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Development of an Advanced Tool-Setting Device for Diamond Turning
Development of an Advanced Tool-Setting Device for Diamond Turning M. Sawa, Y. Maeda, M. Masuda, Production Engineering Research Laboratory, Hitachi, Ltd.; R. Ito, Data Storage Et Retrieval Systems Division, Hitachi, LtdJJapan - Submitted by T. Moriwaki (1) Received on January 12,1993 M. Sawa, Y. Maeda, M. Masuda; Production Engineering Research Laboratory, Hitachi, Ltd. ; R. Ito: Data Storage & Retrieval Systems Division, Hitachi, Ltd. / J a p a n - Submitted by T. Moriwaki (1) Summery: This paper describes development of an advanced tool setting device for diamond turning. In order to machine a magnetic recording disk substrate (Al-Mg alloy) t o a mirror-finished surface of less than 0.03 pm Rmax using a diamond cutting tool, a mechanism has been developed for automatic adjustment of the tool setting angle, which is a very important factor to obtain a smooth machined surface. The adjustment of the tool setting angle, which has previously been done by skilled operators, is now automated and the angular tolerance subjected to the tool replacement has been improved to an accuracy o f f 1.4 x 10-3 degrees. The machined surface roughness has also been improved to less than 0.03 pm Rmax. Moreover, the time required for the tool setting angle adjustment has been shortened to 5 minutes as compared to between 15 and 45 minutes required by the conventional manual adjustment. Key Words: aluminum alloys, diamond tools, diamond turning machines, ultra-precision machining Introduction table with roller guide (minimum traverse: 0.5 p d s t e p ) . Machining A1 alloys t o generate mirror-finished The bed of the machine is made of granite and supported surfaces retains its importance in mass producing parts by four air-servo mounts. such as magnetic disk substrates and optical mirrors. The The cutting conditions shown in Table 1 were adopted accuracy requirement for such parts is becoming stricter for most of the experiments unless otherwise noted, to following advances in performance of the products into machine the end face of a magnetic disk substrate. Figure which such parts are to be integrated. For example, 1shows the geometry of straight tool made of single crystal magnetic disk units have increased the recording density diamond which is employed for the tests. The tool was 20 times in the last decade. Such increase in recording polished after purchasing from a tool manufacturer to density has accompanied reductions in the film thickness make the straightness of the end cutting edge smaller than of the recording medium for the magnetic disk, as well as 0.03 p d l . 2 mm. The profile of the machined surface was decreases in flotation height of the magnetic head. The measured in the tool feed direction with a surface surface roughness of the disk substrate at present must be roughness measuring instrument (TalysurD, and the tool of the order of 0.01 pm Rmax. setting angle was determined based on the plunge cut The surface roughness obtained by machining the disk profile measured off-line with the instrument. In addition, substrate (Al-Mg alloy) to a mirror-like surface using a the machined surface was examined with a Nomarski type diamond tool is closely correlated to the feed rate of the tool microscope (magnification: x200) t o determine whether any a n d t h e theoretical surface roughness, which is defect exists. geometrically determined by the cutting edge profile (1). In order to obtain a good machined surface, the tool setting angle must be adjusted accurately (2). Recently, an ultraprecision lathe with micro-cutting device to realize submicrometer cutting has been developed (3,4,5,6). However, no research has been carried out on tool setting adjustment. The conventional method to adjust the tool I Feed rate I 50pmlrev I setting angle is that a skilled operator machines a surface, using a tool set a t a tool setting angle based on his I DeDth Of C u t 1 1 0 p m I experience, and adjusts the angle while visually observing I CUttlng fluid I White kerosene I the machined surface. With this way of adjusting the tool setting angle, some scatter in roughness is unavoidable among the machined surfaces for different operators. The adjustment of tool setting angle has been a major hindrance in the machining of disk substrates to mirrorlike surfaces using diamond tools in- terms of quality control in mass production. In order to obtain stable mirror-finished surfaces of AlMg alloy magnetic disk substrates using diamond tools, a device is developed that automatically adjusts the tool setting angle on-machine. This device is mounted onto an ultra-precision lathe, which is currently available on the market, and its performance is evaluated 1.
