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ScienceDirect Procedia Engineering 81 (2014) 1970 – 1975
11th International Conference on Technology of Plasticity, ICTP 2014, 19-24 October 2014, Nagoya Congress Center, Nagoya, Japan
Estimation of frictional property of lubricants for hot forging of steel using low-speed ring compression test Kazuhito Asai*, Kazuhiko Kitamura Nagyoa Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Jaopan
Abstract Development of high performance lubricants for hot forging of steel has been strongly needed to expand die life and to improve working environment at factories. Thereupon, graphite lubricants have been altered into non-graphite lubricants in hot forging of simple parts. However, these non-graphite lubricants have insufficient property. In this paper, low-speed ring compression test was proposed to estimate the frictional property of lubricants for hot forging of steel. It was found that each lubricant has critical temperature less than 450 Û&to reduce the friction between the dies and the 1000 Û&billet. © 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2014 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection peer-review under underresponsibility responsibilityofofthe Nagoya University and Toyohashi of Technology. Selection and and peer-review Department of Materials Science University and Engineering, Nagoya University Keywords: Lubrication; Tribology; Hot forging; Testing method
1. Introduction A high performance lubricant has been developed to improve working environment at factories for hot forging of steel. Graphite lubricants have been altered into non-graphite lubricants in hot forging [1]. Nonoyama et al. [2] developed the new lubrication method using glass with a low melting point to apply to backward can extrusion in warm forging of steel. Yang et al. [3] closely investigated the dynamics of lubricant deposition on hot die. They have analyzed the mechanism of the evaporation of lubricant basically [4]. They give important and basic
* Corresponding author. E-mail address:
[email protected]
1877-7058 © 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of the Department of Materials Science and Engineering, Nagoya University doi:10.1016/j.proeng.2014.10.266
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Kazuhito Asai and Kazuhiko Kitamura / Procedia Engineering 81 (2014) 1970 – 1975
information of lubrication for hot forging. Gracious et al. [5] developed the new solid lubricant for hot forging of aluminum. The authors [6] found the combination of a nitrided die and a lubricant to reduce galling for hot forging of aluminum. However, lubrication conditions in hot forging for steel are severer than aluminum due to high pressure and temperature. Especially, for complicated large parts the short die life has been still a big problem in hot forging of steel. In this paper, the frictional properties of the typical non-graphite lubricants for hot forging of steel are estimated by a low-speed ring compression test. It was found that each lubricant has critical temperature less than 450Û& for thermal resistance to reduce the friction between a hot billet at 1000Û& and a die.
2. Testing methods and conditions Fig. 1 shows the conditions of ring compression test. The ring billet is made of 0.45% carbon steel, and has geometries of 30 mm in outer diameter, 15 mm in inner diameter, and 10 mm in height. This billet is heated with an induction heater in air. The elevated temperature of billet is a range of 1060ÛC to 1120ÛC. The reduction in height is in a range of 40% to 49%. The dies are made of high-speed die steel as quenched and tempered. Testing lubricants are three conventional graphite type lubricants: B1, B2, B3 and seven commercial non-graphite type lubricants: W1, W2, W3, W4, W5, W6, and W7. These lubricants are sprayed even to the dies. The lubricants covered with the dies. The covering amount is in the range of 2 to 45 g/m2. The dies are pre-heated at 200ÛC to dry the sprayed lubricants. The dies are cooled to room temperature for easy setting on a mechanical press or a hydraulic press in these tests. This unrealistic setting will be improved in the future work.
Upper die Lubricant
Ring billet Lower die
Ring billet 0.45% carbon steel , 1060ºC-1120ºC Original height: inside diameter: out side dia. = 10:15:30 Dies SKH51 (Q.T.) , R.T. Lubricants Graphite, Non-graphite Presses Mechanical press, Hydraulic press Reduction in height 40% - 49%
Fig. 1. Setup of ring compression test and testing conditions.
