A COMPARATIVE ANALYSIS STUDY OF HOLE FLANGING BY

Journal of Engineering Science and Technology Vol. 16, No. 6 (2021) 4383 - 4403 © School of Engineering, Taylor’s University

4383

A COMPARATIVE ANALYSIS STUDY OF HOLE FLANGING BY INCREMENTAL SHEET

FORMING PROCESS OF AA1060 AND DC01 SHEET METALS

MARWAN T. MEZHER1,*, SULAIMAN MUSTAFA KHAZAAL2, NASRI S. M. NAMER2, RUSUL AHMED SHAKIR3

1Middle Technical University, Institute of Applied Arts, Baghdad, Iraq 2Middle Technical University, Engineering Technical College - Baghdad, Iraq

3 University of Miskolc, Institute of Polymer and Ceramic Engineering, Miskolc, Hungary *Corresponding Author: [email protected]

Abstract

Incremental sheet forming (ISF) of hole flanged parts is recognised as an advanced sheet metal forming process with a high level of economic potential rewarding for small batch production of conical or cylindrical flanges for sheet blank with initial hole diameter. The current work investigates the formability of AA1060 aluminium alloy and DC01 carbon steel sheet metals throughout the hole flanging process by using the incremental forming technique. The process is explored by employing experimental analysis and compared with the numerical simulation results. A three-dimensional finite element model was developed to perform the numerical analysis on the incremental hole flanging process of truncated cone product by using Commercial ANSYS V.18 (Workbench LS-DYNA model) software to evaluate the effect of different pre-cut hole diameters on the quality of the final product. An elastic–plastic behaviour according to Cowper Symonds power-law hardening, assuming isotropic properties was used to simulate the plasticity behaviour of AA1060 and DC01 sheet materials during the hole flanging incremental forming process. The response of different parameters such as final hole diameter, forming depth, forming force, thickness distribution, thinning ratio, fracture behaviour, Von-Mises stress and effective plastic strain had been analysed numerically and experimentally for the verification of the results. The observations of this paper reveal that the DC01 carbon steel exhibit better results of response process parameters in comparison with AA1060 aluminium alloy at different initial hole diameters and the improvements in the results of DC01 as compared to AA1060 were as follow: 2.34% for the final hole diameter, 14.58% for the minimum thickness and 3.7% for the effective plastic strain.

Keywords: AA1060, DC01, Forming depth, Fracture behaviour, Hole flanging, Incremental sheet forming, Numerical simulation, Thickness distribution.

4384 M. T. Mezher et al.

Journal of Engineering Science and Technology December 2021, Vol. 16(6)

1. Introduction Single point incremental forming (SPIF) is a novel and flexible technology that has attracted more attention and become more promising in the industry to manufacture different complex shapes of products due to its benefits compared to the conventional forming process [1, 2]. These advantages of the SPIF process consisting of improvement of formability [3, 4] and manufacturing different 3D complex demanding components in the industry such as biomedical applications [5], automobile [6], and aerospace [7].

Hole flanging operation is a typical sheet metal forming process used for making flanges from pre-cut hole sheets which is provide high stiffness, allow for positioning and fixation of different parts with each other. Recent publication proved that hole flanging operation by using the incremental forming technique is a promising alternative for traditional hole flanging operation due to reducing the cost of dedicated tools (i.e., punch, blank holder and die cavity). Hole flanging operation is widely utilized in press-working processes to increase the strength and give more support to the edge of the holes, in addition to that, it also enhances the holes appearance and add more supplementary backing for joining sheet metal parts to tubes. Generally, the flanges are manufactured by using traditional hole flanging process which is characterized by the rising capital and cost of tools, therefore, the urgent need for appropriate metal forming operation that are qualified to of decreasing the costs of fabrication tools to a scale where the production of small-batch scale becomes economically feasible was the logical reason behind using the hole flanging process by using SPIF.

Many investigations have been conducted in an incremental hole flanging process for different metals by using numerical and experimental analyses. Borrego et al. [8] and Zhang et al. [9] found that the strain rate in hole flanging incremental forming developed from plane strain to biaxial strain conditions first and then changes to uniaxial tension with the increasing in hole-flanging depth.

Paul [10] applied numerical and experimental on the effect of deformation on the necking and failure in hole expansion test, the results point out that the strain is uniform throughout the width of hole flanging specimen. Han et al. [11] they studied experimentally and numerically the deformation behaviour and forming force in the straight hole flanging by using incremental sheet forming technique, the results indicate that the states of the strain are uniaxial as well as the plane strain and the forming force in Z direction decreases with the increase of forming depth.

