Grinding Stability Research Articles

Stability prediction and optimization of multi-regenerative weak stiffness grinding system based on microstructured tool

Chatter is a serious problem in grinding, which will directly affect machining accuracy, efficiency, tool wear and even damage machine tools. In order to understand and avoid grinding chatter, a stability prediction and optimization method of multi-regenerative weak stiffness grinding system based on microstructured tool is innovatively proposed. It is the first time to use microstructured tools to ensure the system stability without sacrificing the material removal rate, which offers promise for weak stiffness grinding. Firstly, a multi-random geometric model of microstructured grinding wheel is established, considering the shape, distribution, microstructure patterns and truing conditions of abrasive grains. On this basis, considering the regulating effect of microstructure patterns on workpiece regeneration delay and tool wear delay of grinding system with large aspect ratio, a multi-regeneration stability model based on microstructure tool is established. Then, the experiments of grinding wheel microstructuring, internal thread grinding and profile measurement are carried out. The results show that the theoretical model established can accurately predict the grinding stability boundaries. The microstructure types can be arranged in descending order according to the optimization degree of grinding chatter: composite type, cross type, oblique type and linear type. Compared with the grinding wheel without microstructures, the microstructured grinding wheel can increase the speed limit deviation by 12.2 % − 54.0 %, which basically solves the chatter problem at high rotation speed. The wear resistance of microstructured grinding wheel is improved by 44.2 %, the tooth profile angle error and bottom fillet radius of workpiece are reduced by 92.3 % and 90.4 % respectively, and the maximum tooth height difference and average tooth height error are reduced by 90.6 % and 87.5 % respectively.

Theoretical and Experimental Analysis of Grinding Stability of Beam Workpiece

Grinding chatter is a kind of self-excited vibration in which the grinding system continuously absorbs energy from the grinding machine, increasing the mechanical energy of the system. Grinding chatter can damage the surface of the workpiece and accelerate the abrasion of the grinding wheel. The theoretical analysis of the grinding chatter for the beam surface was launched based on the behavior of a single abrasive grain, whose cutting thickness is a key factor affecting grinding stability. The dynamic grinding force model has been developed, which is the interaction interface between the grinding wheel and the workpiece. In this paper, rail beam grinding was taken as an example. The vibration performance of the rail beam was described with the Timoshenko beam. The characteristics of the frequency domain of the grinding wheel-workpiece system were observed, and the condition of the stability at any position in the longitudinal direction of the beam was gained, which could be quantitatively characterized with the stability limit curve. The grinding experiments of the rail beam surface demonstrated that as chatter developed, the chatter marks could be investigated on the surface of the rail, and the energy of the chatter signal was mainly concentrated around the chatter frequency, which was higher than the natural frequency of the grinding wheel.

A Fuzzy Adaptive PID Control Method for Novel Designed Rail Grinding Equipment

Rail defects appear in a greater variety and frequency with the rapid development of High-Speed Rail (HSR), which seriously affects the safe operation of trains. Rail grinding is one of the common methods used to eliminate these defects. However, the quality of rail grinding is often limited by the constant power control method. This paper presents a fuzzy adaptive PID control method based on PID control. In this method, a fuzzy rule library of input and output is established according to the experience of experts and grinding operators, and the PID control parameters can be adjusted in real time through the library to achieve the purpose of constant power grinding. Compared with classical PID, the effectiveness of the proposed method was verified by simulation and the rail grinding experiment with the designed equipment. Experimental results showed that the power data of fuzzy adaptive PID control had less fluctuation, which could be basically stabilized at 5KW±0.1KW, and the curve tracking error was reduced by 60.9%. It is concluded that this method can greatly improve the power accuracy and stability of rail grinding.

