Tack Welding Research Articles

Reduction of distortion during laser beam welding by applying an in situ alloyed LTT effect and considering influencing factors

In rail vehicle construction, austenitic stainless steels are used to achieve lightweight design concepts, as the higher specific strength of the material allows the thickness of parts to be reduced. However, when these are welded to create complex structures, increased welding distortion occurs even with low-heat joining processes such as laser beam welding.In order to reduce distortion, an in situ low transformation temperature (LTT) effect has been achieved using commercially available materials rather than specially manufactured LTT alloys. The LTT effect introduces compressive stresses into the weld seam, which counteract the formation of welding distortion due to tensile stresses. However, in the case of complex structures, several other factors influence the formation of distortion. The influence of the LTT effect and other factors such as tack welding, clamping and cooling conditions were analysed by distortion measurements and a maximum distortion reduction was determined.

DESIGN DAN PEMBUATAN BRACKET ASSY BULLDOZER

In this century, the industrial sector is a very important sector to support the national economy. The industrial sector contributed very high so that it succeeded in bringing Indonesia to the 85th rank out of 131 countries in the world's manufacturing industry, the industrial sector was growing very rapidly accompanied by increasing positive growth. Bracket assy is a component or frame structure on a bulldozer that uses SS400 and ST37 type steel metal material, which means that the component is very strong and does not break easily when exposed to heavy loads. Bracket assy is a product that has gone through various fabrication processes. The function of the bracket assy is as a handle for the hydraulic system pipe and also the pedestal of the body or engine cover, the bracket assy is located above the front of the car chassis which is positioned facing up. The process of making the bracket assy, namely, the selection of materials used in the process of making the Bracket Assy, namely Steel SS400 and ST 37, Gas Cutting Machines, Bending Machines, and Welding Machines. In the cutting process of the Gas Cutting Machine, the workpiece is cut. Next is the Bending Machine process where the workpiece is bent. Furthermore, the welding process of the workpiece is welded in 2 stages, namely the first tack welding and full welding / Fillet Weld, then Quality Control is carried out to check whether the product is ready to be distributed, the product is qualified into two types, namely GOOD for products that have passed Quality control and NOT GOOD for products that do not pass Quality Control.

Improving the Weld Heat-Affected-Zone (HAZ) Toughness of High-Strength Thick-Walled Line Pipes

The low-temperature fracture toughness of double-V weld seams is a well-known challenge due to the essential increased heat input for heavy-wall pipelines. A thorough investigation was conducted to explore the impact of the heat input on the grain size and precipitate coarsening, correlating the microstructure with the heat-affected-zone (HAZ) toughness. The results indicated that the actual weldments showed a toughness transition zone at −20 °C, with considerable scattering in Charpy V-notch (CVN) tests. Gleeble thermal simulations confirmed the decreased toughness of the coarse-grained HAZ (CGHAZ) with increasing heat input and prior austenite grain size (PAGS). A specially designed thermal treatment demonstrated its potential for enhancing the toughness of the CGHAZ, with the recommended thermal cycle involving peak temperatures of 700 and 800 °C, holding for 1 s, and rapid cooling. The toughness of the intercritically reheated CGHAZ (ICCGHAZ) improved with higher intercritical reheating temperatures and the removal of necklace-type M–A constituents along the PAG. Despite various thermal treatments, no significant improvements were observed in the toughness of the ICCGHAZ. Future work was suggested for optimising the use of tack welds to reduce the effective heat input (HI) associated with double-sided submerged arc welding (SAW).

Testing of metal waterstops for waterproofing tack welds

The existing information on the study and application of tack weld metal waterstops in Russian construction practice is limited. The authors of the present paper investigate the operation and effectiveness of metal waterstops designed for waterproofing tack welds. An experimental study of metal waterstops made of zinc-coated sheets and installed in a factory-fabricated capacitive monolithic reinforced concrete structure was conducted. In order to provide different exposure conditions for a waterstop, a vessel structure was manufactured with two split-level tack welds on its perimeter. As a result of filling the vessel with water and monitoring the waterstops through special cavities, it was determined that the waterstops mounted with epoxy glue did not provide sufficient sealing, unlike those mounted with a silicone sealant. In addition, some technological advantages and disadvantages of metal waterstops were experimentally revealed. The disadvantages included a relatively high labor intensity of their installation, in particular, joining the elements along the length. The main technological advantage consisted in the inherent rigidity of the product. Further research should investigate the chemical behavior of the waterstop metal in the concrete body. To this end, the steel behavior under increased water pressure and the influence of the waterstop geometry and the chemical activity of the "structural concrete – waterstop metal" complex on the value of the hydrostatic pressure resistance limit should be elucidated.

