High Precision CNC Research Articles

Design of High Precision CNC Vertical Lathe Turning Tool Holder

Design of High Precision CNC Vertical Lathe Turning Tool Holder

Robust modeling for thermal error of spindle of slant bed lathe based on error decomposition

Thermal error of spindle is critical to the slant bed CNC lathe towards high machining precision. The heat generated by the spindle itself contributes to the thermal error indeed. However, the thermal error is also influenced by the thermal deformation of other components such as the turret and lathe bed, especially in complex structured slant-bed CNC lathes where error coupling commonly exists. In order to achieve robust modeling of thermal error, a decomposition method was proposed in this paper to separate the contributions of spindle, turret and lathe bed from the overall measured thermal deformation. The thermal error coupling relationship was established from the perspective of machine tool construction. A specific testing scheme was designed to determine the parameters of decoupling model. Additionally, a comparative experiment was carried out by placing the sensor support horizontally and vertically to verify the effectiveness of thermal error decoupling. Taking T65-750 high-precision CNC lathe as the object, the relationship between thermal error and tilt angle in the X-direction of the headstock, bed, and other components was revealed, achieving robust prediction of thermal error irrespective of the ambient temperature subject to change. Finally, the thermal error model built based on error decomposition was applied to improve the machining accuracy of cylindrical parts dramatically in practice.

Effects of Tooth Modification in the Involute Helical Gear Form-Grinding Process on Loaded Transmission Character with Consideration of Tooth Axial Inclination Error

Due to the existence of machining and installation errors, axis parallelism error of gear pairs occurs, which causes eccentric load and mesh in-out impact, thus weakening loaded transmission character. To solve this problem, the axis parallelism error of gear pairs was equated with tooth axial inclination error based on the gear-meshing principle. On this basis, we established the tooth modification model with tooth axial inclination error as the variable according to involute helical gear form-grinding process. Then, the degradation of loaded transmission character caused by axis parallelism error of gear pairs was quantitatively analyzed. The gear grinding, gear measuring, and gearbox vibration measuring were, respectively, performed on high-precision CNC horizontal gear form-grinding machine tool L300G, Gleason 350 GMS, and JWY-II multifunctional gearbox loading test bench. The results show that the proposed method can effectively reduce eccentric load and mesh in-out impact and significantly improve loaded transmission character. Therefore, it can provide a theoretical and experimental basis for the research of high-performance gear-grinding technology of gear-grinder machines.

Quasi-Elliptical Stub-Based Multi-Resonance Waveguide Filters With Low Manufacturing Complexity for mm-Wave Applications

In this paper, the design and realization of quasi-elliptical waveguide filters with reduced manufacturing complexity are discussed. The filters are based on TE mode cavities, which are loaded with TM mode stubs. It is shown that dual-, triple- and quadruple-resonance segments are obtained by using up to three stubs loaded on the broad side of a TE mode cavity. The structures obtained can either be used as a stand-alone filter or even as a building block suitable for the realization of higher order filters. The multi-resonance blocks reveal several advantages in the mm-wave area: The manufacturing complexity is easy to handle and comparable to simple all-pole filters, which is especially important at high frequencies. Therefore, three prototypes are manufactured as proof of concept in the D-band (110 GHz–170 GHz). Moreover, the building blocks are able to produce <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n-1$</tex-math></inline-formula> transmission zeros (TZs) with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> being the number of resonances. Therefore, the blocks generate between one (dual-resonance) and up to three (quadruple-resonance) TZs. Advantageously, the filters can be cut in the E-plane in order to reduce the insertion loss and hence consist of only two components. Three examples are manufactured by high precision CNC milling and reveal good agreement to the simulation by obtaining unloaded Q-factors of up to 1000.