Cao et al. [12] Made a comparative study of influence using ball-nose and new flanging tools on the deformation behaviour and the accuracy of the final part, results reveal that using new flanging tool generates more meridional bending than stretching deformation that appears in conventional incremental sheet forming and as a consequence of that, more uniform thickness distribution appear on flanging parts. Li et al. [13] and Gatea et al. [14] developed a numerical model by using the GNT model to predict the failure in the cone and pyramid SPIF sheets.

Hapsari et al. [15] applied a numerical study to predict the damage parameters based on Lemaitre's ductile damage evolution law during micro single point incremental forming of copper alloy, the parameters were analysed depend on force measurements of a truncated pyramid. Borrego et al. [16] demonstrated the limit forming ratio obtained in the hole flanging by SPIF is above 1.62 and the failure

A Comparative Analysis Study of Hole Flanging by Incremental Sheet . . . . 4385


appears in the wall of a product instead of at the edge of the flange which is usually noticed in the conventional hole flanging process.

The limit forming ratio depends on the initial hole diameter, forming tool shape, lubrication condition, and the mechanical properties of materials as it is noticed in [17-22]. Morales-Palma et al. [23] proposed a two-stage hole flanging process by SPIF to improve the homogenization of thickness distribution of flanges. Hussain et al. [24] investigated the influence of initial hole diameter on the formability of cylindrical hole flanging in SPIF, the authors reported that the flange thickness increases as the hole diameter increases while Von-Mises stress and formability reduce as the hole size increases.

Montanari et al. [25] conducted a study on hole flanging of SS304 in SPIF and conventional pressing. The results point out that when hoop stresses exceed the load-carrying capacity of metal, the failure will happen. Bambach, et al. [26] found that the hole expansion ratio reached up to 5.5 in hole flanging by using incremental sheet forming (ISF). Mugendirana and Gnanavelbabu [27] observed that the formability improved for the small hole diameter, on the other hand, the wall thickness increases as the hole diameter increases.

Wen et al. [28] they concluded that the spring-back effect reduces as the inclination of tool angle increases. Borrego et al. [8] carried out an experimental study to investigate the ability of the SPIF process to conducted hole flanging in a single stage, parameters such as forming limit ratio, forming force, and thickness distribution is also studied.

Mezher et al. [29, 30] investigated experimentally and numerically the impact of nanoparticles additive on the quality of formed products by using different forming operations and the results showed a significant improvement in the accuracy of the formed parts due to using Nano powder.

Namer et al. [31] studied the impact of lubricant viscosity type on the accuracy of a truncated cone of polymer sheets produced by the SPIF process and the results exhibit a considerable enhancement in the product quality owing to the increasing in the lubricant viscosity. Gao et al. [32] employed experimental and numerical analysis using hot forming process to predict the damage distribution and formability for AA7075-T6 aluminium alloy.

Betaieb et al. [33] used two models, namely a Gurson model and Lemaitre and Chaboche model to predict the cracks for DC01 carbon steel by using SPIF process and the findings show the Gurson model has an excellent accuracy to predict the failure and mechanical properties of the formed part. Changa et al. [34] applied analytical and experimental study to investigate the forming force fluctuations of various aluminium alloy by using several typical incremental sheet forming operations, the results indicate that the force fluctuations are caused by the varied of elastic deflection of the sheet metal.

Mezher et al. [35] adopted FEM and experimental investigations on the formability and spring-back angle by using SPIF process for AA1050 and DC05 sheet metals, the results indicate that the DC05 exhibit higher formability and lower spring-back angle than AA1050. Martinez-Donaire et al. [36] analysed the impact of stress triaxiality of AA7075-O during hole flanging process, the findings show that the local development of stress triaxiality of flanges at fracture point reveals an oscillating style as a consequence of alternative movements of the forming tool.



Salem et al [37] investigated the impact of the tool strain path on thinning and formability of AA7075-O aluminium alloy and they observed that the majority amount of thinning happened beneath the tool due to the development in the thickness reduction. Namer et al. [38] scrutinized the impact of nanoparticles on the tribological behaviour of AA2024-T4 aluminium alloy. Barrak, et.al [39] explored the tensile-shear strength for welded joints throughout employing double pre-holed joining technique.

The current work aims to present a better understanding in the terms of the formability by made a comparative analysis of hole flanging process through using single point incremental forming (SPIF). A series of experimental and numerical tests with different initial hole diameter (do) ranging from (10, 20, 30, 40, 50, 55, 60, 65, 70 and 75) mm of AA1060 aluminium alloy and DC01 carbon steel were studied. Parameters such as final hole diameter, fracture behaviour, formability (forming depth), forming force, thickness distribution, Von-Mises stress and effective plastic strain concerning the initial hole diameters were extensively discussed.