Accuracy of Tool Setting Angle 2.1 Experimental device In order to develop an automatic tool setting device, some preliminary experiments were carried out. For these experiments, an ultra-precision lathe (Model: DPL-400 made by Hitachi Seiko Ltd.) was employed, which consists of a main spindle supported by air bearings (rotational error < 0.05 pm TIR), a sliding table with air hydrostatic guide (yaw error < 0.05 pm / 100 mm), and a cross slide 2.
Annals of the ClRP Vol. 42/1/1993
Fig. 1
Geometry and setting of straight diamond tool
2.2 Method of in-situ measuring and accuracy of tool
setting angle In order to ensure that a magnetic head floats at a height of 0.3 pm above the magnetic disk, it is necessary to
87
finish the surface of the magnetic disk substrate to a roughness within 0.03 um Rmax. Figure 2 (2) shows the surface roughness obtained by machining the magnetic disk substrates with a sharp straight tool set at tool setting angles from - 0.1 degrees to 0.1 degrees. The figure shows that the tool setting angle must be kept within a range of - 0.0100 k 0.0014 degrees ( f 5 ' in order to produce a machined surface of roughness from 0.02 to 0.025 urn Rmax without tearing. This angle tolerance, 1.4 x 10-3 degrees, is equivalent t o the end-cutting edge inclination of 0.03 p d 1 . 2 mm. The resolution of the tool setting angle was therefore set to 0.01 pm.
-
E 0.51
I , ,
-0.1'
-001'
,
-
c3IPoslttve tool settino angle1
!Negative tool sett!no angle)-
rt41~' " '
0 0.GGf' Tool setting angle 8 -0M)l'
GJ1'
i-0
I
"
'
0.1'
'
Fig. 2 Effect of tool setting angle on machined surface roughness
Possible methods of in-situ measuring of the tool setting angle include one that detects the slope of the grooved bottcm formed through plunge cutting by irradiating with a laser beam (7) or by tracing with a stylus-type sensor, as well as one that estimates the machined surface roughness by using optical measuring methods based on focused system, diffraction, interference or gloss techniques (8310). The optical measuring method enables measurement of a workpiece surface while it is rotating; however, its measuring accuracy is adversely affected by the cutting fluid or by fine chips that remain on the machined surface. On the other hand, the stylus-type sensor takes highly reliable measurements in the machining environment of a workshop and easily produces a detection resolution of 0.01 pm although a workpiece must be stopped prior to measurement. For these reasons, the stylus method was adopted to in-situ measuring of the plunge cut profile to detect the tool setting angle.
3. Development of Tool Setting Device 3.1 C o n s t r u c t i o n and operation of tool setting device Figure 3 shows the ultra-precision lathe and the tool setting device developed. A tool holder swivel structure and a stylus-type sensor are installed on the cross slide table of the lathe. Figure 4 shows the construction and the operation of the device schematically. The operation of the device shown in Fig. 4(a) is as follows; firstly, an end face is machined to generate a tool reference plane, secondly, part of the machined end face is plunge cut to transfer the tool profile, thirdly, the transferred tool profile is measured with the stylus-type sensor. The slope of the end cutting edge to the tool reference plane is calculated based on the measured data, and the error in the preset angle is corrected. The whole process is repeated until the tool setting angle falls within the allowable tolerance of 1 . 4 ~ 1 0 -degrees 3 to the preset value. 3.2 Tool holder swivel structure The conventional tool holder swivel structure employs a system which swivels the tool holder with a pair of push pull screws, verifies the amount of travel with the dial indicator, and bolts down the tool holder to the table. Bolting down causes the tool holder to move slightly, which makes it rather difficult to secure an angular accuracy of f 1.4 x 10-3 degrees. The tool holder swivel structure developed here is capable of adjusting the tool setting angle with high accuracy. The structure of the device is shown in Fig. 4(b), (c). In order to prevent the tool holder from becoming distorted when it is bolted down, the tool holder is designed to clamp vertically against its securing surface by the disc spring and the piezoelectric actuator. A
U
PIunae-cut
Measurement
n v
U
v
(a) Operation of device
Tool
(b) Structure of device
holder
Stacked
Fixed suroort/ (c) Sectional view of PZT clamp Fig. 3 Ultra-precision lathe and tool setting device
88
Fig. 4 Schematic illustration of operation and structure of tool setting device
