Claims:We claim:

1. A method for joining coated articles (2) by a resistance seam welding, the method comprising:
positioning, one or more coated articles (2) to be welded in a lap joint configuration between electrodes (1) of a resistance seam welding system, such that overlapping edges of the one or more coated articles (2) to be welded define a weld zone,
wherein, the electrodes (1) are made of an alloy of copper [Cu]-chromium [Cr]-zirconium [Zr] with Cu-Cr composition of 0.1wt% and Zr composition of 0.08wt%; and
resistively heating a portion of material along the weld zone by passing an electrical current of pre-determined intensity to join the one or more coated articles (2) together.

2. The method as claimed in claim 1 comprises imparting pressure of pre-determined range by the electrodes (1) on to the overlapping edges the one or more coated articles (1) while restively heating.

3. The method as claimed in claim 2, wherein the predetermined range of pressure ranges from 2 Kg/cm2 to 4 Kg/cm2.

4. The method as claimed in claim 1 comprises moving the overlapping edges of the one or more articles (2) along the weld zone at a pre-determined speed between the electrodes (1) to join the one or more coated articles (2) along the entire length of the weld zone.

5. The method as claimed in claim 4, wherein the predetermined speed ranges from 0.5 to 2 m/min.

6. The method as claimed in claim 1, wherein the pre-determined intensity of electrical current ranges from 10 to 14 kA.

7. The method as claimed in claim 1, wherein tread width (a) of the electrodes (1) ranges from 4mm - 6mm.

8. The method as claimed in claim 1, wherein nominal width (b) of the electrode (1) ranges from 10mm to 12mm.

9. The method as claimed in claim 1, wherein the one or more coated articles (2) is a steel sheet with a primary coating (c) and a secondary coating (d), the primary coating (c) is a zinc-iron alloy layer, and the secondary coating (d) is a non-metallic organosilane layer.

10. The method as claimed in claim 1, wherein the thickness of the one or more coated article (2) ranges from 0.6mm to 0.8mm.

11. The method as claimed in claim 1, wherein the electrodes are defined with a chamfer angle with respect to the tread, and the chamfered angle ranges from 25° to 35°.

12. The method as claimed in claim 1, wherein the one or more coated components (2) are resistively welded to form a leak-proof joint.

13. An electrode (1) for a resistance seam welding system, the electrode (1) comprising:
an electrode wheel made of alloy of copper [Cu]-chromium [Cr]-zirconium [Zr] with Cu-Cr composition of 0.1wt% and Zr composition of 0.08wt%,
wherein, tread width (a) of the electrode wheel ranges from 4mm - 6mm,
wherein, nominal width (b) of the electrode wheel ranges from 10mm to 12 mm and the chamfer angle with respect to the tread ranges from 25° to 35°

14. The electrode (1) as claimed in claim 13, wherein the tread width (a) is preferably 6 mm.

15. The electrode (1) as claimed in claim 13, wherein the nominal width (b) of the electrode wheel is preferably 12mm.
, Description:TECHNICAL FIELD:

Present disclosure relates in general to a field of manufacturing. Particularly, but not exclusively, the present disclosure relates welding operations. Further embodiments of the present disclosure disclose a resistance seam welding system and a method of performing resistance welding of a coated article.

BACKGROUND OF THE DISCLOSURE:

The art of seam welding is relatively known, in general, seam welding is a resistance welding process that involves making a series of overlapping spot welds by means of passing one or more parts between a pair of welding electrodes. This produces a substantially continuous weld based upon the pressure applied by the welding electrodes and the electrical current passing through them. Seam welding is commonly used in the manufacture of casings, enclosures, and other components where a continuous weld is needed. Two of the more popular applications incorporating seam welding are tubular products and stamped parts. The tubular products are often pipes/tubes that are created from a flat piece of material that is rolled together to form a seam and welded along the seam. The stamped part applications include joining overlapping portions of two or more stamped parts to create another part. For instance, when creating a vessel, such as a fuel tank, two stamped halves of the tank are welded together to form the finished tank.

