Field-assisted machining of difficult-to-machine materials

Difficult-to-machine materials (DMMs) are extensively applied in critical fields such as aviation,semiconductor,biomedicine,and other key fields due to their excellent material properties.However,traditional machining technologies often struggle to achieve ultra-precision with DMMs resulting from poor surface quality and low processing efficiency.In recent years,field-assisted machining (FAM) technology has emerged as a new generation of machining technology based on innovative principles such as laser heating,tool vibration,magnetic magnetization,and plasma modification,providing a new solution for improving the machinability of DMMs.This technology not only addresses these limitations of traditional machining methods,but also has become a hot topic of research in the domain of ultra-precision machining of DMMs.Many new methods and principles have been introduced and investigated one after another,yet few studies have presented a comprehensive analysis and summarization.To fill this gap and understand the development trend of FAM,this study provides an important overview of FAM,covering different assisted machining methods,application effects,mechanism analysis,and equipment design.The current deficiencies and future challenges of FAM are summarized to lay the foundation for the further development of multi-field hybrid assisted and intelligent FAM technologies.

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.

Study of the material removal mechanism of glass-ceramics based on consecutive incremental loading in ductile-regime grinding

Glass-ceramics have many excellent properties and are widely used in various fields. During the grinding process,the workpiece surface is typically subject to material removal by grit of incremental heights, which has rarely been the focus of research. As such, it is necessary to study the material removal mechanism of glass-ceramics under consecutive incremental loading, which more closely reflects the actual grinding process. In this paper,to analyze the plastic deformation and residual stress of lithium aluminosilicate(LAS) glass-ceramics, a finite element model is established based on the Drucker–Prager yield criterion for ductile regimes. A nano-scratch test was also conducted and the test results show that both the residual depth and residual stress increase with an increase in the number of increments, and that consecutive incremental loading promotes the plastic deformation of glass-ceramics and increases the residual stress of the material in the ductile-regime process. These findings provide guidance for achieving higher dimensional accuracy in the actual grinding of glass-ceramics parts.

Molecular dynamics simulation of the material removal in the scratching of 4H-SiC and 6H-SiC substrates

Single crystal silicon carbide(SiC)is widely used for optoelectronics applications.Due to the anisotropic characteristics of single crystal materials,the C face and Si face of single crystal SiC have different physical properties,which may fit for particular application purposes.This paper presents an investigation of the material removal and associated subsurface defects in a set of scratching tests on the C face and Si face of 4H-SiC and 6H-SiC materials using molecular dynamics simulations.The investigation reveals that the sample material deformation consists of plastic,amorphous transformations and dislocation slips that may be prone to brittle split.The results showed that the material removal at the C face is more effective with less amorphous deformation than that at the Si face.Such a phenomenon in scratching relates to the dislocations on the basal plane(0001)of the SiC crystal.Subsurface defects were reduced by applying scratching cut depths equal to integer multiples of a half molecular lattice thickness,which formed a foundation for selecting machining control parameters for the best surface quality.

Energy beam-based direct and assisted polishing techniques for diamond:A review

Diamond is a highly valuable material with diverse industrial applications,particularly in the fields of semiconductor,optics,and high-power electronics.However,its high hardness and chemical stability make it difficult to realize high-efficiency and ultra-low damage machining of diamond.To address these challenges,several polishing methods have been developed for both single crystal diamond(SCD)and polycrystalline diamond(PCD),including mechanical,chemical,laser,and ion beam processing methods.In this review,the characteristics and application scope of various polishing technologies for SCD and PCD are highlighted.Specifically,various energy beam-based direct and assisted polishing technologies,such as laser polishing,ion beam polishing,plasma-assisted polishing,and laser-assisted polishing,are summarized.The current research progress,material removal mechanism,and infuencing factors of each polishing technology are analyzed.Although some of these methods can achieve high material removal rates or reduce surface roughness,no single method can meet all the requirements.Finally,the future development prospects and application directions of different polishing technologies are presented.

