Performance Of Machine Tool Research Articles

Geometric Accuracy of Large Machine Tools

This article describes the issue of geometric accuracy of large machine tools. The operation and maintenance of large CNC machine tools is usually affected by a number of aspects related to large workpieces and spaces at the machine installation site. It is the size of the working space and the large dimensions of the production halls that very often have a major impact on the operation of these machines. Large workpieces remain clamped on the machine for weeks and are therefore affected by the changing environment. The presented study captures and presents changes in the ambient conditions of a large CNC machine tool, including its effects on the geometric accuracy of the machine. The first part of the article describes the geometric errors of the assessed machine. The second part also presents selected ambient conditions of the machine with the resulting measured data. The last part of the presented study summarizes the conclusions describing the influence of ambient conditions on the geometric accuracy of the machine.

Research on automatic monitoring method of face milling cutter wear based on dynamic image sequence

Tool wear is an important factor affecting the quality of finished products, productivity, and the normal operation of machine tools, so tool condition monitoring (TCM) has become a research hotpot in the field of intelligent manufacturing. Compared with traditional monitoring methods, vision-based tool condition monitoring methods are more accurate and intuitive. However, the existing visual monitoring method requires manual adjustment of the tool position, and the degree of automation needs to be improved. Therefore, this paper proposes automatic face milling cutter condition monitoring method based on dynamic image sequence. We first acquire the dynamic image sequence of face milling cutter with the spindle rotating, then forward the dynamic image sequence to the image processing module to extract target area. And the images after image processing are propagated to the image selection module to obtain the image to be measured. Finally, forward the selected image to wear value measurement module to obtain the wear value. The presented automatic face milling cutter condition monitoring method is verified on a five-axis milling center. Compared with the direct measurement results of industrial digital microscope, the measurement error of the proposed method is within 4%, which is a reliable and effective online monitoring method for milling cutter wear.

Dynamic characteristics and energy consumption modelling of machine tools based on bond graph theory

Fossil fuel depletion, air pollution, and climate change are imposing great pressure on industrial sectors, especially for manufacturing sectors. Energy consumption modelling is an important measure to promote the energy efficiency in manufacturing, which offers the fundamental basis for energy efficiency-related optimization. Although dynamic characteristics have a significant effect on operation of machine tools, traditional energy consumption models hardly take dynamic characteristics into consideration. This paper takes the feed system as an example and proposes a dynamic energy consumption model of machine tools with bond graph theory. Based on the structure of feed system, the proposed model is firstly expressed to a physical model and the bond graph model are established according to the law of energy conservation. Subsequently, with the augmented bond graph model, mathematical models of dynamic characteristics and energy consumption are proposed with state variables. Finally, the simulation and analysis of the proposed model are given. Results show that the proposed dynamic characteristics model and energy consumption model based on bond graph theory are reasonable and effective. Additionally, the proposed model can be used to explore the correlation between energy-consuming components and energy consumption of machine tools for realizing the high energy efficiency design of machine tools.

Investigation on Normal Dynamic Contact Characteristics of Mechanical Interface of Machine Tools

The dynamic contact characteristics of mechanical interface significantly impact the performance of machine tools. The static contact behaviors of mechanical interface have been studied. However, most mechanical interfaces are exposed to dynamic load. It is necessary to study the dynamic contact characteristics of mechanical interface. A normal dynamic microcosmic contact model is built using the statistical method, and the interactional effects of adjacent asperities are considered. The influences of the normal preload, vibrational frequency and displacement amplitude on normal contact stiffness and damping of mechanical interface are revealed. The predicted contact stiffness and damping of mechanical interface are verified by a series of simulations and experiments.

