Material Removal Distribution Research Articles

Theoretical model of honing force in bore honing

Honing force is one of the key output variables to evaluate the machining performance of the honing process. However, the measurement of honing force during small-bore honing is difficult. The research on and modeling of honing force can help analyze the mechanism of material removal in the honing process, control the material removal rate, and improve the shape accuracy of the workpiece hole after honing. Recent research on the modeling of single-stone honing tools does not reflect reality well. In this study, a model to predict the honing force of a force-controlled, single-stone honing tool is built. The model is established through a mechanical analysis of the honing tool. This study is the first to propose that the initial shape of the workpiece bore considerably affects honing force due to the self-locking effect of honing tool. The model is verified by experiments, and the honing force predicted by the model fits the measured honing force well. The model can be applied to different sizes of single- or multi-stone tools with the same working principle and therefore has a wide range of applicability. It can guide the selection of honing parameters. Moreover, it can help build a more realistic-fitting model for the prediction of the material removal distribution and is crucial to improving the shape accuracy of the bore.

Research on composite pattern design and lapping performance of fixed abrasive pads controlled by multi-physical fields

The present work provides an innovative method of composite pattern design for fixed abrasive pads, addressing issues such as machining non-uniformity and passivation blockage arising from uneven lapping flow, pressure, and velocity fields in lapping. First, a multi-physical field modeling method is provided, a material removal distribution model and evaluation criteria for the performance of the abrasive pad are established, and the reliability of this model is validated. Second, based on the model, a composite pattern abrasive pad coupled with a spiral groove and concentric micro groove is designed. Comparative experiments are conducted with the grid abrasive pad. The results show that the clogging and passivation performance of the composite pattern abrasive pad is improved, and the pressure distribution is optimized. Compared with the grid abrasive pad, in the pressure range of 20 N–70 N, the surface roughness Ra of sapphire is reduced by 6.4 %–25.42 %, defects such as brittle fracture pits and scratches on the workpiece surface are reduced, and the surface quality of the workpiece is significantly improved. The material removal rate is between 0.23 μm/min to 0.34 μm/min. This confirms the effectiveness of optimizing abrasive pad pattern design based on multi-physics fields. The research results provide a novel approach for abrasive pad pattern design with engineering application value.

Kinematics and trajectory analysis of swinging fixed abrasive plane lapping: Effect of swinging mode on the lapping uniformity

The relative motion between the workpiece and the fixed abrasive pad (FAP) determines the abrasive trajectories and the distribution of abrasives' sliding distance (ASD), and further affects the surface accuracy of the lapping process. To improve the surface accuracy of the swinging fixed abrasive plane lapping (SFAPL), the influence of the workpiece's swinging modes on the lapping uniformity was studied in this paper. The kinematics model of SFAPL was established by the coordinate transformation method based on the kinematical principle of the crank-rocker mechanism. The numerical simulation method was adopted to investigate the abrasive trajectories and the ASD on the workpiece surface in different swinging modes. Furthermore, the regional meshing and statistical methods were applied to visualize the simulation results, and the non-uniformity coefficient (NUC) and root mean square (rms) were employed to quantitatively evaluate the lapping uniformity. Finally, the verification experiments were carried out. Results indicated that the additional swinging could avoid the periodic distribution of material removal on the workpiece surface. The swinging mode significantly affected the lapping efficiency and lapping uniformity. Compared with the traditional lapping method, the lapping uniformity was optimal when the workpiece swung out of the FAP from the bottom and inner sides, and the lapping uniformity could be improved by 44.3 %; The lapping efficiency was the highest when the workpiece swung out of the FAP from the bottom side, and the material removal rate could be increased by 45.23 %. The appropriate swinging mode should be selected based on different processing requirements in SFAPL.

