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Minimum quantity lubrication (MQL) with carbon nanostructured additives in sheet metal forming
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Procedia Manufacturing 25 (2018) 375–381 Procedia Manufacturing 00 (2017) 000–000 www.elsevier.com/locate/procedia
8th 8th Swedish Swedish Production Production Symposium, Symposium, SPS SPS 2018, 2018, 16–18 16–18 May May 2018, 2018, Stockholm, Stockholm, Sweden Sweden
Minimum Minimum quantity quantity lubrication lubrication (MQL) (MQL) with with carbon carbon nanostructured nanostructured additives additives in sheet metal forming Manufacturing Engineering Society International in sheet metal Conference forming 2017, MESIC 2017, 28-30 June 2017, Vigo (Pontevedra), Spain aa aa Lanny Kirkhorn *, Oleksandr Gutnichenko , Sverker Bihagenbb,, Jan-Eric Ståhlaa Lanny Kirkhorn *, Oleksandr Gutnichenko , Sverker Bihagen Jan-Eric Ståhl
Division and Materials Engineering, Lund University, S-22100, Sweden4.0: Trade-off Costing models forofof Production capacity optimization inLund, Industry Division Production and Materials Engineering, Lund University, Lund, S-22100, Sweden Accu-Svenska AB, Västerås, 72132, Sweden Accu-Svenska AB, Västerås, 72132, Sweden between used capacity and operational efficiency a a
Abstract Abstract
b b
A. Santanaa, P. Afonsoa,*, A. Zaninb, R. Wernkeb
This work work is is an an experimental experimental study study covering coveringaminimum minimum quantity lubrication (MQL) in metal This lubrication in sheet sheet metal forming. forming. Two Two different different lubricants lubricants have have been been Universityquantity of Minho, 4800-058(MQL) Guimarães, Portugal studied. been additives to oils in studied. Nanosized Nanosized graphite graphite platelets platelets (GnP) (GnP) has has bUnochapecó, been tested tested as as89809-000 additives Chapecó, to the the base base oils in order order to to improve improve the the lubricant lubricant performance. performance. The The SC, Brazil experiments experiments have have been been performed performed utilizing utilizing aa laboratory laboratory tribotester tribotester based based on on strip strip drawing. drawing. Friction Friction measurements measurements have have been been used used to to study study the the performance performance of of the the lubrication lubrication systems. systems. The The results results demonstrate demonstrate that that MQL MQL as as aa lubrication lubrication method method can can be be aa substitute substitute for for conventional conventional use use of of lubricants lubricants in in sheet sheet metal metal forming forming and and nanosized nanosized graphite graphite can can be be used used to to further further enhance enhance the the lubrication. lubrication.
Abstract © Published by B.V. © 2018 2018The TheAuthors. Authors. Published by Elsevier © 2018 The Authors. Published by Elsevier Elsevier B.V. B.V. Peer-review under responsibility of the scientific of 8th Swedish Production Symposium. Peer-review under responsibility of the scientific committee 8th Swedish Production Symposium. Peer-review under responsibility of the scientific committee committee of the the of 8ththe Swedish Production Symposium.
Under the concept of "Industry 4.0", production processes will be pushed to be increasingly interconnected, Keywords: sheet based metal forming;friction measurement;graphite nanoplatelets;MQL information on a real time basis and, necessarily, much more efficient. In this context, capacity optimization Keywords: sheet metal forming;friction measurement;graphite nanoplatelets;MQL goes beyond the traditional aim of capacity maximization, contributing also for organization’s profitability and value. Indeed, lean management and continuous improvement approaches suggest capacity optimization instead of 1. 1. Introduction Introduction maximization. The study of capacity optimization and costing models is an important research topic that deserves contributions from both the practical andintheoretical perspectives. ThisThe paper presents discusses a mathematical Reduction lubricants is very very important most manufacturing manufacturing facilities. motivation forand doing so is is undeniable. undeniable. Reduction of of lubricants is important in most facilities. The motivation for doing so model for capacity management based on different costing models (ABC and TDABC). Aaregeneric model has been Environmental aspects, costs, cleaner workshops, reduction of washing operations, and health issues just a few things related Environmental aspects, costs, cleaner workshops, reduction of washing operations, and health issues are just a few things related developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization’s to the use of lubricants. to the use of lubricants. The The fundamental method to control control friction and andvs wear in manufacturing manufacturing processes is, however, however,and to add add lubricants in order to value. trade-off capacity maximization operational efficiency is highlighted it is shown in that capacity The fundamental method to friction wear in processes is, to lubricants order to reduce the metal-to-metal contact in the processes. Most of today’s sheet metal forming operations are performed under optimization might hide operational inefficiency. reduce the metal-to-metal contact in the processes. Most of today’s sheet metal forming operations are performed under lubricated conditions. A total total lack lack of lubricant is often often desired desired but but rarely rarely used used because because of of the the wear wear tendency. tendency. In In order order to to make make © 2017 Theconditions. Authors. Published byof Elsevier B.V. lubricated A lubricant is today’s sheet forming production more sustainable, the use of environmentally benign lubricants is necessary as well as using the the Peer-review responsibility the scientific committee ofenvironmentally the Manufacturing Engineering Society International today’s sheetunder forming productionofmore sustainable, the use of benign lubricants is necessary as wellConference as using lubricants more efficiently. Minimum quantity lubrication (MQL) is one possible approach to reduce lubricant use due to the 2017. lubricants more efficiently. Minimum quantity lubrication (MQL) is one possible approach to reduce lubricant use due to the small amount amount needed. needed. small Nanomaterials are attracting attracting moreCapacity and more more attention within within wide Operational range of of applications, applications, including their their use use as as an an additive additive in in Keywords: Cost Models; ABC; TDABC; Management; Idle Capacity; Efficiency including Nanomaterials are more and attention aa wide range industrial lubricants. Martin et al. [1] point out several potential applications in the tribological field and give several examples of industrial lubricants. Martin et al. [1] point out several potential applications in the tribological field and give several examples of different nanosized nanosized materials, materials, such such as as carboncarbon- and and boron-based boron-based nanolubricants. nanolubricants. Tang Tang et et al. al. [2] [2] have have conducted conducted an different an extensive extensive review of stated that that the the combined combined mechanisms mechanisms of of the the friction friction modifier modifier review of the the recent recent developments developments of of friction friction modifiers modifiers and and have have stated 1. Introduction like excellent anti-wear, friction-reducing, extreme pressure and anti-oxidation properties will be the major foci in this field. like excellent anti-wear, friction-reducing, extreme pressure and anti-oxidation properties will be the major foci in this field.
