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To explore the evolution mechanism of multistage machining processes and torsional fatigue behaviour based on strain energy for the first time and provide process optimization of axis parts of low-alloy medium-carbon steel for service performance, four multistage machining processes were applied to the 45CrNiMoVA steel, including the rough turning process (RT), RT + the finish turning process (FRT), FRT+ the grinding process (GFRT) and RT+ the finish turning process on dry cutting condition (FRT0). The result showed that the FRT process’s average low-cycle torsional fatigue life increased by 50% when it evolved from the RT process. The lower surface roughness of Ra 1.3 μm caused the total strain energy to increase by 163.8 Pa mm/mm instead of the unchanged strain energy density, and the crack feature evolved from some specific bulges to flat shear plane characteristics. When the GFRT process evolved from the FRT process, its average fatigue life increased by 1.45 times, compared with the RT process. Plastic strain amplitude decreased by 21%, and the strain energy density decreased by 4% due to more considerable compressive residual stress (-249 MPa). Plastic deformation layer depth had a consistent tendency with surface roughness. In this paper, surface integrity evolutions on cyclic characteristics and fatigue behaviour have also been explained. A fatigue life prediction model based on the energy method for machined surface integrity is proposed.

This study proposes a novel micro-deep-hole drill with variable web thickness and flute width to effectively improve the problem of tool breakage and chip clogging during micro-deep-hole drilling. Firstly, the failure form and failure mechanism of micro-drill are explored by performing drilling experiments, and it is found that the torsion fracture and bending fracture are the main premature failure modes of micro-deep-hole drilling tools. The static simulation analysis of micro-drill is further conducted to investigate the influence of geometric parameters on the stiffness and strength of high-aspect-ratio micro-drill, and the results indicate that the web thickness ratio and flute width have significant effects on drill tip stiffness and spiral groove root strength. To balance the rigidity, strength and chip evacuation capability of micro-deep-hole drilling tools, the new micro-drill with variable web thickness and flute width is developed, supplemented by comparative experiments. The results confirm that the new micro-drill has better chip removal ability, greatly reduces the drilling force, torque, drill tip wear and material peeling phenomenon, and significantly enhances the machining quality of hole wall.

Chatter will cause a series of changes in machining state during the boring process. Due to the difference in the sensitivity and ability of various sensors to resist external interference, the change of machining environment can lead to variation in response and make difference to the characteristics of signal. Therefore, it is essential to extract the features related to chatter from the machining signals. In this study, the dynamic model considering the regenerative effect is constructed, based on which the relationship between the limited cutting width and the spindle speed is determined. In addition, eddy current displacement sensor, vibration acceleration sensor, and acoustic pressure sensor are applied to propose a feasible boring chatter monitoring scheme and collect the machining signals. The time and frequency domain of the collected signals are analyzed to determine the pattern of time–frequency variation for three kinds of sensor signals generated with chatter.

The precision turning process has attracted enormous interest in the standardized and mass production of micro-shafts because it produces more efficiency and lower cost compared with the electrical-discharge machining method and micro-machining method. However, there are many critical factors that influence the dimensional accuracy of micro-shafts, such as the error of workpiece deformation, cutting force, and tool setting error. In this paper, a novel error compensation method was proposed to improve the dimensional accuracy of micro-shafts manufactured with the conventional precision machine tool, based on the constant force cutting method and tool path planning. Firstly, a cutting force model was established considering the effect of the tool nose radius, and the finite element method was used to simulate the turning process and predict the workpiece deformation. Secondly, an error analysis model was created by taking tool setting error, workpiece deformation error, and multi-process cumulative error into account, and the optimized tool path and cutting parameters were obtained. Finally, a series of turning experiments were carried out to verify the error compensation strategy and the cutting force model. The results show that the dimensional error of the micro-shafts with a large length-diameter ratio (l = 5 mm, d = 0.4 mm) can be reduced by 90% by means of the proposed error compensation strategy. In addition, the maximum prediction error of cutting forces is less than 8.6%, and the effect of cutting parameters on cutting forces can be concluded as “feed rate > depth of cut > spindle speed.”

Since cemented carbide has been used as a micro-lens array mold, its processing method and micro-tool is one of the research priorities. In order to achieve high-quality milling of cemented carbide micro-lens array, the design and fabrication of the 0.5-mm diameter polycrystalline diamond (PCD) micro ball-end mill were studied. Based on the space vector, the mathematical model of the plane cutting edge of the PCD tool is established. According to the three processing characteristics of milling, grinding, and milling grinding, the double-edged conical surface micro ball-end mill, spherical micro ball-end mill, and single-edged hemispherical micro ball-end mill were designed respectively. Based on the line-face contact model of the grinding wheel and the movement principle of the CNC tool grinder, the grinding principles and methods of the rake face and the flank face are proposed. The high precision grinding of PCD micro ball-end mills are realized. The micro-groove milling experiment of cemented carbide was conducted; the milling performance of three PCD micro ball-end mills was studied. Considering the surface morphology and roughness of the micro-groove machining, a single-edged hemispherical PCD micro ball-end mill can avoid the phenomenon of chip blocking and depositing and can also fully exert the grinding characteristics of PCD materials to obtain relatively better processing quality.

18Ni maraging steel is normally used to make key components by machining processes. It is necessary to understand the fracture mechanism and behaviour of 18Ni maraging steel for the study and furth...

