Undeformed Chip Research Articles

Study on micro-deformation in micro-grinding of selective laser melting FeCoCrNi high-entropy alloy based on molecular dynamics

Microscopic deformation behavior is an important part of the study of micro-grinding processing. This paper investigates the removal mechanism in the micro-grinding of selective laser melting FeCoCrNiAl0.5 high-entropy alloy. The micro-grinding process is analyzed through simulation using the molecular dynamics simulation method. The study examines how the thickness of the undeformed chip and the grain size affect the microdeformation behaviors of shear strain, micro-grinding force, the evolution of dislocations, and microstructural transformation. The experimental results confirm that the molecular dynamics simulation model accurately predicts the micro-deformation behavior of FeCoCrNiAl0.5 high-entropy alloy during micro-grinding. The micro-deformation mechanism involves dislocation slip and twinning deformation, while the removal mechanism mainly includes the elimination of axial and dendritic crystals. During micro-grinding, the grinding force experiences small to large fluctuations, and the total length of dislocations gradually increases. As the undeformed cutting thickness increases, the micro-grinding force also gradually increases. Simultaneously, the type of dislocations and laminar dislocation nuclei increase, leading to growth in the total length of dislocations. The number of high shear strain atoms, the micro-grinding force, and the degree of fluctuation in the single crystal high-entropy alloy are higher than those in the polycrystalline material, but the total dislocation length is significantly smaller.

Longitudinal torsional ultrasonic vibratory assistant milling of borosilicate glass material removal mechanism based on the thickness of undeformed chips

Borosilicate glass is an ideal material for microfluidic chip substrates due to its excellent light transmittance and stable chemical properties. However, it is also prone to brittle fracture during processing, making it a typical difficult-to-machine material. As an emerging processing technology, longitudinal torsional ultrasonic assistant milling (LTUVAM) can effectively reduce the surface damage of glass materials and improve the proportion of plastic removal of materials. The mechanism of LTUVAM of borosilicate glass was studied in this paper. Critical undeformed chip thickness (hc) is a key factor in achieving plastic material removal. At present, the influence of LTUVAM on the hc is not clear. Therefore, in this paper, the material-specific cutting energy model in the LTUVAM process was established to predict the hc. Firstly, the motion path of LTUVAM was analyzed, and the undeformed chip thickness model and the tool-workpiece separation rate model were established. Then, based on the above model, the material-specific cutting energy model was established according to the material removal principle. Finally, an LTUVAM orthogonal experiment was carried out to study the surface quality of the material. The experimental results showed that with the increase of ultrasonic power, the roughness and side damage area increased first and then decreased. With the increase of spindle speed, it showed that the roughness and side damage area decreased first and then increased. With the increase of feed per tooth, it showed that the roughness increased first and then decreased, and then increased, and the side damage area increased first and then decreased. Through the analysis of the experimental and model results, the increase of the separation rate between the tool and the workpiece contributes to the increase of the hc and the improvement of the processing quality.

Study on the critical conditions for ductile-brittle transition in ultrasonic-assisted grinding of SiC particle-reinforced Al-MMCs

High volume fraction (45 %) silicon carbide particle-reinforced aluminum matrix composites (SiCp/Al-MMCs) play a significant role in various engineering fields due to their outstanding performance. However, damages characterized by SiC particle fracture during machining lead to poor surface integrity, which severely affects the fatigue performance of SiCp/Al composite structural components. Ultrasonic-assisted grinding (UAG) is acknowledged as beneficial for promoting ductile grinding in hard and brittle materials. This study focuses on the critical conditions for ductile-brittle transition in ultrasonic-assisted grinding of SiCp/Al composites and develops a mechanism and data driven model of critical undeformed chip thickness (UCT) for ductile grinding to accurately predict the material removal mode. The model thoroughly integrates considerations of chip morphology, removal mode transition mechanism, and grinding surface damage characteristics. Response surface methodology (RSM) and genetic algorithms (GA) were utilized to correct the impact of processing parameters on the removal regime. Experiments on ultrasonic-assisted side and end grinding were conducted to thoroughly discuss the effects of different undeformed chip thicknesses, grinding speeds and ultrasonic vibration amplitude on surface damage and the critical conditions for the ductile-brittle transition. The findings corroborate the experimental data with the predicted values. Ultrasonic vibration can effectively reduce the brittle fracture of SiC particles in SiCp/Al composites. Appropriately increasing the grinding speed and reducing the chip thickness can enhance the critical chip thickness for ductile grinding and decrease the proportion of brittle surfaces, thereby achieving a balance between surface integrity and grinding efficiency. This research provides guidance for high-performance machining of SiCp/Al composites.

