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Influence of flash design upon process parameters of hot die forging
Journal of Materials Processing Technology 157–158 (2004) 620–623
Influence of flash design upon process parameters of hot die forging B. Tomov∗ , R. Radev, V. Gagov Department of Materials and Processing Technology, University of Rousse, 8 Studentska St., 7017 Rousse, Bulgaria
Abstract The finite element method has been recently developed as one of the most powerful tools for the analysis of various metal forming processes using relevant software packages for numerical simulation. In the paper, this method has been applied for simulation and analysis of closed die forging with respect to flash formation at the end of final impression filling. An analytical expression of the condition for complete die cavity filling is also presented as a starting point for better choice of recommendations for flash land dimensioning. © 2004 Elsevier B.V. All rights reserved. Keywords: Closed die forging; Flash design; Finite element analysis
1. Introduction Both open and closed die forging processes are nonsteady-state operations with at least two or more metal flow directions and irregular stress, strain and strain rate distributions and, moreover, quite complicated final shapes with high quality are often required. In order to assist the process planning and die design at such sophisticated conditions of deformation, some special codes for computer simulation [1–3] have been recently suggested. In the last years, some encouraging results were presented in [4–7] where finite element method has been applied for numerical simulation using FORM-2D software. In this paper, the main attention is focussed on the flash land dimensioning in view of the very important influence of the flash design on the forging process parameters, the die life and the quality of the forged parts. During the years many authors have supposed various expressions [8–18] for flash land design depending mainly on the geometry or on the mass of the forgings. However, the calculated values prove to be quite different for the same forged part and for this reason the following equations have been
∗
Corresponding author. Tel.: +359 82 888310; fax: +359 82 845708. E-mail address: [email protected] (B. Tomov).
0924-0136/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2004.07.124
chosen here for further comparative analysis:
hf = 0.015DF 2 hF bf DF hF = 1.34 − 3.7 + 0.25 + 0.44 2 + 0.21α hf 600 bF bF (1)
0.01DF + 1 0.03 + 100/DF bf = 5(1 + 0.01DF ) hf = 0.016DF bf 63 =√ hf DF hf =
hf = 0.017DF + √
1
(2)
(3)
DF + 5 bf 30 =
hf 3 2 DF 1 + 2DF /HF (2RC + DF ) √ hf = 1.13 + 0.089 mF − 0.017mF bf = 3 + 1.25 exp(−1.09mF ) hf hf = 2.17 + 1.39m0.2 F bf D F = −1.985 + 5.258m0.1 F + 0.0256 hf HF
(4)
(5)
(6)
B. Tomov et al. / Journal of Materials Processing Technology 157–158 (2004) 620–623
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Fig. 2. Real ratio bf /he when the die cavity filling is just completed. Fig. 1. Forging of mild steel for analysis.
2. Results and discussion
Table 1 Flash dimensions obtained from (1) to (6) Equation
Reference
hf (mm)
bf (mm)
bf /hf
(1) (2) (3) (4) (5) (6)
[8] [9] [10] [10] [11] [12]
3.52 4.62 3.76 4.06 4.21 4.52
19.92 16.75 15.45 25.10 12.65 22.27
5.67 3.63 4.11 6.18 3.00 4.93
where hf is the flash thickness, bf the flash width, DF , HF and mF the diameter, the height and the mass of the part to be forged, respectively, RC the distance from the axis of symmetry to the center of gravity of the axial half section, hF -the greatest depth of the die cavity, and bF is the width of the deepest part of the die cavity. 1.1. Numerical analysis The version 2.11 of FORM-2D software [1] has been applied for FEM analysis of flash formation at hot die forging. The forged part being in consideration is the same one as in [7] and it is shown in Fig. 1. The relevant flash land dimensions for this forging are given in Table 1 referring to the equations mentioned above. The computer simulation has been done for 3.2%, 5.8%, 8.4% and 13.6% excess of metal V over the volume of the forging. The initial temperatures have been assumed to be 1200 ◦ C of the billet and 250 ◦ C of the die at modelling of the forging process with 80 MN mechanical press.
