Numerical Control Code Research Articles

A method of improving chatter-free conditions with combined-mode milling

An analytical foundation for proposing a new method of highly productive finish slotting with 3-axis end-milling is presented. This is done by considering process stability of combined-mode end-milling with a combination of both up-milling (conventional) and down-milling (climb) modes. Physically the combined mode occurs when a pre-existing slot exists in what could have been a full-immersion process. A novel geometric consideration is presented for complete definition of size and location of the pre-existing slot in terms of the component radial immersions of the combined mode. The sum of component radial immersions constitutes the effective radial immersion. It is seen that some combinations of size and location of the pre-existing slot could engender heightened stability which reflects as elevated stability lobes with hyper-productive lobbing effects. Procedure for arriving at the stabilizing combinations of size and location of the pre-existing slot is summarized in five steps in the conclusion. This procedure was followed in arriving at combinations that yielded very high MRR per active pass and very low finish-slotting time for a numerically studied system. Incorporation of the productive combinations in Computer Numerical Control (CNC) code for mass finish slotting in future industrial workshops implementing the proposed technology of multi-spindle system with an arrangement of pre-slotting tools stabilizing the finish-slotting tool is expected to considerably reduce of manufacturing time.

Novel method for position-independent geometric error compensation of five-axis orthogonal machine tool based on error motion

It has been proven that error compensation is a key technique to improve machining accuracy. However, existing iteration and recursive compensation algorithm is difficult to realize. Hence, a simple and rapid compensation method is considerably necessary for engineering application. In this paper, a novel compensation strategy just by algebraic operation was first proposed for machining accuracy improvement. Error motion transformation was introduced to build the position-independent geometric error (PIGE) model according to homogeneous transformation matrix (HTM). Then, the analytical numerical control (NC) code expression with error compensation was derived and used for NC code generation. In addition, the presented method is appropriate for post-processing of non-orthogonal machine tool. At last, simulation and cutting experiment were demonstrated to verify the feasibility and effectiveness of the proposed method. Taking hemisphere surface as the test object, the simulation results showed that the effects of PIGEs could be eliminated by the proposed method. The experiment results with compensation indicated that the machining accuracy improved to about 14 % compared with those without compensation.

Interpolation using non-uniform rational B-spline for the smooth milling of ruled-surface impeller blades

The integral impeller is a complex part characterized by highly curved surfaces. Modeling and interpolation methods for manufacturing integral impellers are currently the subject of intensive research. In this study, to represent the shape of the ruled-surface blades, third-order non-uniform rational B-splines are constructed from data points for the hub and shoulder on the pressure and suction sides of the blade. Various methods for determining the tool axis vector offset and the location of the tool center for a cylindrical ball cutter are developed and verified with simulations of machining operations. To obtain a smooth interpolation and high accuracy in machining, a third-order non-uniform rational B-spline interpolation algorithm for ruled-surface blades is developed. This method can create a smooth transition between the hub and the blade shoulders. The method is implemented in an open-architecture computer numerical control controller. Simulations and experimental tests of machining tasks are performed to verify the non-uniform rational B-spline interpolation method. The test results show that this interpolation technique can produce a smooth and continuous path along the axes of motion. The new technique has the advantages of requiring fewer lines of numerical control code and producing higher machining accuracy.

Similarity-based Product Search for Next Generation Process Planning

The main challenges for companies in today's environment are an increased demand for customized products, shorter product life cycles and the resulting higher amount of variants. This leads to significant growth in existing production data. Additionally, improved ICT-systems and networks enable production planners to access a broader range of data, containing previous solutions and best practices and therefore the required knowledge and experience. Currently this knowledge and experience is not sufficiently used, as the process planning, work scheduling and route sheet generation is often a manual process, relying on the personal experience of the planner. This paper presents an approach to support the process planning with the help of an innovative method and corresponding digital tool. The digital tool gathers the master data records and numerical control code from previous products. It provides a library of attributes describing the products and the production processes. Through the employment of the developed method and digital tool, process planning can be sped up and standardize by eliminating or reducing manual search. Double work can be avoided. In total, the method and digital tool enable process planners to react faster and more accurately while gaining a competitive edge in dealing with the challenges on the global markets.

