effect of toolpath strategy and tool ......xu et al. (2013)[2] used aa5052-h32 aluminum alloy with...
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EFFECT OF TOOLPATH STRATEGY AND TOOL ROTATION ON FORMABILITY
IN SINGLE POINT INCREMENTAL FORMING
ZERADAM YESHIWAS & KRISHNAIAH ARKANTI
Department of Mechanical Engineering, University College of Engineering, Osmania University, Hyderabad, India
ABSTRACT
The present study aimed to explore the effect of toolpath strategy and tool rotation on the formability of Drawing
Quality Steel in Single Point Incremental Forming (SPIF). The effect of toolpath strategy was studied using both
experimental and numerical simulation whereas the effect of tool rotation on the formability was limited to the
fabrication and evaluation of the results. Hyperbolic cone and pyramid with varying wall angles were the geometries
that have been chosen to verify the formability. Maximum formability depth or maximum forming angle was achieved
in contour toolpath strategy i.e. 56.34mm (81.5°) and 56.22mm (71.3°) for the hyperbolic cone and pyramid with
varying wall angle respectively. The numerical simulation using ABAQUS explicit also proves that the maximum
formability is achieved using contour toolpath strategy. Furthermore, formability increases with a rotational velocity of
200rpm than a non-rotating tool i.e. >60mm (85°) and 57.89mm (73.4°) for the hyperbolic cone and pyramid with
varying wall angle respectively.
KEYWORDS: Formability, SPIF, Forming Depth, Forming angle, Tool rotation, Toolpath strategy & Drawing quality
steel
Received: Jun 08, 2020; Accepted: Jun 29, 2020; Published: Oct 10, 2020; Paper Id.: IJMPERDJUN20201507
INTRODUCTION
Factors found to be influencing formability in single point incremental forming (SPIF) have been explored in
several studies. M. A. Davarpanah et.al (2015)[1] investigated the effect of rotation of tools on the formability of
polymer materials, i.e. PLA and PVC. The study showed that the speed of tool rotation improves the formability
with a step-depth of 0.2 mm and with a varied feed rate of 1250, 5000, and 7000 rpm. The study also found that,
when the step depth increases from 0.2 mm to 1 mm and the tool's rotational speed increases sheet wrinkling and
sheet galling occurs leading to premature sheet failure.
Xu et al. (2013)[2] used AA5052-H32 aluminum alloy with 1.27 mm sheet thickness, 0.5 step depth, 150
mm / min feed rate, and 10 mm diameter tool to investigate the effect of tool rotation on formability in SPIF. The
study showed that the rotation of the tool and the heat generated by friction can increase the formability
significantly. The study also found that improvement in formability was observed with the shift in rotational
speed from 0 to 250rpm. Relative to the non-rotating tool, the average fracture depth and the corresponding
maximum formable wall angle at 7000 rpm were increased by 48.4% and 20.6% respectively for a rotating tool.
Durante et al., 2009; Hamilton and Jeswiet, 2010[3] used aluminum alloy Al3003-H14 to investigate the
effects of high feed and tool rotational speeds in SPIF. The study proves that temperature increases in the formed
portion at higher spindle speed, which improves sheet formability.
Kumar et al. 2019[4] used AA2024-O aluminum to assess the effect of sheet thickness and rotation of
Orig
ina
l Article
International Journal of Mechanical and Production
Engineering Research and Development (IJMPERD)
ISSN(P): 2249–6890; ISSN(E): 2249–8001
Vol. 10, Issue 3, Jun 2020, 15889-15902
© TJPRC Pvt. Ltd.
15890 Zeradam Yeshiwas & Krishnaiah Arkanti
Impact Factor (JCC): 8.8746 SCOPUS Indexed Journal NAAS Rating: 3.11
tool on conical frustum forming depth. The study found that higher sheet thickness (1.6 mm) and higher spindle speed
(1500 rpm) resulted in effective conical frustum formation up to the specified depth. The study also found that the tool's
higher rotational velocity increases friction in the tool-sheet contact zone which increases the local temperature of the sheet
material and improves sheet formability.