It was found by numerical simulation with various values of V and using an optimized preform [7] for this forged part that the final impression is not entirely filled only when an excess of 3.2% has been provided for flash formation. However, the common tolerances of the diameter and the length of the billet yield to about 3.1% volume variation, and because of that, an excess V of 5.8% for this forging would also be insufficient in practice for complete die cavity filling. The main results obtained at 8.4% of V are shown in Table 2 as total process parameters (force F and work W of deformation) and as local ones (mean contact pressure p, average radial velocity VR and temperature T) just for the metal being deformed in the flash land area. The computer simulations showed, as could be expected, that the die cavity filling begins before starting the flash formation and, if the V values are high enough, ends before closing the die halves to the determined flash thickness. The data obtained for bf /he ratio are shown in Fig. 2. After collecting more numerical data for various forgings it could be possible to look for statistical relations among the forging complexity, the flash dimensions and the excess amount as an extended background of the flash land design. Referring to Tables 1 and 2 it is not yet easy to prefer one or another of the existing expressions for the best determination of the flash dimensions. An additional relation could be derived from the force equilibrium equation for the boundary between the die cavity and the flash land at this instant when the cavity filling is already completed. The flash area for this last forging stage is shown in Fig. 3 as stress state assumed for further analytical estimation and in Fig. 4 as some representative results obtained by FEM analysis in reference to
Table 2 Forging process parameters during the flash formation Equation
b (mm)
he /hc (mm)
Fe /Fc (MN)
We /Wc (kJ)
pe /pc (MPa)
VRe /VRc (m/s)
T (◦ C)
(1) (2) (3) (4) (5) (6)
19.9 16.8 15.4 25.1 12.6 22.3
4.2/3.5 5.3/4.6 4.9/3.8 5.3/4.1 4.9/4.2 5.2/4.5
18/17 16/15 18/17 18/17 17.5/16.5 17.5/16.0
90/102.5 83/104.0 83/104.0 82/103.0 90/101.0 88/100.5
148.9/139.2 158.8/160.7 158.5/180.3 157.3/193.2 0.149/145.2 155.2/162.6
0.74/0.31 0.62/0.24 0.54/0.28 0.47/0.28 0.66/0.25 0.66/0.25
1159–182 1160–183 1160–183 1135–182 1160–183 1136–184
The subscripts “e” and “c” denote the values at the instants when the final impression is just entirely filled and when the die halves are closed to the calculated flash thickness.
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B. Tomov et al. / Journal of Materials Processing Technology 157–158 (2004) 620–623
Fig. 3. Assumption for stresses acting in the flash land.
relation (5).
2µbf σx = σp exp −1 hf
2µbf σz = σp exp hf
τ = µσz σz − σx = σp According to Fig. 3, we can write the force equilibrium equation as follows: pπDF hf ≤ σx πDF hf + 2τπDF bf
Fig. 5. Dimensionless values of cavity filling condition.
and for evaluating the pressure p it is possible to accept p = σ p as in [13]. This condition is in good agreement with Fig. 4c where the mean stress σ m is found to be close to the flow stress σ p in immediate proximity to the dividing line of the die cavity and flash area. Then, we can rewrite the equation mentioned above in the following form: σp πDF hf ≤ σx πDF hf + 2µσz πDF bf where µ is the coefficient of friction. Taking into consideration the stress state assumed in the flash land area and the analytical expressions for stress components description given in Fig. 3 we obtain: 2 ≤ exp 2µ hbff 1 + 2µ hbff or (7) 0.693 ≤ 2µ hbff + ln 1 + 2µ hbff This cavity filling condition is shown in Fig. 5 for the values of bf /hf and µ, which are common at hot die forging. It has no meaning for µ = 0 or hf = 0 but these values are not possible in practice. More important for industrial applications are the following values: bf /hf > 4, when µ = 0.05; bf /hf > 2, when µ = 0.1 and bf /hf > 1, when µ = 0.2. In view of the fact that relation (7) predicts low values of the ratio bf /hf and taking into account Table 1, expression (5) should be preferred as a first step of flash design. Moreover, it should be mentioned here that Table 2 presents for (5) the lowest values of the parameters pe,c , VRe,c and pe,c VRe,c as a preliminary measure of the flash land wear, which could be expected in the course of the manufacturing of forged parts.