Lightweight heavy-duty CNC horizontal lathe based on particle damping materials

With the development of high-precision, high-speed, and green computer numerical controlled (CNC) machine tools, the advantages of lightweight versions of such tools are becoming increasingly obvious. Taking a ZN-XK2840 CNC lathe as an example, in this study a lightweight design method is proposed for CNC machine tools based on particle damping technology. The static performance of conventional CNC machine tools is analyzed using a finite element method, and the wall thickness is optimized. Then, the dynamic characteristics of conventional CNC machine tools, such as the modal characteristics and harmonic response, are analyzed. The particle damping technology can effectively reduce the vibration of the machine structure in the vibration transmission path. In this paper, the discrete element dynamic method is used for the finite element model of a lathe. Based on a traditional machine tool, the dynamic characteristics of the machine tool structure with a particle damper are analyzed. The lathe with a particle damper is manufactured according to the lightweight design. The acceleration and displacement amplitudes of lightweight machine tools are smaller than those of traditional machine tools. The third-order natural frequency of lightweight CNC machine bed is increased by about 28.49%, and the vibration amplitude of harmonic response is reduced by 3.38%. Compared with the similar machine tools used in industry, the light CNC lathe with particle damper reduces the weight by 50.8% on average.

Stiffness matching method for the ball screw feed drive system of machine tools

The static stiffness of machine tools plays an important role in ensuring the performance of machine tools and improving the machining accuracy. In the design stage, stiffness matching provides a theoretical basis for determining the stiffness of each component. This study proposed a stiffness matching design method for machine tools. First, the deformation model of machine tools is established on the basis of the state space model. Through force analysis, the relationships between the deformations and stiffness of each part are determined. Second, the stiffness model of the machine tool is established by combining these relationships with the deformation model. Third, the objective function is determined by performing sensitivity analysis after obtaining the stiffness range. The stiffness matching design results are obtained through multi-objective linear programming. Lastly, the stiffness simulations, theoretical model, and experimental results are analyzed. The maximum errors among the experimental, simulation, and theoretical results (18.8 % and 19.9 %) are within the acceptable range. In conclusion, the proposed method is suitable for designing ball screw feed drive systems that requires rigidity.

Novel methodology for the measurement and identification for quasi-static stiffness of five-axis machine tools

Stiffness is an important characteristic of production machinery, as it contributes to its ability to precisely maintain the pose between a tool center point with respect to a workpiece under load. For machine tools, it directly affects the geometric dimensions and surface properties of the parts, i.e. how closely the parts match their design drawings. This work presents a novel measurement procedure to measure and identify full translational stiffness matrices of 5-axis machining centers using quasi-static circular trajectories. The measurement procedure consists of inducing quasi-static loads, which vary in magnitude and direction, at the tool center point of the machine tool using the Loaded Double Ball Bar and measuring the displacement with three Linear Variable Differential Transformers while the spindle tracks the circular trajectories inscribed by the movement of the rotary axis. The work outlines and quantifies the main components of the uncertainty budget related to the measurement of the translational stiffness matrices. The measurement procedure is implemented in a case study on a 5-axis machining center. Finally, the manuscript concludes with a discussion on the utility value of the translational stiffness matrix for the design and operation of machine tools as well as the possibility to expand the measurement procedure to a calibration procedure for 5-axis machining centers to analyze the translational and rotational stiffness.

An improved static stiffness analysis model for machine tools based on virtual material method

The static stiffness of machine tools can be used for the analysis of thermal deformation because of the uneven temperature field and can further be applied in the thermal error compensation. The prediction of static performance of machine tools is fundamental and essential during the design period. The purpose of this paper is to establish a precise static stiffness model for machine tools. Different from previous models, the proposed method in this paper, basing on the Fractal Geometry, takes both the elastoplastic deformation mechanism and friction into account. By analyzing the normal stiffness and tangential stiffness of joints, equivalent virtual material parameters are acquired for the finite element analysis calculation. An experimental set-up has been established to test X, Y and Z directional deformation of a vertical machine center with a magnitude of 200 kgf load applied to the node of the spindle along the respective direction. The results demonstrate that the proposed model can accurately simulate static characteristics of machine tools.

