Abrassive Flow Machining of Titanium Erdi Karaçal University of Gaziantep Me 499 mechanical engineering graduation project

1. GAZIANTEP UNIVERSITY
ENGINEERING FACULTY
EXPERIMENTAL INVESTIGATION OF
ABRASIVE FLOW MACHINING OF TI6Al4V
SUPERVISIOR
Prof. Dr. ÖMER EYERCİOĞLU
GRADUATION PROJECT
MECHANICAL ENGINEERING
BY
ERDİ KARAÇAL
JANUARY 2014

2. 1
Abrasive Flow Machining of TI6AL4V
Abstract
Abrasive flow machining (AFM) is a non-conventional finishing process by
means of whıch a wide range of applications, from die-mould industry to medical,
aircraft and aerospace components in which critical components must be finished to
within precise or especially demanding tolerances. Ti6Al4V displays high strength,
corrosion and heat resistant properties and are commonly used in high temperature
applications such as turbine blades and rocket engines. It is considered more difficult
to finish using conventional techniques (grinding, lapping, etc.) than other metallic
materials.This paper conducted on the finishing of these difficult to machine
materials. The influence of the AFM processon Ti6Al4V workpieces were
investigated. The results show that the white layer formed during WEDM is
successfully removed by AFM in a few cycles for each workpiece.
Key words: Abrasive Flow Machining, Surface Roughness, EDM, Ti6Al4V

3. 2
Acknowledgements
I would like to thank to my teachers Kürşat Gov and Ömer Eyercioğlu.I have been
with them for two years and these two years have added me so many things.I have
been almost every steps of the experiments thanks to them to give me this chance.
I have gained lots of experience.This experience will be very useful to me in my
business life.Again thanks to them.

4. CONTENT
Abrasive Flow Machining of TI6AL4V ................................................................................. 1
Abstract ................................................................................................................................. 1
Acknowledgements ................................................................................................................ 2
1. Introduction.................................................................................................................... 4
2. Experimental works ....................................................................................................... 5
2.1 The workpiece material .............................................................................5
2.2 The abrasive flow machine ........................................................................6
2.3 The abrasive media ....................................................................................7
2.4 Experimental procedure .............................................................................9
3. Results and discussion .................................................................................................. 10
3.1 Measurements of surface roughness ......................................................... 10
3.2 Material removal ..................................................................................... 11
3.3 SEM Images ............................................................................................ 12
3.4 White layer .............................................................................................. 14
4. Conclusions.................................................................................................................. 15
3

5. 4
1. Introduction
AFM process has a greater potential of being used to deburr, radius, polish and
remove recast layer of component. Basically there are three types of AFM processes.
One way,Two way and Orbital AFM. Commonly we use two way AFM. In two way
AFM process consist of two cylinder stocks, one from the lower cylinder pumping an
Abrasive laden medium throughout and one from the upper cylinder makes up one
process. The polymer abrasive medium which is used in this process possesses
trouble-free flow ability, better nature deformability and excellent abrading capacity.
For the finishing of the components which have complex unsymmetrical
shape/profile, holes and undercut, a need is being felt to expand finishing operations
which can produce parts with superior quality performance and higher productivity.
Especially the internal passages which are difficult to polish by other techniques, are
finished by AFM process successfully, workpiece holder is used to restrict the media
flow over the appropriate surfaces for external passages.
The AFM process can be successfully applied to the aerospace, aircraft, medical,
and other precision manufacturing areas.
The AFM process is an effective finishing process for difficult to machine
materials, aerospace and aircraft components. This paper is focused on the effect of
AFM process on difficult to finish material Ti6Al4V.Specimens were cut by wire
electrical discharge machine (WEDM). The surface roughness (Ra) values were
measured through and perpendicular to the abrasive media flow lines, material
removal (MR) was calculated and scanning electron microscopy (SEM) images were
taken from the surfaces before and after AFM for various processing cycles. The
improvement of the surfaces quality according to the workpiece materials were
observed and compared.