A web-based virtual CNC turn-milling system

This paper presents a different web-based virtual turn-milling system, which aims to address the common problems of existed systems. The system has not only economical value, such as shortening product cycle from design to market, but also scientific interest, like proposing a new trajectory planning method. In other words, it helps sellers and buyers better understand products and enables planners and machinists to make decision or verify CNC codes much more accurate and faster. This system is made up of three levels, which is client browser, server, and database, and every level is divided into several specified functions. Among all the functions, turn-milling simulation function is the most crucial part. To enhance the system’s features, many sub-function modules are also adopted in simulation functions. Through these modules, the system implements material removal function, tool trajectory planning function, numerical control (NC) code inputting and compiling function, and so on. To realize these functions, the whole machining system is developed by using the network superiority of Java language and Virtual Reality Modeling Language (VRML) technology interaction, which will also lead to smaller data volume. Owing to the transportability of Java language and VRML technology as well as the good understandability of the system, this web-based virtual turn-milling system is also suitable to the dynamic demonstration and machining simulation of other NC machine tools. Some future research directions are given to perfect the system in the end.

Design of a Digital Imaging and Machining System Programme for Human Bone Implants

Computer Aided Design and Computer Aided Manufacturing (CAD/CAM) is now used in the medical field as well. This paper outlines the design process and the final software package for a human bone implants. A Computer Tomography (CT) scan was used to scan the knee bone and the scanned pictures were sent to Digital Imaging Communication in Medicine (DICOM) viewer. The DICOM images with Digital Communication in Medicine ( DCM) format were converted to Joint Photographic Expert Group (JPEG) format JPEG format images were converted to to PDF format. Subsequently a PDF to Drawing (DWG) converter was used to convert the PDF file to DWG file format compatible with Mastercam. The final stage of the system involved generation of the NC (Numerical Control) code for the knee bone drawing and machining of the bone implant by the CNC machine. Oracle database express system has been used to design platform. Keywords—Computer Aided Design (CAD), Digital Imaging Communication in Medicine (DICOM), Computer Tomography (CT), Computer Numerical Control (CNC) machines, Human bone Implant, Imaging,.

Automatic Feature Extraction and CNC Code Generation in a CAPP System for Micromachining

Feature extraction from a part model and Computer Numerical Control (CNC) code generation for machine tool control are the two extreme activities of a typical CAPP system. The present work discusses about a new methodology for automatic part feature extraction and CNC code generation for the invention of micro features in tool based micromachining processes. It has two main components; the first one deals with Extensible Mark-up Language (XML) based feature extraction from feature based model and interactive feature recognition. The second one deals with autonomous CNC code generation based on manufacturing features using various mathematical logic. Feature extraction through XML files avoids complex feature extraction process and automation of CNC code generation avoids human expertise and compatibility issues. The developed system integrated with micromachine tool through RS 232 communication interface. Hence for the given micro features, CNC code generation take place automatically and transferred to the micromachine tool in online with minimal user interface. The application of the proposed system verified with a case study. The developed system is limited to the parts having micro external step and drill features. Incorporation of more micro features, consideration of various other process planning activities and its part program generation ensures a complete CAPP system for micromachining.

NC가공에서 허용오차를 고려한 가공속도 최적화에 관한 연구

Article history: In numerical control (NC) machining, a machining error in equipment generally occurs for a variety of reasons. If there is a change in direction in the NC code, the characteristics of the automatic acceleration or deceleration function cause an overlap of each axis of the acceleration and deceleration zones, which in turn causes a shift in the actual processing path. Many studies have been conducted for error calibration of the edge as caused by automatic acceleration or deceleration in NC machining. This paper describes a geometric interpretation of the shape and processing characteristics of the operating NC device. The paper then describes a way to determine a feedrate that achieves the desired tolerance by using linear and parabolic profiles. Experiments were conducted by the validate equations using a three-axis NC machine. The results show that the machining errors were smaller than the machine resolution. The results also clearly demonstrate that the NC machine with the developed system can successfully predict machining errors induced with a change in direction.

Directional morphological approaches from image processing applied to automatic tool selection in computer numerical control milling machine

Automatic tool selection in milling operation has become a very important step in the manufacturing and planning processes for 2.5D piece machining. The main contribution of this article is the development of a new method based on directional morphological approaches, applied to automatic tool selection in computer numerical control milling machines for machining a 2.5D of a geometry piece provided of three-dimensional model of computer-aided design or from an image taken with other devices. First, the image is preprocessed by applying several image processing techniques. Later, mathematical morphology as erosion or dilation to create structural element with the shape of the cutting tool is used. The method displaces a structural element throughout the entire image with the values of the lengths of the piece boundary and the cutting tool to select the correct cutting tool and tool path. Besides, with the same structural element, the zig and zig-zag contour trajectories are obtained in standard computer numerical control code. Results from these experiments show that the method makes it possible to obtain good performance in automatic tool selection when several types of pieces are processed.

