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Tribological investigation of impregnated diamond tools
special feature
Tribological investigation of impregnated diamond tools The introduction of diamond tools and their use has continuously gained favour, and in many cases, has become a substitute for conventional cutting materials. . .
D
ue to their better mechanical properties, diamond tools have largely replaced cemented carbide tools in the stone industry. During the use of diamond tools water cooling is necessary because of the heat development and the diamonds’ tendency to decompose to graphite at high temperatures. However, alkaline waterbased solutions are normally used for cooling, and can contaminate occupied buildings. Therefore new diamond tools
(a)
for dry drilling are of interest. The addition of a material with a low thermal conductivity (alumina, glass) in the diamond segment can improve the wear behaviour and act as a protection shield, which protects the diamonds within the composite. This article focuses on the heat distribution generated due to wear and abrasion along the length of the new diamond segments. Different abrasion tests will be carried out to investigate the difference in the temperature distribution profile.
The temperature distribution computed by ANSYS will be compared with the measured temperature profile. Diamond tools are state of the art when considering redevelopment, renovation and the demolition of buildings. Based on the wide selection of diamond cutting tools available, it is possible to process almost all encountered materials at the construction site [1]. The introduction of diamond tools and their use has continuously gained favour, and in many cases, has become a
(b) size of the bar: 6.25×1×1mm size of diamonds: 250μm size of alumina: 250μm Used element typ: tetraeder
(c) Figure 1. A picture of the theoretically constructed model with the attributes.
14
MPR June 2009
0026-0657/09 ©2009 Elsevier Ltd. All rights reserved.
773,15
719,81
(after 115 ms)
666,48
613,15
559,81
(after 145 ms)
506,48
453,15
(after 210ms) 399,81
349,48
(after 240 ms)
column7
column11
column15
293,15
Figure 2. Heat distribution of the bar (model 1) with only periodically distributed diamonds.
substitute for conventional cutting materials (i.e. cemented carbides). It should, however, be noted that only diamond and cemented carbide cutting tools can be used
metal-powder.net
several times for the processing of heavily machined materials [2], [3]. A disadvantage of cemented carbides is that they achieve their full effect during
drilling operations in mineral materials through a rotary motion with superimposed impact kinematics (i.e. hammer drill). This mechanism results in
June 2009 MPR
15
773,15
719,81
(115 ms)
666,48
613,15
559,81
(145 ms)
506,48
453,15
(210 ms) 399,81
349,48
(240 ms)
column7
column11
column15
293,15
Figure 3: Heat distribution of the bar (model 2) with periodically distributed diamonds and alumina (ellipsoids).
considerable noise development. During the machining with diamond tools, a superimposed kinematic impact is not necessary. On the other hand, cemented carbide tools do not need cooling during the machining operation. Because of the high machining temperatures, the diamonds in the diamond tool have to be protected against graphitisation by external cooling. For the cooling of the diamonds and for the removal of debris, water is employed [4]. However, the employed cooling water can not be kept in the borehole, and so diamond machining is impossible in buildings which are already in use.
Furthermore, disadvantages can occur in antrum blankets and in clinker, since the water distributes itself in the cavities and leaks at undesired places. The realisation of a dry processing of mineral materials with diamond tools will be driven forward by this project and will solve this kind of problem. For machining of concrete it could lead to a paradigm shift. The integration of materials with low thermal conductivity such as alumina or glass in diamond composites is a novel concept to produce this kind of diamond tool [5], [6]. With the continuous erosion of the tool, the diamonds in deeper layers will be protected by this concept
Figure 4. The lathe with PC connection to measure the temperature in the diamond tool during the drilling of concrete.
16
MPR June 2009
against temperature exposure and graphitisation before they are exposed. In this instance, the concept of newly designed diamond tools has been investigated using an FEM model. This model shows the operation mode of this novel material concept and that the heat development in the diamond tools can be affected.