6. 5
2. Experimental works
2.1 The workpiece material
The experiments were performed on Ti6Al4V. The specimens were cut from the
slabs by using wire electro discharge machine (WEDM) to 5x10x20 mm as shown in
Fig.1. The WEDM parameters kept constant for all specimens to ensure the pre-surface
characteristics of the specimens. The surface roughness values of the
specimens before AFM are given in Table1 (Ra), the physical and chemical
properties of Ti6Al4V is given in Table2
.
Fig.1.Workpiece geometry
Table1
Surface roughness values of the specimens before AFM
Ti6AL4V
Specimen Ra
No (μm)
Ti-01 2,78
Ti-02 2,44
Ti-03 2,22
Ti-04 2,13
Ti-05 2,66
Ti-06 2,49

7. 6
Table2
Physical, mechanical and thermal properties of some materials
Material Hardness
(HRC)
Ultimate
Tensile
Strength
(MPA)
Yield
Strentgh
(MPA)
Thermal
Conductivity
(W/m-K)
Melting Point
(Degree
Celcius)
Ti6Al4V 30 1170 1100 6,7 -
2.2 The abrasive flow machine
In this study a two-way AFM machine that has two vertically opposed chambers
was used (shown in Fig.2). The machine contains of a main frame, hydraulic unit,
electronic control unit and heating-cooling unit.The specifications of the machine are
given in Table3.The hydraulic unit ensures adequate movement and media pressure
that can be automatically configured. The control system is designed to control the
volume of abrasive media and the number of cycles. One cycle in two-way AFM is
composed of reciprocating motion of forward and backward of the piston ram in the
media cylinder. Thus cycle time depends on the piston speed and one cycle in the
experimental study takes 2 minutes.
Table3
Abrasive flow machine
Machine specification
Hydraulic pressure 10–400 bar
Media capacity 6litres
Stroke 400 mm
Bore diameter 140 mm

8. 7
Fig.2.Two-way abrasive flow machine
2.3 The abrasive media
The abrasive media that were prepared for the present study is a mixture of
polymeric carrier, silicon carbide (SiC) abrasive particles, and 10% of hydraulic oil.
The polymeric carrier has specific gravity of 1.0 (at 25 oC) and viscosity about 60
Pas. 180 mesh size silicon carbide (SiC) abrasives of 70% ratio by weight were used.
However, the common definition of the percentage abrasive concentration is given
by: weight of abrasive particles x 100/ (weight of abrasive media). Before
performing the experiments, the abrasive media is run for 3–5 cycles with a trial
workpiece, so as to get uniform mixing. The specifications of the abrasive media are
summarized in Table4.Also preparing the abrasive media shown in Fig.3a and Fig.3b
Table4
Abrasive media
Parameters
Viscosity 60 Pas at 25 oC
Abrasive type SiC
Mesh size 180
Abrasive concentration 70 % wt.

9. 8
Preparing the abrasive media was the hardest process for us.Our teacher
Kürşat Gov and I was working on this process very much.We have used Garnet,SiC,
B4C and Al2O3 as a raw material of abrasive media.This material was taken from
water jet cutting machines.They were washed by me as shown in Fig3a. and after
that they were sieved by me to get optimum mesh size of this material.
Fig.3a.Preparing Abrasive Media
Fig.3b.Preparing Abrasive Media

10. 9
2.4 Experimental procedure
The experiments were performed on the Ti6Al4V. The workpiece holder
(seeFig.4) was used to hold the specimens allowing the flow of abrasive media
through the WEDMed surfaces with an opening of 10x20 mm. 12 litres of abrasive
media was flown through in each cycle. The experiments were carried out for
1,3,5,10,20, 50 and 100 cycles. The AFM pressure was 10 MPa and flow rate was 3
l/min. The experiments were repeated for three specimens in each condition and the
averages of the 5 surface roughness measurements were taken by using Mitutoyo SJ
401 surface measuring machine, with the cut off length 0.8 mm. The specimens were
cleaned by ethyl alcohol and weighed before and after the experiment by using
SHIMADZU AUX220 balance.
Fig.4. Workpiece holder
This workpiece holder shown in Fig.4 is machined by wire electrical discharge
machine.