Resistance seam welding as iterated above produces a series of overlapping spots which finally coalesce in the form of a continuous line (also known as seam). Also, because of formation of a continuous weld line resistance seam welding produces a leak tight joint. Owing to this reason, resistance seam welding is suitable for applications where leak-tightness (liquid or gas) is required, e.g., automotive fuel tanks, mufflers, industrial barrels and drum, packaging cans etc. There are several process parameters for resistance seam welding such as, electrode force, current on/off timing, welding current and welding speed. Each of these parameters influences the weld quality separately and synergistically. For example, linear spot density (number of spots per unit length) which is critical for leak-tightness of the joint depends on the current on/off timing and welding speed both. Whereas the tensile properties of weld joint primarily depend on the welding current and welding speed. Hence, proper optimization of process parameters is essential to achieve desired joint properties.

Resistance seam welding being a relatively simple and inexpensive joining process plays an important role in high productivity low-cost mass production for example two wheelers’ fuel tank. Interstitial free steel (IF) with zinc-based coating is mostly used for automotive fuel tank fabrication owing to its enhanced formability and low spring back property. Either hot dip galvanized (HDGI) or hot dip galvannealed (HDGA) coating is used for protecting the steel from corrosion in fuel-air atmosphere. Coating of pure zinc is called HDGI whereas and the zinc–iron alloy coating is called a HDGA coating. Resistance seam welding being a surface dependent process its quality gets influenced heavily from the presence of coating, its type and thickness of coating. Around 8 -12 wt.% iron is present in the HDGA coating which increases the electrical resistivity, hardness, and melting point of the coating and thus resistance spot/seam weldability improves i.e., welding becomes viable at lower current.

Despite the superior performance offered by HDGA coating, different surface pre-treatments (e.g., chrome and phosphating) are also needed in order to ensure the good adhesion of paints to be applied in further process which guarantees long term performance of the steel. These pre-treatments are widely used due to their functional advantages; however, they produce toxic waste during their processes which may be harmful to human health and the environment. Thus, organosialanes based secondary coatings have evolved. Organosialanes are hybrid organic–inorganic molecules, derived from silane and hydrocarbons. These organosialanes are usually applied as thin films ranging from nanometer to few micrometers. Due to the hybrid nature of organosialanes, they act as a bridge between metallic surface and organic coating (primer, paint etc.) to be applied over it. Organosialanes are very effective in promoting adhesion overactive metals such as aluminum, zinc, copper, nickel, and iron. Apart from imparting excellent adhesion properties, organosialanes films also act as a physical barrier that prevents humidity and corrosive ions from reaching the metal because of their high hydrophobicity.

Organosialane based secondary coating on top of zinc based HDGI or HDGA coating modifies the surface characteristics of the steel sheets and thereby affect the resistance weldability. Typically, the contact resistance between electrode to sheet and sheet to sheet increases owing to electrical resistive nature of the secondary coating. If the resistance increases welding becomes impossible. However, a small increase in resistance, as per Joule’s law helps in generating more heat and thus welding of secondary coated steel becomes possible with current lower than that of bare or primary coated steels.
The present disclosure is directed to overcome one or more limitations stated above or any other limitations associated with the conventional arts.

The information disclosed in this background of the disclosure section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

SUMMARY OF THE DISCLOSURE

One or more shortcomings of the conventional arts are overcome by an apparatus and a method as claimed and additional advantages are provided through the provision of apparatus and the method as claimed in the present disclosure.

Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.

In one non-limiting embodiment of the disclosure, a method for joining coated articles by a resistance seam welding is disclosed. The method includes positioning one or more coated articles to be welded in a lap joint configuration between electrodes of a resistance seam welding system. The overlapping edges of the one or more coated articles to be welded define a weld zone. The electrodes are made of an alloy of copper [Cu]-chromium [Cr]-zirconium [Zr] with Cu-Cr composition of 0.1wt% and Zr composition of 0.08wt%. The method further includes resistively heating a portion of material along the weld zone by passing an electrical current of pre-determined intensity to join the one or more coated articles together.

In an embodiment of the disclosure, the method includes imparting pressure of pre-determined range by the electrodes on to the overlapping edges the coated articles while resistively heating. The predetermined range of pressure ranges from 2 Kg/cm2 to 4 Kg/cm2.

