Surface Generation Model Research Articles

Modeling of surface generation and process experiments for grinding Ti-6Al-4V with small-scale grinding tool with regular array structure

Modeling of surface generation and process experiments for grinding Ti-6Al-4V with small-scale grinding tool with regular array structure

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

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

Elliptical vibration chiseling: a novel process for texturing ultra-high-aspect-ratio microstructures on the metallic surface

Highlights Elliptical vibration chiseling is proposed based on a game-changing process principle for the high-efficient texturing of ultrahigh-aspect-ratio surface microstructures. Uniformed microstructures with an aspect ratio of 2–12 in the spacing scale of 1–10 μm have been successfully fabricated using elliptical vibration chiseling. The developed process model of elliptical vibration chiseling has been verified by the measured results of the microstructures’ geometric parameters. An inclined elliptical trajectory of tool vibration is more suitable for elliptical vibration chiseling than the standard elliptical trajectory. The deterministic process effects on the surface generation of microstructure in elliptical vibration chiseling have been demonstrated.

Modeling and simulation of surface generation in manufacturing

The paper describes the state-of-the-art in modeling and simulation of surface texture and topography generation at micro and nano dimensional scales. Three main classes of manufacturing processes used for the generation of engineering surfaces are considered: material removal processes, material conservative processes, and material additive processes. Types of modeling techniques for the simulation of surface generation are reviewed and discussed including analytical models, numerical multi-physics models, and data-driven methods. After presenting the application of those modeling techniques for the prediction of characteristics and geometry of surfaces generated by different manufacturing processes, their performance, implementation, and accuracy are discussed. Finally, a roadmap for the realization of a complete surface generation digital twin in manufacturing is outlined.

Surface deformation errors and self-adaptive compensation for microstructured surface generation of titanium alloys

In diamond servo cutting (DSC) of microstructured surfaces, the oscillated cutting motion inevitably cause non-uniform surface deformation errors. Although static and dynamic geometric errors for DSC have been studied, few studies focus on the prediction and compensation strategies of the surface deformation errors for microstructured surface generation. This study proposes an microstructured surface generation model of titanium alloys by considering the dynamic cutting forces, material microstructure evolution, thermal-mechanical coupling effect and subsurface stress-strain distribution. Harmonic microstructured surfaces are fabricated to characterize the non-uniform surface deformation errors as well as to validate the proposed model. The results show that the proposed model can accurately simulate the variation of surface plastic and elastic deformation errors as a function of undeformed chip thickness and cutting direction. Compared with the downslope cutting direction, the machined surface in upslope direction is subjected to greater plastic strain and plastic deformation errors even at the same depth of cut, due to cutting direction effect. To compensate surface deformation errors, a cooperative servo cutting (CSC) strategy is proposed by incorporating a self-adaptive fast tool servo into conventional servo cutting. The instantaneous compensation motion of CSC is jointly determined by the curvature radius deviation, instantaneous cutting depth and cutting direction. The experimental results show that CSC can make the error distribution more uniform, and greatly decrease the peak-to-valley surface deformation errors from 1.29 to 0.24 μm for different microstructured surfaces.

Computerized design of plunge shaving tool for beveloid gears and plunge shaving characteristic analysis

A design model for beveloid gears with modification is first developed. Then based on the ordinary gear shaving machine tools’ structure, a plunge shaving model for beveloid gears is proposed. Based on the model, the installation relationship of a shaving cutter relative to a beveloid gear is derived and a surface generation model of a shaving cutter for beveloid gear is established. In the next, considering the shaving cutter's installation errors, a shaved beveloid gear model in installation errors is proposed. The effect of the shaving cutter parameters on the geometrical characteristics and the beveloid gear shaving precision is analyzed. The results show that increasing the tooth number of the shaver and the shaft angle can decrease the undercut risk of the shaver surface. Increasing the number of the shaving cutter's teeth and decreasing the shaft angle can weaken the effect of installation errors on the shaving precision. In the end, a simulation platform is established in the Vericut software, the feasibility of the proposed models for beveloid gear plunge shaving is verified. The proposed models achieve plunge shaving of beveloid gears in common gear shaving machine tools and precision manufacturing without distortion of beveloid gears with modification.

