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A study on manufacturing technology for an inclined polygon mirror
Journal of Materials Processing Technology 187–188 (2007) 56–59
A study on manufacturing technology for an inclined polygon mirror Soon-Sub Park ∗ , Ho-Jae Lee, Ki-Young Lee, Yeon Hwang Micro Mold and Die Team, Gwang-Ju Research Center, Korea Institute of Industrial Technology (KITECH), Wolchul-dong 971-35, Buk-gu, Gwang-ju 500-460, Republic of Korea
Abstract Generally, the core component of small precise optical device demands high accuracy of manufacturing processes. Although, the geometry of it is simple, the manufacturing technique to materialize is categorized as the ultra precision machining and it must be done with the specialized machines and by the trained operator. Typical examples of small precise optical device are laser printer and phone camera. The shape is very simple but required manufacturing technology is very difficult. It belongs to fine precision machining technique and needs an ultra precision machining center and an assignment researcher. Laser printers and phone cameras are representative examples in small precise optical device. Recently, small sized display device is being developed and has an inclined polygon mirror as core part. The inclined polygon mirror is different with the previous polygon mirror in the point of view that it has a variety of reflection angle. With the result that, multi lines were achieved at screen. It could not be fabricated with conventional machine for a typical polygon mirror. It was manufactured in the process of fly-cutting with Al material on which was coated electroless-Ni for enhancement of hardness. Owing to process of polishing has bad influence on reflection angle, the inclined polygon mirror must be only fabricated with fly-cutting and have surface roughness Rmax = 10 nm and form error Ra = λ/10 (λ = 632 nm). © 2007 Published by Elsevier B.V. Keywords: Inclined polygon mirror; Fly-cutting; Interrupted machining; Ultra precision
1. Introduction The need for optical elements with ultra fine surface roughness and profile accuracy keeps increasing rapidly because of development of IT industry in recent years. Ultra precision mechanical machining is one of the most fundamental and important facilities to meet sub-micrometer profile accuracy and several nano-meter surface roughness. However, quality of machined mirror surface is limited due to various kinds of noises as vibration, thermal deformation, wear of tool, etc. As a result, great efforts were made towards the development of ultra precision machining, in particular, technology for ultra fine mirror surface of nonferrous metal [1,2]. Previous research works have focused mainly on the development of machining technologies, with great emphasis on tool and equipment, but little has so far been reported on parametric investigation of fly-cutting. One of the most successful applications of fly-cutting is the fabrication of ultra precise polygon mirror for laser scanning units which is a core part of laser printer. To achieve the required profile accuracy Ra ≤ λ/10 (λ = 632 nm) and surface roughness Rmax ≤ 10 nm for mirror surface of aluminum ∗
Corresponding author. Tel.: +82 62 600 6151; fax: +82 62 600 6499. E-mail address: [email protected] (S.-S. Park).
0924-0136/$ – see front matter © 2007 Published by Elsevier B.V. doi:10.1016/j.jmatprotec.2006.11.169
alloy, parametric experiments were performed, utilizing single point diamond bite fly-cutting. 2. Experimental setup and test conditions Fly-cutting experiment carried out on a Toshiba ultra precision grinding machine (ULG100H3) using single diamond bite. Commercial aluminum alloy (S3M) was used as a work piece material. Target inclined polygon mirror has 16 mirror surfaces with θ = 0.03◦ angular difference among the surfaces. Each surface was machined with verified feed rate (F), depth of cut (D) and pitch per cycle (P) and evaluated in terms of profile accuracy and surface roughness [3].
2.1. Target polygon mirror In recent years there has been a considerably interest in new design of faster and compact polygon mirror. One of the significant challenges for new concept of polygon mirror is inclined reflecting surface with different angles. Conventional type polygon mirror reflects laser beam and generate single line but inclined type polygon mirror generates multi line.
