Three-robot system for efficient large-aperture mirror lapping.

The production of metal parts via powder bed fusion (PBF) additive manufacturing is rising exponentially. However, the transition of the PBF process from prototyping to production of critical parts such as fuel injectors, conformal cooling channels, and hydraulic manifolds are hindered by a lack of confidence in the surface quality. The poor surface characteristics of PBF components demand post-process surface finishing. The unique surface morphology of PBF components poses several challenges to existing surface finishing techniques. A novel surface finishing technique with dynamic material removal characteristics is required to enhance the internal surface quality.
\nIn this thesis, a novel surface finishing process: Hydrodynamic cavitation abrasive finishing (HCAF) was developed. The HCAF technique utilizes the multiphase hydrodynamic principles of high-intense cavitation and microparticle abrasion for surface finishing. The cavitation-assisted microparticle abrasion, a phenomenon that was stated uncontrollable and destructive in the late 1800s, is effectively harnessed for internal surface finishing using a closed-loop hydrodynamic apparatus. The multiphase hydrodynamic flow is harnessed for surface finishing using a pressure-controlled chamber integrated into the HCAF apparatus.
\nFirst, the hydrodynamic flow characteristics in the HCAF apparatus is extensively characterized using high-speed camera observations and underwater hydrophone sensors. The flow regime transitioned from non-cavitating to cavitation inception, developing and fully developed cavitating phases. From the observations, two configurations: (a) free-stream and (b) submerged; and three modes: (a) hydrodynamic cavitation finishing (HCF), (b) hydrodynamic abrasive finishing (HAF), and (c) hydrodynamic cavitation-assisted abrasive finishing (HCAF) were identified for surface finishing. The root-mean-squared pressure (P_rms) and acoustic energy (E_A) in the non-cavitating conditions were 225 Pa and 47 kJ; in cavitating conditions were up to 6000 Pa and 84 MJ. The significant difference is attributed to the high-intense cavitation microbubble implosion in the fluid medium.
\nSecond, a parametric study was conducted to study the influence of cavitation and abrasion on surface finish and material removal characteristics in direct metal laser sintered (DMLS) AlSi10Mg internal channels. The parametric study led to the finding of novel material removal mechanisms in the HCAF process. Material removal mechanisms include #1 – cavitation erosion, #2 – microparticle abrasion, and #3 – cavitation-assisted microparticle abrasion. The maximum calculated impact pressure (𝑃𝑖𝑚𝑝𝑎𝑐𝑡) = 108 MPa, arising from cavitation bubble implosion, is less than the yield strength of AlSi10Mg alloy (240–270 MPa). Instant material removal of the substrate is unlikely with a single microjet impact. Hence, material removal was caused by low-cycle fatigue, while the surface texture was homogenized (same spatial frequency) through abrasive microcutting.
\nThe surface finish quality of the internal channels improved with an increase in hydrodynamic upstream pressure (P_u), abrasive concentration (A_c), fluid temperature (T), and processing time (t). However, the surface quality decreased with increase in downstream pressure (P_d) due to increased cavitation collision with the surrounding bubbles. The surface finish quality of the internal channels improved by greater than 90 % (initial arithmetic mean deviation of the assessed profile (Ra) > 25 µm, maximum height of the assessed profile (Rz) > 100 µm to final Ra < 3 µm, Rz < 30 µm) with a process parametric combination of P_u = 0.7 MPa, P_d = 0.1 MPa, T = 50 ± 2.5 °C, and Ac = 1.0 %. The surface-finish improvement saturated due to the presence of sub-surface defects that kept emerging to the surface with further processing. 
\nThird, the surface integrity of the internal channels post-HCAF was investigated. An acceptable thickness loss of 45 µm was noticed with 90 % Ra and Rz improvements. For the microstructure, coarse and irregular grains on the surface (due to loosely attached particles and partially melted powders) were removed; fine and uniform grains (due to fully melted bulk material) were exposed on the surface. Residual stress in the surface was unchanged. However, marginal microhardness improvements (up to 13 %) were noticed. Surface homogenization by microabrasives (abrasive size, A_s = 10 µm) generated a unique microcutting pattern that improved surface wettability by up to 58 %. Moreover, the roughness ratio r ≈ 1 evidenced the uniform and flat surface post-HCAF.
\nFourth, to gain a deep scientific understanding of the cavitation-assisted microparticle material removal phenomenon, comparative investigations were performed in HAF, HCF, and HCAF modes. The erosion rate (ε ̇) in HCAF was higher than the sum of erosion due to HAF and HCF. Thus, it was understood that a synergistic effect stems out from the interaction between cavitation and microparticles. The synergy (E_s), stemming out from the interaction between cavitation bubble-particle interaction increases the erosion rate by 80 %. The synergy coefficient (β = 1.09 and 0.26 at 0.5 % and 1.0 % Ac) suggests that the rate of increase in synergy decreases with an increase in the abrasive concentration. This is because excessive addition of abrasives alters the fluid properties and suppresses cavitation.
\nLast, an industrial scale multi-jet hydrodynamic cavitation abrasive finishing (MJ-HCAF) apparatus was developed to surface finish large and complex PBF components; decrease processing time; reduce abrasive usage. A case study was performed on PBF Inconel 625 fuel injection/spray nozzles using the MJ-HCAF apparatus. The fuel nozzle geometry is split into linear, non-linear, stepped, and branched internal channels. Internal channels up to a diameter of 1 mm and length 100 mm; non-linear channels with diameter up to1 mm and sharp curvatures; fuel injection tips with four internal branches and spray nozzle tips with five internal branches were surface finished using MJ-HCAF. An excellent surface finish with up to 90 % improvements was achieved in all the channels within 15 minutes of processing. The arithmetic mean height of the scale-limited surface (Sa) and maximum height of the scale-limited surface (Sz) were < 1 µm, and < 20 µm, respectively.
\nThe research findings support the hypothesis that cavitation-assisted microparticle abrasion could be used to enhance the surface quality of complex PBF internal channels. The extremely less use of Ac ≤ 1 % weight concentration and eliminating the need to replenish the abrasives using an in-built filtration system makes MJ-HCAF stand out from conventional surface finishing techniques and signifies an emerging class of clean and green manufacturing technology.