Rattanachan(2009)[5] Studied the effect of rotational velocity and feed rate on DIN 1.0037 steel (St 37-2 steel)
formability by forming a dome shell to 100 mm. The result shows, the rotational speed of the tool had a more formability
effect. It also showed that, by increasing tool rotational speed from 100 to 1000 rpm, formability was reduced by
increasing specimen roughness and wear. The tool feed rate had some formability effect, increased feed rate from 300 and
3000 mm / min, reduced formability by lowering specimen depth.
V. Gulati et.al (2016)[6] optimized the formability of SPIF using Aluminum-6063 alloy. The study found that
lubrication has the greatest impact on formability followed by the tool's rotational speed, feed rate, sheet thickness, step
down, and tool radius.
Bagudanch et.al 2015[7] studied the effects of spindle speed, tool diameter, and sheet thickness on the formability
of PVC material in SPIF. The findings indicated that there was an increase in the formability at high spindle speed
(200rev/min) than a non-rotating tool. The study used two different tool sizes (6 mm & 10 mm), and the result showed that
the formability decreases when the tool diameter decreases as well. Regardless of the effect of sheet thickness on the
formability, the study reported that a 2 mm thickness sheet was successfully formed than a 1.5 mm thickness sheet.
A. Kumar and V. Gulati 2019 [8] stated that better formability and surface quality was achieved using the helical
tool path as compared to the profile toolpath.
Liu, Z., Li, Y., & Meehan, P. A. (2013) [9] studied the effects of tool path strategies with different step depth on
the formability using AA7075-O aluminum alloy. The study reported that there is no significant difference in the
formability by using 0.5 mm step depth for both spiral and contour toolpath strategies. The study also found that
formability is higher for a larger step depth (0.5 mm as compared to 0.2 mm).
SAMPLE PARTS
As shown in Figure 1, the hyperbolic cone and a pyramid with varying wall angles were used to demonstrate the effect of
tool-path strategy and tool rotation on the formability. The hyperbolic-cone was modeled with a top opening diameter of
140mm and the pyramid was modeled with a top square opening and the length of its side is 140mm. In both sample parts,
the wall angle is ranging from 32° to 85° (Figure1 and Figure 2).
Effect of Toolpath Strategy and Tool Rotation on Formability in Single Point Incremental Forming 15891
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Figure 1: Part Geometry for the Hyperbolalic-cone
Figure 2: Part Geometry for the Pyramid Frustum
TOOLPATH DEFINITION
To examine the effect of the tool-path strategy on formability, the contour toolpath and the spiral tool-path strategy were
used. In the contour toolpath, deformation occurs at constant step depth from the top to the required maximum depth
(Figure 3). In helical tool-path deformation occurs with a spiral motion from the top to the ultimate depth (Figure 3). Table
1 defines the parameters used to create the toolpath for the chosen sample parts. Figure 4 and Figure 5 displays sample tool
paths developed for the parts chosen.
Table 1: Parameters for the effect of tool-path strategy on Formability Study
Parameters
Part
Hyperbolic cone Pyramid with varying Wall
Angle
Tool-path Strategy Contour Spiral Contour Spiral
Step Depth (mm) 0.5 0.5 0.8 0.8
Feed Rate (mm/min) 1500 1500 1000 1000
Tool Diameter (mm) 10 10 12 12
Wall Angle(°) 32-85 32-85 40-87 40-87
Rotational velocity(rev/min) 0 0 0 0
Trial No. 1 2 3 4
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(a) (b)
Figure 3: (a) Spiral tool-path strategy and, (b) Contour tool-path strategy
Contour finishing tool-path was generated using MastercamX9 software, and coordinate point extraction was
carried out using a Microsoft Excel formula [10, 11]. Spiral tool-paths shown in figure ( b) was created using Matlab
script.
Figure 4: Spiral tool-path defined for the hyperbolic-cone, and the Pyramid Frustum
Figure 5: Contour tool-path defined for the hyperbolalic-cone, and for the Pyramid Frustum
Effect of Toolpath Strategy and Tool Rotation on Formability in Single Point Incremental Forming 15893
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THE EXPERIENTIAL SETUP
For the forming process, hemispheric tipped forming tools of a different radius of 5 mm and 6 mm were selected as shown
in Figure 6. The fixture for the job holding, as shown in Figure 7, was mounted on a machine table with three axes CNC
mill. The material used in the present study was a 290 mm*290 mm*1 mm size cold rolled steel sheet (CR2 / Drawing
quality). During the process of forming, drawing quality metal sheets were fastened along their edges in a specially
designed fixture which was mounted on the CNC machine table. To reduce friction between the forming tool and the sheet,
oil was applied.
