Tool Motion Research Articles

Design of Micro Five-axis CNC Machine Tool and Research on Virtual Simulation Machining

By studying the structure and functional characteristics of five-axis linkage CNC machine tool, design five-axis CNC machine tool with X, Y, Z linear motion axes, B and C rotation axes. The virtual simulation system of miniature five-axis machine tool is built based on the VERICT, and an impeller part was simulated and processed as an example. Check whether the state of each moving axis in the machine tool movement is correct, and judge the rationality of the structure design of the machine tool based on the error information such as interference and collision in the processing. It is proved by simulation that the machine can realize five-axis linkage machining within the design range and meet the design requirements.

Проектирование параметрических циклов фрезерования отверстий на станках с ЧПУ

The paper describes the stages of designing the technological end hole milling cycle and presents the developed CONICALINT software, which generates a G-code with argument lists used to call up a technological cycle from the CNC system memory. The developed algorithm for the technological end hole milling cycle has a branched structure, since it can choose between two methods for calculating the internal cycle parameters and two milling methods – climb down and climb up. The calculation of the internal technological cycle parameters consists of calculating the coordinates of the points necessary to construct the helical path of the cutting tool, as well as the maximum permissible value of the helical pitch within a given set of input parameters. The initial calculation data are represented by thirteen parameters characterizing the geometry of the cutting tool, the geometry of the required machined surface, as well as the parameters that determine the milling method and the method for calculating the cutting mode and the starting points of the cutting tool path. We identified eight boundary conditions that determine the permissible values of the input parameters. Based on these conditions, we designed a system of inequalities with a set of error messages displayed to the user if any of the input parameters is entered incorrectly. The developed Gcode of the technological cycle subprogram for a CNC machine calculates the tool movement both along a helical and a conical helical path, depending on the input parameters, which allows using it to program cylindrical and conical hole milling. The developed CONICALINT software is a visual addition to the developed technological cycle of hole milling. The developed CONICALINT software is a visual addition to the developed technological hole milling cycle, which allows generating a control G-code with a set of twelve arguments.

Simulation of continuous local bending-forming process by elastic composite tool

A continuous process of local bending-forming using an elastic composite tool is considered. The basic mathematical dependencies necessary to determine the shapes of the resulting workpiece and tool, as well as the law of tool movement, are given. The parameters of the Mooney-Rivlin model are calculated based on the conducted experiment on the elastic composite material upsetting. The results of modeling the aluminium AMg6 alloy billet deformation by shells made of the SKU-7L polyurethane and composite material are presented.

A study of microstructure and mechanical properties of friction stir welded joint of Al-Ce-Si-Mg aluminium alloy plates and optimization cum prediction techniques using Taguchi and ANN

In the current research work, the effect of friction stir welding (FSW) on joint strength and evolution of microstructure at the weld zone of the friction stir welded of Al-Ce-Si-Mg aluminium alloy (Al10Mg8Ce3.5Si and Al5Mg8Ce3.5Si) is studied. The experimentations demonstrated that the speed of tool revolution, contour of tool pin and tool movement rate have influence on the quality of the FSW joint of the alloy. It was noticed that the size of grains at nugget zone (NZ) depends upon the speed of tool spin, speed, of tool feed, tool pin contour and composition of the aluminium alloy. The grain size at the bottom of the NZ was discovered to be reducing when compared to that at the top of the NZ. It was also noted that highest hardness was reached at NZ. Lowest hardness was found at heat affected zone (HAZ) and most of the tensile specimens fractured at HAZ. The Taguchi orthogonal array-based design has demonstrated that the tool pin contour had the greatest influence in enhancing the joint strength, followed by speed of tool feed, material composition and speed of tool spin. A speed of revolution of tool of 1000 rpm, tool movement rate of 20 mm/min, triangular contour pin (TCP) tool and Al10Mg8Ce3.5Si aluminium alloy were concluded as the optimum variables of the process. The percentage contribution of each one of these input process parameters on optimum output quality characteristics was also found out and noticed to be lying well within the confidence interval of 95% suggested by the Taguchi design. The current study has shown that the prediction results with artificial neural network (ANN) are better compared to those predicted using statistical methods like Taguchi Techniques.