Numerical Evaluation of Plane Grinding Stability

Numerical Evaluation of Plane Grinding Stability

A uniform allowance matching method for point cloud based on the edge extraction under de-shaping center

For automated grinding, such as robotic grinding, high stability of the manufacturing system is required during the machining process. Little attention has been paid to the effect of the uniformity of the matching margin on the machining stability as a result of visual matching. In fact, it has an important relationship with maintaining the stability of robotic grinding and keeping the uniformity of grinding depth. In this paper, important process features of the blade part are extracted to improve the matching efficiency with a point cloud, while the normal direction of the contour after finishing grinding is used as the normal direction for registration. The objective function of minimization of the allowance variance is constructed to improve the uniformity of the grinding depth. The overall uniformity of the calculation results is also considered, and the effect of no tangential distance tampering is achieved by constraining the shape centers of the two point cloud models. The method in this paper is compared with the classical matching method to verify the feasibility of the margin variance minimization algorithm based on the decentered point cloud edges in terms of algorithm speed, convergence, accuracy, spatial complexity, and the uniformity of the obtained results.

Non-contact grinding/thinning of silicon carbide wafer by pure EDM using a rotary cup wheel electrode

The significantly increased stability of third-generation semiconductors, both mechanically and chemically, presents a significant challenge to traditional wafer grinding. This study develops pure electrical discharge machining as an alternative for non-contact wafer grinding and thinning to achieve high precision and low cost. This method employs a copper-made rotary cup wheel as the tool electrode to replace the conventional diamond wheel to realize electrical discharge grinding. A prototype is built to evaluate the new process with single-crystal SiC. Aiming at ultra-precision machining, the material response of SiC to both single and consecutive discharge is elucidated. The influencing mechanism of pulse conditions on hard, brittle crystalline SiC material is demonstrated via experiments and simulation. Further, the material removal behavior, grinding stability, surface integrity, wafer shape accuracy, and process-induced subsurface damage are comprehensively investigated via single and consecutive discharge experiments under various conditions. In addition, the extreme precision that is achievable by contemporary EDM technology is explored. As a result, a 30 μm thin Φ20 mm SiC wafer with a subsurface damaged layer <1 μm was obtained, showing the potential of EDM for the processing of third-generation semiconductor wafers.

Wheel wear-related instability in grinding of quartz glass

Grinding is a popular method for producing high-quality parts made of hard and brittle materials. A lot of researchers have focused on the impact of grinding parameters on surface quality. However, only a few studies discussed the surface quality instability caused by the grinding wheel wear during a long grinding process. In this paper, through wheel state monitoring and surface quality testing of ground samples, it is found that the relationship between ground surface roughness and theoretical undeformed chip thickness is significantly affected by the grinding wheel wear state rather than maintain steady as described in most available models. By introducing the normal grinding force, a linear relationship was found among normal grinding force, undeformed chip thickness, and ground surface roughness. Besides, sensitivity analysis was conducted to guide the parameter adjustment to maintain the stability of ground surface roughness and grinding state. The mechanism of the effect of wheel wear on normal grinding force was also studied in detail. This study will help to further understand the mechanism of the influence of wheel wear on the grinding stability.

A Study on Bistability Analysis and Chatter Suppression for Roll Grinding Process

ABSTRACT As chatter vibration in roll grinding process is the largest limitation in surface quality of machined roll. In this paper, the bistability analysis and chatter suppression are performed for further discussion of patterns of the grinding chatter to reduce the cost of enterprises. A new three degrees of freedom dynamic model with both the regenerative effect and nonlinear stiffness of grindstone indicated by Duffing oscillator is presented, and its availability is validated by the experiment. By means of the DDE-BIFTOOL, a numerical calculation package, the effect of process parameters on grinding stability is studied extensively, proving that a large grinding width worsens the stability in roll grinding and the parameters locating in unsafe areas should be avoided for a stable grinding operation in practice. In addition, the control techniques involving both the nonlinear velocity feedback and the chaos perturbation are proposed for the suppression of chatter vibration in grinding operation to decrease the amplitude of its vibration. The results show that these techniques give a significant performance for reducing the amplitude of chatter vibration, namely, the stability of grinding process is augmented, which give a new idea for firms in chatter suppression.

