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6-Axis control ultraprecision microgrooving on sculptured surfaces with non-rotational cutting tool
CIRP Annals - Manufacturing Technology 58 (2009) 53–56
Contents lists available at ScienceDirect
CIRP Annals - Manufacturing Technology jou rnal homep age : ht t p: // ees .e lse vi er. com/ci rp/ def a ult . asp
6-Axis control ultraprecision microgrooving on sculptured surfaces with non-rotational cutting tool Y. Takeuchi (1)a,*, Y. Yoneyama a, T. Ishida a, T. Kawai b a b
Dept. of Mechanical Engineering, Graduate School of Engineering, Osaka University, Yamadaoka 2-1, Suita, Osaka, Japan FANUC Ltd., Oshino, Yamanashi, Japan
A R T I C L E I N F O
A B S T R A C T
Keywords: Microgroove Ultraprecision machining 6-Axis control
New optical devices with multi-functions such as diffraction and focusing have been recently required to miniaturize optical systems and to decrease cost. However, their shape is generally very complicated. Typical example is a curved microgroove on a three-dimensional complex surface. To machine the shape, a non-rotational cutting tool is employed in the study. In case of machining microgrooves on sculptured surface with a non-rotational cutting tool, 6-axis control is inevitable to control tool attitude and tool direction. The study deals with the development of CAM system for 6-axis control ultraprecision microgrooving. ß 2009 CIRP.
1. Introduction In optical electronics systems, a variety of fundamental optical devices such as mirrors, lenses, diffraction grating, etc. are used in combination to comprise optical systems [1]. This causes the problem that the arrangement error of these devices influences the total accuracy of the optical systems. The best way to solve such a problem is to realize single multi-function device by forming a diffraction grating and/or refractor on a micro-spherical lens. Then, it is required to accurately create sculptured surfaces as lens or mirror [2] and to finely generate curved microgrooves on their surface [3] as multi-functional devices. To machine such a complicated microgroove, turning or milling by use of a rotational cutting tool is not suitable due to tool interference. Thus, the machining technology by use of nonrotational cutting tools has been studied [4]. The cutting speed in non-rotational cutting is equal to the feed rate, thus resulting in low efficient machining. However, it enables grooving with high degree of freedom, compared with rotational cutting tools. In the case of machining curved microgrooves on sculptured surfaces with a non-rotational cutting tool, 6-axis control is inevitable to control tool attitude and tool direction. This study deals with the development of a CAM system for 6-axis control for ultraprecision microgrooving on sculptured surfaces. 2. Ultraprecision machining center with diamond cutting tool and CAM system 5-Axis control ultraprecision machining center is utilized, which has three translational axes, X, Y, Z and two rotational axes, B and C. The characteristic of the machine tool is that there is no
* Corresponding author. 0007-8506/$ – see front matter ß 2009 CIRP. doi:10.1016/j.cirp.2009.03.124
friction within it. The positioning accuracy of translational axes is 1 nm and the rotational positioning one of rotational axes is 0.000018 [5]. In order to carry out 6-axis control machining, the ultraprecision machining center is equipped with an additional rotational axis A on the B axis. A non-rotational single crystal diamond cutting tool, whose top angle is 908, is mounted on the A axis, and a workpiece is attached to the C axis through a jig. The cutting tool is set so that the tool end can correspond with the rotational center of A and B axes. As the shape of multi-functional optical devices is in general complicated, it is designed by use of 3D-CAD systems. Our own CAM system to generate NC data for 6-axis control ultraprecision machining center is developed, which consists of the mainprocessor and the postprocessor. The mainprocessor generates cutter location (CL) data to make not only sculptured surfaces but also microgrooves from a defined shape of multi-functional optical devices. Sculptures surfaces can be machined by use of rotational cutting tools by 3-axis or 5-axis control. The postprocessor transforms CL data to NC data corresponding to 3-axis, 5-axis and 6-axis control machinings. Especially, the postprocessor for 6-axis control determines a rotational angle of each axis; B and C from the coordinates of a cutting point and the tool axis vector at the cutting point, and A from the cutting direction vector and the calculated angles of B and C. 3. Microgrooving on a spherical surface In order to make sure the validity of the developed CAM system, a simple shape is machined, whose shape has five latticed microgrooves of 30 mm in width and 15 mm in depth on the spherical surface of 3 mm in diameter and in the center radius of curvature, as illustrated in Fig. 1. Two cutting processes such as turning and 6-axis control grooving are usually required to create the figure by
Y. Takeuchi et al. / CIRP Annals - Manufacturing Technology 58 (2009) 53–56
54
Fig. 1. Target object of grid microgrooves on a spherical surface. Fig. 3. Appearances in tuning spherical surfaces and in microgrooving. (a) Turning of a spherical surface. (b) Microgrooving with 6-axis control.