2. Experimental Setup

2.1.Material Selection and characterization: The materials used in the current work are DC01 carbon steel and AA1060 aluminium alloy with 1 mm thickness for both sheet metals. A group of tensile experiments had been conducted on a double-acting hydraulic press with a maximum capacity is 30 tons to identify the mechanical characterization of both sheet metals according to the ASTM-E8 standard [40], the mechanical properties and chemical composition are summarized in Tables 1 and 2 respectively.

Table 1. Mechanical properties of DC01 and AA1060 sheet metals. Properties DC01 AA1060 Tensile strength (MPa) 315 112 Yield strength (MPa) 179 56 Strength coefficient (K) (MPa) 610 168 Hardening exponent (n) 0.25 0.134 Poisson’s ratio (ν) 0.3 0.33 Young modulus (GPa) 200 69

Table 2. Chemical composition of DC01 and AA1060 sheet metals. Item % DC01 AA1060 Item % DC01 AA1060

Si 0.02 0.055 Ti ˂ 0.001 - Mn 0.203 0.007 W ˂ 0.001 - Mg - 0.0001 Nb ˂ 0.001 - Cu 0.075 0.005 C 0.05 - Zn 1.8 0.011 S 0.008 -

other 0.1 0.02 P 0.14 - Al 0.05 Balance Ni 0.056 - Fe Balance 0.168 Cr 0.053 - B ˂ 0.001 - Mo 0.005 - V ˂ 0.001 - Co 0.002 - Pb ˂ 0.001 -



2.2. Hole flanging by single point incremental forming (SPIF) The hole flanging experiments by single point incremental forming processes were performed on a TX32 CNC milling machine and the rig which is used to fix and deform the blank sheet was mounted on the table of CNC milling machine as illustrated in Fig. 1. A clamping arrangement (rig) is manufactured to carry out the experimental setup and it is consisting of a backing plate, clamping plate, lower and upper plate as well as the support pillar. Square sheets of DC01 carbon steel and AA1060 aluminium alloy with (200 X 200 X 1 mm) were used in the present study, the sheet blanks were cut from the centre by water cutting machine with different hole diameters are ranged (10, 20, 30, 40, 50, 55, 60, 65, 70 and 75) mm and the edge around the holes was carefully ground by using grit paper to remove any burrs and sharp edges. The tool path was selected as a spiral path with a step size equal 0.1 mm per revolution and numerically controlled by the CNC milling machine, in addition to that the forming angle was set up equal 75 ̊ to produce truncated cone with 100 mm base diameter. Forming tool diameter 16 mm made from hardened steel with 30 - HRC hardness, spindle speed 600 rev/min, and feed rate 800mm/min had been used as working conditions. These working conditions were selected depend on the primary tests that reveal those parameters were the best to produce a truncated cone without failure. The lubricant used between the blank sheet and the forming tool is Zinol type grease and its properties are listed in Table 3 and Fig. 2 shows some products of a truncated cone.

(a) TX32 CNC milling machine. (b) Forming tool.

Fig. 1. Fixture tools.

Table 3. Properties of Zinol grease type. Properties Value Drop point (at 25°C) 92 Flash point (°C) 176 Viscosity (at 40°C) (Pa.s) 16



Fig. 2. Samples of formed parts.

3. Finite Element Model To establish a reliable verification of experimental hole flanging by the SPIF process, a three-dimensional model was adopted by using the finite element method (FEM) with similar conditions of the experimental methodology of hole flanging process parameters.

FEA was performed by using commercial ANSYS V.18 (workbench LS-DYNA model) to construct the incremental hole flanging process whereas the analysis of the results had been achieved with the aid of LS-PREPOST software as depicted in Fig. 3. In the current study, ANSYS V.18 was utilized for develop a full model of hole flanging to produce a truncated cone of DC01 carbon steel and AA1060 aluminium alloy with different initial hole diameters varying as follow (10, 20, 30, 40, 50, 55, 60, 65, 70 and 75) mm. The blank sheet of both sheet metals assumed to behave an elastic-plastic behaviour, the Cowper Symonds power-law hardening is applied to describe the plasticity behaviour of blank sheets while the elastic behaviour is assumed isotropic which is simulated according to the Young’s modulus and Poisson’s ratio as it is described in Table 1.

The tools (forming tool, backing plate, and clamping plated) are modelled as rigid bodies whereas the blank sheet is modelled as a deformable body. A fully integrated shell element formulation with 7 points integration through-thickness was used to mesh and model the blank sheet and 0.002 mm as the element size has been used for discretized the blank sheet because the convergence study shows that the 0.002 mm is the best element size for meshing the blank sheet. The contact interface between the forming tool and the blank sheet was simulated according to the surface-to-surface forming method and soft constraint formulation is chosen as penalty and Coulomb’s friction law was applied to solve and describe the frictional interface effect between the forming tool and blank sheet, moreover, the coefficient of friction was set up to equal 0.15.

