NC Code Research Articles

Study on Compliant Control by Cutter Radius Compensating for Rotating Curved Surfaces Polishing on NC Lathes

. Lots of new automatic polishing methods and equipments have been developed to solve the problem of low efficiency and quality in the traditional handwork curved surfaces polishing. However, these methods and equipments are complex and difficult to be applied in the industrial production. This paper proposes a new technology of rotate surface compliant polishing based on NC lathe cutter radius compensation. An efficient and compact rotate surfaces compliant polishing system is developed, which consists of a NC lathe, flexible polishing tool, workpiece, fixture and also the automatic programming software MASTERCAM. The polishing tool-path and NC code can be created in MASTERCAM. The value of the cutter radius compensation can also be set in NC code, so that the rotated surfaces can be polished by a traditional NC lathe. Experiment of polishing the aluminum sphere workpiece is taken, and the satisfying surface quality is achieved.

Tool path generation for a four-axis machine to engrave letters on tire sidewall molds

A tire sidewall is that section of the tire that bridges the tread and the bead. It is difficult to manufacture tire sidewall molds with a three-axis CNC machine, because the letters on the sidewall should be engraved perpendicularly to the sidewall surface. In this paper, a four-axis lettering machine that efficiently engraves letters and patterns on the sidewall mold is proposed. A bending projection algorithm is introduced to project letters on the sidewall surface without distortion. The procedures to cut letters and patterns using the four-axis lettering machine is proposed: (1) measuring the profile curve using a mechanical probe, (2) using a bending projection algorithm to project letters onto the sidewall surface without distortion, (3) generating the four-axis CL data, and (4) calculating the inverse kinematics to generate NC codes. The procedure is implemented using a PC-NC (Personal Computer Numerical Control) system, which has an open architecture based on the personal computer. The results demonstrate that the method is useful for manufacturing tire sidewall molds.

Analytical calculation of the envelope surface for generic milling tools directly from CL-data based on the moving frame method

Two closed-form solutions for calculating tool envelope surfaces are proposed based on the moving frame method. They have several advantages: (a) Given a sequence of cutter location (CL) data before post-processing into NC code, although we do not know the special configuration of machine tool, the tool envelope surface can be calculated accurately; (b) The two methods fit for a generic milling tool with a surface of revolution, such as a cylindrical cutter, conical cutter, drum cutter, and so on; (c) Since the calculation is developed based on the representation of the parametric form of the generating curve, it is convenient to use Bézier method, B-Spline or NURBS to unify the representation of the cutters and calculation of tool envelope surfaces. Several examples are presented to prove their effectiveness and good adaptability. The two methods can be used for NC machining simulation, evaluation and correction of the tool path.

DEVELOPMENT OF A PROTOTYPING SYSTEM FOR CUSTOM-CONTOURED FOAM CUSHION USING THE PRESSURE MAPPING METHOD

For people with limited mobility such as wheelchair users, prevention of pressure sore is an important health care issue. To relieve pressure at buttocks, foam cushion enveloping specific contour matching with an individual's buttocks has commonly been employed. This paper presents a prototyping system that generates custom-contoured foam cushion using the pressure distribution at the buttock–cushion interface. Based on the load–deformation characteristics of the foam material, this pressure distribution is converted into the corresponding deformation of the foam. A surface smoothing process approximates all discrete data points into a bi-cubic surface. ASCII NC codes are then generated for CNC fabrication of the cushion with the desired surface contour. This study integrates commercially available products into a fully automated system and can be readily implemented by seat/wheelchair cushion manufacturers.

Key Techniques and Advances of Grinding/Milling Spiral Flutes on NC Machines with Multi-Axis Linkage

Introduced systematically the forming principles and mathematical modeling of grinding/ milling spiral flutes with numeric control machines, overviewed the functions of multi-axis linkage and the determination technique of the number of the linkage axes, discussed the conversion technique of NC—STEP-NC code in programming with EXPRESS, presented advances of controlling systems with high performance. Much attention was paid to the explanation of the error modeling and the tool interference in the real machining with the error-compensation techniques. Trends were envisioned on key technique study of the forming principles for the spatial spiral flutes, function of multi-axes, tool interference in the real machining and simulation of the operation processing, as well as automatic generation of NC codes and the connection /compatibility of the codes with the mainline NC systems, in future.

