Adaptive Grinding Research Articles

Vibration modal analysis of adaptive grinding and polishing tools

Abstract Adaptive grinding and polishing tools have a compact structure, fast response, and stable performance, and they can improve the efficiency of polishing and grinding large welded parts. The vibration frequency of the AGP600 adaptive grinding and polishing tool is abnormal after switching from the blade grinding head to the nylon grinding head, and the vibration is noticeable when the rotational speed is more significant than 4, 000 r/min, which seriously affects the quality of grinding. To analyze the cause of its vibration, this paper adopts HyperWorks to analyze the modal frequency of AGP600, carries out the vibration modal test, and analyses the reasons for the different vibration harmonic frequencies of AGP600. Finally, improvement measures for AGP600 are proposed, through which the vibration of AGP600 grinding tools can be reduced.

Adaptive Grinding Planning of Robotic Arms With Minimal Cost

Adaptive Grinding Planning of Robotic Arms With Minimal Cost

Position‐based force tracking adaptive impedance control strategy for robot grinding complex surfaces system

AbstractAs a key technology of robot grinding, force control has great influence on grinding effects. Based on the traditional impedance control, a position‐based force tracking adaptive impedance control strategy is proposed to improve the grinding quality of aeroengine complex curved parts, which considers the stiffness damping environmental interaction model, modifies the reference trajectory by a Lyapunov‐based approach to realize the adaptive grinding process. In addition, forgotten Kalman filter based on six‐dimensional force sensor is used to denoise the force information and a three‐step gravity compensation process including static base value calculation, dynamic zero update and contact force real‐time calculation is proposed to obtain the accurate contact force between tool and workpiece in this method. Then, to verify the effectiveness of the proposed method, a simulation experiment which including five different working conditions is conducted in MATLAB, and the experiment studying the deviation between the reference trajectory and the actual position is carried out on the robot grinding system. The results indicate that the position‐based force tracking adaptive impedance control strategy can quickly respond to the changes of environmental position, reduce the fluctuation range of contact force in time by modifying the reference trajectory, compensate for the defect of the steady‐state error of the traditional impedance control strategy and improve the surface consistency of machined parts.

Investigation on Surface Integrity of Nodular Cast Iron QT700-2 in Shape Adaptive Grinding

Nodular cast iron QT700-2 is extensively used in automobile engine crankshaft parts due to its prime mechanical properties. The journal of a crankshaft is a curved surface, and traditional wheel grinding easily causes grinding burn and surface and subsurface damage. Shape adaptive grinding (SAG) is a flexible grinding technology, which has the advantages of low grinding force and temperature, and good grinding quality. It is suitable for machining curved surface parts with complex shapes. Therefore, the SAG surface integrity of nodular cast iron QT700-2 was experimentally investigated. The influence of grinding parameters on grinding force, material removal rate, grinding temperature, and surface integrity was studied, and the machining performance of SAG tools was evaluated. It was concluded that the grain size in SAG is the most important factor affecting the grinding force, material removal rate, and surface roughness; the influence of SAG grinding is very weak, mainly removing the workpiece material. Then, the influence law of SAG technology on the surface integrity of nodular cast iron QT700-2 was summarized, and the optimal grinding parameters were obtained, providing a reference for the curved surface grinding of nodular cast iron QT700-2 in the future.

Hybrid tool combining stiff and elastic grinding

The fabrication process chain for optically smooth surfaces tends to include several time-consuming grinding and polishing steps. To reduce process time, a hybrid tool is proposed in which a stiff grinding tool and a shape adaptive grinding (SAG) tool are fused together, by taking advantage of the elastic nature of SAG tools. The material removal achieved by the hybrid tool is equivalent to discretely using the stiff grinding and SAG tools in sequence. Under similar processing conditions, a smooth surface of ∼0.02 μm Ra can be obtained on BK7 glass with the proposed tool, instead of ∼0.2 μm Ra with the stiff grinding tool.

