Surface Shape Accuracy Research Articles

Lightweight Design and Evaluation of Square Reflector

In order to reduce the weight of optical elements in space remote sensors while increasing their stiffness, this paper takes an off-axis system secondary mirror as an example to design a square mirror with a size of 500 mm × 500 mm. The mirror adopts ultra-low expansion glass as the raw material. The paper proposed a lightweight form of gradual reinforcement and conducted the mirror assembly simulation analysis. The analysis results show that the weight of the lightweight mirror is 13.6 kg, and the surface density can reach 54.4 kg/m2. Under the circumstances of 1 g gravity and the temperature change of 15 °C~25 °C, the surface shape accuracy of the mirror assembly can reach 1/90λ (λ = 632.8 nm). Through the final testing, the first-order intrinsic frequency of the reflex mirror components is 167.8 Hz. The gap between the test results and the theoretical simulation results is less than 3%, which proves that the mirror assembly in the lightweight form of gradual reinforcement fully meets the index requirements and can provide a theoretical reference for the assembly of a mirror of similar size and type.

Optimization Design of Large-Aperture Primary Mirror for a Space Remote Camera

Lightweight, high stability, and high-temperature adaptability are the primary considerations when designing the primary mirror of a micro/nano satellite remote sensing camera. In this paper, the optimized design and experimental verification of the large-aperture primary mirror of the space camera with a diameter of Φ610 mm is carried out. First, the design performance index of the primary mirror was determined according to the coaxial tri-reflective optical imaging system. Then, SiC, with excellent comprehensive performance, was selected as the primary mirror material. The initial structural parameters of the primary mirror were obtained using the traditional empirical design method. Due to the improvement of SiC material casting complex structure reflector technology level, the initial structure of the primary mirror was improved by integrating the flange with the primary mirror body design. The support force acts directly on the flange, changing the transmission path of the traditional back plate support force, and has the advantage that the primary mirror surface shape accuracy can be maintained for a long time when subjected to shock, vibration, and temperature changes. Then, a parametric optimization algorithm based on the mathematical method of compromise programming was used to optimize the design of the initial structural parameters of the improved primary mirror and the flexible hinge, and finite element simulation was conducted on the optimally designed primary mirror assembly. Simulation results show that the root mean square (RMS) surface error is less than λ/50 (λ = 632.8 nm) under gravity, 4 °C temperature rise, and 0.01 mm assembly error. The mass of the primary mirror is 8.66 kg. The maximum displacement of the primary mirror assembly is less than 10 μm, and the maximum inclination angle is less than 5″. The fundamental frequency is 203.74 Hz. Finally, after the primary mirror assembly was precision manufactured and assembled, the surface shape accuracy of the primary mirror was tested by ZYGO interferometer, and the test value was 0.02 λ. The vibration test of the primary mirror assembly was conducted at a fundamental frequency of 208.25 Hz. This simulation and experimental results show that the optimized design of the primary mirror assembly meets the design requirements of the space camera.

Application of the Improved Grinding Technology to Freeform Surface Manufacturing

In order to meet the manufacturing requirements of modern space remote sensors for high-precision freeform optical parts, the grinding technology and its application were studied. The objective of this paper was to improve the application effect of traditional grinding technology in the processing of hard and brittle materials, and then apply it in specific fields. Therefore, the influence of key process factors such as cutting speed and removal depth on subsurface damage (SSD) was studied based on orthogonal experiments, and an improved grinding technology characterized by low SSD and high surface shape accuracy was formed. Then, the effect of this grinding technology was further verified by the high-precision manufacturing of freeform surfaces. A surface of a 130 mm diameter freeform surface was machined by improved grinding technology and combined polishing technology, the final root mean square of surface shape reached 12.1 nm. The improved grinding technology can reduce SSD from 20 μm to 10 μm, and improve the manufacturing efficiency of freeform surfaces above 30% when the cut speed is 20 m/s and the remove depth is 10 μm. The proposed technology can be applied to the extreme manufacturing of hard and brittle materials.

Внеосевой асферический коллектор для экстремальной ультрафиолетовой литографии и мягкой рентгеновской микроскопии

By the method of ion-beam shape correction, a small-sized ion beam formed a non–axisymmetric aspherical profile of the collector surface for an extreme ultraviolet radiation source TEUS-S100 with a numerical aperture of NA= 0.25, PV on the surface is 36.3 microns, the surface shape accuracy by standard deviation is 0.074 microns, which allowed to obtain a focusing spot with a width of 300 microns at half-height. To solve the problem, the technological ion source KLAN-53M was upgraded – the flat ion-optical system was replaced with a focusing one. The ion-optical system consisting of a pair of concave grids with a radius of curvature of 60 mm provided the following parameters of the ion beam: the ion current is 20 mA, the width at half–height is 8.2 mm at a distance of 66 mm from the cutoff of the ion source.

