Boring Bar Research Articles

Dynamic simulation of mirror cutting

This article presents a model to simulate the dynamics of mirror cutting process. Mirror cutting is used for machining thin-walled workpiece, consisting of an external turning tool and internal boring bar. The thin-wall workpiece and long slender boring bar are easily subjected to vibrations. It is difficult to ensure the processing quality of the thin-walled workpiece for conventional machining methods, such as turning, boring, and milling. Mirror cutting is a simultaneous machining method for internal boring and external turning and has the same normal uncut chips. In this way, the radial cutting force of the workpiece can be counteracted, thereby reducing radial vibration and enhancing the stability of the system. The mirror cutting is a multi-input–multi-output (MIMO) cutting system consisting of external turning and internal boring. The proposed method simulates the mirror cutting by state space model. By using the state space model, it is possible to simulate the MIMO machining dynamic system. The dynamic simulation of the mirror cutting system in the cutting process is realized and verified by comparison with the measured signal.

Experimental investigation of dry, wet and cryogenic boring of AA 7075 alloy

ABSTRACTIn this research work, an attempt has been carried out to examine (investigate) and study the dry, wet and cryogenic boring of AA 7075 alloy, which is predominantly used in transport applications in defense (aeronautical parts), oceanic and automaker industries. To ensure direct supply of the coolant, and real-time measurement of cutting temperature a modified boring bar is used (modification is carried out using EDM to accommodate placement of a thermocouple to obtain real-time measurement of temperature readings during the boring cycle). It is observed that during cryogenic boring of AA 7075 alloy there is a considerable reduction in the cutting force (Fc), cutting temperature (Tc) and surface roughness (Ra) by 56.16%, 84.70%, 58.98% compared to dry boring and 48.43%, 80.70%, 34.70% compared to wet boring, respectively. Decrease in Fc and Tc leads to a reduction in high stresses at localized points during machining and in turn curtail wear in workpiece and tool. Lubrication provided by cryogenic fluids also plays a sizable role in reduction of Fc and Tc. Reduction in lower Fc and Tc has a glaring effect on the surface characteristics of the hole produced during the boring process. Tool wear is reduced in cryogenic boring by 36.96% and 17.57% compared to dry and wet boring, respectively. Taguchi and ANOVA was carried out which helped in determining feed as an important parameter with respect to Fc and Ra during boring of AA 7075 under dry, wet and cryogenic conditions whereas speed as an important parameter in determining Tc in dry and wet conditions and feed for Tc in cryogenic boring condition. TOPSIS analysis highlighted speed of 770 rpm and feed of 0.055 mm/min as the most closest to ideal solution for all three different cutting conditions. Surface morphology study after boring of AA 7075 highlighted better surface characteristics in cryogenic bored surface compared to dry and wet boring. Roughness measured in AFM for tool used in boring highlighted a decrease in 86.79% and 66.01% in cryogenic boring in juxtaposition with dry and wet boring, respectively. A surge in compressive residual stress is observed in cryogenic bored surface by 10.41% and 3.5% in juxtaposition with dry and wet boring, respectively, highlighting an abatement in tensile residual stress and better workpiece integrity as compared to dry and wet boring conditions.

Adaptive inverse control of chatter vibrations in internal turning operations

Abstract In this article, adaptive inverse control of chatter vibrations in internal turning process is addressed. The active boring bar is composed of a slender steel cutting tool, an electrodynamic shaker as controllable actuator and an IEPE accelerometer as feedback sensor. The SISO control system actuates in the direction normal to the cut surface. A novel adaptive inverse control algorithm is presented in this paper. This algorithm is mainly used in the feed-forward Active Noise Control (ANC) applications and is known as the Filtered-x Normalized Least Mean Square (FxNLMS). In order to extend the application of adaptive inverse control algorithms in the field of Active Vibration Control (AVC), the FxNLMS algorithm with feedback architecture is suggested for the specific problem of chatter suppression in internal turning operations. The performance of developed adaptive feedback controller is experimentally verified during the internal turning of Aluminum alloy 6063-T6. The value of critical limiting depth of cut is anticipated to be nearly 0.2 [mm] for the slender boring bar. However, the stable cutting process is conducted by the active boring bar in the presence of adaptive controller up to depth of cut 2 [mm]. That is, the boundary of stability is enhanced by at least 10 folds. It has been observed that the amplitude of chatter vibrations is efficiently suppressed adjacent to the fundamental resonance peak of the active boring bar. In addition, the feedback FxNLMS controller effectively attenuates the boring bar’s vibration by at least 70 dBs. Moreover, the periodic chatter marks are eliminated from the surface texture of workpiece and the roughness of cut surface is remarkably improved. The obtained results suggest that the practical application of adaptive inverse control algorithms for chatter rejection can be extended to other machining processes as well.

