effect of toolpath strategy and tool ......xu et al. (2013)[2] used aa5052-h32 aluminum alloy with...

www.tjprc.org SCOPUS Indexed Journal [email protected]

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.

http://www.tjprc.org/

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


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




(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



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.




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 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


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)


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




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


Trial No. 1 2 3 4

Maximum formability angle (°) 81.5 71.8 71.3 69

Difference (°)



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



(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




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



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


Trial No. 1 2 3 4

Formability Depth at Failure(mm) > 60 56.34 57.89 54.24

Difference (mm)



>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


Trial No. 1 2 3 4

Maximum formability angle (°) > 85 81.5 73.4 69

Difference (°) (Trial No. 1-Trial No.2)


>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.




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.

REFERENCES

1. Davarpanah, MA., Mirkouei, A., Yu, X., Malhotra, R., Pilla, S. "Effects of incremental depth and tool rotation on failure modes

and microstructural properties in Single Point Incremental Forming of polymers", J Mater Process Technol. 222, pp. 287-300,

2015.

2. Xu, D., Wu, W., Malhotra, R., Chen, J., Lu, B., Cao, J. “Mechanism investigation for the influence of tool rotation and laser

surface texturing (LST) on formability in single point incremental forming”, Int J Mach Tools Manuf. 73, pp. 37-46, 2013.

3. Hamilton, K., Jeswiet, J. “Single point incremental forming at high feed rates and rotational speeds: Surface and structural

consequences”, CIRP Ann - Manuf Technol. 59(1), pp. 311-314, 2010.

4. Kumar, A., Gulati, V., Kumar, P., Singh, V., Kumar, B., Singh, H. “Parametric effects on formability of AA2024-O

aluminum alloy sheets in single point incremental forming,” J. Mater. Res. Technol. 8(1), pp. 1461–1469, 2019.

5. Rattanachan, K. “Formability in Single Point Incremental Forming of Dome Geometry”, Aijstpme. 2, pp. 57-63, 2009.

6. Gulati, V., Aryal, A., Katyal, P., Goswami, A. “Process Parameters Optimization in Single Point Incremental Forming” , J.

Inst. Eng. Ser. C.97(2), pp. 185–193, 2016.

7. Bagudanch, I., Garcia-Romeu, ML., Centeno, G., Elías-Zúñiga, A., Ciurana, J. “Forming force and temperature effects on

single point incremental forming of polyvinylchloride”, J. Mater. Process. Technol. 219, pp. 221–229, 2015.

8. Kumar, A., Gulati, V. “Experimental investigation and optimization of surface roughness in negative incremental forming”,

Meas. J. Int. Meas. Confed. 131(August), pp. 419–430, 2019.

9. Liu, Z., Li, Y., Meehan, PA. “Experimental investigation of mechanical properties, formability and force measurement for

AA7075-O aluminum alloy sheets formed by incremental forming”, International Journal of Precision Engineering and

Manufacturing. 14(11), pp.1891-1899, 2013.

10. Krishnaiah, A. Zeradam, Yeshiwas. “Extraction of Coordinate Points for the Numerical Simulation of Single Point

Incremental Forming Using Microsoft Excel”, Springer International Publishing, 2020.

11. Zeradam, Y., Krishnaiah, “A. Numerical Simulation and Experimental Validation of Thickness Distribution in Single Point

Incremental Forming for Drawing Quality Steel”, International Journal of Applied Engineering Research. 15(1), pp.101–107,

2020.

effect of toolpath strategy and tool ......xu et al. (2013)[2] used aa5052-h32 aluminum alloy with...

Documents