B-spline surface approximation method for achieving optimum dwell time in deterministic polishing

In the computer-controlled optical surfacing (CCOS) process, the accurate calculation of the dwell time map is essential for achieving the desired amount of material removal distribution. However, it remains challenging for current methods to generate a smooth dwell time map that reduces the dynamic requirements of machine tools while maintaining the high finishing capability on freeform optics. This paper proposes a B-spline surface approximation method for obtaining the optimum dwell time in deterministic polishing. The B-spline surface representation allows the dwell time map to be expressed by a small number of control points instead of a large number of discrete dwell points. The dwell time deconvolution then becomes a linear least-squares problem with only a few control points as variables, which significantly reduces the scale of the problem. To achieve a more accurate and smoother dwell time map, a knot position optimization algorithm is proposed to adapt the knots to the geometric features of the target removal surface. Simulation results demonstrate that the proposed B-spline-based dwell time algorithm significantly outperforms common dwell time algorithms in terms of the computational accuracy, efficiency, as well as smoothness of the dwell time map. To validate the effectiveness and practicability of the proposed method, experimental polishing of a bi-sinusoidal optical surface has been carried out. The results show that the developed algorithm has greatly reduced the tracking error of the machine tool caused by dwell time fluctuations, and consequently, the corresponding residual error of material removal in deterministic polishing.

Surface generating mechanism in surface shape error control for thin copper plate with large-diameter based on chemical mechanical lapping

As metal plane flyer, pure copper thin plate is required with extremely low surface shape error. To achieve this goal, some researchers make a significant attempt to develop a deterministic full-aperture polishing/lapping process. However, the detail relationship of surface shape error and vital machining parameter such as machining time which benefits machining efficiency promotion is not given. Besides, the error rate of surface shape error prediction is high. To solve this problem, the surface shape prediction model considering the influence of pressure and relative velocity distribution on material removal amount is established for thin copper plate. Through the product of pressure distribution, relative velocity distribution, Preston coefficient k and machining time T, material removal distribution is obtained. According to initial surface shape characteristic, through targeted adjustment of eccentricity, lapping pad rotation speed, workpiece rotation speed to control pressure and relative velocity distribution, suitable material removal distribution is formed to smooth surface radial profile, realizing deterministic control of surface shape error. By above method, the flatness of pure copper thin plate (Φ200 mm × 2.2 mm) decreases from PV 54.8 μm to PV 1.9 μm with mean error rate of surface shape error prediction <10 %, realizing deterministic control of surface shape error.

Finishing nonuniformity for electrical discharge machined closed complicated flow channels by abrasive flow machining

Abrasive flow machining (AFM) is increasingly preferred to finish closed complicated flow channels machined by electrical discharge machining (EDM) owing to its high machining accessibility, surface integrity, and efficiency. The machining accuracy of closed complicated flow channels by AFM is dependent on the uniformity of material removal distribution (named as finishing nonuniformity here), but few studies on the finishing nonuniformity have been done so far. Firstly the finishing nonuniformity for EDM machined complicated flow channel by AFM was modeled and analyzed theoretically. Then three blisk with EDM surface roughness of Ra 1.5 μm, Ra 2.0 μm, and Ra 3.0 μm were finished by AFM to Ra 0.8 μm, and their finishing nonuniformity was compared. Finally, AFM flow simulation was carried out, and the simulation results were compared with that from the experiments. Theoretical results showed that finishing nonuniformity is resulted from the non-uniform flow field of the abrasive medium, and it increases with increasing EDM surface roughness and decreasing AFM surface roughness. This is verified by the AFM experiments and flow simulations. On this basis, the guideline for parameter optimization in the combined EDM + AFM process was discussed.

The Tailored Material Removal Distribution on Polyimide Membrane Can Be Obtained by Introducing Additional Electrodes.

Reactive ion etching (RIE) is a promising material removal method for processing membrane diffractive optical elements and fabrication of meter-scale aperture optical substrates because of its high-efficiency parallel processing and low surface damage. However, the non-uniformity of the etching rate in the existing RIE technology will obviously reduce the machining accuracy of diffractive elements, deteriorate the diffraction efficiency and weaken the surface convergence rate of optical substrates. In the etching process of the polyimide (PI) membrane, additional electrodes were introduced for the first time to achieve the modulation of the plasma sheath properties on the same spatial surface, thus changing the etch rate distribution. Using the additional electrode, a periodic profile structure similar to the additional electrode was successfully processed on the surface of a 200-mm diameter PI membrane substrate by a single etching iteration. By combining etching experiments with plasma discharge simulations, it is demonstrated that additional electrodes can affect the material removal distribution, and the reasons for this are analyzed and discussed. This work demonstrates the feasibility of etching rate distribution modulation based on additional electrodes, and lays a foundation for realizing tailored material removal distribution and improving etching uniformity in the future.