The chisel-edge axial rake angle has an important effect on the processing performance of helical point micro-drills. In this research, the mathematical modeling for the spiral groove, helical flank, and cross-shaped chisel edge are conducted, and then three types of helical point micro-drills, each having a thinned chisel edge with an unequal axial rake angle, are designed and fabricated. Then, the finite element simulations and processing experiments of micro-drilling are performed separately, and the thrust force, torque, chip morphology, tool wear, and micro-hole machining quality are measured and evaluated. With the rise of the axial rake angle of the chisel edge, the curling degree of the chips and the thrust force were found to decrease owing to the increase of the rake angle along the inner cutting edge. The angle between the tool axis and chip axis was found to gradually decrease due to the reduction of the rake angle gradient along the cutting edge. Additionally, the thickness and width of the uncut chip of the inner cutting edge were found to increase, bringing about the rise in the torque. The wear degree of the micro-drills with a 0° axial rake angle (Type II) was the smallest due to their medium thrust force and torque, and a better micro-hole entrance morphology and minimum roundness were obtained. When drilling to the 30th hole, compared with the micro-drills with a − 10° axial rake angle (Type I) and 10° axial rake angle (Type III), the chisel edge maximum wear width of Type II (δ = 0°) was respectively reduced by 82.43% and 19.69%, and the micro-hole roundness respectively decreased by 26.7% and 11.33%. The thrust force of Type I (δ = − 10°) was the largest, so it caused greater tool wear and poorer micro-hole quality. The larger torque and lower rigidity of the inner cutting edge of Type III (δ = 10°) led to poorer drilling performance. Thus, helical point micro-drills having the 0° chisel edge axial rake angle are suitable for drilling 304 austenitic stainless steel.

The micro channel cold plate is very suitable for the application environment of high heat consumption liquid cooling such as PCB plate and multi-layer components. However, at mesoscale, the titanium alloy micro channel cold plate is micro thin-walled structure of cantilever boundary with weak stiffness, which leads to significant deformation and resultant poor machining accuracy during micro milling. To effectively control and reduce micro thin-walled deformation, a 3D FE cantilever model is established to predict dynamic milling deformation of micro thin wall. The constitutive model of titanium alloy (Ti-6Al-4 V) that includes the strain gradient to consider size effect in micro milling, the edge geometry of milling cutter, the thin-walled microstructure, and micro milling parameters is involved in milling modeling of thin wall. Moreover, a series of micro milling experiments for micro thin wall of titanium alloy at different machining parameters were carried out to investigate the law and mechanism of thin wall deformation in milling micro thin wall subjected to dynamic alternating forces. By comparing numerical and experimental deformation of micro thin wall in micro milling, the accuracy and validity of the prediction model based on cantilever boundary are verified, which provides theoretical support and model basis for the deformation control in milling micro channel cold plate at mesoscale.

Friction modeling between the tool and the workpiece plays an important role in predicting the minimum cutting thickness during TC4 micro machining and finite element method (FEM) cutting simulation. In this study, a new three-region friction modeling is proposed to illustrate the material flow mechanism around the friction zone in micro cutting; estimate the stress distributions on the rake, edge, and clearance faces of the tool; and predict the stagnation point location and the minimum cutting thickness. The friction modeling is established by determining the distribution of normal and shear stress. Then, it is applied to calculate the stagnation point location on the edge face and predict the minimum cutting thickness. The stagnation point and the minimum cutting thickness are also observed and illustrated in the FEM simulation. Micro cutting experiments are conducted to validate the accuracy of the friction and the minimum cutting thickness modeling. Comparison results show that the proposed friction model illustrates the relationship between the normal and sheer stress on the tool surface, thereby validating the modeling method of the minimum cutting thickness in micro cutting.

In five-axis ball-end machining, stability of the milling process is not only determined by the combination of depth of cut and the spindle speed, but also determined by the lead and tilt angles of the milling tool (i.e., the tool orientations). As the degree of freedom increases, five-axis machining machines have more complex dynamic characteristics. Therefore, the influence of the tool-workpiece interactions on the machining performance is more obvious. In this paper, a new five-axis ball-end milling dynamical model which considers the multiple interactions between the tool and workpiece is established for the first time. Based on the established dynamical model, the effects of regenerative effect, structural mode coupling and process damping on the dynamic characteristics of five-axis milling are investigated. In addition, the effects of lead angle and tilt angle on the stability prediction of five-axis milling are investigated. The experimental results show that the proposed five-axis milling dynamical model is more reliable than the traditional one in predicting the stability of five-axis milling.

As a typical single crystal material, the ground surface characteristics of sapphire are influenced by the relationship between machining direction and crystalline orientation. In this paper, the effects of grinding direction on the surface characteristics of the prism-plane sapphire were investigated by a series of sapphire grinding experiments under the orthogonal machining directions. The ground surface topography, surface layer lattice residual stress and degree of lattice distortion were measured. The results show that the grinding force with the grinding direction along the c-axis is greater than the grinding force along the m-axis or the a-axis, and serious damage was generated to the ground surface with grinding direction along the c-axis. The full width at half maximum intensity value of the X-ray rocking curve indicates that the residual stress of the ground surface with machining direction along the c-axis is greater than that along the m-axis or the a-axis, and the molten KOH etching analysis results manifest that the degree of lattice distortion of the ground surface with machining direction along the c-axis is higher than that along the m-axis or the a-axis. Therefore, the grinding direction along the m-axis or the a-axis is better suited to process prism sapphire.

Single-point diamond cutting is an efficient method to fabricate microlens arrays (MLAs). However, machining MLAs at the microscale with high dimensional accuracy and a smooth surface finish is a difficult task. In this study, a method of profile cutting is proposed to machine MLAs on electroless nickel–phosphorus (Ni–P) plating. To improve the dimensional accuracy of MLAs, a precision tool setting method is introduced, via which the precision of MLA sag can be controlled to within 20 nm. In addition, the formation mechanism of corrugation defects is studied via a finite element (FE) simulation of the wedge nano-cutting process and a cutting experiment of concentric ring grooves. By optimizing the tool settings and the machining parameters, high-quality MLAs with apertures of Φ100 μm can be created.

As an unfavorable factor of machining process, chatter threatens the machined quality of workpiece, which determines the assembly and fatigue performance of the workpiece. During the interaction between machine tool and thin-walled workpiece, the process damping effect, multiple modes response and dynamic changes caused by the material removal of the in-process workpiece (IPW) will make the machining process more complicated and introduce great difficulties to dynamic modeling and performance prediction. In this paper, we considered the process damping determined by the indentation volume between flank face of milling tool and machined surface, and used multi-mode model to describe this behavior. In order to establish the assembled material removal model of the IPW dynamics with multiple modes, the structure dynamic modification (SDM) and finite element method (FEM) were combined together. The updated third-order full discretization method was applied to solve the dynamic equation in modal space. Then, the three-dimensional stability lobe diagrams (SLDs) with and without material removal along the tool path were obtained respectively by enveloping multiple modes of the IPW and milling tool together. Finally, the cutting tests were carried out. The experiments showed that the assembled model could predict the dynamics of IPW accurately, and the proposed stability analysis model was relatively close to experimental results. Besides, the modes of thin-walled workpiece with weak rigidity do not always play a dominant role in the process of machining. Although the material removal rate is limited by considering the multiple modes of the system, the processing quality can be ensured.