Figure 6: Forming tools with 10mm and 12mm Diameter Spherical End
Figure 7: Experimental setup for Single Point Incremental Forming
FABRICATION OF PARTS
The initial dimension of the sheet is 290× 290×1mm blank sheet was loaded into the fixture. The forming tools having a
diameter of 10 mm and 12mm were used for the fabrication. As shown in Figure 8 and Figure 9, a total of four parts were
fabricated, the hyperbolic cones were fabricated using both spiral and contour tool-path and the pyramids with varying wall
angles were fabricated using both spiral and contour toolpath.
15894 Zeradam Yeshiwas & Krishnaiah Arkanti
Impact Factor (JCC): 8.8746 SCOPUS Indexed Journal NAAS Rating: 3.11
Figure 8: Necking formation on the pyramid with varying wall angle a) contour tool-path b) spiral tool-path
Figure 9: Necking formation on the hyperbolic cone c) contour tool-path d) Spiral Tool-Path
RESULTS AND DISCUSSIONS
This section attempted to provide a brief overview on how the toolpath strategy and tool rotational velocity influence the
formability through the maximum depth achieved or the maximum wall angle obtained when necking occurs in the sample
parts. After the occurrence of necking the maximum forming depth is measured using vernier height gauge (Figure 10) and
the maximum wall angle associate with this depth is calculated using equation 1.
Figure 10: Depth Measurement Method
Effect of Toolpath Strategy and Tool Rotation on Formability in Single Point Incremental Forming 15895
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EFFECT OF TOOLPATH STRATEGY ON FORMABILITY
Experimental Results
As detailed in Table 2, the toolpath strategy has a significant influence on the maximum depth. The result shows that the
formability depth achieved using the contour toolpath strategy (trial 1 and trial 3), is greater than the one attained using the
spiral toolpath strategy (trial 2 and trial 4). This can be explained by considering that the deformation depth values for the
contour toolpath strategy are higher than that of the spiral toolpath strategy. Crack is formed at a depth of 56.34 mm in a
hyperbolic cone shape with a contour toolpath, and crack is developed at a depth of 52.65 mm in a hyperbolic cone shape
with a spiral toolpath. Crack occurs at a depth of 56.22 mm in a pyramid (varying wall angles) shape with contour toolpath,
and at a depth of 54.24 mm in a pyramid (varying wall angles) shape with a spiral toolpath. The difference in the achieved
formability depth between the hyperbolic cone fabricated using the contour tool path and spiral tool-path is 3.69mm.
Whereas the difference between pyramids with varying wall angle fabricates using the contour tool path and spiral tool-
path is 1.98mm.
Table 2: Results on the effect of tool-path strategy on formability based on Maximum Forming Depth
Parameters Part
Hyperbolic cone Pyramid with varying wall angle
Tool-path Strategy Contour Spiral Contour Spiral
Trial No. 1 2 3 4
Depth at Failure (mm) 56.34 52.65 56.22 54.24
Difference (mm)
(Trial No. 1-Trial No.2)
(Trial No. 3-Trial No.4)
3.69 1.98
The maximum angle of the wall at a crack is the other parameter for evaluating formability in ISF. As shown in
Figure 11, the angle corresponding to the depth at a crack is called the maximum formability angle and it can be computed
using Equation 1.
1tan ( )p
Z
X
(1)
In the above equation, ΔZ/ΔX gives the slope at any point p on the tool-path and represents the wall angle at p.
Figure 11: Slop to Find the Maximum Formability Angle
15896 Zeradam Yeshiwas & Krishnaiah Arkanti
Impact Factor (JCC): 8.8746 SCOPUS Indexed Journal NAAS Rating: 3.11
Table 3 describes the findings obtained from the measurement of the maximum forming angle. Crack is formed at
a wall angle of 81.5° in a hyperbolic cone shape with contour toolpath, and crack is developed at a wall angle of 71.8° in a
hyperbolic cone with spiral toolpath. Crack occurs at a wall angle of 71.3° in a pyramid (varying wall angles) shape with
contour toolpath, and at a wall angle of 69° in a pyramid (varying wall angles) shape with a spiral toolpath. The difference
in the achieved formability wall angle between the hyperbolic cone fabricated using the contour tool path and spiral tool-
path is 9.7°. Whereas the difference between pyramids with varying wall angle fabricates using the contour tool path and
spiral tool-path is 2.3°.
