Effect of chemical treatment on tensile strength and surface roughness of 3D-printed ABS using the FDM process

Fused deposition modelling (FDM) is one of the most commonly used additive manufacturing processes because of its environment-friendly nature and cost-effectiveness. However, it suffers badly from low surface quality due to a larger layer resolution. The surface finish of FDM parts can be enhanced by post chemical treatment using various solvents. The chemical treatment reduces the surface roughness by dissolving the external surfaces of 3D-printed samples. Chemical treatment is an easy, fast and economical technique. In the present investigation, the effect of chemical treatment on surface roughness and tensile strength of acrylonitrile butadiene styrene (ABS) parts made using the FDM process is investigated using two chemicals, namely acetone and 1, 2 dichloroethane. The post chemical treatment dramatically improves the surface finish and dimensional accuracy of ABS specimens. But chemical treatment results in the reduction of the tensile strength. Better tensile strength is obtained while using acetone solvent and a better surface finish is obtained using dichloroethane.     

Epitaxial growth of relaxed germanium layers by reduced pressure chemical vapour deposition on (110) and (111) silicon substrates

The growth of Ge on (110) and (111) oriented Si substrates is of great interest to enhance the mobility of both holes and electrons in complementary metal oxide semiconductor transistors. However, the quality of thick, relaxed Ge layers grown epitaxially on these surfaces is usually much lower than similar layers grown on (100) Si, resulting in both higher defect densities (i.e. threading dislocations and stacking faults) and rougher surfaces. In this work we have investigated the growth of Ge layers on (110) and (111) Si substrates by reduced-pressure chemical vapour deposition using a two temperature process. We have found that the combination of suppressing the Ge seed layer roughness and high temperature post-growth annealing can reduce the rms surface roughness of (110) Ge layers to below 2 nm and the threading dislocation density to below 1 × 10⁷ cm^− 2. Thick (111) Ge layers were found to exhibit a very high density of stacking faults, that could not be reduced by post-growth annealing and a higher rms surface roughness of around 12 nm, which was limited by the Ge seed layer.     

烧结温度对3D打印硅基陶瓷型芯表面形貌及粗糙度的影响

单晶高温合金空心叶片是航空发动机的重要部件, 其内腔结构是采用陶瓷型芯制备的。随着航空发动机推重比提高, 型芯结构越来越复杂, 传统制备工艺受限, 光固化3D打印陶瓷型芯技术为复杂结构型芯的制备提供了一种可行方案。为了改善光固化3D打印陶瓷型芯因台阶效应导致的表面粗糙度较大的问题, 本研究利用固含量体积分数63%的硅基型芯浆料进行光固化3D打印型芯, 并在1100~1300 ℃对型芯素坯进行烧结, 对烧成的硅基陶瓷型芯的微观结构、元素分布、相组成、型芯打印面和打印堆积方向的表面形貌和粗糙度进行分析。研究发现型芯打印面平整, 无明显表面缺陷, 1100、1200和1300 ℃烧结型芯的打印面粗糙度分别为1.83、1.24和1.44 μm; 片层堆积方向的表面有片层结构特征, 片层间出现微裂纹, 1200 ℃以上烧结的型芯表面粗糙度达到空心叶片使用要求(R_a≤2.0 μm)。结果表明不同烧结温度会改变型芯烧结过程中的液相含量、莫来石生成量、莫来石生成形态和颗粒间玻璃相的分布, 从而对光固化3D打印硅基陶瓷型芯的表面粗糙度产生明显影响。光固化3D打印陶瓷型芯技术结合烧结工艺能制备出满足先进空心叶片用硅基陶瓷型芯表面要求的粗糙度。     

High‐Speed 3D Printing of Millimeter‐Size Customized Aspheric Imaging Lenses with Sub 7 nm Surface Roughness

Advancements in three‐dimensional (3D) printing technology have the potential to transform the manufacture of customized optical elements, which today relies heavily on time‐consuming and costly polishing and grinding processes. However the inherent speed‐accuracy trade‐off seriously constrains the practical applications of 3D‐printing technology in the optical realm. In addressing this issue, here, a new method featuring a significantly faster fabrication speed, at 24.54 mm³ h^?1, without compromising the fabrication accuracy required to 3D‐print customized optical components is reported. A high‐speed 3D‐printing process with subvoxel‐scale precision (sub 5 µm) and deep subwavelength (sub 7 nm) surface roughness by employing the projection micro‐stereolithography process and the synergistic effects from grayscale photopolymerization and the meniscus equilibrium post‐curing methods is demonstrated. Fabricating a customized aspheric lens 5 mm in height and 3 mm in diameter is accomplished in four hours. The 3D‐printed singlet aspheric lens demonstrates a maximal imaging resolution of 373.2 lp mm^?1 with low field distortion less than 0.13% across a 2 mm field of view. This lens is attached onto a cell phone camera and the colorful fine details of a sunset moth's wing and the spot on a weevil's elytra are captured. This work demonstrates the potential of this method to rapidly prototype optical components or systems based on 3D printing.     