Analytical modeling of surface generation in ultrasonic ball burnishing including effects of indentation pile-up/sink-in and chipping fracture

In mechanical based machining processes, the surface topography is generated through series of hierarchical pattern. Plastic deformation as result of contact and kinematic of motion are two main factors which determine evolution of surface generation. To basically optimize the surface quality, accurate predictive model of surface generation and constraints are required. In the present work, analytical models of dimple formation and hierarchical surface generation in ultrasonic assisted ball burnishing process are proposed. Pile-up and sink-in as two phenomena of indentation during both of loading and unloading phases were taken into the developed models. Considering interaction of indentation profile and kinematic of motion, three-dimensional surface topography and surface roughness are also analytically predicted. A criterion for surface failure is defined to perform process without any erosion. Confirmation of results have been made by series of single trace and multi-traces burnishing experiments on AA6061-T6 and AISI 1045. The results of indention profile, surface topography, roughness and failure criterion which were derived from predictive models were completely consistent with confirmatory experiments.

Deterioration of form accuracy induced by servo dynamics errors and real-time compensation for slow tool servo diamond turning of complex-shaped optics

Tool servo diamond turning is a promising method for generating complex-shaped optics. Considering the dynamic oscillation of the tool, servo dynamics are essential for the accuracy of the form generated with tool servo turning. Although static geometric errors and multiple compensation strategies for these errors have been studied extensively, the effects of dynamics errors of the servo axis on surface quality have received less attention. In this study, a dynamic surface generation model is established by considering the coupling effect between the servo axis dynamics and the cutting force. Using a micro-lens array (MLA) as an example, the components of the servo dynamics error of the servo motion, including dynamic deformation, resonant vibration, and trajectory tracking error, are characterised. The relationship between the servo dynamics error and the resulting form error is then theoretically identified with experimental verification. To compensate for the servo dynamics error in real-time, the concept of a cooperative tool servo (CTS) is proposed by incorporating a slow tool servo (STS) into a fast tool servo using a master-slave control strategy. Relative to using a STS for turning an MLA, the peak-to-valley (PV) servo motion error when using a CTS decreases from 4.8 μm to 0.3 μm experimentally, and the corresponding PV form error for one hexagonal lenslet decreases from 4 μm to 1.4 μm, demonstrating the effectiveness and superiority of a CTS for dynamics error compensation in the manufacturing of complex-shaped optics.

Development of Surface Roughness Generation Model for CFRTP Manufactured by LFT-D

In this study, we propose a new surface generation model for carbon fiber reinforced thermoplastics (CFRTP) manufactured by the long fiber thermoplastic-direct (LFT-D) method. CFRTP are considered to be a next-generation structural material because of their high productivity as well as high mechanical strength and lightness. Conversely, CFRTP have a rough surface, which does not meet the automotive outer panel standard of a “class A surface.” In the present study, we establish a surface roughness generation model based on a thermal shrinkage mismatch of thermoplastic resin to carbon fiber and non-uniform carbon fiber distribution. Furthermore, we construct a surface roughness estimation formula based on the model. In the calculation, a cross-sectional image of CFRTP is divided into many vertical segments. Subsequently, the thermal shrinkage of each segment is calculated with a standard deviation, an average, and a probability density of the amount of carbon fiber in each segment. The surface roughness of the manufactured CFRTP was measured using a surface profilometer. The result showed that the arithmetic surface roughness increased with the volume fraction of carbon fiber. We applied the surface roughness calculation to cross-sectional images of the specimens. Consequently, the estimated surface roughness showed the same tendency, in which the surface roughness increased with the volume fraction of carbon fiber. The slope of a regression line of the estimated surface roughness with respect to the volume fraction was 0.010, which was almost the same (0.011) as the slope of a regression line of the measured surface roughness. Furthermore, the estimation formula using a thermal shrinkage effective depth of 395 μm was able to estimate the surface roughness within a 3% average error. Using the estimation formula, it was predicted that the surface roughness increased with the standard deviation of the amount of carbon fiber in a segment. To confirm the reliability of the model and the formula, we measured the standard deviation of the amount of carbon fiber in CFRTP specimens, showing that the trend for CFRTP specimens matched the estimated values.

