Claims:We claim:
1. A method for configuring a Tungsten Inert Gas (TIG) welding machine for performing dual-pass TIG welding on a steel plates of 6 mm thick in a square butt joint configuration, the method comprising:
on receiving user input for configuration for dual-pass TIG welding on a steel plates of 6 mm thick in a square butt joint configuration, configuring the setting of the TIG welding machine with:
a. ceriated tungsten electrode – 4 mm diameter with 45° included angle;
b. gap between the electrode tip and work piece - 3±0.5 mm;
c. angle between electrode and workpiece - 70±2°; and
d. voltage 18±0.4V, current 190±5 A, travel speed 150±10 mm/min, root gap 1 mm, Argon gas flow rate 12±5 lit/min.
2. The method as claimed in claim 1, wherein the steel plate is of ultra-high strength / armour grade.
3. The method as claimed in claim 1 and 2, wherein the steel plate is 6 mm thick.
4. The method as claimed in claim 1, wherein the TIG welding machine is Fronius Magic Wave 4000.
5. The method as claimed in claim 1, wherein the steel plates are arranged in square butt joint design configuration with an included angle of 90°.
6. The method as claimed in claim 1, the dual-pass TIG welding performed with the configured TIG welding machine ensures that even the , Description:MACHINE
TECHNICAL FIELD
[0001] The present disclosure, in general, relates to the field of metal processing and, more particularly, to an automated configuration setting system for setting a Tungsten Inert Gas (TIG) welding machine for performing dual-pass TIG welding on a steel plates of 6 mm thick in a square butt joint configuration.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] In modern day battlefield, there is a need for protection against small-arms and light weapons for military vehicles and structures. In design of such protective structures against high speed projectiles, ultra-high strength steel is the material of choice. Although technologically advanced and lightweight composite/ceramics based armours are available none of those materials are commercially viable like steel. Such steels are known as armour grade steels. These are typically quenched and tempered (Q&T) low alloy steels being used in both structural, abrasion resistant and armour applications due to its high strength and toughness obtained from their unique tempered martensitic microstructure toughened with fine coherent precipitates.
[0004] However, during welding these steels perform poorly owing to two distinct phenomena: (1) Hydrogen Induced Cracking (HIC) also known as cold cracking - where internal cracks brought about by trapped hydrogen atoms within the weld region; and (2) Heat Affected Zone (HAZ) softening - due to weld thermal cycle the martensite phase in the HAZ gets tempered and losses its hardness. The ballistic performance of armour steel joints used in combat vehicle also affected badly due to these shortcomings of welding. Hence, it is crucial to optimise of the welding parameters to attain superior toughness. It is a challenge in thick plates because of microstructure variations in the weld joint under the influence of multiple thermal cycles. Further the mechanical properties at the fusion zone and heat affected zone (HAZ) are significantly different from the base metal as they have different thermal history. The toughness of the HAZ can be studied with help of fracture toughness measurements on samples extracted from the HAZ.
[0005] A common problem in welding of ultra-high strength (1800-2000 MPa) steel is unavailability of welding electrodes of matching strength. Commercially available welding electrodes reach (in terms of strength) up to 1000 MPa which is only 50% of the base metal strength. During ballistic test, these softer filler metal would let the ammunition pass through it and thus the join could fail. Such unwanted situation can be avoided by increasing the strength (or hardness) of the fusion zone. There are two possible ways to achieve that: (1) welding with electrodes having strength identical to base metal’s strength; and (2) autogenous welding i.e. using energy source for melting the base metal – no low strength filler metal is used. In the present problem, autogenous welding route has been explored where the electric arc created between a tungsten electrode and base metal has been used as source of energy for melting the base metal which on cooling joins the two plates.

OBJECTS OF THE DISCLOSURE
[0006] In view of the foregoing limitations inherent in the state of the art, some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed hereinbelow.
[0007] It is a general object of the present disclosure to develop a method for obtaining defect free weld in autogenous route (i.e. without using welding electrodes / filler metal) without compromising the fracture toughness of heat affected zone (HAZ) by tweaking the weld parameters which can be easily adoptable in practice.
[0008] It is an object of the present disclosure to do away with any costly and time-consuming post weld heat treatments for improving the mechanical properties of the heat affected zone.
[0009] It is another object of the present disclosure to engineer the microstructure of HAZ to achieve fine grain size which eventually obtains good fracture toughness. HAZ softening and prior excessive austenite grain growth are typical issues welding of ultra-high strength steel sheets which leads to decrease in fracture toughness around the weld zone.