The cost of idle capacity is a fundamental information for companies and their management of extreme importance in*modern production systems. In general, it is defined as unused capacity or production potential and can be measured Corresponding author. Tel.: +46 46 2224529 * Corresponding author. Tel.: +46 46 2224529 E-mail address: [email protected] in several ways: tons of production, available hours of manufacturing, etc. The management of the idle capacity E-mail address: [email protected] * Paulo Afonso. Tel.: +351 253 510 761; fax: +351 253 604 741 E-mail address: [email protected]
2351-9789 © 2018 The Authors. Published by Elsevier B.V.
2351-9789 ©©2018 The Authors. Published by Elsevier B.V. B.V. 2351-9789 2017 The Authors. Published Elsevier Peer-review under responsibility of the scientificby committee of the 8th Swedish Production Symposium. Peer-review under responsibility of the scientific committee of the 8th Swedish Production Symposium. Peer-review under responsibility of the scientific committee of the Manufacturing Engineering Society International Conference 2017. 2351-9789 © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 8th Swedish Production Symposium. 10.1016/j.promfg.2018.06.106
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The interest in using carbon-based nanomaterials in tribological applications has increased significantly since the discovery of graphene, carbon nanotubes (CNTs) and fullerene. This is due to the materials’ excellent mechanical properties and their high chemical stability, according to Stankovich et al. [3], Thostenson et al. [4] and Ku et al. [5]. The use of nanoparticles in lubricants for different applications has been thoroughly investigated in a number of papers, see [6]–[13]. Different materials, particle sizes and geometries have been used, resulting in different influencing effects on the tribological system. The wear-protective and friction-reduction mechanisms during use of nanosized additives can be attributed mainly to four different effects, according to Figure 1, Tang, et al. [2]
(a) rolling effect
(b) protective film
(c) mending effect
(d) polishing effect
Fig. 1. Possible lubrication mechanisms of nanoparticles as friction modifiers, in Lee et al. (2009) and in Tang et al. [2].
The main part of this paper focuses on lubrication using MQL with and without carbon nanostructured additives in sheet metal forming. The frictional behaviour in the process in terms of measured friction coefficient is studied regarding amount and type of lubricant and additives. A new environmentally friendly oil developed for MQL applications is compared to a state-ofthe-art lubricant. 2. Experimental Setup 2.1. Tribotester The tribological test device used in this study is based on strip drawing and has been thoroughly described in previous work [14]. The test procedure and equipment are not based on any available standard for tribological testing depending on limitations in standardized procedures. The device used is specifically developed to handle the parameter setups used in sheet metal forming processes. A schematic illustration of the tribotester can be seen in Figure 2. General specifications are as follows: the maximum normal force, F(t) is 10 kN, maximum push/pull force (shear direction) is 4 kN, maximum speed v(t) is 1.7 m/s and the maximum stroke is 410 mm. The forces in the normal and shear directions are directly measured using a three-axis force measurement platform. The normal force F(t) and the velocity v(t) can be controlled during experiments.
Fig. 2: Schematic of the tribotester.
Friction can be defined as a force that resists motion between two objects in contact. The major obstacles when measuring friction between different contacts are the number of influencing parameters. Stribeck’s parameters, such as velocity, normal pressure and viscosity, are commonly used to define specific test conditions. There are, however, many other parameters including materials, surface conditions, deformations, etc. to consider in order to completely map the frictional conditions for a specific application. The friction coefficient in this work is defined and calculated according to Coulomb’s law of friction; see equation 1, where FT is the measured shear force and FN is the measured normal force during experimenting. 𝜇𝜇 =
2.2. Tool and sheet materials
𝐹𝐹𝑇𝑇
𝐹𝐹𝑁𝑁
(1)
This work focuses on the lubrication aspects of sheet metal forming. The tool- and sheet materials selected for the experimental work are mostly based on availability and because the materials are commonly used in the forming industry. The tool material used in all experiments is Rigor from Uddeholm Tooling and it corresponds to X100CrMoV5. This material is commonly used in cold working applications, such as blanking and stamping in the sheet metal forming industry, due to its high
Lanny Kirkhorn et al. / Procedia Manufacturing 25 (2018) 375–381 Author name / Procedia Manufacturing 00 (2018) 000–000
377 3
resistance to wear and chipping. The tools were heat treated to a hardness of 61 HRC. Elliptical contact was used for all experiments. Figure 3 shows the cylindrical tool and the toolholder. The “wheel” diameter is 25 mm and the curvature has a radius of 200 mm. This geometry gives an elliptical contact with the sheet. All experimental work was performed using an uncoated high-strength steel from SSAB, Docol 600DP, with a thickness of 1.2 mm. The test strips were cut, deburred and visually inspected and all strips with any kind of imperfections were removed and discarded to reduce the scatter during measurement. The dimensions were width = 60 mm and length = 300 mm.
a)
b)
Fig. 3: Tool geometry (a) and corresponding toolholder (b).