100 B1
80 60 W1
40
Heating rate 5 ºC/min Sample weight 1 - 2 mg Atmosphere Air W3 W4
20 0
W2 0
200
400 600 800 Temperature T (ºC)
1000
(a) Thermogravimetry on lubricants of B1, W1 - W4
Heating rate 5 ºC/min Sample weight 1 - 2 mg Air W6 Atmosphere
100 Thermogravimetry (%)
Thermogravimetry (%)
The results of thermogravimetry and thermal differential analysis of the lubricants are shown in Fig. 2 and Fig. 3, respectively. The testing lubricants are dried to make 2-mg sample for these analyses. Each sample is heated from room temperature to 1000ÛC in air at a heating rate of 5 degrees per minute.
80
W5
60
W7
40 B1
20 0
0
200
400 600 800 Temperature T (ºC)
1000
(b) Thermogravimetry on lubricants of B1, W5 - W7
Fig. 2. Thermogravimetry on lubricants of (a): B1, W1 W2, W3, W4, and (b): B1, W5, W6, W7.
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Differential thermal analysis (PV)
Differential thermal analysis (PV)
Kazuhito Asai and Kazuhiko Kitamura / Procedia Engineering 81 (2014) 1970 – 1975
200 150 W4
100 50 0
W2
W3 0
200
400
W1
B1
600
800
1000
Temperature T (ºC)
200 W5
150 100
W6 W7
50 0
B1 0
200
400 600 800 Temperature T (ºC)
1000
(b) Differential thermal analysis on lubricants of B1, W5 - W7
(a) Differential thermal analysis on lubricants of B1, W1 - W4
Fig. 3. Differential thermal analysis on lubricants of (a): B1, W1, W2, W3, W4, and (b): B1, W5, W6, W7.
It is indicated that a large amount of the non-graphite type lubricants rapidly decrease with strong exothermic reaction between 350 and 550 ÛC. This means that the lubricants were resolved into gas around the elevated temperature. It can be presumed that the performance of the non-graphite lubricants deteriorates if the main components of the lubricants are considerably damaged between 350 and 550 ÛC. However, the lubricating performance of the lubricants is difficult to be estimated by these results of thermogravimetry and thermal differential analysis only.
3. Low-speed and high-speed ring compression test 3.1. Influence of pressing speed on results of ring compression test Fig. 4 shows comparison between frictional coefficients determined by two types of ring compression tests for ten lubricants. In one type of high-speed ring compress test, a mechanical press is used. In another type of lowspeed ring compression test, a hydraulic press is used. When the mechanical press is used, the average compression speeds v is 38 mm/s and a compression time t is 0.12 seconds. When the hydraulic press is used, v = 1.3 mm/s and t = 3.3 seconds. The graphite type lubricants and the non-graphite type lubricants show nearly the same frictional coefficients as 0.13 to 0.15 in the case of using the mechanical press. These results indicate the improvement of lubrication performance of the non-graphite lubricants when the mechanical press is used at least. However, the non-graphite type lubricants show higher frictional coefficients than graphite type lubricants when the hydraulic press is used. Since the hydraulic press takes a longer contact time than the mechanical press, the long contact time leads to a severer frictional condition between the dies and the hot billet.
Lubricants
Mechanical press (Contact time t = 0.12 s, Speed v = 38 mm/s) B1 B2 B3 W1 W2 W3 W4 W5 W6 W7
Hydraulic press (t =3.3 s, v =1.3 mm/s) Testing temperature 1060ºC– 1120ºC Initial amount of lubricants Graphite type w = 15-26 g/m2 Non-graphite type w = 20-34 g/m2
0
0.05
0.10
0.15
0.20
0.25
0.30
Coulomb’s frictional coefficient Pby ring compression test
Fig. 4. Frictional coefficients determined by ring compression test for different lubricants using mechanical press and hydraulic press.
Kazuhito Asai and Kazuhiko Kitamura / Procedia Engineering 81 (2014) 1970 – 1975
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3.2. Influence of lubricant amounts on frictional coefficient using ring compression test Fig. 5 shows influence of lubricant amounts on fractional coefficient by low-speed ring compression test. The conventional graphite type lubricants of B1, B2, and B3 show the frictional coefficients within a range of 0.11 and 0.15 when the amounts of these lubricants are between 2 and 45 g/m2. Thus, the graphite type lubricants have an advantageous property of low and stable friction whenever so small amount (for example, 2 g/m2) of the lubricant is applied to the dies.