Fault monitoring and diagnosis of motorized spindle in five-axis Machining Center based on CNN-SVM-PSO

A spindle fault diagnosis method based on CNN-SVM optimized by particle swarm algorithm (PSO) is proposed to address the problems of high failure rate of electric spindles of high precision CNC machine tools, while manual fault diagnosis is a tedious task and low efficiency. The model uses a convolutional neural network (CNN) model as a deep feature miner and a support vector machine (SVM) as a fault state classifier. Taking the electric spindle of a five-axis machining centre as the experimental research object, the model classifies and predicts four labelled states: normal state of the electric spindle, loose state of the rotating shaft and coupling, eccentric state of the motor air gap and damaged state of the bearing and rolling body, while introducing a particle swarm algorithm ( PSO) is introduced to optimize the hyperparameters in the model to improve the prediction effect. The results show that the proposed hybrid PSO-CNN-SVM model is able to monitor and diagnose the electric spindle failure of a 5-axis machining centre with an accuracy of 99.33%. In comparison with the BP model, SVM model, CNN model and CNN-SVM model, the accuracy of the model increased by 10%, 6%, 4% and 2% respectively, which shows that the fault diagnosis model proposed in the paper can monitor the operation status of the electric spindle more effectively and diagnose the type of electric spindle fault, so as to improve the maintenance strategy.

A Review Based on the Control Method of Thermal Error for High-Speed Motorized Spindles

Background: The high-speed motorized spindle system is the main component and the most significant heat source of high-precision CNC machine tools in mechanical processing. Plenty of research shows that 60%~80% of the machining accuracy error comes from the thermal deformation of each part in automated manufacturing. Therefore, it is urgent to study the control method of thermal error for motorized spindle systems. Objective: Some valuable conclusions are drawn through the introduction and discussion of thermal error control methods for motorized spindles in recent years, and we prospect the future research and development of thermal error control methods for motorized spindles. Methods: The patents and papers based on the control methods of thermal error for motorized spindles are studied. The advantages and disadvantages of thermal error control methods and their research status are summarized. Results: With the urging of social as an essential part of CNC machine tools, we cannot ignore the thermal error of high-speed motorized spindles. To improve the machining accuracy, increase efficiency and prolong life, etc., all need a motorized spindle with excellent thermal dynamic performance. Conclusion: We analyze the structural characteristics and the primary heat sources of high-speed motorized spindles, and review a mass of patents and papers related to the motorized spindle thermal error control methods for investigation. By comparing these papers, some valuable conclusions are drawn to predict the future research and development of thermal error control methods for the motorized spindle.

Enhancing the Surface Finish of Product Coming From High Precision CNC- Milling Center by Varaying the Machtine Parameters Through Taguchi Approach

Abstract: The manufacturing process for products with high degree of precision is very critical and hence increasing the surface quality, wherever possible has been the prime motive, so many leading companies are working with high precision CNC-VMC series for operations such as Drilling, Tapping, Turning, Milling, etc. Surface roughness is the most important indicator of surface quality in machined items. So as to achieve that changing machine parameters as per product size and environment is necessary. In this research, the parameters which are taken into account are : spindle speed, feed rate, and depth of cut. Taguchi Design is utilized in this study to find the best combination of parameters to reach out to the maximum surface finish criteria. For various combinations of three parameters: spindle speed, feed rate, and depth of cut, experiments are carried out using the Taguchi orthogonal array. The surface roughness Ra is analyzed for each experiment run using Taguchi. Keywords: Taguchi Method, Spindle Speed, Feed rate, Surface finish, Surface roughness, Depth of cut.

Modeling method of CNC tooling volumetric error under consideration of Abb\xe9 error

The Abbé error is a key factor for high-precision CNC machine tools. Unluckily, it is not taken into account in traditional machine tool volumetric error models. In this respect, based on the traditional machine tool volumetric error models, a new machine tool volumetric error model containing Abbé error is performed by analyzing the mechanism of Abbé error formation tool volumetric and based on 21-item geometric error measurement data, Abbé arm, and angle functional relationship. Moreover, integrated qualitative and quantitative simulation method for evaluation of machine tool space precision are correspondingly presented. Finally, an example was utilized to further verify the value of our model by means of analysis and comparison of the tooling precision prior to and after performance of compensation, and its validity and feasibility were proved. This study provides an important modeling method for high-precision machine tools and has very important theoretical significance and practical value.

