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Wang Peng, Zhang Hao, Jia Yapeng, Yang Kun, Li Weihao. Removal of the single point diamond turning marks by spiral sine trace bonnet polishing process[J]. Infrared and Laser Engineering, 2020, 49(7): 20200212. doi: 10.3788/IRLA20200212
Citation: Wang Peng, Zhang Hao, Jia Yapeng, Yang Kun, Li Weihao. Removal of the single point diamond turning marks by spiral sine trace bonnet polishing process[J]. Infrared and Laser Engineering, 2020, 49(7): 20200212. doi: 10.3788/IRLA20200212

Removal of the single point diamond turning marks by spiral sine trace bonnet polishing process

doi: 10.3788/IRLA20200212
  • Received Date: 2020-04-05
  • Rev Recd Date: 2020-05-10
  • Available Online: 2020-07-23
  • Publish Date: 2020-07-23
  • Single point diamond turing (SPDT) technology has been widely used in the high precision optical surface processing field. However, the micro-nano texture which is mainly composed of turning marks remain on the turned surface will affect performance of optical systems. Therefore, it’s necessary to remove the turning marks for improving the surface quality. Removal of the single point diamond turning marks was studied in the paper. It was found that the removal efficiency was highest when the polishing direction was perpendicular to the turning marks. A new polishing trace called spiral sine trace was presented based on the finding. The design principle was introduced in detail. Contrast experiment of different polishing tracks consisting of spiral sine trace, spiral trace and raster trace utilizing bonnet polishing was carried out. Result shows that the improvement effect of micro-nano texture in spiral sine trace was obviously superior to two other kinds of trace. A germanium aspherical surface manufactured by SPDT was smoothed by spiral sine bonnet polishing. The results shows that the roughness of surface Ra reduce from 1.28 nm to 0.4 nm before and after polishing, the regular turning marks transform to random micro-nano texture, and above all, the surface figure accuracy isn’t damaged during the smoothing process.
  • [1] 杨亮亮. 衍射光学元件斜入射衍射效率的测量[J]. 红外与激光工程, 2018, 47(1): 0117003. doi:  0117003

    Yang Liangliang. Measurement of diffraction efficiency for diffractive optical elements with oblique incidence [J]. Infrared and Laser Engineering, 2018, 47(1): 0117003. (in Chinese) doi:  0117003
    [2] Zhang S J, To S. A theoretical and experimental investigation into multimode tool vibration with surface generation in ultra-precision diamond turning [J]. International Journal of Machine Tools & Manufacture, 2013, 72: 32−36.
    [3] 王朋, 薛栋柏, 张昊, 等. 红外晶体等距恒速单点金刚石车削[J]. 红外与激光工程, 2019, 48(7): 0742001. doi:  10.3788/IRLA201948.0742001

    Wang Peng, Xue Dongbai, Zhang Hao, et al. ESCV cutting method during infrared crystal single point diamond turning process [J]. Infrared and Laser Engineering, 2019, 48(7): 0742001. (in Chinese) doi:  10.3788/IRLA201948.0742001
    [4] Steven C Fawcett, Darell Engelhaupt. Development of WolterⅠX-ray optics by diamond turning and electrochemical replication [J]. Precision Engineering, 1995, 17: 290−297. doi:  10.1016/0141-6359(95)00018-9
    [5] Chon K S , Namba Y, Yoon K H. Precision machining of electroless nickel mandrel and fabrication of replicated mirrorsfor a soft x-ray microscope [J]. JSME Int J Ser C, 2006, 49: 56−62. doi:  10.1299/jsmec.49.56
    [6] Yuetian Huang, Bin Fan, Yongjian Wan, et al. Improving the performance of single point diamond turning surface with ion beam figuring [J]. Optik- International Journal for Light and Electron Optics, 2018, 172: 540−544. doi:  10.1016/j.ijleo.2018.07.039
    [7] Nambaa Y, Shimomura T, Fushiki A, et al. Ultra-precision polishing of electroless nickel molding dies for shorter wavelength applications [J]. CIRP Annals - Manufacturing Technology, 2008, 57: 337−340. doi:  10.1016/j.cirp.2008.03.077
    [8] Li Z Z, Wang J M, Peng X Q, et al. Removal of single point diamond-turning marks by abrasive jet polishing [J]. Applied Optics, 2011, 50(16): 2458−2463. doi:  10.1364/AO.50.002458
    [9] Beaucamp A, Namba Y. Super-smooth finishing of diamond turned hard X-ray molding dies by combined fluid jet and bonnet polishing [J]. CIRP Annals - Manufacturing Technology, 2013, 62: 315−318. doi:  10.1016/j.cirp.2013.03.010
    [10] 王朋, 杜雪, 回长顺. 金刚石车削表面微纳织构的气囊抛光改进[J]. 光学学报, 2015, 35(3): 0322001. doi:  10.3788/AOS201535.0322001