Fig. 2. Machining method of microgrooves on a spherical surface with one cutting tool. (a) Turning of a spherical surface by use of side edge. (b) Microgrooving by use of top edge.
changing the cutting tool and the cutting process. However, the change in process and tool causes the deterioration of the machining accuracy due to the difficulty of the accurate positioning. Thus, the cutting method shown in Fig. 2 is adopted to solve the above problem. At first, the non-rotational tool is mounted to the A axis, and the workpiece to the spindle on the C axis. The spherical surface is machined by using the linear cutting edge of nonrotational tool, while rotating the workpiece, as illustrated in Fig. 2(a). Then, the workpiece is mounted to the C axis by use of a jig. Microgrooves are created by using the top edge of the nonrotational tool, as illustrated in Fig. 2(b). The machining method can partly eliminate the deterioration of machining accuracy although the workpiece is moved. The cutting conditions are listed in Table 1. The work material is oxygen-free copper, and kerosene is used as coolant. Fig. 3(a) and (b) shows the actual spherical cutting and microgrooving, respectively. Fig. 4 shows images of the machined microgrooves from a microscope and a SEM. There seems to be no burr formation on the edge of microgrooves. It is also confirmed that accurate machining is accomplished since two microgrooves precisely cross each other at the intersecting point. In the next stage, as a complicated shape, a curved groove of 30 mm in width and 15 mm in depth is created on a spherical
Fig. 4. Machined grid microgrooves on a spherical surface of 3 mm in diameter. (a) Whole view. (b) Enlarged views of microgrooves.
Fig. 5. Target shape of curved microgrooves on a spherical surface.
surface of 1 mm in diameter and in the center radius of curvature, as illustrated in Fig. 5. The shape is defined by projecting a curved line generated on a plane onto the spherical surface, as illustrated in Fig. 6. Based on the defined shape, our CAM system generates CL data for grooving. Fig. 7 is the generated CL data, where the tool axes are represented as cylinders. The cutting experiment is performed by use of the NC data converted from the CL data under the cutting conditions of Table 2.
Table 1 Machining condition of grid microgrooves on a spherical surface. Turning Rough Spindle rotation (min 1) Feed rate (mm min 1) Depth of cut (mm)
30,000 3 1
Microgrooving Finish
Rough
Finish
1 0.5
– 40 1
10 0.5
Fig. 6. Definition of a curved microgroove on a spherical surface.
Y. Takeuchi et al. / CIRP Annals - Manufacturing Technology 58 (2009) 53–56
55
Fig. 10. Target shape of microgrooves on a sculptured surface. (a) Whole view of sculptured surface. (b) Microgrooves to be machined.
Fig. 7. Generated CL data for microgrooving.
Table 2 Machining condition of curved microgrooves on a spherical surface. Turning
1
Spindle rotation (min ) Feed rate (mm min 1) Depth of cut (mm)
Microgrooving
Rough
Finish
Rough
Finish
30,000 20 1
20 1
– 40 1
10 0.5
Fig. 11. Appearances in milling sculptured surface and in microgrooving. (a) Milling of a sculptured surface with 5-axis control. (b) Microgrooving with 6-axis control.
position error between the tool and the workpiece caused by detaching the workpiece from the C axis and attaching it again to the C axis through a jig. 4. Microgrooving on sculptured surface
Fig. 8. Curved microgroove on a spherical surface of 1 mm in radius. (a) Result of machining simulation. (b) Machined workpiece.