An experimental and numerical study of micro-grinding force and performance of sapphire using novel structured micro abrasive tool

Micro-grinding technology has more competitive advantages than other micro machining technologies in fabricating complex three-dimensional micro parts and micro structures on hard and brittle materials, but the service life of existing micro abrasive tool has become one of the key factors restricting the popularization and application of micro-grinding technology. In this study, a novel structured micro abrasive tool with chip removal micro helical slots and the diameter less than 700μm is designed and prepared by hybrid process aimed at reducing wear and tear and increasing the service life of micro abrasive tool. The micro-grinding force model considering the structural parameters, size effect and material removal mechanism is established, which can reflect the micro-grinding performance and wear resistance of the novel micro abrasive tool. The verified experimental results indicated that the micro-grinding force model can effectively predict time-domain variation of the novel structured micro abrasive tool, and the simulated grinding force signal within 150ms fluctuation range error can be confined to be 7%. Moreover, comparing with the conventional micro abrasive tool, the micro-grinding force of sapphire specimens machined by novel micro abrasive tool is significantly reduced. Besides, the novel micro abrasive tool shows better wear resistance with the increase of grinding times, the novel micro abrasive tool surface roughness increment ∆Ra1 and ∆Rz1 is decreased by 0.2μm and 10μm respectively, and the stability of micro grinding is markedly improved. This work might play an important role in promoting the parameterization and non-standardization design of micro abrasives tools.

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.

Stability analysis for SiC grinding based upon harmonic wavelet and Lipschitz exponent

In order to effectively identify the stability degree of grinding and obtain better surface integrity of machined workpiece in grinding application, in this paper, a quantitative assessment approach based on harmonic wavelet and Lipschitz exponent is proposed, using silicon carbide as an example. To begin with, the Lipschitz exponent is defined and calculated by harmonic wavelet modulus maxima (HWMM) and linear regression algorithm, respectively. Then the Kurtosis based on Lipschitz exponent (KLE) is defined as a quantitative indicator. In grinding experiment, the acceleration signals and grinding force signals of the X/Y directions are selected, and experimental parameters including wheel speed, workpiece speed and grinding depth are employed to investigate the grinding stability in grinding stage. Experimental results show that the grinding stability is relatively worse at low wheel speed, low-high workpiece speed and large grinding depth in terms of KLE index, which may provide a new guidance to explore optimized grinding parameters and thus obtain good surface integrity in engineering applications.

Study of the Vibration Mechanism and Process Optimization for Abrasive Belt Grinding for a Blisk-Blade

The blisk is a key component of aero engines, and its surface processing quality directly affects the service performance of the aero engine. In using the new open belt grinding process, different degrees of vibration will occur, and they seriously affect the dimensional accuracy and surface quality of the blisk-blade profile. In view of the above-mentioned problems, this paper first built the physical model for the blisk-blade abrasive belt grinding and analyzed the weak stiffness characteristics of the blisk-blade abrasive belt grinding system. Then, based on the kinetic analysis method, the grinding mechanism of the abrasive belt of the blisk-blade was studied, and the process parameters and stability grinding conditions affecting the grinding stability of the blisk-blade belt were analyzed. In addition, the grinding process of the blisk-blade profile belt was simulated by a numerical method. The influence of different process parameters on the grinding vibration of the blisk-blade was quantified, and the optimal combination of process parameters was obtained. Finally, the feasibility of process parameter optimization was verified experimentally. Studies have shown that the weak stiffness of the blisk-blade grinding system always runs through the entire grinding process, but the impact size has a primary and secondary order. The grinding vibration of the blisk-blade belt is related to the process parameters, such as the grinding positive pressure, the belt speed, the feed rate, and the contact wheel hardness. The primary and secondary orders of each influencing factor are grinding positive pressure, belt speed, feed rate, and contact wheel hardness. The optimal combination of various factors was obtained: belt speed $v_{b} = 3$ m/s, grinding positive pressure $F_{n}=4$ N, feed rate $v_{g}=0.6$ m/s, and contact wheel hardness Hs/A55. Through the sand belt grinding verification experiment on the blisk-blade, the grinding belt grinding quality of the blisk-blade surface roughness and blade profile precision is improved after the process optimization.