Experimental part The theoretical model was programmed with ANSYS software. In the model, the bar has a size of 6.25×1×1mm3 (Figure 1a). The reason for such a short bar is due to the computer capacity. In
Figure 5. To measure the heat development in the diamond tools at three positions (6mm, 12mm, 18mm) over the length, a hole of 3mm depth has been eroded with a tungsten-cooper electrode. (Roboform S4, Charmilles Technologie).
metal-powder.net
the future, it will be possible to go on the LIDO cluster of the TU Dortmund (464 processors Opteron AMD, 1,216 Tbyte RAM) to evaluate a real size (25×4×4mm) with a realistic number of diamonds in the bar (10 Vol.-%, ~1100 diamonds). In the current models, the sizes of the diamonds and the alumina were equal to 250μm. The diamonds were periodically embedded in the matrix made of either bronze or cobalt, model 1 (Figure 1b). In a second model, one ellipsoid was embedded in front of each diamond according to the real spattered alumina shape, model 2 (Figure 1c). With those two basic models, a comparison of the heat distribution and a clarification of the effect of an additionally embedded material with a very low thermal conductivity can be shown. The starting temperature in the model was 293.15K. For the boundary conditions, a temperature of 793.15K has been chosen, acting from the left side of the segment. The heat propagates through the segment to the right side. The lateral surface of the bar was suitably isolated to enforce the heat transfer. For the simulation with ANSYS, the element type 87, a tetrahedral form with a size of 0.0981mm was used. All the values for the thermal conductivity which were necessary for the evaluation of the model have been taken from [7]. Figure 2 shows the estimated heat distribution of the bar, exclusively embedded with diamonds in a bronze matrix after 115, 145, 210 and 240 ms can be estimated. As a result of the good thermal conductivity of the diamonds compared to the value of the bronze matrix, it can be seen that after 115 ms the heat distribution takes a convex shape around the diamonds. The temperature level in the matrix is equivalent to that of the diamond. In the case of the alumina-diamond composite (Figure 3), the same effect can be seen, owing to the fact that the first column is filled with distributed diamonds. A change in the heat distribution can be seen after 210 ms. Describing model 1, exclusively diamonds, the temperature front moves to the next column of diamonds. Unlike model 2, with the addition of alumina between the columns of diamonds, we can achieve a heat protection shield caused by the very low thermal conductivity of the alumina. As a consequence, a concave heat distribution field forms around the diamonds. This concave heat distribution becomes concentrated; see Figure 3 after
metal-powder.net
240 ms. Following the temperatures of the diamonds, 7, 11, 15 show that the temperature in deeper layers of the bar is much lower in model 2, compared to model 1.
Conclusion and future work Through theoretical simulation, a novel material concept has shown the effect of adding alumina to standard diamond cutting tools in an attempt to be able to use a dry machining process. A more realistic model with random distribution of the diamonds and alumina, and a convection to all sides, will be the next evolution step. A detailed analysis of different sizes and concentrations of each component under different conditions will help to optimise the composition of real diamond tools. Moreover, the promising compositions can then be tested in a turning test (Figures 4 and 5). On an instrumented turning lathe, the temperature in the diamond tools can be measured during the drilling of concrete. In the center of the diamond tool (25×4×4; L×W×H) three holes over the length in 6, 12, 18mm were eroded by die sinking (Roboform S4, Charmilles Technologie) with a tungsten cooper electrode. The first experiments (RPM 755, feed 0.045 mm per rotation) estimated the way in which the redeveloped tool fitting works and what temperature can be expected, and show that an assumption of 500°C for the working temperature is realistic. So the comparison between the FEM approach and the drilling tests will push this novel material concept to real application for dry machining of mineral materials with diamond tools. The next tasks which will have to be performed will be: t realisation of a more realistic model with a random distribution of the diamonds and the alumina or other materials with a low thermal conductivity; t identification of the thermal conductivity of each employed material with a stationary method to embed these values in the next generation of the ANSYS model; t examination of the FEM model with the data of the real measured values from the drilling tests; t and accomplishment of drilling tests with the promising compositions obtained from the FEM models.
