Tool Deflection Research Articles

Force model of two-flute continuous milling based on tool deflection

Accurate modeling of the instantaneous uncut chip thickness is one of the key issues in milling mechanics. Although most current cutting force models take into account the effects of tool deflection and tool run-out, they only consider single-edge continuous milling processes and do not consider processes where multiple edges are simultaneously engaged in milling. Considering the tool runout and tool deflection that affect the end milling process, a novel uncut chip thickness algorithm based on two-flute continuous milling is proposed in this paper, and an analytical force model for actual milling is established. There is no need to use iterative methods, and the predictive power can be obtained by solving a linear system of equations, so the computational cost is greatly reduced. At the same time, stainless steel 316 was processed, and the experimental results showed that the predicted force was in good agreement with the measured force.

A novel ultrasonic-assisted staking process for mechanical fasteners

Increasing material variety in car body engineering causes new challenges regarding the joining processes and therefore, leads to an enhanced usage of mechanical joining technologies. Mechanical fasteners, as self-piercing nuts, can be staked cost-efficiently without a pre-punching operation to create detachable joints. Nevertheless, elevated workpiece strengths lead to high forming forces and a limited application range. One promising approach to reduce tool and workpiece loads in forming operations is superimposing a high-frequency oscillation to the tool movement. The so-called ultrasonic assistance enables an immediate and considerable reduction of the material's flow stress. This beneficial softening effect has been confirmed for several materials and processes. Since the process management and monitoring are highly affected by the frequency-dependent dynamic behavior of the whole test setup, the application of ultrasonic assistance is already challenging for basic forming operations. Hence, only a few studies have been investigating ultrasonic-assisted joining processes. In particular, joining processes with auxiliary elements have been hardly considered. Within the scope of this work, a novel ultrasonic-assisted staking process for mechanical fasteners is proposed. Therefore, the punch movement for the installation of a self-piercing nut into an aluminum sheet is superimposed with a 20 kHz oscillation of 10 µm, 15 µm, and 20 µm amplitude. Ultrasonic assistance in the initial staking phase, characterized by moderate loads, causes irregular tool–specimen contact. Since the effect is promoted by increasing amplitudes, a correlation with the elastic tool deflection is presumed. Additionally, the transferability of the ultrasonic-based force reduction to mechanical joining with auxiliary element is confirmed and a beneficial influence on the joint formation is identified. Thus, ultrasonic assistance is proven as a promising approach for the extension of existing process limits.

Laser pre-structure-assisted micro-milling of Ti6Al4V titanium alloy

High flexibility of the micro-milling process compared to nontraditional methods has led to its growing application in manufacturing complex micro-parts with tight tolerances and high accuracies. However, difficulties such as tool deflection, size effect, and tool wear limit the application of micro-milling. In this regard, the role of laser-assisted machining (LAM) is highlighted to prevent mentioned issues through reduction of machining forces and providing the possibility for using higher feeds. Ti6Al4V as a hard-to-machine material is chosen as the workpiece material. Unlike traditional LAM, Ti6Al4V parts were structured using a picosecond laser before micro-milling. The influence of laser structuring at different structure densities on the reduction of machining forces was analyzed at two feeds of 10 and 50 µm/tooth at a constant cutting speed of 35 m/min. A remarkable reduction in cutting forces was observed at both feeds. Additionally, the role of structure density in cutting force reduction is highlighted.

Study on tool deflection compensation method based on cutting force observer for orbital drilling of CFRP/Ti stacks

Orbital drilling is an alternative hole-making machining process that combines drilling and milling, usually performed with specific devices and industrial robots to make holes in aircraft composite structures. In order to eliminate the adverse effects on the diameter precision of the tool deflection in the orbital drilling process of CFRP/Ti stacks, a novel method that fuses cutting force model prediction and feed-axis disturbance observation is proposed to estimate the radial cutting force. The tool deflection caused by the radial cutting force is calculated based on the equivalent diameter cantilever beam model. Then the tool path is corrected to compensate for the tool deflection and prevent borehole diameter deviation by adjusting the tool eccentricity in real-time. The orbital drilling experiments demonstrate that the geometrical error of the hole was reduced by 50%, and the manufacturing precision requirements of IT9 level can be satisfied after one single shot even the cutting force was increased to twice the initial value caused by tool wear, the proposed method effectively improved the hole-making precision of CFRP/Ti stacks.