Influence of edge-deposited layers on mechanical and corrosion properties of laser beam welds of 15 mm thick AISI 2205 duplex stainless steel

AISI 2205 duplex stainless steel is used in a variety of industries, including the chemical and petrochemical industries. This is due to its high tensile strength combined with good ductility and corrosion resistance. However, in laser beam welding, these properties are negatively affected by the high cooling rates typical of the welding process. The resulting higher ferrite content in the weld metal than in the base material leads to a reduction in the ductility and corrosion resistance of the welded joint. To overcome this problem, in this study, thick plates were coated by direct energy deposition (DED) prior to laser beam welding, whereas a duplex powder mixture containing a higher nickel concentration was used as a coating material. To improve the weld quality for the proposed two-step process, a method of additional material deposition instead of conventional tack weld was investigated. The resulting welded joints showed a well-balanced austenite to ferrite ratio and their properties and microstructure were verified by metallographic analysis, electron backscatter diffraction and Charpy impact testing. Using the standard ASTM G48 test method, it was found that the corrosion resistance of the welds was improved by a factor of four in average compared to the conventionally welded joints. The resulting properties, such as good ductility and corrosion resistance, of the welds with pre-coated edges showed good agreement with those of the base metal and confirmed the proposed two-step process as a promising alternative to the conventional approaches for welding thick duplex stainless steel plates.

PRODUCTION PROCESS OF ZX - 200 5G SIDE FRAME AT PT. OHGISHI INDONESIA

Excavator is one of the heavy equipment used to move material from one place to another. The excavator consists of several parts, one of which is the side frame. The side frame is the bottom part of the excavator which functions to hold the load, steer, support the unit and act as the driving force for the heavy equipment. The data collection method was taken by reading data supporting books, making direct observations and conducting question and answer. The side frame uses SS400 material, SS 400 steel is low carbon steel with carbon content (max 0.17% C) or low carbon steel according to ASTM (American Society for Testing Materials) A36 or JIS (Japanese Industrial Standards) G3101 standards. SS 400 steel can only be hardened by surface hardening such as caburizing. In the process of making the ZX – 200 5G side frame, the first process is tack welding idler bracket and motor bracket which uses 322 watt amperes and 29 – 36 V voltage. Then full idler and motor bracket welding takes ±42 minutes. Followed by the process of full welding of the idler and motor bracket with the middle body using amperes of 275 – 300 A, voltage 33 – 35 V. Then the process of making the center line and ending the process of visual inspection of the welds.

Welding Deformation Characteristics and Mitigation Method of Hub Flange

This paper considers a 3-D thermos-mechanical analysis to investigate the effect of welding direction, tack weld, root gap and welding process on welding deformation in hub flange and pipe joint. Multi-pass welding for a single ‘V’ butt-weld joint geometry is simulated and 3-D weld path analysis is used with realistic weld bead. 3 different welding direction (2-path, 4-path diagonally, 4-path from the bottom) are analyzed and how the presence or absence of tack weld affects deformation was analyzed. Also, 3 different cases for root gaps (2, 3, 4mm) are considered and finite element analysis results are compared. In addition, the effects of the welding process on the hub flange face are determined. From the results, perpendicularity of the hub flange face is found to be strongly dependent on the welding direction and tack welds. On the other hand, root gap has small influence for tilting. The results also showed the feasibility of mitigating and controlling the welding deformation, and optimum selection of welding method was confirmed.

Assessing and mitigating the distortion and stress during electron beam welding of a large shell-flange structure

Electron beam (EB) welding can efficiently join large-scale components using one single autogenous pass, but it still faces challenges associated with weld-induced distortion and stress. This study investigates EB welding in a low-alloy steel thick-section shell-flange structure for a small modular reactor. A 3D thermal-metallurgical-mechanical model is developed to assess the weld-induced distortion and stress, as well as the strategy to mitigate them. When no restraint is imposed on the circumferential weld plane, an opening and sliding gap develops during the EB welding, which can cause weld defects and even process failure. Restraint through tack welds can effectively mitigate the gapping distortion, but it generates high transient tensile stress in the tack weld. Circumferentially continuous tack weld is preferential over circumferentially discrete tack welds to minimise the tensile stress. The final residual stress is insensitive to the tack-weld restraint, and the stress distribution in the steady-state welding region is broadly similar to that found in plate butt welds. However, concentration of residual stresses with high triaxiality occurs in the weld stop region, with high tensile stresses generated just behind the beam stop location, which cannot be diminished by overlap welding or change of weld stop position. The mechanisms responsible for the distortion and the transient and residual stresses are analysed. This study could provide rational basis for designing weld restraint to control distortion and guiding stress mitigation strategy for crack-susceptible region in EB weldments.

