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The role of friction in the extrusion of AA6060 aluminum alloy, process analysis and monitoring
Journal of Materials Processing Technology 191 (2007) 288–292
The role of friction in the extrusion of AA6060 aluminum alloy, process analysis and monitoring M. Schikorra a , L. Donati b,∗ , L. Tomesani b , M. Kleiner a a
b
Institute of Forming Technology and Lightweight Construction, Baroper Strasse 301, 44227 Dortmund, Germany Department of Mechanical Construction Engineering (DIEM), University of Bologna, V. le Risorgimento 2, 40136 Bologna, Italy
Abstract The extrusion of a AA6060 round profile was performed on a laboratory 10 MN press to allow grid test analysis. The billet was equipped with 19-rod markers to evaluate the flow path in the container at different strokes. All process parameters suitable for validating FEM simulations (ram load, container, die and profile temperatures, process speed) were recorded. Two different ram speeds and two strokes have been performed, the results being compared with a billet extruded without rods. The deformed grids were measured in order to estimate the friction effect throughout the billet length. In particular, the distance between each rod, their deformation, and the node displacement at the container wall were measured. © 2007 Elsevier B.V. All rights reserved. Keywords: Extrusion; AA6060; Friction; Grid test
1. Introduction Direct extrusion of aluminum is a well-known technology for flat or hollow shapes production. The increasing interest of such profiles in aero-spatial and automotive industry has led to a demand for a better understanding of some basic mechanics of the process such as solid state welding [1], production speed limits [2], or metallurgy evolution [3]. New extrusionbased processes have also been presented as well: extrusion of curved profiles [4], composite extrusion [5], or indirect extrusion with active friction (ISA) [6], among the others. On the other hand, FEM simulations are becoming powerful instruments that allow a better understanding of the material behavior inside the die. However, the validation of FEM results is still a problem that needs to be addressed; in particular, a lack of accuracy is still present in describing basic mechanisms such as friction and deformation heating [7]. The evaluation of friction is a complex matter, which depends on both material and interface local conditions, such as temperature, strain, strain rate, flow stress, normal pressure and surface roughness.
∗
Corresponding author. E-mail addresses: [email protected] (M. Schikorra), [email protected] (L. Donati), [email protected] (L. Tomesani), [email protected] (M. Kleiner). 0924-0136/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2007.03.096
Many researchers performed grid tests for the evaluation of material flow in the container zones [8,9], but they missed to discuss which friction model and what coefficients would provide the best fit to experimental evidence. More recently, Fitta and Sheppard [10,11] evaluated the role of billet temperature on friction in extruding aluminum alloys, founding a progressive transition from sliding to sticking when temperature increases from 300 to 450 ◦ C. Nevertheless, it emerges from these works that a sticking condition cannot, by itself, completely describe the flow path within the container and, in particular, the material displacements at the container wall. It seems that the billet material is more fixed to the wall than what the sticking condition would allow in FEM simulations. The aim of this work is then to accurately investigate the flow patterns of the deforming material, with particular attention to the contact conditions at the container wall, in order to provide an experimental basis for setting numerical parameters in the simulations developed in part II of this article. Two types of grid tests can be performed: the first is to divide the billet in two parts, then to mark a grid on one part and to recompose the original billet with a thin layer of a release agent in the middle. The two slices are then extruded together. A second way, which was adopted in this work, is to drill equally spaced holes in the billet, then to fill them with rods of a different alloy having a similar flow stress. After a half-stroke extrusion, the billet rest is extracted from the container and machined up to the
M. Schikorra et al. / Journal of Materials Processing Technology 191 (2007) 288–292
Fig. 1. Process sketch (axis symmetry).
Fig. 2. Experimental data.
