Effect of GMAW CMT heat input on weld bead profile geometry for freeform fabrication of aluminium parts

Applied Mechanics and Materials Vols. 465-466 (2011 pp 1370-1374 A (2014) Trans Tech Publications, Switzerland

doi: I 0. 4028/www. scientific. net/AMM. 465-466. I 3 7 0

Effect

of

GMAW-CMT Heat

Input

on

Weld

Bead

Profile

Geometry

for

Freeform Fabrication of

Aluminium

Parts

Abdullah

Wagiman

t'",

Md Saidin Wahab

1'b,

Zazuli Mohidl'",

Azuddin

Mamat2'd

rAdvanced _{Manufacturing and MaterialCentre (AMMC), UniversitiTun Hussein Onn Malaysia,} Johor, Malaysia

2Faculg

of Engineering, Universiti Malaya, Malaysia

"abdulla@uthm.edu.my, bsaidin@uthm.edu.my, ?azuli@uthm.edu.my, dazuddin@um.edu.my

Keyrrordr:

Froeform Fabrication, Gas Metal Arc Welding - Cold MetalTransfer (GMAW-CMT).

Abstract. In developing a new method for weld based freeform fabrication, parameter affecting the

geometry

of

single-pass need to be determined as

it

has great influence on dimensional accuracy

and mechanical property

of

metallic part.

In

this paper, profile geometry and microstructure

of

single pass weld bead developed using Gas Metal Arc Welding

_-

Cold Metal Transfer

(GMAW-CMT)

was investigated. Observation

on

cross sectional weld bead indicates GMAW-CMT has

capability to produce free spatter and crack defect weld bead. Profile geometry measurement shows

weld bead develop at higher heat input has

width

size larger than the weld bead develop at lower heat input. Microstructure examination

in

the substrate reveals formation

of

columnar dendritic, cellular and planar structure while at buildup layer exhibit equiaxed dendritic structure

Introduction

Knowing and understanding customers' needs and want is a key for success in business. Each

business player need to meet timely the customers' need and want in order to survive. The changes

of need and want

of

the customer inculcate the business players more focusing on faster product development and reduce

time

to

reach

the

market. However, new product development phase

involve creating tool and prototype which represents one of the most time consuming and costly.

Therefore, this situation gives a problem to the

firm

if

the order is low-volume products or rapidly

changing high-volume products

In order to overcome the problem, a technology called Rapid Protogping (RP) is introduced in industry. This technology also known as freeform fabrication has been invented since 1990's. [1]. Its originally use for fabrication of prototype models. This technology gives benefits to the user in

term

of

less

time

and cost

in

new product development phase. These benefits have atkacted researchers to apply RP in producing a functional product

in

several applications. This including application

in

producing pattern

for

castings

_[2],

denture

_[3],

scaffold

_[4],

medical devices and

pharmaceutical _{[5], wood furniture [6]} and metallic

partUl.

In the last few years, many researchers have undertaken studies to produce functional component

of

metallic part using weld deposition based due to higher deposition rate, lower cost and safer.

Various arc welding such gas tungsten arc welding _{(GTAW) [8],} gas metal arc welding (GMAW)

[9] and submerge arc _{welding (SAW) [10]} have been investigated. However, these processes have a

drawback on controlling the spaffer and distortion. Other work

in

this area was also look on the

application of non-arc deposition process such as laser _[11] and electron beam _{welding [12].} The

result shows the process capable to produce non-spatter product with less distortion due to localized heating of high energy density. However, these processes incur high initial cost

if

compared with

arc welding.

A new modified GMAW, identified as Gas Metal Arc Welding

_-

Cold Metal Transfer (GMAW-CMT) offer low initial cost, controllable spatter and low _{heat input [13].} GMAW-CMT integrates

the wire motions with metal transfer condition via a digital process control. This integration enables

the

system detecting

the

short

circuit. Every time

the

short

circuit

occurs,

the

system

will

mechanically control the wire retraction to help detach the molten droplet, thus greatly decreasing the heat input and spatter during welding. With the advantages previously described, GMAW-CMT

meets the requirement

of

freeform fabrication

to

develop quality metal parts. During the forming process, geometry

of

single-pass

weld

bead has great influence

on

dimensional accuracy and

mechanical property of metallic part. Therefore, this research work aim to determine the effect

of

heat input on the weld bead profile geometry.

Experimental Equipment and Procedure

The experiment was carried out using GMAW-CMT welding source with an expert system made

by EWM GmbH as shown in Fig. 1. Consumable material used was

Alsis

I

mm in diameter

filler

wire and argon gas at a flow rate

of

15 L/min as the shielding gas. The weld torch was fixed to the 3

axis CNC table to provide a constant welding speed and arc length during the deposition process.

The angle of CMT arc torch was set at 60o with respective to the workpieces.

Al606l-T6

plate is

placed on an

x-y

axis table and used as the substrate

to

build up the weld bead. Prior

to

the

experiment, the surface

of

the samples was

wire

brushed atrd cleaned

by

acetone

to

eliminate aluminium oxide on the surface. Several single-pass layers are produced with different heat input in

the experiments to decide their effects on the weld geometry. Table

I

shows welding parameters

of

different heat inputs. These are the ranges

in

which the deposition was stable. The heat input is calculated using Eq.1.

Fig. 1 GMAW-CMT welding machine

Q =

60:il-x!