Study on prevention method of hot cracking under butt welding

For the automation of butt welding, it has been considered to introduce tack welds instead of out-of-plane restraint jigs to perform welding with large heat input. However, the occurrence of hot cracking has been a significant issue in large heat input welding. In the previous report, the authors have developed a prediction method of hot cracking that can investigate the influence of not only the high-temperature strain generated in the weld metal but also the phenomena related to solidification, such as solidification shrinkage, latent heat of solidification, and crystals growth direction. In this study, the conditions for the prevention of hot cracking were investigated by numerical analysis and experiments by controlling the temperature gradient at solidification temperature using a trailing torch in tandem welding. As a result, it was confirmed that the large strain existing position predicted using the proposed hot cracking analysis has a good agreement with the cracking position observed experimentally in tandem butt weld. It was also found that with increasing the electrode distance, both the columnar crystals' associate angle became larger and the local strain became smaller. It can be concluded that the hot cracking can be successfully prevented in the practical experiments using the proposed large electrode distance.

Fatigue behaviors of aluminum alloy butt joints with backing plates: Experimental testing and traction stress modeling

In this study, the fatigue behaviors and associated failure modes for a series of aluminum alloy butt joints with backing plates are investigated by conducting fatigue testing and Ultrasonic Phased Array Testing (UPAT). When the fatigue properties of butt joints are evaluated according to International Institute of Welding (IIW) and BS7608, the S-N curves of the corresponding welded joints cannot be determined due to irregular positioning of tack welds prepared, following typical manufacturing practices. To gain insights on how the fatigue test data can be correlated with different backing plate positions, traction structural stress method is used for determining both critical fatigue-critical location and corresponding stress value in the test specimens. It is found that the traction stress method is effective in identifying fatigue-critical location caused by backing plate welds and incorporating angular joint misalignment effects.

Integrated weld preparation designs for the joining of L-PBF and conventional components via TIG welding

Laser powder bed fusion (L-PBF) of entire assemblies is not typically practical for technical and economic reasons. The build size limitations and high production costs of L-PBF make it competitive for smaller, highly complex components, while the less complex elements of an assembly are manufactured conventionally. This leads to scenarios that use L-PBF only where it’s beneficial, and it require an integration and joining to form the final product. For example, L-PBF combustion swirlers are welded onto cast parts to produce combustion systems for stationary gas turbines. Today, the welding process requires complex welding fixtures and tack welds to ensure the correct alignment and positioning of the parts for repeatable weld results. In this paper, L-PBF and milled weld preparations are presented as a way to simplify the Tungsten inert gas (TIG) welding of rotationally symmetrical geometries using integrated features for alignment and fixation. Pipe specimens with the proposed designs are manufactured in Inconel 625 using L-PBF and milling. The pipe assembly is tested and TIG welding is performed for validation. 3D scans of the pipes before and after welding are evaluated, and the weld quality is examined via metallography and computed tomography (CT) scans. All welds produced in this study passed the highest evaluation group B according to DIN 5817. Thanks to good component alignment, safe handling, and a stable welding process, the developed designs eliminate the need for part-specific fixtures, simplify the process chain, and increase the process reliability. The results are applicable to a wide range of components with similar requirements.

Numerical Modeling for the Submerging Arc Welding of S700MC Steel

This paper presents a finite element model of submerged arc welding. The modeling of the filler material has been performed by applying the technique for deactivation and subsequent activation of the finite elements involved in the welding seams. The nonlinear material properties are taken into account. The description of the peaks in the specific heat capacity in the phase changes has been done by introducing latent heat. The welding arc is modeled as a heat source with a constant heat flux density. Experiments have been conducted to validate and verify the numerical model. The influence of the ratio between surface and volume of the set heat sources has been studied. Tack welds have been taken into account. Data on the relationship between the accuracy of the obtained results and the number of passages has been presented.