[0010] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY
[0011] This summary is provided to introduce concepts related to an automated configuration setting system for setting a Tungsten Inert Gas (TIG) welding machine for performing dual-pass TIG welding on a steel plates of 6 mm thick in a square butt joint configuration. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0012] In an embodiment, the present disclosure relates to a method for configuring a Tungsten Inert Gas (TIG) welding machine for performing dual-pass TIG welding on a steel plates of 6 mm thick in a square butt joint configuration. In an aspect, on receiving user input of configuring for dual-pass TIG welding on a steel plates of 6 mm thick in a square butt joint configuration, configuring the setting of the TIG welding machine with:
i. Ceriated tungsten electrode – 4 mm diameter with 45° included angle;
ii. Gap between the electrode tip and work piece - 3±0.5 mm;
iii. Angle between electrode and workpiece - 70±2°; and
iv. voltage 18±0.4V, current 190±5 A, travel speed 150±10 mm/min, root gap 1 mm, Argon gas flow rate 12±5 lit/min.
[0013] In an aspect, the steel plate is of ultra-high strength / armour grade.
[0014] In an aspect, the steel plate is 6 mm thick.
[0015] In an aspect, the TIG welding machine is Fronius MagicWave 4000.
[0016] In an aspect, the steel plates are arranged in square butt joint design configuration with an included angle of 90°.
[0017] In an aspect, the dual-pass TIG welding performed with the configured TIG welding machine ensures that even the weakest part of the heat affected zone (HAZ) retains 90% of the fracture toughness of base metal.
[0018] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
[0019] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and methods that are consistent with the subject matter as claimed herein, wherein:
[0020] FIG. 1(a) illustrates a schematic showing the sheet edge preparation required for the welding;
[0021] FIG. 1(b) illustrates an image showing welding setup;
[0022] FIG. 2(a) illustrates a macro-structure of the joint prepared with the parameters: 190 A welding current, 18.1 V, 150 mm/min speed and 0 mm root gap. Incomplete penetration can be seen;
[0023] FIG. 2(b) illustrates a macro-structure of the joint prepared with the parameters: 190 A welding current, 18.1 V, 150 mm/min speed and 1 mm root gap. Complete penetration can be seen;
[0024] FIGS. 3(a) and 3(b) illustrate condition of welded sheets as seen from the top and side;
[0025] FIG. 4(a) illustrates macrostructure of successfully welded joint showing different parts of the region;
[0026] FIG. 4(b) illustrates microstructure of fusion zone;
[0027] FIG. 4(c) illustrates microstructure of coarse grain heat affected zone (CGHAZ);
[0028] FIG. 4(d) illustrates microstructure of fine grain heat affected zone (FGHAZ);
[0029] FIG. 4(e) illustrates microstructure of tempered heat affected zone (THAZ);
[0030] FIG. 4(f) illustrates microstructure of base metal (BM);
[0031] FIG. 5(a) illustrates a microhardness profile across the weld region;
[0032] FIG. 5(b) illustrates a macrostructure showing lines along which microhardness readings have been measured;
[0033] FIG. 6(a) illustrates a schematic showing position of fracture plane in test specimen with respect to weld zone;
[0034] FIG. 6(b) illustrates a fracture toughness specimen geometry;
[0035] FIG. 6(c) illustrates a position of fracture plane in test specimen with respect to weld zone;
[0036] FIG. 7 illustrates a load versus extension plots for all test specimens; and
[0037] FIG. 8 illustrates a fracture plane as observed through stereomicroscope in all test specimens.
DETAILED DESCRIPTION
[0038] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0039] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0040] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, “consisting” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0041] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0042] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0043] The current methodology developed by optimizing the weld parameters was successful in solving issues faced in autogenous tungsten inert gas (TIG) welding such as lack of fusion, under cut, entrapped porosity and cracks. The weld was free of any defects with sufficient penetration in the roots. The subsequent fracture toughness study confirmed superior toughness in the heat affected zone (HAZ). The fracture toughness in the HAZ was as good as the toughness of the base metal.
