Surface roughness in abrasive water jet cutting

SURFACE ROUGHNESS IN
ABRASIVE WATER JET CUTTING
BY:-
PRAVEEN KUMAR (2012178)
Wednesday, November 22, 2017 1

What is Abrasive water jet cutting
A thin, high velocity water jet accelerates abrasive particles that are directed
through abrasive water jet nozzle at material to be cut.
Why ??
Ability to cut all materials , no thermal distortion, high flexibility, small
cutting force and environmental friendly.

Our study
Surface quality is one of the most specified customer requirements and the major factor of
surface quality is the surface roughness.
Surface roughness mainly depends upon some controllable and some uncontrollable process
parameters.
Machine: NC 3015EB AWJM
Water pump: SL-V 50 (max pressure 415 MPa)
Work material: Aluminium
Abrasive: GMT garnet
Abrasive Size: 80 mesh

PARAMETERS TAKEN FOR STUDY
1. Material thickness
2. Traverse speed
3. Mass flow rate
CONSTANT PARAMETERS:
Orifice diameter : 0.20mm
Focusing tube diameter : 0762mm
Water jet pressure : 350Mpa
Abrasive type : GMT garnet
Abrasive Size : 80mesh

Traverse speed and mass flow rate
Material thickness Traverse speed Mass flow rate
15mm 77, 100, 139, 250,350 100, 130,200,250,320
30mm 37, 49, 69,109, 130 240,285,320,350,390
• Average surface roughness measured by using surf test Mitutoyo Style instrument

Effect of traverse speed on roughness
1. Material thickness 15mm
Mass flow rate = 320 g/min (constant)
2. Material thickness 30mm
Mass flow rate = 390 g/min

Effect of abrasive mass flow rate on
surface roughness
Constant traverse speed = 37 mm/min
Thickness = 15mm
Constant traverse speed = 37 mm/min
Thickness = 15mm

Effect of all three parameters together

Effect of feed rate
Surface roughness gradually reaches its maximum value when the cut surface depth reached to
the thickness of the material.
As the depth of cut increase the jet loses its energy due to the jet–material interaction, mutual
particle impacts, etc. This situation results in rougher surface characteristics at the lower parts
of the cut surface. Better surface characteristics where observed on the upper region where
cutting wear mechanism is active.
Surface characteristics are deteriorated at the lower region. where the cut was performed by
deformation wear mechanism. he surface has better characteristics, in the region that starts
from the upper point where AWJ started to cut, to the middle of the thickness. From the middle
of the thickness to the downwards, the surface quality deterioration is observed.

There are not obvious differences between the measured surface roughness results of pure aluminium specimens,
obtained for both of the thickness and feed rates. decreasing the feed rate did not result in much improvement in
surface quality.
Especially for the 5mm thickness specimen only 15% improvement was obtained from surface roughness despite the
93.22% reduction in feed rate.

Surface roughness improvement for 20mm thickness specimen is 8.5% when feed rate is
decreased in the ratio of 67%.

Surface striation formation
Striation formation is believed to be caused by wavy abrasive particles kinetic energy
distribution related to the cut surface.
All factors which have an effect on kinetic energy magnitude and its distribution related to the
cut surface must effect striation patterns and it result in striation irregularity.
Striation also form by some external factors-
a. Fluctuation in process parameter , traverse speed, jet pressure , abrasive flow rate
b. Vibration of work piece and nozzle while cutting
c. Vibration due to nozzle traverse system

Abrasive water jet cutting consist of upper smooth zone which is free from any striation and lower
rough zone where wavy striation are dominant characteristic factor
Work piece thickness should be lesser than the smooth zone depth for striation free machining.
In upper smooth zone kinetic energy of abrasive particle is higher than the destruction energy of
work piece material so the smooth surface and through cut can be obtained.
When the depth of cut increases the kinetic energy of abrasive particle decreases and some of
particles have lesser kinetic energy then the destruction energy of work piece material and effective
jet diameter decreases and the wavy particle distribution become sharp.
The strong forefront particles cluster continues to cut through the surface whilst the weak trailing
particles cluster are unable to do so by their own energy and follow the strong particle traces.
This leaves marks on the surface and these wavy marks are called Striation.

Result and conclusion of this study
Due of comprehensive experimental research, detailed theoretical investigations and performed
analysis, it is possible extract followed conclusions:
1. The experimental results show that traverse speed has great effect on the surface roughness
at the bottom of the cut.
2. he surface being cut by the abrasive water jet was characterized by two types of surface
texture. The first texture was located at the beginning of the cut and was characterized by
the smooth surface. The second texture was located at the bottom of the cut and was
characterized by the rough surface.
3. he optimal solution is the choice of medium traverse speed with which can be achieved
higher productivity with acceptable surface roughness.

4. Decreasing the feed rate did not result in much improvement in surface quality.
5. Weak trailing particles leaves marks on the surface and these wavy marks are
called Striation.
6. Also, in order to reduce processing costs, the abrasive mass flow rate may be
reduced in relation to the manufacturer’s recommended value, because the surface
roughness slightly changes by increasing the abrasive mass flow rate.
7. The most remarkable result is that the surface quality deteriorates as the depth
of the cut gets deeper.

References
1. Derzija Begic-Hajdarevica, Ahmet Cekica, Muhamed Mehmedovic, Almina Djelmica on Experimental
Study on Surface Roughness in Abrasive Water Jet Cutting in 25th DAAAM International Symposium on
Intelligent Manufacturing and Automation, DAAAM 2014.
2. Adnan Akkurt , Mustafa Kemal Kulekci , Ulvi Seker , Fevzi Ercan on Effect of feed rate on surface
roughness In abrasive waterjet cutting applications in Journal of Materials Processing Technology 147
(2004) 389–396.
3. F.L. chen and E. siores on variation on surface striation formation in abrasive water jet cutting in Journal
of Materials Processing Technology 135 (2003) 1–5.

Surface roughness in abrasive water jet cutting

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