The hourglass control is applied according to the Flanagan-Belytschko stiffness form to reduce the integration. Modelling of hole flanging process was carried out in two steps, in the first step the backing plate and the clamping plate were rigidly fixed the blank sheet and the forming tool is constrained to move in the spiral path to achieve 75° as a forming angle of the truncated cone, while in the second step the fixture tools were removed to analyse the degree of spring-back.



Fig. 3. FE model of hole flanging by SPIF process.

4. Results and Discussions

4.1.Final hole diameter and forming depth Final hole diameter in hole flanging by SPIF process is commonly used to describe the stretch flange-ability after forming process and this factor can be defined as the maximum expansion of the final diameter of finished hole sample (dmax) after the completion of forming process. It worth noticing the initial hole diameters (do) less than 50 mm reveal no significant change in the expansion final hole diameter and forming depth as shown in Fig. 4, therefore the later experiments study will be conducted with pre-cut hole diameters larger than 50 mm.

Fig. 4. FEM and Experimental results of final

hole diameter at the initial hole diameter 30 mm.

The comparison of experimental and simulation results of the final hole diameter to the initial hole diameter of AA1060 aluminium alloy and DC01 carbon steel is presented in Fig. 5 respectively.

As can be observed from Fig. 5, the values of the final hole diameter in the experimental work are slightly different than the FEM results of both sheet metals. It worth noticing that from Fig. 5, in the case of initial hole diameter of 55 mm it could be expanded to the final diameter reached to 76 mm without failure and that corresponds the hole expansion ratio (HER) of 1.38, while in the case of 75 mm as initial diameter the final hole diameter is expanded to 90 mm with hole expansion ratio (HER) up to 1.2 for both metals due to inwards material flow from the center of the blank sheet during the forming process and these observations in the HER exceeding significantly the conventional limits in the hole flanging process without using SPIF process and this fairly agree with results found for aluminum alloys in



[17, 18]. The hole expansion mechanism can be attributed to the sever forming angle which leads to increase the meridional stresses along with the profile of the wall and this contributes the plastic deformation to coexist beyond the region of the contact with a forming tool which is considered the main effect that generates the hole expansion during hole flanging process, therefore a plastic deformation produced in the area of the blank sheet that does not have direct contact with forming tool.

Fig. 5. Experimental and FEM simulation results of the final hole diameter at different hole diameters.

Figure 6 shows the relation between the formability (forming depth) and initial hole diameter, it can be seen the forming depth decreases from around 31 mm to 15 mm when the hole diameter increased from 55 mm to 75 mm and that indicate the formability decreases with the increasing in pre-cut hole diameters and this increasing attributed to the decreasing in the volume of the metal available for forming process and this match the results found by Mugendirana and Gnanavelbabu [27].

Fig.6. Correlation between the formability and hole diameter.

Figure 7 illustrates the relation between the Von-Mises stress to the hole diameter, as it is obvious from Fig. 7 the Von-Mises stress increases as the hole diameter decreases and that agree with results reported by Hussain, et.al [24]. Moreover, the elements nearby the flange edge experiences the higher stresses than the elements close to the clamping plate and it can be noticed from Figs. 8 and 9 the stresses decrease after gaining the peak value and that is indicated the deformation behaviour of the elements nearby the flange edge at different hole diameters of both sheet metals is not uniform in comparison with the deformation at the earlier forming process. As it is evident from Figs. 8 and 9, there is no uniform



deformation observed at the end of the flange edge for all different pre-cut hole diameters. Another interesting point the Von-Mises stress of DC01 carbon steel is much higher than the stress of AA1060 aluminium alloy which is attributed to the high tensile strength of DC01 carbon steel in comparison with AA1060 aluminium alloy as it obvious from Table 1.

Fig. 7. Correlation between the Von-Mises stress and hole diameter.

(a) 55 mm. (b) 60 mm.

(c) 65 mm. (d) 70 mm.

(e) 75 mm.

Fig. 8. Von-Mises stress of AA1060 aluminum alloy at different initial hole diameters.



(a) 55 mm. (b) 60 mm

(c) 65 mm. (d) 70 mm.

(e) 75 mm.

Fig. 9. Von-Mises stress of DC01 carbon steel at different initial hole diameters.