2.3. Lubricants Two different lubricants were used in this work, Binol Cut 10 [15] and Ecolubric [16]. Binol is a common lubricant in the industry and used both in cutting applications and in sheet forming operations. Ecolubric is a product developed by AccuSvenska AB with performance, environment and health in mind. The high-quality lubricant is primarily developed for the MQLindustry. 3. Experimental procedure 3.1. Data acquisition The aim of this work is to study and compare two different lubricants in a MQL application as well as to find possible benefits of a graphite additive. In order to reduce the number of experiments, the tryouts were performed with a constant normal load and varying velocity. Five different loads were studied, ranging from 500 N to 4000 N and the velocity was ramped during the experiments from 0 to 0.35 m/s. The velocity range of interest was from 0.05 m/s to 0.25 m/s. Input to a test was a defined normal load and a velocity function and typical acquired data from one experiment is illustrated in Figure 4. The collected data was filtered and the friction calculated. Each test was repeated four times in order to find any instabilities in the testing procedure. Figure 5 illustrates the calculated friction data for one parameter setup and the typical accuracy during experimenting.
(a)
(b)
Fig. 4. Measured normal and shear forces during experimenting (a) and the measured and filtered velocity function (b).
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Fig. 5. Calculated friction as a function of time for one parameter setup.
Figure 6 gives an example of a calculated friction function for one test. Each test was repeated four times to control the repeatability and accuracy of the experiments. The difference between the individual experiments was maximum +/- 5% in the calculated friction coefficient. The range of interest was extracted from the calculated friction function (Figure 6) in order to get rid of the initial static friction and the end of the test. A mean value of the four repetitions was calculated and a least square approximation was done. An example of the resulting curve for the friction coefficient for one parameter setup can be seen in Figure 6b.
(a)
(b)
Fig. 6. Calculated friction with the interest area marked (a). The average friction for the repeated experiments (b).
3.2. Sample preparation and lubricant application All sheets were thoroughly cleaned with alcohol before the lubricant was applied. Two different approaches were used to apply the lubricant – manual application and automatic application with a booster. Manual application of lubricants To compare the two base oils in the experiments, a cloth was used to manually apply the oil. Two different amounts were used during this comparison, 0.8 g/m2 and a thin film in order to simulate a MQL situation. A high-resolution scale (0.1 mg in resolution) was used to measure the weight of the lubricant in the case of the 0.8 g/m2 amount. A uniform distribution could not be guaranteed but was optically controlled. The repeatability of the experiments also points to a good distribution. In the case of the thin film, the lubricant was applied with a cloth and then “totally” removed by drying with paper. This procedure makes it impossible to measure the lubricant by weight due to the very small amount of lubricant present (less than 0.1 g/m2). Available optical devices for film thickness measurements also had too low a resolution to be used. However, here also the accuracy of the experiments pointed to a good distribution. Booster application To compare the MQL technology and the conventional way of applying lubricants under production-like conditions, a MQL Ecolubric Booster System provided by Accu-Svenska AB was used to apply the lubricants. Base oil and graphite-modified base oil were used and the flow rate of the mist was set to 15 ml/h. These experiments were performed only with the Ecolubric base oil. The base oil was compared to base oil modified with 0.2% (vol.) of graphite (GnP) suspension and one case where the graphite was added to the test specimens before it was exposed to the base oil. This was done to increase the carbon content in the contact zone. The graphite suspension was rolled onto the sheets and left to dry before applying the base oil with the MQL system. 4. Results and discussion 4.1. Dry and graphite-lubricated experimenting Initial tests consisted of dry experiments and tests with a pure graphite coating. Figure 7 illustrates the frictional outcome from these experiments. As expected there is a general decrease in friction if the load and velocity increases during the dry experiments and the frictional values are also in the expected range. The pure graphite coating shows a slightly different behaviour. It seems that the tribological system is rather insensitive to the velocity component and the spread in the normal force range is also tighter compared to the dry condition.
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(a)
5
(b)
Fig. 7. Friction as a function of velocity during dry conditions (a) and graphite-lubricated conditions (b) for different applied normal forces.
4.2. Ecolubric versus Binol The Ecolubric oil was compared to the Binol using two different amounts, 0.8g/m2 and a thin film in order so see any differences regarding the frictional performance. The lubricant was applied manually with a cloth. Figures 8 and 9 present the frictional outcome for the different lubricants. What is most surprising is that the large amount of oil (0.8g/m2) has a very small influence on the friction when compared to thin film lubrication, and this applies to both types of oils. These results indicate that an MQL lubrication system has potential to be introduced on a broader front in the sheet metal industry. Of course, there are many other factors that are of major importance for the final forming results, but the friction coefficient is a significant factor in the process. It can also be seen from the results that the two oils have similar frictional performance independent of the amount of lubricant.