In an embodiment of the disclosure, the method includes moving the overlapping edges of the one or more articles along the weld zone at a pre-determined speed between the electrodes to join the one or more coated articles along the entire length of the weld zone. The pre-determined speed ranges from 0.5 to 2m/min.

In an embodiment of the disclosure, the pre-determined intensity of electrical current ranges from 10 to 14kA.

In an embodiment of the disclosure, tread width of the electrodes ranges from 4mm to 6mm. nominal width of the electrode ranges from 10mm to 12mm.

In an embodiment of the disclosure, the one or more coated articles is a steel sheet with a primary coating and a secondary coating. The primary coating is a zinc-iron alloy layer, and the secondary coating is a non-metallic organosilane layer.

In an embodiment of the disclosure, the thickness of the coated article ranges from 0.6mm to 0.8mm.

In an embodiment of the disclosure, the electrodes are defined with a chamfer angle with respect to the tread and the chamfered angle ranges from 25° to 35°.

In an embodiment of the present disclosure, the one or more coated components are resistively welded to form a leak-proof joint.

In another non-limiting embodiment of the disclosure, an electrode for resistance seam welding system is disclosed. The electrode comprising an electrode wheel made of alloy of copper [Cu]-chromium [Cr]-zirconium [Zr] with Cu-Cr composition of 0.1wtz% and Zr composition of 0.08wt%. Tread width of the electrode wheel ranges from 4mm – 6mm, preferably 6mm. Nominal width of the electrode wheel ranges from 10mm to 12mm, preferably 12mm. The chamfer angle with respect to the tread ranges from 25° to 35°.

It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.

The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

The novel features and characteristics of the disclosure are set forth in the appended claims. The disclosure itself, however, as well as a preferred mode of use, further objectives, and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which:

FIG.1 illustrates an exemplary schematic view of a coated article to be welded, in accordance with an embodiment of the present disclosure.

FIG.2 illustrates schematic view of a resistance seam welding system for joining the coated articles, in accordance with an embodiment of the present disclosure.

FIG.3 illustrates a portion of an electrode used in resistance seam welding system of FIG.2 depicting dimensions of the electrode, in accordance with an embodiment of the present disclosure.

FIG.4 is a flow diagram depicting method of seam welding the one or more coated articles, in accordance with an embodiment of the present disclosure.

FIG(s) 5 to 14 illustrates exemplary experimental analysis data.

The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION

The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the claims of the disclosure. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent processes do not depart from the scope of the disclosure as set forth in the appended claims. The novel features which are believed to be characteristics of the disclosure, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.

Embodiments of the present disclosure discloses a method of joining coated articles by a resistance seam welding. The method according to the present disclosure provides a defect-free and a leak-tight joint using resistance seam welding. Since, the method of the present disclosure is performed in an autogenous route, use of consumable electrodes or filler metals is eliminated. Further, the method not only produces leak-tight joints, but the leak tight joints have sufficient tensile/mechanical strength without any costly and time-consuming post weld heat treatments.

According to embodiments of the disclosure, the method of joining coated articles by the resistance seam welding may include positioning one or more coated articles to be welded in a lap joint configuration between electrodes of the resistance seam welding system. In an embodiment, the one or more coated articles may be a steel sheet with a primary coating and a secondary coating. The primary coating is a zinc-iron alloy layer, and the secondary coating is a non-metallic oraganosilane layer. The overlapping edges of the one or more coated articles to be welded may define a weld zone. In an embodiment, the method includes imparting pressure of pre-determined range by the electrodes on to the overlapping edges of the one or more coated articles. The predetermined range of pressure ranges from 2 Kg/cm2 to 4 Kg/cm2. Upon applying pressure of pre-determined range, electrical current of pre-determined intensity ranging from 10 to 14kA may be passed through the electrodes to resistively heat a portion of material along the weld zone to join the one or more coated articles together. In an embodiment, the electrodes are moved along the weld zone at a pre-determined speed to join the one or more articles along the entire length of the weld zone. The pre-determined speed ranges from 0.5m/min to 2m/min.

The terms “comprises…. a”, “comprising”, or any other variations thereof used in the specification, are intended to cover a non-exclusive inclusion, such that an assembly that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or method. In other words, one or more elements in an assembly proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the assembly.