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M. Schikorra et al. / Journal of Materials Processing Technology 191 (2007) 288–292
Table 1 Experimental plan Test 1
Test 2
Test 3
Test 4
Test 5
No rods Full stroke (290 mm) Ram speed: 2 mm/s
Billet with rods Full stroke (290 mm) Ram speed: 2 mm/s
Billet with rods Half stroke (150 mm) Ram speed: 2 mm/s
Billet with rods Half stroke (150 mm) Ram speed: 5 mm/s
Billet with rods 175 mm stroke Ram speed: 2 mm/s
mid plane, where the deformed rods are put in light. The analysis of the shape of the deformed rods allows a comprehension of the material flow and of the friction effect at the billet–container interface. 2. Experimental 2.1. Extrusion tests The tests were carried out on a SMS-Schloemann 10 MN laboratory press. Four billets, having 138 mm diameter and 293 mm length, made by AA6060 alloy (AlMgSi 0.5), were prepared by drilling 19 holes, 5 mm in diameter, equally spaced at 15 mm distance from each other, and filling them with AA4043 (AlSi 5.5) rods. This method, as demonstrated by Kalz [9], can be successfully applied as the flow stress behavior of the two alloys at high temperatures is very similar. One billet without rods, was also extruded as a comparison. The geometry of the experiment is reported in Fig. 1, where measurement sites of temperature are also evidenced. The extruded profile is a simple round profile 36.5 mm in diameter; the global extrusion ratio of the process is 14.3. Five different tests were made according to Table 1: process speed, ram stroke and billet type were changed throughout the experimental plan. The temperature of the container was set to 450 ◦ C and no relevant changes were found during the process; the temperature of the ram was measured at the end of each test, a mean value of 305 ± 5 ◦ C being determined. The oven for billet pre-heating was set to 450 ◦ C, with 10 h residence time. During the loading into the press, the billet was in contact with air for about 1 min, then remaining in contact with the ram and the die for one more minute before extrusion started. The exit temperature of the profile was measured on the surface at 1 m out of the bearing by means of two contact thermocouples of 1 mm diameter, and continuously recorded: a gap in the first stage of the measurement is evidenced due both to the delay of this measurement with respect to the extrusion start and to thermal inertia of the thermocouples; thus, a mean value and an interpolated distribution are reported in the graphs of Fig. 2. One more thermocouple was also used for monitoring the die temperature at the die face, as reported in Fig. 1.
2.2. Grid shapes When the prescribed stroked was completed the billet rests (billets 3–5) were extracted from the container and milled in proximity of the rods middle plane and finally grinded and polished to reach an optimal definition of the rods path (Fig. 3). Some rods are not visible in Fig. 3 because, during deformation, they moved out the middle plane and consequently they are completely milled or not machined at all. An high sticking friction is immediately observable in all the rests: materials flows very fast in the middle of the billet, where small strains are located (the rods remain at the original thickness) while high shears occur in proximity of the surface. If an ideal lubricant (no friction) would be used, all the rods should remain straight (90◦ angle with billet surface), and no thinning effect should be evidenced. The flow becomes more complex near the ram (i.e. x dimension increase): by analyzing the rest of test 3 (Fig. 3) at x = 0 the material looks almost still and rod 1 keeps the original diameter, rods 2 and 3 have the original x-distance (30 and 45 mm, respectively) but an increasing thinning effect is shown. Rods from 4 to 10 again show an high sticking condition and at the same time an increasing thinning effects. Rod no. 10 is the last in contact with the surface of the billet because the starting point of rods 11–19 (as it can be seen in tests 4 and 5) moved from the surface to the inside of the billet, on a path in a radial direction (represented by the blue arrows). This ‘ram effect’ is, thus,
Fig. 3. Billet rests and deformed rod paths.
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291
a flow that removes material from the surface and moves it towards the inside where higher speeds are present. When the ram stroke is increased (test 5), also the rods 8–10 are shifted towards the inside of the billet. Finally, no particular differences are evidenced when higher production rates are used (test 4).