Performance of magnetorheological fluid based tunable frequency boring bar in chatter control

Low stiffness due to high slenderness ratio of the boring bar makes boring operation to be highly prone to machining instability. By providing increased stiffness and damping, the instability due to dynamic nature of the boring bar is successfully addressed in this paper. Maintaining the advantages of conventional viscous fluid damper, a provision to dynamically control the viscosity of the MR fluid is incorporated. Additionally, a rod is mounted as an inverse cantilever inside the primary structure of a specially designed boring bar. The rod vibrates within the MR fluid and the resistance to its movement is influenced by the viscosity of the MR fluid. The primary structure also experiences increased stiffness leading to change in natural frequency. From the dynamic characteristics obtained using impact and shaker excitation tests, stability lobe diagram (SLD) is constructed for a wide range of spindle speeds. For selected machining conditions, amplitude of vibration signals, roughness and roundness error are included in this paper and discussed further. For MR fluid filled condition with an input current of 3.5 A, amplitude of vibration is reduced by 29–44%, while surface roughness and roundness error are reduced by 14–59% and 5–41% respectively, thereby establishing the potential of MR fluid based tunable frequency boring bar for boring operation.

Application of piezoelectric patches for chatter suppression in machining processes

In this paper by applying piezoelectric patches, a new method for vibration and chatter suppression in boring bar is presented. The boring bar is modeled as an Euler–Bernoulli beam, and the nonlinear governing differential equation of motion is derived by considering nonlinear geometrical effects and viscoelastic material properties. Equation of motion is discretized via Galerkin method by using mode shapes of the beam under axial load. Moreover, an explicit equation is proposed to investigate the effects of using piezoelectric patches on the lobe instability region. In addition, the effects of system parameters on the stability lobe diagrams are studied analytically, as well as vibration behavior of the boring bar. Results reveal that piezoelectric patches have significant effect on the stability regions, and reduce the vibration amplitude of the boring bar. Intensity of the effects depends on the patches length, as well as the applied voltage. It is also observed that applying voltage to the patches increases the stability region, and translates the stability region to the left side. Therefore, steady state machining without chatter, occurs at low spindle speeds. Results show obvious improvement of stability performance in comparison with other used methods.

Analysis of the Vibration Characteristics of a Boring Bar with a Variable Stiffness Dynamic Vibration Absorber

Boring bars are widely used in deep hole machining. Due to the low stiffness of the long cantilever boring bar, vibration often occurs in the boring process. Vibration suppression can permit higher productivity and a better surface finish. To improve the performance of boring operations, a variable stiffness dynamic vibration absorber (DVA) is added inside the boring bar to reduce the vibration. The stiffness of the DVA is provided by two rubber bushes placed inside the DVA. By changing the axial compression, the stiffness of the DVA can be adjusted to accommodate different excitation frequencies. By establishing the relationship between the stiffness of the DVA and the axial compression of the rubber bush, the optimal stiffness for different excitation frequencies can always be found. A boring experiment is conducted, and the results show that, by selecting a reasonable axial compression, the vibration of the boring bar can be effectively suppressed.

Evaluation of the influence of different inner cores on the dynamic behavior of boring bars

The material removal rate (MRR) must be increased in order to improve productivity in cutting operations. Here, the achievable maximum is usually limited by induced vibrations caused by dynamic load peaks in high force applications. Boring bars, typically used in internal turning processes, are characterized by a high length-to-diameter ratio, which makes them particularly vulnerable to vibrations. This paper therefore examines the influence of different inner cores inserted in boring bars, consisting of carbon fibre reinforced plastics, on the dynamic behavior using finite element analysis, experimental modal analysis and machining tests, and discusses the results in terms of increasing the MRR.

Modelling the dynamics of a large damped boring bar in a lathe

Boring bars with tuned mass dampers have a passive damper tuned with respect to the frequency of the first bending mode of the tool. When the tool is clamped into the machine tool there is a stiffness loss that lowers the natural frequency of the bar compared to ideal clamping conditions. For large tools the difference can be more than 35%, depending on clamping structure, tool size and overhang. In this paper we investigate a simple two-degree-of-freedom model for the tool-machine interaction consisting of a bending mode coupled with a rotational stiff mode. The model gives good insight into the system behavior and fits well with measurements.

Boring Bar Chatter Control using Feedback Filtered-x Normalized Least Mean Square Algorithm

Abstract This paper deals with the adaptive control of chatter vibrations in boring operations. A novel feedback control method is suggested based upon the well-known filtered-x normalized least mean square (FxNLMS) algorithm. The proposed feedback controller is implemented on the developed active boring bar that is equipped with electrodynamic shaker and accelerometer. The adaptive digital control algorithm utilizes two finite impulse response (FIR) filters in order to efficiently drive the electromagnetic actuator and successfully minimize the mean square of the chatter vibrations. Feasibility of the proposed control algorithm is verified for boring of Aluminum alloy 6063-T6. The performance of feedback FxNLMS controller is compared with the constant-gain direct velocity feedback (DVF) controller. It is observed that both control algorithms attenuate the chatter by more than 70 dB. In addition, the actuator cost is reduced by 50 percent for the optimally tuned adaptive digital controller. As a result, the proposed adaptive controller provides a robust and efficient solution for chatter suppression.

