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Investigation of the effect of drilling conditions on the twist drill temperature during step-by-step and continuous dry drilling
Materials & Design Materials and Design 27 (2006) 446–454 www.elsevier.com/locate/matdes
Investigation of the effect of drilling conditions on the twist drill temperature during step-by-step and continuous dry drilling Eyup Bag˘ci *, Babur Ozcelik Department of Design and Manufacturing Engineering, Gebze Institute of Technology, 41400 Gebze-Kocaeli, Turkey Received 23 July 2004; accepted 22 November 2004 Available online 25 December 2004
Abstract Trustworthy data about cutting tool temperature distribution is main importance in drilling processes. In this paper, the effects of drilling depth, spindle speed and feed rate on the drill bit temperature experimentally have been investigated in step-by-step and continuous dry drilling. Drill temperatures were measured by inserting standard thermocouples through the coolant (oil) hole of TiN/TiAlN coated carbide drills. Experimental studies have been conducted by using two different workpiece materials, AISI 1040 steel and Al 7075-T651. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Drill bit temperature; Step-by-step drilling; Continuous drilling; Thermocouple
1. Introduction Machining operations such as turning, grinding, boring, milling and drilling are used to manufacture a diversity of mechanical products in industry. Drilling is one of the most important machining processes that have been widely applied in manufacturing area. High temperatures in modern metal cutting are the cause of unsatisfactory cutting tool life and limitations on cutting speed. Therefore, the most suitable drilling parameters must be selected. The drilling tool has to withstand greatest environments which include high temperatures, frictional forces and large mechanical and thermal loads in dry drilling. One of the important factors in machining processes is tool wear and this is thought to be closely related to *
Corresponding author. Tel.: +90 262 653 84 97/1287; fax: +90 262 653 84 90. E-mail addresses: [email protected], [email protected] (E. Bag˘ci), [email protected], [email protected], [email protected] (B. Ozcelik). 0261-3069/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2004.11.018
the temperature existing at the wearing surfaces of the tool. The investigation of cutting process in thermal respect has increased in importance thanks to the obtainment high cutting speed levels in modern material removal operations. There have been only a few studies to measure the temperature existing while the drilling process such as effect of the different tool coatings [1], along the cutting edges of a drill [2], on the diameter and cylindricity of dry drilled holes [3], using a model for predicting the heat flow into the workpiece in dry drilling, [4], and analytical models for twist drill [5] for comparison of experimental and analytical [6], on hole quality under dry and wet drilling conditions [7], using numerical analysis [8]. During the drilling process, the most important factor affecting the cutting tool performance and workpiece properties is cutting temperature that emerges between drill bit and chip. The cutting temperature directly influences hole sensitivity, surface roughness, and tool wear. The experimental and numerical investigation of the temperature changes that occur on the cutting tool during the material removal processes is a traditional
E. Bag˘ci, B. Ozcelik / Materials and Design 27 (2006) 446–454
concern. Recently, works to calculate the cutting temperature by using FEM have been also conducted. Chen [9] has developed the 3D finite element model to be able to compute the temperature distribution that may take place at the first cutting edge of the drilling tool and along the flank face. Fuh and Liang [10] calculated the temperature distribution on the conventional drill during the cutting process by means of 3D FEM. In this study, the effects of cutting depth, cutting speed, web thickness, and helix angle on the temperature changes are investigated. Agapiou and Devires [5,6] have analytically calculated the temperature distribution of twist drills on the flank face and cutting edge to explain thermal phenomena during the cutting process. They also have proposed a comparison between experimental and analytical results. On the other hand, Agapiou and Stephenson [11] have described a model for calculating transient and steady-state drill temperatures for drill with arbitrary geometries. They have additionally compared the analytical results acquired to the experimental ones gathered by implementing welded thermocouple and thin wire thermo-junction methods. Despite there are very experimental work on turning and grinding operations in the literature, there is little work directed towards calculating drill temperature. Experimental and finite element approach were used by Nouari et al. [12] to determine tool wear and drill bit temperature in dry machining of aluminum alloys. Bono [2–4] developed a model for predicting the heat flow into the workpiece and investigated the influence of the heat that emerges on hole diameter and cylindricity in dry drilling. Finally, he has presented a comparison between numerical and experimental results. Kalidas et al. [7] measured the workpiece temperature to find out how different drill coatings affects the hole quality under dry and wet cutting conditions. For this purpose, four thermocouples were inserted onto the workpiece and the temperature values for various feed rates and spindle speeds were determined. In this study, the effects of drilling depth, spindle speed and feed rate on the drill bit temperature experimentally have been examined in step-by-step dry drilling for AL 7075 T-651 alloy and AISI 1040 steel materials. Drill temperatures were measured by inserting standard thermocouples through the coolant (oil) hole of TiN/ TiAlN coated carbide drills.
