Improvement and optimisation of various process parameters obtained to maximise ultimate

tensile strength of weld beads using arc welding.

Name- Raiyan Ahmad MakkiDepartment of Mechanical Engineering

B.Tech, 3rd YearIntegral University, Lucknow

Paper ID- 15MEGRES

2nd Mechanical Engineering Graduate Research Symposium (MEGRES’15).

Indian Institute of Technology, Mumbai, India

INTRODUCTION

• This presentation focuses on the comparison of weld beads geometry of Titanium (Ti-6Al-4V) alloy obtained by GTAW, EBW & LBW processes to test the ultimate tensile strength.

• Secondly, this presentation demonstrates the influence of welding parameters like Welding speed, Welding voltage, Welding current.

• Thirdly, presentation represents investigation of effect of welding speed on the tensile strength of the welded joint of Ferrous and non-ferrous by TIG welding. The material selected for preparing the test specimen is Aluminium AA6351 Alloy.

• Finally it deals with the vibratory welding process for tensile strength improvement.

• Welding process of Ti-6Al-4V joints using GTAW.

Gas tungsten arc welding (GTAW) is most preferred welding method for Titanium alloy due to its comparatively easier applicability and better economy.

• Welding process of Ti-6Al-4V joints using LBW supported by mathematical model.

Laser beam welding (LBW) has been used for welding of titanium alloys due to its advantages of small heat affected zone (HAZ), consistent and reliable joints.

Titanium (Ti–6Al–4V) alloy has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to-weight ratio.

• Development of mathematical models to predict tensile properties of pulsed current GTA welded titanium alloy weldment.

• The mathematical models have been developed by response surface method (RSM).

• The adequacy of the models has been checked by ANOVA technique. By using the developed mathematical models, the tensile properties of the joints can be predicted with 99% confidence level.

Al V Fe O N C Ti

Ti-6Al-4V 6.38 4.07 0.19 0.17 0.008 0.012 Bal.

Table-1: Chemical composition of base metal (Weight %)

METHODS & EXPERIMENTSExperimental Setup 1• The rolled plates of 5.4 mm thick Ti6Al4V

alloy were used butt joint configuration was prepared to fabricate the joints using GTAW process.

• Square butt joint configuration was prepared to fabricate the joints using LBW and EBW processes.

• The optimized welding parameters were obtained by trial experiments[1].

• The welding was carried out normally to the rolling direction of the base metal. [1]

Fig.1: Scheme of welding with respect to rolling direction and extraction of specimens(ST: Smooth tensile; NT: Notch tensile)(unit: mm) [1]

Experimental Setup 2• Aluminium AA6351 alloy plates with the

dimensions of 4x50x200 are prepared.• These specimens are then welded with a

root gap distance 1 millimetre.• The plates were welded at single pass. By

changing the weld speeds to 0.3, 0.6, 0.9, 1.2 cm/sec all the samples are welded by keeping the other parameters constant

Fig-2: Sample specimen with bevel angle of 200

MACROSCOPIC STUDY

Process

GTAW LBW EBW

Machine Lincoln,USA

DC035, Slab CO2 Laser from Rofin Sinar Laser

Techmeta, France

Polarity AC - DC

Filler metal ERTi-5 - -

Electrode Tungsten - Tungsten

Shielding gas

100% Argon

100% Helium

100% Argon

Current/A 125 - 0.05

Voltage/V 10 - 50000

Welding speed/mm min-1

60 1500 650

Power/W - 3500 -

Heat input/KJ mm-1

1.25 0.14 0.231

Fig 3: Macrographs of different welded joints (a) GTAW joint (b) LBW joint (c) EBW joint [1,5- unaffected base metal; 2,4- HAZ; 3- weld fusion zone]

Table-2: Welding parameters used to fabricate joints.

Fig 4: Fractographs of tensile specimen: (a) BM (b) GTAW joint;

various sized dimples(c) LBW joint;

parallely aligned dimples (d) EBW joint

; secondary cracks,50µm

Process

GTAW

LBW EBW

Yield strength/

MPa

893 959 960

Ultimate tensile

strength/MPa

939 982 1000

Elongation/%

10.15 15.00 7.70

Reduction in cross

sectional area

17.48 32.00 21.78

Notch tensile

strength/MPa

1047 1148 1077

Notch strength

Ratio

1.11 1.16 1.06

Impact toughness

/J

15.5 10 10

Joint efficiency

93.7 98.1 99.81

Fracture location

Fusion line

Base metal

Base metal

Table-3: Mechanical properties of weld metal Graph set-1: Tensile strength at various welding speed of 0.3 cm/sec, 0.6 cm/sec, 0.9 cm/sec, 1.2 cm/sec.

Fig-5: Tensile testing specimen (all dimensions are in mm.)

a b

c

Fig-6: photographs of (a) GTAW joint (b) EBW joint (c) LBW joint

The welded joints were sliced by wire electric discharge machining (WEDM) to produce tensile test specimen. The smooth tensile specimen were prepared to evaluate yield strength, tensile strength and percentage elongation. The tensile specimens were prepared as per the ASTM E8M-04 standard guidelines

EXPERIMENTAL PROCEDURE• Tensile test was carried out in 100 KN electro-

mechanically controlled Universal testing machine (Make: FIE-BLUE STAR, India Model: UNITEK-94100).