Material removal mechanism of TiCp/Fe composite by multi-diamond-abrasive-grinding considering the random distribution characteristics of particles

The TiC ceramics reinforced Fe matrix composite (TiCp/Fe) exhibits exceptional properties, including high hardness, strength, wear, and heat resistance. This study focuses on investigating the material removal mechanism to achieve high-quality and low-damage surfaces. A three-dimensional particle random distribution algorithm is proposed based on the random distribution characteristics of TiC particles. Furthermore, a multi-diamond-abrasive grinding finite element model is established using the Rayleigh probability distribution model to account for the randomness of undeformed chip thickness during the grinding process. This study combines experimental and simulation analyses to investigate the variations in grinding forces, stress field distributions, and surface and subsurface quality. The results reveal that the material removal process can be categorized into five stages: ploughing of the Fe matrix and TiC particle, TiC particle crack initiation, TiC particle crack extension, and TiC particle fracture. Moreover, the process of removing TiC particles can be further grouped into ductile removal, ductile-brittle removal, and brittle removal, depending on the undeformed chip thickness. This study improves the comprehension of the mechanism of TiCp/Fe composite material and establishes a significant practical guidance for the diamond grinding processing of metal matrix composites.

A Study on the Cutting Characteristics of Bottom Abrasive Grains in Helical Grinding Tools

Helical grinding is crucial for manufacturing small holes in hard-to-machine composite ceramics. This study introduces a geometric model of undeformed chips to analyze the cutting characteristics of abrasive grains on both the bottom and side edges of the tool. It reveals for the first time that the distribution of cutting grains—pure bottom-edge, pure side-edge, and mixed-edge—is influenced by the tool diameter and eccentricity. A novel calculation method for the distribution range (Dp) of pure bottom-edge grains is proposed, demonstrating that using a tool diameter at or below two-thirds of the target hole diameter effectively eliminates pure bottom-edge grains, improving chip evacuation, reducing chip adhesion, and optimizing cutting performance. Experimental validation on small holes in SiCp/Al composites (65% volume fraction) confirmed these findings and provides practical guidance for optimizing cutting parameters and tool design.

Analysis and optimization of microchannel array precision grinding processes with micro-structured micro-grinding tool

Micro-grinding has been widely used in aerospace and other industry. However, the small diameter of the micro-grinding tool has limited its machining performance and efficiency. In order to solve the above problems, micro-structure has been applied on the micro-grinding tool. A morphology modeling has been established in this study to characterize the surface of micro-structured micro-grinding tool, and the grinding performance of micro-structured micro-grinding tool has been analyzed through undeformed chip thickness, abrasive edge width, and effective distance between abrasives. Then deviation analysis, path optimization and parameter optimization of microchannel array precision grinding have been finished to improve processing quality and efficiency, and the deflection angle has the most obvious effects on the rectangular slot depth, micro-structured micro-grinding tool could reduce 10% surface roughness and 20% grinding force compared to original micro-grinding tool. Finally, the microchannel array has been machined with a size deviation of 2 μm and surface roughness of 0.2 μm.