Machine tool architecture selection at the preliminary design stage: application to hard material machining

Abstract The preliminary design stage ensures to evaluate machine tool performances according to the simulation of reduced models. Performance criteria are defined regarding the attempted machining process requirements. In our case, we study the problem of machine tool design for hard metal cutting, where a high level of stiffness is required. In this context, this paper’s aim is to introduce a new methodology of machine tool architectures modeling, optimization, and selection with regards to their stiffness and dynamic performances at the preliminary design stage. However, this type of study requires a quantitative evaluation of performance indicators. Studied machine tool structures are modelled with simplified shape parts. The dimensions of these parts are defined as design variables. Afterward, for each considered architecture, parametric design optimization is performed to minimize its mass under the constraint of a minimal attempted stiffness all over the workspace. This approach allowed restricting the total number of machine tool architectures to be detailed further and analyzed more accurately. In a first time, the paper includes an illustration of the developed methodology through an example of machine tool architecture evaluation and optimization. In a second time, the method is used to compare different kinds of machine tool architectures regarding their ability to be light for an attempted stiffness.

Special Issue on Machine Accuracy Evaluation

The accuracy of a three-dimensional (3D) positioning system can ultimately be evaluated via measurement of a 3D vector between command and actual end-effector positions at arbitrary points over the entire workspace. This is a simple, yet challenging, metrological problem. The motion accuracy of a machine tool is traditionally evaluated on an axis-to-axis basis, with every error motion of every axis being independently measured as part of a one-dimensional measurement process in a different setup. Toward the ultimate goal of 3D position measurement over the entire workspace, research efforts have offered several new, practical measurement technologies. This special issue covers the technical and academic efforts regarding the evaluation of machine tool accuracy. The papers in this special issue clarify the latest research frontiers regarding machine tool accuracy from a metrological viewpoint. In the first paper, by Montavon et al., error calibration technologies and their management are reviewed within the Internet of production concept. Long-term accuracy monitoring and management are clearly among the most crucial technical challenges faced regarding machine tools, and the work by Xing et al. is related to them. Ibaraki et al. presented machining tests to evaluate the thermal distortion of a machine tool. Peukert et al. studied the dynamic interaction between machine tools and their foundations. Various 3D measurement schemes for determining machine error motions have been investigated by many researchers, and some have been implemented in industrial applications. Kenno et al. and Florussen et al. investigated 3D measurement using the R-test for five-axis machines. Miller et al. studied simultaneous measurement of six-degree-of-freedom error motions of a linear axis. Nagao et al. presented an error calibration method for a parallel kinematic machine tool. The editors appreciate the contributions of all the authors, as well as the work of the reviewers. We are confident that this special issue will further encourage research and engineering work for improving the accuracy and performance of machine tools.

Study on chuck performance of ultra-precision machine tool based on CFRP pair bionic structure

Based on the hardness inspiration of the tortoise structure, this study analyzes the innovative application of the parts of ultra-precision machine tools. Aiming at the problems of machining accuracy, efficiency, and machine cost of ultra-precision machine tools, an innovative design and analysis of chuck of ultra-precision machine tools based on carbon fiber-reinforced polymer and its application to turtle shell structure is proposed. Firstly, the G-element model of carbon fiber composites is deduced and analyzed by layered experiments. Secondly, the original parts of ultra-precision machine tool are simulated and analyzed, and the main sixth-order modal of carbon fiber turtle shell structure is deduced. Finally, the structural parameters of carbon fiber composite “turtle shell” were applied to the surface of chuck claw of ultra-precision machine tool, and the results were compared and analyzed. The results show that the maximum displacements of the chuck are all located at the front of the chuck and the maximum displacements and stresses of the chuck are smaller than those of the original chuck. The maximum stress is the most obvious, the difference is about 240.27 MPa, and the first-order mode increases by 23.4% compared with the original mode. The overall relative mass was reduced by 61.2%.

