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Improvements in productivity and formability by water and die quenching in hot stamping of ultra-high strength steel parts
CIRP Annals - Manufacturing Technology 64 (2015) 281–284
Contents lists available at ScienceDirect
CIRP Annals - Manufacturing Technology jou rnal homep age : ht t p: // ees .e lse vi er . com /ci r p/ def a ult . asp
Improvements in productivity and formability by water and die quenching in hot stamping of ultra-high strength steel parts Tomoyoshi Maeno *, Ken-Ichiro Mori (1), Masaki Fujimoto Department of Mechanical Engineering, Toyohashi University of Technology, Toyohashi, Aichi 441-8580, Japan
A R T I C L E I N F O
A B S T R A C T
Keywords: Hot stamping Sheet metal Productivity
To improve the productivity in hot stamping of ultra-high strength steel parts, the parts are quenched not only with dies but also in water during holding at the bottom dead centre. Since the cooling speed for water quenching is higher than that for die quenching, the hold time for hardening is reduced. In hot stamping, water is kept in a lower die to increase the cooling rate during die quenching. In addition, local thinning around the punch corner was prevented by water and die quenching, and thus the drawablity increases. ß 2015 CIRP.
1. Introduction For the reduction in weight and improvement of crash safety for automobiles, hot stamping of quenchable steel sheets is increasingly employed for production of ultra-high strength steel parts. By heating the steel sheets, the forming load is remarkably reduced, the springback is prevented and the formability is improved [1,2]. In addition, the stamped parts are hardened by quenching with dies, and thus the ultra-high strength steel parts having a tensile strength of approximately 1.5 GPa are obtained under a low forming load [3]. In hot stamping, dies are held at the bottom dead centre of a press for about 10 s to harden stamped parts, and thus the productivity of hot stamping is considerably low, 2 and 3 shots per minute (see Fig. 1). The martensite transformation does not occur
for insufficient holding, i.e. no hardening. The cooling speed of die quenching is lower than that of water quenching due to low heat transfer. In addition, the stamped parts have a non-uniform distribution of thickness, and thus are locally in contact with the dies during holding as shown in Fig. 2. Local thinning tends to occur due to a temperature distribution induced by local contact with dies during stamping [4]. Since the cooling speed of die quenching is influenced by the die pressure [5], large holding force is required to increase the cooling speed during die quenching. It is desirable in forming industry to reduce the holding time at the bottom dead centre because of productivity improvement. In the present study, the productivity and formability in hot stamping of ultra-high strength steel parts were improved by water and die quenching. In addition, blankholding was delayed to improve hardening of a flange portion in hot stamping with water and die quenching. 2. Shortening of holding time at bottom dead centre by water and die quenching To improve the productivity in hot stamping of ultra-high strength steel parts, the holding time at the bottom dead centre was shortened by not only die quenching but also water quenching (see Fig. 3). Water is kept in the lower die in order to be in contact
Fig. 1. Rough time for 1 shot in hot stamping and variation in temperature.
* Corresponding author. http://dx.doi.org/10.1016/j.cirp.2015.04.128 0007-8506/ß 2015 CIRP.
Fig. 2. Gaps between stamped part and die during holding at bottom dead centre for die quenching.
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25 mm in height. Since the temperature of tools raises for repeated stamping, the punch and die were heated at about 150 8C by the heaters. A 1500 kN mechanical servo press was used, and no lubricant was applied to the blank and tools. The average speed of the press slide during stamping was 200 mm/s. 3.2. Results of hot stamping using water and die quenching
Fig. 3. Cooling of blank in hot stamping using water and die quenching. (a) Start, (b) stamping and (c) holding at bottom dead centre.
with the blank during stamping. The gaps between the blank and die are filled with the water during holding, and thus the portions without touching the dies are also rapidly cooled. The blank is cooled by high heat transfer and steam of the water.
The cup by hot stamping using water and die quenching is shown in Fig. 6, where t is the holding time at the bottom dead centre. The degrees of oxidation on the surface of the cup with and without the water were almost similar. The wrinkles in the flange were comparatively small even with the spacers. The water hardly splashed even for the maximum ram speed of the servo press, and gave off steam for rapidly cooling the blank. Since the water was poured into the lower die just before stamping, almost no steam was generated up to stamping.