Fig. 8(a) and (b) shows the machining simulation result and a photograph of the machined piece, respectively. Fig. 9 is a SEM image of the machined groove, where no burr formation takes place. Although the microgrooving is well performed, the groove width is not necessarily uniform. This may be due to the relative
The shape to be created as microgrooves on a sculptured surface is illustrated in Fig. 10. The sculptured surface with a maximum undulating difference of 0.1 mm is defined on the area of 1 mm square. Two kinds of microgrooves are machined; parallel ones and curved ones. Parallel microgrooves of 15 mm in depth are divided into two groups by the groove pitch, i.e. 30 and 25 mm. A curved microgroove is S-shaped and 5 mm in depth and 10 mm in width. In this case, the workpiece shape is created by use of 5-axis control machining with a rotational cutting tool and 6-axis control machining with a non-rotational one to reconcile the machining efficiency and the machining error suppression, as illustrated in Fig. 11. A rotational tool is used so as to create a curved surface efficiently. In case of 5-axis control machining using a rotational single crystal diamond tool of 0.04 mm in radius, a high speed spindle with the rotational tool is mounted to the B axis, and a jig with the workpiece is fixed to the C axis, as shown in Fig. 11(a). In case of 6-axis control grooving, as shown in Fig. 11(b), the A axis with a non-rotational diamond tool is mounted on the B axis by removing the spindle. Our CAM system generates CL data for creating a sculptured surface and microgrooves. The curved surface is machined with the pickfeed of 5 mm, whose cusp height is calculated as 100 nm. Table 3 shows the cutting condition.
Table 3 Machining condition of microgrooves on a sculptured surface. Milling Rough
Fig. 9. Machined curved microgroove on a spherical surface of 1 mm in radius. (a) Whole view. (b) Enlarged views of curved microgroove.
Spindle rotation (min 1) Feed rate (mm min 1) Depth of cut (mm)
30,000 80 10
Microgrooving Finish
Rough
Finish
20 1
– 80 1
40 0.5
56
Y. Takeuchi et al. / CIRP Annals - Manufacturing Technology 58 (2009) 53–56
Fig. 12. Whole view of machined workpiece and enlarged views of parallel microgrooves and S-shaped microgroove on the sculptured surface. (a) Whole view of machined workpiece. (b) Enlarged view of parallel microgrooves of 30 mm in pitch (I). (c) Enlarged view of parallel microgrooves of 25 mm in pitch (II). (d) Enlarged view of S-shaped microgroove (III).
The cutting experiments are performed by use of NC data converted from the above CL data with the cutting condition. The work material is oxygen-free copper. Fig. 12(a) shows photographs of the machined microgrooves on the sculptured surface. As seen from Fig. 12(b) and (c), there is no burr formation at the valley of parallel microgrooves, and the sharp edges are observed at the ridgelines. However, slight twist takes place on the ridgelines, and striped pattern is seen on the slope. This may be due to the small chattering. With regard to S-shaped microgroove, no burr is observed on the ridgeline, as shown in Fig. 12(d). The total cutting time of sculptured surface and microgrooves is 33 and 4 h, respectively. 5. Conclusion Aiming at creating complicated small shapes such as multifunctional optical devices accurately and finely, CAM system for 6axis control machining is developed, where non-rotational diamond
cutting tool is used. The system is applied to generate microgrooves on a sculptured surface. From cutting experiments by use of a 5/6axis control ultraprecision machining center, it is found that the system has the potential of creating complicated small shapes. References [1] Takino H, Kawai T, Takeuchi Y (2007) 5-Axis Control Ultra-precision Machining of Complex-shaped Mirrors for Extreme Ultraviolet Lithography System. Annals of the CIRP 55(1):123–126. [2] Suzuki H, Moriwaki T, Yamamoto Y, Goto Y (2007) Precision Cutting of Aspherical Ceramic Molds Wit Micro OCD Milling Tool. Annals of the CIRP 56(1):131– 134. [3] Suzuki N, Haritani M, Yang J, Hino R, Shamoto E (2007) Elliptical Vibration Cutting of Tungsten Alloy Molds for Optical Glass Parts. Annals of the CIRP 56(1):127–130. [4] Flucke C, Glade R, Brinksmeier E (2007) Diamond Micro Chiseling - Cutting of Prismatic Micro Optic Arrays. Proceedings of 7th EUSPEN, 173–176. [5] Takeuchi Y, Sakaida H, Sawada K, Sata T (2000) Development of 5-Axis Control Ultraprecision Milling Machine for Micromachining Based on Non-Friction Servomechanism. Annals of the CIRP 49(1):295–298.