Numerical simulation and experimental study of normal force and particle speed in the robotic stream finishing process

Normal force and particle speed are the two most important parameters in determining the mass removal rate on the workpiece in the stream finishing process. However, quantifying them is still a big challenge due to the complexity of the interaction between media flow and the workpiece. In this study, a continuum-based (μ(I) rheology) numerical model was developed to simulate the granular media flow in a robotic stream finishing (RSF) system and validated with in-house experimental data. A novel frictional wall-slip model was developed to describe the media flow speed on the surface of a rectangular workpiece. The impact of three key process variables: (i) immersion depth (D), (ii) angle of attack (θ), and (iii) radial distance (r) on the resulting normal force and media flow speed was analyzed. The resulting normal force on the workpiece strongly depends on the immersion depth. A small increase in the hydrostatic pressure is amplified through elevated effective viscosity near the workpiece, resulting in a significant increase in the normal force. A critical θ for the dependency of normal force was identified. Below the critical θ, the normal force varies slightly with the increase in θ. Above the critical θ, the normal force decreases rapidly with the increase in θ. The normal force also increases linearly with the increase in radial distance. In general, the media flow speed increases rapidly with θ. However, the increase peaks at θ = 75° due to the wake effect behind the leading edge. As D increases, the media flow speed only changes marginally, given the same θ. The media flow speed increases with radial distance, and the relationship is quadratic. We have validated – through experiments – that the numerical model can reliably predict both normal force and media flow speed on the rectangular workpiece. As the local material removal rate has a direct correlation to the normal force and the media flow speed, this numerical model is capable of predicting material removal distribution on an actual polished component and, therefore, will be an indispensable tool for conducting in-process optimization and toolpath planning.

Computer-controlled finishing via dynamically constraint position-velocity-time scheduler

In a Computer Numerical Controlled (CNC) finishing process, the target material removal from an optical surface is guided by the convolution between the influence function of a machine tool and its dwell time at certain points over the surface. To reduce dynamics stressing and increase machining efficiency, the dwell time must be converted to varying velocities, which are the actual inputs to the machine tool controller. Conventionally, the conversion assumed constant acceleration and relied on linear motion interpolation, which caused discontinuities in velocities. This unsmooth motion affects the material removal distribution, and, thus, the accuracy of the finished surface shape. Many modern CNC machines support the smoother, cubic-polynomial interpolated Position-Velocity-Time (PVT) motion mode; however, the conventional scheduler may fail to provide suitable velocities for the PVT. This study answers this challenge by proposing a novel PVT-based velocity scheduler that achieves smooth motion while considering CNC dynamic limits. Firstly, the principle of the PVT is explained, and the PVT-based velocity scheduler is formulated. Secondly, a quadratic programming is used to optimize the velocities by imposing the CNC dynamic constraints and the C1 continuities (zeroth and first derivatives are continuous) simultaneously. Thirdly, the smoothness and accuracy of the scheduled velocities are studied on different kinds of tool paths via simulation. Finally, a sub-0.3 nm level surface finishing experiment using ion beam figuring is demonstrated to verify the feasibility of the proposed method. The PVT-based scheduler and simulator code is open-sourced.

Investigation of Material Removal Distributions and Surface Morphology Evolution in Non-Contact Ultrasonic Abrasive Machining (NUAM) of BK7 Optical Glasses.

A non-contact ultrasonic abrasive machining approach provides a potential solution to overcome the challenges of machining efficiency in the high-precision polishing of optical components. Accurately modeling the material removal distribution (removal function (RF)) and surface morphology is very important in establishing this new computer-controlled deterministic polishing technique. However, it is a challenging task due to the absence of an in-depth understanding of the evolution mechanism of the material removal distribution and the knowledge of the evolution law of the microscopic surface morphology under the complex action of ultrasonic polishing while submerged in liquid. In this study, the formation of the RF and the surface morphology were modeled by investigating the cavitation density distribution and conducting experiments. The research results showed that the material removal caused by cavitation bubble explosions was uniformly distributed across the entire working surface and had a 0.25 mm edge influence range. The flow scour removal was mainly concentrated in the high-velocity flow zone around the machining area. The roughness of the machined surface increased linearly with an increase in the amplitude and gap. Increasing the particle concentration significantly improved the material removal rate, and the generated surface exhibited better removal uniformity and lower surface roughness.