2. Experimental setup and cutting conditions The cutting experiments were conducted drilling in dry cutting conditions on a DECKEL MAHO DMU 60 P five axis CNC milling machine equipped with a maximum spindle speed of 12,000 rpm and a 15 kW drive motor. Fig. 1 shows the CNC milling machine
447
Fig. 1. CNC milling machine and data measurement equipment used in the experimental works.
where the actual drilling is operated. CNC part programs are created by employing ProENGINEER CAD/CAM software on a personal computer (PC), Intel pentium IV at 2.0 GHz. 2.1. Cutting tools and workpiece materials The drilling tool with the code of R840 1000 A1A that would be utilized in drilling AISI 1040 and Al 7075-T651 material was selected from the Sandvik Coromant Catalog (see Fig. 2). The dimensional and
Fig. 2. The drilling tool with the code of R840 1000 A1A.
Table 1 The dimensional and mechanical properties of the drilling tool Tool diameter Flute Tool overhang Point angle Helix angle Shank type Coating (two layers)
10 mm 2 flute 47 mm 140° 30° Cylindrical TiN/TiAlN
Table 2 Chemical composition of materials (wt%) (a) Al 7075-T651 Zn Si 0.5 0.13 (b) AISI 1040 steel C Si 0.39
0.24
Mn
Cr
Ti
Al
Cu
0.30
0.28
0.2
base
2.0
Mn
P
S
0.71
0.02
0.03
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448 Table 3 Mechanical properties of materials Workpiece material
UTS (MPa)
YS (MPa)
Density (kg/m3)
Elongation (%)
Hardness (Bhn)
AISI 1040 Al7075-T651
515 570
350 505
7845 2800
25 11
170 160
Table 4 Experimental conditions of continuous dry drilling for different holes depth Materials
AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AISI 1040 AISI 1040 AISI 1040 AISI 1040 AISI 1040 AISI 1040 AISI 1040 AISI 1040 AISI 1040
Test No.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Spindle speed (rpm)
Feed rate (mm/rev)
Drilling depth (mm)
2547 2547 2547 2547 2547 2547 2547 2547 2547 955 955 955 955 955 955 955 955 955
0.1 0.15 0.2 0.1 0.15 0.2 0.1 0.15 0.2 0.08 0.12 0.16 0.08 0.12 0.16 0.08 0.12 0.16
20 20 20 30 30 30 40 40 40 20 20 20 25 25 25 30 30 30
mechanical properties of the drilling tool are displayed in Table 1. TiN/TiALN coated carbide drills with diameters of 10 mm tools were used. In the experiments, samples with diameters of 25 mm and lengths of 75 mm that were made of AL 7075-T651 aerospace alloy and AISI 1040 steel materials were used as workpiece. The chemical compositions and mechanical properties of the workpiece materials were presented in Tables 2 and 3, respectively.
Table 5 Experimental conditions of step-by-step dry drilling Materials
Test No.
Spindle speed (rpm)
Feed rate (mm/rev)
AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AISI 1040 AISI 1040 AISI 1040 AISI 1040 AISI 1040 AISI 1040
1 2 3 4 5 6 7 8 9 10 11 12
2547 2547 2547 1910 1910 1910 955 955 955 1433 1433 1433
0.1 0.15 0.2 0.1 0.15 0.2 0.08 0.12 0.16 0.08 0.12 0.16
2.2. Drilling conditions For the purpose of investigation the effect of feed rate, spindle speed and drilling depth in step-by-step and continuous dry drilling for different materials, the experimental tests were run at the 30 different test conditions listed in Tables 4 and 5. Blind holes were drilled in workpiece materials. Drill bit temperatures were recorded during each step-by-step and continuous dry drilling test. For each step-by-step and continuous dry drilling process, 30 workpiece materials and tool-holders (SK 40 GEWEFA-05.029.002-Ø2-25) were used. The workpiece materials were fixed on tool-holders. Drilling processes were done as step-by-step and continuous, and step depth for each step-by-step dry drilling was used
Fig. 3. Design of experimental workpiece for (a) step-by-step and (b) continuous dry drilling processes.