Contents lists available at ScienceDirect
CIRP Annals - Manufacturing Technology jou rnal homep age : ht t p: // ees .e lse vi er. com/ci rp/ def a ult . asp
6-Axis control ultraprecision microgrooving on sculptured surfaces with non-rotational cutting tool Y. Takeuchi (1)a,*, Y. Yoneyama a, T. Ishida a, T. Kawai b a b
Dept. of Mechanical Engineering, Graduate School of Engineering, Osaka University, Yamadaoka 2-1, Suita, Osaka, Japan FANUC Ltd., Oshino, Yamanashi, Japan
A R T I C L E I N F O
A B S T R A C T
Keywords: Microgroove Ultraprecision machining 6-Axis control
New optical devices with multi-functions such as diffraction and focusing have been recently required to miniaturize optical systems and to decrease cost. However, their shape is generally very complicated. Typical example is a curved microgroove on a three-dimensional complex surface. To machine the shape, a non-rotational cutting tool is employed in the study. In case of machining microgrooves on sculptured surface with a non-rotational cutting tool, 6-axis control is inevitable to control tool attitude and tool direction. The study deals with the development of CAM system for 6-axis control ultraprecision microgrooving. ß 2009 CIRP.
1. Introduction In optical electronics systems, a variety of fundamental optical devices such as mirrors, lenses, diffraction grating, etc. are used in combination to comprise optical systems [1]. This causes the problem that the arrangement error of these devices influences the total accuracy of the optical systems. The best way to solve such a problem is to realize single multi-function device by forming a diffraction grating and/or refractor on a micro-spherical lens. Then, it is required to accurately create sculptured surfaces as lens or mirror [2] and to finely generate curved microgrooves on their surface [3] as multi-functional devices. To machine such a complicated microgroove, turning or milling by use of a rotational cutting tool is not suitable due to tool interference. Thus, the machining technology by use of nonrotational cutting tools has been studied [4]. The cutting speed in non-rotational cutting is equal to the feed rate, thus resulting in low efficient machining. However, it enables grooving with high degree of freedom, compared with rotational cutting tools. In the case of machining curved microgrooves on sculptured surfaces with a non-rotational cutting tool, 6-axis control is inevitable to control tool attitude and tool direction. This study deals with the development of a CAM system for 6-axis control for ultraprecision microgrooving on sculptured surfaces. 2. Ultraprecision machining center with diamond cutting tool and CAM system 5-Axis control ultraprecision machining center is utilized, which has three translational axes, X, Y, Z and two rotational axes, B and C. The characteristic of the machine tool is that there is no
* Corresponding author. 0007-8506/$ – see front matter ß 2009 CIRP. doi:10.1016/j.cirp.2009.03.124
friction within it. The positioning accuracy of translational axes is 1 nm and the rotational positioning one of rotational axes is 0.000018 [5]. In order to carry out 6-axis control machining, the ultraprecision machining center is equipped with an additional rotational axis A on the B axis. A non-rotational single crystal diamond cutting tool, whose top angle is 908, is mounted on the A axis, and a workpiece is attached to the C axis through a jig. The cutting tool is set so that the tool end can correspond with the rotational center of A and B axes. As the shape of multi-functional optical devices is in general complicated, it is designed by use of 3D-CAD systems. Our own CAM system to generate NC data for 6-axis control ultraprecision machining center is developed, which consists of the mainprocessor and the postprocessor. The mainprocessor generates cutter location (CL) data to make not only sculptured surfaces but also microgrooves from a defined shape of multi-functional optical devices. Sculptures surfaces can be machined by use of rotational cutting tools by 3-axis or 5-axis control. The postprocessor transforms CL data to NC data corresponding to 3-axis, 5-axis and 6-axis control machinings. Especially, the postprocessor for 6-axis control determines a rotational angle of each axis; B and C from the coordinates of a cutting point and the tool axis vector at the cutting point, and A from the cutting direction vector and the calculated angles of B and C. 3. Microgrooving on a spherical surface In order to make sure the validity of the developed CAM system, a simple shape is machined, whose shape has five latticed microgrooves of 30 mm in width and 15 mm in depth on the spherical surface of 3 mm in diameter and in the center radius of curvature, as illustrated in Fig. 1. Two cutting processes such as turning and 6-axis control grooving are usually required to create the figure by
Y. Takeuchi et al. / CIRP Annals - Manufacturing Technology 58 (2009) 53–56
54
Fig. 1. Target object of grid microgrooves on a spherical surface. Fig. 3. Appearances in tuning spherical surfaces and in microgrooving. (a) Turning of a spherical surface. (b) Microgrooving with 6-axis control.