A Model-Based Trajectory Planning Method for Robotic Polishing of Complex Surfaces

Off-line programming of the polishing tool trajectory for complex workpieces is challenging due to the nontrivial material removal model and the polishing accuracy requirement. Current tool trajectory planning methods are mainly developed for some simple surfaces but cannot handle the increasingly complicated industrial parts, such as the wheel hubs. This article first develops a numerical contact mechanics model for the point-sampled complex workpieces. The contact pressure distribution and the material removal depths on the workpiece point cloud can be predicted efficiently. A novel high-priority subregion searching algorithm is developed to track the most-worth-polishing workpiece points. By selecting the path pattern as direction-parallel, the path direction, tool dwell times, and the path spacings inside each extracted subregion are optimized to minimize the deviation from the desired material removal depths. The effectiveness of the proposed method is verified by performing disk polishing simulations on workpieces with different shapes. A robotic polishing experiment is also conducted on a wheel hub. Both simulation and experimental results show that reasonable tool trajectories can be generated on the workpiece, and the desired material removal depths can be achieved. Note to Practitioners—In robotic polishing industries, it is crucial to plan the tool trajectory (tool path and feed velocity) to achieve desired material removal depths on the workpiece surface, which means high surface quality. In this article, a model-based tool trajectory planning method for robotic polishing of complex surfaces that are represented by the point cloud form is presented. The advantage of using the point cloud is that workpiece surfaces with varying curvatures and complex features, e.g., grooves and holes, need not be expressed explicitly. The proposed method generates high-priority subregions according to the updated material removal distribution dynamically. In this work, the polishing path pattern is chosen as direction-parallel. Based on an efficient numerical contact mechanics and material removal model, the path locations and the tool dwell times inside each subregion are optimized to minimize the deviation between the actual and the desired material removal depths. When the desired material removal depths are attained in an extracted subregion, the algorithm finds the next high-priority subregion until the whole workpiece is well polished. The trajectory planning method can be integrated into an industrial robot with the force-control module. Future work is to integrate the roughness model into the tool trajectory planning method.

Shear-thickening polishing of inner raceway surface of bearing and suppression of edge effect

Shear-thickening polishing is a non-traditional finishing method that uses the shear thickening effect by impacting the non-Newtonian fluid over the machining surface. As a result, it forms a velocity gradient that increases viscosity sharply, producing a flexible fixed abrasive tool to remove the material. Shear-thickening polishing is applied for finishing the outer surface of the rotary workpiece in previous work. The material removal distribution on the inner surface is completely different from those on the outer surface due to the different structures. The thickened slurry tends to form a relatively dense boundary layer on the surface, resulting in a decrease in the polishing quality and efficiency. The present study investigates the effect of the impact angle of slurry and polishing velocity on polishing quality to obtain the uniform surface morphology of the ring’s inner surface by the shear-thickening polishing process. The inner raceway of the outer ring of the tapered roller bearing 30203 was taken as the machining object. The numerical material removal model of the raceway surface was built according to the rheological performance of the shear-thickening slurry. A mathematical geometric model is used to explore the real impact angle of slurry. The model was able to accurately predict the experimental conditions, and the results of the simulation were in good agreement with the model’s predictions. In the fixture, a guide block was introduced to guide the flow of the slurry, ensuring consistent material removal across the whole surface. The optimal experimental results show that the average surface roughness measured by Ra reduces from 300 to 42.9 nm in 30 min, which further drops to 11.16 nm in 90 min with a variance of 0.58 nm2. The conclusion could be drawn from the studies of this paper that a uniform inner raceway surface of the bearing is achievable through a properly designed STP process.