3. Hot stamping of cup having non-hardened flange using tool detachment 3.1. Procedure of hot stamping using water and die quenching The hot stamping process using water and die quenching is shown in Fig. 4. The heated circular blank was drawn into a cup having a flange with the punch and die. Because the flange of the drawn cup is often cut as products, the flange was not hardened by detaching the blankholder from the flange just after reaching at the bottom dead centre. This enables cold shearing of the nonhardened flange [6,7]. To improve the drawability, the resistance to drawing of the flange was reduced by inserting the spacers thicker than the blank between the die and blankholder [4]. The temperature drop of the flange during forming becomes small, because a gap is generated between the blank and the blankholder by the spacers. The water was kept in the lower die just before stamping, and the overflowed one was drained from the holes in the side wall of the die during stamping.
Fig. 6. Hot-stamped cup with water for t = 3 s.
The distributions of temperature in the stamped cup after 1.6 s from the end of holding at the bottom dead centre with and without the water are shown in Fig. 7. The temperature was measured with an infrared thermograph by moving the die upward. The temperature distribution with the water for t = 3 s is similar to the distribution without the water for t = 5 s. On the other hand, the temperature drop of the flange is prevented by the tool detachment from the flange just after reaching at the bottom dead centre.
Fig. 4. Hot stamping process using water and die quenching with tool detachment. (a) Start, (b) drawing, (c) bottom dead centre and (d) holding.
The tools used for the hot stamping process using water and die quenching are shown in Fig. 5. A non-coated quenchable steel sheet 22MnB5 (C: 0.21, Si: 0.25, Mn: 1.2, B: 0.001 mass%) was employed for the stamping experiment. The blank having 1.6 mm in thickness and 170 mm in diameter was heated at 910 8C in 240 s in an electrical furnace, and the temperature just before stamping was about 870 8C. The blank was formed into a taper cup having
Fig. 5. Tools used for hot stamping using water and die quenching.
Fig. 7. Distributions of temperature in stamped cup after 1.6 s from end of holding at bottom dead centre with and without water.
The distributions of Vickers hardness in the stamped cup with and without the water are shown in Fig. 8, where that with the water without the tool detachment is added as a comparison. The hardness distribution with the water for t = 3 s is similar to the distribution
Fig. 8. Distributions of Vickers hardness in stamped cups with and without water and without tool detachment.
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without the water for t = 5 s, i.e. the holding time at the bottom dead centre is shortened. The effect of the height of the water surface in the lower die on the distribution of Vickers hardness in the stamped cup for t = 3 s is shown in Fig. 9. As the height of the water surface increases, the hardness of the taper increases, whereas those of the bottom and flange are independent of the height.
Fig. 12. Effect of water quenching on drawability of cup having non-hardened flange.
4. Hot stamping of cup having hardened flange using delayed blankholding
Fig. 9. Effect of height of water surface in lower die on distribution of Vickers hardness in stamped cups for t = 3 s.
To improve the drawability of cups having a hardened flange, blankholding was delayed by protruding the punch from the blankholder as shown in Fig. 13. In the former stage of stamping, the blank is drawn without blankholding under a small resistance to drawing of the flange, and the blankholder force is applied in the latter stage to eliminate wrinkles. This leads to the reduction in temperature drop of the flange during stamping.
3.3. Improvement in formability by water and die quenching Water and die quenching has the function of not only shortening of holding time but also the prevention of local thinning as shown in Fig. 10. Without water, deformation of the blank tends to concentrate outside the border of the punch corner due to lower flow stress for higher temperature than that at the corner in contact with the punch. Such a deformation concentration is considerably relieved with the water. Fig. 13. Delayed blankholding with protruded punch in hot stamping using water and die quenching. (a) Start, (b) no blankholding, (c) blankholding and (d) holding.
Fig. 10. (a) Local thinning without water and (b) prevention of thinning by water and die quenching in hot stamping.
The tools used for hot stamping using water and die quenching with delayed blankholding are shown in Fig. 14. The protrusion height L and the stroke s of the punch were changed. The depth of the lower die was increased to supply adequate water. Since the tools shown in Fig. 5 are not suitable to examine the drawability because of the limitation of deformation, the hole depth of the lower die is increased to fracture the cup.