Extracting information from the cutting force signal to explain and exploit its discrepancy between up and down slot milling at the same chip thickness

In milling, different cutting forces can occur at the same undeformed chip thickness depending on process kinematics and feed. To clarify and exploit this phenomenon, which has not been reported in the technical literature, the cutting force was recorded during full-width orthogonal milling. The latter process was chosen as the same undeformed chip thickness is developed at certain tool rotation angles and at different feeds, thus allowing the exploration of the effect of these parameters on the cutting force. Using analytical methods to describe the cutting kinematics, the exact rotation angle of the tool corresponding to its engagement with the workpiece was calculated. In addition, the precise relationship between chip thickness and occurring cutting force in up and down slot milling at various feeds was determined. Herein, for increasing the accuracy, the tool path was considered as trochoidal rather than circular. In addition, analytical methods were developed to calculate the cutting force direction, shear angle and chip compression ratio. The measurements of the deformed chip thickness over the deformed chip length verified the assumptions and correctness of the developed analytical procedures. Additionally, based on a FEM simulation of the developed stress fields during material removal, the stress field depth parameter ds was introduced. Using ds and the calculated direction of the cutting force towards the instantaneous workpiece surface, regions of effective material strengthening or weakening were detected within the developing stress field during up and down milling respectively, which change the cutting force. In this way, the discrepancies between the cutting forces occurring in up and down milling at the same undeformed chip thickness and various feeds were clarified and process conditions were proposed to exploit them to reduce cutting loads and energy requirements.

Material Removal Mechanism of SiC Ceramic by Porous Diamond Grinding Wheel Using Discrete Element Simulation.

SiC ceramics are typically hard and brittle materials. Serious surface/subsurface damage occurs during the grinding process due to the poor self-sharpening ability of monocrystalline diamond grits. Nevertheless, recent findings have demonstrated that porous diamond grits can achieve high-efficiency and low-damage machining. However, research on the removal mechanism of porous diamond grit while grinding SiC ceramic materials is still in the bottleneck stage. A discrete element simulation model of the porous diamond grit while grinding SiC ceramics was established to optimize the grinding parameters (e.g., grinding wheel speed, undeformed chip thickness) and pore parameters (e.g., cutting edge density) of the porous diamond grit. The influence of these above parameters on the removal and damage of SiC ceramics was explored from a microscopic perspective, comparing with monocrystalline diamond grit. The results show that porous diamond grits cause less damage to SiC ceramics and have better grinding performance than monocrystalline diamond grits. In addition, the optimal cutting edge density and undeformed chip thickness should be controlled at 1-3 and 1-2 um, respectively, and the grinding wheel speed should be greater than 80 m/s. The research results lay a scientific foundation for the efficient and low-damage grinding of hard and brittle materials represented by SiC ceramics, exhibiting theoretical significance and practical value.

Non-destructive measurement of MUCT in micro-milling using surface topography generated by bi-planer size effects

In mechanical micro-cutting, a Minimum Undeformed Chip Thickness (MUCT) is desired to ensure chip formation by the round-edged tool. Although the MUCT controls several machinability, productivity, and sustainability attributes, its measurement using output responses is a challenging task. This article, for the first time, demonstrates a non-destructive methodology to measure MUCT in micro-milling using the topographical pattern that inherently remains embedded on the micro-milled floor surface in the form of a microscopic step at the ploughing-shearing transition boundary. Simultaneous action of two Size Effect phenomena that occur concurrently in two mutually perpendicular planes owing to rounded-nose and rounded-edge produce microscopic step during surface generation. A methodology to quantify MUCT using this inconsistent surface topography is also demonstrated. MUCT remains within 36–41 % of the edge radius during dry micro-milling of Ti-6Al-4V using TiAlN-coated WC-6Co tool. The same reduces to 33–40 % of the edge radius when cutting fluid is delivered through sustainable Minimum Quantity Lubrication (MQL) strategy. Proportionality between MUCT and edge radius remains valid during abrasive wear regime of the cutting tool. Tool wear significantly deteriorates surface quality, causing Ra roughness to increase from 40 to 350 nm when adhesion deposits on cutting edge. Consequently, the proposed surface-dependent methodology fails to provide precise MUCT data when cutting tool experiences aggressive wear.

