High-speed Machining Center Research Articles

Rotation error separation of a UTF300 high-speed and precision motorized spindle

To improve the measurement accuracy of high-speed and precision motorized spindle rotary error as the research objective, based on the three-point method, an error separation model and an objective optimization function for noise-containing signals are developed. To improve the convergence speed, globally optimize the model objectives, and obtain the best optimization region of the sensor mounting angle, it is proposed that an enhanced adaptive particle swarm optimization algorithm be used. With the improved particle swarm algorithm, the convergence speed was greater than that of the primary particle swarm algorithm by more than 50%. The spindle radial rotation error was experimentally measured and separated using a high-speed vertical machining center, and the deviation between the separation result and the experimental rotation error was 4.5%, indicating that the separation result's accuracy was high. It also proved the correctness and feasibility of the optimization algorithm.

Design and optimization of high-precision servo control system in precision positioning technology

Abstract High-precision control technology, as a general technology in the field of manufacturing and assembly, is widely used in high-end manufacturing equipment such as chip packaging equipment and high-speed CNC machining centers. In this thesis, a permanent magnet synchronous motor is used as the actuator motor of a high-precision servo control system, and vector control strategy and sliding mode observer are adopted to study and realize the servo control of permanent magnet synchronous motor based on sliding mode observer. The current, speed, and position simulation experiments of the high-precision servo control method are also carried out to compare the positioning accuracy before and after the use of the servo control method and to study the performance of the method in precision positioning. The experiments prove the correctness and effectiveness of the SMO-based PMSM high-precision servo control method and the current response speed of the servo control in this paper is fast, and the speed and position estimation errors are maintained within 1.6 r/min and 0.15 rad in steady state condition, and within 20 r/min and 20 rad in the sudden-change condition, which is able to contribute to 11.91% and 19.30% of the machine’s X-axis and Y-axis positioning accuracy improvement. The SMO-based PMSM high-precision servo control method has high steady-state accuracy and immunity to disturbances and can be used for the precision positioning of machine systems.

Deep-Learning Method Based on 1D Convolutional Neural Network for Intelligent Fault Diagnosis of Rotating Machines

Fault diagnosis in high-speed machining centers (HSM) is critical in manufacturing systems, since early detection saves a substantial amount of time and money. It is known that 42% of failures in these centers occur in rotatory machineries, such as spindles, in which, the bearings are fundamental elements for effective operation. Nowadays, there are several machine- and deep-learning methods to diagnose the faults. To improve the performance of those traditional machine-learning tools, a deep-learning network that works on raw signals, which do not require previous analysis, has been proposed. The 1D Convolutional Neural Network (CNN) proposed model showed great capacity of adapting to three types of configurations and three different databases, despite a training set with a smaller number of categories. The network still detected faults at early damage stages. Additionally, the low computational cost shows the Deep-Learning Neural Network’s (DLNN) suitability for real-time applications in industry. The proposed structure reached a precision of 99%; real-time processing was around 8 ms per signal, and standard deviation of repeatability was 0.25%.

Modelling of machining center vibration stability by the D-partitions method

The stability of operation, vibration-free processing of products various types at high-speed machining centers suggests the improvement of research in the field of the dynamics of machine tools and their main forming units. The three-dimensional models of the forming spindle node and the corner table of the machining center for the drilling-milling-boring type in the CAD environment KOMPAS-3D have been developed. An algorithm for analyzing the dynamic quality of the machine elastic parts based on the constructed static and frequency formular in the mathematical environment MAPLE is proposed. Programs have been developed and graphs of the main frequency characteristics and the hodograph of the transfer function for the spindle node in the specialized Signal Processing module have been obtained. The method of D-partitions using to estimate the vibration stability of the forming units on an example of 4 coordinate milling machining centers is introduced. Experiments on two variants of technological adjustments with different dimensions of the tool block (the cantilever part of the spindle assembly) were carried out. The analysis of stability in the plane of the cutting process optimized parameter (specific cutting force) was carried out. The region and the boundary of the stable functioning of the machine and, on this basis, the optimum modes of machining by the criterion of vibration stability are revealed.