Novel actuation approach for active control of slender bars with simulated delayed excitation

This research is motivated by the problem of regenerative chatter vibration, which is a pronounced problem in machining. The problem of chatter vibration is especially critical in the internal turning process, where the material is removed from the inner part of a rotating workpiece using a slender bar. Active mechatronic solutions to the problem of regenerative chatter vibration in internal turning are mostly given by means of piezoelectric actuators embedded into the boring bar. However, due to the volume needed for accommodation of the actuators, it is difficult to apply these solutions to narrow bars. This paper presents a novel actuation approach with a potential application for active control of regenerative chatter vibration in internal turning. This approach involves a bar whose clamping has an ability to move perpendicularly to the bar axis. In addition, it involves two actuators: one of them is placed near the bar clamping, and another one is placed at the bar clamping. The presented actuation approach is compared to the related approaches in the literature. Additionally, this paper presents a method for robustness analysis of the actively controlled cutting process, which is based on the structured singular value methodology. Experiments performed on a specially designed testbed imitating the internal turning process demonstrate the potential applicability of the introduced actuation approach, as well as the utility of presented robustness analysis method.

An Advanced Design of a Boring Bar for Grinding the Cylinder Plugs of the U8-6MA2 Drilling Pump

Methods of restoring the internal surfaces of cylinder plugs of the U8-6MA2 drilling pump with the use of an advanced design of a boring bar possessing a complicated cross-section are proposed. The rigidity and maximal flexure of a boring bar with a machine milled surface are calculated. The economic efficiency of the proposed design is demonstrated, with a 30–40% increase in productivity.

Structural Design and Vibration Analysis of the Built-in Damping Boring Bar

A series of related researches have been carried out in the process of deep hole machining with boring burrs, where the long diameter of the boring bar is relatively prone to chatter. Firstly, the structural design and detailed design of the damping boring bar was completed, a three-dimensional model was established, a dynamic equation was established for the damping system and using ANSYS for modal analysis and harmonic response analysis. Finally, the comparison between the solid boring bar and the analysis results of the damping boring bar is compared and the conclusion that the new type damping boring bar has good damping performance is obtained.

On the self-excitation of vibrations of a boring bar in the process of deep boring

The article presents equivalent mathematical models of a boring bar designed for deep boring, in a distributed and a discrete idealizations. A mathematical model describing coupled torsional and lateral vibrations of a boring bar is constructed in the form of a set of differential equations with lagging of the cutting process dynamics. A methodology for studying stability in small of the deep boring process using a characteristic quasi-polynomial is presented. The numerical-analytical results of the studies made it possible to discern stability regions in the parameter space of the model and to obtain relations for maximal cutting depth as a function of geometrical and technological parameters (stiffness, cutting velocity, feeding etc.) of the boring bar considered. It is noted that the obtained numerical-analytical results are in good agreement with experimental data.

High-performance controller design and evaluation for active vibration control in boring

High quality manufactured components with fast production rate is an increasing demand of modern machine tool industry. Internal machining operations due to the large length to diameter ratio are most prone to intolerable chatter vibrations and proved to be an extremely challenging process. This paper presents a new method for proper design of direct velocity feedback (DVF) controller in order to extend boundaries of stable cutting for internal turning with minimum control effort. Control effort and active damping performance are two counteracting parameters that affect the results of active vibration control. After properly implementing the DVF active control algorithm on the internal turning setup, stable boundaries for different control gains of DVF controller are thoroughly studied. The comparison shows that although high DVF gains may considerably improve dynamic stiffness of the tool, it leads to the maximum control effort and actuator saturation and consequently process instability. The proposed gain selection method results in a significant increase in stable machining over the desired range of cutting conditions. The suggested design approach of the DVF controller can considerably improve limitations of rough machining on long over hang boring bars.

Dynamic Modeling of Composite Boring Bars Considering Different Boundary Conditions

Boring bar for deep hole cutting is often more prone to flutter problems. The traditional boring bar is generally made of metal material. There is a close relationship between the dynamic characteristics of the boring bar and the tightness of the fixed end. In this paper, based on Euler-Bernoulli beam theory, the distributed parametric differential equations of composite boring bar are prensented. The dynamic characteristics of composite boring bar with three different conditions including fixed-free, pinned-pinned-free and spring-spring-free are investigated. The corresponding frequency equations are given. The natural frequency and dynamic stiffness of the composite boring bar are obtained by numerical calculation. The influences of the supporting conditions and the ply angle are studied. The results show that the supporting conditions, layer angle, support spring stiffness and support spacing have an important effect on the dynamic characteristics of the composite boring bar.