3. Discussion In Fig. 2 the recorded data for the five tests are reported. Test 1 was performed with full stroke and without rods, while test 2 was realized with a billet equipped with AA40343 rods. The load stroke diagram is identical in tests 1 and 2, (the same maximum load of 4.2 MN was found), thus revealing, according to [9], that the rods did not influence the process. In both tests, die temperatures increased from 360 to 382 ◦ C, with an increase of 22 ◦ C due to friction and deformation energy. The measurement of aluminum temperature distribution was quite complex to perform: the billets were at 450 ◦ C at the oven exit and during loading decreased to around 430 ◦ C. The starting profile temperature could not be immediately recorded due to thermal inertia of the thermocouples, and the initial reasonable values were generally quite similar to the die temperature, as it could be expected. Nevertheless, the difference in temperature between the billet (430◦ ) and the profile exit (360–380 ◦ C) can be explained by the cooling that the billet underwent due to the contact with the press loading equipment (at 30 ◦ C) and with extrusion tools (ram and die at 305 and 360 ◦ C respectively). Such effects have all been considered during FEM simulations. Test 3, having a shorter stroke than tests 1 and 2, evidenced process variables quite similar to test 2. In test 4 speed was increased: the maximum load also increased, as expected, from 4.2 to 4.9 MN while die temperature increased only of 12 ◦ C, due to the lower contact time. Besides, the profile temperature had only a small amount of recorded data due to very short process time. Finally, test 5 was performed with a little bit longer stroke (175 mm) and at the original speed; a maximum load of 4.7 MN was obtained due to a lower process temperature (around 20 ◦ C). The analysis of the billet rests has generally shown sticking conditions except at the bearing area, where sliding conditions occurs. A particular phenomenon is revealed when the ram removes the material from the container wall. There, a metal path develops from the surface to the inside along the ram face (Fig. 3, blue arrows in test 5); the extremity of the rods, originally located on the surface, are then shifted towards the center of the billet. To better analyze the friction effect, the frictional index R is defined, expressing the ratio between the initial x-distance of a rod from the die surface and its distance in the as-deformed condition (Fig. 4). If totally sticking conditions were present, such index would be equal to 1, while it would decrease if, to some extent, sliding took place. Fig. 4 presents the evaluation of the frictional index R for the performed tests. In test 3, the value of R for the first rod is 0.8, due to the initial increase of billet diameter to the container diameter. R values for rods from 3 to 6 are equal to 1, thus meaning that the rods extremities do not move at all in spite of the ram stroke. Rods 7–10 show a slight decrease in R, meaning that a little sliding is taking place due to the approaching ram. Finally, in rods 11–19 the ‘ram effect’ definitely removes, as explained, the material from the
Fig. 4. Frictional index for the conducted experiments.
Fig. 5. Reference values of R at different press strokes in sticking conditions.
container wall towards the billet center and the frictional index R consequently decreases down to 0.5, due to the forced material displacement in the radial direction. When the stroke is increased (test 5), more rods are involved in the ram effect, as expected. Finally, a very little relationship was found between friction and production rates (test 4), as the frictional ratio R only slightly decreases in rods 6–10 with respect to test 3. Generalizing such results, a diagram for friction calibration can be created (Fig. 5): different strokes determine different ‘ram effect’ curves, while different friction conditions (sticking or sliding) can be evaluated by the maximum R value obtained. 4. Conclusions The material flow and the friction behaviour at the container wall of the aluminium extrusion process were investigated by extruding billets with rod markers embedded. It was shown that, at the billet temperature of 430 ◦ C, the adopted method did not alter the process results. The deformed shape of the rods was measured and analyzed to investigate local friction conditions. It was found that almost perfect sticking was present at the container wall until the ram did not force the material to move toward the billet axis, in an radial direction path. The effect of speed was found to be almost negligible. A frictional index has been
292
M. Schikorra et al. / Journal of Materials Processing Technology 191 (2007) 288–292
used to evaluate the effect of friction and a calibration diagram has been proposed. Acknowledgements This work was carried out with the financial support of the Transregional Collaborative Research Center/TR10 of the German Research Foundation (DFG) and the MIUR (Italian Ministry for Research and Innovations). References [1] L. Donati, L. Tomesani, Extrusion welds in hollow AA 6060 profiles: FEM simulation and product characterization, in: Proceedings of the Eighth ICTP Conference, 2005, pp. 227–228. [2] L. Donati, L. Tomesani, The effect of die design on the production and seam weld quality of extruded profiles, J. Mater. Proc. Technol. 164/165 (2005) 1025–1031. [3] X. Duan, Prediction of flow stress and recrystallization by the FEM during the hot extrusion of aluminum alloys, in: Proceedings of the Eighth Aluminum Extrusion Technology Seminar, vol. I, 2004, pp. 149–158.