Failure Analysis in Lacing Wire Of Last Stage Low Pressure Steam Turbine Blade

The present paper studies a root cause of failure analysis of lacing wire used in the last stage blade of low pressure (LP) steam turbine. The lacing wire is made of Stainless Steel Grade 17-4 PH with a diameter of 1.4 mm. The failure occurred after the unit had been operated for 4 years. The fault occurred several times during the operation periods. The failure location is near the tack weld which has functions as a stopper between the lacing wire and the stub. Macro fractography, light optical microscope and scanning electron microscope were used to examine the fracture surface and microstructure closed to the failures. The cyclic stress was evaluate using harmonic analysis simulation using FEA (finite element analysis) Ansys 2019 R2. The benchmark that is indication of fatigue failure was clearly visible. It is concluded that the failure mechanism is fatigue failure with crack initiation. Improper maintenance procedures especially welding procedures trigger an initial crack and then the initial crack gets a concentrated cyclic load causing lacing wire broken.

Influence of tack operation on metallographic and angular distortion in electron beam welding of Ti-6l-4V alloy

Electron beam welding process is one such advanced fusion welding technique that fabricates structural parts with high dimensional precision and induces minimum thermal stresses and distortion. However, with incorporation of tack procedure prior to full pass electron beam welding process the effect of distortion and stresses in welded parts is lowered significantly. In the present work, an attempt has been made to investigate the effect of incorporation and elimination of tack operation prior to full pass electron beam welding process in 5 mm thick butt-jointed Ti6Al4V alloy plates. The influence of electron beam current is analyzed for tack and full pass electron beam welding procedures with an aim to produce full penetrated defect free weld joint. The characteristics difference in terms of macro and microstructural properties, microhardness distribution and welding induced angular deformation is evaluated for electron beam welded specimens. It is found that the weld width, undercut defect, and angular deformation was reduced by 7.6%, 4.2%, and 22%, respectively due to incorporation of tack procedure prior to full pass welding operation. The refined martensitic phases were observed in the fusion zone of tack welded specimens due to solidification process which enhanced the hardness of the joints. Moreover, finite element results revealed that induced thermal stresses are highly localized and longitudinal stress is more prominent across the weld joint. The angular deflection and plastic strain magnitude is estimated to be lower in specimens that are joined initially with tack operation. Moreover, the numerically computed angular deflection magnitude validates well with the experimentally measured deflection values.

Impact of weld restraint on the development of distortion and stress during the electron beam welding of a low-alloy steel subject to solid state phase transformation

Electron beam (EB) welding has a low tolerance to inter-part gapping distortion and can generate complicated stresses, which pose challenges to weld quality and integrity. This study investigates welding distortion and stresses in an EB welded plate made from SA508 Grade 4N low-alloy steel. A thermal-metallurgical-mechanical model was developed to predict the temperature, micro-constituents, hardness, distortion and stresses in the EB weldment; the predictions are in good agreement with experimental results. Different restraint conditions on the weld plane were modelled to examine their effects on distortion and stresses. If welding is performed with no restraint, inter-part gapping develops ahead of the beam position that could exceed the tolerance for a sound weld. In contrast, tack welds at the plate ends significantly reduce this gapping, but induce additional tensile stress at the stop-end tack weld. This stress is particularly high as the beam approaches the tack weld. Increasing the extent of the tack weld reduces the tensile stress, while increasing number of distantly distributed narrow tack welds does not help. A full through-length restraint eliminates the opening gap and minimises the development of tensile stresses ahead of the beam that could potentially break the restraint. The applied restraint on the weld plane has little effect on the final residual stress field, since this field mostly develops during cooling after the EB weld is complete. The weld-induced martensitic transformation suppressed tension or promoted compression in the EB weld and heat affected zone (HAZ). A steep gradient of residual stress exists, with high tensile stress concentrated in a narrow region immediately outside the HAZ.

Failure Analysis of a Bucket Elevator Shaft

Present work investigates the in-service break down of a bucket elevator in a chemical processing plant. The elevator was used for lifting bulk Di-Ammonium Phosphate and broke down due to premature failure of a shaft made of EN19 steel. The investigation comprises a detailed metallurgical failure analysis involving site visit, visual inspection, fractography, and metallography. The investigation reveals that, about 2 years prior to the failure, the shaft was tack-welded to the sprocket hub and a gib-head key near the keyway to avoid the frequent loosening of the key. The inspection during the site visit confirms that the shaft-sprocket assembly was subjected to in-service jerky loading condition along with uneven stress distribution due to misaligned counterweight. The investigation concludes that a crack was initiated in the shaft at the heat affected zone of the tack-welded spot, propagated transversely by fatigue due to in-service cyclic loading, and terminated catastrophically by a brittle fracture during the service. Tack welding, coupled with uneven stress distribution in the shaft due to misaligned counterweight system, is adjudged the root cause of this failure. Suitable remedial measures are suggested to avoid such a failure in the future.