Henceforth, the present disclosure is explained with the help of one or more figures of exemplary embodiments. However, such exemplary embodiments should not be construed as limitation of the present disclosure.

The following paragraphs describe the present disclosure with reference to FIG(s) 1 to 4. In the figures, the same element or elements which have similar functions are indicated by the same reference signs. For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to specific embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the illustrated methods, and such further applications of the principles of the disclosure as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention pertains.

The following detailed description is merely exemplary in nature and is not intended to limit application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description. It is to be understood that the disclosure may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices or components illustrated in the attached drawings and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions or other physical characteristics relating to the embodiments that may be disclosed are not to be considered as limiting, unless the claims expressly state otherwise. Hereinafter, preferred embodiments of the present disclosure will be described referring to the accompanying drawings. While some specific terms of “upper,” “lower”, “along”, or “between” and other terms containing these specific terms and directed to a specific direction will be used, the purpose of usage of these terms or words is merely to facilitate understanding of the present disclosure referring to the drawings. Accordingly, it should be noted that the meanings of these terms or words should not improperly limit the technical scope of the present invention.

FIG. 1 illustrates a representative coated article of one or more coated articles (2) to be joined by seam welding. In particular, the coated article of the one or more coated articles (2) may be stamped from sheet material, as is well known in the art. The one or more coated article (2) include portion that contact one another and create the area to be welded. Although a skilled person will appreciate that the coated article (2) may form any desired structure, in the embodiment shown, the coated article (2) when welded together form a vessel, such as a fuel tank for an automobile. The coated article of the one or more coated articles (2) according to the present disclosure may include plurality of layers of coatings. The plurality of layers of coating on the coated article may include a primary coating (c) and a secondary coating (d). Although, only primary and secondary coating is described in the present disclosure the same should not be construed as a limitation of the present disclosure. In some embodiments, more than two layers of coating may be deposited and the same falls within the scope of the present disclosure. The primary coating (c) of the present disclosure deposited on substrate i.e., sheet metal may be a zinc-iron alloy layer. The secondary coating (d) deposited on the primary layer (c) may be a non-metallic organosilane coating. The term organosilane used hereinabove and below refers to monomeric silicone-based chemicals, similar to hydrocarbons, which have at least one direct bond between a silicon atom and a carbon atom in the molecule. The organosilane coating provides a variety of improved performance of coating including weathering, adhesion, hardness etc. In an embodiment, the thickness of the one or more coated article (2) ranges from 0.6mm to 0.8mm.

Referring to FIG.2, a welding system for resistance seam welding is shown, and the system may be generally depicted by referral numeral (10). The welding system (10) may also be referred to as a resistance seam welding system (10) and may be alternatively used in the present disclosure. The welding system (10) of the present disclosure may be employed for welding the one or more coated articles (2). As depicted, the welding system (10) may include a welder, such as a seam welder with two electrodes (1). In an embodiment, the electrodes (1) may include opposed rotating electrodes formed of pre-determined composition and configuration which will be elucidated hereinafter. Each of the electrodes (1) may include an electrode wheel made of an alloy of copper [Cu]-chromium [Cr]-zirconium [Zr]. The Cu-Cr composition in the electrode wheel may be 0.1wt% and Zr composition may be 0.08wt%. Further, structure of the electrode wheel including tread width (a), nominal width (b) and the like may be designed within the pre-determined ranges. The tread width (a) [as shown in FIG.3] of the electrode wheel may range from 4mm to 6mm. In the present disclosure, the tread width (a) of the electrode wheel used for welding may be 6mm but not limiting to the same. The nominal width (b) [as shown in FIG.3] of the electrode wheel may range from 10mm to 12mm. In the welding system (10) of the present disclosure, the nominal width (b) of the electrode wheel used maybe 12mm but should not be construed as the same. As shown in FIG.3, the chamfer angle with respect to the tread ranges from 25° to 35°.

As is characteristic with the said configuration of the welder, one of the electrodes (1) may be provided with a positive voltage, while the other with a negative voltage. The welding system (10) may include a first drive mechanism and a second drive mechanism. One of the electrodes (1) may be disposed on the first drive mechanism and other electrode may be disposed on the second drives mechanism. The first and second drive mechanism may be configured to impart rotational force to the electrodes (1) during operation.