The effects of cemented carbide materials on cutting edge fracture mechanism of micro end mills in aluminum alloy 7075 machining are investigated. A series of micro milling experiments on the tool wear were conducted. The surface morphologies of micro end mills were observed, and the end teeth flank wear length and tool total cutting edge length reduction were measured. The results showed that the Co content and WC grain size of cemented carbides have significant effects on tool wear and cutting performance of the micro end mill. With increase of WC grain size, the tool end teeth flank wear length increases and the total cutting edge length reduction of the mill obviously increases. Thus, the micro end mill with finer grain size presents better wear resistance. However, with increase of Co content, the micro end mill exhibits less wear resistance. This can be explained that the adsorption energy between Co atom and Al atom become larger based on first principle calculation of adsorption energy between cemented carbides and aluminum alloy. The Co binder of tool material is dragged off by frequent fall off of built-up edge, resulting in more loss of Co element. Thus, the strength of the tool is decreased.

Diamond cutting is a popular method to fabricate microlens array (MLA) on polymethyl methacrylate (PMMA); however, it is limited by brittle fracture, which is formed easily on the surface of MLA during the cutting process. In this paper, the formation mechanism of the brittle fracture is studied via a series of experiments including the slow tool servo (STS) cutting experiment of MLA, surface scratching experiment and sudden-stop cutting experiment. The effects of undeformed chip thickness, feed rate, and machining track on brittle fracture formation are investigated in detail. In addition, based on the fracture formation mechanism, a bi-directional cutting approach is proposed to eliminate the regional brittle fracture of the microlens during diamond cutting. An experiment was then conducted to verify the method; the results demonstrated that bi-directional cutting could eliminate brittle fracture entirely. Finally, a spherical MLA with the form error (vPV) of 60 nm and the surface roughness (Ra) of 8 nm was successfully fabricated.

Precision glass molding (PGM) has been developed and improved to produce various functional lenses in the optical industry. Tungsten carbide (WC) molds have received increasing attention due to the low thermal expansion coefficient and long service time but the molds are difficult to machine using micro-cutting or micro-grinding methods. Electrical discharge machining (EDM) milling is a promising method for the fabrication of WC molds used for microlens arrays but the significant electrode wear results in low machining accuracy. In this paper, a new method is proposed to address the electrode wear by utilizing in situ electrode trimming during EDM milling; the objective is to improve the accuracy of the WC mold used for microlens array fabrication. The feasibility of the proposed in situ electrode trimming method is verified by comparing the surface roughness of the pits on the mold surface fabricated by EDM milling with and without electrode trimming. In addition, the structure of the copper–tungsten electrode is redesigned to improve the electrode stiffness during in situ trimming. Furthermore, an in situ trimming setup is developed and the trimming process of the electrode is optimized.

Nickel phosphorus (Ni-P) is a promising plating material for the moulds used in the precision glass moulding (PGM) of micropyramid structure components. A transverse planing method for machining Ni-P moulds with a micropyramid array pattern is analysed. Notable defects, including chippings and burrs, are observed on the exit and entry parts, respectively. The defect-forming mechanisms are analysed, and it is confirmed that a large cutting thickness and chip interference in non-free cutting tend to be the most effective methods for eliminating defects. Based on the above analysis, the diamond fly-cutting method is introduced into the micropyramid array Ni-P mould fabrication process. The advantage of the diamond fly-cutting method is revealed through comparison with the transverse planing method. To establish a contrast to the transverse planing method and evaluate the machining quality of the structure in the diamond fly cutting, a maximum effective cutting thickness of the remaining surface is proposed based on theoretical analysis. Finally, an experimental setup of ultraprecision fly cutting is established, and an ultraprecision micropyramid array is fabricated on nickel phosphorus plating.

A new tool strengthening method for micro-tools using pulsed magnetic treatment has been experimentally investigated. Compared with the conventional tool strengthening method, the pulsed magnetic treatment of micro-tools enables effectively reduce tool wear both by improving the mechanical properties of the tool material and changing the tool-chip contact friction mechanism which results in efficient chip removal and good surface quality. On account of this method, the untreated and treated micro-tools and three different magnetic properties of ferromagnetic, paramagnetic, and diamagnetic workpiece materials were used to perform comparative cutting experiments. The tool wear, cutting force, and surface roughness were measured to quantitatively investigate the influence of magnetic treatment on the micro-cutting process. Results showed that wear resistance of micro-tools could be improved when machining ferromagnetic and paramagnetic materials, of which the minor flank wear could be reduced by up to 56%. However, the tool wear increased when machining the diamagnetic materials. On the basis of relationship between micro-tool, micro-chip, and workpiece, the machining mechanism is analyzed in detail in pulsed magnetic treatment for micro-tools.

Chisel edge thinning can effectively improve the drilling performance of austenitic stainless steel. Four kinds of helical point micro-drills, each with a thinned chisel edge of a distinct length, are fabricated based on the mathematics models of the micro-drill by using a six-axis computer numerical control tool grinder. Micro-drilling experiments on 304 stainless steel are conducted. Drilling performance is evaluated according to the measured and observed micro-hole machining quality, chip morphology, thrust force, and tool wear of the micro-drill tip. With a decrease in the chisel edge length, the micro-holes drilled using thinned micro-drills have small entrance burrs, roundness errors, and regular shapes, which are attributed to an increase in self-centering capability. Owing to increased equivalent chip thickness and different directions of chip flow, micro-drills with thinned chisel edge can generate more small-size chips and improve chip breaking. In addition, the inner cutting edge with a positive rake angle replaces the chisel edge with a negative rake angle to cut the workpiece, significantly reducing the chip curl, thrust force, and tool wear of micro-drills. However, helical point micro-drills with critical chisel edge lengths by thinning exhibit less thrust force and tool wear than do helical point micro-drills with no chisel edge because of the increase in the uncut chip width of the micro-drill. Thus, with the selected parameter range, the optimal helical point micro-drill is the micro-drill with a specific chisel edge length by thinning to improve drilling performance.

