Traditional Machine Tools Research Articles

Mechanical properties and damping characteristics of Egyptian granite-epoxy composite material

Vibrations generated during the operations of machine tools, especially at high-speed operation impact several issues in machined parts such as imprecision dimensions and a poor surface finish. This prompts research and studies into alternative materials for machine tool structures to provide considerable damping performance and acceptable stiffness compared to traditional materials. This paper deals with the experimental study of a developed granite-epoxy composite, made from waste granite and local epoxy as an alternative material for machine tool structures. A waste of Egyptian Red Aswan granite was used as filler after being crushed and sifted into three sizes: fine (less than 1 mm), medium (1 to 5 mm), and coarse (5 to 8 mm). A local commercial epoxy resin kemapoxy 150 was added to a granite aggregate mixture having grain proportions 50:25:25 for fine, medium, and large, respectively. The influence of the variation of the epoxy weight ratio on the static and damping characteristics of a proposed granite–epoxy composite material was experimentally investigated. To ensure a coherent granite-epoxy composite, the required minimum resin content of 13.88 wt% was determined, and the granite/epoxy ratios were selected as 85:15 wt%, 80:20 wt%, and 75:25 wt%. The findings exhibit that the largest compressive strength of 76.8 MPa and the greatest flexural strength of 35.4 MPa is achieved at the highest epoxy weight ratio of 25%. The largest damping ratio of 0.0202 is observed at the epoxy ratio of 20% and it decreases to 0.015 when the epoxy ratio is increased to 25%. An Egyptian granite-epoxy composite, made from waste granite and local epoxy, is a promising alternative material for machine tool structures. It offers both economic and environmental benefits, along with high mechanical and damping properties compared to traditional machine tool materials.

Effect of Al7075 and activated carbon reinforced composite on optimizing WEDM responses

This paper presents wire cut electrical discharge machining (WEDM) response characteristics of Aluminium 7075 (Al7075) reinforced with powdered activated carbon (PAC) composite. In recent days WEDM has become a significant machining process in targeting its benefits of contributing improved material removal rate (MRR) and low surface roughness (SR). This is due the rising need for intricate, accurate, and superior structural components, the WEDM process emerges as a formidable alternative to traditional machine tools. In this work Pulse-on time (Ton), pulse-off time (Toff), discharge current (IA) and servo speed rate (SS) are the variables to be given as input and machining responses such as MRR and SR are studied. From Analysis of Variance (ANOVA) study it is found that discharge current and servo speed is the significant parameters. The optimal desirability condition is obtained with input parameters Ip: 2000 mA; Ton: 8.9 μs; Toff: 25 μs and SS: 150 rpm for the precision machining. The optimum response parameters are found as MRR 10.46 mm3/min and SR 3.32 μm. Results shows that the model designed for the prediction of MRR produces an above 98.27% and the prediction of SR is above 97.17%. The error percentage among the experimental and predicted MRR and SR were estimated. Additionally confirmatory test is performed with optimal results achieved from response surface methodology (RSM) and desirability technique. Metallurgical tests like electron backscatter diffraction analysis (EBSD) and microstructure are conducted to confirm the surface properties and atomic force morphology (AFM) analysis is applied to clarify the structural features of machined composites. The results revealed that the variation of hard deflection is caused by depression of eroded materials on the top layers of machined surface.

Development of Machine Tool Disassembly and Assembly Training and Digital Twin Model Building System based on Virtual Simulation

In response to the issues of poor safety and insufficient training equipment in traditional machine tool assembly and disassembly training, this paper proposes a machine tool assembly and disassembly training system based on virtual simulation. The system utilizes Unity 3D to construct an interactive virtual training environment, achieving highly simulated simulations and teaching of the machine tool assembly and disassembly process. Additionally, the system is capable of establishing communication with actual machine tools, achieving bidirectional mapping between digital and physical spaces, allowing learners to observe the dynamic responses of machine tool models through the virtual environment. This virtual-real interaction mechanism enriches the application scenarios of the system, introducing digital twin technology into the virtual simulation of machine tool assembly and disassembly training. This paper also provides a detailed introduction to the design and implementation of core technologies such as the system's overall architecture, scene modeling, and virtual-real interaction, offering significant support for intelligent teaching in machine tool assembly and disassembly.