A model of micro-milling cutting forces based on micro-cutting experiments including tool eccentricity and deflection

In this study, a model of micro-milling cutting forces based on elementary cutting experiments is developed. Elementary cutting tests were used to identify the parameters of a new model that includes the uncut chip thickness and the effect of the cutting edge radius. This model assumes a straight cutting edge and a rigid cutting tool and is divided into two terms that represent the ploughing and shearing regimes. The complex shape of the cutting edge of the micro-end-mill is decomposed into linear elementary edges to which the force model can be applied. The uncut chip thickness during tool rotation includes the tool path deviation due to tool run-out and deflection. Micro-milling experiments were performed using a micro-end-mill with the same cutting edge geometry as the tool used in elementary cutting experiments on AISI 6F7 steel. Comparisons between the force model and the experimental results show a good correlation. This model can be extended to a ball-nose micro-end-mill to consider a wide range of operations and can be used to predict and avoid machining errors due to deflection and even tool breakage.

Investigation of Gyroscopic Effect on the Stability of High Speed Micromilling via Bifurcation Analysis

Catastrophic tool failure due to the low flexural stiffness of the micro-tool is a major concern for micromanufacturing industries. This issue can be addressed using high rotational speed, but the gyroscopic couple becomes prominent at high rotational speeds for micro-tools affecting the dynamic stability of the process. This study uses the multiple degrees of freedom (MDOF) model of the cutting tool to investigate the gyroscopic effect in machining. Hopf bifurcation theory is used to understand the long-term dynamic behavior of the system. A numerical scheme based on the linear multistep method is used to solve the time-periodic delay differential equations. The stability limits have been predicted as a function of the spindle speed. Higher tool deflections occur at higher spindle speeds. Stability lobe diagram shows the conservative limits at high rotational speeds for the MDOF model. The predicted stability limits show good agreement with the experimental limits, especially at high rotational speeds.

FRAMEWORK FOR COUPLED DIGITAL TWINS IN DIGITAL MACHINING

This paper presents a further elaboration of the use of the digital twin concept in digital machining. The main goal of the research is an attempt to combine digital representations of different objects involved in the machining process in a holistic manner. Digital twins of the in-process workpiece, cutting tool, clamping, and machine tool along with the process twin are connected in a framework in which all these elements can influence each other. The framework shows different levels of integration of different digital twins and practical recommendation on the implementation. Besides, the framework supports a simulation layer that provides data for the intensity of the interaction. Such interactions can result in, for instance, cascading calculations of cutter workpiece engagement, cutting forces, tool wear, tool deflection, chatter, and so on. Eventually, a design for a software mockup was elaborated to present the developed framework. The entire workflow to simulate part machining in such a digital representation can be used as an ultimate tool for CAM simulation and NC verification within the Zero Defect Manufacturing paradigm.

The Investigation of the Sensitivity and Direction of the Maximum Surface Error in Peripheral Milling

In this paper, we developed a virtual model predicting the tool deflection induced surface error and investigated the sensitivity and direction of the maximum surface error in various tool geometries and cutting conditions. The characteristics of the error were classified into the axial sensitive, radial sensitive, robust, overcut, and overlap zones according to the depth of cut. The maximum surface error was sensitive to the uncertainty of the radial depth of cut and robust to axial depth variation at the finishing process using a small radial depth of cut. The radial sensitivity was reduced by a large helix angle of tool. The sensitivity was decreased by increasing the depth of cut and it arrived at zero in the robust zone where the maximum surface error was not changed by both radial and axial depths of cut. An overcut occurred if axial and radial depths were deep and the overcut zone was enlarged by the helix angle and the number of teeth.

Anticipatory Online Compensation of Tool Deflection Using a Priori Information from Process Planning

Removing excess material from build-up welding by milling is a critical step in the repair of blades from aircraft engines. This so-called recontouring is a very challenging machining task. Shape deviations often result from the deflection of tool and workpiece due to process forces. Considering the individuality of repair cases, compensation of those deflections by process force measurement and online tool path adaption is a very suitable method. However, there is one caveat to this reactive approach. Due to causality, a corrective movement, following a force variation, is always delayed by a finite reaction time. At this moment, though, the displacement has already manifested itself as a deviation in the machined surface. To overcome those limitations and to improve compensation beyond the reduction of control delays, this study proposes a novel approach of anticipatory online compensation. Flank-milling experiments with abrupt changes in the tool-workpiece engagement conditions are conducted to investigate the limitations of reactive compensation and to explore the potential of the new anticipatory approach.