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449
10 mm (see Fig. 3(a)). The hole depth was selected different values such as 20, 25, 30 mm for AISI 1040 steel and 20, 30, 40 mm for Al 7075-T 651 during the investigation of effects of feed rate, spindle speed on the drill bit temperature in the continuous dry drilling (see Fig. 3(b)). 2.3. Temperature measurement
Fig. 4. The thermocouple was inserted through the oil hole of internal coolant carbide drill.
The response time of the equipment and the place where the temperature is measured are two most important points in measuring the temperature that exist during the cutting process. The equipment employed should acquire the temperature data quickly and should work in wide temperature ranges. In this study, the temperature is measured by means of PFA Teflon Coated K (ChromegaÒ–AlomegaÒ) type
Fig. 5. Schematic representation and close-up photo of experimental setup.
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thermocouples with a diameter of 127 lm. The thermocouple can take measurements to 500 °C and its response time is 10 ls. The thermocouple was inserted through the oil (coolant) hole of internal coolant carbide drills and as it can be seen in Fig. 4, it is fixed closed to the drill bit. Then, the drill is put into a specially designed fixture and fixed on the machine table (see Fig. 5(a)). In Fig. 5(a) and (b),
the experiment set designed for temperature measurement is exhibited.
3. Experimental results and discussion In this study, the bit temperature changes of the twist drill in the different hole depth, spindle speed and feed
Fig. 6. The effects of different hole depth and feed rate values on the drill bit temperature for AISI 1040 steel (a)–(c).
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rate values of the two materials such as AISI 1040 steel and Al 7075-T651 are examined for step-by-step and continuous dry drilling. The study is performed in the two stages. Firstly, the bit temperature of the twist drill is researched for different feed rates and holes depth during continuous dry drilling for AISI 1040 steel and Al 7075-T651 alloy materials. Secondly, the bit temperature of the twist drill is examined for different spindle speed
451
and feed rate values during step-by-step dry drilling for AISI 1040 steel and Al 7075-T651 alloy materials. 3.1. Continuous dry drilling tests Three feed rate (0.08, 0.12, 0.16 mm/rev) and depth of drilling values (20, 25, 30 mm) were used in the drilling tests for AISI 1040 steel materials for same spindle
Fig. 7. The effects of different hole depth and feed rate values on the drill bit temperature for Al 7075-T651 alloy material (a)–(c).
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speeds (955 rpm). In Fig. 6, it can be seen that the temperature values increase on the twist drill bit with increase in the drilling depth for the same feed rate and spindle speed values. Large temperature increase between first (20 mm) and second (25 mm) drilling and small temperature increase between second and third (30 mm) drill is observed in Fig. 6(a) and (b) for 955 rpm, 0.08 and 0.12 mm/rev. However, small temperature increase between first and second drilling and large temperature increase between second and third drill is observed in Fig. 6(c) for 1.6 mm/rev. Additionally, it is noted that the temperature values decrease on the twist drill bit with increase in feed rate for the same spindle speed and drilling depth values. When the feed rate increase 50% and 100%, the drill bit temperature decreased 18.6% and 23.1% (hole depth 20 mm), 19.2% and 29.11%, (hole depth 25 mm) and 20% and 26%, (hole depth 30 mm), respectively, as shown in Fig. 6(a)–(c). Three feed rate (0.1, 0.15, 0.20 mm/rev) and depth of drilling values (20, 30, 40 mm) were used in the drilling tests for Al 7075-T651 alloy materials for same spindle speeds (2547 rpm). Fig. 7 shows the effects of feed rate and drilling depth on the temperature responses on the
twist drill bit during the direct dry drilling process. In Fig. 7, it can be seen that the temperature values increase on the twist drill bit with increase in the drilling depth for the same feed rate and spindle speed values. Small temperature changes were observed for same feed rate values and different holes depth. Additionally, it is noted that the temperature values decrease on the twist drill bit with increase in feed rate for the same spindle speed values. When the feed rate increase 50% and 100%, the drill bit temperature decreased 25.5% and 39.3% (hole depth 20 mm), 10.7% and 36.5%, (hole depth 30 mm) and 14.5% and 38.5%, (hole depth 40 mm), respectively, as shown in Fig. 7(a)–(c). 3.2. Step-by-step dry drilling tests Three feed rates (0.08, 0.12, 0.16 mm/rev) and spindle speed of 955 rpm for AISI 1040 steel and three feed rates (0.1, 0.15, 0.2 mm/rev) and spindle speed of 2547 rpm for Al 7075-T651 alloy materials were used in the stepby-step dry drilling tests. Drilling test was done three steps depth, step depth is 10 mm, for each step-by-step drilling process. In Figs. 8 and 9, it can be seen that the maximum temperature values increase on the twist
Fig. 8. Drill bit temperature distribution in the step-by-step dry drilling for Al 7075-T651 material (a), (b).
