Seminar on Trends in Submerged Arc welding

Under the guidance of Presented by Dr. V.K. Verma Jagdeep Singh M-tech (M.E) 10913006

Submerged Arc Welding Process A welding process in which the joining of

metals is produced by heating with an arc or arcs between a bare metal electrode or electrodes and the work.

The arc is shielded by a blanket of granular fusible material on the work

Pressure is not used Filler metal is obtained from electrode or

from supplementary welding rod.

Principles of Operation The end of a continuous bare electrode is inserted into a

mound of flux that covers the area or joint to be welded An arc is initiated using of an arc starting methods.

Principle operation of SAW

A wire-feeding mechanism that begins to feed the electrode wire towards the joint at a controlled rate, and the feeder is moved manually or automatically along the weld seam

Additional flux is continually fed in front of and around the electrode

Heat evolved by the electric arc progressively melts some of the flux, the end of the wire, and the adjacent edges of the base metal, creating a pool of molten metal beneath a layer of liquid slag

As the welding zone progresses along the seam, the weld metal and the liquid flux cool and solidify, forming a weld bead and a protective slag shield over it.

General Method Semiautomatic Welding Automatic welding Machine Welding

Semiautomatic Welding Done with a hand-held welding gun Electrode is driven by a wire feeder Flux may be applied by a gravity hopper This method features manual guidance using

relatively small diameter electrodes and moderate travel speeds

The travel may be manual or driven by a small gun mounted driving motor.

Automatic Welding Done with equipment that performs the

welding operation without requiring a welding operator.

Expensive self- regulating equipment are in order to achieve high production rates.

Machine Welding Equipment are used that performs the

complete welding operation. Welding operator is to position the work, start

and stop welding, adjust the controls, and set the speed of each weld.

Equipment’s•Power sources: Max 800 to 1600 A; DC & AC

•Wire feeder

•Flux feeding and collection unit

•Travel unit

Submerged Arc Welding Machine

Wire Feeder Wire feeder for submerged arc welding

consists of a DC wire drive motor, reduction gearbox, four-roll drive mechanism and a wire spool holder.

Feed rate is in the range 0f 0.5-2.5 m/min

Power Source AC and DC source welding . For AC 100% duty cycle and for Dc it may be

60% duty cycle.

Torch With Flux Hopper It is a self-contained unit with bent torch head

which has a long hose, flux hopper which can take up to kilograms of flux, and a suitable coupler for connection to the wire feeder.

The flux is fed around the electrode from a cylindrical tunnel along with the electrode

Electrodes The filler wire may be copper-plated in

order to improve electrical contact and to protect against corrosion.

Common wire diameters are 1.6,2.0,2.5,3,4, 5 and 6 mm.

Filler material in the form of strip (e.g. 0.5 x100 mm) is often used when applying stainless steel cladding.

Deposition rate depends on the applied current.

Fluxes Basically performs the same functions of shielding as the

coating in a manual electrode. The flux protects the molten pool and the arc against

atmospheric oxygen and nitrogen by creating an envelope of molten slag.

The slag also cleanses the weld metal

Types of Fluxes Fused fluxes Bonded fluxes Mechanically mixed fluxes

Fused Fluxes To manufacture a fused flux, the raw materials are dry mixed

and melted in an electric furnace. After melting and any final additions, the furnace charge is

poured and cooled. Cooling may be accomplished by shooting the melt through a

stream of water or by pouring it onto large chill blocks. The result is a product with a glassy appearance which is then

crushed, screened for size and packed

Advantages of Fused Fluxes Good chemical homogeneity Easy removal of the fines without affecting the flux

composition Not hygroscopic normally, which simplifies handling, storage

and welding problems Easily through feeding and recovery system

Bonded Fluxes To manufacture a bonded flux, the raw materials are

powdered, dry mixed, and bonded with either potassium silicate, sodium silicate, or a mixture of the two.

After bonding the wet mix is pelletized and baked at a temperature lower than that used for fused fluxes.

The pellets are broken up, screened to size, and packaged.

Advantages of bonded fluxes or Agglomerated fluxes are:

Easy addition of deoxidizers and alloying elements Usable with thicker layer of fluxes when welding Color identification

Mechanically Mixed Fluxes To produce a mechanically mixed flux, two or more fused or

bonded fluxes are mixed in any ratio necessary to yield the desired results.

The main advantages of mechanically mixed fluxes are that several commercial fluxes may be mixed for highly critical requirement of welding operations.

Parameters• Welding current • Arc voltage • Speed of arc travel • Size of electrode • Electrode stick-out • Heat input rate

Applications SAW is used for pressure vessels, line pipe,

storage tanks, , ships, railway wagons and coaches, surfacing and build-up work.

Welding of structural, low alloy and high alloy steels

Welding of thick structures Welding of long weld seams Best suited to materials with t > 5

Advantages of SAW Highest deposition rate Minimum operator protection required High quality welds Efficient use of materials Easily adapted

Literature Review Tanaka et al., (1980) compared the measured and expected

composition of weldments. They proposed that the transfer of a particular element from the slag to the weld metal and vice versa depends on the overall flux composition and the flux basicity index (B.I.). They had also introduced a parameter, defined by AM, which was the difference between the measured and the expected composition of the weld metal. When AM for a particular element was greater than zero, that element was supposed to be transferred from the slag to the weld metal.