Multifunctional PLA/CNTs nanocomposites hybrid 3D printing integrating material extrusion and CO2 laser cutting

Material extrusion (MEX) 3D printing fabricates cost-effective functional polymeric parts, while a new class of materials, such as polylactic acid/carbon nanotubes (PLA/CNTs) nanocomposites, have great potential for use in MEX due to their multi-functional performance. MEX advantages include the construction of lightweight specimens with complex geometry, in minimum time and with minimum waste, while its drawbacks are related to the parts' surface roughness, anisotropic behavior, and shape accuracy. To improve the properties of parts, build with MEX, thus extending their applicability in areas such as biomedical, aeronautics, automotive, printing electronics, and others, the 3D printing parameters need to be controlled, while post-processing further and significantly improve their performance. Combining 3D printing with laser as a post-processing technology highly improves the efficiency of the nanocomposites. In this work, new data are reported on PLA/CNT nanocomposites in thin plates form, manufactured with MEX and pro-processed with low-cost CO2 laser cutting, for the improvement of their shape accuracy and their surface roughness, making them eligible for use in innovative nanocomposite-based applications.

Effect of fabrication method and surface roughness on spray characteristics for small pressure-swirl atomizers

The paper investigates the effect of the fabrication method, precision and surface roughness on atomization nozzle performance. A comprehensive review of the available knowledge on the topic is an integral part and an indispensable prerequisite of the study. It focuses on the requirements for atomizing nozzles and their production from the point of view of surface quality, dimensional and shape accuracy. The published results on the influence of surface quality and roughness on internal flow and atomizer performance are discussed. Available atomizer manufacturing techniques are reviewed with a focus on Rapid prototyping methods, accuracy and geometrical imperfections.Classical Machining and two 3D printing techniques were applied to produce small pressure-swirl atomizers. They were fabricated in a number of versions. The machined nozzles featured several specific defects. Spray quality measurements of these atomizers, at selected operation regimes, were made on a cold test bench using PDA and mechanical patternation to evaluate discharge coefficient (CD), Sauter mean diameter, spray cone angle, nozzle efficiency (ηn), breakup length and liquid distribution in the spray.The results show the important and systematic effects of surface quality and manufacturing imperfections on the atomizer characteristics. The exit orifice imperfections harm the circumferential uniformity and other spray characteristics. The effect becomes significant when the exit orifice shifted out of the nozzle axis by >2 % of the chamber diameter, and the orifice edge is chamfered by >20 % of the orifice length. The swirl chamber surface modified by scratches has a minor effect.Replacement of machining with current commercial 3D printing techniques, namely Selective laser melting and PolyJet technique, is associated with increased surface roughness. It worsens spray quality, liquid distribution uniformity and ηn and increases the CD when relative surface roughness exceeds 0.007.The result presentation using dimensionless criteria allows for generalisation of the outcomes to other atomizer types and scales.

ANALYSIS OF TECHNOLOGICAL PROCESSES LASER SURFACING IN ADDITIVE MANUFACTURING

The prospects for the development of the machine-building complex are largely associated with a reduction in the volume of production waste and the number of operations in the production chain. The realization of this task is possible thanks to the use of technologies that ensure that the workpiece is shaped close to the shape of the finished product in one technological operation. A landmark event in mechanical engineering was the development of additive manufacturing, combining technologies for manufacturing parts based on a three-dimensional CAD model without the use of forming elements and machining. One of such technologies is three-dimensional shaping by laser surfacing. This method of physical and technical processing uses the energy of laser radiation to melt the surfacing material and the underlying layer in order to form a roller on it, metallurgically connected to the base. Laser surfacing is effective when applying coatings and repairing worn parts. The article analyzes the technological processes of laser surfacing in additive manufacturing. Laser surfacing, limited in its technological capabilities, has so far been used for surface modification, restoration and production of medium- and large-sized products with low requirements for surface quality, dimensional and shape accuracy and significant allowances for machining.The creation of precision system technology for laser surfacing made it possible to expand the scope of its application into the submillimeter area and develop an independent direction - microlaser surfacing. In the conditions of growing demand for manufacturing technologies of small-sized products, including thin-walled ones, the development of the technological process of microlaser surfacing is an urgent scientific and technical task. However, its capabilities in the manufacture of small-sized products are limited by the minimal size of the grown element, which, in turn, depends on the size of the impact zone (transverse dimensions of the melt bath and the deposited roller). For this reason, laser surfacing is traditionally used in the production of medium- and large-sized parts with significant allowances for subsequent machining. Scientific and technological progress in laser surfacing technology has created prerequisites for the miniaturization of the processing zone of less than 1 mm and the development on this basis of technological processes of laser surfacing in the submillimeter region (microlaser surfacing) to expand the capabilities of the method in the production of small-sized products, which is an urgent task in the conditions of growing demand for-manufacture of small-sized parts.