2D AutoCAD Geometric Data Extraction and Post- Processing for Numerical Control

In this paper, a method of extracting 2D geometric data from AutoCAD drawing and post- processing for Numerical Control (NC) is presented. Geometric data already available in the Drawing Interchange Files (DXF) can be utilized to accurately and economically prepare part programs for controlling NC/CNC machine tools. AutoCAD, being generalpurpose software, stores its geometric data in a form that cannot be directly applied for automatic generation of Numerical Control (NC) codes. The way around the discrepancy between the structure of a drawing database (DXF files) and the information requirement for part programming is addressed in this work. NC programming of a test componentdrawn in AutoCAD is also presented.

A Three-Dimensional Virtual Manufacturing System with High Confidence for Turning

The tool trace of turning is intensive and complex, and its virtual manufacturing with high confidence level needs to be solved urgently. In response to this pressing need, based on the general mathematical model of master-slave alignment for shaft part profiles, efficient and low-redundancy "dynamic grid" for data structure and "tool driving" exact algorithm for cutting path, the paper built a database that was flexible to adapt the data structure, packaged an Open Graphics Library (OpenGL) to form the automatic three-dimensional engine, and developed a three-dimensional virtual manufacturing system with high confidence level for turning, with numerical control code analysis, error correction, tool path simulation of turning process, parts management, all-round display, virtual manufacturing process control and other functions.

Tool path optimization in postprocessor of five-axis machine tools

Generally, tool path is generated in a computer-aided manufacturing software considering only the geometry of machining parts. It is converted into numerical control (NC) codes in the postprocessor based on the particular machine kinematics. For some special types of five-axis machine tools, e.g., non-orthogonal five-axis machine tools, the generated NC codes may produce unqualified parts because of the existence of the non-linear error. Conventional commercialized postprocessors usually do not have the function of non-linear error checking. Observing that the tool path is a non-smooth trajectory full of corners and a series of connected line segments, cubic spline interpolation is applied to smooth the tool path at regular points in this study. The cutter tip center points are computed by the cubic spine interpolation, while the cutter posture vectors are obtained via linear interpolation. At the splines (for regular points) and the line segments (feature points), more points are chosen to be converted into NC codes to reduce the non-linear error, which is called data densification. Using the cubic spline to smooth the tool path and the data densification to reduce the non-linear error, a novel tool path optimization algorithm in postprocessor is proposed. Experiments were carried out on an inclined rotary spindle axis non-orthogonal five-axis machine tool. It shows that the proposed tool path optimization provides improved accuracy and surface quality.

Collisionless tool orientation smoothing above blade stream surface using NURBS envelope

In five-axis machining, tool orientation above a blade stream surface may lead to tool collision and a decrease in workpiece rigidity. Hence, collisionless tool orientation smoothing (TOS) becomes an important issue. On the basis of a constant scallop height tool path, the triangular facets in the faces, vertices format are constructed from cutter contact (CC) using the Voronoi incremental algorithm. The cutter location (CL) points candidate set is represented by an oblique elliptic cone whose vertex lies at CC using NURBS envelope. Whether the CL point is above its CC is judged by the dot product between the normal vector and the point on triangulation nearest to the CL point. The curvatures at CC are obtained by fitting a moving least square (MLS) quadratic patch to the local neighborhood of a vertex and calculating eigenvectors and eigenvalues of the Hessian matrix. Triangular surface elastic energy is employed as the weight in selection from the NURBS envelope. The collision is judged by NURBS surface intersection. TOS can then be expressed by selecting a CL point for each CC point and converted into a numerical control (NC) code automatically according to the postprocessor type of the machine center. The proposed method is verified by finishing of a cryogenic turboexpander impeller of air separation equipment.

A new interpolation method of variable period and step size in micro-EDM milling based on square constraint

Micro-electrode discharge machining (micro-EDM) milling can machine microparts. However, the micro-EDM milling efficiency is very low, especially for hard-to-machine materials. To improve this efficiency of micro-EDM milling in machining hard-to-machine materials, a new interpolation method with variable period and step size based on square constraint is proposed in the present paper. This method can prevent short circuit. Simultaneously, it can significantly improve the utilization of pulse power supply and machining efficiency. In addition, a new numerical control (NC) code storage strategy based on binary system is available for this method to reduce the NC code amount. Using this method, the efficiency of machining hard-to-machine materials is improved by 30%, and the amount of NC code is only 12.5% of the traditional method. This method can also satisfy the requirements of both real-time and offline interpolation, thus enhancing machining flexibility.

Research on Intelligent Glue-coating Robot Based on Visual Servo

Abstract At present, Glue-coating machines have some shortages, such as unintelligence, complexity of setting glue path for new parts. In this paper, real-time image capture was achieved by using digital camera technology and image processing technology. The captured image is converted into a character vector. Workpiece model is determined through comparing with the standard library and the similarity. The image of workpiece was vectored through frame extracting and fitting. With NC (Numerical Control) code generation technology, the NC code is automatically generated for sprinkler nozzle walking track. By Appling visual servo and embedding the vision system into feedback loop of the robot, the system achieves high-precision robot control. By extracting the glue line curve from image, thinning glue curve by morphological method, and extracting the frame information, the closure and quality of the glue curve can be detected. Results of test show that the effect is satisfactory and the method is effective.