(a)
(b) Fig. 8. Binol 0.8 g/m2 (a) and Binol “thin film” (b).
(a)
(b) Fig. 9. Ecolubric 0.8 g/m2 (a) and Ecolubric “thin film” (b).
In order to study the influence of added graphite to the lubricant, graphite was mixed with the oil and experiments similar to those in Figure 9 were performed. Figure 10 illustrates the results when graphite was added to the Ecolubric oil. The lubricant is also manually applied, as in the experiments in Figure 9. If the results in Figures 10 and 9 are studied and compared there is little to no difference in the frictional results. The graphite additive may have a small positive effect if “thin film” lubrication is used, though generally the concentration of the added graphite seems too low to have a positive effect on the friction.
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(a)
(b)
Fig. 10. Ecolubric 0.8 g/m2 with added graphite (a) and Ecolubric “thin film” with added graphite (b).
4.3. MQL with Ecolubric Figure 11 shows the results from the experiments when applying the lubricant with industrial MQL equipment. Figure 11a shows the calculated friction data for Ecolubric only; Figure 11b presents the results for the graphite-modified Ecolubric and Figure 11c shows the results for when the graphite was applied to the sheet prior to the lubricant in order to increase the amount of graphite on the sheet surface. The graphite solution was left to dry and the MQL system was used to apply the Ecolubric oil. What can be seen here is that the low concentration of graphite used when applied by MQL equipment is too small for the graphite to have any impact on the frictional outcome (Figs 11a and 11b). In Figure 11c, there is a considerably larger amount of graphite compared to 11b, which is also reflected in the calculated friction data. The selected concentration of the graphite mixed in the lubricant was based on initial tryouts to achieve a stable solution without sedimentation in the MQL equipment. There is, however, headroom to increase the concentration without instabilities and find the optimal concentration in future work. In Figure 11c, the friction coefficient’s development with increasing force and velocity can be seen to have the same tendency as the results with graphite lubrication only. The friction coefficient is rather insensitive to changes in applied normal force and velocity when compared to a conventional oil-based lubrication system. This phenomenon probably has its origin in the shearing process of the graphite platelets.
(a)
(b)
(c)
Fig. 11. Frictional outcome for Ecolubric lubricant applied with MQL equipment. Pure Ecolubric lubricant (a), Ecolubric with mixed-in graphite (b) and graphite applied to the strips prior to the lubricant (c).
5. Conclusions Tribological evaluation of different lubrication and lubrication systems has been performed in this work. Two different lubricants, Binol Cut 10 and Ecolubric, have been compared and evaluated. Different amounts of lubricants have been tested, from dry conditions up to 0.8g/m2. The MQL system and the influence of graphite additives to the base oil have also been evaluated. A large number of tests have been carried out under different conditions. The applied normal force was in the range of 500N to 4000N and the velocity was maximum 0.3 m/s. The following conclusions could be drawn from this experimental work:
For the specific combination of tool material, sheet material, lubricants and testing parameters, the amount of lubricant has a relatively small influence on the frictional results. The difference in friction between a thin film and 0.8 g/m2 was very small for the specific setup and this indicates that MQL can be a substitute for conventional lubrication methods in order to minimize the use of lubricants.
Lanny Kirkhorn et al. / Procedia Manufacturing 25 (2018) 375–381 Author name / Procedia Manufacturing 00 (2018) 000–000
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The amount of graphite additives in the lubricant has a significant influence on the frictional performance. Further studies need to be done in order to find the optimal concentration. The frictional response in the experiments demonstrates essentially an expected behaviour regardless of the amount of lubricant. The friction coefficient decreases with an increase in normal force and velocity. Graphite as an additive or used alone as a lubricant has, however, a tendency to be more insensitive to load or velocity changes.
Acknowledgements This work was carried out as a part of the research project “ECOnLub” with support from the MISTRA Innovation Research Programme in product innovation and realization and the Swedish Foundation for Strategic Research (SSF) within the Sustainable Production Initiative (SPI). Their support is gratefully acknowledged. The authors are also grateful to Accu-Svenska AB for their support with the MQL system and consumables. References [1] [2] [3] [4]