Theoretical and experimental analysis of material removal and surface generation in novel fixed abrasive lapping of optical surface

Abstract Fixed abrasive machining, which overcomes the lack of determinacy and efficiency of current loose abrasive polishing or lapping processes, is an alternative technology for fabricating large-aperture aspheric surfaces with high finishing efficiency and high-quality surface finish. A novel fixed abrasive lapping (NFAL) tool, which combines computer-controlled optical surfacing and conventional fixed abrasive lapping process, is introduced in this study to produce off-axis aspheric surfaces efficiently while surface state is controlled and subsurface damage (SSD) is avoided. The removal mechanism analysis shows that fused quartz glass is primarily removed in ductile regime and the SSD depth is 14.7 μm when the tool load is 25 N. The material removal volume is linear with the machining time under the ductile removal mode. The material removal and surface generation models are developed on the basis of the calculation of the spatial distribution of abrasive particles, the pad–particle–workpiece interactions, the single-particle abrasion mechanism, and the linearly cumulative removal of surface generation in the NFAL process. The models are verified through a series of spot and surface lapping experiments. Results show that the theoretical model can be successfully used to predict and optimize the NFAL process. The spot lapping experiments indicate that the material removal volume is linear with the rotation speed, and the maximum depth is limited to the specific value that depends on the stiffness of lapping tool. The surface roughness Ra and Rz values of the measured and simulated surface data decrease with the increase in feed rate and increase with the increase in raster spacing. The power spectral density analysis indicates that high feed rate can distinctly improve the high-frequency errors, and the selection of the raster spacing can principally affect the low-frequency and middle-spatial frequency errors.

Surface generation modeling of micro milling process with stochastic tool wear

Micro milling is widely used to manufacture miniature parts and features at high quality with low set-up cost. To achieve a higher quality of existing micro products and improve the milling performance, a reliable analytical model of surface generation is the prerequisite as it offers the foundation for surface topography and surface roughness optimization. In the micro milling process, the stochastic tool wear is inevitable, but the deep influence of tool wear hasn't been considered in the micro milling process operation and modeling. Therefore, an improved analytical surface generation model with stochastic tool wear is presented for the micro milling process. A probabilistic approach based on the particle filter algorithm is used to predict the stochastic tool wear progression, linking online measurement data of cutting forces and tool vibrations with the state of tool wear. Meanwhile, the influence of tool run-out is also considered since the uncut chip thickness can be comparable to feed per tooth compared with that in conventional milling. Based on the process kinematics, tool run-out and stochastic tool wear, the cutting edge trajectory for micro milling can be determined by a theoretical and empirical coupled method. At last, the analytical surface generation model is employed to predict the surface topography and surface roughness, along with the concept of the minimum chip thickness and elastic recovery. The micro milling experiment results validate the effectiveness of the presented analytical surface generation model under different machining conditions. The model can be a significant supplement for predicting machined surface prior to the costly micro milling operations, and provide a basis for machining parameters optimization.

Modeling of residual tool mark formation and its influence on the optical performance of KH2PO4 optics repaired by micro-milling

In the micro-milling repair process of surface defects on KH2PO4 (KDP) optics, residual tool marks are inevitably introduced on repaired surfaces. These tool marks could present great potential risks in lowering laser-induced damage thresholds of repaired KDP optics, which has not been reported in the previous works. In this work, the formation process of micro-milled tool marks was initially modeled and then the effect of these residual marks on the optical performance of KDP optics was investigated theoretically and experimentally. A 3D surface generation model for repair contours is proposed to predict the profiles of residual tool marks on micro ball-end milled surfaces, and then a numerical FEM model adopting the calculated profiles of residual tool marks is established to investigate the light intensification inside KDP optics based on electromagnetic theory. The relationship between repair machining processes, tool marks profiles and light intensifications as well as laser damage resistance of repaired KDP optics, has been discussed comprehensively and systematically. Practical repair experiments and laser damage tests verified the theoretical results very well. It revealed that the residual height of tool marks can induce apparent diffraction effect, consequently causing severe light intensification inside KDP optics. The micro milling strategies (e.g. a combination of layer-milling and spiral milling paths) can also exert a positive role in improving the laser damage resistance of KDP optics. An optimized repair process flow, adopting layer-milling path as rough milling and employing spiral-milling with path intervals of 10∼15 µm as fine milling, is recommended for the future practical engineering repair of full-aperture KDP optics in ICF facilities.

