DESC:FORM 2

THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENT RULES, 2003

COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

Title of invention:
A METHOD OF MIG-ARC FUSION SPOT WELDING FOR STAINLESS STEEL TO IMPROVE SURFACE QUALITY

Applicant:
BEML Limited
A company Incorporated in India under the Companies Act, 1956
Having Address As:
BEML Soudha, 23/1, 4th Main,
Sampangirama Nagar, Bengaluru - 560 027,
Karnataka, India

The following specification particularly describes the subject matter and the manner in which
it is to be performed.

CROSS-REFERENCE TO RELATED APPLICATIONS AND PRIORITY
[001] The present invention claims priority from Indian patent application numbered IN 202341065817 filed on 29th September, 2023.

FIELD OF THE INVENTION
[002] The present invention relates to the field of welding, more specifically focusing on the establishment of welding process parameters (WPS) for the metal inert gas (MIG-ARC) fusion spot welding for indigenously developed stainless steel sheets to improve its flatness and reduce distortion.

BACKGROUND

[003] In the construction of these rail cars, welding plays an important role. Rail cars use special austenitic grade stainless steel sheets/coils, with specific chemical, mechanical, and metallurgical intergranular corrosion (IGC) tests, dimensional tolerances, etc. The underframe assembly of the rail car is manufactured with the above stainless steel sheets. Due to poor welding, there are issues like weld distortion of cross members and keystone plate assembly. It results in uneven flatness beyond acceptable limits, which required reworks/weld repairs. Also in some cases, the pre-camber values are beyond the limit due to weld distortion and it requires rework. Its outcome is delay in production and increased the cost of production.

[004] Poor welding results in weld cracks, distortion, rough surface finish, and uncontrolled flatness. The weldability of steel depends on many factors like, heat input, wire feed rate, applied current and voltage, shielding gas, etc. Existing technology followed by rail car manufacturers considers different welding parameters. Also wire feed rate and heat input are not considered in order to overcome the above mentioned problems.

Cited Prior arts
Some of the relevant patents covering methods of welding with improved surface finish are as follows:
[005] CN108044223A discloses the welding method of stainless steel belt and being prepared by this method. The welding is carried out using consumable electrode active gases protection (MAG) welding. With small weld heat input, deformation is small, even weld is consistent using the welding method, and ensure that broken belt does not occur during operation for steel band.
[006] IN-CHE-2005-00248A discloses new GMAW process that increases the life of the structures and improves the weld quality by using the combination of CO2 & Ar Mixtures (Ar + CO2 +O2) for welding (in a single joint) with the help of 'V' Connector. This results in nearly flat (less convex) geometry with nil under cuts and spatters.
[007] CN112719704A discloses a steel plate welding method. The steel plate welding method is used for welding and connecting a first steel plate and a second steel plate. According to the steel plate welding method, the gap between the welding face of the first steel plate and the second steel plate is matched with the positioning groove in the gasket base plate to form the positioning welding groove, welding is conducted in the positioning welding groove, a dense welding seam is formed in the positioning welding groove, the defect of cracks formed in the welding seam is avoided, and therefore, the quality of the welding seam is improved.
[008] Hence, to overcome the aforesaid drawbacks, an improved welding parameters are needed.
OBJECTS OF THE INVENTION

[009] Main object of the present disclosure is to provide a method of MIG- ARC fusion spot welding for stainless steel to improve surface quality.
[0010] Another objective of the present disclosure is to provide welding process parameters for MIG-ARC fusion spot welding of similar stainless steel plates.
[0011] Yet another objective of the present disclosure is to provide a way of reducing distortion in welds.
[0012] Another objective of the present disclosure is to provide reduction in pre-cambers values within a specified limit.
[0013] Yet another objective of the present disclosure is to provide flatness of weld within tolerable limits of 3 mm/m.
[0014] Another objective of the present disclosure is to provide optimum heat input, which is less than 1 kJ/mm.
[0015] Yet another objective of the present disclosure is to provide reduction in rework and save time and cost of welding.
[0016] Another objective of the present disclosure is to provide a minimum wire feed rate of welding electrode.