• The specimen were loaded at the rate of 1.5KN/min. The 0.2 % offset yield strength was derived using extensometer.

• The specimens for metallographic examination were sectioned to the required sizes from weld regions and polished using different grades of emery paper. Finally polishing was done in the disc polishing machine.

• The micro structural examination was done by optical microscope (Make: MEIJI, Japan; MODEL: ML7100).

Effect of current on ultimate tensile strength.

Effect of voltage on ultimate tensile strength.

Effect of electrode diameter on ultimate tensile strength.

Effect of welding technique on ultimate tensile strength.

Graph set-2

• The following conclusion may be derived from the graph set-2 investigations:

As current increase impact strength of weld metal increased while hardness decreased.

With increase in welding current ultimate tensile strength decreased.

As electrode diameter increases impact strength decreased while hardness increased.

With increase electrode diameter ultimate tensile strength increased.

• Superior Mechanical properties:

The transverse tensile properties such as yield strength, tensile strength, percentage elongation were evaluated:

Maximum Tensile strength of 230 Mpa was observed at weld speed of 0.6 cm/sec (for 400 bevel and 1.5 bevel height). This indicates the strength of the weldment is weaker than the base metal.

Tensile strength is higher with lower weld speed. This indicates that lower range of weld speed is suitable for achieving maximum tensile strength.

Unwelded base metal: Yield strength- 969 MPa, Tensile strength- 1002 MPa

GTAW Joint: Yield strength-

890 Mpa, Tensile

strength- 940 MPa

LBW Joint: Yield strength-

960 Mpa, Tensile

strength- 985 MPa

EBW Joint: Yield strength-

950 Mpa, Tensile

strength- 1000 MPa

6 % reduction in strength as

compared from base metal in GTAW

process.

2 % reduction in strength as

compared from base metal in LBW process

Higher strength exhibited in EBW process.

Tensile Test Finite Element Analysis by ABAQUS.

Influence of Vibratory welding process for tensile strength improvement.

• In the present work vibratory setup has been used for inducing mechanical vibrations in weld pool region.

• An increase in tensile properties has been observed due to required frequency produced with the amplitude and acceleration in terms of voltages.

• Different frequencies with different amplitude are applied along the weld length, so that weld pool could be mechanically stirred in order to induce favorable micro structural effects.

Specimen piece- Mild steel Composition: 0.9% C, 7.5-10% Mn, 1% Si, 17-19% Cr, 4-6% Ni, 0.06% P, 0.03% S and the base metal

Fe.

After welding.

Tensile test specimen ( with vibration at 230 V input to the vibrometer) after testing in UTM

Tensile test specimen ( with vibration at 150 V input to the vibrometer) after testing in UTM

Tensile test specimen ( with vibration at 70 V input to the vibrometer) after testing in UTM

Tensile test specimen without vibration after testing in UTM

Tensile test specimen before testing in UTM

Line diagram of specimen.

Graph set-3Voltage input to the vibrometer

Without Vibration

70 V 150 V 230 V

Amplitude in mm (RMS)

0 0.236 0.273 0.350

Acceleration in m/sec2 (RMS)

0 18.4 30.33 49.29

Tensile strength (Mpa)

530 596.7 620.25 651

The following conclusions may be derived from the graph set-3 & table-4 investigations:

• Tensile strength of welded joint is increased with respect to the increase in amplitude and acceleration of the specimen in terms of voltage input to the vibrometer.

• Tensile strength of the welded joints prepared with vibration is more compared to without vibration.

Table-4

Microstructure with manual metal arc welding without vibration.

Microstructure with manual metal arc welding without vibration.

• Metallographic study shows that uniform solidification process took place with uniform dendrites with acceleration and amplitude kept constant.

• Long dendrites show coarse structure of weld joint.

Metallographic study with amplitude and acceleration keeps changing, long dendrites get fragmented and break into small dendrites and forms a new nucleation site.

Conclusions :• As current increase impact strength of weld metal

increased while hardness decreased.

• With increase in welding current ultimate tensile strength decreased.

• As electrode diameter increases impact strength decreased while hardness increased.

• With increase electrode diameter ultimate tensile strength increased.

• Maximum Tensile strength of 230 Mpa was observed at weld speed of 0.6 cm/sec (for 400 bevel and 1.5 bevel height). This indicates the strength of the weldment is weaker than the base metal.

• Tensile strength is higher with lower weld speed. This indicates that lower range of weld speed is suitable for achieving maximum tensile strength.

• Tensile strength of the welded joints prepared with vibration is more compared to without vibration.

• Tensile strength of the welded joint prepared under influence of mechanical vibrations is more compared to without vibration.

• As a result tensile strength and hardness is increased with increase in voltage input to the vibrometer and with increase in amplitude and acceleration of the specimen.

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[16] Influence of Welding Speed on Tensile Strength of Welded Joint in TIG Welding Process 1.Ahmed Khalid Hussain, 2.Abdul Lateef, 3.Mohd Javed, 4.Pramesh TDepartment of Mechanical Engineering, Lords Institute of Engineering and Technology,

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Thank You