The distributions of the thickness in the stamped cup with and without the water for t = 3 s are shown in Fig. 11. Local thinning outside the border of the punch corner was relieved by water and die quenching. The deformation behaviour is influenced with the water. The drawing limits for the cups with and without the water are given in Fig. 12, where the diameter of the blank is changed. Although the results for the previous experiments were obtained for 170 mm in blank diameter, the drawing limit was decreased without the spacers between the die and blankholder shown in Fig. 4. The drawability was improved by water and die quenching. Fig. 14. Tools used for hot stamping using water and die quenching with delayed blankholding.
Fig. 11. Distributions of thickness in stamped cup with and without water for t = 3 s.
The deformation behaviour of the flange in hot stamping using water and die quenching with delayed blankholding for L = 12.5 mm is shown in Fig. 15. Although the wrinkles in the flange appeared in the former stage of stamping, the wrinkles were compressed with the blankholder and die in the latter stage, and finally the flange became flat. The effect of the protrusion height of the punch on the drawability with delayed blankholding is shown in Fig. 16. The drawability is increased with the protrusion height. The formability is improved by delayed blankholding. The relationship between the average height of wrinkles of the stamped cup and the protrusion height of the punch is shown in
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Fig. 18. Distributions of Vickers hardness in stamped cup with water and die quenching for L = 12.5 mm and s = 18.5 mm.
Fig. 15. Deformation behaviour of flange during hot stamping using water and die quenching with delayed blankholding for L = 12.5 mm. (a) Start, (b) wrinkles and (c) elimination of wrinkles.
Fig. 16. Effect of protrusion height of punch on drawability with delayed blankholding.
5. Conclusions Die quenching in hot stamping is an innovation for production of high strength steel parts. The quenching process is included in stamping operations. However, the productivity of hot stamping is considerably low because of local contact between the die and blank. On the other hand, water quenching of hot-stamped parts keeping a high temperature leads to high strength but large springback. Water and die quenching in hot stamping is attractive to improve the productivity and springback. Moreover, water and die quenching has the function of increasing the formability due to the temperature control. Although the cup having a flange was dealt with, water and die quenching is effective for large-size pars such as body-in-white reinforcements generally produced by hot stamping because of increase in amount of water in a lower die. The generation of steam during the operation is as well as hot forging using water including graphite powder, and the similar treatment for environmental protection is necessary in practical application. On the other hand, holding of water in the lower die brings about the limitation of shapes of products. An effective approach for supplying water in gaps between the blank and die in holding at the bottom dead centre is required, and the supply from the outside of the dies should be taken into consideration.
References
Fig. 17. Relationship between average height of wrinkles of stamped cup and protrusion height of punch.
Fig. 17. The average height of wrinkles below L = 12.5 mm is very small. The distributions of Vickers hardness in the stamped cup with and without water for L = 12.5 mm and s = 18.5 mm are shown in Fig. 18. The hardness with the water for t = 3 s is above 450 HV20. It was found that water and die quenching is effective in improving both productivity and formability of hot stamping.
[1] Mori K, Maki S, Tanaka Y (2005) Warm and Hot Stamping of Ultra High Tensile Strength Steel Sheets Using Resistance Heating. CIRP Annals – Manufacturing Technology 54(1):209–212. [2] Neugebauer R, Altan T, Geiger M, Kleiner M, Sterzing A (2006) Sheet Metal Forming at Elevated Temperatures. CIRP Annals – Manufacturing Technology 55(2):793–816. [3] Karbasian H, Tekkaya AE (2010) A Review on Hot Stamping. Journal of Materials Processing Technology 210(15):2103–2118. [4] Maeno T, Mori K, Nagai T (2014) Improvement in Formability by Control of Temperature in Hot Stamping of Ultra-High Strength Steel Parts. CIRP Annals – Manufacturing Technology 63(1):301–304. [5] Hoffmann H, So H, Steinbeiss H (2007) Design of Hot Stamping Tools with Cooling System. CIRP Annals – Manufacturing Technology 56(1):269–272. [6] Mori K, Okuda Y (2010) Tailor Die Quenching in Hot Stamping for Producing Ultrahigh Strength Steel Formed Parts Having Strength Distribution. CIRP Annals – Manufacturing Technology 59(1):291–294. [7] Mori K, Maeno T, Mongkolkaji K (2013) Tailored Die Quenching of Steel Parts Having Strength Distribution Using Bypass Resistance Heating in Hot Stamping. Journal of Materials Processing Technology 213(3):508–514.