4.2. Forming Force Figure 10 depicts the predicted forming force by finite element simulation to the period at various hole diameters, the maximum forming force increases with decreasing the pre-cut hole diameter of both sheet metals. As can be seen from Fig. 10 the forming force start to increase when the forming tool touches and begin in contact with the blank sheet and when the hole expanded circumferentially with stretching and bending process that is applied from the forming tool to the blank sheet, the forming force increased rapidly. This forming force exhibits the same evolution for different pre-cut hole diameters of both sheet metals, but later it reaches to a maximum value, and it can be noted it shows a nonzero value at the end of the experiment due to the spring-back force which is applied by the formed flange over the forming tool. DC01 carbon steel reveals higher forming force compared to AA1060 aluminum alloy at the same pre-cut holes which can be attributed to high values of strength coefficient (k) and strain hardening (n) of



DC01 that is more than those values of AA1060 as it is clearly shown in Table 1. When the strength coefficient (k) and strain hardening (n) become higher that is leads to strengthening the wall and flange of the product so that is mean more forces required to deform the blank sheet. For the same metal the increasing in the forming force with decreasing the pre-cut hole happened due to the metals’ volume available will be more and that leads to increase the forming force and the trends of the forming force were similar to those reported in [8, 12].

Fig. 10. forming force at different pre-cut hole diameters.

4.3.Fracture behaviour To clarify the modes of failure during hole flanging experiments by SPIF process in the current investigation which is happened due to localized deformation applied by forming tool and the expanded in the hole flange during the further steps of the forming process which tends to initiate different types of cracks at the flange tip. It can be observed from fractured specimens, there are two types of failure were noticed, the first one took place horizontally on the wall profile as illustrated in Fig. 11(a) and far away from the hole edge as results of maximum principal stresses along the meridional direction, this phenomenon similar to the type of fracture occurs in the conventional hole flanging process and this fairly agree with findings reported in [12]. The cross-section area of the fractured region portrays that the fractured thickness decreased from 1.0 mm to 0.39 mm with small necking. The second type of fracture is occurred at the edge of the expanded hole and take place from the outer surface of the flange towards the inner surface due to maximum principal stress in the circumferential direction and that is demonstrated this area has the biggest hazardous level as clearly illustrated in Fig. 11(b), the inner surface of fracture appears full of small dimples which are attributed to the growth of micro-voids with local ductile damage. The fractured thickness in the cross-section area reduced from 1.0 mm to 0.21 mm with the highest level of necking. These findings of fracture behavior match fairly with results found in [12], also in this paper was found as the hole is expanded during the operation, the cracks have shown tendency to happened at the tip of the flange and this agree with observations in [41]. The relation between the pre-cut hole diameter and the failure mode is when the initial hole diameter decreases, the metal available for forming operation increased, therefore, the thinning will increase and that result more failure.



(a) Horizontally fractured on the wall profile.

(b) Inner surface of fracture.

Fig. 11. Modes of failure in hole flanging by SPIF process.

The observations of fracture demonstrate that the small pre-cut holes with diameters varying from (10 to 60) mm have the dangerous limit of occurring cracks and failure whereas the pre-cut holes with diameters ranging from (65 to 75) mm reveal there are no risks of cracks, and it is considered the safe limit to avoid occurring the fracture as it is evident in Fig. 12, this observation agree with the results found in [18]. The experimental observations of fracture show good agreement with the numerical simulation results by using ANSYS V.18 (workbench LS-DYNA model) in the section of key formability as it clearly shows in Fig. 12.

(a) 70 mm. (b) 30 mm

Fig. 12. Formability limit obtained by finite element simulation.

4.4.Thickness distribution: One of the urgent issues in the hole flanging by SPIF process is the extreme thinning resulted in a non-uniform or uneven thickness distribution along the inclined wall of the formed part. In the present study, an attempt has been made to



improve the wall thickness to be larger using numerical and experimental investigation and the properties of the formed part has been considered as a factor to evaluate the quality response of the product, wall thickness distribution along the inclined wall of a formed part was used as the quality criteria. To calculate the thickness distribution of formed parts, all successful final samples were cut from the half-section. The Thickness variation along the profile product is measured with the use of a micrometer with a point-end type and the accuracy of micrometer is 0.0001inch (0.00254mm). The thickness distribution was measured at five locations evenly distributed along the wall profile of truncated cone in the experimental work as illustrated in Fig. 13.

Fig. 13. Method of thickness distribution measurement.

The thickness distribution is very sensitive to the pre-cut hole diameters in the numerical analysis and experimental work as shown in Figs. 14 and 15.

(a) 55 mm. (b) 60 mm.

(c) 65 mm. (d) 70 mm.



(e) 75 mm.

Fig. 14. FE results of the thickness distribution of AA1060 aluminum alloy at different pre-cut holes.

(a) 55 mm. (b) 60 mm

(c) 65 mm. (d) 70 mm.

(e) 75 mm.

Fig. 15. FE results of the thickness distribution of DC01 carbon steel at different pre-cut holes.