Referring now to FIG.4, which is an exemplary embodiment of the present disclosure, illustrating a flowchart of a method of fusing or joining the one or more coated articles by the said resistance seam welding.

As illustrated in FIG.4, the method comprises one or more blocks illustrating the method of fusing or joining the one or more coated articles by the said resistance seam welding. The method may be described in the general context of computer-executable instructions. Generally, computer- executable instructions can include routines, components, procedures, modules, and functions, which perform functions.

The order in which the method is described is not intended to be construed as a limitation, and any number of the described method blocks can be combined in any order to implement the method. Additionally, individual blocks may be deleted from the methods without departing from the spirit and scope of the subject matter described herein.

In operation and as shown in FIG.4 [in conjunction with FIG(s) 1 to 3], the method of fusing or joining the one or more coated articles by the said resistance seam welding includes positioning of the one or more coated articles (2) to be welded in lap joint configuration between the electrodes (1) [as shown at block 201]. Upon positioning the one or more coated articles (2), the edges of the one or more coated articles (2) overlap. The overlapping edges of the one or more coated articles (2) to be welded define a weld zone. Once the weld zone is positioned between the electrodes (1), pressure of predetermined range may be imparted by the electrodes (1) onto the overlapping edges i.e., the weld zone of the one or more coated articles (2). The pre-determined range of pressure imparted by the electrodes (1) may range from 2 Kg/cm2 to 4 Kg/cm2.

Once the one or more articles (2) is held between the electrodes upon imparting pressure [as shown at 202], a portion of material along the weld zone may be resistively heated by passing an electrical current of pre-determined intensity [as shown at block 203]. The pre-determined intensity of current may range from 10kA to 14kA. Resistively heating a portion of the material along the weld zone melts the material and fuses the one or more coated materials (2) together. In some embodiments, the weld zone formed by the overlapping edges of the one or more coated materials (2) may be moved between the electrodes (1) at a pre-determined speed to join the one or more coated articles (2) along the entire length of the weld zone [at block 104]. The speed at which the electrode is moved along the weld zone may range from 0.5m/min to 2m/min. Welding the one or more coated articles (2) along the weld zone by the said method ensures defect free weld along the entire length of weld zone.

Exemplary Experimental analysis

Following paragraphs may be illustrate exemplary experimental results illustrating test parameters for resistance seam welding. The present experimental analysis deals with two types of coated interstitial free (IF) steel sheets of 0.8mm thickness. The coated IF steel may be galvannealed (Zn-12%Fe alloy coated) steel, with one having a secondary coating on top of the galvannealed coating. Hereinafter, the galvannealed coated steel and the secondary coated galvannealed steel are designated as IF-GA and IF-TC, respectively. The thickness of the galvannealed coating is 6+/-2µm. corresponding to 70gm/m2 of coating deposition on either sides. The secondary coating, non-metallic inorganic coating, is applied by a commercial roll coater maintaining the coating thickness between 1-3 µm.

The seam welding experiment is carried out using a 450kVA medium frequency direct current (MFDC) resistance seam welding machine operating at 1000Hz. A pair of electrodes of the configuration of the present disclosure is used in the welding process. Rectangular pieces of steel sheets are welded in a lap configuration of approximately 100mm of weld zone length. Welding parameters such as welding current and welding speed is varied between 8-18kA and 0.5-2 m/min respectively while electrode pressure was kept constant at 3kg/sq.cm. These welded specimens are peeled off to determine the failure mode which is required to construct the weldability lobe. The mechanical performance of weld joints has been evaluated by tested cross tensile specimens in an instron machine with constant crosshead velocity of 3mm/min. The transverse sections of welds are metallographically prepared followed by two step etching 4% Picral and 2% nital solution, respectively. Optical and electronic examination of the etched specimen are carried out using optical microscope and scanning electronic microscope.