The Authors This paper was written by W. Tillmann 1,a, M. Gathen 1,b, A. Osmanda 1,c, L. Wojarski 1,d, and C. Kronholz 1,e from the Institute of Materials Engineering, Dortmund, Germany.
Acknowledgments This paper was presented at the 2008 World Congress on Powder Metallurgy and Particulate Materials in Washington, D.C. It is published with permission from the Metal Powder Industries Federation.
Reference [1] W. Tillmann, “Trends and market perspectives for diamond tools in the construction industry,” International Journal of Refractory Metals and Hard Materials, 18, 2000, S. 301-306. [2] B. Denkena, H. K. Tönshoff, T. Friemuth, A. Gierse, T. Glatzel, H. Hillmann-Apmann, “Innovative Trennschleifprozesse in der Natursteinbearbeitung,” Werkstatttechnik online, Jahrgang 92, H. 6, 2002, S. 290-296. [3] G. Biasco, “Diamond wire for quarrying hard rocks”, Industrial Diamond Review, 1993, Heft 53, S. 252-255. [4] H. J. Panhorst, “Seilsägen von Granit mit Diamantwerkzeugen,” Dissertation, Universität Hannover, 1974. [5] Diamond composites for dry machining of mineral materials, Conference Proceedings EUROPM 2007, 15. – 17. 10. 2007, Toulouse, Frankreich, Vol. 1, ISBN 978-1899072-29-3, 2007. [6] Thermal Protection Shield Concept for Diamond Impregnated Tools. Materials Science Forum Vols. 534-536 (2007) pp. 1145 – 1148, Trans Tech Publications Ltd., Uetikon/ Zurich, ISBN 0-87849-419-7, ISSN 0255-5476. [7] Y.S. Touloukian, “Thermal Conductivity,” 2 (3), 1970, ISBN 0-306-67022-4.
June 2009 MPR
17
Tribological investigation of impregnated diamond tools The introduction of diamond tools and their use has continuously gained favour, and in many cases, has become a substitute for conventional cutting materials. . .
D
ue to their better mechanical properties, diamond tools have largely replaced cemented carbide tools in the stone industry. During the use of diamond tools water cooling is necessary because of the heat development and the diamonds’ tendency to decompose to graphite at high temperatures. However, alkaline waterbased solutions are normally used for cooling, and can contaminate occupied buildings. Therefore new diamond tools
(a)
for dry drilling are of interest. The addition of a material with a low thermal conductivity (alumina, glass) in the diamond segment can improve the wear behaviour and act as a protection shield, which protects the diamonds within the composite. This article focuses on the heat distribution generated due to wear and abrasion along the length of the new diamond segments. Different abrasion tests will be carried out to investigate the difference in the temperature distribution profile.
The temperature distribution computed by ANSYS will be compared with the measured temperature profile. Diamond tools are state of the art when considering redevelopment, renovation and the demolition of buildings. Based on the wide selection of diamond cutting tools available, it is possible to process almost all encountered materials at the construction site [1]. The introduction of diamond tools and their use has continuously gained favour, and in many cases, has become a
(b) size of the bar: 6.25×1×1mm size of diamonds: 250μm size of alumina: 250μm Used element typ: tetraeder
(c) Figure 1. A picture of the theoretically constructed model with the attributes.
14
MPR June 2009
0026-0657/09 ©2009 Elsevier Ltd. All rights reserved.