2.2. Experimental setup As mentioned, profile accuracy Ra ≤ λ/10 (λ = 632 nm) and surface roughness Rmax ≤ 10 nm are requisites for target polygon mirror. In fly-cutting, process for high accuracy surface can reduce the efficiency of machining and takes much time. Moreover, there are few experimental investigations for optimum machining conditions. Therefore, a full factorial experiment design was adopted to
S.-S. Park et al. / Journal of Materials Processing Technology 187–188 (2007) 56–59
57
Table 1 Experimental conditions Bite (material) Bite radius (mm) Inclined angle (◦ ) Mist Feed rate (mm/min) Depth of cut (m) Pitch per cycle (m) Work piece material (S3M, %)
Single crystal diamond 5 0.03 Semi-dry cutting 10, 30, 50, 70 5, 10 10 ,20, 30, 40, 50 Al(Cu0.001↓, Si0.005↓, Fe0.004↓, Mg3.7–4.5)
investigate the effects of various process parameters: feed rate, depth of cut, pitch per cycle on the surface roughness as shown in Table 1. Experiments were carried out on a four axis controlled ultra precision grinding machine as shown in Fig. 1(a). The machine has nano-meter resolution and wheel spindle is capable of running up to 70,000 rpm. Bites for fly-cutting were attached the work spindle which runs 12,000 rpm.
3. Results and discussion 3.1. Surface roughness and machining conditions For each set of the experiment conditions, 16 fly-cut surfaces were carried out to obtain a more consistent machined surface. In measurement, interferometric surface profiler (NV-E1000) was utilized which is generally adopted for measurement of ultra precision machined surface. For each surface seven data were measured and averaged except maximum and minimum data.
Fig. 2. Surface profile of machined surface measured by interferometric surface profiler: (a) with P = 20 m/cycle and (b) with P = 100 m/cycle.
Fig. 1(b) shows machined polygon mirror and measured data by interferometric surface profiler are shown in Fig. 2. From the repeated experiments, optimum depth of cut was deeper then 5 m and depth of cut is not crucial parameter for this experiment. Therefore, depth of cut was performed on 5 and 10 m. 3.1.1. Feed rate and depth of cut Feed rate and pitch per cycle are core parameters for machining efficiency because these two parameters determine whole machining time. Therefore, feed rate was varied 10–70 mm/min and thus depth of cut 10–50 m/pitch in the experiments. As shown in Fig. 3, 5 m depth of cut were resulted better surface roughness then 10 m but not definitive. Further, more variation of feed rate does not show obvious tendency within 10–70 mm/min and careful comparison reveals the effects of feed rate and depth of cut on surface roughness of machined mirror surface. In conclusion, it is seen that the effects of feed rate is insignificant.
Fig. 1. Experimental setup and machined polygon mirror. (a) Setup for flycutting. (b) Machined polygon mirror.
3.1.2. Pitch per cycle On the other hand, the effect of pitch per cycle on surface roughness shows proportional tendency 10–100 m/cycle as shown in Fig. 4. However, within 10–40 m/cycle, it resulted in small deviation. From the previous results, it could be concluded that pitch per cycle is crucial to surface roughness under over 50 m/cycle but thus not feed rate 10–70 mm/min.
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S.-S. Park et al. / Journal of Materials Processing Technology 187–188 (2007) 56–59
Fig. 3. Surface roughness with variation of feed rates: (a) with 5 m depth of cut and (b) with 10 m depth of cut.
Fig. 4. Surface roughness with variation of pitch per cycles: (a) with 5 m pitch per cycle and (b) with 10 m pitch per cycle.
3.1.3. Wear of bites Fly-cutting is a kind of interrupted machining, and there is few investigation about wear of tools. Thus brief simulations about damaged area and effective range of bite were performed as shown in Fig. 5. At 5 mm radius bite, wear is concentrated in the left side of bite from the center. Geometric contact area which was calculated from Eq. (1) is about 150 m on right side of the bite with maximum depth of cut Dmax = 10 m. Pitch per cycle is down feed and lower part is participated in machining process. As shown in Fig. 5(b), measured effective range, which damaged from machining, is 160 m. And there were craters on the bite which were generated by chips of machining. Mechanism of chip generation needs more experiments and analysis [4–6]. D −1 LEffectiveRange = R sin cos 1− (1) R 3.2. Geometricalanalysis of machined surface Surface roughness is simulated in geometrical view point and compared with experimental results. Machined surface was modeled as Fig. 6 and Rpv is geometrical surface roughness
Fig. 5. Bites wear during fly-cutting process. Bite edge before machining (R = 5 mm) (a) and after machining (R = 5 mm) (b).