3. Conclusions
Fig. 4. FEM results as (a) Lagrangian grid for the whole forging and (b) flow velocities and (c) ratio σ m /σ p in the flash land.
On the basis of both FEM simulation and analytical description it is found that Eq. (5) could be used as a first step of flash land design at hot die forging. The next step should involve an estimation of the elastic deflections of both the die and the machine being in consideration and then, if necessary, followed by flash thickness correction.
B. Tomov et al. / Journal of Materials Processing Technology 157–158 (2004) 620–623
References [1] Form-2D, Finite element system for simulation and analysis of forming processes (version 2.11), User’s Guide, Quantor Ltd., Moscow, 1995. [2] S. Tichkiewitch, Materials Processing Defects, Elsevier, Amsterdam, 1995, pp. 297–310. [3] G. Zhao, et al., Int. J. Mach. Tool Manuf. 35 (1995) 1225–1239. [4] V. Gagov, B. Tomov, Proceedings of AMME Conference, Gliwice, 1997, pp. 75–78. [5] V. Gagov, Proceedings of Science Conference of Air Force Academy, Dolna Mitropolia, 1997, pp. 318–323. [6] B. Tomov, R. Minev, R. Radev, V. Gagov, Gliwice-Wisla, Proceedings of AMME Conference, 1998, pp. 535–539. [7] B. Tomov, R. Radev, V. Gagov, Plovdiv, Proceedings of AMTECH Conference, 1999, pp. 576–581. [8] E. Semenov (Ed.), Forging and Forming Handbook, Hot Die Forging, vol. 2, Mashinostroenie, Moscow, 1986. [9] A. Rebelsky, Die Forging Processes and Technology Parameters, Mashgis, Moscow, 1959. [10] K. Lange, Umformtecnik Band 2, in: Massivumformtechnik, Springer-Verlag, Berlin, 1968.
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[11] H. Wolf, Fertigungstechnik und Betrieb 13 (1963) 168–170. [12] G. Teterin, P. Polukhin, Backgrounds of Process Planning Design for Hot Die Forging, Mashinostroenie, Moscow, 1979. [13] O. Pawelski, Archiv fur Eisenhuttenwesen 35 (1964) 27–36. [14] B. Tomov, R. Radev, An example of determination of preforming steps for hot die forging, in: Proceedings of 10th Jubilee International Conference on Achievements in Mechanical and Materials Engineering, Gliwice-Cracow-Zakopane, Poland, 2001, pp. xlv–xlviii. [15] R. Radev, B. Tomov, Preform Design in Hot Die Forging, in: Proceedings of 11th International Scientific Conference on Achievements in Mechanical and Materials Engineering, Gliwice-Zakopane, Poland, 2002, pp. 455–458. [16] B. Tomov, R. Minev, R. Radev, V. Gagov, About the input data selection at FEM analysis of bulk forming, J. Mater. Process. Technol. 133 (1/2) (2003) 199–202. [17] B. Tomov, R. Radev, Preform design for axis-symmetrical hot die forgings, in: Proceedings of the ICIT 2003 fourth International Conference on Industrial Tools, Bled Celje, Slovenia, 2003, pp. 175–182. [18] B. Tomov, V. Gagov, R. Radev, Numerical simulations of hot die forging processes using finite element method, in: Proceedings of the International Conference on Advances in Materials and Processing Technologies, Dublin, Ireland, 2003, pp. 415–418.
