NC Machine Research Articles

Digitized Modeling and Machining Simulation of Equal Base Bevel Gear

In order to achieve the NC machining to the equal base circle bevel gear with a standard cutter, to plan the machining path efficiently and to predict machining interference, based on the equal base circle bevel gear theory, the machining coordinate system for the bevel gear was established, according to gear tooth surface equations of the bevel gears, the tooth surface discretization function was derived, and through the calculation and get the discrete points, the gear surface was modeled in the software UG, and then the planning of the machining path, automatic programming and simulation processing were done. At last, simulation processing, analysis and comparison to the gear surface were carried on with the software VERICUT, improved that the gear surface modeling and NC machining methods were correct and feasible.

Calculation of linear technological dimensions with adaptation

Technological dimensional calculations are a necessary stage of engineering process and allow to determine machining allowance. The problem is that, when processing hard-to-treat materials on NC machines, it is necessary to provide optimal processing conditions for each workpiece based on reliable information on allowances at each operation. However, according to the existing methodology for calculation of technological dimensions and, accordingly, allowances, for the hypothetical workpiece with wide dimensional tolerances the technological dimensions and allowances are determined once, while it is assumed that the specific workpiece must engage with the tolerances of the hypothetical workpiece. The article deals with an example of calculating linear technological dimensions with adaptation, based on the results of monitoring and performing a separate calculation of the dimensions and allowances for each concrete workpiece in each operation. The calculation is carried out using a processing scheme, a graph, equations of dimensional chains and a computer program. As a result of the study, it was found that the calculation of linear technological dimensions with adaptation makes it possible to determine the actual values of allowances at each transition and thereby ensure predictable processing conditions.

Regular Neural Network Based Machining Parameters Optimization Model Of NC Machine Tool

Energy consumption process is the basis for energy efficiency improvement of machine tools. Most of the existing researches focus on the static modelling of energy consumption of a machine tool; however, there are a few studies that paid attention to that how process parameters influence the energy consumption of machine tools during processing. It is noted that the process parameters can be selected to reduce energy consumption during machining processes without additional investment. In this paper, a characteristic energy consumption model for NC machine tool was proposed. Then, the mapping rule between process parameters and energy consumption of machine tool was studied, and the model was solved with the regular neural network (RNN). Finally, the result was verified with an experiment of milling the surface of aluminium block, which can effectively improve the energy efficiency of machine tool. The experiment results are shown that regular neural network is used to optimize the process parameters and process the same machining characteristics; we analyze the in machining process of machine tool based on the three cutting parameters, and then, a model of energy consumption. We employ to learn, and use this trained model to select optimal parameters.

Development and performance evaluation of ultra-compact NC machine for "Tabletop Sized Factory"

Development and performance evaluation of ultra-compact NC machine for "Tabletop Sized Factory"

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.

Realization of processing with high precision using machining error correction control for small NC machine tools

Realization of processing with high precision using machining error correction control for small NC machine tools

Research on Correlation Analysis between Process Parameters of NC Machining and Quality Data Based on Grey Relational Analysis

With the wide use of CNC machine tools, data resources are gradually enriched. How to use the collected data resources for quality control becomes a hot topic for researchers. This paper introduces the use of grey correlation analysis theory to establish the relationship between the process parameters of CNC machine tools and quality data, and then provides a theoretical basis for the quality control using the process parameters of CNC machine tools.

Residual Life Prediction for NC Machine Tool Based on Performance Degradation

Residual Life Prediction for NC Machine Tool Based on Performance Degradation

Message from editor

Dear Readers,
 
 It is a great honor for us to publish Volume 7, Issue 1 of Global Journal of Computer Sciences: Theory and Research. 
 
 Global Journal of Computer Sciences: Theory and Research (GJCS) is an international online journal for scientists and professionals involved in all aspects of computer sciences. This journal serves as an international platform that fosters theoretical and practical issues and new applications for all scientists and professionals from the field of computer sciences including original research and innovative applications from all parts of the world.
 