Effects of the Lubricants on the Tribology Properties under the Extreme Pressure for the Induction-Treated Linear Guides

In view of the fact that the load on the transmission element under extreme pressure conditions is much greater than that used in traditional machine tools, the contact surface between the ball and the track must bear great stress. Furthermore, it will heat up due to friction after starting and running. These effects are prone to material deformation and fatigue damage, and may even lead to the disappearance of the lubricating oil film. They are prone to surface damage due to metal fatigue, and then a serious situation of large pieces of peeling occurs for the linear guides. In order to prolong the fatigue life of the machine tools, this study investigates the effects of the lubricants on the tribology properties under the extreme pressure for the induction-treated linear guides.

Selection of machine tool equipment when implementing modular technology

This article is about choosing the right machine tool equipment when you're introducing modular technology into engineering production. The objective was to analyze possible solutions and choose the optimal option. We will consider two variants: the first is the creation of new machine tools for the production of surface modules, and the second is the use of existing machine tools. The second option should be studied with traditional machine tools because it is associated with lower time and labor costs. Twenty machine tools of different types, commonly found in machine-building plants, were selected as the object of research. We used a special methodology to identify the technology of the machine tools. The work resulted in the determination of the nomenclature of surface modules produced for each machine tool. This proves that traditional machine tools are suitable for use in modular technology. The distribution of the number of types of surface modules by groups of machine tools clearly shows that all twenty-six types of surface modules can be produced on universal machine tools with program control, including 5-axis milling machines and lathe machining centers.

Topology optimization-based design, development and testing of steel-reinforced epoxy granite vertical machining centre column

The structural vibrations experienced by traditional machine tools made up of cast iron (CI) or cast steel material lead to premature failure of the cutting tool and poor surface finish on the manufactured components. Steel-reinforced epoxy granite (SREG), an alternate material to CI, improves the static and dynamic characteristics of the machine tool structure. However, the addition of steel reinforcement in SREG affects the damping characteristics of epoxy granite (EG). The present work focuses on optimizing both EG and steel reinforcement of the vertical machining centre column to achieve favourable damping characteristics. Initially, parametric analysis is performed to arrive at an optimum configuration of only the EG column. Then, steel reinforcement is integrated into the EG column, and topology optimization is carried out with the objective of maximizing the stiffness and natural frequencies of the SREG column while minimizing the mass of the reinforcement. The multiple design configurations for steel reinforcement evolved from topology optimization are numerically investigated using finite element analysis. The scaled-down prototype of the finalized model was fabricated, after which the dynamic characteristics of the proposed SREG column are measured and compared with that of existing CI and SREG columns. The results revealed six-fold and three-fold improvements in dynamic stiffness along X- and Y-directions, respectively, and a 33% reduction in the mass of steel reinforcement than the existing SREG column.

Early chatter identification based on optimized VMD with multi-band information fusion and compression method in robotic milling process

Undesirable self-excited chatter has always been a typical issue restricting the improvement of robotic milling quality and efficiency. Sensitive chatter identification based on processing signals can prompt operators to adjust the machining process and prevent chatter damage. Compared with the traditional machine tool, the uncertain multiple chatter frequency bands and the band-moving of the chatter frequency in robotic milling process make it more challenging to extract chatter information. This paper proposes a novel method of chatter identification using optimized variational mode decomposition (OVMD) with multi-band information fusion and compression technology (MT). During the robotic milling process, the number of decomposed modes k and the penalty coefficient α are optimized based on the dominant component of frequency scope partition and fitness of the mode center frequency. Moreover, the mayfly optimization algorithm (MA) is employed to obtain the global optimal parameter selection. In order to conquer information collection about the uncertain multiple chatter frequency bands and the band-moving of the chatter frequency in robotic milling process, MT is presented to reduce computation and extract signal characteristics. Finally, the cross entropy of the image (CEI) is proposed as the final chatter indicator to identify the chatter occurrence. The robotic milling experiments are carried out to verify the proposed method, and the results show that it can distinguish the robotic milling condition by extracting the uncertain multiple chatter frequency bands and overcome the band-moving of the chatter frequency in robotic milling process.