Surface-layer defects of M-plane sapphire caused by ultrasonic vibration-assisted cutting were investigated in this paper through comparison cutting experiments. Topography analysis results indicate that when the cutting direction is not along a-axis or c-axis, the spalling defects of conventional cutting groove are asymmetric because the probabilities of activated cleavage/twinning systems vary with machining direction; however, the vibrational cutting groove presents better symmetry and less spalling owning to the propagation of stress wave. The cross-section of cutting groove was obtained by focus ion beam cutting. The cross-section analysis shows that the subsurface defects of conventional cutting groove involve median cracks and lateral cracks, and the main propagating path of cracks is towards downward, which is the cause of the generation of serious spalling; however, lateral cracks are the main defect in the subsurface of the vibrational cutting groove, and they mainly propagate towards the free surface and give rise to material removal. The subsurface quality of cutting groove with ultrasonic assistance is better than that of the conventional cutting groove. It is evident that ultrasonic vibration can prevent the median crack from extending towards bulk material and contribute to improve the uniformity of groove quality.

The stability of micro-milling has an important influence on the machined surface, and choosing proper machining parameters can effectively avoid machining process instability and dynamic error. The frequency response function (FRF) of micro-milling tool point varies with tool overhang lengths, and it affects stability lobe diagram (SLD) of the machining system. During the micro-milling process, the cutting thickness was divided into the shearing zone and the plowing zone. In the shearing zone, the cutting thickness was calculated with considering cycloidal tool path and dynamic cutting thickness. After the micro-milling force model was established, the receptance coupling substructure analysis (RCSA) and experimental modal analysis (EMA) were used to obtain the FRFs at the micro-milling tool point. The 2 three-dimensional diagrams, SLD and surface location error (SLE), were developed comprehensively by means of frequency domain method, and the flank micro-milling experiments were carried out. The validity of the three-dimensional SLD containing tool overhang length and the prediction model of SLE was verified by the experimental results, and surface topography was characterized to show the actual machining state. The experimental results show that, compared with SLE, the change of tool overhang length had more significant influence on SLD, and the chatter remarks were not very obvious on the bottom of the workpiece no matter whether the machining process was stable or not. In unstable region, chatter caused by cutting tool left marks on the machined surface. Under the condition of stable milling, a machined surface with smaller SLE and better topography was obtained. The 2 three-dimensional diagrams can provide good references for the selection of optimal tool overhang length and machining parameters comprehensively.

Micro ball-end milling is an efficient and feasible method for the fabrication of microlens array molds which are widely applied in the aerospace, mechanical electronics, optics, and optoelectronics fields. The geometric structure of the micro ball-end mill plays an important role in micro dimple milling performance. The relief angle, as one of the major geometric parameters of the micro ball-end mill affects the sharpness of the cutting edge and determines friction between the tool and the workpiece. To investigate effective fabrication of a micro ball-end mill with different relief angles, this paper proposes a practical grinding method for the relief face validated by a grinding experiment, in which micro ball-end mills with relief angles of 10°, 20°, and 30° are fabricated. Furthermore, to analyze the influence of the relief angle on milling performance, micro dimple milling experiments on die steel material H13 with fabricated mills are carried out. The milling force, tool wear, and machining quality are measured and analyzed. The experimental results show that the micro ball-end mill with a 20° relief angle is more appropriate for micro dimple milling compared to the other two mills.

Nowadays, micro engine miniaturization is one of the most challenging issues, especially for the design and fabrication of the high-power-density micro Wankel engine. With the decrease of the size of the micro engine, the problem of the heat deformation of the cylinder becomes more serious. In this paper, a micro Wankel engine with microtextures on the outer surface of the cylinder is designed and manufactured to diffuse the heat dissipation and regulate the temperature gradient, so as to increase the power output density. First, a series of finite element simulations are conducted to design a type of ideal surface microtexture. Then, the machining condition is optimized to fabricate microtextures by micro cutting on the cylinder surface by studying the processing parameters. Finally, the performance of the new micro Wankel engine in terms of the temperature gradient regulation and the mechanical power output is tested and compared with that of the un-textured micro engine. The comparison results show that temperature of the textured micro engine was dropped from 185 &deg, C to 125 &deg, C and the mechanical power output increased by 10.74% from that of its un-textured counterpart, verifying the proposed methods for temperature gradient regulation.

Turn-milling is a relatively new cutting process combining the both advantages of turning and milling, during which the tool and the workpiece rotate simultaneously. Due to the small axial cutting force, turn-milling is especially suitable for the machining of miniature parts. Usually, the surface quality is characterized by roughness, but the size of miniature parts is difficult to meet the requirements of the sampling length, which will have a huge influence on the characterization results. This paper introduces the box-counting method for image fractal dimension estimation to evaluate the surface quality of miniature parts during orthogonal turn-milling. The fractal dimension is an independent parameter for scale, which is not influenced by the sampling length. The effect of cutting parameters on surface quality of miniature parts during turn-milling is also studied.

Although SiC p /Al matrix composites possess numerous excellent physical and mechanical properties, high hardness and high wear resistance characteristics of SiC reinforcement lead to low tool life and resultant poor machined surface quality in cutting. The aim of this paper is to investigate the micromechanism underlying the macro-scale wear of diamond tools in drilling of high volume fraction SiC p /Al composites. To achieve this, the worn morphologies and possible crystal structure evolution of diamond tools after drilled 10 holes were examined using Laser Scanning Microscope and Raman spectroscopy, respectively. Additionally, based on drilling forces and hole quality, the machinability assessment of SiC p /Al6063 composites was carried out. The results indicate that the mechanically induced abrasion and thermodynamically activated chemical graphitization is the dominant and common wear mechanisms for PCD and CVD diamond coated tools in drilling of 65 vol% SiC p /Al6063 composites containing copper. The reciprocating actions of thin graphite layer formed by oxidizing hydrogen chemisorbed on diamond surface by Copper oxides and graphite removal due to SiC particulates’ high-frequency scrape lead to continual and significant occurrence of diamond graphitization. In air atmosphere, the thermodynamic conditions of diamond-graphite transformation in machining of SiC p /Al6063 composites containing Copper are investigated. The coupled abrasive-chemical wear model is formulated based on analytical description of diamond wear mechanisms above. In terms of machinability of high volume fraction SiC p /Al composites, CVD diamond coated carbide drill is preferred, due to its stable cutting force, less wear and its ability to produce acceptable machined quality with increasing hole number.

