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Efficiency Analysis of Incremental Forging Processes on Flat Surfaces
Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 132 (2015) 358 – 365
The Manufacturing Engineering Society International Conference, MESIC 2015
Efficiency analysis of incremental forging processes on flat surfaces C. Bernala,*, A. M. Camachoa, M.M. Marína a
Department of Manufacturing Engineering, Universidad Nacional de Educación a Distancia), c/ Juan del Rosal 12, Madrid, 28040, Spain
Abstract Incremental forging processes produce permanent deformations by means of repeated localized compressions of the material in the work piece. These processes has interest from technological point of view because they can be carried out in CNC machines with more flexibility and lower forces requirements than in conventional forging processes. The purpose of this work is the analysis of efficiency of the incremental forming process of flat surfaces by means of simple tools, particularly ball end tools that are capable of forming the surface with lower axial forces. Then the ball-rolling incremental forging process has been investigated and a series of tests have been conducted in order to evaluate the forces produced during the deformation of the surfaces and the feasibility of the process. © by Elsevier Ltd. by This is an open © 2015 2016Published The Authors. Published Elsevier Ltd.access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of MESIC 2015. Peer-review under responsibility of the Scientific Committee of MESIC 2015 Keywords: Incremental forming process; ball-rolling forging process; local hardening; material displaced.
1. Introduction Incremental bulk forming processes are increasingly used in industry due to their economic and technological advantages. These processes have a high flexibility and require less energy and smaller and simpler tools and dies. As described in the literature [1], these processes are generally net-shape, improving both forming ratios and properties of the obtained pieces compared to conventional die operations enhancing hardening and grain structure of the products. Other advantages of incremental bulk forming processes are that global forces, friction and wear of tools are lower, despite the high local loads applied on the tools. In addition, these processes require lower investments with lower tooling costs.
* Corresponding author. Tel.: +3491 3988668 E-mail address: [email protected]
1877-7058 © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of MESIC 2015
doi:10.1016/j.proeng.2015.12.506
C. Bernal et al. / Procedia Engineering 132 (2015) 358 – 365
Examples of incremental bulk forming processes are orbital forming, rotary swaging, roller burnishing [2, 3] or localized-incremental forging processes (LIFP) [4, 5]. Incremental forging processes can be carried out in CNC machines with more flexibility and lower forces requirements and do not require complex dies. In this case, a force is applied on the work piece surface by a punch to produce an impression on the material. The discrete compression process causes permanent plastic deformations, that repeated incrementally let forming the work piece by a localized incremental forging action [6, 7]. The purpose of this work is the analysis of the ball-rolling incremental forging process. First, a comparison of effectiveness of various cylindrical tools in the localized-incremental forging process has been simulated considering axial forces of the tool as a function of the amount of material displaced. Then the forming of the surface by means of a rolling ball tool has been compared with a simple penetration process showing that lower forces are required. In this case the forming of the surface by compressing the material with a rolling ball is continuous along a determined path producing permanent plastic deformation on the surface. Similar processes has been used in material hardening applications, creating on the surface of the part a certain level of residual stress in order to improve damage tolerance and fatigue or stress corrosion performance [8, 9]. In the next step, different test have been done on physical models in order to evaluate the feasibility of the process, the surface obtained, and the forces produced on principal axes during the incremental forging operation. 2. Finite element analysis of incremental forging process 2.1. Indentation process In order to know the behavior of different tools, an elementary indentation process has been simulated with the Finite Element code DEFORM. The axial forces of penetration of different tools has been evaluated according to the volume of material displaced. This volume has been calculated as a function of the penetration depth (tool stroke) and the punch geometry. The tools considered are: hemispherical punch, fillet-end tool (torical tool) and sphericalend punch. These tools are defined by R: radius of the tool; Rp: radius of the spherical end of the tool and r: radius of the torical end of the tool. Three geometries of punches have been analyzed: a) hemispherical punch (R8; Rp8), b) fillet-end tool (R8; r2) and c) spherical-end punch (R8; Rp15). Likewise, another spherical-end tool (R15; Rp15) has also been chosen to analyze the process. In all cases a friction factor of 0.08 is considered. In DEFORM this is the value to take into account for cold forming processes with carbide dies. The material UNS A91100, which is commercially pure aluminum with excellent forming characteristics, is used as reference material. The simulation of the cold forming process is performed using DEFORM F2 implicit solver by means of a 3550 elements plastic workpiece (upper and lower dies are considered rigid) running 200 steps process with intermediate remeshing. In Figure 1 it is observed that forces of penetration of the hemispherical punch (R8, Rp8) are always lower for the same volume of material displaced. In the case of the spherical punch (R8, Rp15), forces required are lower than with the fillet-end punch until the radius of the impression reaches the value R = 8mm. It is due to the fact that for the same volume of material displaced, that tool has a lower projected contact area than the fillet-end punch which applies higher pressures. Curves for the indentation with spherical tools (R15; Rp15) and (R8; Rp15) show the same behavior, until the imprint of the larger tool reaches the equivalent radius R = 8mm. From this value the force increases due to the increase of contact area with the punch. This analysis shows that the displacement of material is easier when using spherical-end tools. The indentation forces decrease with the spherical radius Rp until a minimum value is reached that corresponds to the case of hemispherical punch (ball-end tool). However, the obtained surface after a multiple indentation process presents irregularities that directly depend on the process parameters and on the tool geometry.