Micro texture fabrication by a non-resonant vibration generator

Surface texturing with designed micro-structures exhibits numerous novel functional characteristics and features as compared to ordinary smooth surfaces or surfaces generated by the conventional customary manufacturing processes. Though several micro-scale surface textures generating techniques have been used to fabricate surface textures, most of these techniques are either of low efficiency or lack the flexibility to fabricate sophisticated surface topographies. In this study, a non-resonant vibration generator was used to control the micro surface texturing generation process. The principles of this vibration assisted surface texturing process are analyzed. Furthermore, surface generation models for both the cylindrical and flat surfaces of a cylinder are formulated to serve as a vehicle for generating the desired surface topography. Finally, surface texturing experiments were conducted, and complex micro textured topographies were successfully fabricated.

A theoretical and experimental study of forced spindle vibration under unbalanced magnetic forces in ultra-precision machining

In ultra-precision machining (UPM), a brushless permanent magnet DC motor employed for an air bearing spindle exhibits unbalanced magnetic forces (UMFs). The UMFs exert on the spindle rotor to induce forced spindle vibration, named UMFs induced forced spindle vibration (UMF-FSV). It would significantly deteriorate surface quality in UPM. However, the UMF-FSV is not well understood with its effect on surface generation in UPM. In this study, an analysis model of magnetic forces for a spindle motor is developed along with a surface generation model to study dynamics of UMF-FSV and its effect in UPM. The theoretical and experimental results signify that UMF-FSV is harmonic at a fundamental frequency 2pω (motor’s pole number 2p and spindle speed ω), which produces 2p straight radial patterns without phase shift at a machined surface in UPM.

A Mathematical Model to Evaluate the Impact of the Maintenance Strategy on the Service Life of Flexible Pavements

The structural failure of a flexible pavement occurs when the accumulated fatigue damage produced by all the vehicles that have passed over each section exceeds a certain threshold. For this reason, the service life of pavement can be predicted in terms of the damage caused by the passage of a single standard axle and the expected evolution of traffic intensity (measured in equivalent standard axles) over time. In turn, the damage caused by the passage of an axle depends on the vertical load exerted by the wheels on the pavement surface, as given by the technical standard in application, and the depths and mechanical characteristics of the layers that compose the pavement section. In all standards currently in application, the unevenness of the road surface is disregarded. Therefore, no dynamic effects are taken into consideration and the vertical load is simply given in terms of the static weight carried by the standard axle. However, it is obvious that the road profile deteriorates over time, and it has been shown that the increase in the pavement roughness, when considered, gives rise to important dynamic effects that may lead to a dramatic fall in the expected structural service life. In this paper, we present a mathematical formulation for the fatigue analysis of flexible pavements that includes the effects of dynamic axle loading. A pavement deterioration model simulates the sustained growth of the IRI (International Roughness Index) over time. Time is discretized in successive time steps. For each time step, a road surface generation model provides a profile that renders the adequate value of the IRI. A QHV (Quarter Heavy Vehicle) model provides the dynamic amplification function for the loads exerted on the road surface along a virtual ride. This function is conveniently averaged, what gives the value of the so-called effective dynamic load amplification factor (DLA); this is the ratio between the effective dynamic loading and the static loading at each time step. Finally, the damage caused by the passage of the standard axle can be evaluated in terms of the dynamic loading. The product of this damage times the number of equivalent standard axles gives the total fatigue damage produced in the time step. The accumulated fatigue damage at each moment is easily computed by just adding up the damage produced in all the previous time steps. The formulation has been implemented in the software DMSA (Dynamic & Maintenance Simulation App). This tool has been specifically developed for the evaluation of projects in applications for financing submitted to the European Investment Bank (EIB). DMSA allows for quantifying the expected structural service life of the pavement taking into account both the rise of the dynamic axle loads exerted by the traffic as the road profile deteriorates over time and the different preventive maintenance strategies to be taken into consideration.

Theoretical and experimental investigation of a tool path control strategy for uniform surface generation in ultra-precision grinding