Design and implementation of NC code compiler based on ANTLR

A design model of NC code complier based on ANother Tool for Language Recognition(ANTLR)was presented,which adopted the Extended Backus Naur Form(EBNF)to define the NC program syntax rule.The model was implemented with Java language,which can make it independent of operating system.The design and implementation of compiler were described from different aspects:lexical analysis,syntax and semantic analysis,information draws and so on.The practical results show that the model can construct the compiler prototype efficiently,compile the NC code faster and more correctly,and can be expanded easily.

Automated process planning method to machine A B-Spline free-form feature on a mill–turn center

In this paper, we present a methodology for automating the process planning and NC code generation for a widely encountered class of free-form features that can be machined on a 3-axis mill–turn center. The free-form feature family that is considered is that of extruded protrusions whose cross-section is a closed, periodic B-Spline curve. In this methodology, for machining a part with B-Spline protrusion located at the free end, the part is first rough turned to the maximum profile diameter of the B-Spline, followed by rough profile cutting and finish profiling with axially mounted end mill tools. The identification and sequencing of machining volumes is completely automated, as is the generation of actual NC code. The approach supports both convex and non-convex profiles. In the case of non-convex profiles, the process planning algorithm ensures that there is no gouging of the work piece by the tool. The algorithm also identifies when sections of the tool path lie outside the work piece and utilizes rapid traverses in these regions to reduce cutting time. This methodology presents an integrated turn–mill process planning where by making the process fully automated from design with no user intervention making the overall process planning efficient. The algorithm was tested on several examples and test parts using the unmodified NC code obtained from the implementation were run on a Moriseiki mill–turn center. The parts that were produced met the dimensional specifications of the desired part.

Flank Correction for Spiral Bevel and Hypoid Gears on a Six-Axis CNC Hypoid Generator

Abstract Because the contact patterns of spiral bevel and hypoid gears are highly sensitive to tooth flank geometry, it is desirable to reduce the flank deviations caused by machine errors and heat treatment deformation. Several methods already proposed for flank correction are based on the cutter parameters, machine settings, and kinematical flank motion parameters of a cradle-type universal generator, which are modulated according to the measured flank topographic deviations. However, because of the recently developed six-axis Cartesian-type computer numerical control (CNC) hypoid generator, both face-milling and face-hobbing cutting methods can be implemented on the same machine using a corresponding cutter head and NC code. Nevertheless, the machine settings and flank corrections of most commercial Cartesian-type machines are still translated from the virtual cradle-type universal hypoid generator. In contrast, this paper proposes a flank-correction methodology derived directly from the six-axis Cartesian-type CNC hypoid generator in which high-order correction is easily achieved through direct control of the CNC axis motion. The validity of this flank-correction method is demonstrated using a numerical example of Oerlikon Spirac face-hobbing hypoid gears made by the proposed Cartesian-type CNC machine.

Research on the Robotic Free Abrasive Polishing System for the Rapid Spray Metal Tooling

In the rapid spray metal tooling, metal film is spray-formed on the substrate and supported under the back, which will act as the working surface of the rapid metal tool finally. So the finishing process for the sprayed metal film is important to the quality and the lifecycle of the rapid metal tool. The finishing of the metal mould is frequently carried out manually, these kinds of operations are iterative, time consuming and require experience. Automation can introduce cost reduction minimizing production times on such manual finishing operations. This paper presents a robotic polishing system with free abrasive for the finishing of the rapid spray metal tool, which is consisted of a six-degree-of-freedom industrial robot manipulator, a high speed electrical polishing spindle and a numerical swivel table. Soft polishing pad and free abrasive are also selected for the robotic polishing system. The path planning is so important to the robotic polishing system that a partition & flexible path mapping method basing on UG CAM is developed to generate the uniform robotic polishing path on the complex mould surface. UG/Open GRIP programming module is used to generate the driving paths with different path intervals on the predesigned plane for each partitioned part. When the driving paths are projected to the mould curved surface, the uniform polishing paths with NC code can be generated by the multi-axis CAM module of the UG. And the path with NC code can then be transformed to the robotic polishing path. According to the elastic deformation and the abrasion of the soft polishing tool, the robotic polishing path should be adjusted to keep the smooth polishing process by offsetting the pre-compressed value and the abrasive compensation value along the polishing axis direction. Technical parameters of the robotic polishing process are also optimized through the experiments. Finally, the rapid metal punch mould is finished to test the robotic polishing system.