[4] A. Klaus, D. Arendes, S. Chatti, M. Kleiner, Direct rounding of profiles during extrusion, in: Proceedings of the Seventh Aluminum Extrusion Technology Seminar, vol. I, 2000, pp. 421–438. [5] M. Kleiner, M. Schom¨acker, M. Schikorra, A. Klaus, Manufacture of continuously reinforced profiles using standard 6060 billets, in: Proceedings of the Eighth Aluminum Extrusion Technology Seminar, vol. II, 2004, pp. 461–468. [6] K. M¨uller, Indirect extrusion with active friction (ISA), Key Eng. Mater. 233–236 (2003) 323–328. [7] L. Donati, S. Andreoli, The die in extrusion: influence of the design choices on the performance of extruded profiles for automotive applications, Light Metal Age 64 (2) (2006) 28–33. [8] C. Yao, K. M¨uller, Metal flow and temperatures developed during direct extrusion of AA2024, in: Proceedings of the Sixth Aluminum Extrusion Technology Seminar, vol. II (ET 1996), 1996, pp. 141–146. [9] S. Kalz, Numerische Simulation des Strangpressens mit Hilfe der Methode der finiten Elemente, Thesis (Dr.-Ing.), RWTH Aachen, Germany, 2001. [10] I. Fitta, T. Sheppard, On the mechanics of friction during the extrusion process, in: Proceedings of the Seventh Aluminum Extrusion Technology Seminar, vol. I (ET 2000), 2000, pp. 197–203. [11] I. Fitta, T. Sheppard, Nature of friction in extrusion process and its effect on material flow, Int. J. Mater. Sci. Technol. 19 (2003) 837–846.
The role of friction in the extrusion of AA6060 aluminum alloy, process analysis and monitoring M. Schikorra a , L. Donati b,∗ , L. Tomesani b , M. Kleiner a a
b
Institute of Forming Technology and Lightweight Construction, Baroper Strasse 301, 44227 Dortmund, Germany Department of Mechanical Construction Engineering (DIEM), University of Bologna, V. le Risorgimento 2, 40136 Bologna, Italy
Abstract The extrusion of a AA6060 round profile was performed on a laboratory 10 MN press to allow grid test analysis. The billet was equipped with 19-rod markers to evaluate the flow path in the container at different strokes. All process parameters suitable for validating FEM simulations (ram load, container, die and profile temperatures, process speed) were recorded. Two different ram speeds and two strokes have been performed, the results being compared with a billet extruded without rods. The deformed grids were measured in order to estimate the friction effect throughout the billet length. In particular, the distance between each rod, their deformation, and the node displacement at the container wall were measured. © 2007 Elsevier B.V. All rights reserved. Keywords: Extrusion; AA6060; Friction; Grid test
1. Introduction Direct extrusion of aluminum is a well-known technology for flat or hollow shapes production. The increasing interest of such profiles in aero-spatial and automotive industry has led to a demand for a better understanding of some basic mechanics of the process such as solid state welding [1], production speed limits [2], or metallurgy evolution [3]. New extrusionbased processes have also been presented as well: extrusion of curved profiles [4], composite extrusion [5], or indirect extrusion with active friction (ISA) [6], among the others. On the other hand, FEM simulations are becoming powerful instruments that allow a better understanding of the material behavior inside the die. However, the validation of FEM results is still a problem that needs to be addressed; in particular, a lack of accuracy is still present in describing basic mechanisms such as friction and deformation heating [7]. The evaluation of friction is a complex matter, which depends on both material and interface local conditions, such as temperature, strain, strain rate, flow stress, normal pressure and surface roughness.