Flow rate improvements in additively manufactured flow channels suitable for rocket engine application

This contribution describes the investigation of flow channels which are designed to be directly integrated into an aerospike engine by means of additive manufacturing with laser powder bed fusion (LPBF). During the experimental testing of a previous aerospike engine in 2019, it was observed that high surface roughness of such additively manufactured integrated channels caused a significant reduction in the mass flow rates of the propellants ethanol and liquid oxygen as well as the coolant due to increased pressure drop. In an extensive study within the CFDmikroSAT project, various factors influencing this surface roughness are, therefore, being investigated, which include the geometry of the channels as well as selected manufacturing parameters of the LPBF process, such as layer thickness and component orientation. To further reduce the roughness after manufacturing, suitable post-processing methods are also being investigated for internal cavities, initially analysing the abrasive flow machining process. Within the paper, the overall investigation approach is presented, such as the overview of the considered specimens, and the initial results of a various studies with selected specimens are discussed. These studies consist of the examination of surface roughness reduction, shape accuracy and flow behaviour of post-processed cooling channel specimens. Finally, a brief overview of the already manufactured aerospike demonstrator is presented.

An Exploration into Damage Repair and Manufacturing Technology of Photomask Glass Substrates

There are strict requirements on the surface-shape accuracy, cracks, scratches, and subsurface damage of photomask glass substrates with the advancement of photo-etching technology. In this study, photomask quartz glass substrates were etched with the hydrofluoric (HF) acid etching method after chemical mechanical polishing (CMP), so that the polishing hydrolysis layer could be completely removed. In addition, the surface scratches caused by CMP were observed with a surface quality detection device and a white light interferometer. Second, the high-efficiency array-type magnetorheological polishing technology was employed to eliminate the surface-shape error on the surface of quartz photomask glass substrates. Finally, the removal function rotation angle based magnetorheological polishing technology was utilized to evenly remove the mid-frequency ripples and scratches caused in the preceding technological process. The experimental results demonstrated that these technologies can be used to realize rapid damage removal and high-quality processing of photomask glass substrates.

Effects of machining parameters on surface morphology of porous bronze during monocrystalline diamond cutting

Porous bronze materials manufactured by powder metallurgy require further machining to improve the surface quality and shape accuracy. However, conventional machining with carbide tools and PCD tools can lead to serious pore failure problems. In this paper, monocrystalline diamond (MCD) tools were used to carry out the milling experiments on porous bronze at different machining parameters. The pore area and diameter of the machined surface were used statistically to analyze the effect of different machining parameters on the pore structure during the cutting process. For the porous bronze exhibiting different removal patterns from other materials during the experiments, a novel porous cutting model based on random powder particles was created to verify that the pore structure significantly altered the cutting mechanism of the bronze material at different cutting depths. The experimental results showed that the cutting speed also had a great influence on the porosity, due to the positive strain rate effect of the bronze material, while the influence of feed rate was relatively small. During the cutting process, the material was extruded and rubbed by the cutting edge arc and tool flank face, causing the material to flow into the nearby pores, leading to a decrease in surface porosity. The conformed porosity of the machined surface demonstrates that CNC machines with MCD tools can meet the machining requirements of porous bronze and solve the pore blockage problem in porous materials. This provides a technical reference for the choice of processing methods for porous plastic materials.

An Efficient Electrochemical Polishing Method with Planarization Ability Employing Solid and Liquid Electrolytes

Stress-free polishing is the most potential machining method for high quality surfaces without surface defects. Traditional electrochemical polishing (L-ECP) is immersed in a liquid electrolyte to realize stress-free polishing. However, due to the limitation of its polishing principle, the electrochemical polishing process cannot improve the surface shape accuracy of the workpiece so far. In this work, a new method solid-liquid electrolyte electrochemical polishing (SL-ECP) for electrochemical polishing assisted by a solid electrolyte polishing pad is proposed. Power spectral density (PSD) of the profile of polished surfaces were compared, and it was found that the low-spatial-frequency error was reduced by contacting the flat solid electrolyte surface with the workpiece surface. After SL-ECP, the roughness S a of the workpiece decreased from the initial 82.83 nm to 2.92 nm (10 μm × 10 μm), and the peak-to-valley value of the entire workpiece surface decreased from the initial 16.39 μm to 1.81 μm. And the material removal rate of SL-ECP was 35 times that of L-ECP using the same liquid electrolyte. This study not only proposes an efficient stress-free polishing method for high-quality surfaces, but also contributes to further understanding of the mechanism of electrochemical polishing.