Coulomb's frictional coefficient P measured by ring compression test
0.40
Nonlubricant
Testing temperature 1060ºC - 1120ºC Heating atmosphere Air Hydraulic press W7
0.30
W5 W4
0.20
W6
W3 B2
0.10
W2 W1
B3 B1
0.0 0
10
20 30 40 Amount of lubricant w (g/m2)
50
Fig. 5. Influence of amount of lubricants on frictional coefficient.
The non-graphite type lubricant of W3 shows the frictional coefficients within a range of 0.15 to 0.18. This lubricant of W3 shows the next lower frictional coefficients after the graphite type lubricants. For the other nongraphite type lubricants of W4, W5, and W7 the frictional coefficients increase as the amount of these lubricants decreases. These non-graphite type lubricants are influence of the lubricant amounts on the frictional coefficients. Particularly, when the lubricant amount is small or the lubricant film is thin, the non-graphite type lubricants tend to be damaged by the billet heated at 1000ÛC. 3.3. Influence of heat-treated temperature of lubricant before ring compression test Fig.6 shows the influence of heat treatment of the lubricants on frictional coefficient by the low-speed ring compression test. In this heat treatment, the lubricants are heated at 300ÛC, 350ÛC, or 400ÛC for 3hours and they are heated at 450ÛC for 4 hours by using an electric furnace in an atmosphere of air. The frictional coefficients for the lubricants heat-untreated by heat are also showed for a reference. If the components of these lubricants are damaged by the heat-treatment, the frictional coefficients between the dies and the ring billet increase. The lubricants heat-treated at 300ÛC show almost the same frictional coefficients as the heat-untreated lubricants show. The lubricants heat-treated at 350ÛC show a little inclination to be higher frictional coefficients than the heatuntreated or 300ÛC-treated lubricant. The frictional coefficients of W1, W5, and W7 rapidly increase when the temperature of the heat treatment rises up to 400ÛC. The lubricants of W5 and W7 keep no lubrication performance to reduce friction between the dies and the billet. The frictional performance of W1 declines. Moreover, the lubricant performance of W1 is lost and that of W4 declines after they were heat- treated at 450ÛC. However, the W2 keeps nearly the same level of frictional coefficient as the graphite type lubricant of B1except a small difference. From these results, it is found that the lubricants have critical temperature to reduce the friction between the dies and the billet. The low-speed ring compression test will contribute to development or improvement of non-graphite type lubricant if this critical temperature helps to determine what effective components in reducing the friction are.
Kazuhito Asai and Kazuhiko Kitamura / Procedia Engineering 81 (2014) 1970 – 1975
Coulomb's frictional coefficient P measured by ring compression test
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0.40 W7
Non-lubricant 0.30
0.20
W1 W4 Amount of lubricants B1 15 -20 g/m2 W1 22 -26 g/m2 W2 22 -28 g/m2 W4 18 -29 g/m2 W5 24 -30 g/m2 W7 20 -29 g/m2
W2 W5
B1
0.10 0.0
0
100 200 300 400 500 Temperature of heating lubricants T (ºC)
Fig. 6. Influence of temperature of heating lubricants on frictional coefficient.