A registration-based stitching method for obtaining high-accuracy material removal distribution in the sub-aperture polishing process

In the research of rapidly developed deterministic sub-aperture polishing technologies, the analysis of material removal distribution is vital for promoting the precision, efficiency, and stability of the polishing process. To obtain a high-accuracy material removal distribution over a large-scale freeform surface with a high lateral resolution, sub-aperture stitching measurements are indispensable. Due to the limitation of traditional stitching methods, it remains a great challenge to obtain precise freeform surface topographies. This paper proposes a registration-based stitching method, which minimizes the negative impact of stitching error, to yield a material removal distribution with both high accuracy and fine lateral resolution. Firstly, to obtain an initial estimate of the rigid transformation for each sub-aperture, conventional stitching and registration based on the least-square stitching method and the robust iterative closest point algorithm are implemented. Secondly, a registration-based stitching model considering the invariance characteristic of the unpolished region is developed to cancel out the inconsistent stitching errors for obtaining a more precise material removal distribution. Finally, a polishing experiment has been conducted to validate the effectiveness of the proposed method. The registration-based stitching method and a commercial stitching program are utilized individually to obtain the material removal distribution. Comparison results show that the proposed method can largely improve the measuring accuracy of material removal distribution, which promotes the further study of the deterministic sub-aperture polishing process.

Surface Shape Evolution of Optical Elements during Continuous Polishing of Fused Quartz

Continuous polishing is the first choice for machining optical elements with a large aperture. The lubrication in the continuous polishing is an important factor affecting the surface quality of the optical elements. In this study, the lubrication system between the optic element and polishing lap was analyzed firstly and then was verified by the measurement experiment of the friction coefficient. In addition, the numerical simulation model of the mixture lubrication was established. The polishing pressure distribution and material removal distribution can be obtained by the model. The influences of the rotating speed, optical element load, and surface roughness of the polishing lap on polishing pressure were also analyzed. Finally, the influence rules of the lubrication on the surface shape of optical elements were revealed by the polishing experiments.

Magnetic field-assisted batch superfinishing on thin-walled components

Thin-walled components have been widely used in different kinds of fields such as aviation, automobiles, medical, etc. However, it is difficult to strike a balance between polishing efficiency and accuracy in the polishing of such components. Hence, this paper presents a novel magnetic field-assisted batch superfinishing (MABS) process which makes use of a magnetic field applied by two pairs of magnetic poles rotating outside an annular chamber mounted with a number of workpieces concurrently. The rotating magnetic brushes comprise magnetic particles and abrasives formed inside the chamber which impinge and remove materials from the workpiece. A theoretical and experimental investigation of the material removal in MABS is conducted on typical thin-walled components, including kinematic analysis of the brush motion, simulation of the magnetic field distribution and material removal distribution model. The experimental results indicate that the MABS process can be successfully used for batch polishing of thin-walled components while obtaining nanometric surface roughness. The developed material removal distribution model can be used to predict the material removal, so as to provide theoretical guidance of process optimization.

Shape-adaptive magnetic field-assisted batch polishing of three-dimensional surfaces

The increasing demand of the superfinished three-dimensional (3D) surfaces has stimulated the development and upgrade of the precision polishing technology. However, current ultra-precision polishing methods usually polish the workpiece one-by-one, leading to low production efficiency and high polishing cost. Even though some batch polishing methods have been developed for polishing a number of workpieces simultaneously, it is difficult for them to obtain high form accuracy, as well as nanometre scale surface roughness. Hence, this paper presents a shape-adaptive magnetic field-assisted batch polishing (SAMABP) method which not only implements nanometre scale batch polishing of 3D surfaces, but also achieves high form maintainability. Firstly, the effect of surface shape on the material removal in magnetic field-assisted batch polishing (MABP) is revealed. Secondly, the shape-adaptive optimization (SAO) algorithm is developed to cater for the effect of the material removal variation on different kinds of surface shapes, based on the kinematic analysis of the magnetic brush in MABP, as well as modelling of the material removal distribution. At last, a series of verification experiments are designed and conducted on convex, concave and structured surfaces to validate the proposed method. The surface roughness of 3D surface was significantly reduced from larger than 100 nm to less than 10 nm or even less than 5 nm in arithmetic surface roughness (Sa) after 20 min of polishing. Meanwhile, the surface forms were maintained well, and the deviation of them after polishing were all less than 4 μm in peak-to-valley (PV). These results show that the SAMABP method is effective to obtain nanometric surface roughness together with micrometric form accuracy in the batch polishing of 3D surfaces. This study sheds the light for the applications of SAMABP in batch polishing of optical components and moulds, functional structured surfaces, turbine blades, dental crowns, surgical knives, high-end jewelleries, etc.

