meet the requirement of standard.
The novelty of the fixture development shall be mentioned here is that it is an integrated fixture for cross tensile tests samples preparation and other tests sample preparation. Fig. 3 shows the design of fixture development for lap joints for the above mentioned tests. Fig. 4 is a bottom plan view of the fixture development for welding two sheets together for cross tensile test. Thus the composite fixture can be of very much use for the weldability of new steel sheets for the steel manufacturers.
In Fig.3 shows the view of the fixture designed to have the slot {1} to weld the lap joint for tensile specimen and the circular hole at the centre {2} so that the spot welding tool will come into contact. The job can be placed on the fixture bed with the support screws {3}. The edge of the slots is designed to have to a design {4} to place the

sample before welding and take out the welded specimen after welding easily. Fig. 4 is other view of the composite fixture which designed to carryout spot welding on cross tensile test specimens.
Fig. 5 is a view of the welding fixture as shown in Fig. 3 with electrode mounted therein and the plates in a predetermined location for commencing welding with the two sheets.
Fig. 6 is a view of the welding fixture as shown in FIG. 4 with electrode mounted therein and the plates in a predetermined location for commencing welding of two sheets for cross tensile specimen
Another embodiment of the developed device is the central opening provided in the fixture to accommodate the opening for the bottom electrode in case of resistance welding equipment.
Thus from the foregoing description it is apparent that the present invention provides a novel fixture device for holding two thin sheets in a predetermined location to permit the welding or joining of the two sheets together be disposed to make the joint as lap joint with one side and cross joint at the other side and further the central opening is provided in the fixture so that once the fixture is rigidly secured to the sheets it will in no way interfere with the spot welding operation and it may be continuous.

The device is used for making lap joints on two sheets by having the two sheets together, one over the other with 25mm lap on one side for making the test specimen for shear tensile strength test after joining by spot welding process. Similarly the other side of the fixture can be used for making lap joints on two sheets by having the two sheets together one over the other as cross with the provision of making weld at the centre to prepare the specimen for cross tensile test after joining by spot welding. The device can be used for spot welding of thin sheets of thickness for 1mm to 4mm for its weldability test as per manufacturing code. The device can also be used for spot welding of dissimilar thickness sheets ranging from 1mm to 4mm sheet thickness.
The device is a composite fixture of rectangular shape thick hylum plate on which, the thin sheets are placed for welding. The fixture is made by milling at the middle of the fixture block (F) in one side to form a recess or slot (1) to the required dimension of length width and depth. At the four corners of the slot, four small semicircular grooves (4) are milled to facilitate ejecting of the sheets after welding on the other side of the fixture recess or slots are milled to accommodate sheets for cross tensile welding. In the cross slots, eight numbers of similar grooves (5) are milled at the corner of the cross slots (6).

WE CLAIM
1. A device for lap joining of Thin Sheets by spot welding techniques for manufacturing test samples to carryout weldability studies the said device comprising;
a composite fixture having a straight slot of required dimension on one side and a cross slot of required dimension on the other side to accommodate two thin sheets in one side for making lap joint by having the two sheets together one over other with 25 mm lap on side and by placing the said sheets between a top and a bottom electrodes without air gap to make test specimen after joining the said sheets by spot welding process and to accommodate two sheets on the other side (6) of the fixture (F) placed one over the other in the slots as cross in between the two electrodes wherein the weld is made at the centre of cross for preparing the specimen for cross tensile test, wherein four grooves (4) at four corners of the slot in one side and eight grooves (5) at eight corners of cross slot are disposed for facilitating easy ejection of the sheets after welding, when a circular hole (2) at the centre of fixture block (F) is disposed for allowing spot welding tools to come into contact, wherein the jobs are placed on the fixture bed with support screws (3).