Feature level fusion of vibration and acoustic emission signals in tool condition monitoring using machine learning classifiers

To implement the tool condition monitoring system in a metal cutting process, it is necessary to have sensors which will be able to detect the tool conditions to initiate remedial action. There are different signals for monitoring the cutting process which may require different sensors and signal processing techniques. Each of these signals is capable of providing information about the process at different reliability level. To arrive a good, reliable and robust decision, it is necessary to integrate the features of the different signals captured by the sensors. In this paper, an attempt is made to fuse the features of acoustic emission and vibration signals captured in a precision high speed machining center for monitoring the tool conditions. Tool conditions are classified using machine learning classifiers. The classification efficiency of machine learning algorithms are studied in time-domain, frequencydomain and time-frequency domain by feature level fusion of features extracted from vibration and acoustic emission signature.

Impact of Cutting Environments on Sustainable Machining of H13 Tool Steel Alloy

The use of electrical energy and coolants/lubricants has been widely reported in mechanical machining. However, increased research and process innovation in high speed machining has brought about optimised manufacturing cycle times. This has promoted dry machining and the use of minimum quantity lubrication (MQL). This work understudies the impact of different cutting environments in machining H13 tool steel alloys at transition speed regime with emphasis on sustainable machining of the alloy. To achieve this, end milling tests were performed on AISI H13 steel alloy (192 BHN) on a MIKRON HSM 400 high speed machining centre using milling inserts. After each cutting pass, the milling insert was removed for tool wear measurement on the digital microscope. The electrical power consumed was measured with the Fluke 435 power clamp meter mounted on the three phase cable at the back of the machine. It was discovered that MQL has a promising advantage in terms of tool life with 25 minutes of machining, net power requirement of 10% when compared to dry cutting, and environmental benefits when machining H13 tool steel alloy. This work is fundamentally important in assessing the environmental credentials and resource efficiency regime for green machining of H13 tool steel alloysKeywords— H13 tool steel, green machining, process optimization, tool life, cutting environments, energy consumption

Intelligent Fault Diagnosis for Rotating Machines Using Deep Learning

Abstract The diagnosis of failures in high-speed machining centers and other rotary machines is critical in manufacturing systems, because early detection can save a representative amount of time and cost. Fault diagnosis systems generally have two blocks: feature extraction and classification. Feature extraction affects the performance of the prediction model, and essential information is extracted by identifying high-level abstract and representative characteristics. Deep learning (DL) provides an effective way to extract the characteristics of raw data without prior knowledge, compared with traditional machine learning (ML) methods. A feature learning approach was applied using one-dimensional (1-D) convolutional neural networks (CNN) that works directly with raw vibration signals. The network structure consists of small convolutional kernels to perform a nonlinear mapping and extract features; the classifier is a softmax layer. The method has achieved satisfactory performance in terms of prediction accuracy that reaches ∼99 % and ∼97 % using a standard bearings database: the processing time is suitable for real-time applications with ∼8 ms per signal, and the repeatability has a low standard deviation <2 % and achieves an acceptable network generalization capability.

Necessity of multidimensional evaluation of the high-speed ball-end milled surface of hardened AISI D2 steel from a wear resistance perspective

This paper focuses on revealing the anisotropy of surface integrity and wear resistance of high-speed ball-end milled surfaces of hardened cold work die steel AISI D2. Dry milling tests were performed on a five-axis high-speed machining center by using a two-edged coated solid carbide ball-end milling cutter. Then, wear resistance of a hard milled surface was evaluated through block-on-ring wear tests under unlubricated condition. Results showed that ball-end milled surfaces present anisotropic characteristics in terms of surface topography, subsurface microhardness, and yield strength. Moreover, the wear resistance for ball-end milled surfaces shows dependence on sliding direction because of the anisotropy of surface integrity. Benefiting from surface work hardening, wear loss for the hard milled surface was at least 62% less than that for polished ones in the initial wear stage (10 min). However, the subsurface softening zone induced by a high-speed hard milling process has poor wear resistance due to the decrease of microhardness and yield strength. This study indicates the necessity of multidimensional evaluation for high-speed ball-end milled surfaces and the possibility of improving wear behavior by selecting appropriate sliding direction.

