Wear 249 (2001) 50–55
Effect of water based lubricants on wear of coated material Teisuke Sato a,∗ , Tatsuo Besshi b , Daisuke Sato a , Isao Tsutsui a a
Department of Mechanical Engineering, Faculty of Engineering, The University of Tokushima, 2-1 Minamijosanjima-cho, Tokushima 770-8506, Japan b Tokushima Prefectural Industrial Technology Center, 11-2 Saika-cho, Tokushima 770-8021, Japan Received 27 March 2000; received in revised form 13 December 2000; accepted 17 January 2001
Abstract The effects of water base lubricants on wear of coated tools are examined by a crossed-cylinder wear test from environmental protection viewpoint. The lubricating property of pure water is inadequate. However, the addition of solid lubricant (melamine cyanuric acid adduct, MCA) to water, shows good tribological performance. Such a mixture provides the advantage of separating solid components from the water easily through filtration. The combined use of water base lubricant with addition of 10 wt.% MCA with Ti-base coated tool shows good tribological performance when in contact with carbon steel. The wear rate of Ti-base coated tool in contact with copper is very high. However, good performance results when the lubricant in this case is a combination of water with MCA and CrN or DLC coating. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Water base lubricant; Solid lubricant; Coated tool; Wear test
1. Introduction From the global environmental protection viewpoint, the manufacture and the use of the specific fluorocarbon and chlorides such as trichloroethane widely used as detergent is totally forbidden. In metal forming processes, the lubrication is indispensable, and a suitable environmental friendly lubricant is desired. Therefore, one option is to use the water base lubricants. However, the lubricating properties of the water-soluble lubricants are considerably inferior. Examples of the water-soluble lubricants utilized in the production are rare except for cutting coolant. Kataoka et al.  have attempted the deep drawing test with solid lubricant dispersed in pure water. Such a mixture provides the advantage of separating solid components from the water easily through filtration. Coating material surfaces by physical or chemical vapor depositions technology is frequently done not only for cutting tools but also for metal forming tools. Many applications of coated tools for cutting have been reported [2–5]. Lee et al.  have investigated the effects of TiN-coated dies on the drawing processes of aluminum sheets, proving that TiN-coated dies increase the limiting drawing ratio (LDR) and decrease the drawing force. Sato et al.  have examined the wear and tribological properties of coated tools rubbing against copper used in a crossed-cylinders test∗ Corresponding author. Tel.: +81-88-656-7379; fax: +81-88-656-9082. E-mail address: [email protected]
ing. Sato and Besshi  have also studied the anti-galling performance of coated tools in aluminum sheet forming. Murakawa et al. [9,10] have carried out deep-drawing tests on aluminum sheets using diamond-like carbon-coated dies demonstrating that the diamond-like carbon-coated tools have good anti-galling performance against aluminum, and the deep-drawing of aluminum sheet without lubricant can be worked out with these dies. Although coated tools exhibit excellent performance in laboratory, but in practice, metal forming processes without lubricants are restricted even with coated tools. The effects of the water base lubricant on wear of coated tool are examined using a crossed-cylinders wear test.
2. Experimental procedure 2.1. Wear test The wear test used is a crossed-cylinders test as illustrated in Fig. 1, a cylindrical coated tool is forced and pressed against a cylindrical work material rotating on a lathe. The pressing load by the coated tool specimen is applied by a loaded spring. The details of the crossed-cylinders test has been shown in a previous paper . Two types of tribological tests are possible. One is a fixed type test which is rubbed on the same track (at constant position) and the other is a feed type test which is rubbed on the new surface of the counter
0043-1648/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 3 - 1 6 4 8 ( 0 1 ) 0 0 5 2 2 - 1
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Table 2 Details of lubricanta
Fig. 1. Schematic view of a crossed-cylinders test.