Design and fabrication of lightweight additively manufactured mirrors for aviation.

This paper proposes a design process for additively manufactured mirrors. A central support aspheric mirror and tripod support structure were manufactured via selective laser melting. To achieve substantial weight reduction, an additively manufactured body-centered cubic lattice structure was used in the mirror design. Simulation analysis showed that the mirror had good rigidity. Single-point diamond turning was applied to obtain an optical quality mirror. After assembly, the rms surface shape accuracy of the mirror was 0.069λ (λ=632.8nm). The surface roughness (Ra) of the additively manufactured metal mirror was 8.125 nm. These findings provide a strong theoretical basis and technical support for the preparation and application of lightweight metal mirrors.

Design of a fast steering mirror driven by piezoelectric ceramics

To solve the small-optical aperture and stroke problem of existing fast steering mirror (FSM), we focus on the design of FSM driven by piezoelectric ceramics in space laser communication and lidar systems. The structure design of the FSM and the theoretical analysis of the piezoelectric actuators are carried out. The special structure and installation process of the mirror assembly are designed to ensure the accuracy of the mirror surface. Theoretical calculation and simulation analysis are conducted to evaluate the mirror’s output angle. The dynamic model of the FSM is established to analyze the stiffness. The operating principle and characteristic analysis results of FSM are verified by experimental tests. The results show that the FSM can provide a mechanical excursion angle of ±2.35 mrad, the closed-loop linearity of X axis and Y axis are 0.71% and 0.67%, respectively, and the closed-loop bandwidth of the FSM is 28 Hz. The surface shape accuracy of the mirror after installation can reach 1 / 50λ.

Machining of elliptical curve profile for application in manufacturing industries

Manufacture of products with freeform curves is the need of the day in manufacturing industries like turbine blades, automobile bodies, aerofoils etc. Such profiles are usually manufactured on high precision machines. High precision (CNC) machines are required to enhance product quality at a reasonable cost. CNC programs with preparatory codes (G01, G02, or G03) provide automation, but the machines are restricted to the ability of linear and circular interpolators. Hence, due to the unavailability of appropriate preparatory function, machining of these curved shaped components causes difficulty on CNC machines. The CAD / CAM software divides the profile into the numbers of small linear segments. The transmission of the linear segments from software to CNC machine is subjected to errors. It results in noise and lost data. The discontinuity of the freeform toolpath deteriorates the surface quality and shape accuracy due to linear segments. To enhance the shape accuracy and surface quality, the numbers of linear segments are to be increased. Each linear segment to be machined is adding a single block in the part program. It will increase the size of the part program and program memory size at the cost of the surface quality. To achieve better surface quality and shape accuracy, MACRO programming is required. In the present work, the freeform regular axis-symmetrical profile (i.e. ellipse) is machined on mild steel (MS) and aluminum material using NURBS as well as Hermite interpolators. The curved profiles machined by MACRO and conventional programming methods are examined to measure surface quality using surface roughness tester (i.e., Mitutoyo SJ-210®), while toolpath deviation is examined with the actual profile plotted with CAD software (i.e., AutoCAD®). Radial and chordal errors are the least in the case of NURBS interpolation compared to Hermite interpolation. A better surface finish is observed while the elliptical profile is machined on mild steel and aluminium with MACRO programming

Finite Element Analysis of Compensation of Surface Shape Accuracy of Piezoelectric Bimorph Mirror

Finite Element Analysis of Compensation of Surface Shape Accuracy of Piezoelectric Bimorph Mirror