Table 3: Results on the effect of tool-path strategy on formability based on Maximum Forming Angle
Parameters Part
Hyperbolic cone Pyramid with varying wall angle
Tool-path Strategy Contour Spiral Contour Spiral
Trial No. 1 2 3 4
Maximum formability angle (°) 81.5 71.8 71.3 69
Difference (°)
(Trial No. 1-Trial No.2)
(Trial No. 3-Trial No.4)
9.7 2.3
Numerical Simulation
Numerical simulation was done using ABAQUS/Explicit code. The G-code created was extracted to coordinate points by
using the Excel approach to define the displacement (amplitude versus time) data for the numerical simulation [10]. To
obtain a bounded solution time increment (∆t) is less than the stable time increment (∆tmin) and the value and the ratio of
kinetic energy to internal energy has to be less than 10% [11], all the conditions were satisfied.
The maximum formability depth in the simulation component is measured from the non-deformed portion to the
nodal point where the minimum thinning value was observed, i.e. 0.26 mm and 0.29 mm respectively for the contour and
spiral tool-path (Figure 12). Figure 12 shows the contour plot and Figure 13 presents the thinning versus depth
measurement of the simulated part.
(a) (b)
Figure 12: Contour plot and maximum and min values of thinning (a) Spiral Toolpath, (b) Contour Toolpath
Effect of Toolpath Strategy and Tool Rotation on Formability in Single Point Incremental Forming 15897
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(a) (b)
Figure 13: Depth measurement of the simulated part (a) Contour (b) Spiral
The deformation of the blank sheet reaches the maximum thinning value at a depth of 57.37 mm and 56.8 mm for
the hyperbolic cone with contour and spiral tool-path respectively. The result carried out from the fabricated part is in
good agreement with the one obtained by ABAQUS/Explicit. In both numerical simulation and fabricated parts, the
maximum forming depth is observed in the contour tool-path strategy.
Error Evaluation
Table 4 illustrates the simulation depth along path, fabricated depth at crack, error between simulation and fabricated part
for the two toolpath strategies in forming the hyperbolic cone. When the fracture occurs in the experimental trials, the
depth at fracture (df) were measured and compared with the simulation depth at minimum thinning (ds) achieved from the
numerical simulation. To verify the accuracy of the proposed prediction of formability, the error between the simulation
and experimental forming depth was calculated as shown in Table 3 using equation 2.
(%) *100%s f
s
d dd
d
(2)
Where; Δd, percentage error, df; depth for the fabricated, ds; depth for simulation
Table 4: Error between the numerical simulation and Fabricated Part based on Maximum Forming Depth
Part Tool-path
Strategy
Simulation Depth along
path
Fabricated
Depth at
crack
Error between simulation and Fabricated
Part (%)
Hyperbolic
cone
Contour 57.37mm 56.34mm 1.8
Spiral 55.23mm 52.65mm 4.67
Table 5: Error between the Numerical Simulation and Fabricated Part based on Maximum Forming Angle
Part Tool-path
Strategy
Maximum
forming angle
(Simulation)
Maximum
forming angle
(Fabricated)
Error between
simulation and
fabricated part (%)
Hyperbolic
cone
Contour 83.96° 81.5° 2.9
Spiral 78.90° 73.3° 7
15898 Zeradam Yeshiwas & Krishnaiah Arkanti
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EFFECT OF TOOL ROTATION ON FORMABILITY
The investigation of effect of tool rotation on the formability, the experiment was carried out for a fixed tool (0 rpm) and
tool rotation of 200 rpm were the rotational velocities chosen. Other process parameters were fixed according to the
reference values presented in Table 6.