Fig. 2. Machining method of microgrooves on a spherical surface with one cutting tool. (a) Turning of a spherical surface by use of side edge. (b) Microgrooving by use of top edge.
changing the cutting tool and the cutting process. However, the change in process and tool causes the deterioration of the machining accuracy due to the difficulty of the accurate positioning. Thus, the cutting method shown in Fig. 2 is adopted to solve the above problem. At first, the non-rotational tool is mounted to the A axis, and the workpiece to the spindle on the C axis. The spherical surface is machined by using the linear cutting edge of nonrotational tool, while rotating the workpiece, as illustrated in Fig. 2(a). Then, the workpiece is mounted to the C axis by use of a jig. Microgrooves are created by using the top edge of the nonrotational tool, as illustrated in Fig. 2(b). The machining method can partly eliminate the deterioration of machining accuracy although the workpiece is moved. The cutting conditions are listed in Table 1. The work material is oxygen-free copper, and kerosene is used as coolant. Fig. 3(a) and (b) shows the actual spherical cutting and microgrooving, respectively. Fig. 4 shows images of the machined microgrooves from a microscope and a SEM. There seems to be no burr formation on the edge of microgrooves. It is also confirmed that accurate machining is accomplished since two microgrooves precisely cross each other at the intersecting point. In the next stage, as a complicated shape, a curved groove of 30 mm in width and 15 mm in depth is created on a spherical
Fig. 4. Machined grid microgrooves on a spherical surface of 3 mm in diameter. (a) Whole view. (b) Enlarged views of microgrooves.
Fig. 5. Target shape of curved microgrooves on a spherical surface.
surface of 1 mm in diameter and in the center radius of curvature, as illustrated in Fig. 5. The shape is defined by projecting a curved line generated on a plane onto the spherical surface, as illustrated in Fig. 6. Based on the defined shape, our CAM system generates CL data for grooving. Fig. 7 is the generated CL data, where the tool axes are represented as cylinders. The cutting experiment is performed by use of the NC data converted from the CL data under the cutting conditions of Table 2.
Table 1 Machining condition of grid microgrooves on a spherical surface. Turning Rough Spindle rotation (min 1) Feed rate (mm min 1) Depth of cut (mm)
30,000 3 1
Microgrooving Finish
Rough
Finish
1 0.5
– 40 1
10 0.5
Fig. 6. Definition of a curved microgroove on a spherical surface.
Y. Takeuchi et al. / CIRP Annals - Manufacturing Technology 58 (2009) 53–56
55
Fig. 10. Target shape of microgrooves on a sculptured surface. (a) Whole view of sculptured surface. (b) Microgrooves to be machined.
Fig. 7. Generated CL data for microgrooving.
Table 2 Machining condition of curved microgrooves on a spherical surface. Turning
1
Spindle rotation (min ) Feed rate (mm min 1) Depth of cut (mm)
Microgrooving
Rough
Finish
Rough
Finish
30,000 20 1
20 1
– 40 1
10 0.5
Fig. 11. Appearances in milling sculptured surface and in microgrooving. (a) Milling of a sculptured surface with 5-axis control. (b) Microgrooving with 6-axis control.
position error between the tool and the workpiece caused by detaching the workpiece from the C axis and attaching it again to the C axis through a jig. 4. Microgrooving on sculptured surface
Fig. 8. Curved microgroove on a spherical surface of 1 mm in radius. (a) Result of machining simulation. (b) Machined workpiece.