Surface topography prediction of slider races using formed grinding wheel shape and material removal mechanism

Compared with the roughness, the three-dimensional (3D) topography parameters, surface microstructure geometric characteristics and other information can more fully evaluate the grinding quality of the slider raceway surface. In this paper, based on the 3D topography model of the abrasive particle distribution on the surface of the formed grinding wheel, the material removal mechanism between the abrasive particle and the raceway surface is analyzed. With the undeformed chip thickness distribution model as the intermediate variable, the 3D topography model of the slider raceway surface is established, and the model verification is carried out from the roughness and the geometric characteristics of the surface microstructure, respectively. At the same time, the surface microstructure is extracted from the topography model, and the effects of different grinding process parameters on the geometric characteristics such as the height to width ratio, depth to width ratio and distribution density of groove, convex peak and peak valley structures are studied. Results are shown that AS,TH increase from [0.05 0.6 μm] to [0.25 0.8 μm] and FGH grows from [0.11 1.05 μm] to [0.5 1.61 μm] when the grinding depth rises from 1 μm to 4 μm. AS, TH are firstly decreased from [0.17 0.61 μm] to [0.08 0.52 μm] and then increased to [0.26 0.78 μm], and the FGH declines from [0.34 1.01 μm] to [0.16 0.86 μm] and then increases to [0.51 1.38 μm] with the feeding speed is in [25, 28 m/min]. In addition, in the range of grinding wheel linear velocity [28, 34 m/s], the AS,TH decreases from [0.19 0.81 μm] to [0.1 0.55 μm] and the FGH decreases from [0.55 1.6 μm] to [0.2 1.1 μm]. This can prepare for the subsequent research on the impact of the topography characteristics on the friction coefficient and wear amount of the slider raceway surface.

Influence of diamond abrasives on material removal of single crystal SiC in mechanical dicing

Mechanical dicing is a critical step in producing electronic chips and devices. Single crystal silicon carbide (SiC) is a vital wafer material in modern electronic chips because of its exceptional physical properties, such as wide bandgap and high breakdown voltage. However, the high hardness of SiC makes it extremely challenging to achieve the dicing quality required for the reliable functioning of electronic chips. The removal characteristics of single crystal SiC in mechanical dicing process remains largely unclear. This work aims to systematically investigate the influences of diamond abrasives in ultrathin blades on the dicing force, chipping size, surface roughness, and material removal of single crystal SiC in mechanical dicing. Experimental results indicate the diamond abrasives considerably affect the chipping formation and the material removal of SiC workpieces by changing the undeformed chip thickness. Theoretical analysis based on the classic brittle-ductile transition model reveals that single crystal SiC can be removed in a ductile-like mode using relatively large abrasive size and low concentration, as long as the undeformed chip thickness is sufficiently smaller than the calculated critical depth of cutting. In addition, the mounting method of single crystal SiC workpieces and the wear characteristics of diamond blades play a crucial role in the removal behaviours and, therefore, the dicing quality. An example was given to demonstrate the feasibility of simultaneously improving the dicing quality and the removal rate via appropriately increasing concentration and reducing sizes of abrasives in ultrathin blades. Ultimately, the findings in this research provide a guideline for further optimization of the dicing tools and parameters for other hard-and-brittle solids.

Dynamic response of circular saw blade based on dynamic sawing force model in machining hard aluminum alloys

Carbide circular saw blades are indispensable tools extensively utilized in aerospace and transportation industries. However, modeling of sawing force and dynamic behavior of circular saw blades with large diameter-thickness ratio has rarely been reported. Hence, the aim of this study is to predict the scratches caused by saw tooth vibration on the sawing surface by proposing an axial vibration model for circular saw blades based on the dynamic sawing force. First, the dynamic undeformed chip thickness is established based on the sawtooth element movement method, which presents the circular saw blade geometry, sawing parameters, and so on. A novel dynamic sawing force model is built using this undeformed chip thickness. Then, the axial dynamic response is solved by the additional axial force introduced by the dynamic sawing force. Finally, sawing experiments were carried out, and the results confirmed the feasibility of the model.