Mutual diffusion process for continuous fabrication of graded-index plastic rod lenses

We propose a new process for fabrication of plastic rod lenses based on the traditional method of fiber extrusion. The process consists of the following steps: multilayer conjugate extrusion, monomer diffusion between adjacent layers, and photopolymerization of an uncured strand fiber. We call this process a mutual diffusion process for continuous plastic rod lens fabrication. Characteristics of this process are as follows: fast production speed (approximately 100 cm/min), precision control of refractive-index distribution, high angular aperture, and long-term reliability. The optical resolution of the rod-lens array is 300 dpi, which is high enough for application to G3 facsimiles with transmission time of less than 1 min and monochromatic scanners.     

刀具对中误差对离轴抛物面镜慢刀伺服车削加工的影响

离轴抛物面镜单件高效加工是离轴三反消像散(TMA)结构光学系统的技术难点之一.单点金刚石慢刀伺服车削加工技术可用于离轴非球面加工,加工尺寸范围较大,加工精度较高.此工艺制造的离轴抛物面面型精度可达到亚微米级,粗糙度达到纳米级.因此,可直接用于红外光学应用,若经后续抛光则可用于空间望远镜等更高精度需求的场合.介绍了慢刀伺服车削加工离轴抛物面镜的在轴加工方法,理论推导了刀具对中误差所带来的面形误差的极值分布规律.仿真研究进一步揭示了工件中心区域面形误差的详细分布.实验数据与理论结果和仿真计算结果均吻合.     

连续电子束扫描处理的U-5.5Nb合金的表面层微结构和性能

采用连续电子束扫描处理技术(CEBSP)首次在U-5.5Nb合金表面制备了重熔改性层,通过OM、SEM/EDS、便携式表面粗糙度测量仪及维氏硬度计等分析方法对重熔改性层的微观结构与物性特征进行了表征、分析。研究结果表明:由于快速熔凝会形成含有大量细小夹杂且具有枝晶组织的重熔改性层(厚度为毫米级),使其表面微观硬度从基体的164.5HV0.3升高至重熔改性层的211.5HV0.3。利用Kou模型计算了重熔改性层在快速凝固过程中裂纹敏感性因子-固相分数关系曲线,分析认为凝固裂纹是高Nb含量U-Nb合金在快速熔凝过程中难以避免的一类表面缺陷,也是表面粗糙度Ra从初始相对光滑表面0.193μm升高至重熔改性层表面2.298μm的主要原因。     

Growth of thin Ag films produced by radio frequency magnetron sputtering

Thin Ag films in the thickness range D = 14–320 nm were deposited by radio frequency magnetron sputtering on glass substrates at room temperature inside a vacuum chamber with base pressure of about 5 × 10^− 6 Pa. The growth of the films was studied via X-ray diffraction and atomic force microscopy experiments. The two techniques are complementary and give us the opportunity to study the surface roughness, the statistical distribution and the average value of the grain size, as well as the texture of the samples. It is shown that the film roughness increases negligibly within the first 60 atomic layers of growth. The thicker films (D 300 nm) develop a nanocrystalline structure with a root mean square roughness of about 2.5 nm. The grain size evolves linearly with the thickness from 9.4 nm at D = 54 nm to 31.6 nm at D = 320 nm.     

Design and Fabrication of a Hybrid Diffractive Optical Device for Multiple-Line Generation over a Wide Angle

A new hybrid optical device that is capable of splitting a monochromatic laser beam into an arbitrary number of lines over a wide angle is presented. It consists of a binary surface-relief computer-generated phase hologram and a continuous parabolic surface-relief grating. In this device the phase hologram serves to generate three small, parallel lines while the continuous parabolic surface-relief phase grating acts as an array of diverging parabolic lenses to widen these lines. The binary surface-relief was generated into one side of a quartz substrate through a plasma-etching process, and the parabolic profile was generated into a thick photoresist deposited on the other side of the quartz substrate. Calculations showed that a diverging parabolic lens with a f-number of 0.5 would deliver the desired optical pattern of multiple beams distributed over 90 degrees . A surface-relief depth of 6.0 mum was calculated with consideration of the phase distributions of such lens. The parabolic profiles were fabricated in a 10-mum-thick photoresist, by use of a contact exposure through a mask with a space pattern of repetitive 4- and 6-mum lines. He-Ne laser light was passed through a device that generated three parallel lines over a 90 degrees angle. The resulting diffraction patterns were characterized, and a satisfying result was obtained. The resulting multiple-line pattern can be used in robot vision and other applications.     