Fig. 8(a) and (b) shows the machining simulation result and a photograph of the machined piece, respectively. Fig. 9 is a SEM image of the machined groove, where no burr formation takes place. Although the microgrooving is well performed, the groove width is not necessarily uniform. This may be due to the relative
The shape to be created as microgrooves on a sculptured surface is illustrated in Fig. 10. The sculptured surface with a maximum undulating difference of 0.1 mm is defined on the area of 1 mm square. Two kinds of microgrooves are machined; parallel ones and curved ones. Parallel microgrooves of 15 mm in depth are divided into two groups by the groove pitch, i.e. 30 and 25 mm. A curved microgroove is S-shaped and 5 mm in depth and 10 mm in width. In this case, the workpiece shape is created by use of 5-axis control machining with a rotational cutting tool and 6-axis control machining with a non-rotational one to reconcile the machining efficiency and the machining error suppression, as illustrated in Fig. 11. A rotational tool is used so as to create a curved surface efficiently. In case of 5-axis control machining using a rotational single crystal diamond tool of 0.04 mm in radius, a high speed spindle with the rotational tool is mounted to the B axis, and a jig with the workpiece is fixed to the C axis, as shown in Fig. 11(a). In case of 6-axis control grooving, as shown in Fig. 11(b), the A axis with a non-rotational diamond tool is mounted on the B axis by removing the spindle. Our CAM system generates CL data for creating a sculptured surface and microgrooves. The curved surface is machined with the pickfeed of 5 mm, whose cusp height is calculated as 100 nm. Table 3 shows the cutting condition.
Table 3 Machining condition of microgrooves on a sculptured surface. Milling Rough
Fig. 9. Machined curved microgroove on a spherical surface of 1 mm in radius. (a) Whole view. (b) Enlarged views of curved microgroove.
Spindle rotation (min 1) Feed rate (mm min 1) Depth of cut (mm)
30,000 80 10
Microgrooving Finish
Rough
Finish
20 1
– 80 1
40 0.5
56
Y. Takeuchi et al. / CIRP Annals - Manufacturing Technology 58 (2009) 53–56
Fig. 12. Whole view of machined workpiece and enlarged views of parallel microgrooves and S-shaped microgroove on the sculptured surface. (a) Whole view of machined workpiece. (b) Enlarged view of parallel microgrooves of 30 mm in pitch (I). (c) Enlarged view of parallel microgrooves of 25 mm in pitch (II). (d) Enlarged view of S-shaped microgroove (III).
The cutting experiments are performed by use of NC data converted from the above CL data with the cutting condition. The work material is oxygen-free copper. Fig. 12(a) shows photographs of the machined microgrooves on the sculptured surface. As seen from Fig. 12(b) and (c), there is no burr formation at the valley of parallel microgrooves, and the sharp edges are observed at the ridgelines. However, slight twist takes place on the ridgelines, and striped pattern is seen on the slope. This may be due to the small chattering. With regard to S-shaped microgroove, no burr is observed on the ridgeline, as shown in Fig. 12(d). The total cutting time of sculptured surface and microgrooves is 33 and 4 h, respectively. 5. Conclusion Aiming at creating complicated small shapes such as multifunctional optical devices accurately and finely, CAM system for 6axis control machining is developed, where non-rotational diamond
cutting tool is used. The system is applied to generate microgrooves on a sculptured surface. From cutting experiments by use of a 5/6axis control ultraprecision machining center, it is found that the system has the potential of creating complicated small shapes. References [1] Takino H, Kawai T, Takeuchi Y (2007) 5-Axis Control Ultra-precision Machining of Complex-shaped Mirrors for Extreme Ultraviolet Lithography System. Annals of the CIRP 55(1):123–126. [2] Suzuki H, Moriwaki T, Yamamoto Y, Goto Y (2007) Precision Cutting of Aspherical Ceramic Molds Wit Micro OCD Milling Tool. Annals of the CIRP 56(1):131– 134. [3] Suzuki N, Haritani M, Yang J, Hino R, Shamoto E (2007) Elliptical Vibration Cutting of Tungsten Alloy Molds for Optical Glass Parts. Annals of the CIRP 56(1):127–130. [4] Flucke C, Glade R, Brinksmeier E (2007) Diamond Micro Chiseling - Cutting of Prismatic Micro Optic Arrays. Proceedings of 7th EUSPEN, 173–176. [5] Takeuchi Y, Sakaida H, Sawada K, Sata T (2000) Development of 5-Axis Control Ultraprecision Milling Machine for Micromachining Based on Non-Friction Servomechanism. Annals of the CIRP 49(1):295–298.