Effect of tool geometry on ultraprecision machining of soft-brittle materials:a comprehensive review

Brittle materials are widely used for producing important components in the industry of optics,optoelectronics,and semiconductors.Ultraprecision machining of brittle materials with high surface quality and surface integrity helps improve the functional performance and lifespan of the components.According to their hardness,brittle materials can be roughly divided into hard-brittle and soft-brittle.Although there have been some literature reviews for ultraprecision machining of hard-brittle materials,up to date,very few review papers are available that focus on the processing of soft-brittle materials.Due to the‘soft’and‘brittle’properties,this group of materials has unique machining characteristics.This paper presents a comprehensive overview of recent advances in ultraprecision machining of soft-brittle materials.Critical aspects of machining mechanisms,such as chip formation,surface topography,and subsurface damage for different machining methods,including diamond turning,micro end milling,ultraprecision grinding,and micro/nano burnishing,are compared in terms of tool-workpiece interaction.The effects of tool geometries on the machining characteristics of soft-brittle materials are systematically analyzed,and dominating factors are sorted out.Problems and challenges in the engineering applications are identified,and solutions/guidelines for future R&D are provided.

Generating micro/nanostructures on magnesium alloy surface using ultraprecision diamond surface texturing process

The lightness and high strength-to-weight ratio of the magnesium alloy have attracted more interest in various applications.However,micro/nanostructure generation on their surfaces remains a challenge due to the flammability and ignition.Motivated by this,this study proposed a machining process,named the ultraprecision diamond surface texturing process,to machine the micro/nanostructures on magnesium alloy surfaces.Experimental results showed the various microstructures and sawtooth-shaped nanostructures were successfully generated on the AZ31B magnesium alloy surfaces,demonstrating the effectiveness of this proposed machining process.Furthermore,sawtooth-shaped nanostructures had the function of inducing the optical effect and generating different colors on workpiece surfaces.The colorful letter and colorful flower image were clearly viewed on magnesium alloy surfaces.The corresponding cutting force,chip morphology,and tool wear were systematically investigated to understand the machining mechanism of micro/nanostructures on magnesium alloy surfaces.The proposed machining process can further improve the performances of the magnesium alloy and extend its functions to other fields,such as optics.

Investigation of a dynamics-oriented engineering approach to ultraprecision machining of freeform surfaces and its implementation perspectives

In current precision and ultraprecision machining practice,the positioning and control of actuation systems,such as slideways and spindles,are heavily dependent on the use of linear or rotary encoders.However,positioning control is passive because of the lack of direct monitoring and control of the tool and workpiece positions in the dynamic machining process and also because it is assumed that the machining system is rigid and the cutting dynamics are stable.In ultraprecision machining of freeform surfaces using slow tool servo mode in particular,however,account must be taken of the machining dynamics and dynamic synchronization of the cutting tool and workpiece positioning.The important question also arises as to how ultraprecision machining systems can be designed and developed to work better in this application scenario.In this paper,an innovative dynamics-oriented engineering approach is presented for ultraprecision machining of freeform surfaces using slow tool servo mode.The approach is focused on seamless integration of multibody dynamics,cutting forces,and machining dynamics,while targeting the positioning and control of the tool–workpiece loop in the machining system.The positioning and motion control between the cutting tool and workpiece surface are further studied in the presence of interfacial interactions at the tool tip and workpiece surface.The interfacial cutting physics and dynamics are likely to be at the core of in-process monitoring applicable to ultraprecision machining systems.The approach is illustrated using a virtual machining system developed and supported with simulations and experimental trials.Furthermore,the paper provides further explorations and discussion on implementation perspectives of the approach,in combination with case studies,as well as discussing its fundamental and industrial implications.