As it can be seen from Figs.14 and 15, the thickness distribution along the inclined wall for all specimens depicts a non-uniform profile and there are three distinct regions. Nearby the clamping plate it is noticed that the region with a bent shape is experienced with the continuous thickness reduction while the followed region it is suffered from severe thinning in compared to the other regions, where the conduct in the bottom region was similar behaviour of the first region and this match fairly with the observations reported in [37]. The thinnest region appears as a result of deformation which is caused by effective plastic strain and the correlation between



the pre-cut holes and effective plastic strain indicates to that as the hole diameter increases the effective plastic strain will be decreased as shown in Fig. 16 and this match with findings reported in [24]. The increase in thickness in the following region as a consequence of the material flow towards the edge of the hole.

Fig. 16. Correlation between effective plastic strain and hole diameter.

Figures 17 and 18 portray the variety of experimental and numerical results of thickness distribution to the initial hole diameters along with the profile of formed part of AA1060 aluminum alloy and DC01 carbon steel respectively, it can be noted there is a non-uniform distribution of thickness as it discussed earlier. The results show that the thinning is not uniform along the direction of an inclined flange, another interesting observation the maximum thinning has been observed at the middle region of the flange and the minimum thickness is significantly increased as the hole diameter increases due to reducing in the effective plastic strain as pointed out previously, in addition to that the material under forming tool has not much time to be stretched. The thickness distribution at hole diameter 55 mm decreases at first and later increases due to more material available from the blank sheet for deforming process. The relation between the failure mode and the thickness distribution is when the pre-cut hole decreases that results to deform more metal, therefore, the thinning will be more and hence more failure will be generated, these findings correspond fairly with the trends of thickness distribution that was found in [24]. The experimental results show good agreement with the finite element simulation data.



Fig. 17. Variation in thickness distribution

of AA1060 at different pre-cut holes.

Fig. 18. Variation in thickness distribution of DC01 at different pre-cut holes.



5. Conclusions In the present work, the key response and process parameters such as final hole expanded diameter, forming depth, fracture behavior, forming force and thickness distribution of truncated cone produced during hole flanging by SPIF process of AA1060 aluminum alloy and DC01 carbon steel has been extensively experimentally and numerically investigated. The following conclusions have been summarized as follow:

• The FE simulation results of the parameters (final hole diameter, forming depth, fracture behaviour and thickness distribution correspond fairly with the experimental results. The discrepancy between the experimental and FEM results as it follows: 0.996 % for the final hole diameter and 0.274% for the thickness distribution.

• DC01 carbon steel for different investigated parameters shows good results in comparison with AA1060 aluminium alloy at different initial hole diameters and the percentage of the improvement it was as follow: 2.34% for the final hole diameter, 14.58% for the minimum thickness and 3.7% for the effective plastic strain.

• The final hole diameter and formability (forming depth) are mainly affected by the pre-cut holes, in the case of 55 mm, the obtained final diameter reaches up to 76 mm whereas it is found 90 mm in case of 75 mm. Furthermore, the forming depth for the initial hole diameter 55 mm was 31 mm whilst it is reduced to 15 mm for 75 mm as an initial diameter.

• The forming force was increased by decreasing the pre-cut hole diameter for both sheet metals. The truncated cone of DC01 carbon steel exhibits a higher forming force than AA1060 aluminium alloy at the same conditions of the pre-cut hole.

• Based on the experimental and numerical observations, the facture and initiation of cracks occur in two places, the first one was noted horizontally on the wall profile and far away from the edge hole while the second type of fracture took place at the edge of the expanded hole and start from the outer surface of the flange towards the inner surface.

• Von-Mises stress and effective plastic strain decreases with increasing the initial hole diameter.

• The homogeneity of thickness distribution along the truncated cone profile has been improved with increasing the initial hole diameter.

Nomenclatures dmax Final hole diameter (mm) do

Initial hole diameter (mm) E Young Modulus (GPa) σt Tensile strength (MPa) σy Yield strength (MPa) Greek Symbols ν Poisson’s ratio



Abbreviations

FEM Finite Element Method ISF Incremental Sheet Forming SPIF Single Point Incremental Forming SS Stainless Steel

References 1. Gatea, S.; Ou, H.; and McCartney, G. (2016). Review on the influence of

process parameters in incremental sheet forming. The International Journal of Advanced Manufacturing Technology, 87, 479-499.

2. McAnulty, T.; Jeswiet, J.; and Doolan, M. (2017). Formability in single point incremental forming: A comparative analysis of the state of the art. CIRP Journal of Manufacturing Science and Technology, 16, 43-54.

3. Roll, I.K. (2008). Simulation of sheet metal forming - Necessary developments in the future. Proceeding of the Second International Conference and Workshop on Numerical Simulation of 3D Sheet Metal Forming Processes. Interlaken, Switzerland.