Contents lists available at ScienceDirect
CIRP Annals - Manufacturing Technology jou rnal homep age : ht t p: // ees .e lse vi er . com /ci r p/ def a ult . asp
Improvements in productivity and formability by water and die quenching in hot stamping of ultra-high strength steel parts Tomoyoshi Maeno *, Ken-Ichiro Mori (1), Masaki Fujimoto Department of Mechanical Engineering, Toyohashi University of Technology, Toyohashi, Aichi 441-8580, Japan
A R T I C L E I N F O
A B S T R A C T
Keywords: Hot stamping Sheet metal Productivity
To improve the productivity in hot stamping of ultra-high strength steel parts, the parts are quenched not only with dies but also in water during holding at the bottom dead centre. Since the cooling speed for water quenching is higher than that for die quenching, the hold time for hardening is reduced. In hot stamping, water is kept in a lower die to increase the cooling rate during die quenching. In addition, local thinning around the punch corner was prevented by water and die quenching, and thus the drawablity increases. ß 2015 CIRP.
1. Introduction For the reduction in weight and improvement of crash safety for automobiles, hot stamping of quenchable steel sheets is increasingly employed for production of ultra-high strength steel parts. By heating the steel sheets, the forming load is remarkably reduced, the springback is prevented and the formability is improved [1,2]. In addition, the stamped parts are hardened by quenching with dies, and thus the ultra-high strength steel parts having a tensile strength of approximately 1.5 GPa are obtained under a low forming load [3]. In hot stamping, dies are held at the bottom dead centre of a press for about 10 s to harden stamped parts, and thus the productivity of hot stamping is considerably low, 2 and 3 shots per minute (see Fig. 1). The martensite transformation does not occur
for insufficient holding, i.e. no hardening. The cooling speed of die quenching is lower than that of water quenching due to low heat transfer. In addition, the stamped parts have a non-uniform distribution of thickness, and thus are locally in contact with the dies during holding as shown in Fig. 2. Local thinning tends to occur due to a temperature distribution induced by local contact with dies during stamping [4]. Since the cooling speed of die quenching is influenced by the die pressure [5], large holding force is required to increase the cooling speed during die quenching. It is desirable in forming industry to reduce the holding time at the bottom dead centre because of productivity improvement. In the present study, the productivity and formability in hot stamping of ultra-high strength steel parts were improved by water and die quenching. In addition, blankholding was delayed to improve hardening of a flange portion in hot stamping with water and die quenching. 2. Shortening of holding time at bottom dead centre by water and die quenching To improve the productivity in hot stamping of ultra-high strength steel parts, the holding time at the bottom dead centre was shortened by not only die quenching but also water quenching (see Fig. 3). Water is kept in the lower die in order to be in contact
Fig. 1. Rough time for 1 shot in hot stamping and variation in temperature.
* Corresponding author. http://dx.doi.org/10.1016/j.cirp.2015.04.128 0007-8506/ß 2015 CIRP.
Fig. 2. Gaps between stamped part and die during holding at bottom dead centre for die quenching.
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25 mm in height. Since the temperature of tools raises for repeated stamping, the punch and die were heated at about 150 8C by the heaters. A 1500 kN mechanical servo press was used, and no lubricant was applied to the blank and tools. The average speed of the press slide during stamping was 200 mm/s. 3.2. Results of hot stamping using water and die quenching
Fig. 3. Cooling of blank in hot stamping using water and die quenching. (a) Start, (b) stamping and (c) holding at bottom dead centre.
with the blank during stamping. The gaps between the blank and die are filled with the water during holding, and thus the portions without touching the dies are also rapidly cooled. The blank is cooled by high heat transfer and steam of the water.
The cup by hot stamping using water and die quenching is shown in Fig. 6, where t is the holding time at the bottom dead centre. The degrees of oxidation on the surface of the cup with and without the water were almost similar. The wrinkles in the flange were comparatively small even with the spacers. The water hardly splashed even for the maximum ram speed of the servo press, and gave off steam for rapidly cooling the blank. Since the water was poured into the lower die just before stamping, almost no steam was generated up to stamping.