 Aim of this issue is to give the researchers an opportunity to share the results of their academic studies. There are different research topics discussed in the articles. For example, Musa Peker, Ali Sasar, Osman Ozkaraca and Gurbuz Akcay examined estimation of HbA1c value using artificial neural networks. Fatih Tekmen and Ozgun Tanriover provided an an assessment of a government website by focusing on website usability evaluation with quickly applicable guidelines. In addition, Abdallah Tubaishat and Sara Sumaidaa carried out research on implementation guidelines for green data centres. Mohamed Rahou, Fethi Sebaa and Abdelmadjid Cheikh Sid Ahmed Benmansour discussed error compensation in NC machine tools. Amel Ourici, Wafa Tourab and Merabet Leila examined direct control of active and reactive power of a doubly fed induction machine. Sekhane Hocine and Labed Djamel investigated standard IEEE test systems 57-bus and Algerian 59-bus together and they concluded that the results of power flow compared with the popular MATPOWER software environment show the exactitude of our code calculation, and the enhancement of voltage profile, especially in buses where STATCOM is placed. Finally, Cigdem Bakir proposed a speech recognition system for Turkish language with hybrid method. 
 
 A total number of ten (10) manuscripts were submitted for this issue and each paper has been subjected to double-blind peer review process by the reviewers specialized in the related field. At the end of the review process, a total number of seven (7) high quality research papers were selected and accepted for publication.
 We present many thanks to all the contributors who helped us to publish this issue.
 Best regards
 Prof. Dr. Dogan Ibrahim
 Editor – in Chief

Error compensation in NC machine tools

This work contributes to the development of new approaches to tolerancing for machining using a machine tool with digital control. Our research is focused in two directions. First, it focuses on the manufacturing tolerances. The aim was to establish procedures for validating ranges of light manufacturing dispersions, manufacturing errors and machine tools with digital control, and cover various types of critical tolerances targeted. The second deals with design tolerances, for which we proposed a method for calculating functional tolerances.
 Keywords: Errors, tolerance, manufacturing.

Effect of geometric feature and cutting direction on variation of force and vibration in high-speed milling of TC4 curved surface

Curved surface parts with difficult-to-machine material are widely used in the industrial applications, and the three-axis NC machining with ball-end cutter is the commonly adopted method for some simple curved surface parts machining due to its high stiffness and simple operation. Due to the geometric feature variation for the curved surface and the bigger cutting force of the difficult-to-machine material, the cutting area and the cutting speed are changing all the time along the determined tool-path which results in a severe variation of cutting force and cutting vibration in high-speed milling process. This may not only affect the machining quality but also the tool life. In this way, the effect of the geometric feature of the curved surface and the cutting direction along the tool-path on the variation of force and vibration in high-speed milling of TC4 curved surface is studied. The experimental results show that both the cutting force and the cutting vibration increase when the tool-path curvature radius increases, while the cutting force decreases when the effective cutting radius increases and the cutting vibration will increase many times when the cutting area increases. Besides, the uphill cutting method for curved surface machining can obtain good machining quality and prolong milling cutter life. It can provide guidance for machining strategy selection especially for the cutting direction selection in the tool-path planning. The achievement, that can make both cutting force and cutting vibration small based on the geometric feature and the cutting direction, provides guidance for the machining planning of TC4 curved surface, which leads to improving machining quality and reducing tool wear.

A local smoothing interpolation method for short line segments to realize continuous motion of tool axis acceleration

In traditional processing, a large number of G01 blocks are adopted to discretize free surface or curve for NC machining. But, the continuity of G01 line segments is only C0, which may lead to discontinuity of axis acceleration, resulting in the frequent fluctuation of tool motion at the junctions in high-speed machining, deteriorating the quality of work piece, and reducing processing efficiency. To solve this problem, a local smoothing interpolation method is proposed in this paper. At first, the analytic relationship between the continuity of the trajectory and the continuity of the axes motion is first systematically described by formula. Based on this relationship, a local smoothing algorithm and a feed-rate scheduling method are proposed to generate a C2 continuous tool path motion with axis-acceleration continuity. The local smoothing algorithm smoothes the corners of G01 blocks by the cubic B-spline according to the cornering error tolerance specified by the user. After the feed rate at critical points of smoothed tool path was determined by a modified bidirectional scanning algorithm by considering constrains of chord error and kinematic property, an iterative S-shape feed rate scheduling is employed to minimize residual distance caused by round of time while ensuring the continuity of feed rate and acceleration. Then, a look-ahead interpolation strategy combined with smoothing algorithm and feed-rate scheduling as mentioned is proposed for real-time interpolation of short line segments. At last, simulations are conducted to verify the effectiveness of the proposed methods. Compared with the traditional G01 interpolation, it can significantly improve the processing efficiency and shorten the processing time within error tolerance.