Micro ball-end milling is an efficient method for the fabrication of micro lens array molds. However, it is difficult to meet the machining quality of micro dimple molds due to the wear and breakage of the milling cutter, which presents large challenges for designing geometric structure and edge strength of micro ball-end mills. In this study, a new configuration of a micro ball-end mill for micro dimple milling is designed and named the micro conical surface ball-end mill. The cutting edge is formed by intersecting the conical surface and the inclined plane. A practical grinding method is proposed based on the kinematic principle of the six-axis computer numerical control (CNC) grinding machine for micro conical surface ball-end mills and is validated by grinding simulations and experiments. Micro dimple milling experiments are conducted on the hardened die steel H13 to investigate the cutting performance of the mill. The milling force, the micro dimple roundness error, and the tool wear morphology are observed and analyzed. The results show that the radial milling force is more stable and the wear resistance is improved for the micro conical surface ball-end mill compared to the traditional micro spiral blade ball-end mill. Therefore, a more stable roundness at the entrance hole of the micro dimple can be obtained by using this design after a number of micro dimples have been milled.

The serrated chip is a remarkable characteristic in the machining of the Ti-6Al-4 V alloy, but its formation mechanism is not completely understood. Finite element modeling is an effective method for studying the complex thermo-mechanical problems that occur during the machining process. The constitutive model plays a key role in the simulation, and Johnson-Cook (JC) model is the most commonly used model. However, the JC model neglects the coupled effects of the strain, strain rate, and temperature, and the material is assumed to be homogeneous. Thus, the JC model is applicable for studying macroscale machining. In fact, cutting is a complex thermo-mechanical process, and there are material defects in the Ti-6Al-4 V alloy. First, a modified JC model is proposed based on the THAN law, which is derived from material defects considering the coupled effects of the strain, strain rate, temperature, and strain softening. Then, the serrated chip morphology and cutting force predicted by the JC-THAN model are compared with experimental data. Finally, the serrated chip formation mechanism from macroscale machining to microscale machining is analyzed considering the material defects based on the JC-THAN model, and the dominated formation mechanism at each scale is found.

The surface topography of milled workpieces often defines their performances, and it directly affects the precision and service life of parts. In view of the influence of tool inclination angle on the 3D surface topography in micro-ball-end milling, this paper carries out micro-milling surface predictions and tests based on the theoretical model of cutting edge trajectory model, providing technical basis for the high-precision machining of micro-surface. A theoretical model for the description of the cutting edge trajectory is established prior which takes inclination of cutter, flutter, run-out, cutting force, and plastic deformation of the material into account. Then, the surface topography and roughness are predicted based on the model. In addition, a series of newly designed surface topography experiments are carried out to verify the prediction. Through the comparison of the simulated micro-surface with the experimental results, the theoretical model showed considerable reliability, which means the 3D surface topography could be well controlled with the parameter recommended by the constructed model under certain conditions. The above research has a great significance in improving machining quality.

Chalcogenide glass (ChG) Ge 22 Se 58 As 20 is a significant material in infrared optical systems, and it is usually machined by ultraprecision single point diamond turning (SPDT) for aspheric lens and freeform surface. However, as a soft brittle material, the surface is easily cracked during cutting. With the increasing demand for imaging quality, the surface integrity of chalcogenide glasses becomes increasingly important. This paper proposes a method to achieve high-precision and high-efficiency aspheric lens by SPDT. First, to study the material properties, the Vickers hardness of Ge 22 Se 58 As 20 is tested, and the element components and microstructure are analysed by EDS. Second, through orthogonal cutting, the critical cutting thickness of the brittle-ductile transition is tested to be 1.2 μm and the minimum depth of cut for chip formation of 100 nm is identified. The material removal rate under ductile machining in face turning was calculated. Finally, by optimizing the machining condition, an aspheric lens with surface roughness of Ra 6.47 nm and form error of PV 120.82 nm was successfully fabricated.

Crystalline nickel-phosphide (c-Ni-P) plating is a newly developed mold material for precision glass molding (PGM) to fabricate microgrooves. In the ultraprecision cutting process of the c-Ni-P plating material, the neighboring microgrooves are required to adjoin with each other to ensure acute microgroove ridges and miniaturize the microgroove size. Generally, defects of burrs and fracture pits can easily occur on the ridges when the plating layer is grooved. Burrs appear when tears dominate in material removal with a large adjacent amount. With the change of the adjacent amount, the removed material is sheared out from the workpiece, and when the cutting depth of the groove ridge is over the brittle-ductile transition thickness, fracture pits arise. To restrict these defects, a small cross-angle microgrooving method is proposed to test the critical adjacent amount range efficiently. It is found that an acute ridge of the microgroove is formed with a small enough adjacent amount; when this amount is in the range of 570 nm~720 nm in the microgroove machining process, fracture pits begin to arise on the gradient edge. High-quality microgrooves can be obtained based on this methodology.