3. Hot stamping of cup having non-hardened flange using tool detachment 3.1. Procedure of hot stamping using water and die quenching The hot stamping process using water and die quenching is shown in Fig. 4. The heated circular blank was drawn into a cup having a flange with the punch and die. Because the flange of the drawn cup is often cut as products, the flange was not hardened by detaching the blankholder from the flange just after reaching at the bottom dead centre. This enables cold shearing of the nonhardened flange [6,7]. To improve the drawability, the resistance to drawing of the flange was reduced by inserting the spacers thicker than the blank between the die and blankholder [4]. The temperature drop of the flange during forming becomes small, because a gap is generated between the blank and the blankholder by the spacers. The water was kept in the lower die just before stamping, and the overflowed one was drained from the holes in the side wall of the die during stamping.
Fig. 6. Hot-stamped cup with water for t = 3 s.
The distributions of temperature in the stamped cup after 1.6 s from the end of holding at the bottom dead centre with and without the water are shown in Fig. 7. The temperature was measured with an infrared thermograph by moving the die upward. The temperature distribution with the water for t = 3 s is similar to the distribution without the water for t = 5 s. On the other hand, the temperature drop of the flange is prevented by the tool detachment from the flange just after reaching at the bottom dead centre.
Fig. 4. Hot stamping process using water and die quenching with tool detachment. (a) Start, (b) drawing, (c) bottom dead centre and (d) holding.
The tools used for the hot stamping process using water and die quenching are shown in Fig. 5. A non-coated quenchable steel sheet 22MnB5 (C: 0.21, Si: 0.25, Mn: 1.2, B: 0.001 mass%) was employed for the stamping experiment. The blank having 1.6 mm in thickness and 170 mm in diameter was heated at 910 8C in 240 s in an electrical furnace, and the temperature just before stamping was about 870 8C. The blank was formed into a taper cup having
Fig. 5. Tools used for hot stamping using water and die quenching.
Fig. 7. Distributions of temperature in stamped cup after 1.6 s from end of holding at bottom dead centre with and without water.
The distributions of Vickers hardness in the stamped cup with and without the water are shown in Fig. 8, where that with the water without the tool detachment is added as a comparison. The hardness distribution with the water for t = 3 s is similar to the distribution
Fig. 8. Distributions of Vickers hardness in stamped cups with and without water and without tool detachment.
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without the water for t = 5 s, i.e. the holding time at the bottom dead centre is shortened. The effect of the height of the water surface in the lower die on the distribution of Vickers hardness in the stamped cup for t = 3 s is shown in Fig. 9. As the height of the water surface increases, the hardness of the taper increases, whereas those of the bottom and flange are independent of the height.
Fig. 12. Effect of water quenching on drawability of cup having non-hardened flange.
4. Hot stamping of cup having hardened flange using delayed blankholding
Fig. 9. Effect of height of water surface in lower die on distribution of Vickers hardness in stamped cups for t = 3 s.
To improve the drawability of cups having a hardened flange, blankholding was delayed by protruding the punch from the blankholder as shown in Fig. 13. In the former stage of stamping, the blank is drawn without blankholding under a small resistance to drawing of the flange, and the blankholder force is applied in the latter stage to eliminate wrinkles. This leads to the reduction in temperature drop of the flange during stamping.
3.3. Improvement in formability by water and die quenching Water and die quenching has the function of not only shortening of holding time but also the prevention of local thinning as shown in Fig. 10. Without water, deformation of the blank tends to concentrate outside the border of the punch corner due to lower flow stress for higher temperature than that at the corner in contact with the punch. Such a deformation concentration is considerably relieved with the water. Fig. 13. Delayed blankholding with protruded punch in hot stamping using water and die quenching. (a) Start, (b) no blankholding, (c) blankholding and (d) holding.
Fig. 10. (a) Local thinning without water and (b) prevention of thinning by water and die quenching in hot stamping.
The tools used for hot stamping using water and die quenching with delayed blankholding are shown in Fig. 14. The protrusion height L and the stroke s of the punch were changed. The depth of the lower die was increased to supply adequate water. Since the tools shown in Fig. 5 are not suitable to examine the drawability because of the limitation of deformation, the hole depth of the lower die is increased to fracture the cup.