Investigation of the trajectory uniformity in water dissolution ultraprecision continuous polishing of large-sized KDP crystal

Large-sized potassium dihydrogen phosphate(KDP)crystals are an irreplaceable nonlinear optical component in an inertial confinement fusion project.Restricted by the size,previous studies have been aimed mainly at the removal principle and surface roughness of small-sized KDP crystals,with less research on flatness.Due to its low surface damage and high machining efficiency,water dissolution ultraprecision continuous polishing(WDUCP)has become a good technique for processing large-sized KDP crystals.In this technique,the trajectory uniformity of water droplets can directly affect the surface quality,such as flatness and roughness.Specifically,uneven trajectory distribution of water droplets on the surface of KDP crystals derived from the mode of motion obviously affects the surface quality.In this study,the material removal mechanism of WDUCP was introduced.A simulation of the trajectory of water droplets on KDP crystals under different eccentricity modes of motion was then performed.Meanwhile,the coefficient of variation(CV)was utilized to evaluate the trajectory uniformity.Furthermore,to verify the reliability of the simulation,some experimental tests were also conducted by employing a large continuous polisher.The results showed that the CV varied from 0.67 to 2.02 under the certain eccentricity mode of motion and varied from 0.48 to 0.65 under the uncertain eccentricity mode of motion.The CV of uncertain eccentricity is always smaller than that of certain eccentricity.Hence,the uniformity of trajectory was better under uncertain eccentricity.Under the mode of motion of uncertain eccentricity,the initial surface texture of the100 mm×100 mm×10 mm KDP crystal did achieve uniform planarization.The surface root mean square roughness was reduced to 2.182 nm,and the flatness was reduced to 22.013μm.Therefore,the feasibility and validity of WDUCP for large-sized KDP crystal were verified.

Fabrication of a biomimetic controllable adhesive surface by ultraprecision multistep and layered scribing and casting molding

Wedge-shaped microstructures have the ability to reproduce the excellent adhesive properties of geckos’feet because of their unique anisotropic structure.In particular,the controllability of the wedge-shaped microstructures on adhesion is beneficial to the undisturbed grasp or the capture of space targets.However,the problem currently remains of how to process it efficiently and with high quality.Here a strategy called ultraprecision multistep and layered scribing is proposed for the manufacture of the biomimetic controllable adhesive surface.The results show that the metal master mold prepared based on the manufacturing strategy has not only good surface topography but also high reliability and durability.Furthermore,the controllable adhesive surface of 1.96 cm2,fabricated by the proposed manufacturing strategy,has a normal adhesion of 1.012 N,and the corresponding shear friction and adhesion coefficient are 3.105 N and 4.82,respectively.Additionally,the controllable adhesive surface has been shown to be approximately superhydrophobic and also to possess the properties of controllable adhesion and dynamic adhesion.Also,after 250 adhesion-detachment cycles,the normal adhesion and shear friction only decrease by 5%and 3%,respectively.The research realizes an environmentally friendly and efficient method by which to manufacture a durable metal mold for fabricating a biomimetic controllable adhesive surface,laying a foundation for its effective application in the adherence of space-floating targets.

Micro-optical fabrication by ultraprecision diamond machining and precision molding

Ultraprecision diamond machining and high volume molding for affordable high precision high performance optical elements are becoming a viable process in optical industry for low cost high quality microoptical component manufacturing. In this process, first high precision microoptical molds are fabricated using ultraprecision single point diamond machining followed by high volume production methods such as compression or injection molding. In the last two decades, there have been steady improvements in ultraprecision machine design and performance, particularly with the introduction of both slow tool and fast tool servo. Today optical molds, including freeform surfaces and microlens arrays, are routinely diamond machined to final finish without post machining polishing. For consumers, compression mold- ing or injection molding provide efficient and high quality optics at extremely low cost. In this paper, first ultrapreci- sion machine design and machining processes such as slow tool and fast too servo are described then both compression molding and injection molding of polymer optics are discussed. To implement precision optical manufacturing by molding, numerical modeling can be included in the future as a critical part of the manufacturing process to ensure high product quality.