SUMMARY

[0017] Before the present MIG-ARC fusion spot welding for stainless steel to improve surface quality is described, it is to be understood that this application is not limited to a particular MIG-ARC fusion spot welding for stainless steel to improve surface quality as there may be multiple possible embodiments, which are not expressly illustrated in the present disclosures. It is also to be understood that the terminology used in the description is for the purpose of describing the particular implementations, versions, or embodiments only, and is not intended to limit the scope of the present application. This summary is provided to introduce aspects related to a MIG-ARC fusion spot welding for stainless steel to improve surface quality. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.
[0018] The invention provides a method of MIG- ARC fusion spot welding for stainless steel to improve surface quality. Stainless steel sheets welding method to solve the technical problems of weld cracks, distortion in welds, pre-camber value due to poor weld and improved flatness of weld.
[0019] The present invention provides a method of the metal inert gas (MIG-ARC) fusion spot welding for stainless steel to improve surface quality for rail car under-frame assembly. Indigenously developed stainless steel & special corrosion resistant steel made keystone plates are welded on the underframe assembly of the rail car. To ensure the flatness & optimum pre-camber values, additional weld parameters like wire feed rate & heat input rate are considered. The welding parameters are developed to suit special requirements of keystone plate’s flatness and achieve pre-camber values as per drawing. The distortion in cross member of underframe assembly is also controlled. MIG-ARC fusion spot welding is carried out on samples of stainless steel sheets. These samples are prepared with 4 mm thickness and 0.8 mm thickness from stainless steel sheets for lap joint, the MIG- ARC fusion spot welding is carried out with a certified welding operator on calibrated robotic welding machine. Several trials are carried out by varying parameters like current, voltage and gas flow rate. First current is controlled between 160 -180 A in step of 15 A and voltage is controlled between 20 – 22 V in step of 1V and the gas flow rate is maintained at a rate of 14-16 L/min in step of 2 L/min.

[0020] To check the quality of weld, 3 sets of each combination of samples are tested. A weld spot is observed with surface diameter of 15 mm, nugget diameter of 4.5 mm and depth of penetration is 15% as per quality requirement. Also, the heat input rate for each sample is observed to be within the range of less than 1 kJ/mm. It reduces the distortion in the weld spot. Based on the above detailed testing, optimum weld parameters are established to meet specific requirements. Also, distortion of weld spot is also controlled.

STATEMENT OF INVENTION

[0021] The present invention discloses a method of metal inert gas (MIG-ARC) fusion spot welding for stainless steel sheets comprising steps of pre-treating of stainless steel sheets to be welded; tack welding the pre-set stainless steel sheets to be welded; MIG-ARC fusion spot welding of stainless steel sheets to obtain a single beaded weld with a predefined range of gas flow rate of shielding gas, a predefined range of voltage, a predefined range of current, a predefined wire feed rate, a preselected consumable metal wire and a predefined torch angle of the welding gun.

[0022] The present invention also discloses the pre-treating of the said stainless steel sheets is configured by shearing or laser cutting or grinding or cleaning. The shielding gas is configured from 98 % of argon and 2% of oxygen. The predefined range of gas flow rate is configured to be between 14-16 litre/min in step of 2 litre/min. The predefined range of voltage is configured to be between 20 Volts to 22 Volts in a step of 1Volt. The predefined range of current is configured to be between 160 Ampere to 180 Ampere in step of 15 Ampere. The predefined wire feed rate is 8.5 mm/min. The preselected consumable metal wire is of designation ISO 14343 (AWS SFA 5.9 ER 308L) with diameter of 1.2 mm. The predefined torch angle of the welding gun is configured to be within a range of 70-90 degrees. The flatness of the said single beaded weld of the stainless steel sheet is configured to be less than 3 mm/m.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The foregoing summary, as well as the following detailed description of embodiments, is better understood when read in conjunction with the appended drawings. For illustrating the disclosure, there is shown in the present document example constructions of the disclosure. The detailed description is described with reference to the following accompanying figures.

[0024] Figure 1 illustrates a flow diagram for a method of MIG- ARC fusion spot welding for stainless steel in a preferred embodiment of the present invention.

[0025] Figure 2 illustrates the elevation and plan of the rail car floor assembly indicating welded spots in a preferred embodiment of the present invention.

[0026] Figure 3 illustrates a details of weld preparation in a preferred embodiment of the present invention.

[0027] Figure 4 illustrates pre-camber values of the underframe assembly of the rail car in a preferred embodiment of the present invention.

[0028] The figure depicts various embodiments of the present disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following discussion 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 OF INVENTION

[0029] Some embodiments of this disclosure, illustrating all its features, will now be discussed in detail. The words "comprising", “having”, and "including," and other forms thereof, are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. It must also be noted that as used herein and in the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Although any devices and methods similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present disclosure, the exemplary, devices and methods are now described. The disclosed embodiments are merely exemplary of the disclosure, which may be embodied in various forms.

[0030] Various modifications to the embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. However, one of ordinary skill in the art will readily recognize that the present disclosure is not intended to be limited to the embodiments illustrated, but is to be accorded the widest scope consistent with the principles and features described herein.