Perkin-Elmer fabricated two 9.5 in. (24.1 cm) diameter beryllium mirror blanks using an advanced powder metallurgy process to produce mono-lithic, lightweight (2.16 lb = 0.98 kg) structures with honeycomb interiors. The new beryllium material exhibits improved isotropy as measured by x-ray diffrac-tion techniques. The mechanical properties meet or exceed the published values for commercially available vacuum hot pressed beryllium block. In addition, the material is readily polished to good figure and surface quality and has demonstrated potential for lower scatter than standard material. The monolithic sandwich construction demonstrated in the program is exceptionally stiff, permitting large lightweight mirrors to be constructed. A scaled-up 36 in. (91.4 cm) diameter mirror would weigh only 31 lb (14.1 kg) using the technology demonstrated in the project. It is estimated that with minor modification in the process this weight could be halved.

Additive manufacturing (AM) and machining in a single machine colloquially known as Hybrid manufacturing help to produce customized and complex products without assembling including greater design freedom and reduced material wastage. A CNC-based grinding mechanism is introduced in the same system to overcome those defects and enhance the quality. To increase productivity and improve product surface quality, evolving additive manufacturing demand and finishing subtractive processes must be combined on the same platform. For the additive manufacturing method, Fused Deposition Modeling (FDM) has been employed, and a grinding operation can be performed for surface finishing. A camera module is used to capture surface images for defect detection such as stringing, rashing, and surface cracking after the AM process. Convolutional Neural Network (CNN) is applied to the captured image for the defect detection process. If the CNN analysis reveals any surface defects, a grinding operation will be performed on the surface for better surface quality. The architecture has provided a platform to collect data from the image captured by the camera module for evaluating and identifying surface defects using CNN. CNN model provided 89% accuracy for surface defects detection. As a result, the CNC grinding operation can be done on that particular surface of the product for smoothing the partially roughened surfaces. Therefore, this study demonstrates to improve the surface quality, reduce cycle time, set up time reduction & improve the product's sustainability. The proposed approach of a hybrid manufacturing system also provides a basic framework to increase efficiency, reduce downtime, increase efficiency, improve end part consistencies of the product as a consequence of post-processing & defect detection in the same system, and enable I4.0

Effects of slurry pH on chemical and mechanical actions during chemical mechanical polishing of YAG