Modeling and analysis for material removal and surface roughness in fluid jet polishing of optical glass

luid jet polishing(FJP)is a non-contact polishing technology that can fabricate free-form optical surfaces with sub-micron-level form accuracy and nano-level surface roughness,especially for hard and brittle materials.The surface generation model of FJP can be used to guide the determination and optimization of process parameters and is of great significance for understanding the evolution mechanism of surface microtopography.However,predictive models for the microscopic topography of polished surfaces are still lacking.This study established a macroscopic surface profile model for predicting 3D material removal characteristics and surface texture by combining the 3D computer fluid dynamics(CFD)simulation model and single-particle erosion mechanism.A fractal theory-based erosion model has been built to calculate the material removal caused by the erosion of a single abrasive particle on the rough surface;thus,it predicts the micro-topography and surface roughness of the polished samples.A series of polishing experiments were conducted to analyze the feasibility and accuracy of the model quantitatively and study the influence mechanism of process parameters on the material removal characteristics and surface quality.Results indicated that the models could well predict material removal and surface roughness.The prediction accuracy of the surface roughness Ra and maximum removal depth is better than 91.6%and 90%,respectively.It is also found that the material removal rate of FJP could reach 0.517 mm3/min,and the surface roughness convergence rate could reach 62.9%.

Plasma-enabled electrochemical jet micromachining of chemically inert and passivating material

Electrochemical jet machining(EJM)encounters significant challenges in the microstructuring of chemically inert and passivating materials because an oxide layer is easily formed on the material surface,preventing the progress of electrochemical dissolution.This research demonstrates for the first time a jet-electrolytic plasma micromachining(Jet-EPM)method to overcome this problem.Specifically,an electrolytic plasma is intentionally induced at the jet-material contact area by applying a potential high enough to surmount the surface boundary layer(such as a passive film or gas bubble)and enable material removal.Compared to traditional EJM,introducing plasma in the electrochemical jet system leads to considerable differences in machining performance due to the inclusion of plasma reactions.In this work,the implementation of Jet-EPM for fabricating microstructures in the semiconductor material 4H-SiC is demonstrated,and the machining principle and characteristics of Jet-EPM,including critical parameters and process windows,are comprehensively investigated.Theoretical modeling and experiments have elucidated the mechanisms of plasma ignition/evolution and the corresponding material removal,showing the strong potential of Jet-EPM for micromachining chemically resistant materials.The present study considerably augments the range of materials available for processing by the electrochemical jet technique.

High Efficiency Axial Deep Creep-Feed Grinding Machining Technology of Engineering Ceramics Materials

Axial deep creep-feed grinding machining technology is a high efficiency process method of engineering ceramics materials, which is an original method to process the cylindrical ceramics materials or hole along its axis. The analysis of axial force and edge fracture proved the cutting thickness and feed rate could be more than 5-10 mm and 200 mm/min respectively in once process, and realized high efficiency, low-cost process of engineering ceramics materials. Compared with high speed-deep grinding machining, this method is also a high efficiency machining technology of engineering ceramics materials as well as with low cost. In addition, removal mechanism analyses showed that both median/radial cracks and lateral cracks appeared in the part to be removed, and the processed part is seldom destroyed, only by adjusting the axial force to control the length of transverse cracks.

Vibration-assisted material damage mechanism:From indentation cracks to scratch cracks

Vibration-assisted grinding is one of the most promising technologies for manufacturing optical components due to its efficiency and quality advantages.However,the damage and crack propagation mechanisms of materials in vibration-assisted grinding are not well understood.In order to elucidate the mechanism of abrasive scratching during vibration-assisted grinding,a kinematic model of vibration scratching was developed.The influence of process parameters on the evolution of vibration scratches to indentation or straight scratches is revealed by displacement metrics and velocity metrics.Indentation,scratch and vibration scratch experiments were performed on quartz glass,and the results showed that the vibration scratch cracks are a combination of indentation cracks and scratch cracks.Vibration scratch cracks change from indentation cracks to scratch cracks as the indenter moves from the entrance to the exit of the workpiece or as the vibration frequency changes from high to low.A vertical vibration scratch stress field model is established for the first time,which reveals that the maximum principal stress and tensile stress distribution is the fundamental cause for inducing the transformation of the vibration scratch cracking system.This model provides a theoretical basis for understanding of the mechanism of material damage and crack propagation during vibration-assisted grinding.