[0044] In accordance with an embodiment, the present disclosure relates to an automated configuration setting system for setting a Tungsten Inert Gas (TIG) welding machine for performing dual-pass TIG welding on a steel plates of 6 mm thick in a square butt joint configuration. The system includes a memory storing TIG welding machine configuration data and a controller operatively coupled to the memory. In an aspect, on receiving user selection of configuration data for dual-pass TIG welding on a steel plates of 6 mm thick in a square butt joint configuration, said controller performs the configuration setting of the TIG welding machine with:
v. Ceriated tungsten electrode – 4 mm diameter with 45° included angle;
vi. Gap between the electrode tip and work piece - 3±0.5 mm;
vii. Angle between electrode and workpiece - 70±2°; and
viii. voltage 18±0.4V, current 190±5 A, travel speed 150±10 mm/min, root gap 1 mm, Argon gas flow rate 12±5 lit/min.
[0045] In an aspect, the steel plate is of ultra-high strength / armour grade.
[0046] In an aspect, the steel plate is 6 mm thick.
[0047] In an aspect, the TIG welding machine is Fronius MagicWave 4000.
[0048] In an aspect, the steel plates are arranged in square butt joint design configuration with an included angle of 90°.
[0049] In an aspect, the dual-pass TIG welding performed with the configured TIG welding machine ensures that even the weakest part of the heat affected zone (HAZ) retains 90% of the fracture toughness of base metal.
Welding study
[0050] The present disclosure describes about design of square butt groove for welding and subsequent procedure of steel of thickness 6 mm with a semi-automatic TIG welding set-up. A non-consumable electrode made of ceriated tungsten having 4 mm diameter was used in this process. The tip of the electrode grounded mechanically to achieve 45° included angle. No welding filler wire/electrode was used. Argon was used as shielding gas to protect the molten metal pool from oxidation. The plates were cut into rectangular shape of 150 mm by 300 mm with the edge prepared as square butt [FIG. 1(a)]. The root gap (i.e. gap maintained initially between two joining edges) were varied between 0 to 1 mm. This configuration of the groove doesn’t need any filler electrode to fill the groove and ensured a straight HAZ which is suitable for subsequent fracture toughness study. The electrode was held at an angle of 70° to the opposite direction of electrode movement. The gap between the electrode tip and workpiece was maintained at 2.5±0.5 mm. The plates were held tightly to the welding table with a rigid clamping arrangement to avoid any misalignment between the plates due to thermal stress during welding as given in FIG. 1(b). No preheating was required. The welding was carried out in two steps. At first, welding run is made on one side of the joint. Then the workpiece ensemble was left for natural cooling to at least 40°-50°C. After that, the ensemble was taken out of the clamped arrangement and put back upside down and re-clamped. Another welding run was made and the process is complete. The accumulated oxide/slag particles were removed with a metallic brush between subsequent passes to ensure proper fusion. The welding parameters followed in the optimization process is listed in the Tables 1 and 2:
Table 1: Welding parameters
Sl No Current
(A) Voltage
(V) Speed (mm/min) Heat Input (kJ/cm) Remarks
1 120 11.8 150 5.1 No weld
2 130 12.7 150 5.9 No weld
3 150 13.9 150 7.5 Low penetration
4 160 14.6 150 8.4 Low penetration
5 175 15.9 150 10.0 Incomplete penetration
6 180 16.5 150 10.2 Incomplete penetration
7 190 18.1 150 12.4 Incomplete penetration
8 200 18.9 150 13.6 Excessive melting
9 210 19.5 150 14.7 Excessive melting
10 220 20.1 150 15.9 Excessive melting

Table 2: Welding parameters with root gap
Sl No Current
(A) Voltage
(V) Speed (mm/min) Root Gap (mm) Remarks
1 190 18.1 150 0 Incomplete penetration
2 190 18.1 150 0.5 Incomplete penetration
3 190 18.1 150 1.0 Complete penetration

[0051] The effect of root gap can be well observed in the FIGS. 2(a) and 2(b). The depth of arc penetration increases appreciably by incorporating 1 mm root gap from no root gap while the other welding parameters remain constant.
[0052] The appearances of a successfully welded joint i.e. top view and side view are presented in FIGS. 3(a) and 3(b) respectively. No presence of undercut, crack (top view) and distortion (side view) can be seen in these photographs. Welded joints were characterized by optical microscopy carried out on the metallographically prepared cross-sectional plane. The resulting photo-micrograph has been presented in the FIG. 4(a). Five different zones such as, fusion zone [FIG. 4(b)], coarse grain heat affected zone (CGHAZ) [FIG. 4(c)], fine grain heat affected zone (FGHAZ) [FIG. 4(d)], tempered heat affected zone (THAZ) [FIG. 4(e)] and base metal [FIG. 4(f)] is clearly visible in the FIG. 4(a).