Stability and dynamics of parallel plunge grinding

To improve the performance of conventional cylindrical plunge grinding processes, this paper introduces parallel grinding which employs an extra grinding wheel opposite to the original one, simultaneously cutting workpiece. Depending on the relative location of the two wheels, the cutting areas are divided into non-overlapped and overlapped zones. In the overlapped zone, the two wheels mutually interact with each other via the regenerative effect in the workpiece surface. Due to the newly introduced wheel, the static elastic deflection of the grinding system is significantly reduced so that the geometry accuracies of components can be improved. Meanwhile, it is found by linear analysis that the grinding stability and cutting efficiency can be largely improved by the parallel grinding when the two wheels are partially overlapped. Moreover, nonlinear analysis reveals unsafe cutting in the parallel grinding process, where loss of contact may take place either in the non-overlapped or in the overlapped cutting zones. As a result, the area of unsafe zones is shrunk by the parallel cutting method, which enhances the grinding safety.

Influence of Depth of Cut on Quality of Ground Surface and Cutting Force when Grinding Cermet

Grinding of cermet was studied to determine the impact of the depth of the cut on the grinding process and the final quality of the finished surface. Depth of cut is an important cutting parameter which affects the whole grinding process in terms of grinding stability, cutting forces, vibrations, spindle load, etc. It is also connected with other cutting parameters such as cutting speed and feed rate which should be optimized to ensure the required surface quality in the required process time. The effect of different depths of cuts on the surface quality in terms of roughness was observed during grinding of two types of cermet rods. An IFM G4 optical device was used for monitoring the surface roughness during tests. The progress of the spindle load was monitored on the grinding machine during grinding. This was used for calculating the resulting cutting forces. Experimental grinding was carried out with a diamond grinding wheel which was dressed before each grinding test. The results of this work will be used for better understanding of the process of grinding cermet.

Technological capabilities of increasing surface quality of workpieces made of titanium alloy VT22 and stability of surface grinding

Surface grinding of flat workpieces made of alloy VT22 was conducted by the periphery of a highly porous wheel (HPW) from cubic boron nitride CBN30 B107 100 OV K27 КF40 with three processing techniques (ij). They are 10 - cross-feed per stroke, HPW cutting into a workpiece changes alternately from up to down; 12 – cross-feed per double stroke during the up HPW cutting-in at the working stroke; 22 – cross-feed per double stroke during the down HPW cutting-in at the working stroke. With the involvement of artificial neural network models, it was revealed that to improve the quality of surfaces and stability of its formation, grinding should be conducted if ij = 12.

The effect of the grinding wheel modification on the state of the workpiece surface layer after internal cylindrical grinding of steel C45

Internal cylindrical grinding is one of the most difficult grinding processes due to the very long zone of contact between the grinding wheel and the workpiece surface. Such conditions limit delivery of the grinding fluid into the grinding zone, as well as impeding the removal of chips from it. As a result, during the internal cylindrical grinding process, difficult thermal conditions occur in the machining zone which finally could lead to grinding defects. One of the most efficient and cost-effective ways of improving the grinding stability and repeatability is modifying the grinding wheel structure. As such, modifications usually do not require interfering with the construction of the grinding machine or its equipment, they are universal and, possibly, widely applicable. This article presents a modified grinding wheel with helical grooves shaped on its active surface. Such modification was developed to reduce the thermal load of the workpiece surface and the occurrence of thermal defects. The effectiveness of the proposed grinding wheel modification was examined experimentally in the reciprocal circumferential internal cylindrical grinding process of 45C steel. The goal of the described tests was to determine the influence of the suggested grinding wheel modification on the condition of the workpiece surface layer (the surface roughness and residual stresses). The test results obtained indicated that application of the modified grinding wheel has a positive influence on the residual stresses in the workpiece surface layer, resulting in better delivery of the grinding fluid into the area of contact between the wheel and the machined material. Moreover, a decrease of the Ra parameter value by approximately 7–19%, as compared to the results of the process carried out with the (unmodified) reference grinding wheel was indicated.