A new machining method for lens molds using tilt electrical discharge milling (ED milling) has been experimentally investigated. Compared with the conventional ED milling, the tilt ED milling enables efficient enlargement of discharge gap by adjusting the tilt angles of the workpiece which results in efficient chip removal and burnish surface quality. On account of this method, micro lens craters were fabricated on the tungsten carbide (WC) and silicon carbide particulate reinforced aluminum metal matrix composite (SiCp/Al) at the optimized machining parameters under various tilt angles of the workpiece. The surface morphology and material removal rate were determined with a laser scanning microscope VK-X100 (KEYENCE, Japan). Experimental results present a 60% rise in surface quality at 25° in tilt ED milling. On the basis of electromagnetic effect, the machining mechanism is analyzed in detail in tilt ED milling for lens molds.

n view of the influence of cutting heat and cutting force on the machining precision of micro-machining, this paper carries out micro-milling temperature measurements and deformation measurement tests based on the theoretical model of temperature field distribution of workpiece and the simulation model of workpiece deformation, providing technical basis for the high-precision machining of precision micro-parts. A theoretical model for the description of the increase in the cutting temperature of the workpiece is established prior to using an inverse evaluation method for solving the heat source intensity iteratively. During the finite element analysis of the distribution of the temperature field and heat distortion, the process of the heat transfer is simplified as a process of applying a series surface heat source to workpiece. Besides, this paper carried on a series of micro-milling experiments, used a fast-response thermocouple which has a property of self-renewal for the measurement of the change of the workpiece temperature, the response time of the applied thermocouple is within the magnitude of microsecond, and then, a high-frequency amplifier and an electric potential acquisition equipment were used to gain the transient temperature in the cutting area; meanwhile, a dynamometer is applied to measure the three-directional forces, and finally, the workpiece deformation would be measured by the Keyence microscope. Through the comparison of the simulated temperature and deformation with the experimental results, the simulation model showed considerable reliability.

Micro mills are widely applied in the micro manufacturing and mainly fabricated using the grinding method. Cutting edges have significant influences on the performance of micro mills such as the micro mill life and machining quality. In this paper, the cutting edge damage mechanisms in the grinding of cemented carbides micro mills are investigated. The micro end mills grinding experiments are carried out and the cutting edge maximum edge damage width and surface roughness of the end teeth flank are measured. The results show that the micro fractures and micro cracks are generated in the cutting edge following micro pits in the grinding surface. The grain size and composition of cemented carbides have significant impacts on the damage of the cutting edge. The maximum edge damage width increases with the increase of Co binder content and WC grain sizes. However, a better flank quality with less micro pits is obtained as the reduction of Co binder content and grain size of WC.

Single-point diamond cutting is an efficient method to generate the V-shape microgrooves, but the burr forms easily at the microgroove edge when cutting ductile material, especially at small (micron level) cutting depth, and the burr increases with the reduction in the cutting depth. In this paper, the effects of plastic side flow in micro cutting are taken into account to explain the formation of burrs in ultraprecision machining process. The edge radius of diamond tool is measured by scanning probe microscope (SPM), and the mechanism of the burr formation is revealed with considering the edge radius of diamond tool and the cutting depth in machining nickel phosphide (Ni-P). In this way, an approach to restrain the burr formation is established so as to generate fine microgrooves.

The residual stress has an important influence on the performance of parts such as fatigue life, and many researches have been carried out for the quantitative evaluation or prediction of residual stress. However, the quantitative evaluation of residual stress achieved by the instrument will cause damage to the parts or consume a long time. Moreover, some analytical models for machining-induced residual stress prediction are quite complex with poor universality. In this research, surface residual stress under different cutting parameters and machining features were investigated. The optimal feature set and feature importance were analyzed by random forest algorithm. A new method for predicting machining-induced surface residual stress was proposed based on Gaussian process regression and other machine learning algorithms were also utilized to verify the performance of the proposed approach. The values of quantitative evaluation indicators showed that the prediction model provides a robust framework for surface residual stress prediction.

Electroless nickel phosphide (Ni–P) plating is used to fabricate microgrooves for precision glass molding (PGM) due to its excellent mechanical properties as a mold material. To achieve a high-quality microgroove fabrication, the causes of the machining defect, like burrs on the mold surface during the microgrooving of amorphous nickel phosphide (a-Ni–P) by single-point diamond cutting, are investigated. We find that the burrs can be eliminated by increasing the brittleness of a-Ni–P, so the brittleness enhancement of the material is conducted by crystallization. Then, the machined surface and the chip morphology during cutting crystalline nickel phosphide (c-Ni–P) are analyzed and compared with that during a-Ni–P microgrooving. Through this innovation, the surface quality of the microgroove is improved with minimized burrs.

Micro cutting is widely used in the machining of micro components and micro features of conventional size components. During the micro cutting process, the manufactured components and characteristics usually belong to mesoscale, and the final geometric accuracy and surface quality are affected by many factors. In this paper, a series of micro milling tests based on heat-resistant stainless steel (12Cr18Ni9) are carried out to figure out the influence of different factors on machining quality of mesoscale low-rigidity characteristics. During the study, the small displacement torsors (SDT) theory are employed to characterize the perpendicularity tolerance of mesoscale surface. Optical microscopic measurement method is used to obtain SDT parameters, then the width of the tolerance zone is obtained; based on which, the effect of different factors on machining quality is systematically studied. In addition, the surface roughness and micro topography of the machined surface are also analyzed, and the phenomenon of surface deterioration caused by high-temperature chip is effectively controlled. Finally, a general method for ensuring the processing quality of mesoscale low-rigidity characteristics is proposed.

Micro milling forces can easily induce bending deflection when machining micro complex components, which makes the tool center deviate the desired trajectory and causes dimension error. So this study is mainly focused on analysis of dimension error in micro ball end milling. The analytical prediction model of dimension error is proposed based on the deflection of micro ball-end milling cutter induced by micro milling forces, which referenced to Euler Bernoulli cantilever beam equations. The micro milling forces acting on ball end milling cutter can be acquired by numerical integration. And the proposed models using two-section and three-section cantilever beam equation separately were analyzed by comparison. The proposed machining deflection’s error prediction model is validated by micro ball end mill on stainless steel workpiece. The experimental results show that the model based on three-section cantilever beam equation has a better correlation with the simulation results. The proposed theoretical model offers a basis for controlling machining deflection as well as manufacturing process optimization.