A new method for deburring of servo valve core edge based on ultraprecision cutting with the designed monocrystalline diamond tool

Deburring of high-precision components to their micrometer features without any damage is very important but of great difficulty as the burr-to-functionality size ratio increases. To this end, this paper proposes a new deburring method in which the micro burr should be directly removed based on ultraprecision cutting with the designed monocrystalline diamond tool. To determine the feasibility of the proposed method, this paper applies it for deburring of the precision working edge of the servo valve core. Firstly, the monocrystalline diamond tool is carefully designed by covering a variety of topics like rake angle,clearance angle, edge radius. Then, the finite element(FE) simulation was conducted to characterize the deburring performance during the removal of the micro burr produced by the single abrasive grinding. Finally, an innovative self-designed deburring system was introduced and the deburring process was evaluated in terms of cutting forces, temperatures, tool wear mechanisms and deburring quality of the working edges by experiments. The FE simulation results indicate the suitability of the proposed deburring method. Meanwhile, the experimental findings agree well with simulation results and show that ultraprecision cutting with the specialized monocrystalline diamond tool could be successfully used for deburring of servo valve core edge without any damage. This work can provide technical guidance for similar engineering applications, and thus brings an increase to the machining efficiency for the manufacture of precision components.

Manufacturing technologies toward extreme precision

Precision is one of the most important aspects of manufacturing.High precision creates high quality,high performance,exchangeability,reliability,and added value for industrial products.Over the past decades,remarkable advances have been achieved in the area of high-precision manufacturing technologies,where the form accuracy approaches the nanometer level and surface roughness the atomic level.These extremely high precision manufacturing technologies enable the development of high-performance optical elements,semiconductor substrates,biomedical parts,and so on,thereby enhancing the ability of human beings to explore the macroand microscopic mysteries and potentialities of the natural world.In this paper,state-of-the-art high-precision material removal manufacturing technologies,especially ultraprecision cutting,grinding,deterministic form correction polishing,and supersmooth polishing,are reviewed and compared with insights into their principles,methodologies,and applications.The key issues in extreme precision manufacturing that should be considered for future R&D are discussed.

Fabrication of Microlens Array and Its Application:A Review

Microlens arrays are the key component in the next generation of 3D imaging system, for it exhibits some good optical properties such as extremely large field of view angles, low aberration and distortion, high temporal resolution and infinite depth of field. Although many fabrication methods or processes are proposed for manufacturing such precision component, however, those methods still need to be improved. In this review, those fabrication methods are categorized into direct and indirect method and compared in detail. Two main challenges in manufacturing microlens array are identified: how to obtain a microlens array with good uniformity in a large area and how to produce the microlens array on a curved surface? In order to effectively achieve control of the geometry of a microlens,indirect methods involving the use of 3D molds and replication technologies are suggested. Further development of ultraprecision machining technology is needed to reduce the surface fluctuation by considering the dynamics of machine tool in tool path planning. Finally, the challenges and opportunities of manufacturing microlens array in industry and academic research are discussed and several principle conclusions are drawn.

FORMING PRINCIPLE OF TWO SIDE-DIRECTION BURR AND IT'S PREDICTION IN METAL CUTTING

The burr is one of the common phenomena occurring i n metal cutting operations The mathematical mechanical model of two side dir ection burr formation and transformation is established with plane stress strain theory,based on the orthogonal cutting The main laws of formation and change of the burr are revealed,and it is confirmed by experiment result,which first realizes prediction of the forming and changing of the two side direction burr in metal cutting operation.

TOOL FORCE MODEL FOR DIAMOND TURNING

A new tool force model to be presented is based upon process geometry and thecharacteristics of the force system, in which the forces acting on the tool rake face, the cuttingedge rounding and the clearance face have been considered, and the size effect is accountable forthe new model. It is desired that the model can be well applicable to conventional diamond turningand the model may be employed as a tool in the design of diamond tools. This approach is quitedifferent from traditional investigations primarily based on empirical studies. As the depth of cutbecomes the same order as the rounded cutting edge radius, sliding along the clearance face due toelastic recovery of workpiece material and plowing due to the rounded cutting edge may becomeimportant in micro-machining, the forces acting on the cutting edge rounding and the clearance facecan not be neglected. For this reason, it is very important to understand the influence of someparameters on tool forces and develop a model of the relationship between them.