Precision Grinding of Reaction Bonded Silicon Carbide Using Coarse Grain Size Diamond Wheels

Reaction bonded SiC（RBSiC） is attractive for optical application because of its favorable properties and low fabrication cost. However, the difficultness and cost involved in RBSiC grinding limit its application. The investigation on high efficient and low-cost machining with good grinding quality is desired. Generally, high efficient machining for RBSiC is realized by using coarse grain size grinding wheels, but serious grinding damage is inevitable. In this paper, monolayer nickel electroplated coarse grain size diamond grinding wheels with grain sizes of 46 μm, 91 μm, and 151 μm were applied to the grinding of RBSiC. An electrolytic in-process dressing（ELID） assisted conditioning technique was first developed by using cup shape copper bonded conditioning wheels with grain sizes of 15 μm and 91 μm to generate the conditioned coarse grain size wheels with minimized wheel run-out error within 2 μm, constant wheel peripheral envelop as well as top-flattened diamond grains. Then, the grinding experiments on RBSiC were carried out to investigate the grinding performance and material removal mechanism. The experimental results indicate that the developed conditioning technique is applicable and feasible to condition the coarse grain size diamond wheels under optimal conditioning parameters, and the material removal mechanism involved in RBSiC grinding is the combination of brittle fracture and ductile deformation to generate smooth ground surface. This research is significant for the high efficient and low-cost precision grinding of RBSiC with good ground surface quality.

Material removal rate in chemical-mechanical polishing of wafers based on particle trajectories

Distribution forms of abrasives in the chemical mechanical polishing（CMP） process are analyzed based on experimental results.Then the relationships between the wafer,the abrasive and the polishing pad are analyzed based on kinematics and contact mechanics.According to the track length of abrasives on the wafer surface,the relationships between the material removal rate and the polishing velocity are obtained.The analysis results are in accord with the experimental results.The conclusion provides a theoretical guide for further understanding the material removal mechanism of wafers in CMP.

Material removal mechanism of copper chemical mechanical polishing with different particle sizes based on quasi-continuum method

In this paper,the material removal mechanism of copper chemical mechanical polishing was studied by the quasicontinuum method that integrated molecular dynamics and the finite element method.By analyzing the abrasive process of different particle sizes on single crystal copper,we investigated the internal material deformation,the formation of chips,the stress distribution,and the change of cutting force.Results showed that shear band deformation was generated along the cutting direction at approximately 45° inside the workpiece material.The deformation was accompanied by dislocations and sliding phenomena in the shear band region.Smaller abrasive particle size led to poor quality of the workpiece,while a larger particle size led to better quality.However,larger particle size resulted in greater plastic deformation and deeper residual stress inside the workpiece.Size change of abrasive particles had little effect on the tangential cutting force.

Material removal model of magnetorheological finishing based on dense granular flow theory

Magnetorheological finishing(MRF)technology is widely used in the fabrication of high-precision optical elements.The material removal mechanism of MRF has not been fully understood because MRF technology involves the integration of electromagnetics,contact mechanics,and materials science.In this study,the rheological properties of the MR polishing fluid in oscillation model have been investigated.We propose that the shear-thinned MR polishing fluid over the polishing area should be considered a dense granular flow,based on which a new contact model of MRF over the polishing area has been constructed.Removal function and processing force test experiments were conducted under different working gaps.The normal pressure and effective friction equations over the polishing area were built based on the continuous medium and dense granular flow theories.Then,a novel MRF material removal model was established.A comparison of the results of the theoretical model with actual polishing results demonstrated the accuracy of the established model.The novel model proposed herein reveals the generation mechanism of shear force over a polished workpiece and realizes effective decoupling of the main processing parameters that influence the material removal of MRF.The results of this study will provide new and effective theoretical guidance for the process optimization and technology improvement of MRF.