[0031] The present subject matter discloses a method of metal inert gas (MIG-ARC) fusion spot welding for stainless steel to improve surface quality. Indigenously developed stainless steel & special corrosion resistant steel made keystone plate are welded on the underframe assembly of the rail car. To ensure the flatness & optimum pre-camber value, additional weld parameters like wire feed rate & heat input rate are considered.

[0032] Referring to figure 1, wherein figure 1 discloses a flow diagram for MIG-ARC fusion spot welding for stainless steel to improve surface quality. A method (100) of metal inert gas (MIG-ARC) fusion spot welding for stainless steel sheets comprising steps of pre-treating of stainless steel sheets to be welded (102). The shearing or laser cut or grinding or cleaning method is utilized for pre-treating the stainless steel sheets (102). Once the stainless steel sheets are pre-treated, tack welding is done before starting of actual welding process (104). Further, MIG-ARC fusion spot welding is done to obtain a single beaded weld with a predefined range of gas flow rate of the shielding gas; a predefined range of voltage, a predefined range of current, a predefined wire feed rate, a preselected consumable metal wire and a predefined torch angle of the welding gun (106).

[0033] Referring to figure 2, in an embodiment, the underframe assembly of the rail car (200) is shown. The stainless steel plates are welded to the underframe assembly (200). The stainless steel plates are welded with MIG-ARC fusion spot welding method (100). The specification of stainless steel sheets is GR/TD/1456 rev5, grade SUS 301L ST-2B finish, thickness 0.8 mm & 4 mm. The stainless steel sheets are utilized as keystone plate. The MIG-ARC fusion spot welding is performed to weld keystone plates to under assembly (200) forming a lap joint, under observation of a certified operator. The MIG-ARC fusion spot welding is done on a robotic welding machine. A torch angle of the welding gun is maintained between 70-90 degrees. A shielding gas consisting of argon 98% and oxygen 2%. During the MIG-ARC fusion spot welding, the shielding gas protects the welding arc and weld pool from the environment and contaminants. The gas flow rate is controlled at rate of 14-16 litre/min in step of 2 litre/min. The 135 (MAG) welding process creates heat from an electric arc between a consumable metal wire and stainless steel sheets or keystone plates. This creates a weld pool and fusing them together and forming a lap joint. The consumable metal wire used for welding is of designation ISO 14343 (AWS SFA 5.9 ER 308L) with diameter of 1.2 mm. A wire feed rate is maintained at 8.5 mm/min during welding. The mode of material transfer is short circuiting current. The direction of current flow in welding circuit is direct current electrode positive (DCEP). The voltage is controlled between 20 Volts to 22 Volts in a step of 1Volt. The current is controlled between 160 Ampere to 180 Ampere in step of 15 Ampere. A run out length is controlled at rate of 350/65 mm/sec. The heat generated with the said input is less than 1kJ/min.

[0034] In an embodiment, referring to Figure 3, the keystone plates are formally welded. A sample welding test is conducted for keystone plates with thickness of 0.8 mm, 0.8 mm & 4 mm. For each combination, 3 set of samples are tested for weld spots. It is observed that surface diameter of weld spot is 15 mm and nugget diameter is 4.5 mm. The depth of penetration is observed as 15% as per quality requirement. The flatness observed with this welding method is less than 3 mm/meter, where flatness indicates optimum variations in any surface.

[0035] Referring to figure 4, figure 4 discloses the underframe assembly or floor assembly of the rail car with pre-camber values. Further, the pre-camber value requirement is also fulfilled with this technique, where pre-camber value indicates the curve structure of the floor assembly of rail car underframe.

[0036] Using the above stated method, for welding keystone plates to the underframe assembly of rail car, the surface quality of the welded surface is improved in terms of reduced weld cracks and distortions. It also helps in achieving required pre-camber value and further it reduces the flatness of the weld below 3 mm/m. This method also reduces the reworking of older welds and saves time and cost on welding.
[0037] Exemplary embodiments discussed above may provide certain advantages. Though not required to practice aspects of the disclosure, these advantages may include those provided by the following features.

[0038] The present invention discloses a method of metal inert gas (MIG-ARC) fusion spot welding (100) for stainless steel sheets comprising steps of pre-treating (102) of stainless steel sheets to be welded; tack welding (104) the pre-set stainless steel sheets to be welded; MIG-ARC fusion spot welding (106) of stainless steel sheets to obtain a single beaded weld with a predefined range of gas flow rate of shielding gas, a predefined range of voltage, a predefined range of current, a predefined wire feed rate, a preselected consumable metal wire and a predefined torch angle of the welding gun.