    Wang Peng, Suet To, Hui Changshun. Improvement of the diamond turned surface texture by bonnet polishing process [J]. Acta Optica Sinica, 2015, 35(3): 0322001. (in Chinese) doi:  10.3788/AOS201535.0322001
    [11] Dumas P, Golini D, Tricard M. Improvement of figure and finish of diamond turned surfaces with magneto-rheological finishing[C]// Proc SPIE, 2005, 5786: 296–304 .
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Removal of the single point diamond turning marks by spiral sine trace bonnet polishing process

doi: 10.3788/IRLA20200212
  • Tianjin Institute of Jinhang Technical Physics, Tianjin 300380, China

Abstract: Single point diamond turing (SPDT) technology has been widely used in the high precision optical surface processing field. However, the micro-nano texture which is mainly composed of turning marks remain on the turned surface will affect performance of optical systems. Therefore, it’s necessary to remove the turning marks for improving the surface quality. Removal of the single point diamond turning marks was studied in the paper. It was found that the removal efficiency was highest when the polishing direction was perpendicular to the turning marks. A new polishing trace called spiral sine trace was presented based on the finding. The design principle was introduced in detail. Contrast experiment of different polishing tracks consisting of spiral sine trace, spiral trace and raster trace utilizing bonnet polishing was carried out. Result shows that the improvement effect of micro-nano texture in spiral sine trace was obviously superior to two other kinds of trace. A germanium aspherical surface manufactured by SPDT was smoothed by spiral sine bonnet polishing. The results shows that the roughness of surface Ra reduce from 1.28 nm to 0.4 nm before and after polishing, the regular turning marks transform to random micro-nano texture, and above all, the surface figure accuracy isn’t damaged during the smoothing process.

    • 因具备优异的加工性能和加工效率,单点金刚石车削技术已经广泛应用于高精度光学表面的制造领域。但受加工方式的限制,其不可避免会在被加工表面残留规律性的车削刀痕微纳织构,产生衍射和散射效应进而影响光学系统的性能,该缺陷在短波光学系统、多模复合光学系统的应用中更为突出。因此,如何消除此类刀痕以提升光学系统质量成为当前研究的重点之一[1-3]

      当前,消除此类车削刀痕最有效的方法为车削后抛光光滑处理。20世纪90年代,Fawcett等人设计的专门的抛光机床,用于抛光单点金刚石车削后的WolterⅠ型X射线模压用模芯[4]。之后K. S. Chon也针对此类电解镍的模芯的加工,描述了其采用手工抛光方式来消除刀痕,并指出手工抛光的方式很难兼顾粗糙度和面形精度[5]。随着“确定性”抛光技术的不断发展,研究人员针对车削刀痕的抛光去除开展了一系列的研究,气囊抛光、射流抛光、磁流变抛光、离子束抛光、计算机控制小工具抛光以及几种方式相互组合等,都被用来消除单点金刚石车削刀痕,以期获得更好的效果[6-11]。参考文献[10]介绍了气囊抛光方式改进金刚石车削表面微纳织构,利用Taguchi正交实验的方法得到了气囊抛光优化微纳织构的最优参数,并进行了试验验证,样件表面质量得到大幅改善。Paul Dumas利用磁流变抛光方式改善了单点金刚石车削Si非球表面的质量,彩虹纹消失[11]。虽然上述各研究过程均使得金刚石车削表面微纳织构得到了改善,但都是参考类似于研磨表面的抛光过程,且仅以去除刀痕为目的。与研磨表面杂乱无章的离散结构不同,车削刀痕织构为规律性的阿基米德螺旋结构,其抛光去除过程亦有其特殊性,需要进一步研究。

      在前期刀痕抛光去除研究中发现,当抛光方向与刀痕垂直时,织构的改善效率最快。基于此特点,文中将设计一种螺旋正弦抛光轨迹,用于刀痕微纳织构的改善,以提升改善效率,并进行实验验证。