Body diagonal error measurement and evaluation of a multiaxis machine tool using a multibeam laser interferometer

To comprehensively evaluate the accuracy and performance of machine tools, in this paper, a novel measuring method for the body diagonal error of a machine tool using a multibeam laser interferometer as the measuring instrument is proposed. On this basis, a three-dimensional evaluation method for the body diagonal error of a machine tool is proposed. First, a method of measuring the body diagonal error of a machine tool by using a multibeam laser interferometer is proposed. Six errors for the body diagonal of a machine tool can be measured simultaneously, including three position deviations and three angle errors. The mathematical model of the relationship between the measured data and the volumetric error is established. Second, a new evaluation method for the body diagonal error is presented that takes the position deviation and attitude error into consideration. The advantage of this evaluation method is that it fills in the blanks in the evaluation method for the body diagonal error. The method can also be applied to the evaluation of linear axis error. Finally, the proposed measurement method is applied to a vertical three-axis machining centre, and the experimental results show that this measuring method is quite convenient and effective for measuring the body diagonal error of a machine tool. The proposed method is used to evaluate the body diagonal error from measurement data. The results show that the positioning error of the machine tool is 49.37 ??m; the repeatability of the positioning error is 36.85 ??m; and the angle errors are ??????22.47 ??m/m, ??????70.9 ??m/m and 29.7 ??m/m. The traditional method (ISO230-6) is used to evaluate the body diagonal error from measurement data. The results show that the positioning error of the machine tool is 49.4 ??m. Compared with the traditional method, the information from the proposed evaluation method is more abundant, and the evaluation method is systematic and universal.

Improving the machining dynamics performance and efficiency for complex channel part manufacturing by planning the tool orientations and feed rate sequence

Improving the machining dynamics performance and efficiency of machine tools is extremely important to finish the processing of complex channel parts with high quality in a short time. In this paper, a three-step frame is adopted to achieve this goal by planning the tool orientations and feed rate, which includes C-spaces determination, collaborative optimization of toolpath and feed rates, and the adjustment for over-limitation dynamic parameters. Firstly, a conical ball-end cutter is used and the feasible C-spaces computation method is provided based on the envelop theory. Secondly, a multi-objective mathematical model with multi-constraint conditions for optimizing the dynamics performance and machining efficiency is built. Thirdly, the solving algorithms for the model but simplified is designed to generate the optimal toolpath and initial variable feed rate sequence. To design the efficient algorithms, the Closed-region Parametric Encoding (CPE) method for data structure and the Parametric Data Algorithm Design (PDAD) for algorithm design are proposed, which can transform the geometric constraints into the parametric surfaces in C-space and compute with the continuous parameters to implement the adaptive local subdivision. The algorithms can automatically generate the different shape of toolpath curve to obtain better optimization results. Finally, considering the dynamic parameters limitation, an adjustment algorithm is designed to adjust the feed rates for reducing the over-limitation dynamic parameters. At the end of the paper, two sets of comparative experiments are given for verification. The first set experiment shows that our approach can efficiently improve the machining dynamics performance and efficiency for complex channel parts. The second set experiment shows that the solving algorithm designed by the CPE method and PDAD method has the better computation efficiency and optimization effect.

Full-load analysis model and experimental study on the static characteristics of linear rolling guideway joints

Linear rolling guideways have been widely used in machine tools. The overall performance of machine tools is directly influenced by the linear rolling guideway characteristics. In this study, a contact model for a single ball–raceway joint surface is established based on the fundamental characteristic parameters of the joint surface, which are obtained experimentally. Based on this model, a novel full-load analysis model of the linear rolling guideway joint is proposed, and six linear rolling guideway-joint stiffness types, namely the tangential, normal compressive, and normal tensile stiffnesses and the pitch, yaw, and roll angular stiffnesses, are obtained. Testing devices are developed for the six stiffness types. The stiffnesses of the medium preloaded HJG-DA35AA, HJG-DA45AA, and HJG-DA55AA linear rolling guideways are achieved using the developed testing devices, and the results obtained from the full-load analysis model are approximately consistent with the experimental results.