The increasing demand of a high-quality surface in optics has imposed stringent requirement to improve the accuracy and uniformity of a machined surface. At present, ultra-precision grinding is a primary machining process in fabricating optical elements. However, in the grinding process, the unbalanced vibration of the wheel frequently appeared, which will seriously affect the precision and surface quality of the parts. A tool path as a critical factor directly determines the form error and surface quality in ultra-precision grinding. In conventional tool path planning, the constant angle method is widely used, which leads to the inhomogeneous ground surface that resulted from the different relative speeds between the grinding wheel and the workpiece with respect to different radical positions, degrading the functional performance of optical elements. From the edge area of the workpiece to the rotation center of the workpiece, the surface profile height is gradually decreased with decreasing linear speed. In this paper, a novel method of control strategy for the grinding wheel is presented so as to make the distribution of surface profile height and waviness on the machined surface uniform. The surface generation model along the circumference direction is first developed to relate the vibration amplitude of the machine tool and the spatial amplitude of the ground surface profile. Hence, the distribution of the cutting points on the workpiece surface is determined by considering the variation of linear speed, and a constant scallop height model is established. The results show that the uniform surface generation can be achieved by controlling the cutting point distribution of the grinding wheel. In addition, the sinusoidal surface texture by adopting this control strategy agrees well with that for the machined surface. The surface profile height can be held constant. Moreover, it is found that the amplitude of the waviness of the ground surface can be reduced by controlling the cutting point distribution.

Modelling of the Influence of Tool Runout on Surface Generation in Micro Milling

Micro milling is a flexible and economical method to fabricate micro components with three-dimensional geometry features over a wide range of engineering materials. But the surface roughness and micro topography always limit the performance of the machined micro components. This paper presents a surface generation simulation in micro end milling considering both axial and radial tool runout. Firstly, a surface generation model is established based on the geometry of micro milling cutter. Secondly, the influence of the runout in axial and radial directions on the surface generation are investigated and the surface roughness prediction is realized. It is found that the axial runout has a significant influence on the surface topography generation. Furthermore, the influence of axial runout on the surface micro topography was studied quantitatively, and a critical axial runout is given for variable feed per tooth to generate specific surface topography. Finally, the proposed model is validated by means of experiments and a good correlation is obtained. The proposed surface generation model offers a basis for designing and optimizing surface parameters of functional machined surfaces.

Modelling and experimental investigation on textured surface generation in vibration-assisted micro-milling

This paper investigates the textured surface generation mechanism in vibration-assisted micro milling through modelling and experimental approaches. To decouple the effects of tool geometry and kinematics of vibration-assisted milling, a surface generation model based on homogenous matrices transformation is proposed. On this basis, series of simulations are performed to provide insights into the effects of various vibration parameters (frequency, amplitude and phase difference) on the generation mechanism of typical textured surfaces in 1D and 2D vibration-assisted milling. Furthermore, the wettability tests are performed on the machined surfaces with various surface texture topographies. The fish-scale textured surfaces are found to exhibit better wettability than those with wavy-structure. The results indicate that vibration-assisted milling is an effective method to generate certain surface textures with controllable wettability.

On the generation of chatter marks in peripheral milling: A spectral interpretation

Abstract Chatter vibration induces a characteristic pattern on the milled surface, known as chatter marks, causing a poor surface quality. While several works deal with the prediction of the machined surface in stable condition, surface under chatter vibration has not been extensively studied: it is not clear how vibrations at high chatter frequency return highly spaced chatter marks on the surface. This paper investigates the chatter marks generation mechanisms focusing on this issue, i.e., on the surface spectral proprieties. The generation of the surface profile is regarded as a problem of sampling at the tooth pass frequency (in the time domain) and reconstruction (in the spatial domain) of the cutting tool displacements. Using this analogy, the paper highlights two main effects (aliasing and pseudo moire), proposing specific formulations. The method is validated by a numerical investigation, based on a surface generation model coupled with a time-domain simulator of the milling process. Finally, an experimental validation is proposed. The formulations presented in this work provide an insight in the relation between chatter frequency and chatter marks pattern. Therefore, if the chatter frequency pattern over the spindle speed is known (e.g., identified via simulations or experiments), the proposed method could support the selection of cutting parameters which results in an acceptable surface, even in highly unstable cutting conditions.

A novel 3D surface generation model for micro milling based on homogeneous matrix transformation and dynamic regenerative effect

A novel 3D surface generation modelling method for micro milling which considers the effect of machining nonlinear dynamics is proposed based on homogeneous matrix transformation. Considering the effects of machining process kinematics, tool run-out and the nonlinear dynamic regenerative effect of the machining system, the relationship between machining process and surface topography is established. On this basis, three typical machining cases, namely static stable, dynamic stable and unstable machining, are investigated in this paper. The machining experiment results demonstrate that the proposed surface generation model can accurately predict surface topography generation and roughness values with different machining conditions. Thus, it can be used not only to optimize the machining parameters for improving the micro-milled surface quality but also to predict the surface topography under pre-defined machining parameters.