Improving the processing accuracy of the valve seats of internal combustion engines using diagnostic measurements

Currently, the main tool of quality management at the enterprises of various industries are statistical methods of quality management. In the literature, mostly on examples of the successful application of control charts for dimensions. More sophisticated measures of quality details not given. The article illustrates a practical application of control charts applied to technologically sophisticated measure of the accuracy of the key indicator affecting the operation of the engine - radial runout of valve seat cylinder head. Data of measurements made in accordance with the standard metrological definitions are processed in the software product “Attestator”. As a result, identify the potential percentage of possible marriage, revealed the existence of special reasons to change the values of individual indicators, the index of reproducibility and stability of the process, the decision about the certification process, but the factors of the process that need to be addressed to improve the quality of the products is not revealed. A universal methodology consisting of four steps, the implementation of which allows to develop such a scheme of measurement, which significantly improves the search performance of important technological factors. For example, the same technological operations and the accuracy rate shows the application of the methods. The result of the survey revealed two main factors of the process is bending of the boring bar and the error of the satellite-based suppression will significantly improve the quality of manufacturing of parts.

Analysis of the Radial Stiffness of Rubber Bush Used in Dynamic Vibration Absorber Based on Artificial Neural Network

Rubber bush is used in dynamic vibration absorber as dissipating devices in damping boring bar. These devices actually have to support radial load in compression when chattering occurs. Mastering the behavior of the radial stiffness of the rubber bush implies an accurate understanding of dynamic vibration absorber. The behavior is, however, complex due to the changeable cross-sectional shape and boundary conditions of the rubber bush. By using artificial neural network, the radial stiffness can be predicted efficiently. According to the authors’ knowledge, simulations and tests on radial stiffness of the rubber bush under combined different cross-sectional shape and boundary conditions by using artificial neural network have not been performed yet. The purpose of this study is thus to find the law of radial stiffness of rubber bush under different cross-section shapes and axial pre-compression conditions. In order to achieve this aim, simulations and tests under different chamfering sizes and axial pre-compression by using artificial neural network were first carried out.

A robotic boring system for intersection holes in aircraft assembly

PurposeThe purpose of this paper is to introduce a robotic boring system for intersection holes in aircraft assembly. The system is designed to improve the boring quality and position accuracy of the intersection holes.Design/methodology/approachTo improve the boring quality of intersection holes, a robot posture optimization model is established. The target of the model is to maximize the robot stiffness and the variate is location of the robot on the guideway. The model is solved by the iterative IKP algorithm based on the Jacobian matrix. To improve the position accuracy of intersection holes, a robot positioning accuracy compensation method is introduced. In the method, a laser tracker is used to measure the actual position and orientation of the boring bar. Combined with the desired position and orientation, the error can be obtained and compensated.FindingsIn practical case of the robotic boring system, the robot stiffness is effectively improved and the surface roughness of intersection holes achieves a grade of Ra0.8. Besides, the robot end achieves a position accuracy of 0.05 mm and an orientation accuracy of 0.05°.Practical implicationsThe robotic boring system has been applied successfully in one of the aircraft assembly projects in northwest China.Originality/valueThe robotic boring system can be applied for machining intersection holes in an aircraft assembly. With the robot posture optimization method and accuracy compensation method, the boring quality and position accuracy of the intersection holes can be guaranteed.

A Receptance Coupling Approach to Optimally Tune and Place Absorbers on Boring Bars for Chatter Suppression

A receptance coupling based method to optimally tune and place a tuned mass damper (TMD) on slender boring bars is presented. The boring bar and the TMD are treated as separate substructures. Substructural receptances are synthesized while optimizing TMD parameters as well as its location on the bar to target an increase in dynamic stiffness of the boring bar to improve chatter-free cutting conditions. Simulation based results with the proposed approach agree with classical analytical models reported in the literature. Methods presented are generalizable and can be extended to other slender cantilevered tools to increase their resistance against chatter vibrations.

Improving the Surface roughness and Flank wear of the boring process using particle damped boring bars

In modern boring related industry, the issue of mechanical vibrations induced due to high over hang of the tool has emerged as a major challenge for the researchers. In this paper, an innovative chatter suppression method based on particle damping technique is attempted to reduce chatter in boring tool and thereby study the improvement in surface finish and tool wear. Granules of steel are used. The granules were filled into the boring bar through the hole drilled at the rear of the boring tool. Experiments were conducted with different tool overhang values, spindle speeds and feed rates. It was therefore established that particle damping plays a leading role in improving surface finish and reducing tool wear in boring operation