Micro end milling is a main method for the fabrication of microgroove parts which are widely applied in biology, electronics, precision machinery, and other fields. However, the machining quality of microgroove is difficult to meet requirements due to size effect, and the machined grooves easily produce high surface roughness and poor form accuracy during micro milling. In this paper, in order to investigate the effects of machining inclination angles on the performance of micro ball end milling, the micro milling experiments on Ti-6Al-4V are carried out by setting the micro ball end mill with different inclination angles in feed direction, cross-feed direction, and the combination of the two directions, respectively. The results show that the tool orientation strategy has significant influences on the quality of microgroove and can reduce the roughness and improve the form accuracy. With increase of the absolute value of inclination angle along feed direction from 0° to 45°, the surface roughness has a decreasing trend, and the chips adhesion and texture becomes inconspicuous. When inclination angle along feed direction is 30° and 45°, the combination inclination angle strategy has no obvious influences on the surface roughness with increase of inclination angle along cross-feed direction. However, the combination inclination angles strategy can reduce the maximum form deviation and improve the form accuracy of the groove. Based on the results, an optimal combination inclination angles with feed direction 45° and cross-feed direction 20° strategy is proposed to machining the microgroove.

Integral impeller is the most important component of a mini-engine. However, the machining of a mesoscale impeller with a complex integral surface is difficult because of its compact size and high accuracy requirement. A mesoscale component is usually manufactured by milling. However, a conventional milling tool cannot meet the machining requirements because of its size and stiffness. For the fabrication of a complex integral impeller, a micro-ball-end mill is designed in accordance with the non-instantaneous-pole envelope principle and manufactured by grinding based on the profile model of the helical groove and the mathematical model of the cutting edge curve. Subsequently, fractal theory is applied to characterize the surface quality of the integral impeller. The fractal theory-based characterization shows that the completed mesoscale integral impeller exhibits a favorable performance in terms of mechanical properties and morphological accuracy.

Deflection problems are important causes of deterioration to the dimensional precision of machining micro thin-walled components. Under mesoscale, the deflection of the cutting tool and micro thin-walled workpiece model is established based on the Euler-Bernoulli cantilever beam theory. Then a novel average thickness prediction model of micro straight thin wall is set up considering the runout, cutting tool, and workpiece deflection. Afterwards, based on experimental data, the model is modified by introducing a scale factor K. This modified model has been calibrated and validated with Ti-6Al-4V titanium alloy, and it can provide very accurate prediction results for the micro straight thin wall at average thickness. In addition, the law of micro thin wall milling forces is also studied. In the end, the effect of different micro straight thin-walled stiffness on micro thin-walled dimensional accuracy is analyzed. The study found that for the thickness of micro straight thin walls, 100 μm is an inflection point to distinguish dimension precision between macroscale and mesoscale.

This paper presents a study of the Taguchi application to optimize surface quality based on fractal theory in meso-scale end-milling operation. Usually, the surface quality is characterized by roughness, but in the meso-scale area, the size of the workpiece will be difficult to meet the requirements of the sampling length, which will have a huge influence on the characterization results. Although there are many algorithms for adjusting, the operation process is very cumbersome; for this reason, characterization method based on fractal theory is introduced and applied to evaluate the machined surface in the research. Also, the Taguchi method is applied to search the optimal parameters combination, during which spindle speed, depth of cut, and feed rate are considered as the control factors. Specifically, firstly, the machining surface characterization method based on fractal theory is introduced in details; then, an orthogonal array of L25(53) is used for the experimental study; through ANOVA analyses, the significant factors which affect surface quality are established, and the optimal cutting parameter combination is determined; later, confirmation tests are carried out to verify the applicability of the characterization methods for the meso-scale cutting surface. Research shows that fractal characterization method is better to evaluate the surface quality in the meso-scale.

Electroless nickel phosphide (Ni–P) plating is used as a new mold material to fabricate microgrooves on glass molding process because of its excellent mechanical properties and machinability. Amorphous Ni–P will be crystallized at high temperature during the glass molding process. Crystalline Ni–P plating leads to mold deformation, which may reduce the mold accuracy and shorten the service life. In this study, the amorphous plating is heated to its annealing temperature at nearly 600 °C to make it transform to crystalline state in advance. Thus, the hardness of the plating increased from 614 to 941 HV; the deformation of the mold with crystalline plating similar to glass molding condition is removed by ultraprecision turning. Finally, microgrooves are fabricated on crystalline Ni–P plating. In the experiments, matrices with amorphous plating and crystalline plating are used in microgroove machining on an ultraprecision machine. Subsequently, machined form accuracy and surface quality for the two plating layers are compared. Under the condition of different cutting speeds, the surface roughness of the crystalline Ni–P plating distributed in the interval of about 60 nm; the amorphous Ni–P plating distributed in the interval of about 80 nm correspondingly. The results proved that the microgrooves machined on the crystalline plating exhibited better performance than its amorphous counterpart.

Purpose The purpose of this study was to clarify the applicable conditions for coatings with different element contents. Surface coating on existed tool material is an effective way to improve the cutting tool properties in extremely adverse machining conditions. These coatings are generally non-metering compounds. Each coating with a certain element ratio has a specific application condition, and the relationship between element contents and performance should be defined. Design/methodology/approach (Zr, Ti)N hard coatings with different element contents were deposited on cemented carbide. The ball-on-disk method reciprocating sliding wear tests against 40Cr hardened steel were carried out. This paper was focused on analysis of the friction and wear behaviors of these (Zr, Ti)N coatings with different element contents. Findings The results indicated that atomic ratio of Zr and Ti was the main factor that decided the friction coefficients. The friction coefficient and wear rate showed a gradual downward trend at 10 N with the increase of Zr content. The wear rate was the smallest at the atomic percentage of nitrogen 0.466. If the lattice distortion of the coatings gets too severe, the coatings would have a high wear rate. Originality/value The optimal application conditions of the coatings were defined, and this was important for customized design or choice of the coatings under different cutting parameters.

Tool wear is a significant issue for the application of micro end mills. This can be significantly improved by coating materials on tool surfaces. This paper investigates the effects of different coating materials on tool wear in the micro milling of Ti-6Al-4V. A series of cutting experiments were conducted. The tool wear and workpiece surface morphology were investigated by analyzing the wear of the end flank surface and the total cutting edge. It was found that, without coating, serious tool wear and breakage occurred easily during milling. However, AlTiN-based and AlCrN-based coatings could highly reduce cutting edge chipping and flank wear. Specifically, The AlCrN-based coated mill presented less fracture resistance. For TiN coated micro end mill, only slight cutting edge chipping occurred. Compared with other types of tools, the AlTiN-based coated micro end mill could maximize tool life, bringing about an integrated cutting edges with the smallest surface roughness. In short, the AlTiN-based coating material is recommended for the micro end mill in the machining of Ti-6Al-4V.