laminated piezoelectric actuator was selected, which generates a thrust force of 3500 N to clamp the tool holder. The stroke of the piezoelectric actuator is as small as 25 pm (when unloaded). The tool holder is clamped with the rod and the disc spring a t a constant thrust force of 1600 N. When the tool holder is unclamped, the rod is lifted up for 15 pm as a DC voltage is applied to the piezoelectric actuator. The tool holder is rotated by the stepping motor through the lead screw arranged at the side of the lever of the holder. The resolution of the linear displacement of the lead screw is set t o 1.25 pdpulse, which is equivalent t o the rotational resolution of 7.0 x 10-4 degrees of the tool holder. In order to prevent positioning errors caused by the frictional force acting on the surface of the lever, a preload (3.1 Nm) equivalent t o the static frictional force, but higher than the starting torque (1Nm), is applied from the opposite side of the lead screw. Figure 5 shows the performance of the tool holder swivel structure. The linear displacement of the lead screw was measured, and the rotating angle of the tool holder can be obtained by converting the linear displacement measured against the rotating radius of 103.1 mm. The following remarks are derived from Fig. 5. a. Over 30 pm of travel, the linear positioning error is 2 pm. This error is equivalent to the rotational positioning error of 1.1x 10-3 degrees over a range of 1.7 x 10-2 degrees. b. The repeatability is 0.1 pm, which is equivalent to 6.0 x 10-5 degrees. c. The backlash is 0.2 pm, which is equivalent to 1.1 x 1 0 - 4 degrees. The above results indicate that the tool setting device developed is capable of producing a rotational resolution of f 1.4 x 10-3degrees.
Positioning
error
Reoeatablib
Backlash
Fig. 5
Performance of tool setting device
the profile, a stylus with a tip radius of 5 pm was employed a t a contact pressure of 0.5 mN. Figure 6 indicates differences in the burr height of the plunge cut groove due to differences in the contact pressure and the stylus tip radius. Except for this, the measured tool profile patterns in the grooved bottom are almost identical. The sensitivity of the stylus-type sensor is 1.125 V/pm, and the resolution becomes 0.005 pm when the entire measuring range of 20 pm is converted with an A/D converter of 12 bits. The tracing speed of the stylus and sampling interval are set to 0.5 mm/s and 5 ms respectively, which gives a resolution of 2.5 pm in the direction of tracing. The tracing speed was adjusted t o not fluctuate by more than 0.008 m d s . The fluctuation in tracing speed corresponds t o 2.0 x 10-4 degrees when converted into the tool setting angular error.
Fig. 6 Profiles of plunge cut surface measured with Talysurf and with developed device
3.4 Calculation of tool setting angle
Figure 7 shows how to calculate the slope of the endcutting edge from the profile of the tool left on the reference plane. The Y-axis in the figure shows the reading of the profile along the tool feed direction. Y-axis data (Yi) are simply averaged to obtain the average value Ys. The group of data (Yi - Ys) 2 0 are assumed to represent the tool reference plane, while those of (Yi - Ys) < 0 is the tool profile. Linear regression of both the tool reference plane data and the tool profile data in the equation y = ax + b produces two straight lines. The difference in the linear slope a1 and a2 is defined as the tool setting angle em. The difference between the preinput tool setting angle 6 and the measured tool setting angle 6m is input to the stepping motor of the tool holder swivel structure to correct the tool setting angle.
5
-
3.3 Detection of tool setting angle A stylus-type sensor was placed horizontally when taking measurements on the face lathe. A stylus with a tip radius of 8 pm was adopted and its contact pressure was selected to be 0.9 mN, in order to minimize flaws that would be produced on the machined surface when the surface is measured with the stylus-type sensor. Figure 6 compares the profiles of the cutting edge generated by plunge cutting: one of which is measured offline using a Talysurf and the other is measured in-situ using the developed device. For off-line measurement of
!2
A
TOO1 s e t t i n g angle:-0.0069" r
0
0
: j.5 Measuring
2
2.5
length
3
3.5
d
(mm)
Fig. 7 Profile measured and tool setting angle calculated
89
Experimental Results and Discussions Figure 8 compares the tool setting angle measured insitu using the device and that measured off-line using the stylus-type surface roughness measuring instrument (Talysurf). This figure indicates that the angular error in the tool setting falls within k 1.4 x 10-3 degrees. 4.