Effects of quantities and pole-arrangements of magnets on the magneto-rheological polishing (MRP) performance of sapphire hemisphere

To improve the polishing effectiveness of sapphire hemisphere, the effects of quantities and pole-arrangements of magnets in magnetic field generator on the magneto-rheological polishing (MRP) performance of sapphire hemisphere were investigated through simulation and experiment. After analyzing the distribution of magnetic field on sapphire hemisphere surface and its change with the relative motion between sapphire surface and magnetic field generator during MRP, we developed a material removal rate (MRR) model based on the Preston equation, and the material removal distribution and average removal depth of polished sapphire surface could be predicted. Then according to the calculated material removal distribution, a surface roughness model of polished sapphire was established. Both simulation and experiment results showed that the MRR of polished sapphire increases with the quantity of magnets, while the surface roughness Ra of polished sapphire decreases with the quantity of magnets. As for the effect of pole-arrangement, the cross-stacking arrangement produced a surface of Ra 2.97 nm with MRR of 0.496 μm/h, and the cross-involute arrangement achieved a smoother surface of Ra 0.79 nm with MRR of 0.435 μm/h in MRP. These results showed that the cross-involute and cross-stacking pole-arrangements are favorable for the MRP of sapphire hemisphere. The good agreement between experimental and theoretical results verified the reliability of the established MRR and Ra models.

Effect of material removal characteristics with varying incident angle in fluid jet polishing process

Fluid jet polishing process is a non-contact type polishing process which is used to manufacture different kind of precise components in various engineering sectors. Such processes require more deterministic material removal distribution to better understand the position of the workpiece material and impingement angle. In this paper attempt is made to simulate the three dimensional Fluid Jet Polishing (FJP) model at vertical and oblique impingement mode. It was observed from the simulation that the shape of Tool Influence Function (TIF) is unsymmetrical and achieve more material removal when jet strikes at oblique impingement mode. Also, concluded that material removal rate becomes more when impingement angle increases from normal axis of rotation.

Digital twin modeling for loaded contact pattern-based grinding of spiral bevel gears

To distinguish with the conventional tooth flank grinding only considering geometric accuracy, an innovative digital twin modeling is proposed for loaded contact pattern based grinding of spiral bevel gears. Where, data-driven grinding simulation, sensitivity analysis strategy, adaptive decision and control are developed. Focusing on loaded contact pattern optimization, numerical loaded tooth contact analysis (NLTCA) considering noncentrosymmetric problem and tooth flank roughness is developed for data-driven relationship establishment. Then, an adaptive data-driven tooth flank grinding decision and control model is established. Where, the universal motion concept (UMC) machine settings is selected as the optimal design variable. It is actually an infinite approximation to the target tooth flank in form of an adaptive control system. Moreover, with point-to-point material removal distribution, the different optimization strategies are proposed for accurate tooth flank grinding. In particular, the overcutting problem on the tooth flank grinding programming is investigated. Finally, Levenberg-Marquardt method is applied to solve the established nonlinear lease square model for the accurate machine tool settings having modification variations. Thus, this accurate data-driven digital twin modeling can achieve loaded contact pattern-based grinding. The provided numerical and test instances can verify the proposed digital twin modeling.

Identification and optimization of CNC dynamics in time-dependent machining processes and its validation to fluid jet polishing

In time dependent CNC processes such as polishing, a target material removal profile is obtained by creating and inputting G-codes with varying feed into the controller of a machine tool. The input G-codes are firstly filtered by a CNC interpolator, and the real-time generated signal then goes to a feed drive system of the machine. Through these steps, the original signal is distorted and the ideal feed profile cannot be achieved in some areas. This distortion affects the material removal distribution, and thus the accuracy of the final polished surface profile. While a number of methods have been developed for predicting polished surfaces, most of them fail to consider the influence of controller dynamics. In this paper, a method for accurate prediction of polished surfaces is proposed that considers the error contribution from control signal distortion, and a strategy for compensation of this error. Firstly, the principles of identification of control system behavior in a machine tool are explained, and a process model for Fluid Jet Polishing (FJP) is introduced. Secondly, the transfer functions of the control system are identified, and the process model calibrated against experimental data. Thirdly, a simulator for predicting polished surface profiles is implemented that combines the control system and process model. A micro-groove polishing experiment is carried out that validates the reliability of the proposed method, and shows its limitations. Finally, an algorithm based on particle swarm optimization is proposed for reducing the impact of controller dynamics in micro-groove polishing.