The weldability lobes of IF-TC and IF-GA steels have been depicted in FIG.5a and 5b, respectively. The line “G” in the weldability lobes indicates the lower boundary whereas the line “P” constitutes the upper boundary. The topmost line “R” denotes heavy copper ingression in the weld surface. So, below the line “G” the weld is expected to fail in either IF or PPF mode owing to underdeveloped nugget growth, which is not acceptable in the auto-industry. If the weld current exceeds the upper boundary (i.e., the line P) copper ingression in the weld surface and zinc ingression in the copper electrode would take place and thereby restrict the working life of electrodes.

Referring now to FIG.6 (a and b), which depicts nugget growth behavior i.e., nugget width measured in peel test plotted against the welding current corresponding to different welding speeds for IF-TC and IF-GA steels, respectively. It can be noted from FIG.6a for IF-TC steel that the nugget width varies from 2.20mm at 7.0kA to 7.11mm at 15.0 kA for different welding speeds between0.5-2 m/min. Similarly, for IF-GA steel [refer FIG.6b] the nugget width varies from 2.3mm at 9.0kA to 6.14mm at 15.0kA. For both the steels, the nugget width monotonically increases with welding current. Higher welding current results into higher heat input and thereby helps in nugget growth. Further, FIG.7(a and b) shows maximum load bearing capacity of the welded joints as functions of welding current for IF-TC and IF-GA steel, respectively. For IF-TC steel, the maximum load carrying capacity is found to be independent of welding current and welding speed varied between 9-14kA and 0.5-2.0m/min respectively. All welded joints shown 7.25+/-0.25kN maximum load bearing capacity for IF-TC steel. However, for IF-GA steel, the maximum load increase as the welding current increases. For welding speed of 1m/min, maximum load increases from 3.6kN to 6.5kN as the current increases from 9kA to 10kA thereafter it becomes constant. However, for welding speed 1.5 and 2m/min, joints failed prematurely when welded with 9kA current. Joints welded with 10kA showed maximum load at 3.5-4kN which increase to 6.5kN when welded with 12 and 14kN of current. Higher welding speed leads to lower heat input and smaller nugget. 9kA of welding current is insufficient to produce proper joint when working with IF-GA steel. On contrary, IF-TF steel, owing to its larger weld-nugget and thereby resulted into joints which are 15% stronger than the joints with IF-GA steels under identical welding condition.

FIG.8a shows an etched macrostructure of longitudinal section of an IF-TC joint welded with 12kA current, 1.5 m/min speed and 3kg/cm2 electrode force. This set of welding parameters belongs to center of the weldability lobe. Two major observations may be made from the image 7a, firstly there is no presence of mating line that is usually there when the welding is not done with proper set parameters. This indicates that the specimen produces through good welding condition. It also, re-established the importance of weldability lobe for identifying the right parameter window for continuous production purpose. Secondly, there are few enclosed micro-voids which can be observed. However, they are almost spherical in shape and very small compared to weld nuggets. Hence, those micro voids would not affect the mechanical performance of the joints. The same specimen when tested in tensile mode recorded the maximum load bearing capacity as 7kN [FIG.7a], which indeed indicates that the defects did not affect the joints mechanical performance. Also, being enclosed defects, these voids would not create a continuous path for a fluid to leak across the weld hence suitable for producing leak tight components such as automotive fuel tanks.

FIG.8 (b) shows a representative macrostructure of weld cross section of the same specimen represented in FIG.8 (a). This image shows conspicuously three different regions formed due to welding such as base metal (BM), heat affect zone (HAZ) and fusion zone (FZ). The high magnification microstructures of each of these three zones are given in FIG(s) 8 (c), 8 (d) and 8 € respectively. The BM consists of equiaxed ferrite grains typical of IF steel. The ferrite grain morphology remains unchanged as this part did not get exposed to high temperatures during welding. At the center of the welded specimen, the elliptical nugget area is the FZ which again shows equiaxed grains. The equiaxed nature of the grains in the FZ originates from the forging action of the electrodes as well as presence of near circular/elliptical temperature fields. The columnar grains present between the BM and FZ consist of the HAZ. Directional heat flow from FZ to BM through the HAZ leads to columnar grains formation which is retained after transformation to ferrite. The structures observed in the FZ could be referred to as quasi-polygonal ferrite and bainite.