773,15
719,81
(after 115 ms)
666,48
613,15
559,81
(after 145 ms)
506,48
453,15
(after 210ms) 399,81
349,48
(after 240 ms)
column7
column11
column15
293,15
Figure 2. Heat distribution of the bar (model 1) with only periodically distributed diamonds.
substitute for conventional cutting materials (i.e. cemented carbides). It should, however, be noted that only diamond and cemented carbide cutting tools can be used
metal-powder.net
several times for the processing of heavily machined materials [2], [3]. A disadvantage of cemented carbides is that they achieve their full effect during
drilling operations in mineral materials through a rotary motion with superimposed impact kinematics (i.e. hammer drill). This mechanism results in
June 2009 MPR
15
773,15
719,81
(115 ms)
666,48
613,15
559,81
(145 ms)
506,48
453,15
(210 ms) 399,81
349,48
(240 ms)
column7
column11
column15
293,15
Figure 3: Heat distribution of the bar (model 2) with periodically distributed diamonds and alumina (ellipsoids).
considerable noise development. During the machining with diamond tools, a superimposed kinematic impact is not necessary. On the other hand, cemented carbide tools do not need cooling during the machining operation. Because of the high machining temperatures, the diamonds in the diamond tool have to be protected against graphitisation by external cooling. For the cooling of the diamonds and for the removal of debris, water is employed [4]. However, the employed cooling water can not be kept in the borehole, and so diamond machining is impossible in buildings which are already in use.
Furthermore, disadvantages can occur in antrum blankets and in clinker, since the water distributes itself in the cavities and leaks at undesired places. The realisation of a dry processing of mineral materials with diamond tools will be driven forward by this project and will solve this kind of problem. For machining of concrete it could lead to a paradigm shift. The integration of materials with low thermal conductivity such as alumina or glass in diamond composites is a novel concept to produce this kind of diamond tool [5], [6]. With the continuous erosion of the tool, the diamonds in deeper layers will be protected by this concept
Figure 4. The lathe with PC connection to measure the temperature in the diamond tool during the drilling of concrete.
16
MPR June 2009
against temperature exposure and graphitisation before they are exposed. In this instance, the concept of newly designed diamond tools has been investigated using an FEM model. This model shows the operation mode of this novel material concept and that the heat development in the diamond tools can be affected.
Experimental part The theoretical model was programmed with ANSYS software. In the model, the bar has a size of 6.25×1×1mm3 (Figure 1a). The reason for such a short bar is due to the computer capacity. In
Figure 5. To measure the heat development in the diamond tools at three positions (6mm, 12mm, 18mm) over the length, a hole of 3mm depth has been eroded with a tungsten-cooper electrode. (Roboform S4, Charmilles Technologie).
metal-powder.net
the future, it will be possible to go on the LIDO cluster of the TU Dortmund (464 processors Opteron AMD, 1,216 Tbyte RAM) to evaluate a real size (25×4×4mm) with a realistic number of diamonds in the bar (10 Vol.-%, ~1100 diamonds). In the current models, the sizes of the diamonds and the alumina were equal to 250μm. The diamonds were periodically embedded in the matrix made of either bronze or cobalt, model 1 (Figure 1b). In a second model, one ellipsoid was embedded in front of each diamond according to the real spattered alumina shape, model 2 (Figure 1c). With those two basic models, a comparison of the heat distribution and a clarification of the effect of an additionally embedded material with a very low thermal conductivity can be shown. The starting temperature in the model was 293.15K. For the boundary conditions, a temperature of 793.15K has been chosen, acting from the left side of the segment. The heat propagates through the segment to the right side. The lateral surface of the bar was suitably isolated to enforce the heat transfer. For the simulation with ANSYS, the element type 87, a tetrahedral form with a size of 0.0981mm was used. All the values for the thermal conductivity which were necessary for the evaluation of the model have been taken from [7]. Figure 2 shows the estimated heat distribution of the bar, exclusively embedded with diamonds in a bronze matrix after 115, 145, 210 and 240 ms can be estimated. As a result of the good thermal conductivity of the diamonds compared to the value of the bronze matrix, it can be seen that after 115 ms the heat distribution takes a convex shape around the diamonds. The temperature level in the matrix is equivalent to that of the diamond. In the case of the alumina-diamond composite (Figure 3), the same effect can be seen, owing to the fact that the first column is filled with distributed diamonds. A change in the heat distribution can be seen after 210 ms. Describing model 1, exclusively diamonds, the temperature front moves to the next column of diamonds. Unlike model 2, with the addition of alumina between the columns of diamonds, we can achieve a heat protection shield caused by the very low thermal conductivity of the alumina. As a consequence, a concave heat distribution field forms around the diamonds. This concave heat distribution becomes concentrated; see Figure 3 after
metal-powder.net
240 ms. Following the temperatures of the diamonds, 7, 11, 15 show that the temperature in deeper layers of the bar is much lower in model 2, compared to model 1.