∗
Corresponding author. E-mail addresses: [email protected] (M. Schikorra), [email protected] (L. Donati), [email protected] (L. Tomesani), [email protected] (M. Kleiner). 0924-0136/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2007.03.096
Many researchers performed grid tests for the evaluation of material flow in the container zones [8,9], but they missed to discuss which friction model and what coefficients would provide the best fit to experimental evidence. More recently, Fitta and Sheppard [10,11] evaluated the role of billet temperature on friction in extruding aluminum alloys, founding a progressive transition from sliding to sticking when temperature increases from 300 to 450 ◦ C. Nevertheless, it emerges from these works that a sticking condition cannot, by itself, completely describe the flow path within the container and, in particular, the material displacements at the container wall. It seems that the billet material is more fixed to the wall than what the sticking condition would allow in FEM simulations. The aim of this work is then to accurately investigate the flow patterns of the deforming material, with particular attention to the contact conditions at the container wall, in order to provide an experimental basis for setting numerical parameters in the simulations developed in part II of this article. Two types of grid tests can be performed: the first is to divide the billet in two parts, then to mark a grid on one part and to recompose the original billet with a thin layer of a release agent in the middle. The two slices are then extruded together. A second way, which was adopted in this work, is to drill equally spaced holes in the billet, then to fill them with rods of a different alloy having a similar flow stress. After a half-stroke extrusion, the billet rest is extracted from the container and machined up to the
M. Schikorra et al. / Journal of Materials Processing Technology 191 (2007) 288–292
Fig. 1. Process sketch (axis symmetry).
Fig. 2. Experimental data.
289
290
M. Schikorra et al. / Journal of Materials Processing Technology 191 (2007) 288–292
Table 1 Experimental plan Test 1
Test 2
Test 3
Test 4
Test 5
No rods Full stroke (290 mm) Ram speed: 2 mm/s
Billet with rods Full stroke (290 mm) Ram speed: 2 mm/s
Billet with rods Half stroke (150 mm) Ram speed: 2 mm/s
Billet with rods Half stroke (150 mm) Ram speed: 5 mm/s
Billet with rods 175 mm stroke Ram speed: 2 mm/s
mid plane, where the deformed rods are put in light. The analysis of the shape of the deformed rods allows a comprehension of the material flow and of the friction effect at the billet–container interface. 2. Experimental 2.1. Extrusion tests The tests were carried out on a SMS-Schloemann 10 MN laboratory press. Four billets, having 138 mm diameter and 293 mm length, made by AA6060 alloy (AlMgSi 0.5), were prepared by drilling 19 holes, 5 mm in diameter, equally spaced at 15 mm distance from each other, and filling them with AA4043 (AlSi 5.5) rods. This method, as demonstrated by Kalz [9], can be successfully applied as the flow stress behavior of the two alloys at high temperatures is very similar. One billet without rods, was also extruded as a comparison. The geometry of the experiment is reported in Fig. 1, where measurement sites of temperature are also evidenced. The extruded profile is a simple round profile 36.5 mm in diameter; the global extrusion ratio of the process is 14.3. Five different tests were made according to Table 1: process speed, ram stroke and billet type were changed throughout the experimental plan. The temperature of the container was set to 450 ◦ C and no relevant changes were found during the process; the temperature of the ram was measured at the end of each test, a mean value of 305 ± 5 ◦ C being determined. The oven for billet pre-heating was set to 450 ◦ C, with 10 h residence time. During the loading into the press, the billet was in contact with air for about 1 min, then remaining in contact with the ram and the die for one more minute before extrusion started. The exit temperature of the profile was measured on the surface at 1 m out of the bearing by means of two contact thermocouples of 1 mm diameter, and continuously recorded: a gap in the first stage of the measurement is evidenced due both to the delay of this measurement with respect to the extrusion start and to thermal inertia of the thermocouples; thus, a mean value and an interpolated distribution are reported in the graphs of Fig. 2. One more thermocouple was also used for monitoring the die temperature at the die face, as reported in Fig. 1.