plane by plunge cutting, the profile of the cutting edge is measured with a stylus-type sensor to calculate and the inclination of the tool profile, and the tool setting angle is adjusted. (2) The following improvement is accomplished by introducing the automatic tool setting device as compared with the previous manual adjustment done by skilled operators: a. The angular tolerance subjected t o t h e tool replacement has been improved to k 1.4 x 10-3 degrees; b. The machined surface roughness has been improved to less than 0.03 pm Rmax; c. The time for the tool setting angle adjustment has been shortened to 5 minutes as compared with between 15 and 45 minutes required by the conventional manual adjustment.
Tool setting angle measured Talysurf
with
Fig. 8 Relationship between tool setting angles measured with Talysurf and with developed device Figure 9 compares the tool setting angle, the machined surface roughness, and the time required t o adjust the tool setting angle obtained by the conventional tool setting procedure and by the tool setting device developed. In the conventional procedure, the tool setting angle is adjusted manually based on the visual evaluation of the machined surface. The following - 9. - remarks are derived from Fig. The tool setting angle adjusted manually shows a large scatter from - 4.6 x 10-3degrees to - 2.0 x 10-2degrees, whereas that of automatic adjustment is reduced as low as - 8.6 x 10-3degrees to - 1.1 x 10-2 degrees. The machined surface roughness is closely correlated with the tool setting angle. Due to decrease in the scatter of the tool setting angle, surface roughness is reduced down to 0.02 to 0.03 pm Rmax by adjusting the tool setting automatically. The time required to adjust the tool setting angle is reduced between 15 and 45 minutes to 5 minutes by adopting the automatic adjustment. -0.03’-
N=29
Manual -0.02’-
___
-O.M.--
-a
setlma
0-
Fig. 9 Evaluation of the tool setting device
Conclusions A mechanism of automatic tool setting angle adjustment has been developed for an ultra-precision lathe so that the magnetic recording disk substrates (Al-Mg alloy) can be machined to mirror-finished surfaces of less than 0.03 pm Rmax. The following remarks are concluded. (1) The method to adjust the tool setting angle automatically has been newly developed, which works as follows; i.e. the reference plane is diamond turned, the profile of the cutting edge is transferred onto the
90
References (1) Takasu, S., Masuda, M., Nishiguchi, T., 1985, Influence of Steady Vibration with Small Amplitude upon Surface Roughness in Diamond Machining, Annals of CIRP, 34:463 - 467. (2) Nishiguchi, T., Maeda, Y., Masuda, M., Sawa, M., Ito, R., 1988, Mechanism of Micro Chip Formation in Diamond Turning of Al-Mg Alloy, Annals of CIRP, 37:117 - 121. (3) Wills-Moren, W.J., Modjarrad, H., Read, R.F.J., Mckeown, P.A., 1982, Some Aspects of the Design and Development of a Large High Precision CNC Diamond Turning Machine, Annals of CIRP, 31: 409 - 414. (4) Furukawa, Y., Moronuki, N., Kitagawa, K., 1986, Development of Ultra Precision Machine Tool Made of Ceramics, Annals of CIRP, 35: 279 - 282. (5) Moriwaki, T., 1988, Thermal Deformation and Its OnLine Compensation of Hydrostatically Supported Precision Spindle, Annals of CIRP, 37: 393 - 396. (6) Hara, Y., Motonishi, S., Yoshida, K., 1990, A new Micro-Cutting Device with High Stiffness and Resolution, Annals of CIRP, 39: 375 - 378. (7) Kawana, 1985, Tool Setting Equipment for Precision Lathe, Japan Patent Bulletin, 1985:271(No. 60 34248). (8) Brodmann, R., Gast, Th., Thurn, G., 1984, An Optical Instrument for Measuring the Surface Roughness in Production Control, Annals of CIRP, 33:403 - 406. (9) Lee, C. S., Kim, S. W., 1987, An In-Process Measurement Technique Using Laser for Non-Contact Monitoring of Surface Roughness and Form Accuracy of Ground Surface, Annals of CIRP, 36:425 - 428. (lO)Whitehouse, D. J., 1991, Nanotechnology instrumentation, Measurement and Control, 24:37 46.