The distributions of the thickness in the stamped cup with and without the water for t = 3 s are shown in Fig. 11. Local thinning outside the border of the punch corner was relieved by water and die quenching. The deformation behaviour is influenced with the water. The drawing limits for the cups with and without the water are given in Fig. 12, where the diameter of the blank is changed. Although the results for the previous experiments were obtained for 170 mm in blank diameter, the drawing limit was decreased without the spacers between the die and blankholder shown in Fig. 4. The drawability was improved by water and die quenching. Fig. 14. Tools used for hot stamping using water and die quenching with delayed blankholding.
Fig. 11. Distributions of thickness in stamped cup with and without water for t = 3 s.
The deformation behaviour of the flange in hot stamping using water and die quenching with delayed blankholding for L = 12.5 mm is shown in Fig. 15. Although the wrinkles in the flange appeared in the former stage of stamping, the wrinkles were compressed with the blankholder and die in the latter stage, and finally the flange became flat. The effect of the protrusion height of the punch on the drawability with delayed blankholding is shown in Fig. 16. The drawability is increased with the protrusion height. The formability is improved by delayed blankholding. The relationship between the average height of wrinkles of the stamped cup and the protrusion height of the punch is shown in
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Fig. 18. Distributions of Vickers hardness in stamped cup with water and die quenching for L = 12.5 mm and s = 18.5 mm.
Fig. 15. Deformation behaviour of flange during hot stamping using water and die quenching with delayed blankholding for L = 12.5 mm. (a) Start, (b) wrinkles and (c) elimination of wrinkles.
Fig. 16. Effect of protrusion height of punch on drawability with delayed blankholding.
5. Conclusions Die quenching in hot stamping is an innovation for production of high strength steel parts. The quenching process is included in stamping operations. However, the productivity of hot stamping is considerably low because of local contact between the die and blank. On the other hand, water quenching of hot-stamped parts keeping a high temperature leads to high strength but large springback. Water and die quenching in hot stamping is attractive to improve the productivity and springback. Moreover, water and die quenching has the function of increasing the formability due to the temperature control. Although the cup having a flange was dealt with, water and die quenching is effective for large-size pars such as body-in-white reinforcements generally produced by hot stamping because of increase in amount of water in a lower die. The generation of steam during the operation is as well as hot forging using water including graphite powder, and the similar treatment for environmental protection is necessary in practical application. On the other hand, holding of water in the lower die brings about the limitation of shapes of products. An effective approach for supplying water in gaps between the blank and die in holding at the bottom dead centre is required, and the supply from the outside of the dies should be taken into consideration.
References
Fig. 17. Relationship between average height of wrinkles of stamped cup and protrusion height of punch.
Fig. 17. The average height of wrinkles below L = 12.5 mm is very small. The distributions of Vickers hardness in the stamped cup with and without water for L = 12.5 mm and s = 18.5 mm are shown in Fig. 18. The hardness with the water for t = 3 s is above 450 HV20. It was found that water and die quenching is effective in improving both productivity and formability of hot stamping.
[1] Mori K, Maki S, Tanaka Y (2005) Warm and Hot Stamping of Ultra High Tensile Strength Steel Sheets Using Resistance Heating. CIRP Annals – Manufacturing Technology 54(1):209–212. [2] Neugebauer R, Altan T, Geiger M, Kleiner M, Sterzing A (2006) Sheet Metal Forming at Elevated Temperatures. CIRP Annals – Manufacturing Technology 55(2):793–816. [3] Karbasian H, Tekkaya AE (2010) A Review on Hot Stamping. Journal of Materials Processing Technology 210(15):2103–2118. [4] Maeno T, Mori K, Nagai T (2014) Improvement in Formability by Control of Temperature in Hot Stamping of Ultra-High Strength Steel Parts. CIRP Annals – Manufacturing Technology 63(1):301–304. [5] Hoffmann H, So H, Steinbeiss H (2007) Design of Hot Stamping Tools with Cooling System. CIRP Annals – Manufacturing Technology 56(1):269–272. [6] Mori K, Okuda Y (2010) Tailor Die Quenching in Hot Stamping for Producing Ultrahigh Strength Steel Formed Parts Having Strength Distribution. CIRP Annals – Manufacturing Technology 59(1):291–294. [7] Mori K, Maeno T, Mongkolkaji K (2013) Tailored Die Quenching of Steel Parts Having Strength Distribution Using Bypass Resistance Heating in Hot Stamping. Journal of Materials Processing Technology 213(3):508–514.