FIG.9 (a) represents the same IF-TC weld cross section shown in FIG.8 (b) where three areas were marked with number 1, 2, and 3. Few inclusions/intrusions have been observed in those areas. High resolution SEM photomicrographs of those defects are presented in FIG(s) 9 (b), 9 (c) and 9 (d), respectively. FIG.9b depicts the small (10-12 micrometer) metallic intrusions that have been percolated from the surface’s GA coating to inside along the ferrite grain boundaries. The EDS spectra of these intrusion indicate presence of appreciable amount Cu (58%) and Zn (19.3%). These intrusions are small in size and would hardly affect the tensile performance of the joint. However, as the welding current increased to 16kA (keeping other parameters constant) the dimensions of such surface intrusions became appreciably large, as 100 micrometer. Also, in few cases, complicated network structures were formed instead of liner intrusion. FIG(s) 11 and 12 represent such cases. Elemental mapping (as shown in FIG.11) of such intrusions qualitatively indicate presence of Al and O along with Cu and Zn. Intrusion length of around 100 micrometer in a sheet thickness of 0.8mm is a serious threat, as it occupies nearly 12.5% of the thickness and thereby should be avoided.

The SEM images of the defects observed in the area marked as 2 and 3 in FIG.9a are presented in FIG(s) 9 (c) and 9 (d), respectively. These defects are spherical Zn rich inclusions. The typical size of such inclusions varies between 5 micrometer to 25micrometer. EDS spectra obtained from such inclusions show [FIG.10b] presence of Si (12%), O (34%), Al (11%), Mn (1.8%) and Ti (0.9%) along with Zn (28%). However, presence of Cu in the inclusions is not detected. The Cu in the surface intrusions must have come from the welding electrode which is not detected. The Cu in the surface intrusions must have come from the welding electrode which was in contact with the steel surface in the area marked 1. On the contrary, area marked 2 and 3 is not in contact with the steel surface in the area marked 1. On the contrary, area marked 2 and 3 are not in touch with electrodes and thus devoid of Cu. During welding, temperature in these zone (above melting point of steel i.e., 1500 deg. Celsius) reaches well above the boiling point of Zn (910°C) and other Zn-FE phases present in the GA coating. Those liquid and gaseous phases in the molten weld pool accumulate around the already present intrinsic inclusions formed by Si-Al-Mn-O and rapidly solidifies due to the extremely fast cooling imposed by the resistance seam welding electrodes and direct water quenching. Unlike surface intrusions, the dimensions of these inclusions do not change with welding current or heat input. Further, the experimental results for leak performance of the joints are elucidated.

The leak performance of seam welded joint has been evaluated by measuring the maximum air pressure that the pillow made by resistance seam welding can withstand. These tests are carried out in a specially designed leak test facility. The pillow specimens is pressurized slowly (using compressed air) [pressurization curve is shown in FIG.14] to desired pressure (max upto 5kg/sq.cm) and the leak rate is being monitored. If there is any major leak the pillow specimen is submerged in the water automatically to identify the leak location. Leak performance of the joints produces with different weld current between11kA to 14kA is presented in FIG.14. The maximum pressure where the leak occurred, and the corresponding leak rates are plotted as function of welding current. Also, the corresponding leak rates have been decreased. This is expected as higher welding current leads to bigger weld nugget which eventually reduces the chance of defects which may lead to leakage.

In an embodiment, the method according to the present disclosure provides a defect-free and a leak-tight joint using resistance seam welding. Since, the method of the present disclosure is performed in an autogenous route, use of consumable electrodes or filler metals is eliminated. Further, the method not only produces leak-tight joints, but the leak tight joints have sufficient tensile/mechanical strength without any costly and time-consuming post weld heat treatments.

It is to be understood that a person of ordinary skill in the art may develop a system of similar configuration without deviating from the scope of the present disclosure. Such modifications and variations may be made without departing from the scope of the present invention. Therefore, it is intended that the present disclosure covers such modifications and variations provided they come within the ambit of the appended claims and their equivalents.

Equivalents

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

It will be understood by those within the art that, in general, terms used herein, are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding the description may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated in the description.

Referral Numerals:
Description Reference number
Resistance seam welding system 10
Electrodes 1
Coated article 2
Tread width a
Width of electrode b
Primary coating c
Secondary coating d
201-204 Flow chart blocks