Засоби керування кроковим двигуном та вимірювання зусиль під час дослідження процесу згинання аркушевого матеріалу

The improvement of the equipment for the forming of the volumetric shape of packages and containers requires a detailed study of the phenomena in the folding process of sheet material with a complex structure (corrugated cardboard). A stand has been created to study process parameters, successful research on which should be provided by programmed control of tool movement and synchronous transfer of measured data to a computer for further processing. Moving tools (punches) are driven by a stepper motor. The movement of the stepper motor shaft is programmed to obtain both a uniform movement and movement according to a certain law, which can be different for the working and reverse moves. Forces are measured by a strain gauge clamp, the signal from which is also transmitted to external devices for visualization and processing. The basis of the motor control and measurement unit is the Arduino Uno microcontroller, which, together with the Arduino Nano controller and the analog-to-digital converter, significantly expands the functionality of the stand. The diagram and operation of the created control and measurement unit is described. A special program has been created to study the geometric, kinematic and power parameters of the process, the possibility of quickly changing the law of motion, providing various ratios and laws of motion to the working and reverse motion of punches. The laws of motion for the motor shaft are presented in it in the form of matrices of values, which are accessed before starting the measurement from the stand control panel. The parameters of the process of simultaneous folding of corrugated cardboard, which were investigated using a stand, are described. The developed measurement technique and means of controlling the movement of the stepper motor of the tool drive allowed to estimate the maximum effort, the nature of the change during the work cycle, to compare different types of material and folding modes. The result of determining the optimal parameters of the process of operational packaging & container formation is the creation of recommendations necessary for the design of modern energy-saving equipment.

Hot extrusion of high carbon steel cone hollow products

The work is devoted to researching a new method of hot direct-reverse extrusion of hollow conical products from high-carbon steel and determinated parameters for technological design. The considered method makes it possible to obtain in one step hollow products with different wall thickness in height, while the wall thickness in the upper part of the product can be greater than the thickness in the bottom part. The dimensions of the initial workpiece are determined by modeling using the finite element method, which ensures the simultaneous flow of metal in the forward and reverse directions during the process of forming the product, which reduces the deformation force. The use of this method also leads to a decrease in the heating of the deforming tool due to a decrease in the contact area of the deformed workpiece with the tool. The strain rate is determined to ensure the temperature interval of extrusion. The dependencies of the force of extrusion, removal of the punch from the deformed workpiece, pushing the product out of the matrix on the movement of the corresponding tool are established. The final shape and dimensions of the product with the distribution of temperature and deformations were found. For the maximum amount of extrusion force, the distributions of specific forces on the contacting surfaces of the punch, matrix, ejector and stress on the volume of the deformed workpiece were found. According to the obtained data, the technology of direct-reverse extrusion can be developed and implemented on universal press equipment, which has high productivity due to the reduction of the number of stamping steps. The design of the stamp for extruding products of certain sizes with forced cooling of the matrix is given.

Molecular dynamics simulation on crystal defects of single-crystal silicon during elliptical vibration cutting

In recent years, elliptical vibration cutting (EVC) has become a promising technique to fabricate high quality surface of single-crystal silicon. However, our understanding for its cutting mechanism, especially the evolution of the crystal defects in subsurface workpiece is insufficient. In this paper, molecular dynamics simulation was carried out to explore the formation mechanism of crystal defects in single-crystal silicon during EVC. A three-dimensional MD model was adopted to demonstrate the interaction between subsurface damage and tool movement in one vibration cycle. The results indicate that the formation mechanism of surface morphology including elastic recovery and side flow is greatly determined by the cutting stage in EVC. Meanwhile, the preferred slip motion during subsurface damage formation is distinct in the extrusion and shear stage. Furthermore, the influence of cutting temperature and speed on the formation of crystal defects was investigated. It is found that at elevated temperature, the proportion of the Shockley partial dislocations are apparently increased, and recrystallization process is apparently promoted on the interface of the distorted/crystal region. As the speed ratio increases, the generation and propagation of the crystal defects are suppressed, which is advantageous for suppressing the subsurface damage. These findings provide a comprehensive theoretical basis for improving the understanding in the formation mechanism of crystal defects of single-crystal silicon in EVC.

Atomic-scale analysis of mechanical and wear characteristics of AlCoCrFeNi high entropy alloy coating on Ni substrate

High entropy alloys (HEAs) are potential materials for coating due to their high hardness and wear resistance. This study builds molecular dynamics models to explore the mechanical characteristic and wear behavior of AlCoCrFeNi HEA coating on Ni substrate during scratching. The scratching force and friction coefficient of HEA coating on Ni are larger than the pure Ni due to the HEA coating with high strength and good adhesion. The Ni substrate protection mechanism exhibits deformation absorbed by the HEA coating, so the shear strain of HEA coating is more severe than the pure Ni. The Ni substrate is protected by HEA coating, which causes less wear, as shown by the higher wear atom number of pure Ni than the HEA coating on Ni. More resistance to tool motion as increased scratching depth results in an increased friction coefficient, while the friction coefficient decreases with increasing scratching speed due to the influence of thermal softening and strain rate hardening. The accumulation of scratched atoms and energy due to insufficient relaxation time around the tool leads to considerable deformation and temperature increase. The HEA coating reduces the wear of Ni substrate when the scratching depth is smaller than the HEA coating thickness.