Accuracy of Tool Setting Angle 2.1 Experimental device In order to develop an automatic tool setting device, some preliminary experiments were carried out. For these experiments, an ultra-precision lathe (Model: DPL-400 made by Hitachi Seiko Ltd.) was employed, which consists of a main spindle supported by air bearings (rotational error < 0.05 pm TIR), a sliding table with air hydrostatic guide (yaw error < 0.05 pm / 100 mm), and a cross slide 2.
Annals of the ClRP Vol. 42/1/1993
Fig. 1
Geometry and setting of straight diamond tool
2.2 Method of in-situ measuring and accuracy of tool
setting angle In order to ensure that a magnetic head floats at a height of 0.3 pm above the magnetic disk, it is necessary to
87
finish the surface of the magnetic disk substrate to a roughness within 0.03 um Rmax. Figure 2 (2) shows the surface roughness obtained by machining the magnetic disk substrates with a sharp straight tool set at tool setting angles from - 0.1 degrees to 0.1 degrees. The figure shows that the tool setting angle must be kept within a range of - 0.0100 k 0.0014 degrees ( f 5 ' in order to produce a machined surface of roughness from 0.02 to 0.025 urn Rmax without tearing. This angle tolerance, 1.4 x 10-3 degrees, is equivalent t o the end-cutting edge inclination of 0.03 p d 1 . 2 mm. The resolution of the tool setting angle was therefore set to 0.01 pm.
-
E 0.51
I , ,
-0.1'
-001'
,
-
c3IPoslttve tool settino angle1
!Negative tool sett!no angle)-
rt41~' " '
0 0.GGf' Tool setting angle 8 -0M)l'
GJ1'
i-0
I
"
'
0.1'
'
Fig. 2 Effect of tool setting angle on machined surface roughness
Possible methods of in-situ measuring of the tool setting angle include one that detects the slope of the grooved bottcm formed through plunge cutting by irradiating with a laser beam (7) or by tracing with a stylus-type sensor, as well as one that estimates the machined surface roughness by using optical measuring methods based on focused system, diffraction, interference or gloss techniques (8310). The optical measuring method enables measurement of a workpiece surface while it is rotating; however, its measuring accuracy is adversely affected by the cutting fluid or by fine chips that remain on the machined surface. On the other hand, the stylus-type sensor takes highly reliable measurements in the machining environment of a workshop and easily produces a detection resolution of 0.01 pm although a workpiece must be stopped prior to measurement. For these reasons, the stylus method was adopted to in-situ measuring of the plunge cut profile to detect the tool setting angle.
3. Development of Tool Setting Device 3.1 C o n s t r u c t i o n and operation of tool setting device Figure 3 shows the ultra-precision lathe and the tool setting device developed. A tool holder swivel structure and a stylus-type sensor are installed on the cross slide table of the lathe. Figure 4 shows the construction and the operation of the device schematically. The operation of the device shown in Fig. 4(a) is as follows; firstly, an end face is machined to generate a tool reference plane, secondly, part of the machined end face is plunge cut to transfer the tool profile, thirdly, the transferred tool profile is measured with the stylus-type sensor. The slope of the end cutting edge to the tool reference plane is calculated based on the measured data, and the error in the preset angle is corrected. The whole process is repeated until the tool setting angle falls within the allowable tolerance of 1 . 4 ~ 1 0 -degrees 3 to the preset value. 3.2 Tool holder swivel structure The conventional tool holder swivel structure employs a system which swivels the tool holder with a pair of push pull screws, verifies the amount of travel with the dial indicator, and bolts down the tool holder to the table. Bolting down causes the tool holder to move slightly, which makes it rather difficult to secure an angular accuracy of f 1.4 x 10-3 degrees. The tool holder swivel structure developed here is capable of adjusting the tool setting angle with high accuracy. The structure of the device is shown in Fig. 4(b), (c). In order to prevent the tool holder from becoming distorted when it is bolted down, the tool holder is designed to clamp vertically against its securing surface by the disc spring and the piezoelectric actuator. A
U
PIunae-cut
Measurement
n v
U
v
(a) Operation of device
Tool
(b) Structure of device
holder
Stacked
Fixed suroort/ (c) Sectional view of PZT clamp Fig. 3 Ultra-precision lathe and tool setting device
88
Fig. 4 Schematic illustration of operation and structure of tool setting device