Fiber orientation effects on grinding characteristics and removal mechanism of 2.5D C_(f)/SiC composites

Carbon fiber reinforced silicon carbide(C_(f)/SiC)composites are widely used in aerospace for their excellent mechanical properties.However,the quality of the machined surface is poor and unpredictable due to the material heterogeneity induced by complex removal mechanism.To clarify the effects of fiber orientation on the grinding characteristics and removal mechanism,single grit scratch experiments under different fiber orientations are conducted and a three-phase numerical modelling method for 2.5D C_(f)/SiC composites is proposed.Three fiber cutting modes i.e.,transverse,normal and longitudinal,are defined by fiber orientation and three machining directions i.e.,MA(longitudinal and normal),MB(longitudinal and transverse)and MC(normal and transverse),are selected to investigate the effect of fiber orientation on grinding force and micro-morphology.Besides,a three-phase cutting model of 2.5D C_(f)/SiC composites considering the mechanical properties of the matrix,fiber and interface is developed.Corresponding simulations are performed to reveal the micro-mechanism of crack initiation and extension as well as the material removal mechanism under different fiber orientations.The results indicate that the scratching forces fluctuate periodically,and the order of mean forces is MA>MC>MB.Cracks tend to grow along the fiber axis,which results in the largest damage layer for transverse fibers and the smallest for longitudinal fibers.The removal modes of transverse fibers are worn,fracture and peel-off,in which normal fibers are pullout and outcrop and the longitudinal fibers are worn and push-off.Under the stable cutting condition,the change of contact area between fiber and grit leads to different removal modes of fiber in the same cutting mode,and the increase of contact area results in the aggravation of fiber fracture.

Collaborative manufacturing technologies of structure shape and surface integrity for complex thin-walled components of aero-engine:Status,challenge and tendency

Presently,the service performance of new-generation high-tech equipment is directly affected by the manufacturing quality of complex thin-walled components.A high-efficiency and quality manufacturing of these complex thin-walled components creates a bottleneck that needs to be solved urgently in machinery manufacturing.To address this problem,the collaborative manufacturing of structure shape and surface integrity has emerged as a new process that can shorten processing cycles,improve machining qualities,and reduce costs.This paper summarises the research status on the material removal mechanism,precision control of structure shape,machined surface integrity control and intelligent process control technology of complex thin-walled components.Numerous solutions and technical approaches are then put forward to solve the critical problems in the high-performance manufacturing of complex thin-wall components.The development status,challenge and tendency of collaborative manufacturing technologies in the high-efficiency and quality manufacturing of complex thin-wall components is also discussed.

Chemically-induced active micro-nano bubbles assisting chemical mechanical polishing:Modeling and experiments

The material loss caused by bubble collapse during the micro-nano bubbles auxiliary chemical mechanical polishing(CMP)process cannot be ignored.In this study,the material removal mechanism of cavitation in the polishing process was investigated in detail.Based on the mixed lubrication or thin film lubrication,bubble-wafer plastic deformation,spherical indentation theory,Johnson-Cook(J-C)constitutive model,and the assumption of periodic distribution of pad asperities,a new model suitable for micro-nano bubble auxiliary material removal in CMP was developed.The model integrates many parameters,including the reactant concentration,wafer hardness,polishing pad roughness,strain hardening,strain rate,micro-jet radius,and bubble radius.The model reflects the influence of active bubbles on material removal.A new and simple chemical reaction method was used to form a controllable number of micro-nano bubbles during the polishing process to assist in polishing silicon oxide wafers.The experimental results show that micro-nano bubbles can greatly increase the material removal rate(MRR)by about 400%and result in a lower surface roughness of 0.17 nm.The experimental results are consistent with the established model.In the process of verifying the model,a better understanding of the material removal mechanism involved in micro-nano bubbles in CMP was obtained.

Key technologies and development trends of the soft abrasive flow finishing method

This paper reviews recent developments of the soft abrasive flow finishing(SAF)method in constraint space.The multiphase fluid dynamics modeling,material removal mechanism,auxiliary strengthening finishing techniques,and observation of surface impact effects by abrasive particles and cavitation bubbles are presented in brief.Development prospects and challenges are given for four aspects:thin-walled curved surfaces,biomedical functions,electronic information,and precise optical components.