Experimental study on the reliability and the precision maintenance of the ultra-precision grinding machine based on the key subsystem platforms

The development of high-reliability, high-precision large-scale CNC ultra-precision grinding machines is essential for the efficient processing and manufacturing of large-diameter optical components. In this paper, we studied the reliability and the precision-maintenance of the ultra-precision grinding machine tool experimentally. First, the subsystems with poor performance were identified based on former operating data, which turned out to be the hydrostatic spindle subsystem and the feed subsystem. Then, we set up specific experimental platforms for these two subsystems to study the thermal deformation and thermal characteristics. The temperature difference between the inflow and outflow oils of the hydrostatic systems is used as the key parameter to model the accuracy evolution. Our results may provide a method to reveal the relationship between the thermal characteristics and the operating parameters of the subsystems, and therefore compensate the thermal error of the whole ultra-precision grinding machine.

Optimization of thrust force in drilling of carbon-basalt hybrid composites through Taguchi and RSM

The main object of the present work is to obtain better quality holes during drilling operation. Carbon-Basalt hybrid composite is a better performing composite with lesser price. For the present work, the hybrid composite test specimen was prepared by hand layup method. General purpose polyester resin is used as the matrix material. During the manufacturing process, alternate layers of carbon and basalt are stacked to prepare the composite. The maintained weight fraction of the fiber is 50%. The thickness of the obtained composite specimen is 6 mm. Delamination is the major reason for the rejection of drilled composites. The magnitude of delamination is directly proportional to the thrust force generated during drilling. Hence in the present work, an attempt has been made to reduce the thrust force to minimize the damage by optimizing the machining variables using Taguchi and RSM methods. The experiments were designed by DOE method. Taguchi’s 3 levels and 3 factors array was used to get the combination of parameters for each experiments. Totally 27 holes are drilled with different combinations of process parameters. The considered process parameters and their levels are: Drill diameter (6 mm, 8 mm & 10 mm), feed rate (50 mm/min, 75 mm/min & 100 mm/min) and spindle speed (750 rpm, 1000 rpm & 1250 rpm). Drilling process was carried out on a high precision CNC machine using HSS drill bits. The thrust force was measured by a Kistler dynamometer. Using ANOVA, the significant effect of considered parameters on the generated thrust force was also predicted. The result reveals that, the parameter feed rate has the most significant effect on thrust force, which is followed by the drill diameter. The least significant parameter is spindle speed. Both Taguchi and RSM methods suggest that, DD1, F1 and S3 combination parameters yields the lowest thrust value.

Servo axis incipient degradation assessment of CNC machine tools using the built-in encoder

Servo axis system has been widely applied in the high-precision CNC machine tools. Its performance degradation may lead to the degradation of whole machine and ultimately result to the accuracy degradation of parts manufacturing. Thus, health assessment of the servo axis is very essential, especially for those in-service CNC machine tools. However, restricted by the complexity of servo axis structure, weak signal of incipient degradation, and limited sensors’ installation space, traditional degradation evaluation methods, such as the vibration based scheme, are very difficult to be applied in real service environment directly. In this paper, a new methodology is established for servo axis incipient degradation assessment by reusing the position fluctuation information captured by built-in encoder. Firstly, to highlight the torsional behavior of the servo axis components, the instantaneous angular acceleration (IAA) is estimated by using the position fluctuation information with frequency domain weighting (FDW) method. After that, the wavelet packet transform (WPT) is employed for decomposition of these nonstationary IAA signals. Finally, a Gini index (GI)–guided denoising scheme is established for incipient degradation feature reconstruction. The effectiveness of the proposed method is investigated by simulations; thereafter, it is applied for the X-axis assessment of an in-service high-precision vertical machining center. All the results illustrate that the proposed method is sensitive to incipient degradation of the rotating components and offers an alternative solution for health assessment of servo axis.