INFLUENCE OF TACK WELDS DISTRIBUTION AND WELDING SEQUENCE ON THE ANGULAR DISTORTION OF TIG WELDED JOINT

In this paper the influence of tack welds distribution and welding sequence on angular distortion of the Tungsten Inert Gas (TIG) welded joint was tested. Additionally, the effect of welding current on angular distortion was assessed. For research X2CrTiNb18 (AISI 441) stainless steel (2.5 mm thick) was chosen. During research specimens were prepared with different distributions of tack welds. Then they were welded by different welding sequences with the use of different welding current values. After welding the angular distortion of each specimen was measured by using the coordinate measuring machine. In the next step specimens were cut. Cross-sections were polished and the metallographic macroscopic testing was conducted to check the geometry of performed welds. Performed experiments allowed determining the optimal tack weld sequence and welding parameters for welding thin stainless steel sheets.

Effective thermal elastic plastic finite element computation for welding distortion investigation of pozidriv-type welded structure with rectangular pipes and its mitigation

Welding distortion of pozidriv-type welded structure with rectangular pipes by 20 welding passes was examined with experimental and computational approaches, and mitigation techniques were also investigated for precision fabrication. Welding experiment to fabricate pozidriv type welded structure was conducted beforehand, and out-of-plane welding distortion was measured with contact type displacement sensor. Effective thermal elastic plastic finite element computation with iterative substructure method and parallel computation was developed, and then employed to examine the thermal-mechanical response during the entire welding process and predict the residual out-of-plane welding distortion. Good agreement between computed results and measurement data was observed with comparison. The influences of welding sequence and clamping constraint with tack welding on welding distortion were considered, which were also practiced for out-of-plane welding distortion mitigation. Both experiment and finite element computation show that out-of-plane welding distortion with welding sequence optimization and clamping constraint can be significantly reduced with about 38% and 56% magnitude of original welding distortion, respectively, while their mechanisms were also clarified by means of stiffness variation of solving welded structure.

Influence of Tack Weld on Physical and Mechanical Properties of MIG Welding of AA5083H116

The research objective is to determine the effect of tack weld on physical and mechanical properties of tandem-MIG (T-MIG) welding of AA5083H116 materials. A Tenjima 200S MIG machine, sample dimension of 300mm × 75mm × 3mm, and 0.8mm diameter ER5356 electrode were used. The distance between electrodes of T-MIG was varied of 18, 27, 36mm. Welding speed of 12.5mm/s, and welding process was shield using argon gas. First, T-MIG welding were employed for untacked and tacked welding. The leading current was 125A and trailing current was 120A, but current wave of each T-MIG welding machine was not taken into account. The welding voltage was set the same. Second, parameters resulting in better physical and mechanical properties were then employed for single-MIG (S-MIG) tack weld using 8, 10, 12mm/s welding speeds. The result shows that T-MIG tacked weld produced in bowing distortion and T-MIG untack weld in downward bending distortion. Higher peak temperature resulted in larger distortion. T-MIG tacked weld results in welding efficiency 76% being similar with that of bending strength (75%) in comparison with that of as received material. T-MIG tack weld results in better penetration and 37% shorter welding time in comparison with S-MIG tack weld.

Application of Optical Measurement Technology in Welding Simulation of Box Complex Structure

To verify the correctness of the sample quality and the finite element model, optical measurement technology is applied in this study. Unable to consider the quality of tack welding during the established modeling, a three-dimensional scanner is used to detect box complex structures after welding. The finite element model of box structure is established for the study of welding deformation of box structure with short, multi space and multi staggered distributed weld seam. The accuracy of the model is verified by global detection of the structural parts. The results show that the deformation trend warps at the boundary of the left and right plate and concaves in the center of the plate. The maximum deformation of the vertical plate center is 1.714mm. The bottom pad produces the extruding tendency, and the deformation near two sides of the plate is about 0.51mm, which is greater than that of 0.34mm away from the two sides of the plate. The deformation is not consistent in the front and back sides of the Z plate. The maximum error of the sample parts takes place in the front Z shape plate with an error of - 0.03mm~0.12mm. There is a certain size difference under the influence of the welding gap, but it still meets the requirements of the engineering application to eliminate the influence of the welding quality on the deformation measurement. By comparing the results of the simulation and the global measurement of the structural parts, the difference between the vibration seat and the front Z plate has a large difference that is 0.12mm∼0.24mm, and the deviation satisfies the requirements of the engineering application, and it can effectively guide the production.