Adaptive grinding method and experimental verification of worm gear tooth surface knife marks

Adaptive grinding method and experimental verification of worm gear tooth surface knife marks

A Novel Toolpath for Robotic Adaptive Grinding of Extremely Thin Blade Edge Based on Dwell Time Model

High precision and high efficiency in robotic grinding of aero-engine extremely thin blade edges is a challenging problem. In this article, a novel toolpath planning method is proposed based on the derived dwell time calculation model and the developed interpolation algorithm. The dwell time of each cutter contact point is solved based on the matrix method by consideration of the revised material removal model and machining allowance distribution. To optimize the previous interpolation algorithm based on geometric intersection, an arc length and Taylor binary expansion optimization are proposed to plan cutter contact points according to the dwell time and the curvature changes of blade edges. Subsequently, the tool orientation is corrected based on a double-vector controlling method to avoid the processing interference. Simulation results show that the proposed interpolation algorithm has improved the path coverage by 17.6%, and its computational efficiency is 34 times higher than that in previous algorithm. The comparative robotic grinding experiment results show that the proposed toolpath has improved the surface profile accuracy of blade edge to 0.042 mm, and its machining accuracy is 14.3–46.2% higher than that of other methods.

Predictive model of the surface topography for compliant grinding of brittle materials

During uneven and time-dependent compliant grinding of brittle materials, the surface topography is difficult to predict as ductile and brittle regions are coupled due to compliance occurring in macro/micro tool-workpiece contact. This paper proposed a predictive model for surface topography prediction by considering its ductile-brittle transition in compliant grinding. Shape adaptive grinding and monocrystalline silicon were chosen as an example to validate the proposed model based on progressive grinding tests (spot, line, area). Feed-Spindle Projection Angles are further investigated, revealing that 0° angle can obtain a ground surface with lower area roughness and smaller brittle fragments than 45° and 90°

A Review on End-effectors of Robotic Grinding

Background: As a kind of device applied to grinding, the robot grinding end-effector, combining force control structure, adaptive structure, and other structures, has been widely used in machine grinding. Grinding end-effectors can greatly help industrial robot technology used in operations that require continuous contact, such as polishing, grinding, deburring, chamfering, and assembly. Therefore, the structure design of the end-effector will become an inevitable trend in the research on robot grinding in the future. Objective: The existing grinding end-effectors for robot grinding are summarized, and their classification, characteristics, and development are introduced. Method: Various products and designs related to grinding end-effectors are summarized. The structural features, differences, and applications of typical grinding end-effectors are introduced. Results: Three typical end-effectors are analyzed. The structural features and functions are summarized, and the development trend has been prospected. The current situation and future research direction of grinding end-effector products and patents are discussed. Conclusion: Grinding end-effectors are classified into the force-controlled grinding end-effector, the adaptive grinding end-effector, and the special structure grinding end-effector. The grinding end-effector plays an important role in promoting the development of the robot grinding industry, improving the surface quality of parts and the finishing process. The grinding end-effector needs further improvement in image processing, humanization, force control, and so on. More in-depth research should be carried out in this direction.

Theoretical and experimental investigation of material removal rate in shape adaptive grinding of HVOF sprayed WC-Co coating

Shape adaptive grinding (SAG) is conducted on the ground tungsten carbide-cobalt coating using diamond polishing pad. A material removal rate (MRR) model is proposed by considering the indentation of active abrasive particle, cross-sectional area and actual length of the finishing grooves. The effects of tool speed, tool compression, backing pad hardness and abrasive particle size of the polishing pads on the normal force, MRR and surface roughness are investigated. With an increase of the tool compression, the contact pressure increases and the surface peaks get sheared off at an enhanced rate that results in a higher MRR and lower surface roughness. On the other hand, SAG with harder tool (i.e., higher backing pad hardness) produces many deep finishing grooves owing to the aggressive mechanical interaction with the workpiece surface and that increases the surface roughness. Therefore, it is perceived that the harder SAG tool is not suitable as the final finishing step for precision finishing of cermet coating. The effect of tool speed on normal force is found to be insignificant as the contact area or pressure does not vary much with the tool speed. The polishing pad with lower particle size gets partially loaded at a higher tool compression and that impedes the reduction rate of surface roughness. By performing SAG with the polishing pads of reducing particle sizes in sequence, areal surface roughness (Sa) of 7 nm is attained. The residual stress of the finished coating is reduced to - 81 ± 7 MPa (compressive) which is around 29% of the ground surface. No abnormality is observed in the sub-surface of the finished coating.