material. Fixed type test is used in the following experiment with inclination angle of 10◦ as illustrated in Fig. 1. The following function λ is introduced to evaluate the wear resistance of coatings and the tribological performance of the lubricant as shown in previous paper . λ=
where δ is maximum wear depth, PN a normal load applied and L sliding distance. The coating performance is exhibited when the maximum wear depth reaches the thickness of the coating layer. Thus, the sliding distance at which the maximum wear depth reaches the thickness of the coating layer is defined as the effective sliding distance of coating. In this case, Eq. (1) can be expressed as follows. λm =
t PN L0
where L0 is the effective sliding distance and t the thickness of the coating layer. The parameter λm , defined as the effective mean wear rate, expresses the anti-wear performance of coating itself. A low λm in testing of a certain lubricant signifies a good tribological performance. The ratio PT /PN is defined as apparent frictional coefficient; PN is the normal load and PT the tangential load (frictional) and are calculated easily from measured horizontal load, vertical load and inclination angle . 2.2. Coated tools and work materials Coating details are provided are in Table 1. The substrate is a hardened high speed tool steel, SKH51 (JIS) (C: 0.80–0.90%, Cr: 3.80–4.50%, Mo: 4.50–5.50%, W: 5.50–6.70%, V: 1.60–2.20%), having hardness and surface roughness as 925 HV and 0.2 m Ry or less, respectively. Table 1 Details of coating tool
Dry White spindle Water H0.5 P0.5 P2.0 P4.0 M10.0 P0.5/M1.0 H0.5/P0.5 H0.5/P2.0 H0.5/P4.0 H0.5/P0.5/M1
Dry White spindle Water Water + HMT 0.5 wt.% Water + PAA 0.5 wt.% Water + PAA 2.0 wt.% Water + PAA 4.0 wt.% Water + MCA 10.0 wt.% Water + PAA 0.5 wt.% + MCA 1.0 wt.% Water + HMT 0.5 wt.% + PAA 0.5 wt.% Water + HMT 0.5 wt.% + PAA 2.0 wt.% Water + HMT 0.5 wt.% + PAA 4.0 wt.% Water + HMT 0.5 wt.% + PAA 0.5 wt.% + MCA 1.0 wt.% Water + HMT 0.5 wt.% + PAA 0.5 wt.% + MCA 4.0 wt.% Water + HMT 0.5 wt.% + PAA 0.5 wt.% + MCA 7.0 wt.% Water + HMT 0.5 wt.% + PAA 0.5 wt.% + MCA 10.0 wt.% Water + HMT 0.5 wt.% + MCA 10.0 wt.%
H0.5/P0.5/M4 H0.5/P0.5/M7 H0.5/P0.5/M10 H0.5/M10
a HMT: hexamethylenetetramine, melamine cyanuric acid adduct.
In this experiment, the 10 mm diameter coated specimen is selected. A plain carbon steel (S45C) (JIS) (C: 0.42–0.48%, 211 HV, 9.8 N) and a commercially pure copper bar stock (105 HV, 9.8 N) having a mean diameter of 47.5 mm are employed as the work materials. 2.3. Lubricant The details and the symbols of lubricant are given in Table 2. When the pure water is used as a lubricant for the carbon steel, the rust is generated in a short period. To prevent this, up to 0.5 wt.% hexamethylenetetramine (HMT) is added to the water as corrosion inhibitor. The polyacrylamide (PAA) is dissolved in water to increase the viscosity. As a solid lubricant, melamine cyanuric acid adduct (MCA) (Sumico Lubricant Co.) which is possible to disperse homogeneously in the water without dispersing agent, is used. The properties of MCA are given in Table 3. The symbols of the lubricants are abbreviated from the capital letter of the additives and its content. For example, H0.5/P0.5/M1 is used to introduce the lubricant having 0.5 wt.% PAA, 1.0 wt.% MCA and 0.5 wt.% water solution of HMT. The lubricant Table 3 Properties of MCA
Surface roughness (m Ra)
White fine powder
TiN TiAlN CrN CrN/TiN superlattice DLC
SKH51 SKH51 SKH51 SKH51 SKH51
1.3 1.5 5.7 2.8 1.7
0.3 0.2 0.2 0.2 0.2
Specific gravity Particle diameter (m) Solubility Thermal stability Combustibility
1.52 0.5–5 Insoluble in water Stable under 573 K Nonflammable
T. Sato et al. / Wear 249 (2001) 50–55
Fig. 2. Relationship between sliding distance and maximum wear depth.
Fig. 4. Relationship between PAA content and viscosity.
is supplied at the sliding contact point by a brush. The viscosity of liquid lubricant is measured by RheoStress RS75 (Haake).