Repair of damaged parts using wire arc additive manufacturing in machine tools

Mechanical parts manufactured using additive manufacturing (AM) processes are used in various fields, such as the aerospace, automobile, and machine tool fields. Recently, many researchers have been actively researching AM processes, owing to their advantages in fabricating complex-shaped components that are difficult to process using conventional processes such as rolling, forging, and casting. One of the AM processes, wire arc additive manufacturing (WAAM), is widely used for manufacturing and repair. Mechanical parts usually suffer from severe damage, such as wear and cracks, during operation. Therefore, research on the damaged parts is often required for repairs. This study was performed to investigate the repair of damaged parts using WAAM in machine tool remanufacturing. In general, these parts are often damaged owing to falls of the workpieces and the inexperience of workers; the cross slide is one of the parts damaged most often in a lathe. Accordingly, this study used the cross slide as an example. First, the damaged area was partially cut flat. Second, it was filled with a metal wire using WAAM. Third, post-processing was performed to adjust the surface quality and shape accuracy. Then, the microstructure, chemical composition, and mechanical property of the repaired part were analyzed. Finally, the repaired cross slide was used to replace damaged parts. In general, this method can be applied to various mechanical parts such as impellers, turbine blades, and machine tools.

Adjustable carbon fiber reinforced plastic panel for a large-aperture telescope

Segmented mirrors are commonly used to construct large-aperture telescopes. We present a methodology for structural analysis and experimental results of an adjustment of a mm- to far-IR range (10 mm to 70 μm) segmented mirror panel to correct its deviation from an optimum paraboloid of rotation. The panel is made of high-modulus carbon fiber–reinforced plastic and has a shape of a 15-deg sector with a 1207 × 390 mm2 reflecting surface area. A system of mechanically operated adjusters for correcting large-scale surface deformations is described. We used our original method to correct fabrication errors and improved the surface shape accuracy from 23.8 to 4.5 μm (RMS values). The method is based on distance-to-target-surface minimization using vector influence functions and arbitrary movements. The results of the long-term panel shape stability monitoring and the effect of cooling the panel down to 77 K are also presented.

Micro-stress bonding analysis of high precision and lightweight mirrors.

We propose analysis methods for mirror bonding. The functional relationship between the shrinkage of the adhesive layer and the shape accuracy of the mirror is established numerically. By designing the structural form of the optical mounting and setting an appropriate stiffness ratio between the mirror and bonding position of the optical mounting, the theoretical surface shape accuracy change can be determined. Accordingly, the mirror is bonded, and the surface shape accuracy of the mirror after bonding is found to be 0.020λ. This approach is useful in mirror design applications that require rapid preparation and accuracy control.

Effect of chromium coating thickness on surface adhesion of polyethylene terephthalate optical film

Surface accuracy and shape accuracy are the two key factors that determine the reflective performance of electroforming replication mold. However, the adhesion between the master mold and the replica mold sometimes causes the deformation, fracture and stretching of the microstructure of the mold surface. The reflective performance of the mold surface is reduced. For this reason, this paper proposed a method for reducing the adhesion force by means of a metal Cr transition layer, which was deposited on polyethylene terephthalate (PET) optical film using direct current (DC) magnetron sputtering. The effect of the Cr coating thickness on adhesion force was investigated. The surface of the film was analyzed by the measurement of contact angle, surface energy, surface chemical composition and micro-morphology. The measurements indicate that the surface energy of the PTE films is reduced after being deposited with a thin Cr coating. The reduced surface energy could be due to the fact PET′s polar functional groups were covered by the Cr coating, which must have lower surface energy than the PTE′s surface. In addition, the reduction of surface roughness also helps to reduce the adhesion of PET film surface. The study showed that Cr coating can effectively reduce the surface adhesion of PET optical mold and improve the surface quality of duplicated mold. The work provides a new method to reduce the surface adhesion of PET optical molds for application in electroforming demoulding technology and interfacial adhesion can be adjusted by the thickness of the Cr coating.

Method to improve the surface shape of BK7 glass in full-aperture polishing.

Full aperture polishing is a significant process to fabricate optical workpieces with nano figure precision. It has the characteristics of excellent full spectrum uniform removal ability, fast convergence speed, high machining accuracy, and low production cost, which makes it the first choice for the processing of large-aperture optical elements. However, with BK7 glass it is difficult to achieve deterministic processing due to its large thermal expansion coefficient and other factors, and the surface shape accuracy is difficult to improve. In this paper, the thermal deformation of BK7 glass is analyzed first, and then the temperature distribution in the element is measured during full-aperture polishing. The influence of the temperature field in the optics on the accuracy of the final surface shape is analyzed, and the quantitative relationship between the temperature difference and the surface shape is established. In addition, the methods of deterministically controlling the surface shape of optics such as polishing liquid temperature control and immersion polishing are proposed. Finally, the model of quantitative control of the surface shape of optics is verified by experiments, which improve the surface shape accuracy of 600 mm BK7 optics to 0.2λ.