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Fig. 1. Axial forces on punch vs volume of material displaced in an elementary indentation process (UNS A91100 material, cold forming)
2.2. Ball-rolling incremental forging process Next a ball-rolling incremental forging process has been simulated in order to compare the forces required in the forming operation. The simulation has been done using the DEFORM implicit solver with a 2081 elements model. In an indentation process, the axial force depends on the stroke, the friction coefficient and the tool geometry. In the ball rolling forming process the displacement of the tool generates axial and lateral forces on the tool. In this case, the relevant forces to take into account are the lateral forces, since during the ball-rolling incremental forging operation there is no displacement of the tool in axial direction. In order to compare the indentation process and the rolling process, the loads has been simulated and calculated as a function of the material displaced during the movement of the tool. Figure 2 show the finite element model of the ball-rolling incremental forging operation implemented in DEFORM.
Fig. 2. Effective stress on the work piece in ball-rolling incremental forging operation
The case of ball rolling process is interesting because lower forces are required. In this case only the lateral force is considered since, in the considered process, there is no displacement or mechanical work in axial direction (axis of the tool). As expected, for the same volume of material displaced, the rolling process requires less force than the indentation process. In the first case the registered loads are the lateral loads and for the case off indentation process we take into account the axial force applied on the punch. Figure 3 displays loads versus volume of material
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C. Bernal et al. / Procedia Engineering 132 (2015) 358 – 365
displaced for the axial indentation and ball rolling process. In both cases a spherical tool of Rp = 8 mm has been used.
Fig. 3. Loads versus volume of material displaced (Ball-end tool -UNS A91100)
3. Methodology and testing procedure 3.1. Test material All tests were performed on tin plates with a fineness of 99.9 %. This metal is very malleable and has the advantage of its very high workability. The recrystallization temperature of tin is room temperature and do not have strain hardening. This is a requirement for testing in order to prevent machine overloading [10]. Hardness test was performed with Emco-test N3 durometer using the Brinell Hardness scale (ball indentation). In the Brinell hardness scale the indentation is measured and hardness calculated as [11-15]:
HBS
2F
S .D D D 2 d 2
(1)
where F is the applied force (kgf), D the diameter of indenter (mm) and d the diameter of indentation (mm). Considering the material, a force of 15 kgf with an indenter of 2.5 mm of diameter has been applied during 60 s resulting the following hardness for the tin (fineness of 99.9 %): 5.65 HBS 2.5/15/60 Considering the hardness of the material employed it is possible to approximate reference values of indentation forces as a function of indenter diameter and diameter of indentation. This information is required to determine the forces in testing machine. 3.2. Tools and testing machine The machine used for indentation and ball rolling test is a machining center Tongtai TMV-510 with Fanuc 0i controller. The tin plate has been screwed on a dynamometer Kistler 9257B with 5070 control unit. In order to obtain reliable results, a face milling was performed on the tin plates due to the roughness of the surface from casting (Figure 5).