Prediction of cutting force based on machining parameters on AL7075‐T6 aluminum alloy by response surface methodology in end milling

AbstractCutting forces modeling is the basic to understand the cutting process, which should be kept in minimum to reduce tool deflection, vibration, tool wear and optimize the process parameters in order to obtain a high quality product within minimum machining time. In this paper a statistical model has been developed to predict cutting force in terms of geometrical parameters such as rake angle, nose radius of cutting tool and machining parameters such as cutting speed, cutting feed and axial depth of cut. Response surface methodology experimental design was employed for conducting experiments. The work piece material is Aluminum (Al 7075‐T6) and the tool used is high speed steel end mill cutter with different tool geometry. The cutting forces are measured using three axis milling tool dynamometer. The second order mathematical model in terms of machining parameters is developed for predicting cutting forces. The adequacy of the model is checked by employing ANOVA. The direct effect of the process parameter with cutting forces are analyzed, which helps to select process parameter in order to keep cutting forces minimum, which ensures the stability of end milling process. The study observed that feed rate has the highest statistical and physical influence on cutting force.

Numerical and Experimental Investigation of the Temperature Rise of Cutting Tools Caused by the Tool Deflection Energy

Tool temperature variation in flank milling usually causes excessive tool wear, shortens tool life, and reduces machining accuracy. The heat source is the primary factor of the machine thermal error in the process of cutting components. Moreover, the accuracy of the thermal error modeling is greatly influenced by the formation mechanism of the heat source. However, the tool heat caused by the potential energy of the tool bending and twisting has essentially not been taken into consideration in previous research. In this paper, a new heat source that causes the thermal error of the cutting tools is proposed. The potential energy of the tools’ bending and twisting is calculated using experimental data, and how tool potential energy is transformed into heat via friction is explored based on the energy conservation. The temperature rise of the cutting tool is simulated by a lattice-centered finite volume method. To verify the model, the temperature separation of a tool edge is measured experimentally under the given cutting load. The results of the numerical analysis show that the rise in tool temperature caused by the tool’s potential energy is related to the time and position of the cutting edge involved in milling. For the same conditions, the predicted results are consistent with the experimental results. The proportion of temperature rise due to tool potential energy is up to 6.57% of the total tool temperature rise. The results obtained lay the foundation for accurate thermal error modeling, and also provide a theoretical basis for the force–thermal coupling process.

A Comprehensive Micro-Milling Force Model for a Low-Stiffness Machining System

Abstract Micro-milling is widely used in various crucial fields with the ability of machining micro- and meso-scaled functional structures on various materials efficiently. However, the micro-milling force model is not comprehensively developed yet when tool feature sizes continually decrease to under 200 µm in a low-stiffness system. This paper proposes an analytical force model considering the influence of tool radius, size effect, tool runout, tool deflection, and the actual trochoidal trajectories and the interaction of historical tool teeth trajectories (IHTTT). Different micro-milling status are recognized by analyzing the cutting process of different tool teeth. Conditions of single-tooth cutting status are determined by a proposed numerical algorithm, and entry angle and exit angle are analyzed under various cutting conditions for the low-stiffness system. Three micro-milling status, including single-tooth cutting status, are distinguished based on the instantaneous undeformed chip thickness resulting in three types of material removal mechanisms in predicting micro-milling force components. Discontinuous change rates of undeformed chip thickness are found in the low-stiffness micro-milling system. The proposed micro-milling force model is then verified through experiments of micro slot milling Elgiloy alloy with a 150-μm-diametrical two-teeth micro-end mill. The experimental results show a root-mean-square error (RSME) of 0.092 N in the predicted resultant force, accounting for approximately 5.12% of the measured force, by which the proposed theoretical model is verified to be of good prediction accuracy.