离子束倾斜入射抛光对表面粗糙度的影响

基于光学元件离子束高精度确定性抛光技术,在自行研制的离子束抛光机床上,本文研究了离子束倾斜入射抛光对光学材料熔石英表面粗糙度的影响.为了在离子束抛光中改善表面粗糙度,采用了0°～80°之间不同入射角度的离子束倾斜抛光和倾斜45°入射均匀去除两种实验方案进行研究,其中不同入射角度抛光实验研究结果表明:离子束垂直入射抛光较难改善表面粗糙度,倾斜入射抛光可以较好地改善表面粗糙度,入射角为30°～60°之间时抛光效果最佳,表面粗糙度得到明显改善;倾斜45°入射均匀去除抛光实验结果表明表面粗糙度的RMS值由抛光前(0.92±0.06)nm下降到(0.48±0.04)nm,提高了光学零件的表面质量,验证了离子束倾斜入射抛光可以较好地改善表面粗糙度,实现了离子束倾斜抛光超光滑表面的生成.     

Investigation on the effect of surface modification of 3D printed parts by nanoclay and dimethyl ketone

Fused deposition modeling (FDM) has emerged as one of the most utilized 3D printing technique. However, the surface properties of the FDM built parts lacks integrity due to layer by layer manufacturing technique. Therefore, post treatment is done on FDM printed parts. In the present research work, an effort has been made to improve the surface properties of the 3D printed parts by surface modification via chemical/nanoparticles. Nanoclay and dimethyl ketone were utilized for the surface modification of acrylonitrile butadiene styrene specimens. Parameters namely nanoclay content, immersion time, heat treatment and layer thickness were investigated to study their effect on surface roughness, surface hardness and dimensions. Also, the effect of nanoclay on UV absorbance of 3D printed parts was observed. Structural and morphological analysis was performed to characterize the surface of the 3D printed specimens after surface modification process. The results show that the surface roughness was reduced by 94.9%, surface hardness was increased by 9.7% while maintaining minimum dimensional deviation of ?0.03 and +0.07?mm. Also, UV absorbance was increased in 350–380?nm range. The results of the present study highlight the capability of the surface modification process for improving the surface properties of FDM parts.     

Microstructure of magnesium fluoride films deposited by boat evaporation at 193 nm

Single layer magnesium fluoride (MgF2) was deposited on fused-silica substrates by a molybdenum boat evaporation process at 193 nm. The formation of various microstructures in relation to the different substrate temperatures and deposition rates were investigated. The relation between these microstructures (including cross-sectional morphology, surface roughness, and crystalline structures), the optical properties (including refractive index and optical loss) and stress, were all investigated. It was found that the laser-induced damage threshold (LIDT) would be affected by the microstructure, optical loss, and stress of the thin film. To obtain a larger LIDT value and better optical characteristics, MgF2 films should be deposited at a high substrate temperature (300 degrees C) and at a low deposition rate (0.05 nm s(-1)).     

Partial-Ductile Grinding, Lapping, and Polishing of Aspheric and Spherical Surfaces on Glass

This paper discusses partial-ductile-mode grinding, lapping and polishing of aspheric and spherical surfaces on glass. Industrial manufacture of glass lenses usually involves three operations: grinding (known as milling in the optical industry), tapping, and polishing. The fracture mode of material removal is dominant in the grinding process. While these three operations have been successful for machining spherical lenses, aspheric lenses have been manufactured in the absence of the lapping process, because of the considerable amount of ductile mode of material removal in grinding. The parameters that helped identify and solve problems in manufacturing were surface roughness, micro-fractures and ductile streaks on glass surfaces, and interferometric fringes.     

Microforging technique for rapid, low-cost fabrication of lens array molds

Interest in micro-optical components for applications ranging from telecommunications to life sciences has driven the need for accessible, low-cost fabrication techniques. Many microlens fabrication processes are unsuitable for applications requiring 100% fill factor, apertures approximately 1000 microm with high numerical aperture, and scalability to large areas (e.g., tens of centimeters to meters) with millions of lenses. We report on a flexible, low-cost mold fabrication technique that utilizes a combination of milling and microforging. The technique involves first performing a rough cut with a ball-end mill. Final shape and sag height are then achieved by pressing a sphere of equal diameter into the milled divot. Using this process, we have fabricated molds for rectangular arrays of 1-10,000 lenses with apertures of 25-1600 microm, sag heights of 3-130 microm, interlens spacings of 250-2000 microm, and fill factors up to 100%. Mold profiles have a roughness and figure error of 68 nm and 354 nm, respectively, for 100% fill factor, 1000 microm aperture lenses. The required forging force was modeled as a modified open-die forging process and experimentally verified to increase nearly linearly with surface area. The optical performance of lens arrays injection molded from microforged molds was characterized by imaging the point spread function and was found to be in the range of theoretical values. The process can be easily adapted to lenticular arrays as well. Limitations include milling machine range and accuracy.     