    • 在前期对刀痕抛光去除特性的研究中发现,抛光运动方向与车削刀痕夹角θ不同时,表面改善的效果则截然不同。在同一车削表面上,完全相同的抛光条件下,得到的抛光后微纳织构如图1所示(图中横坐标x和竖坐标y代表采图区域,颜色条表示采图后数据点高度范围与颜色的对应关系)。当θ≈90°时粗糙度降到Ra=73.69 nm(图1(a)),而θ<90°时,粗糙度则仅降到Ra=106.06 nm(图1( b))。之后又对此进行了进一步研究,发现车削表面微纳织构在抛光方向与刀痕方向夹角越接近90°,表面的改善程度越大,越接近于0°,改善程度越小。因此,为了获得最高效的改善效果,有必要设计一种抛光运动轨迹,使得抛光方向尽可能地与刀痕方向垂直。

      Figure 1.  Effect of polishing direction on rate of surface improvement

      一般车削刀痕为阿基米德螺旋线结构,在刀痕光滑处理的过程中为了尽可能使抛光轨迹与刀痕轨迹垂直,文中提出了螺旋正弦运动轨迹,如图2所示。此轨迹以阿基米德螺旋轨迹为基础,叠加上正弦运动,实现与螺旋轨迹尽可能垂直,从而实现微纳织构的最大快速改善。

      Figure 2.  Spiral sine polishing path

    • 图2所示的螺旋正弦轨迹由三个主要参数决定,分别为螺距P、正弦弧长周期S和正弦幅值A。横坐标和纵坐标代表的仿真范围(单位mm)。三个参数设计的基础为小磨头抛光时去除函数的直径D,并遵循如下原则。

      (1)在一个抛光周期内,保证抛光区域能够均匀覆盖整个车削表面;

      (2)正弦弧长周期S为常数;

      (3)螺距P应大于被加工表面的车削刀纹间距且≤0.5D

      遵循上述原则,文中将采用气囊抛光的方式抛光去除刀痕,设计的抛光运动轨迹的参数如下。

      轨迹螺旋轴线螺距P为:

      正弦轨迹幅值A为:

      正弦轨迹弧长周期S为:

      式中:D为抛光时小磨头抛光接触区域的直径。

    • 文中将采用气囊抛光的方式去除单点金刚石车削刀痕,并将此螺旋正弦轨迹与常用的螺旋式和光栅式的抛光方式进行抛光对比实验,以验证此抛光轨迹的实际效果。

    • 文中选择镍铜合金作为抛光实验的基底材料,粗车成平面以后,应用IL300型单点金刚石车床对表面进行单点金刚石车削。为了使对比抛光实验结果更加明显,便于分析,选择了如表1所示的车削参数。

      Turning parametersValue
      Tool nose radius/mm1.457
      Spindle speed/r·m-11500
      Feed rate/mm·min-110
      Cut depth/μm2

      Table 1.  SPDT parameters for the samples

    • 参考文献[10]中对气囊抛光技术进行了详细介绍,这里不在赘述。文中实验中气囊抛光头正压于工件表面,选择的气囊半径(R)、压深(d)、抛光头转速(ωt)、压力(P)和抛光角度(α)等参数如表2所示(表中1 bar=105 Pa)。

      Bonnet polishing parametersValue
      Bonnet radius R/mm20
      Spindle speed ωt /r·m-11 200
      Polishing pressure P/bar0.5
      Polishing angle α/(°)5
      Polishing depth d/mm0.2

      Table 2.  Bonnet polishing parameters

      抛光过程中抛光布为聚氨酯材料,抛光液选用了粒度为50 nm的SiO2抛光液。

    • 气囊抛光时抛光接触区域的直径D由公式(4)计算得出:

      表2中给出的气囊抛光参数可以得到抛光的接触区域直径D=5.64 mm。将此结果代入公式(1)~(3),得到螺旋正弦轨迹的各个主要参数如表3所示。通过这些参数得到如图2所示的螺旋正弦抛光轨迹,其中抛光时的进给速度F为100 mm/min。

      Sprial +sineRasterSprial
      P=1.692 mmSpace (SP)
      0.4 mm
      Workpiece rotating speed (ωp) 200 r·m-1
      S=5.64 mm
      A=0.846 mm
      Feed rate (F) 100 mm/minFeed rate (F) 100 mm/minFeed rate (F) 4.99 mm/min

