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EFFECT OF END LOAD AND TOOL SPEED ON
TORQUE AND TEMPERATURE OF FRICTION
DRILLING PROCESS: AN EXPERIMENTAL STUDY
BY:
VARUN KUMAR
SHYAMAL SATODIA

Introduction
Current sheet metal joining techniques include:
Arc welding
Resistance spot welding
These operations have drawbacks since:
Extra material is added, and quality issues are inevitable
Aluminum alloys, integral to automotive industry today can not be welded
easily

Introduction (Contd.)
Friction drilling is a new alternative for joining sheet bodies.
Also known as thermal or flow drilling, the heat generated due to
friction between rotating tool and work piece is used to soften,
penetrate and plastically deform the material to create a hole with a
process generated sleeve, to be used for tapping later.
A conical shaped Silicon Carbide tool is used for the process due to
high working temperature.
The height of the bush is almost twice the thickness of sheet metal

Friction Drilling process
 Step 1: Approaching conical tool
 Step 2: Penetration of tool tip
into softened work piece
 Step 3: Material deformation due
to heating
 Step 4: End of drilling process and
formation of collar by shoulder
 Step 5: Tool retraction

Research background
Authors/year Parameters studied Limitation of the study
Streppel and Kal, 1983 Variations in end load, frictional
moment and tool wear
A theoretical model for calculation
of thrust force, torque, frictional
moment and wear rates missing.
Kerkhofs et. al, 1994 Effect of tool coating of wear
resistance, nature of tool failure
Absence of Tool wear prediction
time and tool failure prediction
model
Scott Miller et al. (2005-2007) Torque generation, thrust force
model, heat generation rate,
microstructural changes in work
piece and tool, FEM modeling
Nature of coefficient of friction
undefined, tool feed not considered
in torque models, model for
temperature field absent,
relationship between end load and
process output missing.
Qu and Blau, 2008 Model to calculate friction
coefficient and shear stress
Relation between end load and
process output parameters.

Research motivation
 Absence of a correlation between the applied end load and tool
speed on dependent variables of the process like torque, heat
generation and temperature.
Lack of understanding about the nature of contact prevailing during
drilling operations leaves doubts about the applicability of prior
models developed.

Theoretical background
 Deformation of metal takes place due to development of shear zone at
tool- workpiece interface
 Three different kinds of contact exist in thermal drilling process:
sticking condition, sliding condition and partial sticking+sliding
condition.
The relationship between contact pressure and shear stress is as
follows in sticking condition is
Where, p = contact pressure, μ = coefficient of friction
shear p 

Theoretical background (cont.)
 Torque developed for a conical tool is given as:
 Rate of heat generation in conical tool is given as:
Temperature field in workpiece can be evaluated using
3 3 2
2 1
2 (h h ) tan
2
3cos
2
p
T





3 3 3
2 1
(h h ) tan2 2( )
3 sin
2
p
q



&
( ) 2
0 0
2
(( ( v) ).r)
2
v y vtq H
T T e Y
kg g



 
  

FEM model
 To evaluate temperature generated in workpiece during thermal drilling, a FEM
model was used.
The boundary conditions for the model include:
 Surface convection on top and bottom surfaces of plate
 Surface radiation from top of plate
 Dirichlet boundary conditions on side walls of the plate
Heat generated by the tool was applied in steps as the tool advances through
the material to observe transient temperature field.

 Deprag Flowform Screwdriving (FFS)
• AISI 1020 steel tool was used and Al 6063 alloy was used
as work piece
• ThermoVision A40 Infrared Camera was used for
temperature measurement
• Two different samples of 3.4 mm and two 1.3 mm (used
together as 2.6 mm) were used
• The top surface of the work piece was painted black to
increase the emissivity of surface for temperature
detection from camera
Experimental Setup
Workpiece holder
Tool holder
Infrared camera

Experimental procedure
 6 tests were conducted with for different conditions of speed and end load.
Each condition was repeated with three samples to nullify process and material
variations.
Test conditions have been shown in Annex A
No lubricant was used during the process
IR camera was used to generate the temperature variation while the servo
motor mechanism in the drilling machine generated the torque variation during
process.

Results from experiment
Cycle time is calculated between points A and B
Also, two peak torque locations were obtained for data
points 1 and 2 corresponding to drilling and tapping
operation respectively
The average cycle time (average of three samples tested for
each condition) have been shown in table
A B
1
2
Speed,
(rpm)
End load, (N) Thickness,
(mm)
Time
(Sec)
6000 575 2.6 2.10
6000 650 2.6 1.088
5000 650 2.6 2.36
6000 700 3.4 1.728
6000 950 3.4 2.776
5000 950 3.4 3.87

Results (Contd.)
 Hypotheses H1a and H2a: Effect of end load and torque on cycle
time.
The experimental conditions are shown in table below
The plot clearly shows that frictional torque experienced by the
tool increases as end load is increased.
Speed, rpm End load, N Thickness,
mm
6000 575 2.6
6000 650 2.6

Results (Contd.)
 Hypothesis H1b: Effect of rotational speed on torque
Test conditions are shown in table below.
It was observed that increasing speed indeed reduces the
frictional moment experienced by the tool
Speed, (rpm) End load, (N) Thickness, (mm)
6000 950 3.4
5000 950 3.4

Results (Contd.)
 Hypothesis H3a: Effect of end load on temperature
 Test conditions are shown in the table below
 It can be seen that higher end loads reduce the
maximum temperature attained in the material
Speed, (rpm) End load, (N) Thickness, (mm)
6000 575 2.6
6000 650 2.6

FEM Results
Although the FEM model was not a complete
representation of drilling process, its results could still
predict the maximum temperatures
Test conditions were 650 N end load and 6000 rpm
speed.
A maximum temperature of 197℃ can be seen in the
workpiece. However, the maximum temperature
observed in experiment was 206 deg.C for test condition
with speed = 6000 RPM and end load = 650 N.

Joint Quality
Process parameters for drilling affect the quality of the drill to a
great extent
The bushing of the left hole is comparatively smoother and of
good quality as compared to the one on the right which shows
the material of the bushing deformed in a very abnormal
fashion

Future scopes
Friction drilling process finds a huge scope in automotive industry for metal joining process in
chassis and body
Joint quality is much better as compared to resistance spot welding as the plate itself has a
threaded bushing for fastening
Its very clean process as its void of any lubrication which thereby do not contaminated the work
piece

Annexure A- Experiment test conditions
Test no.
End load
(N)
Speed
(RPM)
Sheet
thickness
(mm)
1 575 6000 2.6
2 575 6000 2.6
3 575 6000 2.6
4 650 6000 2.6
5 650 6000 2.6
6 650 6000 2.6
7 950 6000 3.4
8 950 6000 3.4
9 950 6000 3.4
10 700 6000 3.4
11 700 6000 3.4
12 700 6000 3.4
13 650 5000 2.6
14 650 5000 2.6
15 650 5000 2.6
16 950 5000 3.4
17 950 5000 3.4
18 950 5000 3.4

Friction drill Tool
• The tool has 5 regions each playing a
significant role in the process
Center region: Tool penetration
Conical region: Heat generating region
Cylindrical region: Shapes the hole
Shoulder region: Collar formation in the bush
Shank region: Tool holding
• There can be threaded tool which
relegates the need of separate tapping

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Kumar&Satodia_AUE867_P02

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