Fast extraction of cutter-workpiece engagement for milling force prediction in multi-axis machining

The paper proposes a fast extraction method for cutter-workpiece engagement (CWE), which greatly facilitates the milling force prediction during multi-axis machining. One of the key cores of the method is to reconstruct the nearby cut-off material of workpiece using a set of past neighboring cutter location points (CLPs), and obtain the CWE entity through local Boolean operation among the current tool, workpiece blank, and reconstructed entity. Moreover, by performing 2-dimensional (2D) image mapping, the engagement boundary of CWE entity will be quickly obtained. Combining with the analytical formula of instantaneous undeformed chip thicknesses (IUCTs), the composite IUCT for tool side and bottom cutting edges during actual immersion is further derived. Finally, accurate and fast prediction of milling force with consideration of tool attitude, corner feature and bottom cutting effect is achieved. The results reveal that the method can predict milling force with an excellent performance of first-order computation complexity.

Features of using the power skiving method for multi-pass cutting of internal gears

The paper presents the results of a simulation on a 3D model of undeformed chips and cutting forces during three-pass gear cutting using the power skiving method. At the level of individual blades and teeth in successive angular cutting positions, the main component of the cutting force and the tangential force on the cutter axis are shown. The analysis of the forces acting on a single gear tooth and the continuous cutting forces allowed the development of a methodology for the selection of rational cutting modes – the value of the axial feed, the number of passes with different cutting depths in order to ensure the minimum time consumption and to achieve the required accuracy of the gears in terms of the parameter of the permissible angular deviation of the profile of the cut gear. It is shown that, provided the required machining accuracy is ensured, higher productivity is achieved by increasing the axial feed at a lower depth of cut and increasing the number of passes, rather than by reducing the feed and increasing the depth of cut.

Prediction of undeformed chip thickness distribution and surface roughness in ultrasonic vibration grinding of inner hole of bearings

Prediction of undeformed chip thickness distribution and surface roughness in ultrasonic vibration grinding of inner hole of bearings

An Integrated Model Based Prediction of Machining Accuracy for Milling Machine

The accuracy of machining can be predicted during the design process of CNC machine tools, while the prediction accuracy depends on the prediction model. However, when establishing the prediction model, the coupling effect among the machine tool’s different components is always ignored for modeling efficiency, so this will lead to its reliability cannot be guaranteed. To address this problem, the model reduction theory and the lumped parameter method are used in this study to set the state-space equations of the essential structural parts. Moreover, the electro-mechanical coupling parameter equation of the servo system is transformed into a state-space equation. Then the state-space equations of the components and the servo system are coupled to establish the machine tool dynamic model. Furthermore, a theoretical model of instantaneous undeformed chip thickness is found, and according to the linear relationship between the micro-cutting force and the instantaneous undeformed chip thickness, the instantaneous cutting force model of the cylindrical milling cutter is established. Based on these, the integrated model, which considers the mechanical structure, control system and cutting force, is obtained and further used in Simulink to build the machining accuracy prediction platform, as well as the accuracy of the integrated prediction model is verified. Moreover, the prediction model established by the integrated modeling method can effectively simulate the actual machining conditions of the machine tool, and the superiority of prediction is confirmed by comparing the simulated and measured results in peripheral milling applications. The results show the error in the system response efficiency is 14.8%, while the error in position accuracy and delay characteristics is less than 10%, the error between the predicted size of the prediction model and the actual size is within 28 μm, a minimum prediction error is 7 μm.

Evolution of undeformed chip thickness and grinding forces in grinding of K4002 nickel-based superalloy using corundum abrasive wheels

The undeformed chip thickness and grinding force are key parameters for revealing the material removal mechanism in the grinding process. However, they are difficult to be well expressed due to the ununiformed protrusion height and random position distribution of abrasive grains on the abrasive wheel surface. This study investigated the distribution of undeformed chip thickness and grinding force considering the non-uniform characteristics of abrasive wheel in the grinding of K4002 nickel-based superalloy. First, a novel grinding force model was established through a kinematic-geometric analysis and a grain-workpiece contact analysis. Then, a series of grinding experiments were conducted for verifying the model. The results indicate that the distribution of undeformed chip thickness is highly consistent with the Gaussian distribution formula. The increase in the grinding depth mainly leads to an increase in the average value of Gaussian distribution. On the contrary, the increase in the workpiece infeed speed or the decrease in the grinding speed mainly increases the standard deviation of Gaussian distribution. The average and maximum errors of the grinding force model are 4.9% and 14.6% respectively, indicating that the model is of high predication accuracy.