Table 6: Parameters to study the effect of Tool Rotation on Formability
Parameters Part
Hyperbolic cone
Pyramid with
varying wall angle
Tool-path Strategy Contour Contour Spiral Spiral
Step Depth (mm) 0.5 0.5 0.8 0.8
Feed Rate (mm/min) 1500 1500 1000 1000
Tool Diameter (mm) 10 10 12 12
Wall Angle(°) 32-85 32-85 40-87 40-87
Rotational velocity(rev/min) 200 0 200 0
Trial No. 1 2 3 4
A total of four sample parts were fabricated to demonstrate the effect of tool rotation on the formability. Trial 1
and 2 were hyperbolic cones with contour toolpath strategy and fabricated with tool rotational velocity of 200rpm and
without rotational velocity respectively. Trial 3 and 4 were pyramids with varying wall angles using spiral toolpath strategy
and fabricated with tool rotational velocity of 200rpm and without rotational velocity. The sample parts were fabricated as
shown in Figures 14 and 15. To determine the forming depth, the depth at crack was determined using vernier height
gauge.
Figure 14: Hyperbolic Cone Fabricated Until Crack (a) without Tool Rotation (b) with 200rpm rotational velocity
Figure 15: Pyramid with varying wall angle fabricated until crack (c) with 200rpm rotational velocity (d) without
tool rotation
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As shown in Table 7, in the case of the hyperbolic cone formed using contour too-path without tool rotation crack was
developed at the depth of 56.34mm. However with tool rotation of 200rpm crack was not developed until the depth of
60mm. It shows that the maximum depth achieved using tool rotation is greater that 60mm. In the case of pyramid with
varying wall angle formed using spiral tool-path with fixed tool rotation crack was developed at the depth of 54.24mm.
However with tool rotation of 200rpm crack was developed at the depth of 57.89mm.
Table 7: Effect of Tool Rotation on Formability (Maximum Forming Depth)
Parameters Part
Hyperbolic cone
Pyramid with
varying wall angle
Tool-path Strategy Contour Contour Spiral Spiral
Trial No. 1 2 3 4
Formability Depth at Failure(mm) > 60 56.34 57.89 54.24
Difference (mm)
(Trial No. 1-Trial No.2)
(Trial No. 3-Trial No.4)
>3.66 3.65
As shown in Table 8, in the case of the hyperbolic cone formed using contour too-path without tool rotation crack
was developed at wall angle of 81.5°. However with tool rotation of 200rpm crack was not developed until the wall angle
of 85°. In the case of pyramid with varying wall angle formed using spiral tool-path with fixed tool rotation crack was
developed at the wall angle of 69°. However with tool rotation of 200rpm crack was developed at wall angle of 73.4°.
Table 8: Effect of Tool Rotation on formability (Maximum Forming Angle)
Parameters Part
Hyperbolic Cone
Pyramid with
varying Wall Angle
Tool-path Strategy Contour Contour Spiral Spiral
Trial No. 1 2 3 4
Maximum formability angle (°) > 85 81.5 73.4 69
Difference (°) (Trial No. 1-Trial No.2)
(Trial No. 3-Trial No.4)
>3.5 4.4
Based on the results of the experiment we can conclude that greater formability can be achieved using rotational
velocity than a sliding movement of the tool. The error between the hyperbolic cone fabricated using 0rpm and 200rpm is
>3.66mm. Whereas the error between pyramids with varying wall angle fabricate during 0rev/min and 200rpm is 3.65.mm.
CONCLUSIONS
The present research aimed to examine the effect of toolpath strategy and tool rotation on the formability of drawing
quality steel in single point incremental forming (SPIF). The findings indicate that tool rotation and toolpath strategy have
a significant influence on the formability in SPIF. The following conclusions can be made from the results of the study.
The investigation of the effect of toolpath strategy on the formability has shown that greater formability can be
achieved using a contour toolpath strategy than a spiral toolpath strategy.
The second major finding was that greater formability can be achieved using a rotating tool than a non-rotating
tool.
15900 Zeradam Yeshiwas & Krishnaiah Arkanti
Impact Factor (JCC): 8.8746 SCOPUS Indexed Journal NAAS Rating: 3.11
Numerical simulate can successfully predict formability in SPIF.
The error between the numerical simulation and the fabricated part was also reduced when we used the contour
tool-path strategy
The formability of the rotating tool increases the formability due to the stretching of the sheet resulting from the
heat generated due to friction at the local deformation zone.
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