2.2. Grid shapes When the prescribed stroked was completed the billet rests (billets 3–5) were extracted from the container and milled in proximity of the rods middle plane and finally grinded and polished to reach an optimal definition of the rods path (Fig. 3). Some rods are not visible in Fig. 3 because, during deformation, they moved out the middle plane and consequently they are completely milled or not machined at all. An high sticking friction is immediately observable in all the rests: materials flows very fast in the middle of the billet, where small strains are located (the rods remain at the original thickness) while high shears occur in proximity of the surface. If an ideal lubricant (no friction) would be used, all the rods should remain straight (90◦ angle with billet surface), and no thinning effect should be evidenced. The flow becomes more complex near the ram (i.e. x dimension increase): by analyzing the rest of test 3 (Fig. 3) at x = 0 the material looks almost still and rod 1 keeps the original diameter, rods 2 and 3 have the original x-distance (30 and 45 mm, respectively) but an increasing thinning effect is shown. Rods from 4 to 10 again show an high sticking condition and at the same time an increasing thinning effects. Rod no. 10 is the last in contact with the surface of the billet because the starting point of rods 11–19 (as it can be seen in tests 4 and 5) moved from the surface to the inside of the billet, on a path in a radial direction (represented by the blue arrows). This ‘ram effect’ is, thus,
Fig. 3. Billet rests and deformed rod paths.
M. Schikorra et al. / Journal of Materials Processing Technology 191 (2007) 288–292
291
a flow that removes material from the surface and moves it towards the inside where higher speeds are present. When the ram stroke is increased (test 5), also the rods 8–10 are shifted towards the inside of the billet. Finally, no particular differences are evidenced when higher production rates are used (test 4).
3. Discussion In Fig. 2 the recorded data for the five tests are reported. Test 1 was performed with full stroke and without rods, while test 2 was realized with a billet equipped with AA40343 rods. The load stroke diagram is identical in tests 1 and 2, (the same maximum load of 4.2 MN was found), thus revealing, according to [9], that the rods did not influence the process. In both tests, die temperatures increased from 360 to 382 ◦ C, with an increase of 22 ◦ C due to friction and deformation energy. The measurement of aluminum temperature distribution was quite complex to perform: the billets were at 450 ◦ C at the oven exit and during loading decreased to around 430 ◦ C. The starting profile temperature could not be immediately recorded due to thermal inertia of the thermocouples, and the initial reasonable values were generally quite similar to the die temperature, as it could be expected. Nevertheless, the difference in temperature between the billet (430◦ ) and the profile exit (360–380 ◦ C) can be explained by the cooling that the billet underwent due to the contact with the press loading equipment (at 30 ◦ C) and with extrusion tools (ram and die at 305 and 360 ◦ C respectively). Such effects have all been considered during FEM simulations. Test 3, having a shorter stroke than tests 1 and 2, evidenced process variables quite similar to test 2. In test 4 speed was increased: the maximum load also increased, as expected, from 4.2 to 4.9 MN while die temperature increased only of 12 ◦ C, due to the lower contact time. Besides, the profile temperature had only a small amount of recorded data due to very short process time. Finally, test 5 was performed with a little bit longer stroke (175 mm) and at the original speed; a maximum load of 4.7 MN was obtained due to a lower process temperature (around 20 ◦ C). The analysis of the billet rests has generally shown sticking conditions except at the bearing area, where sliding conditions occurs. A particular phenomenon is revealed when the ram removes the material from the container wall. There, a metal path develops from the surface to the inside along the ram face (Fig. 3, blue arrows in test 5); the extremity of the rods, originally located on the surface, are then shifted towards the center of the billet. To better analyze the friction effect, the frictional index R is defined, expressing the ratio between the initial x-distance of a rod from the die surface and its distance in the as-deformed condition (Fig. 4). If totally sticking conditions were present, such index would be equal to 1, while it would decrease if, to some extent, sliding took place. Fig. 4 presents the evaluation of the frictional index R for the performed tests. In test 3, the value of R for the first rod is 0.8, due to the initial increase of billet diameter to the container diameter. R values for rods from 3 to 6 are equal to 1, thus meaning that the rods extremities do not move at all in spite of the ram stroke. Rods 7–10 show a slight decrease in R, meaning that a little sliding is taking place due to the approaching ram. Finally, in rods 11–19 the ‘ram effect’ definitely removes, as explained, the material from the
Fig. 4. Frictional index for the conducted experiments.