Microstructural evolution in Ti-6Al-4V alloy joints using the process of friction stir spot welding

ABSTRACTFriction Stir Spot Welding (FSSW) is a subject that has recently gained interest and been developed, mainly in Titanium alloys, since there are existing studies on alloys of aluminium, magnesium, steels and polymers. Titanium alloys are widely used in the aeronautical industry, mainly as components of undercarriages for commercial planes. This work focuses on the Ti-6Al-4V alloy; this type of alloy has alpha (α) and beta (β) phases and provided better balance in terms of the mechanical properties of hardness and tensile stress. The FSSW process was performed using a high-speed machining centre, using a rotational speed of 500 RPM, a plunge speed of the tool of 2 mm/s and 3 s as dwell time, on plates with a thickness of 1.5 mm and an overlap length of 20 mm. The results showed the effect of the variables of the FSSW welding process on the microstructure of the Ti–6Al–4V alloy caused by the thermal effect and the plastic deformation of the welding process, concluding that the right combination of parameters provides a joint without any defects.

Development and experimental validation of a mechanistic model of cutting forces in micro- ball end milling of full slots

ABSTRACTIn the present work, a mechanistic model of cutting forces is developed with a novel approach to arrive at the cutting edge geometry as well as the cutting mechanics. The geometry of cutting elements derived and verified using a virtual tool generated in CAD environment is considered. The cutting and edge force coefficients at every discrete point on the cutting edge of micro-ball end mill are established in a novel way from the basic metal cutting principles and fundamental properties of materials, considering edge radius and material strengthening effects. Further, measured edge radius is used in the model. Full slot micro-ball end milling experiments are conducted on a high-precision high-speed machining center using a 0.4 mm diameter tungsten carbide tool and cutting forces are measured using a high-sensitive piezo-electric dynamometer. It is established that the predicted as well as experimental cutting forces are higher at very low uncut chip thickness in comparison with the cutting edge radius in micro-ball end milling also. Amplitudes of cutting forces and instantaneous values with incremental rotation of the tool are compared with predicted values over two revolutions for validation of proposed model.

Research on Thermal Deformation of Feed System for High-speed Vertical Machining Center

Thermal deformation is one of the most significant factors influencing the precision of NC machining. This paper studies the thermal deformation mechanism of ball screw feed system (BSFS) for high-speed vertical machining center. Based on the thermal condition of feed system, the temperature field model of BSFS is established. By changing machining parameters such as rotational speed, loads and the flow rate of coolant, different results of thermal deformation are obtained. By analyzing the effects of machining parameters, we get the influence factors of BSFS’s thermal deformation. This work can help us reduce thermal deformation effectively, and improve the precision of NC machining.

Stiffness optimization for high-speed double-locking toolholder-spindle joint using fractal theory

The higher contact stiffness of the double-locking toolholder-spindle (BTF40-type) joint is helpful in improving the machining accuracy and cutting stability of high-speed machining center. In this article, an optimization technique is introduced to obtain the high contact stiffness of BTF40 toolholder-spindle joint at the high speed. The torsional and radial stiffness at 25,000 r/min can be obtained by using the macro–micro hybrid method. The contact ratio of taper surface and maximum nodal pressure of contact surfaces is used as constraint conditions to ensure the connection reliability and the working life of the toolholder-spindle system. The particle swarm optimization algorithm with suitable parameters for this problem is used to search the optimal stiffness of joint automatically. The optimal stiffness of joint and pressure distribution of taper surface are compared with the initial values for validating the effectiveness of the optimization results. This research is valuable for guiding the application of BTF-type toolholder-spindle system at the high speed 25,000 r/min.