Effect of Tool Geometry in Nanometric Cutting

With the development of science and technology, the ultra-precision manufacturing of the brittle and hard materials with superior quality have become a new attractive subject. Brittle materials (such as engineering ceramics, optical glass, semiconductor and so on) are widely used in electronics, optics, aeronautics and other high technology fields, so there are important theory significance and practical value to systematically study its machining mechanism and technology. Single crystal silicon is one of the typical brittle materials. Single crystal silicon wafer is a basic component of large and ultralarge integrated the circuit, its surface roughness and flatness are the key factor of improving its integration. With the successfully producing of the large diameter single crystal silicon wafer, its manufacturing technology became attractive subject again. This paper carries out computer simulation of nanometer cutting on single crystal silicon. Molecular Dynamics method which is different from continuous mechanics is employed to investigate the features of grinding energy dissipation, grinding force, stress state and grinding temperature, constructs the atom model of tool and work piece, and explains the microscale mechanism of material remove and surface generation of nanometer(subnanometer) manufacturing. This paper also investigates the variation of cutting force, thrust force, specific energy and surface deformation with different tool edge radius, different depth of cut.

Ultra-precision machining of cerium-lanthanum alloy with atmosphere control in an auxiliary device

Cerium–lanthanum alloys are the main component of nickel–metal hydride batteries,and they are thus an important material in the greenenergy industry.However,these alloys have very strong chemical activity,and their surfaces are easily oxidized,leading to great difficulties in their application.To improve the corrosion resistance of cerium–lanthanum alloys,it is necessary to obtain a nanoscale surface with low roughness.However,these alloys can easily succumb to spontaneous combustion during machining.Currently,to inhibit the occurrence of fire,machining of this alloy in ambient air needs to be conducted at very low cutting speeds while spraying the workpiece with a large amount of cutting fluid.However,this is inefficient,and only a very limited range of parameters can be optimized at low cutting speeds;this restricts the optimization of other cutting parameters.To achieve ultraprecision machining of cerium–lanthanum alloys,in this work,an auxiliary machining device was developed,and its effectiveness was verified.The results show that the developed device can improve the cutting speed and obtain a machined surface with low roughness.The device can also improve the machining efficiency and completely prevent the occurrence of spontaneous combustion.It was found that the formation of a build-up of swarf on the cutting tool is eliminated with high-speed cutting,and the surface roughness(Sa)can reach 5.64 nm within the selected parameters.Finally,the oxidation processes of the cerium–lanthanum alloy and its swarf were studied,and the process of the generation of oxidative products in the swarf was elucidated.The results revealed that most of the intermediate oxidative products in the swarf were Ce^(3+),there were major oxygen vacancies in the swarf,and the final oxidative product was Ce^(4+).

Tool path generation and optimization for freeform surface diamond turning based on an independently controlled fast tool servo

Diamond turning based on a fast tool servo(FTS)is widely used in freeform optics fabrication due to its high accuracy and machining efficiency.As a new trend,recently developed high-frequency and long-stroke FTS units are independently driven by a separate control system from the machine tool controller.However,the tool path generation strategy for the independently controlled FTS is far from complete.This study aims to establish methods for optimizing tool path for the independent control FTS to reduce form errors in a single step of machining.Different from the conventional integrated FTS control system,where control points are distributed in a spiral pattern,in this study,the tool path for the independent FTS controller is generated by the ring method and the mesh method,respectively.The machined surface profile is predicted by simulation and the parameters for the control point generation are optimized by minimizing the deviation between the predicted and the designed surfaces.To demonstrate the feasibility of the proposed tool path generation strategies,cutting tests of a two-dimensional sinewave and a micro-lens array were conducted and the results were compared.As a result,after tool path optimization,the peak-to-valley form error of the machined surface was reduced from 429 nm to 56 nm for the two-dimensional sinewave by using the ring method,and from 191 nm to 103 nm for the micro-lens array by using the mesh method,respectively.