Fig. 5. Reference values of R at different press strokes in sticking conditions.
container wall towards the billet center and the frictional index R consequently decreases down to 0.5, due to the forced material displacement in the radial direction. When the stroke is increased (test 5), more rods are involved in the ram effect, as expected. Finally, a very little relationship was found between friction and production rates (test 4), as the frictional ratio R only slightly decreases in rods 6–10 with respect to test 3. Generalizing such results, a diagram for friction calibration can be created (Fig. 5): different strokes determine different ‘ram effect’ curves, while different friction conditions (sticking or sliding) can be evaluated by the maximum R value obtained. 4. Conclusions The material flow and the friction behaviour at the container wall of the aluminium extrusion process were investigated by extruding billets with rod markers embedded. It was shown that, at the billet temperature of 430 ◦ C, the adopted method did not alter the process results. The deformed shape of the rods was measured and analyzed to investigate local friction conditions. It was found that almost perfect sticking was present at the container wall until the ram did not force the material to move toward the billet axis, in an radial direction path. The effect of speed was found to be almost negligible. A frictional index has been
292
M. Schikorra et al. / Journal of Materials Processing Technology 191 (2007) 288–292
used to evaluate the effect of friction and a calibration diagram has been proposed. Acknowledgements This work was carried out with the financial support of the Transregional Collaborative Research Center/TR10 of the German Research Foundation (DFG) and the MIUR (Italian Ministry for Research and Innovations). References [1] L. Donati, L. Tomesani, Extrusion welds in hollow AA 6060 profiles: FEM simulation and product characterization, in: Proceedings of the Eighth ICTP Conference, 2005, pp. 227–228. [2] L. Donati, L. Tomesani, The effect of die design on the production and seam weld quality of extruded profiles, J. Mater. Proc. Technol. 164/165 (2005) 1025–1031. [3] X. Duan, Prediction of flow stress and recrystallization by the FEM during the hot extrusion of aluminum alloys, in: Proceedings of the Eighth Aluminum Extrusion Technology Seminar, vol. I, 2004, pp. 149–158.
[4] A. Klaus, D. Arendes, S. Chatti, M. Kleiner, Direct rounding of profiles during extrusion, in: Proceedings of the Seventh Aluminum Extrusion Technology Seminar, vol. I, 2000, pp. 421–438. [5] M. Kleiner, M. Schom¨acker, M. Schikorra, A. Klaus, Manufacture of continuously reinforced profiles using standard 6060 billets, in: Proceedings of the Eighth Aluminum Extrusion Technology Seminar, vol. II, 2004, pp. 461–468. [6] K. M¨uller, Indirect extrusion with active friction (ISA), Key Eng. Mater. 233–236 (2003) 323–328. [7] L. Donati, S. Andreoli, The die in extrusion: influence of the design choices on the performance of extruded profiles for automotive applications, Light Metal Age 64 (2) (2006) 28–33. [8] C. Yao, K. M¨uller, Metal flow and temperatures developed during direct extrusion of AA2024, in: Proceedings of the Sixth Aluminum Extrusion Technology Seminar, vol. II (ET 1996), 1996, pp. 141–146. [9] S. Kalz, Numerische Simulation des Strangpressens mit Hilfe der Methode der finiten Elemente, Thesis (Dr.-Ing.), RWTH Aachen, Germany, 2001. [10] I. Fitta, T. Sheppard, On the mechanics of friction during the extrusion process, in: Proceedings of the Seventh Aluminum Extrusion Technology Seminar, vol. I (ET 2000), 2000, pp. 197–203. [11] I. Fitta, T. Sheppard, Nature of friction in extrusion process and its effect on material flow, Int. J. Mater. Sci. Technol. 19 (2003) 837–846.