laminated piezoelectric actuator was selected, which generates a thrust force of 3500 N to clamp the tool holder. The stroke of the piezoelectric actuator is as small as 25 pm (when unloaded). The tool holder is clamped with the rod and the disc spring a t a constant thrust force of 1600 N. When the tool holder is unclamped, the rod is lifted up for 15 pm as a DC voltage is applied to the piezoelectric actuator. The tool holder is rotated by the stepping motor through the lead screw arranged at the side of the lever of the holder. The resolution of the linear displacement of the lead screw is set t o 1.25 pdpulse, which is equivalent t o the rotational resolution of 7.0 x 10-4 degrees of the tool holder. In order to prevent positioning errors caused by the frictional force acting on the surface of the lever, a preload (3.1 Nm) equivalent t o the static frictional force, but higher than the starting torque (1Nm), is applied from the opposite side of the lead screw. Figure 5 shows the performance of the tool holder swivel structure. The linear displacement of the lead screw was measured, and the rotating angle of the tool holder can be obtained by converting the linear displacement measured against the rotating radius of 103.1 mm. The following remarks are derived from Fig. 5. a. Over 30 pm of travel, the linear positioning error is 2 pm. This error is equivalent to the rotational positioning error of 1.1x 10-3 degrees over a range of 1.7 x 10-2 degrees. b. The repeatability is 0.1 pm, which is equivalent to 6.0 x 10-5 degrees. c. The backlash is 0.2 pm, which is equivalent to 1.1 x 1 0 - 4 degrees. The above results indicate that the tool setting device developed is capable of producing a rotational resolution of f 1.4 x 10-3degrees.
Positioning
error
Reoeatablib
Backlash
Fig. 5
Performance of tool setting device
the profile, a stylus with a tip radius of 5 pm was employed a t a contact pressure of 0.5 mN. Figure 6 indicates differences in the burr height of the plunge cut groove due to differences in the contact pressure and the stylus tip radius. Except for this, the measured tool profile patterns in the grooved bottom are almost identical. The sensitivity of the stylus-type sensor is 1.125 V/pm, and the resolution becomes 0.005 pm when the entire measuring range of 20 pm is converted with an A/D converter of 12 bits. The tracing speed of the stylus and sampling interval are set to 0.5 mm/s and 5 ms respectively, which gives a resolution of 2.5 pm in the direction of tracing. The tracing speed was adjusted t o not fluctuate by more than 0.008 m d s . The fluctuation in tracing speed corresponds t o 2.0 x 10-4 degrees when converted into the tool setting angular error.
Fig. 6 Profiles of plunge cut surface measured with Talysurf and with developed device
3.4 Calculation of tool setting angle
Figure 7 shows how to calculate the slope of the endcutting edge from the profile of the tool left on the reference plane. The Y-axis in the figure shows the reading of the profile along the tool feed direction. Y-axis data (Yi) are simply averaged to obtain the average value Ys. The group of data (Yi - Ys) 2 0 are assumed to represent the tool reference plane, while those of (Yi - Ys) < 0 is the tool profile. Linear regression of both the tool reference plane data and the tool profile data in the equation y = ax + b produces two straight lines. The difference in the linear slope a1 and a2 is defined as the tool setting angle em. The difference between the preinput tool setting angle 6 and the measured tool setting angle 6m is input to the stepping motor of the tool holder swivel structure to correct the tool setting angle.
5
-
3.3 Detection of tool setting angle A stylus-type sensor was placed horizontally when taking measurements on the face lathe. A stylus with a tip radius of 8 pm was adopted and its contact pressure was selected to be 0.9 mN, in order to minimize flaws that would be produced on the machined surface when the surface is measured with the stylus-type sensor. Figure 6 compares the profiles of the cutting edge generated by plunge cutting: one of which is measured offline using a Talysurf and the other is measured in-situ using the developed device. For off-line measurement of
!2
A
TOO1 s e t t i n g angle:-0.0069" r
0
0
: j.5 Measuring
2
2.5
length
3
3.5
d
(mm)
Fig. 7 Profile measured and tool setting angle calculated
89
Experimental Results and Discussions Figure 8 compares the tool setting angle measured insitu using the device and that measured off-line using the stylus-type surface roughness measuring instrument (Talysurf). This figure indicates that the angular error in the tool setting falls within k 1.4 x 10-3 degrees. 4.