Tool-tip vibration prediction based on a novel convolutional enhanced transformer

Superior surface finish remains a fundamental criterion in precision machining operations,and tool-tip vibration is an important factor that significantly influences the quality of the machined surface.Physics-based models heavily rely on assumptions for model simplification when applied to complex high-end systems.However,these assumptions may come at the cost of compromising the model's accuracy.In contrast,data-driven techniques have emerged as an attractive alternative for tasks such as prediction and complex system analysis.To exploit the advantages of data-driven models,this study introduces a novel convolutional enhanced transformer model for tool-tip vibration prediction,referred to as CeT-TV.The effectiveness of this model is demonstrated through its successful application in ultra-precision fly-cutting(UPFC)operations.Two distinct variants of the model,namely,guided and nonguided CeT-TV,were developed and rigorously tested on a data set custom-tailored for UPFC applications.The results reveal that the guided CeT-TV model exhibits outstanding performance,characterized by the lowest mean absolute error and root mean square error values.Additionally,the model demonstrates excellent agreement between the predicted values and the actual measurements,thus underlining its efficiency and potential for predicting the tool-tip vibration in the context of UPFC.

Design and fabrication of a gecko-inspired surface for improving the grasping ability of a humanoid dexterous hand

Many studies have examined the design,fabrication and characteristics of gecko-inspired adhesives,but applied research on gecko-inspired surfaces in humanoid dexterous hands is relatively scarce.Here,a wedged slanted structure with a curved substrate suitable for humanoid dexterous fingers was designed and manufactured via ultraprecision machining and replica molding.The adhesion and friction properties of the wedged slanted structure show obvious anisotropic characteristics in the gripping and releasing directions,and the influence of structural parameters and motion parameters on the adhesion and friction was systematically studied.The humanoid dexterous fingers with gecko-inspired surfaces greatly increased the grasping force limit(increase to 4.02 times)based on the grasping of measuring cups with different volumes of water and improved the grasping stability based on the picking up of smooth steel balls of different diameters.This study shows that this process,based on ultraprecision machining and replica molding,is a green,high-efficiency,and low-cost method to fabricate large-area biomimetic surfaces that has potential applications in dexterous humanoid hands to improve grasping ability,stability and adaptability.

Bridging the Divide Between Iterative Optical Polishing and Automation

Several recent business reports have described the global growth in demand for optical and photonic components,paralleled by technical reports on the growing shortage of skilled manufacturing staff to meet this demand.It is remarkable that producing ultraprecision surfaces remains so dependent on people,in contrast to other sectors of the economy,e.g.,car manufacturing.Clearly,training can play some role,but ultimately,only process automation can provide the solution.This paper explores why automation is a challenge and summarizes multidisciplinary work aiming to assemble the building blocks required to realize automation.

Fundamental Investigations in the Design of Five-Axis Nanopositioning Machines for Measurement and Fabrication Purposes

The majority of nanopositioning and nanomeasuring machines(NPMMs)are based on three independent linear movements in a Cartesian coordinate system.This in combination with the specific nature of sensors and tools limits the addressable part geometries.An enhancement of an NPMM is introduced by the implementation of rotational movements while keeping the precision in the nanometer range.For this purpose,a parameter-based dynamic evaluation system with quantifiable technological parameters has been set up and employed to identify and assess general solution concepts and adequate substructures.Evaluations taken show high potential for three linear movements of the object in combination with two angular movements of the tool.The influence of the additional rotation systems on the existing structure of NPMMs has been investigated further on.Test series on the repeatability of an NPMM enhanced by a chosen combination of a rotary stage and a goniometer setup are realized.As a result of these test series,the necessity of in situ position determination of the tool became very clear.The tool position is measured in situ in relation to a hemispherical reference mirror by three Fabry-Perot interferometers.FEA optimization has been used to enhance the overall system structure with regard to reproducibility and long-term stability.Results have been experimentally investigated by use of a retroreflector as a tool and the various laser interferometers of the NPMM.The knowledge gained has been formed into general rules for the verification and optimization of design solutions for multiaxial nanopositioning machines.