Non-linear analysis and quench control of chatter in plunge grinding

This paper aims at mitigating regenerative chatter in plunge grinding. To begin with, a dynamic model is proposed to investigate grinding dynamics, where eigenvalue and bifurcation analyses are adopted, respectively, for prediction of grinding stability and chatter. Generally, it is found that most grinding chatter is incurred by subcritical Hopf bifurcation. Compared with supercritical instability, the subcritical generates coexistence of stable and unstable grinding in the stable region and increases chatter amplitude in the chatter region. To avoid these adverse effects of the subcritical instability, bifurcation control is employed, where the cubic non-linearity of the relative velocity between grinding wheel and workpiece is used as feedback. With the increase of feedback gain, the subcritical instability is transformed to be supercritical not only locally but also globally. Finally, the conditionally stable region is completely removed and the chatter amplitude is decreased. After that, to further reduce the chatter amplitude, quench control is used as well. More specifically, an external sinusoid excitation is applied on the wheel to quench the existing grinding chatter, replacing the large-amplitude chatter by a small-amplitude forced vibration. Through the method of multiple scales, the condition for quenching the chatter is obtained.

Rounding and stability in centreless grinding

The paper presents a method for selecting grinding conditions and assists researchers to understand the complex dynamics of centreless grinding. It overcomes the problem of deriving dynamic stability charts for particular geometries and difficulty of interpreting such charts to adjust work speed to overcome lobing problems. Classic dynamic stability charts cannot assess stability levels in proximity to integer lobes, a particular problem for centreless grinding. The paper overcomes these problems employing a simply calculated new dynamic stability parameter Adyn. The new parameter Adyn simplifies the optimisation of grinding variables including set-up geometry and work speed in relation to resonant frequency. It is difficult to interpret relative dynamic stability of centreless grinding by classical methods for different set-ups, work speeds and numbers of lobes. A new method is employed in this paper based on the well-established Nyquist stability criterion. The dynamic stability parameter Adyn is based on the real part of the characteristic equation. It is easily computed and presented on a single chart for particular work speed, resonant frequency and for a wide range of numbers of lobes. The method clearly shows the effect on rounding strength both for stable and unstable conditions. Most authors computing dynamic stability charts have ignored positive down boundaries and negative up boundaries showing a lack of a comprehensive treatment for a situation that conflicts with recommendations for conventional positive up boundaries. The new method simplifies this problem.Small differences in set-up geometry and work speed selection can be easily assessed. The new method can be used as a diagnostic tool for adjusting grinding conditions to overcome roundness problems. The user is not constrained by a historic set-up range since there are practical situations where other set-ups are preferred such as small tangent angles for large and heavy work-pieces, and even negative tangent angle for some types of centreless machine.Previous research is reviewed to provide an understanding of the need for a new approach to stability. Practical implications are explained for selection of grinding conditions. The method is supported by reference to experimental results.

Suppression of Regenerative Chatter in a Plunge-Grinding Process by Spindle Speed

This paper utilizes an effective control strategy to suppress the regenerative chatter in a plunge-grinding process. To begin with, the dynamical interaction between the workpiece and the grinding wheel is considered as a major factor influencing the grinding stability. Mathematically, the grinding stability is studied through numerical eigenvalue analysis. Consequently, critical chatter boundaries are obtained to distinguish the chatter-free and the chatter regions. As known, the grinding is unstable and the chatter happens in the chatter region. To observe the chatter vibrations, an analytical method and numerical simulations are employed. As a result, chatter vibrations both with and without losing contact between the workpiece and the wheel are obtained. Meanwhile, the coexistence of the chatter and the stable grinding is also found in the chatter-free region. Finally, a control strategy involving spindle speed variation (SSV) is introduced to suppress the chatter. Then, its effectiveness is analytically investigated in terms of the method of multiple scales (MMS).

Study on Processing Optimization in Ultrasonic-Assisted Grinding of SiCp/Al Thin-Walled Workpiece

Thin-walled workpieces have the characteristics to withstand a greater load with less material and they are used in aerospace field widely. SiCp/Al composite has high strength and stiffness, which meets the requirements of the aerospace workpieces well. The optimization method is studied with grinding stability and material removal rate as constraint conditions in this paper. The processing parameters optimization of a SiCp/Al thin-walled cylinder is analyzed according to stability lobe diagram. The grinding parameters optimization could be achieved by this method and the chatter could be prevented effectively.