Extended object model for grinding operation

The article discusses the issues of building a dynamic model of a flat grinding operation, taking into account the statistical characteristics of the disturbances. Deviations of the shape of the grinding wheel in a static mode are random in nature and, when analyzing the processing process, can be taken into account by introducing an additional link into the system - the corresponding shaping filter. Such a filter can be built on the basis of profile analysis for any particular grinding wheel with a representation of the effect on the system in the state space as equations of state and observation. On the basis of the developed model for grinding operations in floating workshops, it is possible to use high-precision CNC machines equipped with adaptive control systems based on optimal systems with a stochastic process controller.

Design of a low-gain high-power W-band sheet-beam traveling wave tube using a double-staggered grating slow wave structure

In order to further improve the output power of W-band traveling wave tube (TWT), a low gain TWT was proposed as a secondary amplifier. It uses a double staggered grating slow wave structure (DSG-SWS) and a sheet beam. Firstly, the design of DSG-TWT was given. Through simulation, the DSG-TWT could provide a saturation output power of more than 1000 W in the frequency range of 93–97 GHz, and the maximum output power could reach 1200 W at 95 GHz. No oscillation and current interception were found. Then DSG-SWS was fabricated by E-plane partition method using high-precision CNC milling. The SWS was fed with a high-power input-output coupler which consists of a mode converter and an impedance transformer. Simulation and cold-test results were presented, showing that the S11 is less than −10 dB and the voltage standing wave ratio (VSWR) is less than 2.0 in the frequency range of 93–100 GHz.

Recent Patents on the Structure of High-Speed Motorized Spindle

Background: As one of the core components of high-speed CNC machine tool, high-speed motorized spindle is the core functional component of high precision CNC machine tool, which has become the key research and development object of the world. Objective: By comparing and discussing the patents of high-speed motorized spindle, some valuable conclusions have been drawn to predict the future research and development of high-speed motorized spindle. Methods: By analyzing the characteristics of high-speed motorized spindle structure, the influence of high-speed motorized spindle on high-speed machining technology was explicated. Combining with the key technology of high-speed motorized spindle, the patents related to high-speed motorized spindle structure were used for investigation. Results: With the rapid development of high-speed cutting and numerical control technology and the need of practical application, the requirement for high-speed spindle performance has increased. Motorized spindle technology has the characteristics of high speed, high strength, high power, high torque and low speed, high precision, high reliability and long life, offering diversified bearing and lubrication cooling methods and serving as an intelligent system. Conclusion: The different levels of improvement and renovation of the structure with high-speed motorized spindle, by adding lubrication and cooling device to the spindle have improve the performance of spindle, addressing the loopholes in the technology and making it more practical.

Development of high-speed and high-precision CNC coordinate measuring machine

Development of high-speed and high-precision CNC coordinate measuring machine

WR-3 Waveguide Bandpass Filters Fabricated Using High Precision CNC Machining and SU-8 Photoresist Technology

This paper presents two WR-3 band (220–325 GHz) filters, one fabricated in metal using high precision computer numerically controlled milling and the other made with metallized SU-8 photoresist technology. Both are based on three coupled resonators, and are designed for a 287.3–295.9-GHz passband, and a 30-dB rejection between 317.7 and 325.9 GHz. The first filter is an extracted pole filter coupled by irises, and is precision milled using the split-block approach. The second filter is composed of three silver-coated SU-8 layers, each 432 μm thick. The filter structures are specially chosen to take advantage of the fabrication processes. When fabrication tolerances are accounted for, very good agreement between measurements and simulations are obtained, with median passband insertion losses of 0.41 and 0.45 dB for the metal and SU-8 devices, respectively. These two filters are potential replacements of frequency selective surface filters used in heterodyne radiometers for unwanted sideband rejection.