Influence of flash design upon process parameters of hot die forging B. Tomov∗ , R. Radev, V. Gagov Department of Materials and Processing Technology, University of Rousse, 8 Studentska St., 7017 Rousse, Bulgaria
Abstract The finite element method has been recently developed as one of the most powerful tools for the analysis of various metal forming processes using relevant software packages for numerical simulation. In the paper, this method has been applied for simulation and analysis of closed die forging with respect to flash formation at the end of final impression filling. An analytical expression of the condition for complete die cavity filling is also presented as a starting point for better choice of recommendations for flash land dimensioning. © 2004 Elsevier B.V. All rights reserved. Keywords: Closed die forging; Flash design; Finite element analysis
1. Introduction Both open and closed die forging processes are nonsteady-state operations with at least two or more metal flow directions and irregular stress, strain and strain rate distributions and, moreover, quite complicated final shapes with high quality are often required. In order to assist the process planning and die design at such sophisticated conditions of deformation, some special codes for computer simulation [1–3] have been recently suggested. In the last years, some encouraging results were presented in [4–7] where finite element method has been applied for numerical simulation using FORM-2D software. In this paper, the main attention is focussed on the flash land dimensioning in view of the very important influence of the flash design on the forging process parameters, the die life and the quality of the forged parts. During the years many authors have supposed various expressions [8–18] for flash land design depending mainly on the geometry or on the mass of the forgings. However, the calculated values prove to be quite different for the same forged part and for this reason the following equations have been
∗
Corresponding author. Tel.: +359 82 888310; fax: +359 82 845708. E-mail address: [email protected] (B. Tomov).
0924-0136/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2004.07.124
chosen here for further comparative analysis:
hf = 0.015DF 2 hF bf DF hF = 1.34 − 3.7 + 0.25 + 0.44 2 + 0.21α hf 600 bF bF (1)
0.01DF + 1 0.03 + 100/DF bf = 5(1 + 0.01DF ) hf = 0.016DF bf 63 =√ hf DF hf =
hf = 0.017DF + √
1
(2)
(3)
DF + 5 bf 30 =
hf 3 2 DF 1 + 2DF /HF (2RC + DF ) √ hf = 1.13 + 0.089 mF − 0.017mF bf = 3 + 1.25 exp(−1.09mF ) hf hf = 2.17 + 1.39m0.2 F bf D F = −1.985 + 5.258m0.1 F + 0.0256 hf HF
(4)
(5)
(6)
B. Tomov et al. / Journal of Materials Processing Technology 157–158 (2004) 620–623
621
Fig. 2. Real ratio bf /he when the die cavity filling is just completed. Fig. 1. Forging of mild steel for analysis.
2. Results and discussion
Table 1 Flash dimensions obtained from (1) to (6) Equation
Reference
hf (mm)
bf (mm)
bf /hf
(1) (2) (3) (4) (5) (6)
[8] [9] [10] [10] [11] [12]
3.52 4.62 3.76 4.06 4.21 4.52
19.92 16.75 15.45 25.10 12.65 22.27
5.67 3.63 4.11 6.18 3.00 4.93
where hf is the flash thickness, bf the flash width, DF , HF and mF the diameter, the height and the mass of the part to be forged, respectively, RC the distance from the axis of symmetry to the center of gravity of the axial half section, hF -the greatest depth of the die cavity, and bF is the width of the deepest part of the die cavity. 1.1. Numerical analysis The version 2.11 of FORM-2D software [1] has been applied for FEM analysis of flash formation at hot die forging. The forged part being in consideration is the same one as in [7] and it is shown in Fig. 1. The relevant flash land dimensions for this forging are given in Table 1 referring to the equations mentioned above. The computer simulation has been done for 3.2%, 5.8%, 8.4% and 13.6% excess of metal V over the volume of the forging. The initial temperatures have been assumed to be 1200 ◦ C of the billet and 250 ◦ C of the die at modelling of the forging process with 80 MN mechanical press.