Martin, J.M. and N. Ohmae (Eds.) Nanolubricants, Wiley, England, 2008. Tang Z and S. Li (2014) A review of recent developments of friction modifiers for liquid lubricants (2007–present). Curr. Opin. Solid State Mater. Sci. (2014). Stankovich, S, D.A. Dikin, G.H.B. Dommett, K.M. Kohlhaas, E.J. Zimney, E.A. Stach, et al. (2006) Graphene-based composite materials. Nature, 442, 282. Thostenson, E.T., Z. Ren and T.-W. Chou (2001) Advances in the science and technology of carbon nanotubes and their composites: A review. Compos. Sci. Technol., 61, 1899. [5] Ku, B.-C., Y.-C. Han, J.-E. Lee, J.-K. Lee, S.-H. Park and Y.-J.Hwang (2010) Tribological effects of fullerene (C60) nanoparticles added in mineral lubricants according to its viscosity. Int. J. Precis. Eng. Man., 11, 607. [6] Lee, C.G., J.H. Yu, M.C. Young, J.K. Lee, C. Choi, and J.-M. Oh (1990) A Study on The Tribological Characteristics of Graphite Nano Lubricants. Int. J. Precis. Eng. Man., 10(1), 85–90. [7] Huang, H.D., J.P. Tu , L.P. Gan and C.Z. Li (2006) An investigation on tribological properties of graphite nanosheets as oil additive. Wear, 261, 140–144. [8] Shubrajit B., S. Prabhu, V. Karpurapu and N. Uppala (2013) Extreme pressure property of Carbon Nano Tubes (CNT) based nanolubricant. Journal of Chemical Engineering and Materials Science, 4(8), 123–127. [9] Senatore, A., V. D’Agostino, V. Petrone, P. Ciambelli, M. Sarno (2013) Graphene Oxide nanosheets as Effective Friction Modifier for Oil Lubricant: Materials, Methods, and Tribological Results. Tribology, 2013, Article ID 425809. [10] Kyung-Hee, P., E. Brent and P.Y. Kwon (2011) Effect of Nano-Enhanced Lubricant in Minimum Quantity Lubrication Balling Milling. Journal of Tribology, Vol. 133. [11] Ingole, S., A. Charanpahari, A. Kakade, S.S. Umare, D.V. Bhatt and J. Menghani (2013) Tribological behavior of nano TiO2 as an additive in base oil. Wear, 301, 776–785. [12] Flavio, A.C.V. and A.F. Avila (2014) Tribological Investigation of Nanographite Platelets as Additive in Anti- Wear Lubricant: a Top-Down Approach. Journal of Tribology, Vol. 136. [13] Luo, T., X. Wei, X. Huang, L. Huang and F. Yang (2014) Tribological properties of Al2O3 nanoparticles as lubricating oil additives. Ceramics International, 40, 7143–7149. [14] Kirkhorn. L. Instrumentation for tribological analysis of sheet metal forming operations, PhD thesis, 2015. [15] http://www.binol.com/product/binol-cut-10-10ep. 2018-03-05. [16] http://www.accu-svenska.se/skerhetsdatablad. 2018-03-05.
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Available Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Procedia Manufacturing 00 (2018) 000–000 Procedia Manufacturing 00 (2018) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Manufacturing 25 (2018) 375–381 Procedia Manufacturing 00 (2017) 000–000 www.elsevier.com/locate/procedia
8th 8th Swedish Swedish Production Production Symposium, Symposium, SPS SPS 2018, 2018, 16–18 16–18 May May 2018, 2018, Stockholm, Stockholm, Sweden Sweden
Minimum Minimum quantity quantity lubrication lubrication (MQL) (MQL) with with carbon carbon nanostructured nanostructured additives additives in sheet metal forming Manufacturing Engineering Society International in sheet metal Conference forming 2017, MESIC 2017, 28-30 June 2017, Vigo (Pontevedra), Spain aa aa Lanny Kirkhorn *, Oleksandr Gutnichenko , Sverker Bihagenbb,, Jan-Eric Ståhlaa Lanny Kirkhorn *, Oleksandr Gutnichenko , Sverker Bihagen Jan-Eric Ståhl
Division and Materials Engineering, Lund University, S-22100, Sweden4.0: Trade-off Costing models forofof Production capacity optimization inLund, Industry Division Production and Materials Engineering, Lund University, Lund, S-22100, Sweden Accu-Svenska AB, Västerås, 72132, Sweden Accu-Svenska AB, Västerås, 72132, Sweden between used capacity and operational efficiency a a
Abstract Abstract
b b
A. Santanaa, P. Afonsoa,*, A. Zaninb, R. Wernkeb
This work work is is an an experimental experimental study study covering coveringaminimum minimum quantity lubrication (MQL) in metal This lubrication in sheet sheet metal forming. forming. Two Two different different lubricants lubricants have have been been Universityquantity of Minho, 4800-058(MQL) Guimarães, Portugal studied. been additives to oils in studied. Nanosized Nanosized graphite graphite platelets platelets (GnP) (GnP) has has bUnochapecó, been tested tested as as89809-000 additives Chapecó, to the the base base oils in order order to to improve improve the the lubricant lubricant performance. performance. The The SC, Brazil experiments experiments have have been been performed performed utilizing utilizing aa laboratory laboratory tribotester tribotester based based on on strip strip drawing. drawing. Friction Friction measurements measurements have have been been used used to to study study the the performance performance of of the the lubrication lubrication systems. systems. The The results results demonstrate demonstrate that that MQL MQL as as aa lubrication lubrication method method can can be be aa substitute substitute for for conventional conventional use use of of lubricants lubricants in in sheet sheet metal metal forming forming and and nanosized nanosized graphite graphite can can be be used used to to further further enhance enhance the the lubrication. lubrication.
Abstract © Published by B.V. © 2018 2018The TheAuthors. Authors. Published by Elsevier © 2018 The Authors. Published by Elsevier Elsevier B.V. B.V. Peer-review under responsibility of the scientific of 8th Swedish Production Symposium. Peer-review under responsibility of the scientific committee 8th Swedish Production Symposium. Peer-review under responsibility of the scientific committee committee of the the of 8ththe Swedish Production Symposium.