Evaluation of Critical Geometrical Parameters and Alignment Corrections of Large Size Aerospace Systems

Metrological assessment of geometrical, form parameters plays an important role in development of quality hardware of aerospace systems such as missiles. These parameters are critical for mission performance and system evaluation studies. High precision CNC Coordinate Measuring Machines (CMMs) are extensively used for evaluating geometrical, form parameters in alignment checks of large missile subsystems, assemblies and tooling. These high precision metrological tools can also be used for geometrical and alignment corrections of critical missile subsystems. Alignment check of integrated missile is an important activity carried out during development of missile system. The critical aerodynamic parameters viz. nose tip deviation, cant angle and orthogonality of wings & fins and propulsion parameters such as thrust axis misalignment are evaluated using geometrical features available on integrated missile. These aerodynamic and propulsion parameters are used for aerodynamic studies and predicting missile trajectory during pre-flight simulation analysis. The deviation in these values directly affects the missile performance during flight. In case of high deviations, the above parameters are corrected mechanically in order to meet the design requirements. This paper brings out the applications and methodologies developed for evaluation and correction of geometrical and form parameters in alignment checks of integrated missiles

A new mathematical method of modeling parts in virtual CNC lathing and its application on accurate tool path generation

In industry, many taper shafts are designed with tolerances of a few microns. To cut them in finish turning, paths of the tool in virtual machining should be accurately generated beforehand. For this purpose, the dimension errors and surface roughness of the virtually cut workpiece should be predicted. Unfortunately, the current tool path generation methods cannot accurately calculate the errors and the roughness, resulting in the taper errors larger than the part tolerance. Our research formulates equations of the effective turning edge to accurately calculate the dimension errors and the surface roughness, and then proposes a new approach to CNC programming for high-precision CNC turning. It lays a theoretical foundation of modeling parts in virtual turning and can generate tool paths to machine taper parts with high accuracy.

An Intelligent Prediction of Surface Roughness on Precision Grinding

Precision grinding is generally used as the final finishing process, and it determines the surface quality of the machined component. It’s very difficult to achieve on-line measurement of the surface roughness. The purpose of this research was to study the surface roughness prediction and avoid the defect happening in the grinding process. A surface roughness prediction model was proposed in this paper, which presented the relationship between surface roughness and the wear condition of grinding wheel and grinding parameters. An AE sensor was used to collect the grinding signals during the grinding process to obtain the grinding wheel wear condition. Besides, a fuzzy neural network was used to obtain the prediction surface roughness. Grinding trials were performed on a high precision CNC cylindrical grinder (MGK1420) to evaluate the surface roughness prediction model. Experiment verified that the developed prediction system was feasible and had high prediction accuracy.

The Analysis and Optimization of Machining Precision Based on Electromechanical Matching in High-Speed Machine Tools

With the development of the high-speed and high-precision CNC machine tools, the interaction between mechanical system and servo drive torque in the feed system becomes more and more serious which affects the surface quality of the workpiece. In this paper, taking a small-sized vertical milling center as the research object, the characteristics of servo torque and mechanical system are analyzed, respectively. Then the influence of electromechanical matching on the tracking fluctuation of the feed system is discussed. Furthermore, aiming at the surface roughness of the workpiece, the influence of the interaction between servo torque and mechanical system on the surface quality of the workpiece is analyzed under different milling ways. Finally, a large number of experiments are carried out to verify the analysis above. At last, the optimization methods of machining precision based on electromechanical matching are put forward. It can be found that in the high-speed machining, the servo torque has lots of harmonics which act on the mechanical system with kinds of modals, leading to the vibration. The surface quality of the workpiece will be deteriorated rapidly when the mode of vibration is consistent with the sensitive direction of machining error. The surface quality of the workpiece can be significantly improved through optimizing the feed velocity and the processing method and realizing the electromechanical matching.