It was found by numerical simulation with various values of V and using an optimized preform [7] for this forged part that the final impression is not entirely filled only when an excess of 3.2% has been provided for flash formation. However, the common tolerances of the diameter and the length of the billet yield to about 3.1% volume variation, and because of that, an excess V of 5.8% for this forging would also be insufficient in practice for complete die cavity filling. The main results obtained at 8.4% of V are shown in Table 2 as total process parameters (force F and work W of deformation) and as local ones (mean contact pressure p, average radial velocity VR and temperature T) just for the metal being deformed in the flash land area. The computer simulations showed, as could be expected, that the die cavity filling begins before starting the flash formation and, if the V values are high enough, ends before closing the die halves to the determined flash thickness. The data obtained for bf /he ratio are shown in Fig. 2. After collecting more numerical data for various forgings it could be possible to look for statistical relations among the forging complexity, the flash dimensions and the excess amount as an extended background of the flash land design. Referring to Tables 1 and 2 it is not yet easy to prefer one or another of the existing expressions for the best determination of the flash dimensions. An additional relation could be derived from the force equilibrium equation for the boundary between the die cavity and the flash land at this instant when the cavity filling is already completed. The flash area for this last forging stage is shown in Fig. 3 as stress state assumed for further analytical estimation and in Fig. 4 as some representative results obtained by FEM analysis in reference to
Table 2 Forging process parameters during the flash formation Equation
b (mm)
he /hc (mm)
Fe /Fc (MN)
We /Wc (kJ)
pe /pc (MPa)
VRe /VRc (m/s)
T (◦ C)
(1) (2) (3) (4) (5) (6)
19.9 16.8 15.4 25.1 12.6 22.3
4.2/3.5 5.3/4.6 4.9/3.8 5.3/4.1 4.9/4.2 5.2/4.5
18/17 16/15 18/17 18/17 17.5/16.5 17.5/16.0
90/102.5 83/104.0 83/104.0 82/103.0 90/101.0 88/100.5
148.9/139.2 158.8/160.7 158.5/180.3 157.3/193.2 0.149/145.2 155.2/162.6
0.74/0.31 0.62/0.24 0.54/0.28 0.47/0.28 0.66/0.25 0.66/0.25
1159–182 1160–183 1160–183 1135–182 1160–183 1136–184
The subscripts “e” and “c” denote the values at the instants when the final impression is just entirely filled and when the die halves are closed to the calculated flash thickness.
622
B. Tomov et al. / Journal of Materials Processing Technology 157–158 (2004) 620–623
Fig. 3. Assumption for stresses acting in the flash land.
relation (5).
2µbf σx = σp exp −1 hf
2µbf σz = σp exp hf
τ = µσz σz − σx = σp According to Fig. 3, we can write the force equilibrium equation as follows: pπDF hf ≤ σx πDF hf + 2τπDF bf
Fig. 5. Dimensionless values of cavity filling condition.
and for evaluating the pressure p it is possible to accept p = σ p as in [13]. This condition is in good agreement with Fig. 4c where the mean stress σ m is found to be close to the flow stress σ p in immediate proximity to the dividing line of the die cavity and flash area. Then, we can rewrite the equation mentioned above in the following form: σp πDF hf ≤ σx πDF hf + 2µσz πDF bf where µ is the coefficient of friction. Taking into consideration the stress state assumed in the flash land area and the analytical expressions for stress components description given in Fig. 3 we obtain: 2 ≤ exp 2µ hbff 1 + 2µ hbff or (7) 0.693 ≤ 2µ hbff + ln 1 + 2µ hbff This cavity filling condition is shown in Fig. 5 for the values of bf /hf and µ, which are common at hot die forging. It has no meaning for µ = 0 or hf = 0 but these values are not possible in practice. More important for industrial applications are the following values: bf /hf > 4, when µ = 0.05; bf /hf > 2, when µ = 0.1 and bf /hf > 1, when µ = 0.2. In view of the fact that relation (7) predicts low values of the ratio bf /hf and taking into account Table 1, expression (5) should be preferred as a first step of flash design. Moreover, it should be mentioned here that Table 2 presents for (5) the lowest values of the parameters pe,c , VRe,c and pe,c VRe,c as a preliminary measure of the flash land wear, which could be expected in the course of the manufacturing of forged parts.