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Two ball rolling tools have been manufactured in two diameters: 15 and 20 mm (Figure 4). The tests have been carried out with 15 mm tool.
Fig. 4. Sketch of ball rolling tool
A linear rolling cycle has been programmed as follows: 1. 2.
z axis penetration from the reference plane (surface of the tin plate). The maximum stroke on z axis was determined calculating maximum z load from equation (1). Keeping z fixed, a point to point command is executed for each penetration value (Figure 5).
This cycle was repeated for z values of 0.1; 0.2; 0.3 and 0.35 mm.
Fig. 5. Linear rolling test with the tin plate mounted on dynamometer.
4. Results The loads xyz were recorded by the dynamometer during the linear rolling test. The loads are indicated in N as a function of the time of cycle t. For the four values of penetration tested (0.1; 0.2; 0.3 and 0.35 mm), the dynamometer records loads during 25 seconds of linear movement. The results corresponding to the linear rolling cycle with a depth of pass of 0.1 mm are shown in Figure 6. During the penetration stroke, only the force along z axis increases. When the linear rolling movement starts, the forces along y and z axis increases. The increment of material displaced in front of the rolling ball produces increased forces in z direction. After a while the force in z tends to remain constant.
C. Bernal et al. / Procedia Engineering 132 (2015) 358 – 365
Fig. 6. RMS values of loads vs time (0.1 mm pass)
Figures 7, 8 and 9 show the root mean square values of xyz loads for the values of depth 0.2, 0.3 and 0.35 mm. The values of loads are given in N and the time of cycle in s. As expected, the loads along y and z axes increase with depth of pass, with a force along the x axis close to zero but nonzero due to possible misalignment of the dynamometer. In these tests it is noticed that, in the first step of the cycle (penetration), z force increases rapidly. Then, rolling forces also increase after penetration movement due to the increment of material in front of the rolling ball that produces increased forces in z and y. In this case there is not strain hardening, taking into account the recrystallization temperature of tin. Later, forces tend to remain constant. The ball-rolling incremental forging process shows that the lateral forces applied on the tool during the deformation of the surface are lower than the axial penetration forces and there is no z axis displacement during the rolling incremental forging process.
Fig. 7. RMS values of loads vs time (0.2 mm pass)
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Fig. 8. RMS values of loads vs time (0.3 mm pass)
Fig. 9. RMS values of loads vs time (0.35 mm pass)
5. Conclusions The efficiency analysis of the incremental forging process of flat surfaces by means of different tools shows that the displacement of material is easier when using spherical-end tools and particularly with hemispherical tools (ballend tools). With ball end tools it is possible to form the surface with lower axial forces. Moreover, the ball-rolling incremental forging process shows that the lateral forces applied on the tool during the deformation of the surface are lower than the axial penetration forces. Since during rolling there is no displacement along z axis (penetration of tool) the rolling process is more efficient and consume less energy. In addition, using standard CNC machines, incremental forging processes provide more flexibility and better process control. It is also possible to control the local deformation that produces hardening of the material and better
C. Bernal et al. / Procedia Engineering 132 (2015) 358 – 365
grain structure. Moreover, despite the high local loads applied on the tools, these processes can be carried out in lighter machines with simpler and smaller tools. Acknowledgements This work has been financially supported by the Annual Grant Call of the ETSI Industriales of UNED (reference 2014-ICF04). References [1] J.M. Allwood, H. Utsunomiya, A survey of flexible forming processes in Japan, Int J of Mach Tool Manuf. 46 (2006) 1939-1960. [2] J. Nowak, G. Madej, F. Grosman, M. Pietrzyk, Material flow analysis in the incremental forging technology, Int J Mater Form. 3 (2010) 931-934. [3] S. Bruschi, S. Casotto, T. Dal Negro, R. Icarelli, Modelling material behaviour in incremental bulk forming processes, Proc. ICTP 2005, Verona. [4] C. Bernal, A.M. Camacho, M. Marín, B. de Agustina, Methodology for the evaluation of 3D surface topography in multiple indentation processes, The Int J of Adv. Manuf. Techn. 