The application of pellet extrusion forming in aerospace and medical is limited due to challenges such as unstable forming quality, low manufacturing precision, and poor surface quality. To address these issues, this study proposes a hybrid manufacturing technology integrating pellet extrusion with milling. This approach combines the rapid forming and complex structure fabrication capabilities of additive manufacturing with the precision machining strengths of subtractive manufacturing, enabling high-precision and high-surface-quality fabrication of complex components. To improve internal forming quality and reduce defects like stringing and overflow in cavities, an innovative retraction strategy with pre-retraction buffering was developed. Orthogonal experiments and Taguchi analysis identified optimal retraction parameters, while simulations revealed the critical influence of filling speed on overflow quality, enabling parameter optimization. Experimental results show a significant reduction in the relative error of circular hole diameters, from 4.45% to 0.35%. To further enhance mechanical properties and surface quality, the impact of alternating additive and subtractive processes on tensile performance and surface roughness was systematically analyzed. Results demonstrate that process switching significantly reduces tensile strength at bonding interfaces, with hybrid components achieving only 37.7% of the tensile strength of purely additively manufactured parts. By optimizing extrusion speed, layer height, and introducing ironing, interfacial bonding performance improved by 164.8% compared with conventional methods. Surface roughness was found to depend heavily on milling allowance and extrusion path spacing, achieving optimal roughness when the final surface aligns with the middle of the deposited filament. Surface quality was also maximized when milling direction aligned with extrusion paths. The proposed hybrid pellet extrusion and milling process significantly improves internal quality, dimensional accuracy, and surface quality of thermoplastic particle components, expanding its potential applications in industrial fields.

While fundamentals of DFMA (design for manufacturing and assembly) are widely accepted and used in the engineering community, many CAD environments lack tools that address manufacturing concerns by providing rapid feedback about costs resulting from design choices. This article presents an experiment-based testing and validation of a rapid feedback tool that provides users history-based prediction of manufacturing time based on the current state of the design. A between-subject experiment is designed to evaluate the impact of the tool on design outcomes based on modeling time, part mass, and manufacturing time. Participants in the study included mechanical engineering graduate and undergraduate students with at least one semester of experience using solidworks. The experiment included three modeling activities and three tool conditions. Participants completed up to three sessions with different experimental conditions. Analysis of the data collected shows that the use of the design tool results in a small but nonsignificant increase in modeling time. Moreover, the use of the tool results in reduced part mass on average (both between subjects and within subjects). Tool use reduced manufacturing time in open-ended activities, but increased manufacturing time when activities focus more on mass reduction. Participant feedback suggests that the tool helped guide their material removal actions by showing the impact on manufacturing time. Finally, potential improvements and future expansions of the tool are discussed.

We describe progress on the Nautilus Space Observatory concept that is enabled by novel, very large (8.5mdiameter), ultralight-weight, multi-order diffractive lenses that can be cost-effectively replicated. The scientific goal of Nautilus is the rigorous statistical exploration of one thousand potentially life-bearing planets and the assessment of the diversity of exo-earths. Here we review the science requirements and key design features of Nautilus. The new optical technology (MODE lenses) at the heart of the Nautilus telescopes also poses exciting new optical fabrication and metrology challenges. We will summarize these challenges and provide an overview of emerging solutions.

An analysis of the process of grinding and polishing of lenses and mirrored surfaces using a computer numerically controlled machine is presented. This analysis provides the motivation for the study of L 1 approximation of continuous functions by nonstandard approximants. Under suitable conditions, L 1 convergence is established for a space of material removal profiles based on a piecewise continuous material removal rate. A linear programming algorithm is used to find the best discrete L 1 approximation. Numerical examples are included

The objective of this study is to explore the influence of grinding stone granularity on the grinding force and rail material removal behaviors using a rail grinding friction machine. The results indicate that with the increase in granularity, the grinding force, and friction coefficient in the grinding interface obviously increase, which brings about a rise in the hardness and grinding temperature-rise of rail specimens. The increase in the grinding stone granularity causes a fall in the grinding volume and surface roughness of rail materials and brings about stronger vibration in the grinding interface owing to different material removal mechanisms. In view of the experimental results, the optimization of grinding stone granularity is significant for improving the rail grinding efficiency and surface quality.