Utilization of CFRP in High-Speed Stamping Presses and its Gigacycle Fatigue Testing at Resonance Frequency

Carbon fiber reinforced polymer (CFRP) utilization meets the requirements of stiffness, damping, and light weight for enhanced performance of machine tools. Stamping presses are expected to function for billions of cycles, resulting in the fatigue of the employed materials and parts. High-speed stamping presses, such as the Bruderer BSTA-200, should fulfil the increasing customer requirement of enhancing both quality and quantity of the delivered parts. Among the quickest presses currently available in the market, these BSTA presses can reach speeds up to 2000 strokes per minute (spm) with a stroke of 8 mm and still continue operating for many decades. For this project, new requirements were defined: a 25% increase of the stamping speed reaching up to 2500 spm, while maintaining the same stroke of 8 mm. The ram was redesigned by making use of CFRP, and because of its high stiffness and strength, it enabled a weight reduction of 65%. Owing to the stamping force of 200 kN and the impact of the stamping process, the material of the ram is highly strained. A major concern in utilizing CFRP in machine tools is the fatigue and change in material properties with increasing stress cycles. Therefore, the fatigue behavior of CFRP had to be validated in the very high cycle fatigue (VHCF) range. This was performed using a newly developed fatigue test bench. To complete 109cycles within a few weeks, the testing occurred at the specimen’s resonance frequency with a constant and controlled strain of 0.1%. Aspects such as resonance frequency testing, heating of the specimen, and an accurate measuring system were considered. The specimens had to be designed and optimized for this type of testing, thus resulting in a cylindrical tube shape with a unidimensional (UD) arrangement of the fibers in longitudinal and transverse direction.

A novel hybrid MCDM model for machine tool selection using fuzzy DEMATEL, entropy weighting and later defuzzification VIKOR

Machine tool selection has been an important issue in the manufacturing industry because improper machine tool selection can have a negative effect on productivity, accuracy, flexibility, and the responsive manufacturing capabilities of a company. The current multi-criteria decision making (MCDM) approach of machine tool selection mostly focuses on the subjective perspective. However, as the objective evaluation represents the actual performance of machine tools, both subjective and objective perspectives need to be considered when choosing an appropriate machining tool. Therefore, this study proposes a machine tool selection method based on a novel hybrid MCDM model. Firstly, the presented method employs a comprehensive weight technique integrating subjective weights obtained using fuzzy decision-making trial and evaluation laboratory (FDEMATEL) with objective weights obtained using entropy weighting (EW). Secondly, later defuzzification VIKOR (LDVIKOR) is put forward to rank the optional alternatives. Finally, a case application verifies the effectiveness of the proposed method. The evaluation results indicate that the best and worst selected machine tool of the proposed method keeps high conformance with the actual ranking in real factory. Additionally, sensitivity analysis results of the effect of parameters φ on the decision outcome show that irrespective of the variations in this parameter, the best decision outcome will be not influenced. These indicate that the presented hybrid model has advantages in granting flexibility to the preferences of decision makers.

Performance Comparison of Subtractive and Additive Machine Tools for Meso-Micro Machining

Several series of experiments were conducted to compare the performance of selected sets of subtractive and additive machine tools for meso-micro machining. Under the MicroCutting Project, meso-micro machining of a reference part was conducted to compare the performance of several machine tools. A prototype flexure of the microspline of an asteroid gripper under development at NASA/JPL was selected as the reference part for the project. Several academic, research institutes, and industrial firms were among the collaborators participating in the project. Both subtractive and additive machine tools were used, including abrasive waterjets, CNC milling, lasers, 3D printing, and laser powder bed fusion. Materials included aluminum, stainless steel, and nonmetal resins. Each collaborator produced the reference part in its facility using materials most suitable for their tools. The finished parts were inspected qualitatively and quantitatively at OMAX Corporation. The performance of the participating machine tools was then compared based on the results of the inspection. Test results show that the two top performers for this test part are the CNC precision milling and micro abrasive waterjet. For machining a single flexure, the CNC precision milling had a slight edge over the micro abrasive waterjet machining in terms of part accuracy and edge quality. The advantages disappear or the trend even reverses when stack machining with taper compensation is adopted for the micro abrasive waterjet.