Bendell A et al., (1989), used taguchi method to optimize designs for performance, quality, and cost. The parameter design based on the Taguchi method can optimize the quality characteristics through the settings of process parameters and reduce the sensitivity of the system performance to sources of variation.

Tarng et al., (1990) used fuzzy logic in the Taguchi Method for the optimization of the Submerged Arc Welding Process. The result shown that performance characteristics such as deposition rate and dilution can be simultaneously improved through this approach instead of using engineering.

Contd.

Elsayed et al., (1993) suggested that parameter design, based on the Taguchi method, can optimize the performance characteristic through the setting of process parameters and can reduce the sensitivity of the system performance to sources of variation.Pandey et al., (1994) studied the influence of submerged arc welding (SAW) parameters and flux basicity index on the weld chemistry and transfer of elements. . The results show that welding current and voltage have an appreciable influence on element transfer, as well as on weld composition while , the basicity index of the fluxes has only a minor influence.Lee et al., (2000) discussed the effect of welding parameters on the size of the heat affected zone (HAZ) and its relative size as compared to the weld bead of submerged arc welding. The result shows that welding current had the greatest influence on HAZ while voltage, electrode diameter and stick out have no significant effect on it.

Contd.

Kanjilal et al., (2005) studied the combined effect of flux mixture and welding parameters on submerged arc weld metal chemical composition and mechanical properties. The result shows that Weld metal yield strength and hardness were determined by welding parameters; whereas the impact toughness is determined by flux mixtures variables.

Datta et al., (2006) tried to evaluate an optimal parameter combination to obtain acceptable quality characteristics of bead geometry in submerged arc bead-on-plate weldments on mild steel plates. Grey relational analysis coupled with the Taguchi method to optimize the parameters. It is identified that current and flux basicity index was significant on the area of penetration and total bead cross-sectional area. The optimal weld can be produced using current= 150 A, slag-mix percentage=20% and flux basicity index=1.2. 

Gin et al., (2007) discussed the sensitivity analysis of submerged arc welding process parameters. . Changeable parameters such as welding current welding voltage and welding speed are used as design variables to construct mathematical model. The results shows that even small changes in these parameters play an important role in the quality of welding operation while penetration was almost non-sensitive to the variations in voltage and speed.

Cond.

Prasad et.al., (2008) investigated the influence of the submerged arc welding (SAW) process parameters (welding current and welding speed) on the microstructure, hardness, and toughness of HSLA steel weld joints. The hardness reduced with the increase in welding current and reduction in welding speed while toughness decrease with increase in current.

Design of Study The present trend in fabrication industry is the use of

automated welding processes to obtain high production rates and high precision. To automate a welding process it is essential to establish a relationship between process parameter and weld bead geometry to predict and control the weld quality.

This may be achieved by developing a mathematical expression that fed in computer for optimizing the parameter. The research work is carried in following steps.

(i) Identifying the important process control variables and finding their upper and lower limits,

(ii)Developing the design matrix;

(iii)Conducting the experiments as per the design matrix;

(iv)Recording the response parameters;

(v) Developing models and calculating the regression coefficients

(vi) Checking the adequacy of models;

(vii) Testing the significance of coefficients and arriving to the final models;

(viii) Presenting the direct and interaction effects of process parameters on bead geometry in graphical form

(ix) Analysis of results.

(x) Some investigations into flux consumption shall be carried out.

References Tanaka J, Kitada T, Naganawa Y, Kunisada Y and Nakagawa H (1980), “Element transfer behavior during

submerged arc welding”, Weld. pool chemistry and material. The WI Cambridge, UK, Vol. 8, pp. 279-288.

Bendell, Disney and Pridmore W.A (1989) “Taguchi Methods: Applications in World Industry”, IFS Publications U.K., Vol. 2, pp.77-354

Tarng Y.S (1990), “The use of fuzzy logic in the taguchi method for the optimization of the submerged arc welding process”, Int. Advance Manufacturing Technology, Vol.16, pp. 688-694.

Elsayed E.A, Chen A (1993), “Optimal levels of process parameters for products with multiple characteristics”, International Journal Production Research, Vol. 31, pp.17-32.

Pandey N.D, and Bharti A (1994), “Effect of submerged arc welding parameters and fluxes on element transfer behavior and weld-metal chemistry”, Journal of Materials Processing Technology, Vol. 40, pp.195-211

Lee C.S and Baker (2000), “Effect of Welding Parameters on the size of heat affected zone of submerged arc welding” Materials and Manufacturing Processes, Vol. 15, No.5, pp. 649-666

Kanjilal P, Pal and Majumdar S.K (2005), “Combined effect of flux and welding parameters on chemical composition and mechanical properties of submerged arc weld metal”, Journal of Materials Processing Technology, Vol. 171, pp. 223-231.

Datta S (2006), “Modeling and optimization of features of bead geometry including percentage dilution in submerged arc welding using mixture of fresh flux and fused slag”, Verlag London Limited.

Patnaik, A, Biswas, and Mahapatra (2007), “An evolutionary approach to parameter optimization of submerged arc welding in the hard facing process”, Int. J. Manufacturing Research, Vol. 2, pp. 462-483.

Prasad and Dwivedi (2008), “Application of Taguchi philosophy for parametric optimization of bead geometry and HAZ width in submerged arc welding using a mixture of fresh flux and fused flux”, Int. J Adv. Manufacturing Technology Vol. 36, pp. 475-483.

THANKS