Predictive topography model for shape adaptive grinding of metal matrix composites

Compliant finishing (e.g. shape adaptive grinding) can routinely achieve nanoscale roughness on diverse metal and ceramic materials. However, when processing multiphase materials consisting of distinct phases with different mechanical properties, non-uniform material removal often occurs and the inherent mechanism remains unclear. Here, a deterministic and stochastic model to predict processed surface topography is derived from the different material removal behaviours across phases. Experimental topographies, profiles and roughness on three selected Si-SiC samples show high consistency with theoretical predictions. Both model and experiments indicate that improved and stable surface finish can be achieved on metal matrix composites with small grain size.

In-process measurement of Barkhausen noise and resulting productivity increase potential in grinding of case hardened steel

The micromagnetic Barkhausen Noise (BN) measurements bear the capability of providing non-destructively information about the condition of the surface integrity of ground workpieces. No unambiguous statements about the surface and subsurface area state can be made by evaluating single measured micromagnetic values if a superposition of different effects in the microstructure as a consequence of high thermomechanical loads occur. Especially for highly stressed components in automotive industry or in wind energy systems, case hardenend steels are deployed. These steels are often finished at the end of their process chain by a grinding process. At this point, the workpieces to be ground have already achieved enormous created added value. For productivity reasons, grinding should be carried out close to the process limit. To avoid undesirable phase transformations in the microstructure, process models such as the process model from Malkin can be used. If a grinding process consists of several process steps it must be ensured that the final process step leads to the intended surface and subsurface properties. In order to make the process design as productive as possible, an in-process measurement signal which correlates to the current state of the surface and subsurface area can help to achieve this result. Ideally this signal is applicable to generate an adaptive grinding process.Such a signal is investigated in this paper by application of BN as an in-process measurement technology. The paper shows the reliability of BN measurements as well as that there are different maximum BN amplitudes for different material removal rates. It is expected that these BN values correlate particularly to the residual stresses in the surface and subsurface area since Malkin's grinding burning limit was used to exclude (strong) phase transformations. Considering a micromagnetic parameter measured in-process a reduction of process time of 37% and thus a significant process improvement was achieved.

An adaptive grinding method for precision-cast blades with geometric deviation

Precision-cast blades are core components in aeroengines, and their machining precision has a considerable effect on the performance of the aeroengine. In this paper, an adaptive grinding method for precision-cast blades with geometric deviation is proposed to improve the machining precision, machining efficiency, and automation level of precision-cast blade grinding. A scheme for adaptive grinding of precision-cast blades with geometric deviation is developed, a grinding process for precision-cast blades is formulated, and a robotic grinding system is constructed. An optimal model to match the blade measurement data to the design model is then established, and a corresponding optimal matching matrix is solved to determine a position reference for precision-cast blades. Further, the theoretical cutter contacts are extracted, and the machining allowance of the precision-cast blade profile is measured. An estimation model of grinding material removal (MR) of precision-cast blades based on a neural network algorithm is established, and the correctness of the model is verified. Finally, an adaptive grinding experiment is performed on the concave surface (CC) of a precision-cast blade to verify the accuracy of the proposed grinding method. The experimental results show that, after adaptive grinding, the machining allowance of CC is distributed in the range of − 0.05 mm to 0.05 mm, which meets the machining precision requirements of the blade.