69, (2012) 2091-2098. [5] C. Bernal, A.M. Camacho, J. M. Arenas, E.M. Rubio, Analytical procedure for geometrical evaluation of flat surfaces formed by multiple indentation processes. Applied Mechanics and Materials (2012), pp. 2351-2356. [6] A.M. Camacho, M.M. Marin, C. Bernal, M.A. Sebastián, Implicit and explicit techniques for Localized-Incremental Forging processes analysis by Computer Aided Engineering. The International Journal of Computer Aided Engineering and Technology (2013). [7] A.M. Camacho, M.M. Marin, C. Bernal, M.A. Sebastián, Simulation and experimental techniques for the analysis of localised-incremental forging operations. Proceedings of the European Simulation and Modelling Conference 2011, edited by EUROSIS, Ghent University. [8] P.S. Prevey, N. Jayaraman, Overview of low plasticity burnishing for mitigation of fatigue damage mechanism. Proceedings of ISCP 9 (2005), Paris [9] D. Hornbach, P. Prevey, M. Piche, D. Rivest, The influence of surface enhancement by low plasticity burnishing on the corrosión of 7475T7351 and 2024-T351. Proceedings of Aerospace Conference ISCP 10 (2008), Tokyo. [10] O. Tuysuz, Y. Altintas, H. Feng, Prediction of cutting forces in three and five axis ball-end milling with tool indentation effect. International Journal of Machine Tolls & Manufacture, 66 (2013), pp. 66-81. [11] ISO 18265 (2013) Metallic materials-Conversion of hardness values, International Organization for Standardization (ISO), Geneva. [12] ISO 4498 (2010) Sintered metal materials, excluding hardmetals, Determination of apparent hardness and microhardness, International Organization for Standardization (ISO), Geneva. [13] ISO 6506-2 (2014) Metallic materials, Brinell hardness test, Part 2: Verification and calibration of testing machines, International Organization for Standardization (ISO), Geneva. [14] ISO 6506-3 (2014) Metallic materials, Brinell hardness test, Part 3: Calibration of reference blocks, International Organization for Standardization (ISO), Geneva. [15] ISO 6506-4, Metallic materials, Brinell hardness test, Part 4: Table of hardness values, International Organization for Standardization (ISO), Geneva.
365
ScienceDirect Procedia Engineering 132 (2015) 358 – 365
The Manufacturing Engineering Society International Conference, MESIC 2015
Efficiency analysis of incremental forging processes on flat surfaces C. Bernala,*, A. M. Camachoa, M.M. Marína a
Department of Manufacturing Engineering, Universidad Nacional de Educación a Distancia), c/ Juan del Rosal 12, Madrid, 28040, Spain
Abstract Incremental forging processes produce permanent deformations by means of repeated localized compressions of the material in the work piece. These processes has interest from technological point of view because they can be carried out in CNC machines with more flexibility and lower forces requirements than in conventional forging processes. The purpose of this work is the analysis of efficiency of the incremental forming process of flat surfaces by means of simple tools, particularly ball end tools that are capable of forming the surface with lower axial forces. Then the ball-rolling incremental forging process has been investigated and a series of tests have been conducted in order to evaluate the forces produced during the deformation of the surfaces and the feasibility of the process. © by Elsevier Ltd. by This is an open © 2015 2016Published The Authors. Published Elsevier Ltd.access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of MESIC 2015. Peer-review under responsibility of the Scientific Committee of MESIC 2015 Keywords: Incremental forming process; ball-rolling forging process; local hardening; material displaced.
1. Introduction Incremental bulk forming processes are increasingly used in industry due to their economic and technological advantages. These processes have a high flexibility and require less energy and smaller and simpler tools and dies. As described in the literature [1], these processes are generally net-shape, improving both forming ratios and properties of the obtained pieces compared to conventional die operations enhancing hardening and grain structure of the products. Other advantages of incremental bulk forming processes are that global forces, friction and wear of tools are lower, despite the high local loads applied on the tools. In addition, these processes require lower investments with lower tooling costs.