3. Experimental results 3.1. Case of rubbing against S45C The effect of the water base lubricants on wear of TiN coating tool is studied. The relationship between the sliding distance and the maximum wear depth used in H0.5 lubricant (water containing only 0.5 wt.% inhibitor) is shown in Fig. 2. Throughout the tests, sliding velocity is kept to 1.0 m/s. When the normal load of 30 N is employed, the maximum wear depth is too small at the sliding distance L = 3000 m. The normal load is increased to P N = 50 N for easy comparison of the maximum wear depth for each lubricant. The change of maximum wear depth with the sliding distance is shown in Fig. 3. There is a slight wear prevention effect of H0.5 lubricant in comparison to the case without lubricant (dry). However, when it is compared to the spindle oil lubrication, the wear prevention effect of H0.5 lubricant is much inferior. 3.1.1. Effect of addition of polyacrylamide (PAA) One of the reasons of inferior tribological property of water base lubricant might be attributed to be the low viscosity. Then, the effect of increasing the viscosity of water by adding the PAA is examined. The relationship between
Fig. 3. Relationship between sliding distance and maximum wear depth.
Fig. 5. Relationship between PAA content and effective mean wear rate.
PAA content and viscosity of water is shown in Fig. 4. The maximum allowable PAA content is limited to 4 wt.% considering environmental protection view point. The relationship between the effective mean wear rate (λm ), the apparent frictional coefficient (PT /PN ) and PAA content are shown in Figs. 5 and 6, respectively. The λm value is lowered when adding PAA. Within the tested range of PAA content, the differences in λm values are small. It is desirable to keep the content of organic additives as low as possible from the environmental protection view point. Next, PAA content in water is kept to 0.5 wt.% and the effect of the solid lubricant (MCA) addition is examined. 3.1.2. Effect of solid lubricant (MCA) addition The effect of 1.0 wt.% solid lubricant (MCA) addition to the water (H0.5/P0.5) is examined. The change of the effective mean wear rate (λm ) is shown in Fig. 7. The wear
Fig. 6. Relationship between PAA content and apparent frictional coefficient.
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Fig. 10. Relationship between sliding distance and maximum wear depth. Fig. 7. Comparison of effective mean wear rate with lubricant.
3.1.3. Effect of different coating tools The wear tests of TiN, CrN/TiN, TiAlN, CrN and DLC coating are carried out with H0.5/M10 lubricant. Results of these tests are shown in Fig. 10. The λm value calculated from the data of Fig. 10 is shown in Fig. 11. In the case of rubbing against carbon steel (S45C), the combination of Ti-base coating tool with H0.5/M10 lubricant results the excellent performance. The coatings CrN and DLC are broken, because the test load of 50 N is too high for these coatings. 3.2. Case of rubbing against copper Fig. 8. Relationship between MCA content and effective mean wear rate.
prevention effect of 1.0 wt.% MCA addition is not sufficient. By changing the content value of MCA, the wear prevention effect is examined. The change of λm value with the MCA content is shown in Fig. 8. The value of λm at 10 wt.% MCA is almost the same as in the case where the white spindle oil is used as lubricant. The λm value of lubricant H0.5/P0.5/M10 is four orders smaller in magnitude than that of no lubricant (dry). However, the dispersion of MCA in the water when adding PAA becomes difficult. Then, λm value of H0.5/M10 (without PAA) is compared to λm value of H0.5/P0.5/M10 (with PAA). These results are shown in Fig. 9. There is little difference between the λm values, thus it is proven that H0.5/M10 can be used as a lubricant. MCA is insoluble in water and it is easily separated through filtration.
In the previous paper , it has been shown that the wear of TiN rubbing against copper was too much. Then, CrN/TiN is used in this test because the wear rate of CrN/TiN rubbing against copper is lower than that of the TiN. The testing load is selected to 3 N, because the wear rate of coatings in contact with copper is much higher than that of the case rubbing against carbon steel. The sliding velocity is 1.0 m/s as preceding tests. In the case of copper contact, the rust-prevention agent: HMT, is not used, because the corrosion does not occur even if pure water is used as a lubricant. The relationship between the sliding distance and maximum wear depth is shown in Fig. 12. Although the water shows a slight wear prevention effect, but this effect is not sufficient. The relationship between the sliding distance and maximum wear depth obtained in the cases of M10, with white spindle oil or without lubricant is shown in Fig. 13. M10 shows almost the same wear
Fig. 9. Comparison of effective mean wear rate with lubricant.