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453
Fig. 9. Drill bit temperature distribution in the step-by-step dry drilling for AISI 1040 steel (a), (b).
drill bit with increase in the drilling step for all drilling tests. Additionally, it is noted that the temperature values increase on the twist drill bit with increase in spindle speed for the same feed rate values during the stepby-step dry drilling (see Figs. 8 and 9). Large temperature increase between first (0–10 mm) and second (10–20 mm) drilling steps and small temperature increase between second and third (20–30 mm) drilling steps are observed in Figs. 8 and 9. In the same drilling conditions (N = 2547 rpm, f = 0.10 mm/rev and depth of drilling = 30 mm) during drilling of the AL 7075-T651 aluminum alloy, the maximum drill bit temperature for step-by-step and continuous drilling is 203 and 271 °C, respectively (see Figs. 8(b) and 7(b)). It was seen that the maximum temperature increase 33% in the continuous drilling. The drilling conditions have feed rate of 0.08 mm/rev, spindle speed of 955 rpm and depth of drilling of 30 mm for AISI 1040 steel were examined to obtain the maximum drill bit temperature during continuous and stepby-step drilling. The maximum drill bit temperature for step-by-step and continuous drilling was plotted
251 and 380 °C, respectively, (see Figs. 6(c) and 9(a)). It was seen that the maximum temperature increase 51% in the continuous drilling.
4. Conclusions In this study, drill bit temperature distributions measured by the thermocouple for twist drills method are presented experimentally during step-by-step and continuous dry drilling operation. In the drilling processes, cutting conditions have different spindle speed, drilling depth and feed rate were used. Drill temperatures were measured by inserting standard thermocouples through the coolant (oil) hole of TiAlN-coated carbide drills. Experimental study was conducted by using two different workpiece materials, AISI 1040 steel and Al 7075T651 alloy materials. During the continuous dry drilling process of the AISI 1040 steel and AL 7075-T651 materials, it is observed that the temperature increase together with drilling depth for same speeds and feed rates. Additionally, it is noted that the temperature values decrease on the twist drill
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bit with increase in feed rate for the same spindle speed and drilling depth values. The maximum temperature values increase on the twist drill bit with increase in the drilling step for all drilling tests was observed for AISI 1040 steel and AL 7075T651 materials. The temperature values increase on the twist drill bit with increase in spindle speed was seen for the same feed rate values during the step-by-step dry drilling for AISI 1040 steel materials. However, the drill bit temperature decreased when the spindle speed increase for AL 7075-T651 materials.
Acknowledgement Authors thank Research Fund Chairmanship of Gebze Institute of Technology for their support in scope of research project (Project No: 02-B-03-08-01).
References [1] Do¨rr J, Mertens Th, Engering G, Lahres M. ÔIn-situÕ temperature measurement to determine the machining potential of different tool coatings. Surf Coat Technol 2003;174–175:389–92. [2] Bono M, Ni J. A method for measuring the temperature distribution along the cutting edges of a drill. J Manuf Sci Eng 2002;124:921–3.