Using AI and computer vision to analyze technical proficiency in robotic surgery.

Intraoperative skills assessment is time-consuming and subjective; an efficient and objective computer vision-based approach for feedback is desired. In this work, we aim to design and validate an interpretable automated method to evaluate technical proficiency using colorectal robotic surgery videos with artificial intelligence. 92 curated clips of peritoneal closure were characterized by both board-certified surgeons and a computer vision AI algorithm to compare the measures of surgical skill. For human ratings, six surgeons graded clips according to the GEARS assessment tool; for AI assessment, deep learning computer vision algorithms for surgical tool detection and tracking were developed and implemented. For the GEARS category of efficiency, we observe a positive correlation between human expert ratings of technical efficiency and AI-determined total tool movement (r = -0.72). Additionally, we show that more proficient surgeons perform closure with significantly less tool movement compared to less proficient surgeons (p < 0.001). For the GEARS category of bimanual dexterity, a positive correlation between expert ratings of bimanual dexterity and the AI model's calculated measure of bimanual movement based on simultaneous tool movement (r = 0.48) was also observed. On average, we also find that higher skill clips have significantly more simultaneous movement in both hands compared to lower skill clips (p < 0.001). In this study, measurements of technical proficiency extracted from AI algorithms are shown to correlate with those given by expert surgeons. Although we target measurements of efficiency and bimanual dexterity, this work suggests that artificial intelligence through computer vision holds promise for efficiently standardizing grading of surgical technique, which may help in surgical skills training.

Study on the mechanism affecting the quality of micro-hole in ultrasonic-assisted drilling of high-speed circuit boards

High-speed circuit boards are created to meet the high-speed signal transmission requirements of 5G communication technology, but the non-polar resins, flat glass fibers, and multiple and hard fillers used for this purpose have posed new challenges to their micro-hole processing. The quality of micro-hole has always been a decisive factor in board performance. Therefore, this paper aims at proposing a new processing method for improving the micro-hole drilling quality of high-speed circuit boards. By establishing an ultrasonic-assisted drilling tool motion model, analyzing the changes in drilling method, material deformation, chip breakage, and chip removal during ultrasonic-assisted drilling of printed circuit boards, the influence mechanism on micro-hole quality during ultrasound-assisted drilling is studied prudently. Besides, an experimental platform for ultrasonic-assisted drilling is designed and built, and single-factor experiments for verification of ultrasonic effects, optimization of drilling parameters, and orthogonal experiments for ultrasonic-assisted drilling of high-speed circuit boards are conducted on this platform. The experimental results show that the loading of ultrasonic vibration has made an obvious improvement on several machining defects including hole wall roughness, entrance burr, and nail head in micro-hole drilling of high-speed circuit boards. In addition, the influence order of each processing parameter and a better combination of them are discovered, which provides a theoretical research basis and instructions for the improvement of micro-hole quality of high-speed circuit boards.

Screw rotor manufacturing via 5-axis flank CNC machining using conical tools

We propose a new method for 5-axis flank computer numerically controlled (CNC) machining of screw rotors using conical tools. The flanks of screw rotors consist of helical surfaces, which predetermines the motion of the milling tool and reduces the search space for tool positioning to only 4-parametric family, which allows a quick search for good initial positions of a given conical tool. We initialize the search by looking at second order line contact between the tool and the helical flank of the rotor. Several positions of the tool are found, covering major part of the flank of the rotor, followed by global optimization that further reduces the tool-surface error and makes sure that there are no gaps between neighboring sweeps of the tool. We demonstrate our approach on several benchmark screw rotors, showing that our approach meets fine industrial tolerances with only few sweeps of the tool.