Tool-path planning with constraint of cutting force fluctuation for curved surface machining

Curved surface parts are widely used in the industrial applications and the three-axis NC machining with ball-end cutter is the commonly adopted method for certain curved surface parts machining due to its high stiffness and simple operation. With the usage of this approach, the cutting area for different machining positions of the curved surface is changing all the time which results in a severe cutting force fluctuation among the machining process and the cutting force fluctuation is one of the vital factors that affect the machining quality of curved surface parts and the tool life. For the tool-path becomes the main factor that influences the cutting force fluctuation under the condition that the processing condition is determined, an appropriate tool-path planning method with the constraint of cutting force fluctuation for the curved surface machining is crucial for not only guaranteeing machining quality but also prolonging tool life. Based on the cutter location points obtained by the constant scallop-height method, cutting path interval and cutting step length are optimized and the cutter location mesh units are divided firstly, so as to meet the geometry accuracy for the curved surface machining. Taking the nodes of the cutter location mesh units as the cutter location points, the tool-path planning with the constraint of small cutting force fluctuation for the curved surface machining is carried out to improve the surface quality. Taking a saddle surface workpiece as an example, the experimental results show that the novel tool-path planning method proposed in this study has the smallest cutting force fluctuation compared with the other three traditional tool-path planning methods and can truly improve the machining quality of the curved surface parts. This research puts forward an novel tool-path planning approach on account of both the geometric feature of curved surface and the cutting force fluctuation in machining process of the curved surface parts, which provides a guidance for superior quality and high efficiency machining.

An efficient algorithm for calculating the cutter location point based on projection method

Aiming at improving the efficiency of calculating the cutter location point with toroid cutter based on the projection method in NC machining for surface, a new algorithm is proposed to calculate the cutter location point directly by torus surface approximating the surface to be machined. According to the geometric information of the points on the surface, the geometrical conditions of the two tangential tori are figured out, and then the contact point is obtained by solving multivariate non-linear equations. Parameters of the tangent point on the surface to be machined are calculated in the next step. Finally, the cutter location point is calculated by a small adjustment. The proposed algorithm is applied to calculate the cutter location point with toroid cutter in surface machining and compared with the existing algorithm. The results show that the computing time of the proposed algorithm in this paper saved about 63–78%.

Dynamic modal prediction and experimental study of thin-walled workpiece removal based on perturbation method

Because of the removal of the material, the material quality and stiffness matrix of the thin-walled parts will be directly changed and the dynamic characteristics will be significantly changed in the aviation thin-walled parts of the NC machine. When the structural parameters caused by the removal process frequently change slightly, it is necessary to solve the generalized feature problem, by using the classical method to obtain the dynamic characteristics repeatedly or the measured mode. However, it is clear that these methods are time consuming, labor intensive, and are not suitable for efficient prediction of dynamic modes. The method of matrix perturbation is proposed in order to solve the natural modal of the modified thin-walled structure. The finite element method is used to analyze the free vibration of the thin-walled structured blades. Based on the frequency, stiffness matrix, mass array, and vibration data which were extracted from the analysis results, the natural frequency of the modified structural parameters is calculated by the matrix perturbation method; then, the calculated results are compared with the finite element calculation results as well as the measured results. These results show that the process of applying the matrix perturbation method to modify the natural mode is effective, reliable, and time saving in the dynamic mode prediction of thin-walled NC machine, which lays the foundation for the establishment of three-dimensional stability domain. Finally, it can also provide theoretical basis for the resonance suppression of milling process by analyzing the evolutional rule of thin-walled part milling.