* Corresponding author. Tel.: +3491 3988668 E-mail address: [email protected]
1877-7058 © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of MESIC 2015
doi:10.1016/j.proeng.2015.12.506
C. Bernal et al. / Procedia Engineering 132 (2015) 358 – 365
Examples of incremental bulk forming processes are orbital forming, rotary swaging, roller burnishing [2, 3] or localized-incremental forging processes (LIFP) [4, 5]. Incremental forging processes can be carried out in CNC machines with more flexibility and lower forces requirements and do not require complex dies. In this case, a force is applied on the work piece surface by a punch to produce an impression on the material. The discrete compression process causes permanent plastic deformations, that repeated incrementally let forming the work piece by a localized incremental forging action [6, 7]. The purpose of this work is the analysis of the ball-rolling incremental forging process. First, a comparison of effectiveness of various cylindrical tools in the localized-incremental forging process has been simulated considering axial forces of the tool as a function of the amount of material displaced. Then the forming of the surface by means of a rolling ball tool has been compared with a simple penetration process showing that lower forces are required. In this case the forming of the surface by compressing the material with a rolling ball is continuous along a determined path producing permanent plastic deformation on the surface. Similar processes has been used in material hardening applications, creating on the surface of the part a certain level of residual stress in order to improve damage tolerance and fatigue or stress corrosion performance [8, 9]. In the next step, different test have been done on physical models in order to evaluate the feasibility of the process, the surface obtained, and the forces produced on principal axes during the incremental forging operation. 2. Finite element analysis of incremental forging process 2.1. Indentation process In order to know the behavior of different tools, an elementary indentation process has been simulated with the Finite Element code DEFORM. The axial forces of penetration of different tools has been evaluated according to the volume of material displaced. This volume has been calculated as a function of the penetration depth (tool stroke) and the punch geometry. The tools considered are: hemispherical punch, fillet-end tool (torical tool) and sphericalend punch. These tools are defined by R: radius of the tool; Rp: radius of the spherical end of the tool and r: radius of the torical end of the tool. Three geometries of punches have been analyzed: a) hemispherical punch (R8; Rp8), b) fillet-end tool (R8; r2) and c) spherical-end punch (R8; Rp15). Likewise, another spherical-end tool (R15; Rp15) has also been chosen to analyze the process. In all cases a friction factor of 0.08 is considered. In DEFORM this is the value to take into account for cold forming processes with carbide dies. The material UNS A91100, which is commercially pure aluminum with excellent forming characteristics, is used as reference material. The simulation of the cold forming process is performed using DEFORM F2 implicit solver by means of a 3550 elements plastic workpiece (upper and lower dies are considered rigid) running 200 steps process with intermediate remeshing. In Figure 1 it is observed that forces of penetration of the hemispherical punch (R8, Rp8) are always lower for the same volume of material displaced. In the case of the spherical punch (R8, Rp15), forces required are lower than with the fillet-end punch until the radius of the impression reaches the value R = 8mm. It is due to the fact that for the same volume of material displaced, that tool has a lower projected contact area than the fillet-end punch which applies higher pressures. Curves for the indentation with spherical tools (R15; Rp15) and (R8; Rp15) show the same behavior, until the imprint of the larger tool reaches the equivalent radius R = 8mm. From this value the force increases due to the increase of contact area with the punch. This analysis shows that the displacement of material is easier when using spherical-end tools. The indentation forces decrease with the spherical radius Rp until a minimum value is reached that corresponds to the case of hemispherical punch (ball-end tool). However, the obtained surface after a multiple indentation process presents irregularities that directly depend on the process parameters and on the tool geometry.
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Fig. 1. Axial forces on punch vs volume of material displaced in an elementary indentation process (UNS A91100 material, cold forming)
2.2. Ball-rolling incremental forging process Next a ball-rolling incremental forging process has been simulated in order to compare the forces required in the forming operation. The simulation has been done using the DEFORM implicit solver with a 2081 elements model. In an indentation process, the axial force depends on the stroke, the friction coefficient and the tool geometry. In the ball rolling forming process the displacement of the tool generates axial and lateral forces on the tool. In this case, the relevant forces to take into account are the lateral forces, since during the ball-rolling incremental forging operation there is no displacement of the tool in axial direction. In order to compare the indentation process and the rolling process, the loads has been simulated and calculated as a function of the material displaced during the movement of the tool. Figure 2 show the finite element model of the ball-rolling incremental forging operation implemented in DEFORM.