Cutting to the Point: Directly Machined Metal Molds for Directional Gecko-Inspired Adhesives

Abstract Fabrication techniques for gecko-inspired adhesives generally target mold durability, adhesive performance, and process efficiency and simplicity. With these goals in mind, we present a micromachining process for creating reusable aluminum molds used to fabricate directional dry adhesives. The molds require deep, narrow and overhanging grooves to create sharp and angled adhesive features. This geometry precludes most traditional machining and lithographic material removal processes. The presented process is a hybrid of indenting and orthogonal machining, using a diamond-coated microtome blade as the tool. An finite element analysis reveals the local extent of work hardening as each groove is created, and helps to define a trajectory that reduces the effects of tool deflection and chip build up. The results of a series of experiments agree with predictions from the analysis and reveal a range of blade approach angles and a lower bound on groove spacing to achieve the desired geometry. This range is narrower than for molds machined from wax in previous work. Nonetheless, adhesive samples cast from the new metal molds achieve comparable performance to those previously cast from wax.

Stochastic Force-based Insertion Depth and Tip Position Estimations of Flexible FBG-Equipped Instruments in Robotic Retinal Surgery.

Vitreoretinal surgery is among the most delicate surgical tasks during which surgeon hand tremor may severely attenuate surgeon performance. Robotic assistance has been demonstrated to be beneficial in diminishing hand tremor. Among the requirements for reliable assistance from the robot is to provide precise measurements of system states e.g. sclera forces, tool tip position and tool insertion depth. Providing this and other sensing information using existing technology would contribute towards development and implementation of autonomous robot-assisted tasks in retinal surgery such as laser ablation, guided suture placement/assisted needle vessel cannulation, among other applications. In the present work, we use a state-estimating Kalman filtering (KF) to improve the tool tip position and insertion depth estimates, which used to be purely obtained by robot forward kinematics (FWK) and direct sensor measurements, respectively. To improve tool tip localization, in addition to robot FWK, we also use sclera force measurements along with beam theory to account for tool deflection. For insertion depth, the robot FWK is combined with sensor measurements for the cases where sensor measurements are not reliable enough. The improved tool tip position and insertion depth measurements are validated using a stereo camera system through preliminary experiments and a case study. The results indicate that the tool tip position and insertion depth measurements are significantly improved by 77% and 94% after applying KF, respectively.

Improvement of Machining Accuracy by Correcting Tool Deflection Based on Identification of Actual Feed Speed Associated with Acceleration/Deceleration Control of Machine Tool

Improvement of Machining Accuracy by Correcting Tool Deflection Based on Identification of Actual Feed Speed Associated with Acceleration/Deceleration Control of Machine Tool

Simulation-Based and Experimental Investigation of Micro End Mills with Wiper Geometry.

One of the major advantages of micromachining is the high achievable surface quality at highly flexible capabilities in terms of the machining of workpieces with complex geometric properties. Unfortunately, finishing operations often result in extensive process times due to the dependency of the resulting surface topography on the cutting parameter, e.g., the feed per tooth, fz. To overcome this dependency, special tool shapes, called wipers, have proven themselves in the field of turning. This paper presents the transfer of such tool shapes to solid carbide milling tools for micromachining. In this context, a material removal simulation (MRS) was used to investigate promising wiper geometries for micro end mills (d = 1 mm). Through experimental validation of the results, the surface topography, the resulting process forces, and tendencies in the residual stress state were investigated, machining the hot work tool steel (AISI H11). The surface-related results show a high agreement and thus the potential of MRS for tool development. Deviations from the experimental data for large wipers could be attributed to the non-modeled tool deflections, friction, and plastic deformations. Furthermore, a slight geometry-dependent increase in cutting forces and compressive stresses were observed, while a significant reduction in roughness up to 84% and favorable topography conditions were achieved by adjusting wipers and cutting parameters.