[3] Bono M, Ni J. The effects of thermal distortions on the diameter and cylindricity of dry drilled holes. Int J Mach Tool Manuf 2001;41:2261–70. [4] Bono M, Ni J. A model for predicting the heat flow into the workpiece in dry drilling. J Manuf Sci Eng 2002;124:773–7. [5] Agapiou JS, DeVries MF. On the determination of thermal phenomena during a drilling process – part I, analytical models of twist drill temperature distributions. Int J Mach Tool Manuf 1990;30:203–15. [6] Agapiou JS, DeVries MF. On the determination of thermal phenomena during a drilling process – part II, comparison of experimental and analytical twist drill temperature distributions. Int J Mach Tool Manuf 1990;30:217–26. [7] Kalidas S, DeVor RE, Kapoor SG. Experimental investigation of the effect of drill coatings on hole quality under dry and wet drilling conditions. Surf Coat Technol 2001;148: 117–28. [8] Jen TC, Gutierrez G, Eapen S, Barber G, Zhao H, Szuba PS, et al.. Investigation of heat pipe cooling in drilling applications: part I: preliminary numerical analysis and verification. Int J Mach Tool Manuf 2002;42:643–52. [9] Chen W. Effect of the cross-sectional shape design of a drill body on drill temperature distributions. Int Commun Heat Mass Tran 1996;23(3):355–66. [10] Fuh K, Liang WC. Temperature rise in twist drills with a finite element approach. Int Commun Heat Mass Tran 1994;21(3): 345–58. [11] Agapiou JS, Stephenson DA. Analytical and experimental studies of drill temperatures. J Eng Ind 1994;116(1):54–60. [12] Nouari M, List G, Girot F, Coupard D. Experimental analysis and optimisation of tool wear in dry machining of aluminum alloys. Wear 2003;255:1359–68.
Investigation of the effect of drilling conditions on the twist drill temperature during step-by-step and continuous dry drilling Eyup Bag˘ci *, Babur Ozcelik Department of Design and Manufacturing Engineering, Gebze Institute of Technology, 41400 Gebze-Kocaeli, Turkey Received 23 July 2004; accepted 22 November 2004 Available online 25 December 2004
Abstract Trustworthy data about cutting tool temperature distribution is main importance in drilling processes. In this paper, the effects of drilling depth, spindle speed and feed rate on the drill bit temperature experimentally have been investigated in step-by-step and continuous dry drilling. Drill temperatures were measured by inserting standard thermocouples through the coolant (oil) hole of TiN/TiAlN coated carbide drills. Experimental studies have been conducted by using two different workpiece materials, AISI 1040 steel and Al 7075-T651. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Drill bit temperature; Step-by-step drilling; Continuous drilling; Thermocouple
1. Introduction Machining operations such as turning, grinding, boring, milling and drilling are used to manufacture a diversity of mechanical products in industry. Drilling is one of the most important machining processes that have been widely applied in manufacturing area. High temperatures in modern metal cutting are the cause of unsatisfactory cutting tool life and limitations on cutting speed. Therefore, the most suitable drilling parameters must be selected. The drilling tool has to withstand greatest environments which include high temperatures, frictional forces and large mechanical and thermal loads in dry drilling. One of the important factors in machining processes is tool wear and this is thought to be closely related to *
Corresponding author. Tel.: +90 262 653 84 97/1287; fax: +90 262 653 84 90. E-mail addresses: [email protected], [email protected] (E. Bag˘ci), [email protected], [email protected], [email protected] (B. Ozcelik). 0261-3069/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2004.11.018
the temperature existing at the wearing surfaces of the tool. The investigation of cutting process in thermal respect has increased in importance thanks to the obtainment high cutting speed levels in modern material removal operations. There have been only a few studies to measure the temperature existing while the drilling process such as effect of the different tool coatings [1], along the cutting edges of a drill [2], on the diameter and cylindricity of dry drilled holes [3], using a model for predicting the heat flow into the workpiece in dry drilling, [4], and analytical models for twist drill [5] for comparison of experimental and analytical [6], on hole quality under dry and wet drilling conditions [7], using numerical analysis [8]. During the drilling process, the most important factor affecting the cutting tool performance and workpiece properties is cutting temperature that emerges between drill bit and chip. The cutting temperature directly influences hole sensitivity, surface roughness, and tool wear. The experimental and numerical investigation of the temperature changes that occur on the cutting tool during the material removal processes is a traditional
E. Bag˘ci, B. Ozcelik / Materials and Design 27 (2006) 446–454