plane by plunge cutting, the profile of the cutting edge is measured with a stylus-type sensor to calculate and the inclination of the tool profile, and the tool setting angle is adjusted. (2) The following improvement is accomplished by introducing the automatic tool setting device as compared with the previous manual adjustment done by skilled operators: a. The angular tolerance subjected t o t h e tool replacement has been improved to k 1.4 x 10-3 degrees; b. The machined surface roughness has been improved to less than 0.03 pm Rmax; c. The time for the tool setting angle adjustment has been shortened to 5 minutes as compared with between 15 and 45 minutes required by the conventional manual adjustment.
Tool setting angle measured Talysurf
with
Fig. 8 Relationship between tool setting angles measured with Talysurf and with developed device Figure 9 compares the tool setting angle, the machined surface roughness, and the time required t o adjust the tool setting angle obtained by the conventional tool setting procedure and by the tool setting device developed. In the conventional procedure, the tool setting angle is adjusted manually based on the visual evaluation of the machined surface. The following - 9. - remarks are derived from Fig. The tool setting angle adjusted manually shows a large scatter from - 4.6 x 10-3degrees to - 2.0 x 10-2degrees, whereas that of automatic adjustment is reduced as low as - 8.6 x 10-3degrees to - 1.1 x 10-2 degrees. The machined surface roughness is closely correlated with the tool setting angle. Due to decrease in the scatter of the tool setting angle, surface roughness is reduced down to 0.02 to 0.03 pm Rmax by adjusting the tool setting automatically. The time required to adjust the tool setting angle is reduced between 15 and 45 minutes to 5 minutes by adopting the automatic adjustment. -0.03’-
N=29
Manual -0.02’-
___
-O.M.--
-a
setlma
0-
Fig. 9 Evaluation of the tool setting device
Conclusions A mechanism of automatic tool setting angle adjustment has been developed for an ultra-precision lathe so that the magnetic recording disk substrates (Al-Mg alloy) can be machined to mirror-finished surfaces of less than 0.03 pm Rmax. The following remarks are concluded. (1) The method to adjust the tool setting angle automatically has been newly developed, which works as follows; i.e. the reference plane is diamond turned, the profile of the cutting edge is transferred onto the
90
References (1) Takasu, S., Masuda, M., Nishiguchi, T., 1985, Influence of Steady Vibration with Small Amplitude upon Surface Roughness in Diamond Machining, Annals of CIRP, 34:463 - 467. (2) Nishiguchi, T., Maeda, Y., Masuda, M., Sawa, M., Ito, R., 1988, Mechanism of Micro Chip Formation in Diamond Turning of Al-Mg Alloy, Annals of CIRP, 37:117 - 121. (3) Wills-Moren, W.J., Modjarrad, H., Read, R.F.J., Mckeown, P.A., 1982, Some Aspects of the Design and Development of a Large High Precision CNC Diamond Turning Machine, Annals of CIRP, 31: 409 - 414. (4) Furukawa, Y., Moronuki, N., Kitagawa, K., 1986, Development of Ultra Precision Machine Tool Made of Ceramics, Annals of CIRP, 35: 279 - 282. (5) Moriwaki, T., 1988, Thermal Deformation and Its OnLine Compensation of Hydrostatically Supported Precision Spindle, Annals of CIRP, 37: 393 - 396. (6) Hara, Y., Motonishi, S., Yoshida, K., 1990, A new Micro-Cutting Device with High Stiffness and Resolution, Annals of CIRP, 39: 375 - 378. (7) Kawana, 1985, Tool Setting Equipment for Precision Lathe, Japan Patent Bulletin, 1985:271(No. 60 34248). (8) Brodmann, R., Gast, Th., Thurn, G., 1984, An Optical Instrument for Measuring the Surface Roughness in Production Control, Annals of CIRP, 33:403 - 406. (9) Lee, C. S., Kim, S. W., 1987, An In-Process Measurement Technique Using Laser for Non-Contact Monitoring of Surface Roughness and Form Accuracy of Ground Surface, Annals of CIRP, 36:425 - 428. (lO)Whitehouse, D. J., 1991, Nanotechnology instrumentation, Measurement and Control, 24:37 46.