Under the concept of "Industry 4.0", production processes will be pushed to be increasingly interconnected, Keywords: sheet based metal forming;friction measurement;graphite nanoplatelets;MQL information on a real time basis and, necessarily, much more efficient. In this context, capacity optimization Keywords: sheet metal forming;friction measurement;graphite nanoplatelets;MQL goes beyond the traditional aim of capacity maximization, contributing also for organization’s profitability and value. Indeed, lean management and continuous improvement approaches suggest capacity optimization instead of 1. 1. Introduction Introduction maximization. The study of capacity optimization and costing models is an important research topic that deserves contributions from both the practical andintheoretical perspectives. ThisThe paper presents discusses a mathematical Reduction lubricants is very very important most manufacturing manufacturing facilities. motivation forand doing so is is undeniable. undeniable. Reduction of of lubricants is important in most facilities. The motivation for doing so model for capacity management based on different costing models (ABC and TDABC). Aaregeneric model has been Environmental aspects, costs, cleaner workshops, reduction of washing operations, and health issues just a few things related Environmental aspects, costs, cleaner workshops, reduction of washing operations, and health issues are just a few things related developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization’s to the use of lubricants. to the use of lubricants. The The fundamental method to control control friction and andvs wear in manufacturing manufacturing processes is, however, however,and to add add lubricants in order to value. trade-off capacity maximization operational efficiency is highlighted it is shown in that capacity The fundamental method to friction wear in processes is, to lubricants order to reduce the metal-to-metal contact in the processes. Most of today’s sheet metal forming operations are performed under optimization might hide operational inefficiency. reduce the metal-to-metal contact in the processes. Most of today’s sheet metal forming operations are performed under lubricated conditions. A total total lack lack of lubricant is often often desired desired but but rarely rarely used used because because of of the the wear wear tendency. tendency. In In order order to to make make © 2017 Theconditions. Authors. Published byof Elsevier B.V. lubricated A lubricant is today’s sheet forming production more sustainable, the use of environmentally benign lubricants is necessary as well as using the the Peer-review responsibility the scientific committee ofenvironmentally the Manufacturing Engineering Society International today’s sheetunder forming productionofmore sustainable, the use of benign lubricants is necessary as wellConference as using lubricants more efficiently. Minimum quantity lubrication (MQL) is one possible approach to reduce lubricant use due to the 2017. lubricants more efficiently. Minimum quantity lubrication (MQL) is one possible approach to reduce lubricant use due to the small amount amount needed. needed. small Nanomaterials are attracting attracting moreCapacity and more more attention within within wide Operational range of of applications, applications, including their their use use as as an an additive additive in in Keywords: Cost Models; ABC; TDABC; Management; Idle Capacity; Efficiency including Nanomaterials are more and attention aa wide range industrial lubricants. Martin et al. [1] point out several potential applications in the tribological field and give several examples of industrial lubricants. Martin et al. [1] point out several potential applications in the tribological field and give several examples of different nanosized nanosized materials, materials, such such as as carboncarbon- and and boron-based boron-based nanolubricants. nanolubricants. Tang Tang et et al. al. [2] [2] have have conducted conducted an different an extensive extensive review of stated that that the the combined combined mechanisms mechanisms of of the the friction friction modifier modifier review of the the recent recent developments developments of of friction friction modifiers modifiers and and have have stated 1. Introduction like excellent anti-wear, friction-reducing, extreme pressure and anti-oxidation properties will be the major foci in this field. like excellent anti-wear, friction-reducing, extreme pressure and anti-oxidation properties will be the major foci in this field.
The cost of idle capacity is a fundamental information for companies and their management of extreme importance in*modern production systems. In general, it is defined as unused capacity or production potential and can be measured Corresponding author. Tel.: +46 46 2224529 * Corresponding author. Tel.: +46 46 2224529 E-mail address: [email protected] in several ways: tons of production, available hours of manufacturing, etc. The management of the idle capacity E-mail address: [email protected] * Paulo Afonso. Tel.: +351 253 510 761; fax: +351 253 604 741 E-mail address: [email protected]
2351-9789 © 2018 The Authors. Published by Elsevier B.V.
2351-9789 ©©2018 The Authors. Published by Elsevier B.V. B.V. 2351-9789 2017 The Authors. Published Elsevier Peer-review under responsibility of the scientificby committee of the 8th Swedish Production Symposium. Peer-review under responsibility of the scientific committee of the 8th Swedish Production Symposium. Peer-review under responsibility of the scientific committee of the Manufacturing Engineering Society International Conference 2017. 2351-9789 © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 8th Swedish Production Symposium. 10.1016/j.promfg.2018.06.106
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The interest in using carbon-based nanomaterials in tribological applications has increased significantly since the discovery of graphene, carbon nanotubes (CNTs) and fullerene. This is due to the materials’ excellent mechanical properties and their high chemical stability, according to Stankovich et al. [3], Thostenson et al. [4] and Ku et al. [5]. The use of nanoparticles in lubricants for different applications has been thoroughly investigated in a number of papers, see [6]–[13]. Different materials, particle sizes and geometries have been used, resulting in different influencing effects on the tribological system. The wear-protective and friction-reduction mechanisms during use of nanosized additives can be attributed mainly to four different effects, according to Figure 1, Tang, et al. [2]
(a) rolling effect
(b) protective film
(c) mending effect
(d) polishing effect
Fig. 1. Possible lubrication mechanisms of nanoparticles as friction modifiers, in Lee et al. (2009) and in Tang et al. [2].
The main part of this paper focuses on lubrication using MQL with and without carbon nanostructured additives in sheet metal forming. The frictional behaviour in the process in terms of measured friction coefficient is studied regarding amount and type of lubricant and additives. A new environmentally friendly oil developed for MQL applications is compared to a state-ofthe-art lubricant. 2. Experimental Setup 2.1. Tribotester The tribological test device used in this study is based on strip drawing and has been thoroughly described in previous work [14]. The test procedure and equipment are not based on any available standard for tribological testing depending on limitations in standardized procedures. The device used is specifically developed to handle the parameter setups used in sheet metal forming processes. A schematic illustration of the tribotester can be seen in Figure 2. General specifications are as follows: the maximum normal force, F(t) is 10 kN, maximum push/pull force (shear direction) is 4 kN, maximum speed v(t) is 1.7 m/s and the maximum stroke is 410 mm. The forces in the normal and shear directions are directly measured using a three-axis force measurement platform. The normal force F(t) and the velocity v(t) can be controlled during experiments.