concern. Recently, works to calculate the cutting temperature by using FEM have been also conducted. Chen [9] has developed the 3D finite element model to be able to compute the temperature distribution that may take place at the first cutting edge of the drilling tool and along the flank face. Fuh and Liang [10] calculated the temperature distribution on the conventional drill during the cutting process by means of 3D FEM. In this study, the effects of cutting depth, cutting speed, web thickness, and helix angle on the temperature changes are investigated. Agapiou and Devires [5,6] have analytically calculated the temperature distribution of twist drills on the flank face and cutting edge to explain thermal phenomena during the cutting process. They also have proposed a comparison between experimental and analytical results. On the other hand, Agapiou and Stephenson [11] have described a model for calculating transient and steady-state drill temperatures for drill with arbitrary geometries. They have additionally compared the analytical results acquired to the experimental ones gathered by implementing welded thermocouple and thin wire thermo-junction methods. Despite there are very experimental work on turning and grinding operations in the literature, there is little work directed towards calculating drill temperature. Experimental and finite element approach were used by Nouari et al. [12] to determine tool wear and drill bit temperature in dry machining of aluminum alloys. Bono [2–4] developed a model for predicting the heat flow into the workpiece and investigated the influence of the heat that emerges on hole diameter and cylindricity in dry drilling. Finally, he has presented a comparison between numerical and experimental results. Kalidas et al. [7] measured the workpiece temperature to find out how different drill coatings affects the hole quality under dry and wet cutting conditions. For this purpose, four thermocouples were inserted onto the workpiece and the temperature values for various feed rates and spindle speeds were determined. In this study, the effects of drilling depth, spindle speed and feed rate on the drill bit temperature experimentally have been examined in step-by-step dry drilling for AL 7075 T-651 alloy and AISI 1040 steel materials. Drill temperatures were measured by inserting standard thermocouples through the coolant (oil) hole of TiN/ TiAlN coated carbide drills.
2. Experimental setup and cutting conditions The cutting experiments were conducted drilling in dry cutting conditions on a DECKEL MAHO DMU 60 P five axis CNC milling machine equipped with a maximum spindle speed of 12,000 rpm and a 15 kW drive motor. Fig. 1 shows the CNC milling machine
447
Fig. 1. CNC milling machine and data measurement equipment used in the experimental works.
where the actual drilling is operated. CNC part programs are created by employing ProENGINEER CAD/CAM software on a personal computer (PC), Intel pentium IV at 2.0 GHz. 2.1. Cutting tools and workpiece materials The drilling tool with the code of R840 1000 A1A that would be utilized in drilling AISI 1040 and Al 7075-T651 material was selected from the Sandvik Coromant Catalog (see Fig. 2). The dimensional and
Fig. 2. The drilling tool with the code of R840 1000 A1A.
Table 1 The dimensional and mechanical properties of the drilling tool Tool diameter Flute Tool overhang Point angle Helix angle Shank type Coating (two layers)
10 mm 2 flute 47 mm 140° 30° Cylindrical TiN/TiAlN
Table 2 Chemical composition of materials (wt%) (a) Al 7075-T651 Zn Si 0.5 0.13 (b) AISI 1040 steel C Si 0.39
0.24
Mn
Cr
Ti
Al
Cu
0.30
0.28
0.2
base
2.0
Mn
P
S
0.71
0.02
0.03
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448 Table 3 Mechanical properties of materials Workpiece material
UTS (MPa)
YS (MPa)
Density (kg/m3)
Elongation (%)
Hardness (Bhn)
AISI 1040 Al7075-T651
515 570
350 505
7845 2800
25 11
170 160
Table 4 Experimental conditions of continuous dry drilling for different holes depth Materials
AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AISI 1040 AISI 1040 AISI 1040 AISI 1040 AISI 1040 AISI 1040 AISI 1040 AISI 1040 AISI 1040
Test No.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Spindle speed (rpm)
Feed rate (mm/rev)
Drilling depth (mm)
2547 2547 2547 2547 2547 2547 2547 2547 2547 955 955 955 955 955 955 955 955 955
0.1 0.15 0.2 0.1 0.15 0.2 0.1 0.15 0.2 0.08 0.12 0.16 0.08 0.12 0.16 0.08 0.12 0.16
20 20 20 30 30 30 40 40 40 20 20 20 25 25 25 30 30 30
mechanical properties of the drilling tool are displayed in Table 1. TiN/TiALN coated carbide drills with diameters of 10 mm tools were used. In the experiments, samples with diameters of 25 mm and lengths of 75 mm that were made of AL 7075-T651 aerospace alloy and AISI 1040 steel materials were used as workpiece. The chemical compositions and mechanical properties of the workpiece materials were presented in Tables 2 and 3, respectively.
Table 5 Experimental conditions of step-by-step dry drilling Materials
Test No.