S.-S. Park et al. / Journal of Materials Processing Technology 187–188 (2007) 56–59
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value. But with P ≥ 50 m, surface roughness is proportionally increased to 20 nm ≤ Rpv . 4. Concluding remarks This study deals with machined surface roughness of flycutting for inclined polygon mirror with the parameters: feed rate, pitch per cycle and depth of cut. Experimental results were compared with geometrical simulations and conclusion is as following.
Fig. 6. Geometrical surface roughness in fly-cutting process.
(1) Feed rate within 0–70 mm/min is not crucial parameter to surface roughness. (2) Between 5 and 10 m in depth of cut does not much affect the surface roughness. (3) In lower range of pitch per cycle (P ≤ 30 m), experiments resulted with similar values in surface roughness, Rpv ≤ 10 m, with geometric simulation but over 50 m/cycle shows much difference with simulation. (4) In bite, damaged range after machining was close to effective range of simulation. (5) More experiments need for analyzing mechanism of chip generation in fly-cutting and wear of bite [9,10]. References
Fig. 7. Simulated and experimental surface roughness.
which does not consider pile up of the machined surface. These geometrical simulation based on Eq. (2) and can be simplified to approximated equation in terms of bite radius R and pitch per cycle P [7,8]. P2 −1 P/2 Rpv = R 1 − cos sin ≈ (2) R 8R Fig. 7 shows the comparison between simulated roughness and measured surface roughness. In Fig. 7, though there appears to have increasing tendency in both simulated and measured value with the increasing pitch per cycle. The effect of pitch per cycle in fly-cutting is less proportional to surface roughness then simulation. With the condition of P ≤ 30 m, F ≤ 50 mm/min, effect of pitch per cycle to surface roughness is not significant. Furthermore, when pitch per cycle is 10–30 m/cycle, surface roughness of machined surface is close or better then simulated
[1] J. Chae, S.S. Park, T. Freiheit, Investigation of micro-cutting operations, Int. J. Mach. Tools Manuf. 46 (March (3–4)) (2006) 313–332. [2] K. Liu, X.P. Li, M. Rahman, Characteristics of high speed micro-cutting of tungsten carbide, J. Mater. Process. Technol. 140 (September (1–3)) (2003) 352–357. [3] B.P. O’Connor, E.R. Marsh, J.A. Couey, On the effect of crystallographic orientation on ductile material removal in silicon, Precision Eng. 29 (January (1)) (2005) 124–132. [4] K. Liu, S.N. Melkote, Effect of plastic side flow surface roughness in microturning process, Int. J. Mach. Tools Manuf., in press. [5] Y. Ohbuchi, T. Obikawa, Adiabatic shear in chip formation with negative rake angle, Int. J. Mech. Sci. 47 (September (9)) (2005) 1377–1392. [6] A. Moufki, A. Devillez, D. Dudzinski, A. Molinari, Thermomechanical modelling of oblique cutting and experimental validation, Int. J. Mach. Tools Manuf. 44 (July (9)) (2004) 971–989. [7] J. Yan, K. Syoji, J. Tamaki, Some observations on the wear of diamond tools in ultra-precision cutting of single-crystal silicon, Wear 255 (August–September (7–12)) (2003) 1380–1387. [8] M.C. Shaw, Metal Cutting Principles, Oxford University Press Inc., New York, 1984. [9] H.A. Abdel-Aal, J.A. Patten, L. Dong, On the thermal aspects of ductile regime micro-scratching of single crystal silicon for NEMS/MEMS applications, Wear 259 (July–August (7–12)) (2005) 1343–1351. [10] T.P. Leung, W.B. Lee, X.M. Lu, Diamond turning of silicon substrates in ductile-regime, J. Mater. Process. Technol. 73 (January (1–3)) (1998) 42–48.