Fig. 2: Schematic of the tribotester.
Friction can be defined as a force that resists motion between two objects in contact. The major obstacles when measuring friction between different contacts are the number of influencing parameters. Stribeck’s parameters, such as velocity, normal pressure and viscosity, are commonly used to define specific test conditions. There are, however, many other parameters including materials, surface conditions, deformations, etc. to consider in order to completely map the frictional conditions for a specific application. The friction coefficient in this work is defined and calculated according to Coulomb’s law of friction; see equation 1, where FT is the measured shear force and FN is the measured normal force during experimenting. 𝜇𝜇 =
2.2. Tool and sheet materials
𝐹𝐹𝑇𝑇
𝐹𝐹𝑁𝑁
(1)
This work focuses on the lubrication aspects of sheet metal forming. The tool- and sheet materials selected for the experimental work are mostly based on availability and because the materials are commonly used in the forming industry. The tool material used in all experiments is Rigor from Uddeholm Tooling and it corresponds to X100CrMoV5. This material is commonly used in cold working applications, such as blanking and stamping in the sheet metal forming industry, due to its high
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resistance to wear and chipping. The tools were heat treated to a hardness of 61 HRC. Elliptical contact was used for all experiments. Figure 3 shows the cylindrical tool and the toolholder. The “wheel” diameter is 25 mm and the curvature has a radius of 200 mm. This geometry gives an elliptical contact with the sheet. All experimental work was performed using an uncoated high-strength steel from SSAB, Docol 600DP, with a thickness of 1.2 mm. The test strips were cut, deburred and visually inspected and all strips with any kind of imperfections were removed and discarded to reduce the scatter during measurement. The dimensions were width = 60 mm and length = 300 mm.
a)
b)
Fig. 3: Tool geometry (a) and corresponding toolholder (b).
2.3. Lubricants Two different lubricants were used in this work, Binol Cut 10 [15] and Ecolubric [16]. Binol is a common lubricant in the industry and used both in cutting applications and in sheet forming operations. Ecolubric is a product developed by AccuSvenska AB with performance, environment and health in mind. The high-quality lubricant is primarily developed for the MQLindustry. 3. Experimental procedure 3.1. Data acquisition The aim of this work is to study and compare two different lubricants in a MQL application as well as to find possible benefits of a graphite additive. In order to reduce the number of experiments, the tryouts were performed with a constant normal load and varying velocity. Five different loads were studied, ranging from 500 N to 4000 N and the velocity was ramped during the experiments from 0 to 0.35 m/s. The velocity range of interest was from 0.05 m/s to 0.25 m/s. Input to a test was a defined normal load and a velocity function and typical acquired data from one experiment is illustrated in Figure 4. The collected data was filtered and the friction calculated. Each test was repeated four times in order to find any instabilities in the testing procedure. Figure 5 illustrates the calculated friction data for one parameter setup and the typical accuracy during experimenting.
(a)
(b)
Fig. 4. Measured normal and shear forces during experimenting (a) and the measured and filtered velocity function (b).
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Fig. 5. Calculated friction as a function of time for one parameter setup.
Figure 6 gives an example of a calculated friction function for one test. Each test was repeated four times to control the repeatability and accuracy of the experiments. The difference between the individual experiments was maximum +/- 5% in the calculated friction coefficient. The range of interest was extracted from the calculated friction function (Figure 6) in order to get rid of the initial static friction and the end of the test. A mean value of the four repetitions was calculated and a least square approximation was done. An example of the resulting curve for the friction coefficient for one parameter setup can be seen in Figure 6b.
(a)
(b)
Fig. 6. Calculated friction with the interest area marked (a). The average friction for the repeated experiments (b).
3.2. Sample preparation and lubricant application All sheets were thoroughly cleaned with alcohol before the lubricant was applied. Two different approaches were used to apply the lubricant – manual application and automatic application with a booster. Manual application of lubricants To compare the two base oils in the experiments, a cloth was used to manually apply the oil. Two different amounts were used during this comparison, 0.8 g/m2 and a thin film in order to simulate a MQL situation. A high-resolution scale (0.1 mg in resolution) was used to measure the weight of the lubricant in the case of the 0.8 g/m2 amount. A uniform distribution could not be guaranteed but was optically controlled. The repeatability of the experiments also points to a good distribution. In the case of the thin film, the lubricant was applied with a cloth and then “totally” removed by drying with paper. This procedure makes it impossible to measure the lubricant by weight due to the very small amount of lubricant present (less than 0.1 g/m2). Available optical devices for film thickness measurements also had too low a resolution to be used. However, here also the accuracy of the experiments pointed to a good distribution. Booster application To compare the MQL technology and the conventional way of applying lubricants under production-like conditions, a MQL Ecolubric Booster System provided by Accu-Svenska AB was used to apply the lubricants. Base oil and graphite-modified base oil were used and the flow rate of the mist was set to 15 ml/h. These experiments were performed only with the Ecolubric base oil. The base oil was compared to base oil modified with 0.2% (vol.) of graphite (GnP) suspension and one case where the graphite was added to the test specimens before it was exposed to the base oil. This was done to increase the carbon content in the contact zone. The graphite suspension was rolled onto the sheets and left to dry before applying the base oil with the MQL system. 4. Results and discussion 4.1. Dry and graphite-lubricated experimenting Initial tests consisted of dry experiments and tests with a pure graphite coating. Figure 7 illustrates the frictional outcome from these experiments. As expected there is a general decrease in friction if the load and velocity increases during the dry experiments and the frictional values are also in the expected range. The pure graphite coating shows a slightly different behaviour. It seems that the tribological system is rather insensitive to the velocity component and the spread in the normal force range is also tighter compared to the dry condition.