[0053] The microhardness profile measured across the welded joint with a Vickers micro-indentor (1000 gm load) is presented in FIGS. 5(a) and 5(b). Hardness of the different zones can be observed here. The microhardness of base metal was 630±20 VHN. The softest part was the tempered HAZ with microhardness of 500-550 VHN and the hardest part is FGHAZ with microhardness of 650-675 VHN. Clearly no major softening in the entire weld zone can be observed.

Fracture toughness assessment
[0054] Fracture toughness of different parts of the HAZ (i.e. CGHAZ, FGHAZ and THAZ) was evaluated by determining plane strain fracture toughness parameters KIC while keeping the fracture plane through corresponding zones. A schematic in FIG. 6(a) shows the relative position of the test specimens with respect to weld line (or HAZ). A 3-point bend specimen was adopted for the tests. Three-point single-edge bend, [SE(B)] specimens were prepared according to ASTM –E1290 standard from the welded plates. The design of the specimen is given in FIG. 6(b). An initial notch of length equal to 0.40w was machined by electro discharge machining (EDM) where w stands for the width of the specimen. Subsequently, fatigue pre-cracking was done to attain a length to width ratio of ao/w˜ 0.5 where ao stands for the initial crack length of the specimen.
[0055] Fracture toughness tests were conducted on a Instron 8850 servo-hydraulic system. Single specimen technique was adopted for obtaining the Load vs. Crack Mouth Opening Displacement (CMOD). A clip gauge of 5 mm gauge length and 12 mm travel length was used for measurement of crack mouth opening displacement. The specimens were then loaded monotonically until fracture. Unloading compliance method was used to monitor the crack growth during the loading–unloading cycles. The provisional fracture toughness parameter KQ is then calculated from the load vs. crack extension data [FIG. 7] as described by ASTM E1290 standard. In that process, experimentally determined final crack [FIG. 8 – final crack length measured from stereomicroscopy] length was used.
[0056] The results of the KIC tests are listed in the Table 3:

Table 3: Provisional plane strain fracture toughness (MPavm) measured in different zones of the heat affected zones and base metal
Sl No Specimen dK/dt
(MPavm / s) PQ
(kN) Pmax
(kN) Pmax/PQ KQ
(MPavm)
1 BM-1 2.59 4.86 5.36 1.102 57.9
2 BM-2 2.71 5.23 5.94 1.134 63.2
3 CGHAZ-1 2.62 5.26 6.84 1.300 61.7
4 CGHAZ-2 2.55 5.33 6.82 1.279 62.4
5 FGHAZ-1 2.57 5.55 6.21 1.118 66.3
6 FGHAZ-2 2.64 5.65 6.26 1.109 67.2
7 THAZ-1 2.65 4.55 5.62 1.234 55.5
8 THAZ-2 2.64 4.68 5.87 1.255 56.6

[0057] Few important observations can be made from this table:
(1.) In all cases the ratio Pmax to PQ (Pmax – Maximum load achieved in load vs. crack extension plot. PQ – intersection between load vs. crack extension data and 95% secant line (100% - considering slope of the initial linear part of load vs. crack extension data)) is greater than 1.1 – thus violating the condition of achieving valid geometry independent KIC value; rather only provisional fracture toughness i.e. KQ is obtained. However, for all tests the specimen geometry was identical and hence these KQ values can be compared amongst themselves.
(2.) The KQ values for base metal are 57.9 and 63.2 MPavm. However, for CGHAZ the fracture toughness increases marginally and for FGHAZ it reached the maximum value. Fine prior-austenite grains led to homogeneous and finer final microstructure in the FGHAZ which is responsible for this increment in the fracture toughness.
(3.) Minimum fracture toughness is obtained in the THAZ. Brittle carbide precipitates might be responsible for such lowering of fracture toughness. However, even in this minimum fracture toughness is only 7.5% less than the fracture toughness of the base metal. Thus, the welding procedure ensured even the weakest part of the HAZ (i.e. THAZ) retains 90% of the fracture toughness of base metal.
[0058] Furthermore, those skilled in the art can appreciate that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[0059] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[0060] While the foregoing describes various embodiments of the present disclosure, other and further embodiments of the present disclosure may be devised without departing from the basic scope thereof. The scope of the present disclosure is determined by the claims that follow. The present disclosure is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.