Conventional Orthogonal Cutting Machining on Unidirectional Fibre Reinforced Plastics

The results of orthogonal cutting tests on unidirectional carbon and glass fibre reinforced plastics are presented. The specimens were under shape of rectangular plates, circular disks and cylinders with different fibre architectures and a milling machine, a lathe machine and a five-axis high-speed vertical machining centre, were used for the experimental tests. The cutting speed was varied. During the tests, performed at low cutting speed, avoiding thermal effects, and high speed, to investigate about the effect of the cutting velocity on the cut quality, the fibre orientation respect to the cutting direction, the tool rake angle and the depth of cut were varied to investigate their influence on the phenomenon. A high speed steel tool in different geometries, was used.The mechanisms of chip formation and the cutting quality were investigated. A tentative to correlate the mechanisms of chip formation and cutting forces signals was done. Since the anisotropy, the mechanisms of chip formation consists of different failure modes occurring simultaneously and their identification, on the basis of the cutting force evolution, is very complex. Only in particular conditions, the features of cutting forces allow a precise identification of the chip development and detachment.The results indicated that the fibre orientation respect to the cutting direction determines the mechanisms of chip formation and influences the cutting quality. It was noted that for fibre orientation higher than 60°, the quality of the surface was revealed unacceptable. These conclusions were obtained independently of the particular shape of specimen tested and of the speed adopted.

Evolución Microestructural en Uniones de la Aleación Ti-6Al-4V Mediante el Proceso de Soldadura de Punto por Fricción-agitación

Resumen La soldadura de punto por fricción-agitación (Friction Stir Spot Welding, FSSW) es un tema de reciente desarrollo e interés, principalmente en aleaciones de Titanio, ya que existen estudios previos realizados en aleaciones de aluminio, magnesio, aceros y polímeros. Las aleaciones de Titanio tienen una amplia aplicación en la industria aeronáutica, principalmente como componentes en el tren de aterrizaje en aviones comerciales, por lo cual este trabajo se centra en la aleación Ti-6Al-4V, este tipo de aleación presenta fases alfa (α) y beta (β), brindado mejor balance en propiedades mecánicas de dureza y esfuerzo a la tensión. El proceso FSSW se realizó mediante un centro de maquinado de alta velocidad, utilizando una velocidad de rotación de 500 RPM, una velocidad de penetración de la herramienta de 2 mm/s y 3 s en tiempo de sostenimiento, en láminas con un espesor de 1,5 mm y una longitud de traslape de 20 mm. Los resultados mostraron el efecto de las variables del proceso de soldadura FSSW sobre la microestructura de la aleación Ti-6Al-4V ocasionada por el efecto térmico y la deformación plástica del proceso de la soldadura, concluyendo que una adecuada combinación de parámetros permite realizar una unión sin defectos.

A synthetical modelling for machine tool feed drives

The machine dynamic performance depends on not only the mechanical structure and components but also the control system and electronic drives. This paper proposes a holistic integrated dynamic design and modelling approach, which supports analysis and optimisation of the feed drive system dynamic performance at the early design stage. The modelling and simulation cover the dynamics of the machine structure, moving components, control system and the machining process. Based on the theoretical derivation, a co-simulation platform for machining centre (MC) has been established and it consists of the generation of tool path instructions, AC servo control system, multi-body system dynamics and elasticity. Using the integrated platform, a real-time simulation of a CAM trajectory curve is presented, whose result indicates that the proposed simulation platform can be used to analyse and evaluate overall dynamic characteristics of high-speed MC.