Fig. 2. Effective stress on the work piece in ball-rolling incremental forging operation
The case of ball rolling process is interesting because lower forces are required. In this case only the lateral force is considered since, in the considered process, there is no displacement or mechanical work in axial direction (axis of the tool). As expected, for the same volume of material displaced, the rolling process requires less force than the indentation process. In the first case the registered loads are the lateral loads and for the case off indentation process we take into account the axial force applied on the punch. Figure 3 displays loads versus volume of material
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C. Bernal et al. / Procedia Engineering 132 (2015) 358 – 365
displaced for the axial indentation and ball rolling process. In both cases a spherical tool of Rp = 8 mm has been used.
Fig. 3. Loads versus volume of material displaced (Ball-end tool -UNS A91100)
3. Methodology and testing procedure 3.1. Test material All tests were performed on tin plates with a fineness of 99.9 %. This metal is very malleable and has the advantage of its very high workability. The recrystallization temperature of tin is room temperature and do not have strain hardening. This is a requirement for testing in order to prevent machine overloading [10]. Hardness test was performed with Emco-test N3 durometer using the Brinell Hardness scale (ball indentation). In the Brinell hardness scale the indentation is measured and hardness calculated as [11-15]:
HBS
2F
S .D D D 2 d 2
(1)
where F is the applied force (kgf), D the diameter of indenter (mm) and d the diameter of indentation (mm). Considering the material, a force of 15 kgf with an indenter of 2.5 mm of diameter has been applied during 60 s resulting the following hardness for the tin (fineness of 99.9 %): 5.65 HBS 2.5/15/60 Considering the hardness of the material employed it is possible to approximate reference values of indentation forces as a function of indenter diameter and diameter of indentation. This information is required to determine the forces in testing machine. 3.2. Tools and testing machine The machine used for indentation and ball rolling test is a machining center Tongtai TMV-510 with Fanuc 0i controller. The tin plate has been screwed on a dynamometer Kistler 9257B with 5070 control unit. In order to obtain reliable results, a face milling was performed on the tin plates due to the roughness of the surface from casting (Figure 5).
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C. Bernal et al. / Procedia Engineering 132 (2015) 358 – 365
Two ball rolling tools have been manufactured in two diameters: 15 and 20 mm (Figure 4). The tests have been carried out with 15 mm tool.
Fig. 4. Sketch of ball rolling tool
A linear rolling cycle has been programmed as follows: 1. 2.
z axis penetration from the reference plane (surface of the tin plate). The maximum stroke on z axis was determined calculating maximum z load from equation (1). Keeping z fixed, a point to point command is executed for each penetration value (Figure 5).
This cycle was repeated for z values of 0.1; 0.2; 0.3 and 0.35 mm.
Fig. 5. Linear rolling test with the tin plate mounted on dynamometer.
4. Results The loads xyz were recorded by the dynamometer during the linear rolling test. The loads are indicated in N as a function of the time of cycle t. For the four values of penetration tested (0.1; 0.2; 0.3 and 0.35 mm), the dynamometer records loads during 25 seconds of linear movement. The results corresponding to the linear rolling cycle with a depth of pass of 0.1 mm are shown in Figure 6. During the penetration stroke, only the force along z axis increases. When the linear rolling movement starts, the forces along y and z axis increases. The increment of material displaced in front of the rolling ball produces increased forces in z direction. After a while the force in z tends to remain constant.
C. Bernal et al. / Procedia Engineering 132 (2015) 358 – 365
Fig. 6. RMS values of loads vs time (0.1 mm pass)
Figures 7, 8 and 9 show the root mean square values of xyz loads for the values of depth 0.2, 0.3 and 0.35 mm. The values of loads are given in N and the time of cycle in s. As expected, the loads along y and z axes increase with depth of pass, with a force along the x axis close to zero but nonzero due to possible misalignment of the dynamometer. In these tests it is noticed that, in the first step of the cycle (penetration), z force increases rapidly. Then, rolling forces also increase after penetration movement due to the increment of material in front of the rolling ball that produces increased forces in z and y. In this case there is not strain hardening, taking into account the recrystallization temperature of tin. Later, forces tend to remain constant. The ball-rolling incremental forging process shows that the lateral forces applied on the tool during the deformation of the surface are lower than the axial penetration forces and there is no z axis displacement during the rolling incremental forging process.