[0039] The present invention also discloses the pre-treating of the said stainless steel sheets is configured by shearing or laser cutting or grinding or cleaning. The shielding gas is configured from 98 % of argon and 2% of oxygen. The predefined range of gas flow rate is configured to be between 14-16 litre/min in step of 2 litre/min. The predefined range of voltage is configured to be between 20 Volts to 22 Volts in a step of 1Volt. The predefined range of current is configured to be between 160 Ampere to 180 Ampere in step of 15 Ampere. The predefined wire feed rate is 8.5 mm/min. The preselected consumable metal wire is of designation ISO 14343 (AWS SFA 5.9 ER 308L) with diameter of 1.2 mm. The predefined torch angle of the welding gun is configured to be within a range of 70-90 degrees. The flatness of the said single beaded weld of the stainless steel sheet is configured to be less than 3 mm/m.
[0040] Some embodiments of the present subject matter is to provide a method of MIG- ARC fusion spot welding for stainless steel to improve surface quality.
[0041] Some embodiments of the present subject matter is to provide welding process parameters for MIG-ARC fusion spot welding of similar stainless steel plates.
[0042] Some embodiments of the present subject matter is to provide a way of reducing distortion in welds.
[0043] Some embodiments of the present subject matter is to provide reduction in pre-cambers values within a specified limit.
[0044] Some embodiments of the present subject matter is to provide flatness of weld within tolerable limits of 3 mm/m.
[0045] Some embodiments of the present subject matter is to provide optimum heat input, which is less than 1 kJ/mm.
[0046] Some embodiments of the present subject matter is to provide reduction in rework and save time and cost of welding.
[0047] Some embodiments of the present subject matter is to provide a minimum wire feed rate of welding electrode.
[0048] Following is a list of elements and reference numerals used to explain various embodiments of the present subject matter.
Reference Numeral Element Description
100 A method of MIG- ARC fusion spot welding for stainless steel
102 Pre-treating/ repairing and cleaning of stainless steel sheets to be welded
104 Performing tack weld on the pre-set stainless steel sheets to be welded
106 Performing MIG ARC fusion spot welding to obtain a single beaded weld with controlled gas flow rate of shielding gas; controlled voltage, controlled current and controlled wire feed rate, a preselected consumable metal wire and a predefined torch angle of the welding gun.
200 An underframe assembly of rail car

Equivalents
[0049] 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.
[0050] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) 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 following appended claims 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, claims, 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."
[0051] Although implementations for the specified a method of MIG-ARC fusion spot welding for stainless steel to improve surface quality in language specific to structural features and/or system, it is to be understood that the appended claims are not necessarily limited to the specific features or described. Rather, the specific features are disclosed as examples of implementations.
,CLAIMS:
1. A method of metal inert gas (MIG-ARC) fusion spot welding (100) for stainless steel sheets comprising steps of:
? pre-treating (102) of stainless steel sheets to be welded;
? tack welding (104) the pre-set stainless steel sheets to be welded;
? MIG-ARC fusion spot welding (106) of stainless steel sheets to obtain a single beaded weld with a predefined range of gas flow rate of shielding gas, a predefined range of voltage, a predefined range of current, a predefined wire feed rate, a preselected consumable metal wire and a predefined torch angle of the welding gun.

2. The method (100) as claimed in claim 1, wherein the pre-treating of the said stainless steel sheets is configured by shearing or laser cutting or grinding or cleaning.

3. The method (100) as claimed in claim 1, wherein the shielding gas is configured from 98 % of argon and 2% of oxygen.

4. The method (100) as claimed in claim 1, wherein the predefined range of gas flow rate is configured to be between 14-16 litre/min in step of 2 litre/min.

5. The method (100) as claimed in claim 1, wherein the predefined range of voltage is configured to be between 20 Volts to 22 Volts in a step of 1Volt.

6. The method (100) as claimed in claim 1, wherein the predefined range of current is configured to be between 160 Ampere to 180 Ampere in step of 15 Ampere.

7. The method (100) as claimed in claim 1, wherein the predefined wire feed rate is 8.5 mm/min.

8. The method (100) as claimed in claim 1, wherein the preselected consumable metal wire is of designation ISO 14343 (AWS SFA 5.9 ER 308L) with diameter of 1.2 mm.

9. The method as claimed in claim 1, wherein the predefined torch angle of the welding gun is configured to be within a range of 70-90 degrees.

10. The method (100) as claimed in claim 1, wherein the flatness of the said single beaded weld of the stainless steel sheet is configured to be less than 3 mm/m.