Research on 5 Axis Tool-Path Based on Constant Shearing Stress for Milling Thin-Wall Ceramics

Ceramics is a material of hardness and brittle, so crack arises easily when it is machined. To improve its cutting performance and enhance machining quality, a dynamic model based on constant-shearing-stress is built for milling ceramics, therefore some cutting parameters can be optimized by the model for no crack machining; moreover, an algorithm of 5 axis tool-path designed with constant-shearing-stress is put forward. According to the model and the algorithm, 5 axis tool paths of decreasing-cutting-depth and decreasing-feed-rate are realized; these are really accurate and smooth through VERICUT software simulating. Using Mikron high-speed machining center, several experiments were done to find a good method of crack control in milling thin-wall ceramics. The results show that the experiment based on the 5 axis tool paths with high pressure air cooling and regional cutting is rather successful because of no cracking in cutting thin-wall ceramics, compared to others.

Surface fractal topography-based contact stiffness determination of spindle–toolholder joint

Accurate modeling of contact stiffness is crucial in predicting the dynamic behavior and chatter vibration of spindle–toolholder system for high-speed machining centers. This paper presents a fractal theory-based contact model of spindle–toolholder joint to obtain the contact stiffness and its real contact area. Topography of the contact surfaces of spindle–toolholder joint is fractal featured and determined by fractal parameters. Asperities in micro-scale are considered as elastic or plastic deformation. Then, the contact stiffness, the real contact area, the elastic contact force, and the plastic contact force of the whole contact surface are calculated by integrating the micro asperities. The relationship of the contact stiffness and the drawbar force follows a power law, in which the power index is determined by the fractal parameters. Experiments are conducted to verify the efficiency of the proposed model. The results from the fractal contact model of spindle–toolholder joint have good agreement with those of experiments.

A Spiral Toolpath for Machining of Elliptical Pockets Using Partial Differential Equation

In the present work, a method for creating spiral toolpath for CNC machining of elliptical pockets using Partial Differential Equation (PDE) is carried out. Algorithms are developed using MATLAB® software for pre-processing, solving and post-processing of PDE. The toolpath begins at the center of the pocket as spiral and slowly morphs to the shape of elliptical pocket boundary as the tool gradually progress towards the boundary. The spiral toolpath for elliptical pockets with ratio of minor axis to major axis as 1.0, 0.8, 0.6, 0.4 and 0.2 are generated and their toolpath lengths are compared. The results show that as the ratio of minor axis to major axis of the ellipse decreases, the toolpath length increases drastically, for the same area of the pocket machined. The experimental validation of toolpath was carried out on high speed machining center.

Friction Model Identification Based on Robust Estimation of the Linear Motor

Linear motor is one of the most important drive units for high-speed machining centers. Nonlinear friction is an important factor affecting the positioning accuracy of linear motor drive system. One of the most important topics for controlling linear motor is how to accurately estimate the parameters of the friction and effectively compensate it. In this paper, to solve the problem existing in traditional estimation methods that the estimation accuracy is not high enough, a novel estimation method based on robust estimation algorithm is proposed. The proposed method can effectively void the modeling error of the least squares algorithm, which will greatly improve the estimation accuracy of the nonlinear LuGre friction model. First, LuGre friction model is introduced in linear motor servo system; then, the robust estimator is design to identify the static and dynamic friction parameters in the LuGre model. Finally, simulation results verify the effective- ness of the proposed estimation scheme.

Design of Special Ultrasonic Device in Composite Materials Processing

According to the unique advantage of the ultrasonic vibration processing in brittle materials, a new processing method, combining ultrasonic vibration and high-speed milling, was presented in this paper, to investigate an adaptation of high-quality and efficient processing in carbon fiber composites. Based on vibration theory, the special ultrasonic vibration milling device suitable for high speed machining centers was designed. Taking into account of a range of issues existing in contact electrical transport under high-speed processing, the contactless induction power transmission system was developed, and the impacts of load, frequency, air gap size as well as the existence of compensation on the transmission performance was discussed. The study shows that carbon fiber composites processed under ultrasonic vibration with high speed, high quality and high efficiency are adapted. Keywords: ultrasonic vibration milling; carbon fiber composites; contactless induction; tool wear