4. Katipelli, L.R.; Agarwal, A.; and Dahotre, N.B. (2000). Laser surface engineered TiC coating on 6061 Al alloy: Microstructure and wear. Applied Surface Science, 153(2-3), 65-78.

5. Lu, B.; Ou, H.; Shi, S.Q.; Long, H.; and Chen, J. (2016). Titanium based cranial reconstruction using incremental sheet forming. International Journal of Material Forming, 9, 361-370.

6. Oleksik, V.; Pascu, A.; Deac, C.; Fleacă, R.; Bologa, O.; and Racz, G. (2010). Experimental study on the surface quality of the medical implants obtained by single point incremental forming. International Journal of Material Forming, 3, 935-938.

7. Ji, Y.H.; and Park, J.J. (2008). Incremental forming of free surface with magnesium alloy AZ31 sheet at warm temperatures. Transactions of Nonferrous Metals Society of China, 18(Supplement 1), s165-s169.

8. Borrego, M.; Morales-Palma, D.; Martínez-Donaire, A.J.; Centeno, G.; and Vallellano, C. (2016). Experimental study of hole-flanging by single-stage incremental sheet forming. Journal of Materials Processing Technology, 237, 320-330.

9. Zhang, H.; Zhang, Z.; Ren, H.; Cao, J.; and Chen, J. (2018). Deformation mechanics and failure mode in the stretch and shrink flanging by double-sided incremental forming. International Journal of Mechanical Sciences, 44, 216-222.

10. Paul, S.K. (2019). The effect of deformation gradient on necking and failure in hole expansion test. Manufacturing Letters, 21, 50-55.

11. Han, K.; Li, X.; Peng, X.; Wang, H.; Li, D.; Li, Y. and Li, Q. (2019). Experimental and numerical study on the deformation mechanism of straight flanging by incremental sheet forming. International Journal of Mechanical Sciences, 160, 75-89.



12. Cao, T.; Lu, B.; Ou, H.; Long, H.; and Chen, J. (2016). Investigation on a new hole-flanging approach by incremental sheet forming through a featured tool. International Journal of Machine Tools and Manufacture, 110, 1-17.

13. Li, J.; Li, S.; Xie, Z.; and Wang, W. (2015). Numerical simulation of incremental sheet forming based on GTN damage model. The International Journal of Advanced Manufacturing Technology, 81, 2053-2065.

14. Gatea, S.; Ou, H.; Lu, B.; and McCartney, G. (2017). Modelling of ductile fracture in single point incremental forming using a modified GTN model. Engineering Fracture Mechanics, 186, 59-79.

15. Hapsari, G.; Hmida, R.B.; Richard, F.; Thibaud, S.; and Malécot, P. (2017). A procedure for ductile damage parameters identification by micro incremental sheet forming. Procedia Engineering, 183, 125-130.

16. Borrego, M.; Morales-Palma, D.; Martínez-Donaire, A.J.; Centeno, G.; and Vallellano, C. (2015). On the study of the single-stage hole-flanging process by SPIF. Procedia Engineering, 132, 290 - 297.

17. Cui, Z.; and Gao, L. (2010). Studies on hole-flanging process using multistage incremental forming. CIRP Journal of Manufacturing Science and Technology, 2(2), 124-128.

18. Centeno, G.; Silva, M.B.; Cristino, V.A.M.; Vallellano, C.; and Martins, P.A.F. (2012). Hole-flanging by incremental sheet forming. International Journal of Machine Tools and Manufacture, 59, 46-54.

19. Cristino, V.A.M.; Montanari, L.; Silva, M.B.; Atkins, A.G.; and Martins, P.A.F. (2014). Fracture in hole-flanging produced by single point incremental forming. International Journal of Mechanical Sciences, 83, 146-154.

20. Cristino, V.A.M.; Silva, M.B.; Wong, P.K.; Tam, L.M.; and Martins, P.A.F. (2015). Hole-flanging of metals and polymers produced by single point incremental forming. International Journal of Materials and Product Technology, 50(1), 37-48.

21. Ali, S.S.; Raafat, S.M.; and Al-Khazrji, A. (2020). Improving the performance of medical robotic system using H∞ loop shaping robust controller. International Journal of Modelling, Identification and Control, 34(1), 3-12.

22. Ali, S.S. (2020). Position control of ball and beam system using robust H∞ loop shaping controller. Indonesia Journal of Electrical Engineering and Computer Science, 19(1), 91-98.

23. Morales-Palma, D.; Borrego, M.; Martínez-Donaire, A.J.; López-Fernández, J.A.; Centeno, G.; and Vallellano, C. (2018). Numerical study on the thickness homogenization in hole-flanging by single-point incremental forming. Proceeding of the 11th International Conference and Workshop on Numerical Simulation of 3D Sheet Metal Forming Processes. Tokyo, Japan.