Fabrication of mechanically durable slippery surface on HVOF sprayed WC-Co coating

The limitations of the existing art and the fragility of the developed hydrophobic surfaces limit its applications to the real field. Hence, the fabrication of slippery surface with the required durability has been considered to be an important academic and industrial challenge. The WC-Co coating possesses exceptional mechanical and tribological properties and is considered as one of the most durable surfaces available. The WC-Co coating with nanoscale surface roughness is in high demand in aerospace and automobile industries. In this study, shape adaptive grinding (SAG) is conducted to attain nanoscale surface roughness on hard WC-Co coatings. The static and dynamic wetting behaviour of as-sprayed, ground and nanofinished WC-Co coating are studied by analysing the static contact angle, sliding angle, and contact angle hysteresis (CAH). A model is proposed to predict the apparent contact angle of the coatings. The nanofinished coating exhibits a lower sliding angle and contact angle hysteresis and the water droplets get completely released from the surface in dynamic condition. This is attributed to the lower surface retention force and the presence of trapped air inside the porosities and the nano-well of the coating surface. The durability test of the nanofinished surface is also performed by abrasion test and sand impact test and it is observed that the surface can retain its original topographical features and wetting properties. This report presents a sustainable method for the fabrication of a mechanically durable slippery surface.

An adaptive grinding chatter detection method considering the chatter frequency shift characteristic

At present the majority of the research works on machining chatter detection are based on energy level monitoring of certain chatter frequencies which are premised to be invariant. However, chatter frequencies are very complicated with multi-frequency/frequency band, time-variant characteristics and are also affected by many factors in the machining process. These characteristics make the traditional chatter detection methods vulnerable under the practical complex machining conditions. In this study, the complexity of grinding chatter frequency was investigated firstly. The influence from change of machining parameters and machine tool dynamic characteristics on grinding chatter frequencies were analyzed theoretically. Then a high accuracy and robust chatter detection method adaptable for dealing with complex machining conditions was proposed. Specifically, information fusion of feed motor current and vibration signal based on cross wavelet transform was utilized to extract chatter information adaptively and completely, whereas the harmonics of forced vibration and other noises were eliminated. To assess the grinding stability, two chatter indicators, i.e. normalized spectral entropy and logarithmic spectrum distance based on the cross wavelet transform spectrogram were devised. The efficacy of the proposed method was successfully verified through grinding operations in which both constant and variable machining were carried out. The results show that the developed method is capable of robustly detecting chatter in all the tested machining conditions and both the indicators have suitable properties to enable them for adaptive chatter detection. By comparison, spectrum distance has a monotonic relationship with the severity of chatter vibration, which makes it a comparatively better indicator.

Investigation of elastic grinding pins

AbstractIn order to develop a grinding tool for shape adaptive grinding, elastic grinding pins are used as an example to investigate the behaviour of those tools. In the following, we describe the results for test tubes machined with elastic grinding pins. Therefore, the surface profile of the test tubes is analysed for different parameter sets. The varied parameters are the size of the grinding particles and the stiffness of the base material.The interdependencies between the parameters are as expected: larger particles and stiffer material lead to a rougher surface. This is the case for both acrylic glass and steel tubes. However, irregularities in the uniformity of the specimens surface indicate that the manufacturing process has still to be improved at different points.

Integration of heterogeneous system information in machining-detection logistics for titanium alloy blade with adaptive belt grinding

ABSTRACTAs a key part of an aircraft engine, the profile accuracy and surface quality of the titanium alloy bladesignificantly influence engine usability. Belt grinding is one of the most effective ways to increase thesurface integrity of blades. However, several issues, includingthe elastic contact, change in shape owing to weak rigidity and so on, make it difficult to ensure satisfactory profile accuracy and surface quality.Self-adaptive manufacturing with machining-detection logistics has been reported as a means forsolving these problems. However, as there are different system network architectures and communication protocols in the equipment, sharing information and interoperation isimpossible, integrating these systems is difficult. This study researches the information integration process of three heterogeneous systems, namely 840D, 828D, and Win3Ds, and reportson the concept of homogenising these heterogeneous systems in the network structure based on theindustrial Ethernet network platform using the object linking and embedding for process control (OPC)technology to unify their communication interfaces. Moreover, a self-adaptive belt grinding experimentfor a titanium alloy blade is conducted with a heterogeneous system based on this method. The resultsdemonstrate that this method can achieve information integration in the heterogeneous system of self-adaptive beltgrinding.