      Table 3.  Parameters of different polishing trace

      表3中同样给出了光栅式和螺旋式的抛光轨迹的参数,根据这些参数仿真的运动轨迹见图3。其中光栅式轨迹的主要参数:进给速度 F为100 mm/min,间隔为0.4 mm;螺旋式轨迹主要参数:零件转速ωp为200 r·m−1,进给速度F为4.99 mm/min。图中,横坐标和纵坐标代表的仿真范围(单位mm)。

      Figure 3.  Polishing trace comparison

    • 按照设计的抛光参数和运动轨迹参数,应用非球面抛光机床自带的气囊抛光模块进行了对比抛光实验,各连续光滑了两遍。

      为了考察各个运动轨迹下表面微纳织构的改善情况,抛光前后应用白光干涉仪对样件的特定对应区域进了测试,测试结果如图4所示,其中图4(a)为单点金刚石车削后未进行抛光改善的微纳织构;图4(b)~(d)分别为经过螺旋正弦轨迹、螺旋式轨迹和光栅式轨迹抛光后的微纳织构。

      Figure 4.  Micro-nano texture before and after polishing

      图4的测试结果可以看出,螺旋正弦式抛光方法得到了最优的表面,其粗糙度达到了Ra=11.95 nm,相对于原始表面粗糙度降低了58%;其次为螺旋式抛光方式,螺旋式抛光后表面粗糙度Ra降到了20.95 nm,相对于原始表面降低了26.4%;改善效果最差的为光栅式的抛光方式,粗糙度仅达到23.98 nm,仅降低了15.85%。上述结果说明:在相通的抛光条件下,文中所提出的螺旋正弦式抛光轨迹较其他常用的抛光轨迹方式更适于金刚石车削微纳织构的改善,达到了预期目的。

    • 应用所设计的螺旋正弦连续轨迹抛光方法,对一直径ᴓ100 mm口径单点金刚石车削锗基底非球表面进行了气囊抛光光滑处理,具体的非球面参数如表4所示。抛光参数与表3中螺旋正弦连续光滑参数相同,光滑处理工序抛光一遍。抛光过程中使用阻尼布抛光垫,氧化铝抛光液。光滑处理前后微纳织构和面形精度分析结果如图5~7所示。

      R0KA2A4A6
      684.400–6.24E–08–3.266E–13

      Table 4.  Parameters of aspheric test mirror

      Figure 5.  Comparison of the texture before and after polishing

      Figure 6.  Compare of the PSD before and after polishing

      Figure 7.  Comparison of the figure error before and after polishing

      图5为光滑前后自由曲面微纳织构对比图,通过螺旋正弦连续抛光处理后,表面粗糙度Ra由1.28 nm(如图5(a)所示)降低到0.4 nm(如图5(b)所示),通过观察可以看到:规律性的微纳刀痕消失,取而代之的是随机分布微纳织构形式。对比抛光前后微纳织构的功率谱密度(PSD),如图6所示。抛光后PSD较抛光前明显光滑且降低了许多,中高频误差得到有效改善,主频的PSD值由4.2×104 Å2·μm−1(1 Å=0.1 nm)降低到0.05×104 Å2·μm−1,效果明显。通过抛光前后微纳织构形式的变化和PSD变化,可以看出,微纳织构得到明显改善,说明螺旋正弦抛光轨迹对微纳织构改善的有效性。

      光滑处理过程一个重要原则是保证抛光前后的面形精度。抛光前后分别用Talyor接触式轮廓仪对其表面轮廓形状进行了测量,结果如图7所示。通过对比可以发现抛光前后面形形貌基本吻合,面形精度PV由抛光前0.449 μm变化为抛光后的0.35 μm,抛光后有所改善,说明所采用的正弦螺旋连续抛光法能够保证面形精度。

      通过对此锗非球面的抛光光滑实验,说明文中所提出的螺旋正弦抛光轨迹能够对在保持面形精度的前提下,实现微纳织构的改善,证明此方法的可行性。

    • 针对单点金刚石车削表面残留微纳织构的光滑处理技术进行了研究。在分析微纳织构特性改善效果的基础上,提出了一种螺旋正弦抛光运动轨迹,以期获得更好的抛光去除效果。通过与传统螺旋式和光栅式气囊抛光对比实验,证明了所提出轨迹的有效性。应用所提出的轨迹对一单点金刚石车削锗非球面进行了抛光光滑实验,经过一次抛光,在保证面形精度基本未发生变化的前提下,使得表面微纳织构得到了改善,达到了预期目的。

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