From the results of thermogravimetry as shown in Fig. 2, the amount of the lubricants decreased with increasing temperature. Furthermore, this reduction in the amount of the lubricants leads to increase in frictional coefficients between the dies and the billet. Thus, Fig. 7 also shows the relationship between the residual amount of the lubricants detected by thermogravimetry and the frictional coefficient measured by low-speed ring compression test. As the residual amount of lubricants decreases, the frictional coefficient increases. The graphite lubricant of B1 and the non-graphite lubricant of W2 show lower frictional coefficients than other. It was found that W2 indicated nearly the same frictional coefficient as B1. Thus, the low-speed ring compression test for the heat-treated lubricants contributed to find the lubricant of W2 demonstrating the high performance of lubrication. The lubricant of W1 declines the high performance to reduce friction when the residual amount of this W1 decreases in about 70%. The lubricants of W4, W5, and W7 show the same frictional coefficients when they are heat-untreated. However, W5 and W7 considerably decrease in the lubrication performance when the residual amount of W5 and W7 is less than 90%, while W4 gradually increases in friction when the residual amount of lubricant is larger than 70%. The lubricant of W4 rapidly increases in friction when the residual amount decreases below 70%. These lubricants have large differences in a critical residual amount that the friction begins to rise rapidly. The lubricants of W1, W2, and W4 show a tendency to keep the lubrication performance even if the residual amount of lubricant decreases until about 80%. However, in the case of W5 and W7, a small reduction in the
Coulomb's frictional coefficient P measured by ring compression test
Contact time t= 3.3 s, Compression speed v =1.3 mm/s 0.40 W7
W5
W1
Non-lubrication
0.30 W4
R.T. 300ºC 350ºC 400ºC 450ºC
0.20 W2 0.10 0.0 100
B1
90
80
70
60
50
40
0
Residual amount of lubricant (%)
Fig. 7. Influence of residual amount of lubricants by thermogravimetry and frictional coefficient by low-speed ring compression test.
Kazuhito Asai and Kazuhiko Kitamura / Procedia Engineering 81 (2014) 1970 – 1975
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residual amount of lubricant results in an extreme increase in friction. By the low-speed ring compression test, it was determined that the decrease in quantity of the lubricant and the deterioration of quality of the lubricants leads to decline the lubrication performance.
4. Conclusions Typical lubricants for hot forging of steel were estimated by a high-speed ring compression test using a mechanical press and by a low-speed ring compression test using a hydraulic press. The following results were obtained: (1) There is a small difference in the frictional performance of the graphite type lubricants and the non-graphite type lubricant when the mechanical press is used. However, most non-graphite type lubricants show the higher frictional coefficients than the graphite type lubricant when the hydraulic press is used with the long contact time. This long contact time with heating at high temperature must bring the lubricants under a severer frictional condition. It was found that a tested non-graphite lubricant indicated nearly the same frictional coefficient as the graphite type lubricant in the high-and low-speed ring compression test. (2) The graphite type lubricants demonstrated low friction whenever so small amount of the lubricant is applied to the dies. The non-graphite type lubricants, however, declined in the lubrication performance because the lubricants tend to be damaged by a hot billet heated at 1000ÛC. (3) By referring to the results of TG and DTA of the non-graphite lubricant, after these lubricants were heattreated at 300ºC, 350ºC, 400ºC, and 450ºC, the lubrication performance of the lubricants were also estimated by the low-speed ring compression test. It was found that the lubricants retained the lubrication performance below each heat-treatment temperature less than 450ºC. This temperature means a critical temperature to help us find out effective components for a higher performance lubricant for hot forging. The critical temperature of the lubricant is related to a heat transfer of lubricant between the die and the hot billet. In the future work, hot forging will be analyzed with considering this heat transfer. References [1] Morishita, H., 2007. Tribology in Manufacturing Processes of Automobiles at TOYOTA. Proc. ICTMP 2007, 1–9. [2] Nonoyama, F., Kitamura, K., Danno, A., 1993. New Lubricating Method for Warm Forging of Steel with Boron Oxide (B 2 O 3 ), CIRP Annals-Manufacturing Technology, 42, 1, 353-356. [3] Yang, L., Liu, C., Shivpuri, R., 2005. Physiothermodynamics of Lubricant Deposition on Hot Die Surfaces. CIRP Annals-Manufacturing Technology 54, 1, 253–256. [4] Yang, L., Shivpuri, R., 2007. A Water Evaporation Based Model for Lubricant Dryoff on Die Surfaces Heated Beyond the Leidenfrost Point. Journal of Manufacturing Science and Engineering 129, 717–725. [5] Gracious, N., Botz, F., 2008. Performance of Graphite and Boron-Nitride-Silicone Based Lubricants and Associated Lubrication Mechanisms in Warm Forging of Aluminum. Journal of Tribology, 130, 021801-1 –021801-7. [6] Asai, K., Kitamura, K., Terano, M. 2011. Evaluation on Anti-Galling Property of Surface-Hardening Tools for Hot Forging of Aluminum Using Tapered-Plug Penetration Test, Steel Research International Special Edition, 235-239.