Robotic milling stability optimization based on robot functional redundancy

PurposeCompared with the high stiffness of traditional CNC machine tools, the structural stiffness of industrial robots is usually less than 1 N/µm. Chatter not only affects the quality of robotic milling but also reduces the accuracy of the milling process. The purpose of this paper is to reduce chatter in the robotic machining process.Design/methodology/approachFirst, the mode coupling chatter mechanism is analyzed. Then the milling force model and the principal stiffness model are established. Finally, the robot milling stability optimization method is proposed. The method considered functional redundancies, and a new robot milling stability index is proposed to improve the quality of milling operations.FindingsThe experimental results prove a significant reduction in force fluctuations and surface roughness after using the proposed robotic milling stability optimization method.Originality/valueIn this paper, a new robot milling stability index and a new robot milling stability optimization method are proposed. This method can significantly increase the milling stability and improve the milling quality, which can be widely used in the industry.

Procedures and performance of a robotic machining system with metrology-in-the-loop feedback control

In recent years, the use of industrial robots in advanced manufacturing applications has become increasingly popular. With larger workspaces and lower costs relative to more traditional machine tools, the use of robots has significant upsides in machining applications. However, due to their relatively low accuracy, the use of industrial robots in these applications is limited. One way to improve robot accuracy is to provide feedback control via external sensors such as laser trackers. This paper presents several techniques used to identify key parameters for a laser tracker controlled robotic machining system. Specifically, transformations between the coordinate frames within the system are crucial to its performance since error in these parameters are generally not observable by the feedback system. The identification methods are used to perform full-scale machining experiments. These experiments demonstrate the improved machining performance of the laser tracker controlled robotic machining system when compared to the machining performance without feedback control.

A parallel machining robot and its control method for high-performance machining of curved parts

The curved part with open-and-close angle conversion features is a kind of well-known difficult-to-machine part. Using traditional five-axis serial machine tools (SMTs) may cause efficiency and accuracy reduction at open-and-close angle conversion regions because of the singular points in their orientation workspace. How to achieve high-efficiency and high-precision machining of this kind of curved part is a challenging issue in the field. In order to solve this problem, a parallel machining robot (PMR) with five degrees of freedom (DoFs) is developed. Accordingly, the attitude coupling adjustment mechanism of the developed PMR is disclosed, which indicated that a small change of the tool orientation will never lead to a large range motion of the driving limbs. Thus the robot has the potential to pass through open-and-close angle conversion regions smoothly. In order to take full use of the advantages of the developed PMR in attitude adjustment, a control method is proposed by fitting tool orientation spline in unit spherical coordinate system. On this basis, toolpath planning and machining experiments are carried out to verify the performance of the developed PMR and the proposed control method when machining parts with open-and-close angle conversion features. Experimental results demonstrate that the developed machining robot integrated with the proposed control method can improve the machining efficiency and accuracy significantly when compared with the SMT. This proves that the attitude coupling motion property of PMRs can solve the difficulty in high-performance machining of open-and-close angle conversion features. The findings of this study fundamentally provide a feasible way to overcome the abnormal phenomena when machining curved parts with open-and-close angle conversion features.