A disk tool cutting method for bevel gear manufacture on a five-axis machine

Two main popular cutting methods for bevel gear mass production, face milling and face hobbing, both require dedicated tools and machines available from only a few machine tool companies, which makes production more costly. This paper thus proposes a cheaper, more flexible alternative for producing small or medium batches of large bevel gears, a disk tool cutting method using a five-axis machine. In this method, the machine coordinates are derived based on tooth surfaces. The target’s topographic points of tooth surface are applied to construct a fitted surface which is then used to further refine the cutter-contact points to improve the precision of the gear produced. At the same time, mathematical models are established for both the tool and the machine. A coordinate transformation matrix is then generated by aligning the coordinate system of the tool’s reference point with each of the work gear cutter-contact points. Because different machines employ identical transformation matrices for producing the same workpiece, the machine’s five-axis coordinates can be derived using inverse kinematics. These coordinates are the resource to generate the NC machining data that allows NC verification software to perform cutting simulations. The simulation results verify the correctness of the mathematical models.

A circumscribed corner rounding method based on double cubic B-splines for a five-axis linear tool path

Linear segments are widely used to describe the tool path in five-axis NC machining. However, the geometrical discontinuity of adjacent segments will inevitably result in the feedrate fluctuation and excessive acceleration, thus deteriorating the machining accuracy and machining quality. In this paper, a new circumscribed corner rounding method for a five-axis linear tool path is proposed based on double cubic B-splines. Compared with commonly used inscribed corner rounding method, the transition curves generated by the circumscribed method have smaller curvatures, which is benefit of improving the feedrate of the corner regions of the tool path. A configuration of control points for the circumscribed corner transition spline is first given, and double cubic B-splines are subsequently employed to smooth the trajectories of the tool tip point and the second point on the tool axis according to the maximum approximation error. Then, based on the parametric synchronization between the bottom and top B-splines, the first and second geometrical derivative continuous conditions of the tool orientation are derived at the junctions between the remaining linear tool path and the transition curves. The proposed corner rounding method is capable of achieving tool orientation continuous change without any iteration, which can be used in a high-efficiency way. Simulations are performed to show the feasibility and efficiency of the proposed method.

Study on Temperature Measurement Point Optimization and Thermal Error Modeling of NC Machine Tools

Background: In precision machining, thermal error is the main source of machine tool error. And thermal error compensation is an effective method to reduce thermal error. Objective: In order to improve the prediction accuracy and computational efficiency of thermal error model, a new optimization method used for the selection of temperature measurement point is proposed. Method: This method is based on stepwise regression. According to the results of partial-F statistic, new variable is selected one by one, unapparent variables are deleted, and optimization selection of temperature measurement point is fulfilled, thermal error model of the NC machine tool is presented. Result: The new modeling method was used on NC machine tool, which reduced the temperature point number from 24 to 5. Moreover, model residual was less than 5µm after compensation. Conclusion: The result shows that the new thermal error model has higher prediction accuracy and less temperature variables.

Research on surface normal measurement and adjustment in aircraft assembly

Drilling and riveting are commonly used in aircraft panel assembly process. Due to the fixture positioning error and the deformation of workpiece, the real position and orientation of the workpiece as well as its 3D geometry at the drilling position varies from the nominal CAD model, which would cause an unfavorable impact on assembly quality. Therefore, surface normal measurement and adjustment at the drilling position is of great importance. In this paper, a fast and effective non-contact measurement method for normal vector and height of moderately curved surfaces is accomplished by four laser displacement sensors, and a dedicated NC machine tool is also developed for normal adjustment. Firstly, a novel sensor calibration method based on laser tracker is introduced, which can acquire the sensors’ position and orientation in Tool Coordinate System (TCS) at the same time. The normal vector at hole position is calculated by cross product of any two non-parallel vectors constructed by the four laser projection points on the panel surface. Secondly, the kinematic model of the machine tool is established to calculate the adjustment of each axis of the machine tool with the Homogeneous Transformation Matrix (HTM). Besides, an innovative method to identify the distance of two rotary centers based on two laser interferometers is proposed. Finally, a series of experiments are conducted to validate the feasibility of the proposed method. The results show that the angle deviation can be reduced to less than 0.5° after adjustment, while the accuracy of the surface height is ±0.04mm.

Use neutral data interfaces for Numerical Controllers Computerized

The standard used for programming CNC, ISO 6983 is still based on the same code system G / F inherited the programming of the first NC machines. Despite significant advances made in software and machines to CNC, there is the lack of a common infrastructure for information CAD / CAPP / CAM / CNC. This article describes the new standard STEP-NC (ISO14649), aspects of the development of CAD / CAM systems adhering to STEP-NC and integration of product data models and manufacturing using STEP-NC, STEP and OpenCNC architecture.