Hypothesis of the nature of cross-sectional shape distortion of the cold-pilgering mill die groove during dry pipe rolling

The paper provides results on the further development of a method for calculating heat emissions during plastic strain in its instantaneous deformation zone in the course of cold pilgering of pipes, such as the ones that affect the working tool deflection in coldpilgering mills and mechanical properties of wrought pipe metal. It was determined that a decrease in the cross-sectional depth of the coldpilgering mill die groove due to thermal distortions (thermal effect) caused by plastic strain of a pipe in the instantaneous deformation zone is in direct proportion to the distance of the die groove longitudinal section considered to the roll barrel edge. It was found that sections located closer to the roll barrel receive thermal distortion of a lesser degree. A method is proposed for thermal distortion compensation in roll-pass design calculation. Experiments on applying marks on the roll barrel surface near the groove taper showed that the maximum galling of marks takes place directly near tapers. This indicates the local nature of thermal expansion. Dependencies are presented to determine the value of tool geometry variation depending on the heating temperature. The presented dependencies were tested experimentally and were introduced as a basis for developing the method of calculating the transversal die groove parameters for the cold-pilgering mill taking into account local thermal expansion in the instantaneous deformation zone. The inferred law allows taking into account the influence of cold pilgering peculiarities on the variation of the die groove cross-section geometry in the cold-pilgering mill, pipe dimensions and performance parameters.

Tool geometry analysis for plunge milling of lead-free CuZn-alloys

Plunge milling is a critical process step in mass manufacturing of rectangular shapes in electrical connector components. These shapes are manufactured by drilling a pilot hole and subsequent plunge milling with a radial offset (pitch) one or more times. The plunged cavity serves as guidance for the final broaching cut. In light of new legislative initiatives, the electronics industry is forced to use lead-free Cu-Zn-Alloys for mass manufacturing of these connectors. The plunging tool is deflected due to the higher cutting forces experienced in machining of lead-free CuZn-alloys in comparison to alloys with lead. This results in an offset of the milled cavity and negatively impacts tool guidance in the subsequent broaching process. Therefore, the geometric tolerances cannot be met. In this paper, the effect of tool geometry and cutting parameters on the workpiece geometry in plunge milling is investigated. The effect of the microstructure of the work-piece materials CuZn37, CuZn42 and CuZn21Si3P on the tool deflection and cutting force components is examined. The tools used vary regarding the design of the corner in terms of the corner chamfer and the inner shaft thickness. Friction between chips in the tools inner flutes and the cavity walls reduced workpiece accuracy. Improvements were achieved by reducing the width of the cutting corner chamfers, using large inner flutes and applying low cutting parameters.

Uncut chip geometry determination for cutting forces prediction in orthogonal turn-milling operations considering the tool profile and eccentricity

The cutting forces generated in machining are responsible for the tool deflection, part distortion, and features as chatter; therefore, their accurate estimation is fundamental to defining stable and safe working conditions to increase workpiece accuracy and productivity. Turn-milling is a conventional milling operation while the workpiece is simultaneously rotating. These operations enable manufacturing pieces with bosses or eccentricities; particularly, in large-sized industries such as aeronautics, naval power, and nuclear energy. Despite its wide use, relatively few studies are available regarding cutting forces and their implication in the process. Then, the effects of some cutting parameters over the process are not well detailed, for example, the tool profile and eccentricity. The numerical model presented in this research covers the cases of tool eccentricity and tool profile, such as torus and spherical end mills in orthogonal turn-milling operations. The model accurately determines the uncut chip geometry, validated theoretically against a CAD representation of the chip with errors below 3%. Furthermore, a set of milling trials was proposed to compare the chip mass and the cutting forces estimated by the model with those measured from the trials in torus and spherical profiles. The experimental validation results correlate in both tests presenting in the case of the mass errors below 3.5% and the cutting-forces errors around 12%. The validated model allows exploring a wider scenario of simulations where the eccentricity and the tool profile are the studied variables. The main findings drawn from the experiments and simulations are that the tool profile and the eccentricity affect the material removal rate. Its wrong selection reduces the chip volume and leaves material where it is supposed to be removed; then, the geometrical errors force to reprocess the workpiece, negatively impacting manufacturing productivity.

Study on the prediction method of drilling tool deflection ability

The build rate of the tools is a key point in trajectory control and prediction of horizontal well, which is based on the mechanical analysis and geometry analysis of tools. But if the tools have initial bending, the application of “beam-column theory” is limited. With a method of equivalent loading, this problem can be solved. Through the analysis of tools, the side force of bit can be calculated, and then a method, named “method of modified three-point fix Round” is used to determine the build rate of tools at the basis of VB program.