Fig. 7. RMS values of loads vs time (0.2 mm pass)
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Fig. 8. RMS values of loads vs time (0.3 mm pass)
Fig. 9. RMS values of loads vs time (0.35 mm pass)
5. Conclusions The efficiency analysis of the incremental forging process of flat surfaces by means of different tools shows that the displacement of material is easier when using spherical-end tools and particularly with hemispherical tools (ballend tools). With ball end tools it is possible to form the surface with lower axial forces. Moreover, the ball-rolling incremental forging process shows that the lateral forces applied on the tool during the deformation of the surface are lower than the axial penetration forces. Since during rolling there is no displacement along z axis (penetration of tool) the rolling process is more efficient and consume less energy. In addition, using standard CNC machines, incremental forging processes provide more flexibility and better process control. It is also possible to control the local deformation that produces hardening of the material and better
C. Bernal et al. / Procedia Engineering 132 (2015) 358 – 365
grain structure. Moreover, despite the high local loads applied on the tools, these processes can be carried out in lighter machines with simpler and smaller tools. Acknowledgements This work has been financially supported by the Annual Grant Call of the ETSI Industriales of UNED (reference 2014-ICF04). References [1] J.M. Allwood, H. Utsunomiya, A survey of flexible forming processes in Japan, Int J of Mach Tool Manuf. 46 (2006) 1939-1960. [2] J. Nowak, G. Madej, F. Grosman, M. Pietrzyk, Material flow analysis in the incremental forging technology, Int J Mater Form. 3 (2010) 931-934. [3] S. Bruschi, S. Casotto, T. Dal Negro, R. Icarelli, Modelling material behaviour in incremental bulk forming processes, Proc. ICTP 2005, Verona. [4] C. Bernal, A.M. Camacho, M. Marín, B. de Agustina, Methodology for the evaluation of 3D surface topography in multiple indentation processes, The Int J of Adv. Manuf. Techn. 69, (2012) 2091-2098. [5] C. Bernal, A.M. Camacho, J. M. Arenas, E.M. Rubio, Analytical procedure for geometrical evaluation of flat surfaces formed by multiple indentation processes. Applied Mechanics and Materials (2012), pp. 2351-2356. [6] A.M. Camacho, M.M. Marin, C. Bernal, M.A. Sebastián, Implicit and explicit techniques for Localized-Incremental Forging processes analysis by Computer Aided Engineering. The International Journal of Computer Aided Engineering and Technology (2013). [7] A.M. Camacho, M.M. Marin, C. Bernal, M.A. Sebastián, Simulation and experimental techniques for the analysis of localised-incremental forging operations. Proceedings of the European Simulation and Modelling Conference 2011, edited by EUROSIS, Ghent University. [8] P.S. Prevey, N. Jayaraman, Overview of low plasticity burnishing for mitigation of fatigue damage mechanism. Proceedings of ISCP 9 (2005), Paris [9] D. Hornbach, P. Prevey, M. Piche, D. Rivest, The influence of surface enhancement by low plasticity burnishing on the corrosión of 7475T7351 and 2024-T351. Proceedings of Aerospace Conference ISCP 10 (2008), Tokyo. [10] O. Tuysuz, Y. Altintas, H. Feng, Prediction of cutting forces in three and five axis ball-end milling with tool indentation effect. International Journal of Machine Tolls & Manufacture, 66 (2013), pp. 66-81. [11] ISO 18265 (2013) Metallic materials-Conversion of hardness values, International Organization for Standardization (ISO), Geneva. [12] ISO 4498 (2010) Sintered metal materials, excluding hardmetals, Determination of apparent hardness and microhardness, International Organization for Standardization (ISO), Geneva. [13] ISO 6506-2 (2014) Metallic materials, Brinell hardness test, Part 2: Verification and calibration of testing machines, International Organization for Standardization (ISO), Geneva. [14] ISO 6506-3 (2014) Metallic materials, Brinell hardness test, Part 3: Calibration of reference blocks, International Organization for Standardization (ISO), Geneva. [15] ISO 6506-4, Metallic materials, Brinell hardness test, Part 4: Table of hardness values, International Organization for Standardization (ISO), Geneva.
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