Surface modification improving the biological activity and osteogenic ability of 3D printing porous dental implants

Objective: To explore the mechanical properties, biological activity, and osteogenic ability of 3D printed TC4 titanium (Ti) alloy dental implants treated with surface modification.Methods: Dental implants with 30% porosity were manufactured using selective laser melting (SLM) technology (group 3D), while traditional numerically-controlled machine tools (CNC) were used to manufacture implants without porosity (group SL). The implants were then surface modified through sandblasting and acid etching (groups 3DA1 and SLA1), and then alkali etching (groups 3DA2 and SLA2). The physicochemical properties of the implants were measured using a Vickers hardness instrument, scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), and profilograph before and after surface modification. Next, the biocompatibility, bioactivity, and osteogenic ability of the implants were evaluated using apatite deposition experiments, alkaline phosphatase (ALP) activity, and semiquantitative analysis of extracellular matrix mineralization.Results: There were significant differences in morphology, geometric accuracy, mechanical properties, surface roughness, and hydrophilicity between groups 3D and SL. Furthermore, surface modification improved the physicochemical properties of the porous implants. Implants with sandblasting, acid etching, and alkali etching demonstrated better biocompatibility, bioactivity, and osteogenic ability than implants without surface modification in both groups 3D and SL. Additionally, the implants of groups 3D have higher bioactivity than that of groups SL.Conclusion: Surface modification and the macroporous structure of implants can improve their bioactivity and osteogenic ability, enhancing the application of Ti alloy dental implants.

“4+2” axis ultra-precision diamond shaping for partially overlapping Fresnel lenses based on an ultra-precision machine tool and two additional rotational axes

Optical surfaces and microstructures with high form accuracy and excellent surface quality are widely utilized nowadays and the diamond machining technology is still preferable for the fabrication of these workpieces. However, when machining surfaces featuring a high aspect ratio or intricate microstructures like monolithic microstructural optics, the machining efficiency is quite low and the cutting tool interference is inevitable for the existing diamond turning techniques. Hence, a novel method is proposed to machine such microstructures by introducing two additional rotational motions into the traditional ultra-precision machine tool. In this way, the arbitrary adjustment of the tool posture may be achieved in the machining process and intricate microstructures like monolithic microstructural optics can also be machined by the side cutting edge with high efficiency. The whole mechanical system and machining principle are presented firstly. Next, the tool path planning and the compensation for the tool tip offset are introduced. Then, the partially overlapping Fresnel lens array consisting of two segmented Fresnel lenses are fabricated and inspected. Finally, the measurement data are analyzed and the proposed method is validated to be able to fabricate such complex microstructures with high profile accuracy and surface quality successfully.

Ultra-precision time-controlled grinding for flat mechanical parts with weak stiffness

High-precision flat mechanical parts are widely used, such as in aerostatic bearing, which requires a rather high machining precision. Due to large size, low stiffness and other machining problems, traditional ultra-precision grinding machine tool cannot directly achieve the final precision, so manual grinding is necessary to meet the manufacturing requirements, resulting in low efficiency. Based on the computer-controlled optical surfacing (CCOS) method and the flexible grinding process, the time-controlled grinding method (TCG) is proposed to achieve quantitative material removal at each position on the workpiece. Combined with the material removal mechanism, the removal function with good linearity and stability is extracted by controlling corresponding parameters. By applying a novel measuring and processing method of surface data with high precision and high efficiency, the flatness error and parallelism error are accurately obtained and used as grinding reference to carry out the time-controlled grinding experiment on one spacer ring with a diameter of 190 mm. The final flatness error converges from 1.5–2 μm to 0.6–0.7 μm and parallelism error converges from ~2 μm to ~0.6 μm, while the roughness converges from 273 nm Ra to 65 nm Ra, achieving the goal of ultra-precision digital machining of submicron level. The machining precision is better than traditional ultra-precision grinding machine tool, and the potential for time-controlled grinding method of ultra-precision machining in flat mechanical parts especially with low stiffness is verified.