Conclusion and future work Through theoretical simulation, a novel material concept has shown the effect of adding alumina to standard diamond cutting tools in an attempt to be able to use a dry machining process. A more realistic model with random distribution of the diamonds and alumina, and a convection to all sides, will be the next evolution step. A detailed analysis of different sizes and concentrations of each component under different conditions will help to optimise the composition of real diamond tools. Moreover, the promising compositions can then be tested in a turning test (Figures 4 and 5). On an instrumented turning lathe, the temperature in the diamond tools can be measured during the drilling of concrete. In the center of the diamond tool (25×4×4; L×W×H) three holes over the length in 6, 12, 18mm were eroded by die sinking (Roboform S4, Charmilles Technologie) with a tungsten cooper electrode. The first experiments (RPM 755, feed 0.045 mm per rotation) estimated the way in which the redeveloped tool fitting works and what temperature can be expected, and show that an assumption of 500°C for the working temperature is realistic. So the comparison between the FEM approach and the drilling tests will push this novel material concept to real application for dry machining of mineral materials with diamond tools. The next tasks which will have to be performed will be: t realisation of a more realistic model with a random distribution of the diamonds and the alumina or other materials with a low thermal conductivity; t identification of the thermal conductivity of each employed material with a stationary method to embed these values in the next generation of the ANSYS model; t examination of the FEM model with the data of the real measured values from the drilling tests; t and accomplishment of drilling tests with the promising compositions obtained from the FEM models.
The Authors This paper was written by W. Tillmann 1,a, M. Gathen 1,b, A. Osmanda 1,c, L. Wojarski 1,d, and C. Kronholz 1,e from the Institute of Materials Engineering, Dortmund, Germany.
Acknowledgments This paper was presented at the 2008 World Congress on Powder Metallurgy and Particulate Materials in Washington, D.C. It is published with permission from the Metal Powder Industries Federation.
Reference [1] W. Tillmann, “Trends and market perspectives for diamond tools in the construction industry,” International Journal of Refractory Metals and Hard Materials, 18, 2000, S. 301-306. [2] B. Denkena, H. K. Tönshoff, T. Friemuth, A. Gierse, T. Glatzel, H. Hillmann-Apmann, “Innovative Trennschleifprozesse in der Natursteinbearbeitung,” Werkstatttechnik online, Jahrgang 92, H. 6, 2002, S. 290-296. [3] G. Biasco, “Diamond wire for quarrying hard rocks”, Industrial Diamond Review, 1993, Heft 53, S. 252-255. [4] H. J. Panhorst, “Seilsägen von Granit mit Diamantwerkzeugen,” Dissertation, Universität Hannover, 1974. [5] Diamond composites for dry machining of mineral materials, Conference Proceedings EUROPM 2007, 15. – 17. 10. 2007, Toulouse, Frankreich, Vol. 1, ISBN 978-1899072-29-3, 2007. [6] Thermal Protection Shield Concept for Diamond Impregnated Tools. Materials Science Forum Vols. 534-536 (2007) pp. 1145 – 1148, Trans Tech Publications Ltd., Uetikon/ Zurich, ISBN 0-87849-419-7, ISSN 0255-5476. [7] Y.S. Touloukian, “Thermal Conductivity,” 2 (3), 1970, ISBN 0-306-67022-4.
June 2009 MPR
17