11. 10
3. Results and discussion
3.1 Measurements of surface roughness
From the Fig.5 the surface roughness value decreased with increase in number of
cycles for each specimens. The surface roughness (Ra)decreased significantly in the
third cycle for Ti6Al4V specimens, the surface roughness after 20 cycles for
Ti6Al4V are decreased slightly.
SURFACE ROUGHNESS
Fig. 5.Surface roughness values
4
3,5
3
2,5
2
1,5
1
0,5
0
0 20 40 60 80 100
Ra μm
Number of Cycles
T6Al4V

12. 11
3.2 Material removal
The Fig.6 shows that the material removal (MR) increases nonlinearly with the
increase in the number of cycles. And the rate of MR decreasing with number of
cycles. The reason for this slight decrease in material removal rate can be explained
as the result of asperities on the workpiece surface before AFM. When the abrasive
particles within the media machine the peaks, they become flatter than before and in
the following cycles, the material removal is decreased.In the case of the Ti6Al4V
workpiece total material removal is low.
MR
Fig. 6. Change in material removal with respect to AFM cycles
90
80
70
60
50
40
30
20
10
0
0 10 20 30 40 50 60 70 80 90 100
mg
Number of Cycle
T6Al4V

13. 12
3.3 SEM Images
The EDMed surface is unlike that produced by any traditional machining
process; it is characterized by globules and random debris of re-deposited and recast
material. The high temperature changes the metallurgy of the material. The region
affected by these thermal changes is referred to as the heat-affected zone (HAZ). The
HAZ is included of a recast layer (white layer) of material that has been melted and
re-solidified at the surface, white layer that is harder than the original material;
contains micro cracks.
For B4C and SiC based media. In the case of, five and twenty cycles were
required to fully remove the globules and debris.
Microscopic photographs of the white layers for four groups of specimens are
given inthe first cycles of the AFM process, the white layer is removed for specimens
which were finished by B4C and SiC based media. From Fig.5 the improvement in
the surface roughness values are similar and best improvement was occurred in
specimens which were finished by B4C and SiC based media these results are well
agreement to each other.
After removal of the white layer, abrasion behaviours of the four groups were
changed. In the specimens (finished by B4C and SiC based media) has less smearing
and ploughing. And no indentation of the abrasive particles to the surfaces was
observed and the final surface roughness is better.
For Al2O3 based media finished specimen, the globules were fully removed from
the surface in the fifth cycle but the lay of craters were fully removed after twentieth
cycle and also have less ploughing. For specimen that were finished by Garnet based
media, the globules were fully removed in the fifth cycle, but the debris was fully
removed after fiftieth cycle.

14. 13
Fig.7.SEM images of specimens

15. 14
3.4 White layer
Fig. 8 illustrates the removal of white layer with respect to the number of AFM
cycles for DIN 1.2379 55 HRC specimens. The results of SEM images and the
sectional microscopic views are in well agreement. The white layers were fully
removed in the first cycle of B4C and SiC based media. In the case of Al2O3 and
Garnet based media, five and twenty cycles were required to fully remove the white
layers.
Fig. 3. WLT views of specimens

16. 15
4. Conclusions
I have worked almost every steps of this experiments for two years.I helped my
teacher Kürşat Gov and Ömer Eyercioğlu when productions of workpiece holder.
I have been in a part of preparing the specimens.I took away them to Organized
Industry for cutting with wire electrical discharge machine.
I have also worked when preparing the abrasive media.I sieved them for the
optimum mesh sizes.This process took our days.
We worked on parameter which is mesh size, flow rate, to understand how will
change roughness of workpiece. We worked on titanium specimen. The surface
titanium of surface roughness is tired to desired measurement by AFM.
The effect of abrasive types (SiC, Al2O3, B4C and Garnet) of WEDMed DIN
1.2379 cold-work tool steel on abrasive flow machining was investigated. From the
experimental results, the following conclusions have been derived:
The white layer formed during WEDM is successfully removed by using all
types of abrasives.
The results of SEM images and the sectional microscopic views are in well
agreement. The white layers were fully removed in the first cycle of B4C and SiC
based media. In the case of Al2O3 and Garnet based media, five and twenty cycles
were required to fully remove the white layers.
Although the trends of surface roughness measurements are similar for all media
groups, the results show that the media prepared by B4C and SiC has more surface
improvement than Al2O3 and Garnet.
The surface improvement nearly the same for B4C and SiC therefore, SiC can be
preferred due to its lower cost and better performance.
According to the desired finishing condition the Garnet can be used for its better
cost.

17. 16
REFERENCES
Gov K, Eyercioglu O, Cakir MV. Hardness Effects on Abrasive Flow Machining.
Journal of Mechanical Engineering. 2013; 59: 626-31.
Eyercioglu O, CAKIR MV, GOV K. Influence of machining parameters on the
surface integrity in small-hole electrical discharge machining. Proceedings of the
Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture.
2013.