Optical properties of the thermal oxide-GaAs rough interface

The surface roughness of GaAs originating during thermal oxidation at a temperature of 450 °C was studied using multiple-angle-of-incidence ellipsometry at 632.8 nm and reflectometry on samples after the dissolution of the oxide film. The rough surface is represented by an effective layer with optical constants determined in the Bruggeman effective medium approximation. Experimental data were used to determine the thickness of the effective layer and the volume fraction of voids. The properties of the natural oxide film on the surface of the samples are also discussed.     

Grinding of Toroidal and Cylindrical Surfaces on SiC Using Diamond Grinding Wheels

This paper presents the methods and experimental results for grinding toroidal and cylindrical surfaces made of silicon carbide using diamond grinding wheels and an inexpensive CNC machining center. The mirrors were successfully obtained by automatic grinding operations with good shape accuracy, mirror surface finish, and low roughness heights. The time consumed in the process is very short. Industrial manufacture of lenses usually involves three operations — grinding without dressing, lapping, and polishing. In the laboratory studies, however, mirrors and lenses have been manufactured only with grinding process, because of 100% ductile-mode material removal in grinding with dressing. These processes were individually evaluated for surface roughness and surface integrity using surface roughness testers and a scanning electron microscope.     

Fluid jet polishing of optical surfaces

We present a new finishing process that is capable of locally shaping and polishing optical surfaces of complex shapes. A fluid jet system is used to guide a premixed slurry at pressures less than 6 bars to the optical surface. We used a slurry comprising water and 10% #800 SiC abrasives (21.8 mum) to reduce the surface roughness of a BK7 sample from 350 to 25 nm rms and to vary the shape of a polished sample BK7, maintaining its surface roughness of 1.6 nm rms, thereby proving both the shaping and polishing possibilities of the presented method.     

Influence of rf-power on the plasma carbonitriding of titanium

The present work reports on the effect of input plasma processing power in the range of 350–650 W on the microstructure and mechanical properties of plasma nitrided Ti. The plasma processing time was 20 min and a gas mixture of 15% C₂H₂ and 85% N₂ was used. The characteristics of the carbonitrided layer have been investigated by microhardness measurements, surface roughness measurements, optical microscopy, and X-ray diffraction. The measured surface hardness values of the compound layer shows a maximum of 2050 HV0.1 for the sample treated at a plasma power of 550 W. The thickness of the carbonitrided layer continuously increases as the plasma power increases. Moreover, the highest carbonitriding rate of 3.52 μm²/s was observed when the input plasma power was adjusted at 600 W. This high carbonitriding rate of treated titanium samples is ascribed to the high concentration of active carbon and nitrogen species in the plasma atmosphere and the formed microcracks in the near surface of the sample during the plasma processing.     

Influence of the surface roughness on the properties of Au films measured by surface plasmon resonance and X-ray reflectometry

Thickness and refractive index of Au films thermally evaporated onto glass substrates and with an underlayer of Cr are determined from surface plasmon resonance. The results for the thickness are found to agree very well with those from X-ray reflectivity when a simple model of layers with flat interfaces is used. Plasmon propagation along thin films is influenced by radiative damping due to scattering from surface roughness. To study this influence the surface roughness of the glass substrate, Cr an Au layers are measured by X-ray reflectometry and the results used to introduce three intermediate layers with effective refractive indices and thicknesses corresponding to the roughness. Then Fresnel's equations are used to fit the reflectivity and to deduce the layer properties. It is found that the roughness affects to a great extent the optical parameters of the Au films even when it is smaller than 1 nm. In particular, the absolute value of real part of the dielectric constant decreases while its imaginary part increases when those effects are not taken into account.     

光学元件聚氨酯抛光特性研究

本文研究了应用于平面光学元件的快速抛光技术,从材料去除率、元件面形和表面粗糙度出发,对快速抛光技术应用于平面大口径元件的加工效果进行了探讨。研究了在快速抛光技术中压力和主轴转速对材料去除率的影响,验证了Preston公式在快速抛光中的适用性,快速抛光技术的去除效率可达10μm/h;其次,研究了聚氨酯抛光元件面形的精度,对于330mm×330mm元件可达～1.0λ（λ=632.8nm）;最后,对快速抛光系统中抛光粉颗粒大小及形态随使用时间的变化进行了观测,并测量了使用300目和500目抛光粉时快速抛光元件表面粗糙度以及其随抛光粉使用时间的变化。