Parasitic Motions of 3-PRS Parallel Mechanisms with Two Different Branch Chain Arrangements

The kinematics of 3-PRS parallel mechanisms (PMs), an important category of 2R1T PMs, is very important for the motion control and error compensation of PMs. In order to produce a spindle head that could meet the requirements of various machining accuracy levels, a definite kinematics analysis of the PMs par should be taken with caution firstly. Here, the mathematical models of two 3-PRS PMs with different branch chain arrangements were established using the Euler angle. The kinematic equations of two 3-PRS PMs were obtained by establishing the closed-vector loop equation according to structural conditions. Parasitic motions that would cause a great effect were obtained, and their variations with structural and kinematic parameters were also obtained through MATLAB. Since the relationship between parasitic motions, and the given structural and kinematic parameters, is inextricable, an analysis is performed for the purpose of reducing or eliminating parasitic motion to ensure the accuracy of end-effector movement. The caused effect of parasitic motion can be improved with scale optimization and precision compensation. Lastly, two improved 3-PRS PMs without the parasitic motion of different branch chain arrangements used as the spindle head were obtained. Parasitic motion was related to the mechanism configuration and could be avoided in the configuration design stage with the comprehensive optimization of the structural and kinematic parameters, which provides a reference to obtain a sufficient workspace and improve the precision of traditional five-axis CNC machine tools.

Early chatter detection in robotic milling under variable robot postures and cutting parameters

Chatter in robotic milling is closely related to robot postures and cutting parameters. The chatter frequency varies over a wide range compared with that in the milling process using traditional machine tools. These features pose a significant challenge to chatter detection in robotic milling. The objective of this paper is to propose a novel approach for early and reliable chatter detection in robotic milling under variable robot postures and cutting parameters. First, the inertance frequency response function under each robot posture is used to filter the corresponding vibration signals. This minimizes the influence of robot postures on the measured vibration signals. Second, based on the filtered vibration data, a dual-tree complex wavelet packet transform is applied to extract the energy of different frequency bands, from which the fractional energy entropy is obtained to characterize the chatter state. Therefore, the chatter state can be characterized as independent of the variable cutting parameters and chatter frequencies. Third, online chatter detection is achieved using the sequential probability ratio test, with which significance tests for the chatter states are conducted. Consequently, the detection threshold does not need to be manually set. Extensive case studies demonstrate that the proposed approach can realize early and reliable chatter detection in robotic milling under variable robot postures and cutting parameters.

Developing and Testing the Proto Type Structure for Micro Tool Fabrication

Compared with traditional machine tools, the micro machine tools have advantages of small volume, low cost, less energy consumption, high efficiency and high flexibility. Therefore, it is regarded as an important equipment for micro-cutting machining which has been used widely all over the world and. As a key component of the micro-cutting machine tools, the body structure directly influences the machining performance. Thus, an integral column and base structure for micro machining tools was proposed in this work, and the detailed structural parameters were designed based on parameter analysis. Besides, the static and dynamic performance of the proposed machine were analyzed and compared between the integral structure and the separated one. The deformation and stress of the proposed structures under typical working conditions were studied by numerical simulation, along with the natural frequencies, vibration modes and frequency response peaks. Further, optimization was performed on the integral body structure, the prototype of the micro-machine tool was trial-produced, and the positioning accuracy of each coordinate axis was qualitatively analyzed. In addition, the micro-milling test was carried out with 6061 aluminum alloy to show the performance of the novel cutting machine. The results revealed that the proposed integrated micro-machine bed structure is superior to the separated structure in terms of static deformation and harmonic response characteristics, with good comprehensive mechanical properties, greatly improved static and dynamic performance of the machine tool, significantly improved structural accuracy, improved processing quality of the specimen and good application value.