This paper presented the influence of machined surface texture on fretting cracks behaviors of Titanium alloy Ti–6Al–4V under radial loading in conformal contact. The contacted holes of specimen were machined with combined helical and flank milling before fretting fatigue tests, and a special fretting fatigue test apparatus was proposed to focus on conformal contact fretting fatigue (CCFF) test under radial loading. The test results showed that all the specimens failed at the contact area where characterizes an inner obtuse angle between the material flow direction (or cutting direction) and the direction of the tangential component of the contact force. The area with higher surface skewness and kurtosis values was also prone to nucleate fretting fatigue crack. These results suggested that the corresponding machining conditions in hole-making and surface strengthen processes should be adjusted to guide the production of surface texture properties, in terms of obtaining desirable lower skewness and kurtosis features to relieve nucleation of fretting cracks. Additionally, the debris in conformal contact tended to aggregate towards the partial slip zone (PSZ) due to the conformal geometry and form a compacted layer in the gross slip zone (GSZ) subjected to radial loading. These characteristics exacerbated and alleviated fretting damage in the PSZ and GSZ, respectively. In this research, a set of suitable milling parameters for the hole flank milling process in terms of prolonging fretting fatigue life were also defined.

To obtain a superior machined surface quality, predicting cutting force is important for planning and optimizing cutting process before actual machining. This paper established a novel analytical cutting force model for end milling of curved surfaces. Taking the variation of cutter geometry into account, cutting force coefficients were characterized by physical parameters, e.g., the normal friction angle, the normal shear angle, the chip flow angle, and the shear stress. Based on an oblique cutting model, a mathematical relationship of the physical parameters was obtained by the minimum energy principle. A Newton iterative algorithm was utilized to solve the established non-linear equations for calibrating the cutting force coefficients. Taken the variable radial depths of cut into account, a vector method was derived to calculate the equivalent feed rates and the entry/exit angles. After calibrating the cutting force coefficients with performing straight milling tests, two typical curved surfaces were investigated. The one was a circular curved surface with constant radial depth of cut, while the other was a Bezier curved surface with variable radial depth of cut. The predicted cutting forces were compared with experimental results, and a good correlation was obtained.

In present research, micro-milling of heat-resistant stainless steel (12Cr18Ni9) is conducted with the purpose of revealing influence mechanism of cutting tool edge radius and cutting parameters on specific cutting energy. In order to clarify the relationship between specific cutting energy and the geometrical characteristics of the cutting tools as well as cutting parameters, a newly designed experimental method is put forward, thereafter, the evolution rules of specific cutting energy along with cutting parameters is researched in detail. Furthermore, a prediction model of the minimum chip thickness is built by using fuzzy logic method based on experimental data, objective to optimize cutting parameters during micro-milling of 12Cr18Ni9, good agreements are achieved between predicted results and experimental results in verification tests, which means the specific cutting energy can be well controlled with the parameter recommended by the constructed model. The above research has great significance in improving tool life and machining quality.

The elliptical ultrasonic assisted grinding (EUAG) method has been proved to be promising in machining of hard and brittle materials, e.g., sapphire and silicon. However, its potential has not been sufficiently developed because the processing mechanism has not been clearly explained. This paper focuses on the surface formation mechanism in EUAG of monocrystal sapphire by investigating the fractal behavior of ground surface. The EUAG experiments on monocrystal sapphire were performed on the constructed apparatus by installing an elliptical ultrasonic vibrator on a CNC surface grinder. For comparison, the conventional grinding (CG) experiments were also carried out on the same experimental apparatus without ultrasonic vibration. The ground surfaces obtained were analyzed by fractal method, and results show that: (1) the great improvement of the surface quality with lower surface roughness is achieved in EUAG compared with those in CG. Moreover, the fractal dimension of ground surface in EUAG is larger than that in CG. It is also found that the fractal dimension is more sensitive to surface defect compared with the surface roughness. (2) The fractal dimension changes differently comparing CG with EUAG as the depth of cut increases from 0.4 to 3.2 μm. From the variations of the fractal dimension with different depth of cut, it is found that there are two variation regions, i.e., steady region and deteriorated region both in EUAG and CG, but the depth of cut in steady-deteriorated transition point of EUAG is larger than that in CG, meaning that the EUAG can achieve a deeper ductile depth of cut. (3) In EUAG, elliptic motion trajectories of adjacent abrasive grains interact with each other, causing the lower side walls of grooves and more exquisite microstructures. Thus the higher surface fractal dimension in EUAG is obtained and a better surface quality is achieved. Therefore, the surface formation characteristics in EUAG of monocrystal sapphire can be investigated by fractal analysis.

With the rapid development of aerospace technology, Al7075 has been widely used for structural components. High-speed milling is one of the most effective ways to improve machining efficiency of Al7075. During the milling process, regenerative chatter which restricts the milling quality and productivity often occurs. With the aim of avoiding regenerative chatter, stability lobe diagram (SLD) is widely used to obtain chatter-free parameters. This work presents a stability prediction method by using shifted Chebyshev polynomials. The milling dynamics with consideration of the regenerative effect is described by time periodic delay-differential equations (DDEs). The transition matrix of the milling system is constructed with the help of Chebyshev–Gauss–Lobatto (CGL) points. In order to demonstrate the accuracy of the proposed method, the rate of convergence of the proposed method is compared with that of the classical benchmark methods. On the other hand, in the process of thin-walled workpiece milling, the dynamic behavior of the workpiece depends on the tool position. To study the influence of the tool position dependent dynamics on the chatter stability of the thin-walled workpiece, a three-dimensional SLD is obtained. The verification experiments are conducted to verify the reliability of the proposed method. The results show that the experimental results are consistent with the predicted results.