Machining of SiC ceramic matrix composites:A review

Continuous fiber reinforced SiC ceramic matrix composites(FRCMCs-SiC)are currently the preferred material for hot section components,safety–critical components and braking components(in the aerospace,energy,transportation)with high value,and have triggered the demand for machining.However,the high brittleness,anisotropy,and heterogeneity of materials bring great challenges to machining,due to high mechanical and thermal loads,severe tool wear,and poor machining quality.With the increasing demand of FRCMCs-SiC parts,high-quality and high-efficient machining has become a hot issue.This review paper provides a detailed literature survey on the machining of FRCMCs-SiC.The material removal mechanism,defect form,and interfacial mechanical properties of FRCMCs-SiC were summarized.The machining processes of FRCMCs-SiC were introduced,and their respective advantages and disadvantages were compared.Given the low machinability(high hardness,high brittleness,anisotropy,and heterogeneity)of FRCMCs-SiC,preliminary experiments have proved that ultrasonic-assisted machining and laser-assisted machining have shown unique advantages in reducing force and tool wear,improving machining quality and machining efficiency.The machined surface integrity was discussed,the influence of process parameters on the machined surface quality was analyzed,and the machining defects of FRCMCs-SiC were summarized.But for FRCMCs-SiC,the existing quantitative evaluation of the machined surface integrity was weak and unsystematic.

Fiber-reinforced composites in milling and grinding:machining bottlenecks and advanced strategies

Fiber-reinforced composites have become the preferred material in the fields of aviation and aerospace because of their high-strength performance in unit weight.The composite components are manufactured by near netshape and only require finishing operations to achieve final dimensional and assembly tolerances.Milling and grinding arise as the preferred choices because of their precision processing.Nevertheless,given their laminated,anisotropic,and heterogeneous nature,these materials are considered difficult-to-machine.As undesirable results and challenging breakthroughs,the surface damage and integrity of these materials is a research hotspot with important engineering significance.This review summarizes an up-to-date progress of the damage formation mechanisms and suppression strategies in milling and grinding for the fiber-reinforced composites reported in the literature.First,the formation mechanisms of milling damage,including delamination,burr,and tear,are analyzed.Second,the grinding mechanisms,covering material removal mechanism,thermal mechanical behavior,surface integrity,and damage,are discussed.Third,suppression strategies are reviewed systematically from the aspects of advanced cutting tools and technologies,including ultrasonic vibration-assisted machining,cryogenic cooling,minimum quantity lubrication(MQL),and tool optimization design.Ultrasonic vibration shows the greatest advantage of restraining machining force,which can be reduced by approximately 60%compared with conventional machining.Cryogenic cooling is the most effective method to reduce temperature with a maximum reduction of approximately 60%.MQL shows its advantages in terms of reducing friction coefficient,force,temperature,and tool wear.Finally,research gaps and future exploration directions are prospected,giving researchers opportunity to deepen specific aspects and explore new area for achieving high precision surface machining of fiber-reinforced composites.

Novel three-body nano-abrasive wear mechanism

Current three-body abrasive wear theories are based on a macroscale abrasive indentation process,and these theories claim that material wear cannot be achieved without damaging the hard mating surface.In this study,the process of three-body nano-abrasive wear of a system including a single crystalline silicon substrate,an amorphous silica cluster,and a polyurethane pad,based on a chemical mechanical polishing(CMP)process,is investigated via molecular dynamics simulations.The cluster slid in a suspended state in smooth regions and underwent rolling impact in the asperity regions of the silicon surface,realizing non-damaging monoatomic material removal.This proves that indentation-plowing is not necessary when performing CMP material removal.Therefore,a non-indentation rolling-sliding adhesion theory for three-body nano-abrasive wear between ultrasoft/hard mating surfaces is proposed.This wear theory not only unifies current mainstream CMP material removal theories,but also clarifies that monoatomic material wear without damage can be realized when the indentation depth is less than zero,thereby perfecting the relationship between material wear and surface damage.These results provide new understanding regarding the CMP microscopic material removal mechanism as well as new research avenues for three-body abrasive wear theory at the monoatomic scale.