A study on manufacturing technology for an inclined polygon mirror Soon-Sub Park ∗ , Ho-Jae Lee, Ki-Young Lee, Yeon Hwang Micro Mold and Die Team, Gwang-Ju Research Center, Korea Institute of Industrial Technology (KITECH), Wolchul-dong 971-35, Buk-gu, Gwang-ju 500-460, Republic of Korea
Abstract Generally, the core component of small precise optical device demands high accuracy of manufacturing processes. Although, the geometry of it is simple, the manufacturing technique to materialize is categorized as the ultra precision machining and it must be done with the specialized machines and by the trained operator. Typical examples of small precise optical device are laser printer and phone camera. The shape is very simple but required manufacturing technology is very difficult. It belongs to fine precision machining technique and needs an ultra precision machining center and an assignment researcher. Laser printers and phone cameras are representative examples in small precise optical device. Recently, small sized display device is being developed and has an inclined polygon mirror as core part. The inclined polygon mirror is different with the previous polygon mirror in the point of view that it has a variety of reflection angle. With the result that, multi lines were achieved at screen. It could not be fabricated with conventional machine for a typical polygon mirror. It was manufactured in the process of fly-cutting with Al material on which was coated electroless-Ni for enhancement of hardness. Owing to process of polishing has bad influence on reflection angle, the inclined polygon mirror must be only fabricated with fly-cutting and have surface roughness Rmax = 10 nm and form error Ra = λ/10 (λ = 632 nm). © 2007 Published by Elsevier B.V. Keywords: Inclined polygon mirror; Fly-cutting; Interrupted machining; Ultra precision
1. Introduction The need for optical elements with ultra fine surface roughness and profile accuracy keeps increasing rapidly because of development of IT industry in recent years. Ultra precision mechanical machining is one of the most fundamental and important facilities to meet sub-micrometer profile accuracy and several nano-meter surface roughness. However, quality of machined mirror surface is limited due to various kinds of noises as vibration, thermal deformation, wear of tool, etc. As a result, great efforts were made towards the development of ultra precision machining, in particular, technology for ultra fine mirror surface of nonferrous metal [1,2]. Previous research works have focused mainly on the development of machining technologies, with great emphasis on tool and equipment, but little has so far been reported on parametric investigation of fly-cutting. One of the most successful applications of fly-cutting is the fabrication of ultra precise polygon mirror for laser scanning units which is a core part of laser printer. To achieve the required profile accuracy Ra ≤ λ/10 (λ = 632 nm) and surface roughness Rmax ≤ 10 nm for mirror surface of aluminum ∗
Corresponding author. Tel.: +82 62 600 6151; fax: +82 62 600 6499. E-mail address: [email protected] (S.-S. Park).
0924-0136/$ – see front matter © 2007 Published by Elsevier B.V. doi:10.1016/j.jmatprotec.2006.11.169
alloy, parametric experiments were performed, utilizing single point diamond bite fly-cutting. 2. Experimental setup and test conditions Fly-cutting experiment carried out on a Toshiba ultra precision grinding machine (ULG100H3) using single diamond bite. Commercial aluminum alloy (S3M) was used as a work piece material. Target inclined polygon mirror has 16 mirror surfaces with θ = 0.03◦ angular difference among the surfaces. Each surface was machined with verified feed rate (F), depth of cut (D) and pitch per cycle (P) and evaluated in terms of profile accuracy and surface roughness [3].
2.1. Target polygon mirror In recent years there has been a considerably interest in new design of faster and compact polygon mirror. One of the significant challenges for new concept of polygon mirror is inclined reflecting surface with different angles. Conventional type polygon mirror reflects laser beam and generate single line but inclined type polygon mirror generates multi line.