Effect of rotation of abrasives on material removal in chemical mechanical polishing using a proposed three-body model: Molecular dynamics simulation

The unknown mechanism of lapping damage on different InP crystal surfaces constrains the device performance optimization. This study establishes a molecular dynamics (MD) model for nanoscale lapping of InP (100)/(110)/(111) surfaces using the Vashishta potential, combined with gradient lapping experiments (1 μm rough, 500 nm fine, 100 nm ultrafine diamond grits), to systematically reveal differences in material removal mechanisms and surface quality. The results show that the MD simulation agrees well with the experiments. The simulation predicts that the (100) crystal face has the highest material removal due to continuous chip formation, and the experiment confirms that it has the highest material removal rate (181.27 μm/h). In terms of surface quality, the simulation showed that the (100) crystalline face had the best atomic plastic flow; the (110) crystalline face needed to accumulate a critical amount of chips to activate plastic flow, and the (111) crystalline face had the worst plasticity. Morphological inspection shows that the lowest roughness (Sa = 2.126 nm) is obtained for the (100) crystalline surface, but deep scratches lead to large error fluctuations; the (110) and (111) crystalline surfaces show surface chipping due to abrasive grain sizes close to the critical value for brittle-plastic transition. It is demonstrated that the grain surface orientation dominates the material removal mechanism by regulating the activation of the slip system and dislocation evolution, which provides a theoretical basis for the selective processing of InP wafers and the optimization of device performance.

Improving monocrystalline silicon surface quality with chemical mechanical polishing using the slurry with the additive of isopropanol

Despite the prevalent application of 18% Ni maraging steel in critical sectors such as aerospace and automotive due to its unique characteristics, including high ductility, yield strength, and hardenability, its machining presents enormous challenges, categorizing it as a difficult-to-machine material. The cutting tool’s geometry is crucial in machining, significantly affecting chip formation, cutting forces, power consumption, and obtainable surface quality. In particular, wiper insert technology, characterized by its multi-radius design, offers an increased contact area compared to conventional inserts, potentially enhancing the quality of the machined surface. This study explores the effectiveness of wiper inserts in the face-milling of maraging steel 350, conducting a comparative analysis across three distinct machining setups. These setups vary by alternating the number of wiper and conventional inserts within the same cutter, thereby examining the influence of insert configuration on machining outcomes. The research employs a reliable and well-established statistical approach to evaluate how different variables, such as cutting speed and feed rate, affect surface quality, power consumption, and material removal rate (MRR). It also sheds light on the material removal mechanisms facilitated by each type of insert. The findings reveal that incorporating a higher number of wiper inserts significantly enhances the surface finish but concurrently increases power consumption. Thus, the study successfully identifies an optimal set of process parameters that attain a balance between achieving superior surface quality and maintaining energy efficiency in the machining of maraging steel 350. This balance is crucial for optimizing manufacturing processes while adhering to the stringent quality and sustainability standards required in aerospace and automotive manufacturing.

Gears’ surface quality and modification characteristic have an important influence on its working performance. Pulse Electrochemical Finishing (PECF) could get excellent surface topography. In this project, PECF with a scanning cathode is used to finishing the cylinder gear. Tooth profile modification is realized by PECF with an uneven interelectrode gap distribution along the tooth profile and tooth lead modification is realized by PECF with a variable moving velocity of the cathode. The experimental results show that the tooth surface roughness could be decreased from Ra 3.9μm to Ra 0.35μm, which means that the PECF process possesses the finishing ability for the raw surface tooth, and the difference of material removal of PECF with an uneven interelectrode gap distribution could be 46μm and the material removal could be controlled by regulating the moving velocity of the cathode, which means tooth profile and lead modification could be realized by PECF.

AZ91 magnesium alloys have poor machinability when conventional chip removal processes are used due to their low thermal stability and high susceptibility to softening and oxidation at elevated temperatures, which lead to excessive tool wear, poor surface quality, and deformation-induced machining challenges. This study investigated the impact of wire electrical discharge machining (WEDM) parameters on material removal rate (MRR) and surface roughness (SR) using magnesium. For this purpose, an analysis of variance (ANOVA) and Grey Relational Analysis (GRA) were performed to find the optimal settings. Findings indicate that pulse-on time (Ton) significantly affects both MRR and SR: higher Ton increases MRR but worsens SR, while shorter Ton improves SR but reduces MRR. Pulse-off time (Toff) and wire feed rate (WF) have secondary effects. Longer Toff improves surface quality but slightly reduces MRR, and lower WF improves cutting efficiency and MRR. The optimal settings identified by the Taguchi method were observed to be 123 μs Ton, 55 μs Toff, and 6 mmin−1 WF for high MRR; and 123 μs Ton, 58 μs Toff, and 4 mmin−1 WF for reduced SR. In summary, understanding how WEDM parameters affect MRR and SR allows manufacturers to achieve efficient material removal and desired surface quality.