Hazards That Can Affect CNC Machine Tools during Operation—An AHP Approach

CNC (computer numerically controlled) machine tools are highly advanced technological systems, used to machine parts by means of metal cutting processes. Their structure and kinematics are very complex, involving accurate coordinated motions on three to five axes. Operating CNC machine tools is a complicated process, which can easily be affected by errors. Nowadays, safety systems and devices are developed in order to make this process safer and more user friendly. Modern CNC controllers are designed to deal with obvious sources of hazards, such as overloads (by means of various sensor systems) and collisions (by checking the NC code syntax and simulating it on the machine). However, despite of these safety systems, various unwanted events still occur during machining operations on CNC machine tools. These means that there are still certain hazards, not so obvious, which can severely affect the operation of CNC machine tools. This work tries to identify and hierarchize the above-mentioned hazards by using an AHP (analytic hierarchy process) approach. The results of the AHP emphasize which hazard has the biggest influence upon the CNC machine tools operation and consequently should be avoided. The results of this work could be used by the machine tools designers to develop new safety features for the existing CNC controllers. Also, the users of the machine tools could focus some of the safety measures during the machining process upon the most significant hazards pointed by the results of the research.

A novel method for evaluating the validity of dynamic accuracy test pieces for five-axis machine tools

The detection method for direct machining the standard test pieces, which is commonly employed to exhibit the machining precision of five-axis machine tools, can truly reflect the dynamic accuracy of five-axis machine tools in the actual machining process. Existing theories on explaining the phenomenon that the ability of S-shaped test pieces to detect dynamic accuracy for five-axis machine tools are stronger than those of NAS979 test pieces mostly used the qualitative research methods, and they cannot be quantitatively used to reveal the mathematical relationship between machine tools and test pieces. Therefore, this article makes the first attempt to investigate the quantitative evaluation method for the validity of dynamic accuracy test pieces. The dynamic error function of the servo feed system in the frequency domain was derived first by establishing the mechanical system model and control system model. The method of dipole cancellation was used to acquire a simplified transfer function for the dynamic error affected by the input. Based on the zero-order hold property of the discrete input signals, the expression of dynamic error affected by input in the time domain, which intuitively shows the mathematical relationship among the machine tool performances, the test piece characteristics and the dynamic error of the servo feed system, was obtained. Then, the novel evaluation methods of the linear combinatorial value and the combinatorial linear combinatorial value were proposed. A series of comparative analyses between an S-shaped test piece and an NAS979 test piece were carried out based on the proposed new evaluation methods. A machining experiment conducted on a five-axis machine tool is used to verify the evaluation results.

Comparison of different mathematical models for prediction of self-excited vibrations occurance in milling process

In modern production, despite the existence of other production methods, metal cutting still plays an important role. The performance of machine tools has a decisive role in terms of productivity and quality of production increase. Undoubtedly, productivity and quality of production are two mail requirements which are key elements to stay on top in a competitive market. One of the most influencing factor that affect the machine tools are vibrations. The most unwanted vibrations that can appear during metal cutting process are self-excited vibrations, which are one of the three kinds of mechanical vibration, free vibration, forced vibration, and self-excited vibration. When it comes to improving the performance of machine tools, the analysis of the appearance of self-excited vibrations and their isolation occupy a significant place. The aim of this paper derives from trends and limitations exists in metal production. The way to isolate the self-excited vibrations is to predict their occurrence by defining the stability lobe diagram. The paper presents two popular analytical methods for identifying stability lobe diagrams in milling, which shows the boundary between stable and unstable zone of machining operations, depending on the number of revolutions of the spindle and cutting depth. First considered method is Fourier series approach and second one id average tooth angle approach. Lather, both stability lobe diagrams were compared with results obtained experimentally.