Diffraction characteristics and formation mechanism of nanogratings in tip-based down-milling

Structural coloration of metal surfaces based on the diffraction mechanism of blazed gratings has considerable value for use in anti-counterfeiting and information encryption applications. When the grating period is comparable to the wavelength of the incident light, the diffraction process will generate only two propagating orders, comprising the 0th order and the −1st order, resulting in lower dispersion. Improvement of the diffraction efficiency of the −1st order spectrum, which has a light splitting ability, is essential to improve the colouring quality of the diffraction structure. Such improvement of efficiency is closely related to the geometric features of the structure, but the relationship is insufficiently clear at present. The novelty of the approach in this paper lies in its use of a combination of optical and mechanical analyses of nano grating structures fabricated by tip-based nanoscale down-milling with the aim of establishing a connection between the diffraction characteristics of the structure and its processing formation. First, profiles of the nanograting structures are generated numerically by taking both the trajectory shape and the cutting edge radius into account. Using the finite-difference time-domain method, a diffraction model is then established to simulate the far-field spectral distributions of the generated profiles. It is concluded from these analyses that the grating height is an important factor that affects the −1st order diffraction efficiency. When the grating height is in the range of 155–185 nm with a grating period of 400 nm, the diffraction efficiency can reach up to 75 %–90 %, depending on the conditions of incidence. Then, with the aim of controlling the grating height, the nanograting structure fabrication processes are investigated under different revolving trajectory conditions by finite element analysis. The results show that the grating structures are formed mainly by extrusion caused by the moving tip, which results in the grating heights being affected by the undeformed chip thickness in each cycle and by the plastic deformation of the material. Under the optimal down-milling trajectory condition, nanograting structures with the expected height and good geometric consistency are obtained.

Analytical Modelling of the Cutter Workpiece Engagement and the Undeformed Chip Thickness for Circular Ball end Milling Path for Adaptive Feed Rate

Analytical Modelling of the Cutter Workpiece Engagement and the Undeformed Chip Thickness for Circular Ball end Milling Path for Adaptive Feed Rate

Ductile–brittle transition and ductile-regime removal mechanisms in micro- and nanoscale machining of ZnS crystals

The ductile–brittle transition and ductile-regime removal mechanisms of ZnS crystal, a typical soft-brittle infrared optical material, have remained unclear at the micro- and nanoscale. In this context, this study modeled the energies consumed in two machining modes, namely ductile deformation and brittle fracture, during the ultraprecision cutting of ZnS crystal. Subsequently, based on the transition point of the energy mode, the critical undeformed chip thickness (CUCT) for the ductile–brittle transition of the material was determined. Additionally, the effect of tool parameters on CUCT was quantitatively analyzed, and the correctness of the model was verified by scratch experiments. Moreover, the cutting parameters that affect the maximum undeformed chip thickness (MUCT) were analyzed. By comparing the MUCT and CUCT, the cutting conditions to realize ductile-regime machining were predicted. The correctness of the ductile-regime machining conditions was also verified through surface quality characterization after face-cutting experiments. The MUCT can be controlled to be less than the CUCT by using a cutting tool with a sufficiently large tool rake angle, a nose radius and a reduced feed rate, thus realizing the ductile-regime removal of the material. The surface morphology, chip morphology, and surface roughness of machined ZnS crystal confirmed the validity of the model. Using a diamond cutting tool with a large cutting edge angle (–25°) and nose radius (1.2 mm) as well as a low feed rate (0.5 μm/rev) and depth of cut (3 μm), the generation of cracks and pits was effectively inhibited, resulting in a smooth surface with a surface roughness of 1.60 nm. Overall, the findings of this study provide important insights into the superfinishing of soft–brittle materials such as ZnS crystal.