Spindle speed (rpm)
Feed rate (mm/rev)
AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AL 7075-T651 AISI 1040 AISI 1040 AISI 1040 AISI 1040 AISI 1040 AISI 1040
1 2 3 4 5 6 7 8 9 10 11 12
2547 2547 2547 1910 1910 1910 955 955 955 1433 1433 1433
0.1 0.15 0.2 0.1 0.15 0.2 0.08 0.12 0.16 0.08 0.12 0.16
2.2. Drilling conditions For the purpose of investigation the effect of feed rate, spindle speed and drilling depth in step-by-step and continuous dry drilling for different materials, the experimental tests were run at the 30 different test conditions listed in Tables 4 and 5. Blind holes were drilled in workpiece materials. Drill bit temperatures were recorded during each step-by-step and continuous dry drilling test. For each step-by-step and continuous dry drilling process, 30 workpiece materials and tool-holders (SK 40 GEWEFA-05.029.002-Ø2-25) were used. The workpiece materials were fixed on tool-holders. Drilling processes were done as step-by-step and continuous, and step depth for each step-by-step dry drilling was used
Fig. 3. Design of experimental workpiece for (a) step-by-step and (b) continuous dry drilling processes.
E. Bag˘ci, B. Ozcelik / Materials and Design 27 (2006) 446–454
449
10 mm (see Fig. 3(a)). The hole depth was selected different values such as 20, 25, 30 mm for AISI 1040 steel and 20, 30, 40 mm for Al 7075-T 651 during the investigation of effects of feed rate, spindle speed on the drill bit temperature in the continuous dry drilling (see Fig. 3(b)). 2.3. Temperature measurement
Fig. 4. The thermocouple was inserted through the oil hole of internal coolant carbide drill.
The response time of the equipment and the place where the temperature is measured are two most important points in measuring the temperature that exist during the cutting process. The equipment employed should acquire the temperature data quickly and should work in wide temperature ranges. In this study, the temperature is measured by means of PFA Teflon Coated K (ChromegaÒ–AlomegaÒ) type
Fig. 5. Schematic representation and close-up photo of experimental setup.
450
E. Bag˘ci, B. Ozcelik / Materials and Design 27 (2006) 446–454
thermocouples with a diameter of 127 lm. The thermocouple can take measurements to 500 °C and its response time is 10 ls. The thermocouple was inserted through the oil (coolant) hole of internal coolant carbide drills and as it can be seen in Fig. 4, it is fixed closed to the drill bit. Then, the drill is put into a specially designed fixture and fixed on the machine table (see Fig. 5(a)). In Fig. 5(a) and (b),
the experiment set designed for temperature measurement is exhibited.
3. Experimental results and discussion In this study, the bit temperature changes of the twist drill in the different hole depth, spindle speed and feed
Fig. 6. The effects of different hole depth and feed rate values on the drill bit temperature for AISI 1040 steel (a)–(c).
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rate values of the two materials such as AISI 1040 steel and Al 7075-T651 are examined for step-by-step and continuous dry drilling. The study is performed in the two stages. Firstly, the bit temperature of the twist drill is researched for different feed rates and holes depth during continuous dry drilling for AISI 1040 steel and Al 7075-T651 alloy materials. Secondly, the bit temperature of the twist drill is examined for different spindle speed
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and feed rate values during step-by-step dry drilling for AISI 1040 steel and Al 7075-T651 alloy materials. 3.1. Continuous dry drilling tests Three feed rate (0.08, 0.12, 0.16 mm/rev) and depth of drilling values (20, 25, 30 mm) were used in the drilling tests for AISI 1040 steel materials for same spindle
Fig. 7. The effects of different hole depth and feed rate values on the drill bit temperature for Al 7075-T651 alloy material (a)–(c).