3. Conclusions
Fig. 4. FEM results as (a) Lagrangian grid for the whole forging and (b) flow velocities and (c) ratio σ m /σ p in the flash land.
On the basis of both FEM simulation and analytical description it is found that Eq. (5) could be used as a first step of flash land design at hot die forging. The next step should involve an estimation of the elastic deflections of both the die and the machine being in consideration and then, if necessary, followed by flash thickness correction.
B. Tomov et al. / Journal of Materials Processing Technology 157–158 (2004) 620–623
References [1] Form-2D, Finite element system for simulation and analysis of forming processes (version 2.11), User’s Guide, Quantor Ltd., Moscow, 1995. [2] S. Tichkiewitch, Materials Processing Defects, Elsevier, Amsterdam, 1995, pp. 297–310. [3] G. Zhao, et al., Int. J. Mach. Tool Manuf. 35 (1995) 1225–1239. [4] V. Gagov, B. Tomov, Proceedings of AMME Conference, Gliwice, 1997, pp. 75–78. [5] V. Gagov, Proceedings of Science Conference of Air Force Academy, Dolna Mitropolia, 1997, pp. 318–323. [6] B. Tomov, R. Minev, R. Radev, V. Gagov, Gliwice-Wisla, Proceedings of AMME Conference, 1998, pp. 535–539. [7] B. Tomov, R. Radev, V. Gagov, Plovdiv, Proceedings of AMTECH Conference, 1999, pp. 576–581. [8] E. Semenov (Ed.), Forging and Forming Handbook, Hot Die Forging, vol. 2, Mashinostroenie, Moscow, 1986. [9] A. Rebelsky, Die Forging Processes and Technology Parameters, Mashgis, Moscow, 1959. [10] K. Lange, Umformtecnik Band 2, in: Massivumformtechnik, Springer-Verlag, Berlin, 1968.
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[11] H. Wolf, Fertigungstechnik und Betrieb 13 (1963) 168–170. [12] G. Teterin, P. Polukhin, Backgrounds of Process Planning Design for Hot Die Forging, Mashinostroenie, Moscow, 1979. [13] O. Pawelski, Archiv fur Eisenhuttenwesen 35 (1964) 27–36. [14] B. Tomov, R. Radev, An example of determination of preforming steps for hot die forging, in: Proceedings of 10th Jubilee International Conference on Achievements in Mechanical and Materials Engineering, Gliwice-Cracow-Zakopane, Poland, 2001, pp. xlv–xlviii. [15] R. Radev, B. Tomov, Preform Design in Hot Die Forging, in: Proceedings of 11th International Scientific Conference on Achievements in Mechanical and Materials Engineering, Gliwice-Zakopane, Poland, 2002, pp. 455–458. [16] B. Tomov, R. Minev, R. Radev, V. Gagov, About the input data selection at FEM analysis of bulk forming, J. Mater. Process. Technol. 133 (1/2) (2003) 199–202. [17] B. Tomov, R. Radev, Preform design for axis-symmetrical hot die forgings, in: Proceedings of the ICIT 2003 fourth International Conference on Industrial Tools, Bled Celje, Slovenia, 2003, pp. 175–182. [18] B. Tomov, V. Gagov, R. Radev, Numerical simulations of hot die forging processes using finite element method, in: Proceedings of the International Conference on Advances in Materials and Processing Technologies, Dublin, Ireland, 2003, pp. 415–418.