Development of cryogenic assisted machining strategy to reduce the burr formation during micro-milling of ductile material

Micro-milling is an inevitable machining process for the fabrication of products with complex shapes and high dimensional accuracy. However, this process usually needs post-processing operations to remove the burrs formed from the ductile materials. This research work focuses on the development of a micro-milling strategy to suppress the formation of burrs during machining and hence avoid post-processing operations, consequently reducing the cost of the products. During micro-milling, a LN2 jet was positioned ahead of the tool movement loci resulting in a change of microstructure at the top layer of the workpiece surface, enhancing its mechanical properties with the subsequent reduction of excessive plastic flow during the shearing process. Micro-hardness tests were performed below the top layer to conform the speculation and evaluate the effect of cryogenic treatment and a significant increase in micro-hardness was found. The experimental results reveal a significant decrease in the burrs formation due to the cryogenic treatment with an enhanced machining quality in terms of cutting forces, chip morphology and surface roughness.

스핀들의 가속도 데이터와 이송계의 변위 데이터를 이용한 스핀들의 변위 추정 알고리즘

In the existing machine tool field, the focus was on the displacement of the feed system from the viewpoint of the motion of the machine tool. The displacement of the tool or spindle of a machine tool is useful for developing various functions. In this study, using the acceleration data of the spindle, we proposed an algorithm that tracked the displacement of the spindle with respect to the pseudo-step waveform motion. In order to solve the bandwidth problem of the pseudo-step waveform, the displacement data measured by the motor encoder of the feed system was used. In addition, in order to solve the drift problem due to double integration, a new drift removal filter was proposed and a displacement estimation algorithm was implemented. In order to examine the performance and possibility of the proposed spindle displacement estimation algorithm, it was applied to a gantry-type engraver and its excellent performance was confirmed compared to other algorithms.

Piecewise Decoupling Tool Orientation Re-Scheduling for Four-Axis Reciprocal Toolpaths of Blades Based on S-θ Plane with Monotonicity Constraint

Reciprocal toolpaths with four-axis simultaneous motion of five-axis or four-axis machine tools are commonly used in the machining of blades which are widely applied in high-end equipment such as the aero-engine and the marine steam turbine. Due to the complex geometry of the blades, the tool orientation always suffers from frequent swing for this kind of toolpaths, which induces unnecessary acceleration/deceleration of the feed axes, thus degrading processing efficiency and quality. Although there are tool orientation optimization methods aiming at solving the above problem, they are mainly proposed for universal processing of the toolpaths for complex surfaces. Different from them, this paper proposes a piecewise decoupling tool orientation re-scheduling method for this kind of toolpath specifically, which takes full use of the characteristic of the reciprocal toolpaths of the blades, and takes the monotonous variation of rotation axes as an additional constraint. The re-scheduling process is realized based on the construction of a S-θ plane, where the scheduling problem is converted to the adjustment of a S-θ curve inside a feasible channel. Through two procedures, namely linearization scheduling and control-point assigning-based smoothing, the tool orientation path expressed by the S-θ curve can be effectively scheduled in a piecewise manner, and the smoothness between two adjacent pieces of the toolpaths can be ensured directly. The whole algorithm is lightweight and does not involve complex iterative operations or functional optimization solutions. Simulation and experimental tests verify the feasibility and superiority of this method. The results show that the machining efficiency of the blade is improved by 24.5%, due to the reduction of the requirement on highest feed-axis kinematics parameters after rescheduling. In addition, compared with the existing methods, the proposed method not only can improve the dynamics of feed axes in multi-axis machining, but also has advantages in computational complexity and monotonic variation property of the tool orientation.

유한요소해석 모델을 이용한 스핀들 유닛의 열변형 예측

High-speed machining is essential in the manufacturing field, and it involves the removal of material through rotational and translational tool motion. Existing methods used for simulating the thermomechanical behavior of spindle systems in machining require extensive calculations owing to the geometry complexity and thermomechanical properties. This article presents a simplified model of an angular contact ball bearing and a simulation method for predicting the thermomechanical behavior of a spindle system. A commercially available software, ANSYS, was used to analyze the coupled behavior. The Matrix27 element was adopted to substitute the stiffness/damping characteristics of the angular contact ball bearing. Validated values of the thermal contact conductance for the contact option were adjusted to match the measured thermal characteristics of angular contact ball bearings. Experimental measurements of the temperature and deformation of a spindle were used to verify the simulated results for several preload conditions.

Design, development and evaluation of an ergonomically designed dual-use mechanism for robot-assisted cardiovascular intervention.