Freeform manufacturing of a microoptical lens array on a steep curved substrate by use of a voice coil fast tool servo

We report what is to our knowledge the first approach to diamond turn microoptical lens array on a steep curved substrate by use of a voice coil fast tool servo. In recent years ultraprecision machining has been employed to manufacture accurate optical components with 3D structure for beam shaping, imaging and nonimaging applications. As a result, geometries that are difficult or impossible to manufacture using lithographic techniques might be fabricated using small diamond tools with well defined cutting edges. These 3D structures show no rotational symmetry, but rather high frequency asymmetric features thus can be treated as freeform geometries. To transfer the 3D surface data with the high frequency freeform features into a numerical control code for machining, the commonly piecewise differentiable surfaces are represented as a cloud of individual points. Based on this numeric data, the tool radius correction is calculated to account for the cutting-edge geometry. Discontinuities of the cutting tool locations due to abrupt slope changes on the substrate surface are bridged using cubic spline interpolation.When superimposed with the trajectory of the rotationally symmetric substrate the complete microoptical geometry in 3D space is established. Details of the fabrication process and performance evaluation are described.

A General Method of Numerical Simulation for Incremental Forming

This paper presents a general simulation method for sheet metal incremental forming(ISF). Firstly, a three-dimensional finite element model based on Dynaform was developed to simulate the process. The tool path during the process simulation was directly defined by numerical control (NC) code and so identical with that in operation. Then, the results of numerical simulations with different process parameters, such as tool diameter, depth increment and wall angle, were discussed in details. The simulations reveal that with the decreasing depth step, increasing tool diameter and wall inclination angle, the axial stress reduces and leads to thinning reduction and more uniform thickness distribution. In addition, as the definition of the tool path was in accord with the genuine motion trajectory of the tool, the results deduced from this model may be more precise compared with those from other previously simplified models.

Analysis and estimation of energy consumption for numerical control machining

Understanding and estimating the energy consumed by machining are essential tasks as the energy consumption during machining is responsible for a substantial part of the environmental burden in manufacturing industry. Facing the problem, the present paper aims to analyse the correlation between numerical control (NC) codes and energy-consuming components of machine tools, and to propose a practical method for estimating the energy consumption of NC machining. Each energy-consuming component is respectively estimated by considering its power characteristics and the parameters extracted from the NC codes, and then the procedure estimating energy consumption is developed by accounting for the total energy consumption of the components via the NC program. The developed method is verified by comparing the estimated energy consumption with the actual measurement results of machining two test workpieces on two different machine tools, an NC milling machine and an NC lathe, and is also applied to evaluate the energy consumption of two different NC programs on the NC milling machine. The results obtained show that the method is efficient and practical, and can help process planning designers make robust decisions in choosing an effective energy-efficient NC program.

Development of Five-Axis Machine Tool Cutting Simulation System with Nonorthogonal Linear Axis

Five-axis machine tools with two additional rotational degrees of freedom provide more flexibility in tilting the tool axis to various orientations than conventional three-axis machine tools do, subsequently increasing the cutting efficiency and avoiding tool collision against a workpiece. Also, the risk of programming error can be avoided by simulating the five-axis Numerical Control (NC) code before real machining. This work presents a five-axis machine tool cutting simulation system with a nonorthogonal linear axis configuration. A window-based cutting system written by Borland C++ Builder and OpenGL is also developed based on the kinematics model of the proposed machine tool. Furthermore, implementing and verifying the five-axis NC code demonstrates the effectiveness of the proposed scheme.

5-axis Interpolation and Synchronous Servo Process with NURBS Method

Abstract Nowadays, NURBS (Non-Uniform Rational B-Spline) method is widely used in CAD/CAM (Computer-Aided Design/Computer-Aided Manufacturing) to represent sculptured curves or surfaces. In this paper, we develop a 5-axis NURBS real-time interpolator and realize it in our developing CNC(Computer Numerical Control) system. At first, we use two NURBS curves to represent tool-tip and tool-axis path respectively. According to feedrate and Taylor series extension, servo-controlling signals of 5 axes are obtained for each interpolating cycle. Then, generation procedure of NC(Numerical Control) code with the presented method is introduced and the method how to integrate the interpolator into our developing CNC system is given. And also, the servo-controlling structure of the CNC system is introduced. Through the illustration, it has been indicated that the proposed method can enhance the machining accuracy and the spline interpolator is feasible for 5-axis CNC system.