(1)

(S

_x

1000)

Where Q is welding heat input in kJ/mm,

V

is the mean welding voltage in volts,

I

is the mean

welding eunent in ampere and S is the welding speed in mm/min.

Single pass weld bead were build up on 27 specimens.

All

specimens were

first

inspected by liquid die penetration to obtain non-crack weld bead. Then the weld beads were cut cross-sectioned

into small specimen using

a

diamond cut-off wheel and mounted

in

epoxy

for

bead dimension measurement and metallographic analysis.

The

bead dimension

was

measured using profile projector. Meanwhile, specimens for microskucture examination undergoes grinding and polishing before etch

with

keller

reagent.

The

microstructure examination was examined using optical

[image:2.593.218.372.351.483.2]

1372

4th Mechanical and Manufacturing Engineering

Table

w

Specimen Voltage, (V) Current (Amp) Weldine Soeed (mm/min) Heat Input (kJimn)

l8 00 400 0.270

2 l8 05 500 0.227

J l8 10 600 0.198

4 l8 00 500 0.219

5 l8 00 600 0,180

6 l8 05 400 0.284

1 _{t8 l0 400 0.297}

I

l8 05 600 0.189

9 l8 l0 500 0.238

0 19 05 500 0.239

t9 00 400 0.285

2 t9 t0 600 0.209

l9 00 500 0.228

4 t9 00 600 0.190

5 l9 105 400 0.299

6 19 05 600 0.200

l9 l0 500 0.251

I

l9 10 400 0.314

9 20. l0 600 0.221

20 20. 105 500 0.253

71 20. 100 400 0.302

22 20. lt0 500 0.265

23 20. 110 400 0.332

24 20 105 600 0-21I

25 20. 105 400 0.3r7

26 20. 100 500 o.241

27 20. 100 600 0.20I

Result and Discussion

Weld Bead

Profile

Geometry. Fig.

2

shows an image observed by profile projector on selected cross section of single pass weld bead. The single pass weld bead present half-ellipse shape and free

spatter defect.

Fig.2 Cross sectioned weld bead

Fig.3 (a-b) shows the effect

of

heat input on the weld bead profile geometry. The weld bead

width increases with an increase of heat input.

A

model fitted using linear regression on the data

(Fig. 3 (a)) produced

Y:

21.98X

+

1.31

with

coefficient determination,

Rl of

0.8. The

R'value

near

to

1 shows the weld bead width is highly dependent

with

the heat input. Similar trend was

found to the height of the weld bead as shown in Fig. 3 (b). The height of the weld bead increases

with an increase of heat input. The data produce linear regression model of

Y:2.76X +

1.24 and has R2 of 0.53. The R2 value of 0.53 indicates that abaut 53o/o of the variation in weld bead height can be explained by the relationship to the heat input. The result shows that the weld bead developed at

higher heat input has width size larger than the weld bead developed at lower heat input. This could

be explained by the effect of welding current, arc voltage and welding speed on the heat input. The

heat

input

is

directly proportional

to

the

welding current and

arc

voltage besides inversely proportional to the welding speed. Increasing the welding current and arc voltage

will

increase the

heat input, so that more heat were supply to the

AlSi)

and result

in

more metal deposited on the substrate. However the situation

is

reversed

if

increasing the welding speed. The heat input is decreases

with

an increase

in

the welding speed; thus, results

in

less

AlSi5

deposited on the

aluminium substrate and cause the weld bead width size decrease. However, effect of gravity and

solidification rate giving constrains to weld bead to increase on height.

y _{=2.76x+ !.24} R'= 0.53

e2

bo

{)

1

9

^t

Tt

$e

F5

4

0.2

0.25

0.3

0.35

Heat input (kJ/mm)

(a)

0.2

0.25

0.3

0.3s

Heat input (kJ/mm)

(b)

Fig, 3 Effect of heat input on weld bead profile (a) Effect on width (b) Effect on height

;,..

PM^Z

(a)

-'r)'n

.,,L,4Ti

.A

-

^\*

(c)

(b)

(d)

Fig.4 Microstructure images of various location on deposited layer and substrate obtained using

OPM (a) FZ at Buil-up layer X50 (b) interface of FZ andPMZ at substrate

(c)HAZ

at substrate

1374

4th Mechanical and Manufacturing Engineering

Microstructure

examination. The microstructures

of

the deposited AlSis are dependent on the

location. Each location has different heating and cooling rate during the process. Rapid cooling

yield finer grain while slow cooling result

in

coarse grain. Fig. 4 shows the microstructure in the deposited layer, interface between firsion zone (FZ) and partially melted zone (PMZ), heat affected

zone (HAZ) and substrate base material which unaffected. The microstructure at the buildup layer exhibit equiaxed dendritic structure. This structure is formed due to air cooling on fusion of AlSis

filler

material which deposited on

the

substrate. Meanwhile, microskucture examination

in

the

substrate (penetration location) reveals formation

of

columnar dendritic, cellular and planar

structure.

Conclusion

Observation on cross sectional weld bead indicates GMAW-CMT has capabilify to produce free spatter defect AlSis weld bead that build-up

an

A1606lT6 substrate. Heat input of GMAW-CMT is

strongly affect the profile geometry of weld bead width. The width size increases significantly with an increase in the heat input. The effect of heat input on width size is more pronounced than the

height. Investigation

on the

microstructures

of

the

deposited

AlSi5

reveals

the

structure is

dependent on the location. Each location has different heating temperature and cooling rate during

the process. Rapid cooling yield finer grain while slow cooling result in coarse grain. References

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