Robot-assisted cardiovascular intervention has been recently developed, which enables interventionists to avoid x-ray radiation and improve their comfort. However, there are still some challenges in the robotic design, such as the inability of the interventionist to freely perform natural clinical techniques and the limited motion travel of the interventional tool. To overcome these challenges, this paper proposes an ergonomically designed dual-use mechanism for cardiovascular intervention (DMCI). DMCI can work as an ergonomic interface or a compact slave robot with unlimited motion travel. Our kinematic analysis of DMCI includes motion decoupling and coupling. Motion decoupling decomposes the translation and rotation from the interventionist's natural clinical actions at the master side. Motion coupling can calculate the input pulses of motors according to the desired rotation and translation, thus composing the motion of the intervention tool at the slave side. Our kinematic analysis of DMCI has been experimentally verified, where the overall mean rotational errors are all less than 1° and translational errors are all less than 1mm. We also evaluated the performance of the DMCI-based master-slave system, where the overall rotational and translational errors are 0.821 ± 0.753° and 0.608 ± 0.512mm. Moreover, operators were found to be generally more efficient when using the DMCI-based interface compared to the conventional joystick. We have validated our kinematic analysis of DMCI. The master-slave teleoperation experiment demonstrated that operators can freely perform natural clinical techniques through the DMCI-based interface, and the slave robot can replicate the operators' manipulation at the master side well.

Vibrational Motion of Soil-Compaction Tools in Agriculture

Vibrational Motion of Soil-Compaction Tools in Agriculture

Active Chatter Mitigation by Optimal Control of Regenerative Machining Process Dynamics

Chatter vibrations are a type of self-exited vibrations observed in many subtractive manufacturing processes. They limit achievable material remove rate (MRR), reduce tool life, resulting in poor surface finish, and even damage the manufacturing equipment. This article proposes a novel control system design for machine tool feed drives, which modulates cutting tool motion based on the in-process vibration measurements to mitigate chatter vibrations. The proposed approach has two key contributions. First, as opposed to introducing modal damping to the structure, the proposed approach stabilizes machining process dynamics by controlling its governing delay differential equation. H∞ control framework is used to design the controller and ensures robust process stability. The controller design problem is postulated as a convex optimization problem with linear matrix inequalities, which is solved to global optimality. Second, the proposed controller is implemented as an add-on compensator that works jointly with an existing servo motion control system to realize both positioning and chatter vibration control. Experimental validations are conducted on a lathe equipped with a fast tool servo actuator. It is shown that regenerative chatter vibrations in the orthogonal turning process can be suppressed robustly and up to five times increase in MRR (productivity) can be achieved.

Five-axis toolpath planning for aero-integral blisk cavities

Integral blisks generally made of high-temperature alloys (such as titanium alloys) are important components in aero-engines. During machining, the tool load is large and the tool wear is serious. Because trochoidal milling can maintain a small contact angle between the tool and the workpiece during the cutting process, it is widely used in the processing of complex aviation blisks. However, when the traditional U-shaped trochoidal toolpath or the maximum inscribed trochoidal toolpath is applied, there are high cutting vibration and low efficiency. Therefore, this paper proposes a new five-axis trochoidal side milling strategy, which is suitable for machining more complex three-dimensional cavities by adjusting the shape of the inscribed arc. Different from the traditional trochoidal pattern, the proposed method can generate a spatial UV parameter line-based tool path from a given complex 3D cavity and map it to the machining surface. In addition, a scheme to optimize the tool orientation of the boundary tool is proposed, so that the machine tool motion axis can run smoothly, thus the blisk can be roughened efficiently. Finally, the proposed schemes are verified by computer simulation and physical cutting experiments, and results show the validity and effectiveness.

Investigation of AA6061-T6's mechanical and microstructural properties by modification on the tool path in friction stir welding

Friction stir welding employs an axis-lead tool movement pattern, in which the tool revolves around its axis while moving in the xy plane at the same time. As a process, every tool may come into prolonged contact with the workpiece. Because of this, the two parent materials are completely mixed, yielding a high-quality weld. This study attempted to characterize the butt joints of AA6061-T6, 6 mm thick sheets using axis-lead (xy tool movement) on friction stir welding. The importance of specific tool movement patterns was examined by mechanical testing, energy-dispersive X-ray analysis, and microstructure analysis. A combination of 1500 rpm, 1.0 mm step size, and 150 mm/minute weaving rate was found to have excellent mechanical attributes. By combining a square wave tool pattern with a 1.0 mm step size, microstructural studies revealed improved grain refinement and homogeneous dispersion of micro components. The results revealed that 1.0 step size /150 mm/minute /1200 rpm combination parameters exhibited the highest tensile strength of 232 N/mm2 and hardness value of 76 HV. The use of a square wave tool pattern provided improved grain refinement and homogeneous dispersion of micro components and confirmed the performance of the axis-lead approach in a normal manner.