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(a)
5
(b)
Fig. 7. Friction as a function of velocity during dry conditions (a) and graphite-lubricated conditions (b) for different applied normal forces.
4.2. Ecolubric versus Binol The Ecolubric oil was compared to the Binol using two different amounts, 0.8g/m2 and a thin film in order so see any differences regarding the frictional performance. The lubricant was applied manually with a cloth. Figures 8 and 9 present the frictional outcome for the different lubricants. What is most surprising is that the large amount of oil (0.8g/m2) has a very small influence on the friction when compared to thin film lubrication, and this applies to both types of oils. These results indicate that an MQL lubrication system has potential to be introduced on a broader front in the sheet metal industry. Of course, there are many other factors that are of major importance for the final forming results, but the friction coefficient is a significant factor in the process. It can also be seen from the results that the two oils have similar frictional performance independent of the amount of lubricant.
(a)
(b) Fig. 8. Binol 0.8 g/m2 (a) and Binol “thin film” (b).
(a)
(b) Fig. 9. Ecolubric 0.8 g/m2 (a) and Ecolubric “thin film” (b).
In order to study the influence of added graphite to the lubricant, graphite was mixed with the oil and experiments similar to those in Figure 9 were performed. Figure 10 illustrates the results when graphite was added to the Ecolubric oil. The lubricant is also manually applied, as in the experiments in Figure 9. If the results in Figures 10 and 9 are studied and compared there is little to no difference in the frictional results. The graphite additive may have a small positive effect if “thin film” lubrication is used, though generally the concentration of the added graphite seems too low to have a positive effect on the friction.
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(a)
(b)
Fig. 10. Ecolubric 0.8 g/m2 with added graphite (a) and Ecolubric “thin film” with added graphite (b).
4.3. MQL with Ecolubric Figure 11 shows the results from the experiments when applying the lubricant with industrial MQL equipment. Figure 11a shows the calculated friction data for Ecolubric only; Figure 11b presents the results for the graphite-modified Ecolubric and Figure 11c shows the results for when the graphite was applied to the sheet prior to the lubricant in order to increase the amount of graphite on the sheet surface. The graphite solution was left to dry and the MQL system was used to apply the Ecolubric oil. What can be seen here is that the low concentration of graphite used when applied by MQL equipment is too small for the graphite to have any impact on the frictional outcome (Figs 11a and 11b). In Figure 11c, there is a considerably larger amount of graphite compared to 11b, which is also reflected in the calculated friction data. The selected concentration of the graphite mixed in the lubricant was based on initial tryouts to achieve a stable solution without sedimentation in the MQL equipment. There is, however, headroom to increase the concentration without instabilities and find the optimal concentration in future work. In Figure 11c, the friction coefficient’s development with increasing force and velocity can be seen to have the same tendency as the results with graphite lubrication only. The friction coefficient is rather insensitive to changes in applied normal force and velocity when compared to a conventional oil-based lubrication system. This phenomenon probably has its origin in the shearing process of the graphite platelets.
(a)
(b)
(c)
Fig. 11. Frictional outcome for Ecolubric lubricant applied with MQL equipment. Pure Ecolubric lubricant (a), Ecolubric with mixed-in graphite (b) and graphite applied to the strips prior to the lubricant (c).
5. Conclusions Tribological evaluation of different lubrication and lubrication systems has been performed in this work. Two different lubricants, Binol Cut 10 and Ecolubric, have been compared and evaluated. Different amounts of lubricants have been tested, from dry conditions up to 0.8g/m2. The MQL system and the influence of graphite additives to the base oil have also been evaluated. A large number of tests have been carried out under different conditions. The applied normal force was in the range of 500N to 4000N and the velocity was maximum 0.3 m/s. The following conclusions could be drawn from this experimental work:
For the specific combination of tool material, sheet material, lubricants and testing parameters, the amount of lubricant has a relatively small influence on the frictional results. The difference in friction between a thin film and 0.8 g/m2 was very small for the specific setup and this indicates that MQL can be a substitute for conventional lubrication methods in order to minimize the use of lubricants.
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The amount of graphite additives in the lubricant has a significant influence on the frictional performance. Further studies need to be done in order to find the optimal concentration. The frictional response in the experiments demonstrates essentially an expected behaviour regardless of the amount of lubricant. The friction coefficient decreases with an increase in normal force and velocity. Graphite as an additive or used alone as a lubricant has, however, a tendency to be more insensitive to load or velocity changes.
Acknowledgements This work was carried out as a part of the research project “ECOnLub” with support from the MISTRA Innovation Research Programme in product innovation and realization and the Swedish Foundation for Strategic Research (SSF) within the Sustainable Production Initiative (SPI). Their support is gratefully acknowledged. The authors are also grateful to Accu-Svenska AB for their support with the MQL system and consumables. References [1] [2] [3] [4]
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