Joint-Smooth Toolpath Planning by Optimized Differential Vector for Robot Surface Machining Considering the Tool Orientation Constraints

The flexible robot has more advantages over the traditional machine tools in machining complex workpieces like the 3D-printed part which has less residual material for removal. In robot machining, the geometric smoothness of moving joints is vital for enhancing efficiency and accuracy and the tool orientation should be limited in certain regions considering the interfering requirements. As the robot has six DoFs at least, redundant DoFs are observed for robot surface machining, which can be employed to optimize the smooth machining process under the tool orientation requirements. In this paper, the tool posture differential vector along the tool-tip path curve is optimized firstly. The whole trajectory is numerically integrated by the optimized differential vector subsequently. In each step, the minimum 2-norm of the joints’ differential vector along the tool path curve is set as part of the optimization objective to ensure the minimal change of joints. Furthermore, a state-related optimization objective for the differential vector is established to keep the tool orientation away from the boundary of the feasible region. Combining with the two objectives, the tool posture differential vector along the tool-tip path is optimized and the whole machining process is obtained by the numerical integration method. As a case study, the joint trajectories for an inclined butterfly curve are planned by the algorithm and machined by the UR-5 robot with the ROS controller. In addition, a comparative experiment is also provided to verify the effectiveness and optimality of the proposed method.

High-order joint-smooth trajectory planning method considering tool-orientation constraints and singularity avoidance for robot surface machining

Compared with the traditional machine tools, robots are low-cost and flexible for the machining process. However, owing to the complex constraints in the operation space and the redundant degrees of freedom (DoFs), it is challenging to obtain a joint-smooth optimal trajectory for the robotic machining. This article develops a high-order smooth joint trajectory planning method for robot surface machining considering with the tool posture constraints (the collision avoidance and cutting angles limits) and the robot state limits (the singularity avoidance). In the proposed method, the whole trajectory of the tool posture is integrated by the optimized differential vector in steps. In every integrating step, the differential vector is optimized from the redundant DoFs with the combined and balanced optimization objective considering the joint-smooth requirements, tool orientation limits and robot state constraints. At the same time, the upper limit of the second-order differential is given to limit the change rate of the optimized differential vector and to smooth the generated trajectory further. As the drastic change of the feasible region and tool-tip path curve, the boundary of the feasible region should be smoothed in advance to compensate for the hysteresis of the numerical integration method. In the end, two cases of robot surface machining are provided to verify the method. In the experimental process, an UR-5 robot with Robot Operating System (ROS) controller is used and the complex curve is machined by the robot.

Research on stability of robotic longitudinal-torsional ultrasonic milling with variable cutting force coefficient

With their successful applications in handling, spraying, arc welding and other processing fields, industrial robots are gradually replacing traditional CNC machine tools to complete machining tasks due to the wider working envelope and the higher flexibility. Aiming at the chatter problem, a robotic longitudinal-torsional ultrasonic milling method with variable force coefficient is proposed in this paper. Taking carbon fiber-reinforced plastics (CFRP) as the processing object, the influence of the fiber layup angle on the milling force is analyzed first; then, the robot milling force parameters are determined, and the robot milling kinematics model is established. Furthermore, the ultrasonic function angle is defined, and the cutting layer thickness model, the dynamic milling force model, and the dynamic differential equation under ultrasonic vibration are established to analyze the stability of robotic longitudinal-torsional ultrasonic milling of CFRP. Finally, the full discrete method is used to obtain stability lobe diagrams.

Dynamic Modeling and Simulation of a Hybrid Robot

Abstract The unique structure of hybrid robot makes its dynamic characteristic different from that of the traditional machine tools. Therefore, the dynamic model is crucial to both designing and application of hybrid robot. In this paper, a new type of five-degrees-of-freedom (5DoF) hybrid robot is introduced, and its dynamic model is established. First, the kinematic formulas are derived for all the component, and then, the inertia forces or moments are calculated. Second, the active forces or moments in the joints are assumed as variables and the number of variables is reduced by analyzing joint types. Then, an equation set of 36 equilibrium equations with 38 variables is obtained using D'Alembert's principle. Based on the spatial deformation compatibility analysis of two branches, two supplementary equations are derived to determine the solution of dynamic model of the hybrid robot with redundant constraints in its parallel mechanism. Several cases are studied by comparing with ADAMS simulation. The result shows the good accuracy of the proposed dynamic model, which provides a practical method to calculate the reaction force or moment in any joint at any instant for the hybrid robot and thus facilitates dimensional synthesis, trajectory optimization, and smoothing control.