Theoretical and experimental investigation of material removal mechanism in compliant shape adaptive grinding process

Modeling of grinding process, especially the grinding forces, has been studied extensively. Most previous work concerns the conventional grinding process using a rigid wheel, where the forces are generally based on the preset depth of grinding. However, for compliant grinding such as Shape Adaptive Grinding (SAG) that adopts an elastic tool covered with abrasive pellets, the penetration depth of individual abrasive grains is not simply equal to the preset value. As elastic contact occurs between the tool and workpiece, previous models are not able to estimate the material removal mechanism. Besides, the progressive transitions in grain-workpiece interaction for compliant cutting tools have not been reported yet. To fill these gaps and to offer a fundamental understanding of the compliant grinding process, we propose in this study a new multi-scale model spanning from macroscopic tool-workpiece contact to microscopic grain-workpiece interaction in the unique conditions of using a compliant grinding tool, i.e. SAG tool. Based on the spring-grain model and considering the stochastic nature of grain size and wear flat area, the static penetration and dynamic removal of individual grain can be predicted. Particularly, the removal mechanism is clarified with a new consideration of the transition between rubbing, plowing and cutting stages for each individual grain of the compliant tool. Experiments including scratch tests and removal footprints were carried out, and the high consistency with theoretical predictions validates the proposed model. Finally, considering the progressive abrasive wear in grinding, in-process wear compensation was conducted to enable consistent material removal on aspheric steel molds. The proposed method is not only meaningful to reveal the mechanism of SAG process, but also offers a new foundation for studying other compliant grinding processes in future.

An investigation into the wear mechanism of zirconia-alumina polishing pad under different environments in shape adaptive grinding of WC-Co coating

Shape adaptive grinding (SAG) is a relatively newer finishing process to achieve nanoscale surface roughness of difficult to machine materials. The wear mechanism of zirconia-alumina polishing pads is investigated after performing SAG and chemical assisted SAG (CA-SAG) for the finishing of WC-Co coating. The numbers of active abrasive particles in SAG increases due to the existence of the elastic medium and that leads to a smaller depth of penetration. This phenomenon along with the presence of tough zirconia phase in abrasive particles limits the possibility of the fracture wear. Smooth and elongated grooves along the finishing direction are observed on the wear flats which indicate that the plastic deformation is the predominant wear mechanism rather than micro-fracture. A phenomenological model for the attritious wear of the polishing pads is developed using the experimental findings. The radial pad wear and pad loading are analysed quantitatively using surface texture parameters. The wear mechanism in CA-SAG is immensely affected by the use of chemical reagent in the process. A substantial pad loading is observed owing to the deposition of the passivation layer in the inter-grit spaces. Thus, shelling of the abrasive particles and pad loading are identified as the dominant wear mechanisms.

Ultra-precision finishing of low expansion ceramics by compliant abrasive technologies: A comparative study

Advanced ceramics have many attractive features such as high stability and wear resistance that find broad applications in various fields, e.g. optics, aerospace, etc. However, the accompanying difficult-to-machine property with complex geometry brings great challenges to the commonly used laser machining and rigid wheel based grinding in industry. To achieve optical surface quality with surface roughness below 10 nm Ra, three promising ultra-precision compliant machining technologies using adaptive elastic tools are presented in this paper, including bonnet polishing, compliant pitch polishing and shape adaptive grinding with fine grain size. A comparative study was conducted by machining three different low thermal expansion ceramics while continuously increasing attack angle, spindle speed and tool offset across rectangular regions. Material removal rate (MRR) and surface roughness (Ra) with respect to different process conditions are compared. With sufficient data, the processing ability using above three compliant machining technologies is summarized based on the MRR-Ra plots for different ceramics. In addition, microscopic observation and X-ray diffraction analysis are conducted to characterize differences in material behavior.