24. Hussain, G.; Valaei, H.; Al-Ghamdi, K.A.; and Khan, B. (2016). Finite element and experimental analyses of cylindrical hole flanging in incremental forming. Transaction of Nonferrous Metals Society of China, 26(9), 2419-2425.

25. Montanari, L.; Cristino, V.M.A.; Silva, M.B.; and Martins, P.A.F. (2013). On the relative performance of hole-flanging by incremental sheet forming and conventional press-working. Proceedings of the Institutions of Mechanical Engineer, Part L: Journal of Materials: Design and Applications, 228(4), 312-322.



26. Bambach, M.; Voswinckel, H.; and Hirt, G. (2014). A new process design for performing hole-flanging operations by incremental sheet forming. Procedia Engineering, 81, 2305-2310.

27. Mugendiran, V.; and Gnanavelbabu, A. (2018). Analysis of hole flanging on AA5052 alloy by single point incremental forming process. Materials Today: Proceedings, 5(2), 8596-8603.

28. Wen, T.; Zhang, S.; Zheng, J.; Huang, Q.; and Liu, Q. (2016). Bi-directional dieless incremental flanging of sheet metals using a bar tool with tapered shoulders. Journal of Materials Processing Technology, 229, 795-803.

29. Mezher, M.T.; Namer, N.S.M.; and Nama, S.A. (2018). Numerical and experimental investigation of using lubricant with nano powder additives in SPIF process. International Journal of Mechanical Engineering and Technology, 9(13), 968-977.

30. Mezher, M.T.; Saad, M.L.; Barrak O.S.; and Shakir, R.A. (2020). Finite element simulation and experimental analysis of nano powder additives effect in the deep drawing process. International Journal of Mechanical and Mechatronics Engineering, 20(1), 166-180.

31. Namer, N.S.M.; Naáma, S.A.; and Mazhir, M.T. (2015). Influence of lubricant viscosity on the surface roughness of PEHD and PVC plastic sheets in single point incremental forming process. International Journal of Engineering and Applied Sciences, 7(2), 27-30.

32. Gao, T.; Ying, L.; Hu, P.; Han, X.; Rong, H.; Wu, Y.; and Sun, J. (2020). Investigation on mechanical behavior and plastic damage of AA7075 aluminum alloy by thermal small punch test: Experimental trials, numerical analysis. Journal of Manufacturing Processes, 50, 1-16.

33. Betaieb, E.; Yuan, S.; Guzman, C.F.; Duchȇne, L.; and Habraken, A.M. (2019). Predication of cracks within cones processed by single point incremental forming. Procedia Manufacturing, 29, 96-104.

34. Chang, Z.; Li, M.; and Chen, J. (2019). Analytical modeling and experimental validation of the forming force in several typical incremental sheet forming processes. International Journal of Machine Tools and Manufacture, 140, 62-76.

35. Mezher, M.T.; Barrak, O.S.; Nama, S.A.; and Shakir, R.A. (2021). Predication of forming limit diagram and spring-back during SPIF process of AA1050 and DC04 sheet metals. Journal of Mechanical Engineering Research and Developments, 44(1), 337-345.

36. Martínez-Donaire, A.J.; Borrego, M.; Morales-Palma, M.; Centeno, G.; and Vallellano, C. (2019). Analysis of the influence of stress triaxiality on formability of hole-flanging by single-stage SPIF. International Journal of Mechanical Sciences, 151, 76-84.

37. Salem, E.; Shin, J.; Nath, M.; Banu, M.; and Taub, A.I. (2016). Investigation of thickness variation in single point incremental forming. Procedia Manufacturing, 5, 828-837.

38. Namer, N.S.M.; Nama, S.A.; and Mezher, M.T. (2019). The influence of nano particles additive on tribological properties of Aa2024-T4 coated with Tin or Sin thin films. Journal of Mechanical Engineering Research and Developments, 42(3), 30-34.



39. Barrak, O.S.; Saad, M.L.; Mezher, M.T.; Hussein, S.K.; and Hamzah, M.M. (2020). Joining of double pre-holed aluminum alloy AA6061-T6 to polyamide PA using hot press technique. Proceeding of the Third International Conference on Sustainable Engineering Techniques. Baghdad, Iraq.

40. ASTM E8M-04 (2004). Standard test methods for tension testing of metallic materials, American Society for Testing Materials, Pennsylvania, United States of America.

41. Kacem, A.; Krichen, A.; Manach, P.Y.; Thuillier, S.; and Yoon, J.W. (2013). Failure prediction in the hole-flanging process of aluminium alloys. Engineering Fracture Mechanics, 99, 251-265.

Documents

A COMPARATIVE ANALYSIS STUDY OF HOLE FLANGING BY