2.2. Experimental setup As mentioned, profile accuracy Ra ≤ λ/10 (λ = 632 nm) and surface roughness Rmax ≤ 10 nm are requisites for target polygon mirror. In fly-cutting, process for high accuracy surface can reduce the efficiency of machining and takes much time. Moreover, there are few experimental investigations for optimum machining conditions. Therefore, a full factorial experiment design was adopted to
S.-S. Park et al. / Journal of Materials Processing Technology 187–188 (2007) 56–59
57
Table 1 Experimental conditions Bite (material) Bite radius (mm) Inclined angle (◦ ) Mist Feed rate (mm/min) Depth of cut (m) Pitch per cycle (m) Work piece material (S3M, %)
Single crystal diamond 5 0.03 Semi-dry cutting 10, 30, 50, 70 5, 10 10 ,20, 30, 40, 50 Al(Cu0.001↓, Si0.005↓, Fe0.004↓, Mg3.7–4.5)
investigate the effects of various process parameters: feed rate, depth of cut, pitch per cycle on the surface roughness as shown in Table 1. Experiments were carried out on a four axis controlled ultra precision grinding machine as shown in Fig. 1(a). The machine has nano-meter resolution and wheel spindle is capable of running up to 70,000 rpm. Bites for fly-cutting were attached the work spindle which runs 12,000 rpm.
3. Results and discussion 3.1. Surface roughness and machining conditions For each set of the experiment conditions, 16 fly-cut surfaces were carried out to obtain a more consistent machined surface. In measurement, interferometric surface profiler (NV-E1000) was utilized which is generally adopted for measurement of ultra precision machined surface. For each surface seven data were measured and averaged except maximum and minimum data.
Fig. 2. Surface profile of machined surface measured by interferometric surface profiler: (a) with P = 20 m/cycle and (b) with P = 100 m/cycle.
Fig. 1(b) shows machined polygon mirror and measured data by interferometric surface profiler are shown in Fig. 2. From the repeated experiments, optimum depth of cut was deeper then 5 m and depth of cut is not crucial parameter for this experiment. Therefore, depth of cut was performed on 5 and 10 m. 3.1.1. Feed rate and depth of cut Feed rate and pitch per cycle are core parameters for machining efficiency because these two parameters determine whole machining time. Therefore, feed rate was varied 10–70 mm/min and thus depth of cut 10–50 m/pitch in the experiments. As shown in Fig. 3, 5 m depth of cut were resulted better surface roughness then 10 m but not definitive. Further, more variation of feed rate does not show obvious tendency within 10–70 mm/min and careful comparison reveals the effects of feed rate and depth of cut on surface roughness of machined mirror surface. In conclusion, it is seen that the effects of feed rate is insignificant.
Fig. 1. Experimental setup and machined polygon mirror. (a) Setup for flycutting. (b) Machined polygon mirror.
3.1.2. Pitch per cycle On the other hand, the effect of pitch per cycle on surface roughness shows proportional tendency 10–100 m/cycle as shown in Fig. 4. However, within 10–40 m/cycle, it resulted in small deviation. From the previous results, it could be concluded that pitch per cycle is crucial to surface roughness under over 50 m/cycle but thus not feed rate 10–70 mm/min.
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S.-S. Park et al. / Journal of Materials Processing Technology 187–188 (2007) 56–59
Fig. 3. Surface roughness with variation of feed rates: (a) with 5 m depth of cut and (b) with 10 m depth of cut.
Fig. 4. Surface roughness with variation of pitch per cycles: (a) with 5 m pitch per cycle and (b) with 10 m pitch per cycle.
3.1.3. Wear of bites Fly-cutting is a kind of interrupted machining, and there is few investigation about wear of tools. Thus brief simulations about damaged area and effective range of bite were performed as shown in Fig. 5. At 5 mm radius bite, wear is concentrated in the left side of bite from the center. Geometric contact area which was calculated from Eq. (1) is about 150 m on right side of the bite with maximum depth of cut Dmax = 10 m. Pitch per cycle is down feed and lower part is participated in machining process. As shown in Fig. 5(b), measured effective range, which damaged from machining, is 160 m. And there were craters on the bite which were generated by chips of machining. Mechanism of chip generation needs more experiments and analysis [4–6]. D −1 LEffectiveRange = R sin cos 1− (1) R 3.2. Geometricalanalysis of machined surface Surface roughness is simulated in geometrical view point and compared with experimental results. Machined surface was modeled as Fig. 6 and Rpv is geometrical surface roughness
Fig. 5. Bites wear during fly-cutting process. Bite edge before machining (R = 5 mm) (a) and after machining (R = 5 mm) (b).