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speeds (955 rpm). In Fig. 6, it can be seen that the temperature values increase on the twist drill bit with increase in the drilling depth for the same feed rate and spindle speed values. Large temperature increase between first (20 mm) and second (25 mm) drilling and small temperature increase between second and third (30 mm) drill is observed in Fig. 6(a) and (b) for 955 rpm, 0.08 and 0.12 mm/rev. However, small temperature increase between first and second drilling and large temperature increase between second and third drill is observed in Fig. 6(c) for 1.6 mm/rev. Additionally, it is noted that the temperature values decrease on the twist drill bit with increase in feed rate for the same spindle speed and drilling depth values. When the feed rate increase 50% and 100%, the drill bit temperature decreased 18.6% and 23.1% (hole depth 20 mm), 19.2% and 29.11%, (hole depth 25 mm) and 20% and 26%, (hole depth 30 mm), respectively, as shown in Fig. 6(a)–(c). Three feed rate (0.1, 0.15, 0.20 mm/rev) and depth of drilling values (20, 30, 40 mm) were used in the drilling tests for Al 7075-T651 alloy materials for same spindle speeds (2547 rpm). Fig. 7 shows the effects of feed rate and drilling depth on the temperature responses on the
twist drill bit during the direct dry drilling process. In Fig. 7, it can be seen that the temperature values increase on the twist drill bit with increase in the drilling depth for the same feed rate and spindle speed values. Small temperature changes were observed for same feed rate values and different holes depth. Additionally, it is noted that the temperature values decrease on the twist drill bit with increase in feed rate for the same spindle speed values. When the feed rate increase 50% and 100%, the drill bit temperature decreased 25.5% and 39.3% (hole depth 20 mm), 10.7% and 36.5%, (hole depth 30 mm) and 14.5% and 38.5%, (hole depth 40 mm), respectively, as shown in Fig. 7(a)–(c). 3.2. Step-by-step dry drilling tests Three feed rates (0.08, 0.12, 0.16 mm/rev) and spindle speed of 955 rpm for AISI 1040 steel and three feed rates (0.1, 0.15, 0.2 mm/rev) and spindle speed of 2547 rpm for Al 7075-T651 alloy materials were used in the stepby-step dry drilling tests. Drilling test was done three steps depth, step depth is 10 mm, for each step-by-step drilling process. In Figs. 8 and 9, it can be seen that the maximum temperature values increase on the twist
Fig. 8. Drill bit temperature distribution in the step-by-step dry drilling for Al 7075-T651 material (a), (b).
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Fig. 9. Drill bit temperature distribution in the step-by-step dry drilling for AISI 1040 steel (a), (b).
drill bit with increase in the drilling step for all drilling tests. Additionally, it is noted that the temperature values increase on the twist drill bit with increase in spindle speed for the same feed rate values during the stepby-step dry drilling (see Figs. 8 and 9). Large temperature increase between first (0–10 mm) and second (10–20 mm) drilling steps and small temperature increase between second and third (20–30 mm) drilling steps are observed in Figs. 8 and 9. In the same drilling conditions (N = 2547 rpm, f = 0.10 mm/rev and depth of drilling = 30 mm) during drilling of the AL 7075-T651 aluminum alloy, the maximum drill bit temperature for step-by-step and continuous drilling is 203 and 271 °C, respectively (see Figs. 8(b) and 7(b)). It was seen that the maximum temperature increase 33% in the continuous drilling. The drilling conditions have feed rate of 0.08 mm/rev, spindle speed of 955 rpm and depth of drilling of 30 mm for AISI 1040 steel were examined to obtain the maximum drill bit temperature during continuous and stepby-step drilling. The maximum drill bit temperature for step-by-step and continuous drilling was plotted
251 and 380 °C, respectively, (see Figs. 6(c) and 9(a)). It was seen that the maximum temperature increase 51% in the continuous drilling.
4. Conclusions In this study, drill bit temperature distributions measured by the thermocouple for twist drills method are presented experimentally during step-by-step and continuous dry drilling operation. In the drilling processes, cutting conditions have different spindle speed, drilling depth and feed rate were used. Drill temperatures were measured by inserting standard thermocouples through the coolant (oil) hole of TiAlN-coated carbide drills. Experimental study was conducted by using two different workpiece materials, AISI 1040 steel and Al 7075T651 alloy materials. During the continuous dry drilling process of the AISI 1040 steel and AL 7075-T651 materials, it is observed that the temperature increase together with drilling depth for same speeds and feed rates. Additionally, it is noted that the temperature values decrease on the twist drill
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bit with increase in feed rate for the same spindle speed and drilling depth values. The maximum temperature values increase on the twist drill bit with increase in the drilling step for all drilling tests was observed for AISI 1040 steel and AL 7075T651 materials. The temperature values increase on the twist drill bit with increase in spindle speed was seen for the same feed rate values during the step-by-step dry drilling for AISI 1040 steel materials. However, the drill bit temperature decreased when the spindle speed increase for AL 7075-T651 materials.
Acknowledgement Authors thank Research Fund Chairmanship of Gebze Institute of Technology for their support in scope of research project (Project No: 02-B-03-08-01).
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