Fig. 11. Comparison of effective mean wear rate with coating tool.
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Fig. 12. Relationship between sliding distance and maximum wear depth.
Fig. 16. Relationship between sliding distance and maximum wear depth.
Fig. 13. Relationship between sliding distance and maximum wear depth. Fig. 17. Comparison of effective mean wear rate with coating tool.
tests are shown in Fig. 16. The λm value calculated from the data in Fig. 16 is shown in Fig. 17. The maximum wear depth of DLC and CrN is so small that the wear depth cannot be measured. Therefore, λm values of CrN and DLC are calculated using L = 1000 m, δ = 0.01 m. In the case of rubbing against copper, the combination of M10 and CrN or DLC results in excellent performance.
Fig. 14. Comparison of effective mean wear rate with lubricant.
prevention effect as that of white spindle oil. The effective mean wear rate (λm ) and the apparent frictional coefficient (PT /PN ) are shown in Figs. 14 and 15, respectively. The wear tests of TiN, CrN/TiN, TiAlN, CrN and DLC are also carried out with M10 as lubricant. Results of these
Fig. 15. Comparison of apparent frictional coefficient with lubricant.
4. Conclusions A crossed-cylinders wear test rubbing against carbon steel and pure copper has been carried out in order to evaluate the effects of water base lubricants on wear of coating tools. 1. The effect of increasing viscosity of water (lubricant base) by addition of PAA is examined. Within the content of PAA tested, the wear prevention effect is small. 2. The sufficient wear prevention effect is obtained having added up to 10 wt.% solid lubricant (MCA) to the water. 3. The lubricating ability of the combined use of Ti-base coating tools with MCA containing water and that of white spindle oil are equivalent against steel. 4. The wear rate of Ti-base coating rubbing against copper is higher than that of the case against steel. However, addition of MCA with 10 wt.% to the water shows the equivalent wear prevention effect to white spindle oil. 5. In the case of rubbing against copper, CrN and DLC show the excellent tribological performance. Moreover,
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the combination of M10 and CrN or DLC shows the excellent performance. 6. MCA is insoluble in water and it is easily separated through filtration. 7. The combination of MCA containing water and coating tools can be used for the deep drawing and the cold forging.
Acknowledgement The authors wish to thank Sumico Lubricant Co. for supplying the solid lubricant. References  S. Kataoka, T. Tanaka, M. Katou, Lubricity of pure water with the solid lubricant in deep drawing, J. Mater. Testing Res. Assoc. Japan 43 (4) (1998) 265–270.  W. Munz, Titanium aluminum nitride films: A new alternative to TiN coatings, J. Vac. Technol. A4 (6) (1986) 2717–2724.  W. Konig, R. Fritsch, D. Kammermier, New approaches to characterizing of coated cutting tools, Ann. CIRP 41 (1) (1992) 49– 54.  G. Byrne, B. Bienia, Tool life when milling with TiN-coated HSS indexible inserts, Ann. CIRP 40 (1) (1991) 45–48.  S. Katayama, M. Hasimura, T. Tanaka, H. Imamura, Effect of microcracks in CVD-coated layer on transverse rupture strength and chipping resistance, Ann. CIRP 40 (1) (1991) 57–60.
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Teisuke Sato received his doctorate degree in mechanical engineering from Kyoto University in Japan. He is currently a professor at University of Tokushima, Japan. His research interests are tribology in metal forming and near net-shape forming of ceramics. Tatsuo Besshi, a graduate of Akita University in Japan, is currently a chief at the Tokushima Prefectural Industrial Technology Center, Materials Science and Processing Division, Tokushima, Japan. His research interests are near net-shape forming of ceramics. Daisuke Sato is currently a graduate student of the University of Tokushima in Japan. Isao Tsutsui, a graduate of College of Industrial Technology, The University of Tokushima, is currently a staff at University of Tokushima.