S.-S. Park et al. / Journal of Materials Processing Technology 187–188 (2007) 56–59
59
value. But with P ≥ 50 m, surface roughness is proportionally increased to 20 nm ≤ Rpv . 4. Concluding remarks This study deals with machined surface roughness of flycutting for inclined polygon mirror with the parameters: feed rate, pitch per cycle and depth of cut. Experimental results were compared with geometrical simulations and conclusion is as following.
Fig. 6. Geometrical surface roughness in fly-cutting process.
(1) Feed rate within 0–70 mm/min is not crucial parameter to surface roughness. (2) Between 5 and 10 m in depth of cut does not much affect the surface roughness. (3) In lower range of pitch per cycle (P ≤ 30 m), experiments resulted with similar values in surface roughness, Rpv ≤ 10 m, with geometric simulation but over 50 m/cycle shows much difference with simulation. (4) In bite, damaged range after machining was close to effective range of simulation. (5) More experiments need for analyzing mechanism of chip generation in fly-cutting and wear of bite [9,10]. References
Fig. 7. Simulated and experimental surface roughness.
which does not consider pile up of the machined surface. These geometrical simulation based on Eq. (2) and can be simplified to approximated equation in terms of bite radius R and pitch per cycle P [7,8]. P2 −1 P/2 Rpv = R 1 − cos sin ≈ (2) R 8R Fig. 7 shows the comparison between simulated roughness and measured surface roughness. In Fig. 7, though there appears to have increasing tendency in both simulated and measured value with the increasing pitch per cycle. The effect of pitch per cycle in fly-cutting is less proportional to surface roughness then simulation. With the condition of P ≤ 30 m, F ≤ 50 mm/min, effect of pitch per cycle to surface roughness is not significant. Furthermore, when pitch per cycle is 10–30 m/cycle, surface roughness of machined surface is close or better then simulated
[1] J. Chae, S.S. Park, T. Freiheit, Investigation of micro-cutting operations, Int. J. Mach. Tools Manuf. 46 (March (3–4)) (2006) 313–332. [2] K. Liu, X.P. Li, M. Rahman, Characteristics of high speed micro-cutting of tungsten carbide, J. Mater. Process. Technol. 140 (September (1–3)) (2003) 352–357. [3] B.P. O’Connor, E.R. Marsh, J.A. Couey, On the effect of crystallographic orientation on ductile material removal in silicon, Precision Eng. 29 (January (1)) (2005) 124–132. [4] K. Liu, S.N. Melkote, Effect of plastic side flow surface roughness in microturning process, Int. J. Mach. Tools Manuf., in press. [5] Y. Ohbuchi, T. Obikawa, Adiabatic shear in chip formation with negative rake angle, Int. J. Mech. Sci. 47 (September (9)) (2005) 1377–1392. [6] A. Moufki, A. Devillez, D. Dudzinski, A. Molinari, Thermomechanical modelling of oblique cutting and experimental validation, Int. J. Mach. Tools Manuf. 44 (July (9)) (2004) 971–989. [7] J. Yan, K. Syoji, J. Tamaki, Some observations on the wear of diamond tools in ultra-precision cutting of single-crystal silicon, Wear 255 (August–September (7–12)) (2003) 1380–1387. [8] M.C. Shaw, Metal Cutting Principles, Oxford University Press Inc., New York, 1984. [9] H.A. Abdel-Aal, J.A. Patten, L. Dong, On the thermal aspects of ductile regime micro-scratching of single crystal silicon for NEMS/MEMS applications, Wear 259 (July–August (7–12)) (2005) 1343–1351. [10] T.P. Leung, W.B. Lee, X.M. Lu, Diamond turning of silicon substrates in ductile-regime, J. Mater. Process. Technol. 73 (January (1–3)) (1998) 42–48.