Implementation of online NURBS curve fitting process on CNC machines

The study aims to develop a method for implementing an online non-uniform rational B-spline (NURBS) curve fitting process on CNC machines for improving the quality and efficiency of machining. Conventional CAD/CAM/CNC systems usually induce some machining difficulties and limit the machining results in real applications. Therefore, some researchers have proposed various methods for improving the machining results. An online NURBS curve fitting process consists of the fetching and fitting stages for CNC machines is developed in this paper. The fetching stage fetches a block of NC code and generates motion commands for obtaining data points. The fitting stage executes the NURBS curve fitting method along with a given set of data points. Moreover, the optimal search method is designed for obtaining good results in the NURBS curve fitting process. Simulations and machining tests carried out on a vertical machining center show that the proposed approach reduces the machining time to about 23% while maintaining the machining quality for the sample test.

Study of applying reverse engineering to turbine blade manufacture

A turbine blade has complex shaped free-form surfaces that can be modelled as surfaces with variable curvature by high-degree polynomials. Industry typically utilizes a turnkey system and special-purpose machine tool to manufacture turbine blades. A turkey system is a closed form design. Users need only input relevant data to this system to manufacture the product directly. However, users are unaware of the internal operation of the system. With rapidly advances in computing technology, commercial CAD/CAM systems can be utilized to design freeform surfaces and generate a tool path for the designed surfaces. This study uses a reverse engineering technology that is used to reconstruct the CAD model for a turbine blade. The prototype is measured by a coordinate measuring machine to obtain the geometrical control data points that are used to generate the CAD model in the UniGraphics (UG) CAD/CAM system. The UG/GRIP (GRaphics interactive Programming) language is used to generate the cutter location data rather than using the default UG CAM module. A five-axis NC code is acquired by the developed postprocessor and verified by the solid cutting simulation software VERICUT®. Real turbine blade machining is performed on a table/spindle tilting five-axis machine tool, demonstrating the effectiveness of the proposed approach.

Experimental investigation and simulation of machining thin-walled workpieces

An enhanced simulation model is presented in this paper to predict form deviations in end milling processes of thin-walled structures. The calculation of tool engagement is based on level curves representing surface geometry of the workpiece and the NC code driven sweep volume. To consider influences of force-induced deflections resulting in static form errors on machined surface of the workpiece, a model for superposed stresses is enclosed. Derived from the tool engagement, the cutting force is predicted using a parametric force model. The experimental investigations within the measuring of static and dynamic form errors during processing and afterwards are shown and measurement results are compared with results of the cutting simulation to verify the proposed method. The presented achievements are deduced from research activities aiming at an increased understanding of shape deviation induced by interactions between tool, workpiece and clamping device during machining.

A re-configurable cross-sectional imaging system for reverse engineering based on a CNC milling machine

This paper presents a novel reverse engineering digitizing system for full part geometry, which is based on a cross-sectional imaging device built in a NC milling machine. The system successively captures a picture for each planar cross-section contour of the part by end-milling and CCD imaging, and builds the geometry for both external and internal surfaces of the complex 3D part based on a set of the vectored cross-sectional contours. The system mainly consists of three components: a NC milling machine, a cross-sectional imaging device and a computer control unit. Some issues involving the principle and process flow of the system, encasing materials, cross-sectional imaging and NC code generation, etc. are described in detail. Built on an existing NC milling machine, a portable device for capturing the cross-sectional images is designed, which includes an isolated light source, a digital camera, a protective case, a rigid arm and a robust tripod. The device, connected to a computer control unit, serves as a highly flexible accessory for the NC milling machine, constructing the cross-sectional imaging system for reverse engineering. Furthermore, the error analysis and accuracy assessment of the system are also addressed. A typical case is discussed in detail to illustrate the applications of the system. Such a re-configurable digitizing system for reverse engineering offers a number of advantages, such as the functional extension of an existing NC milling machine, low costs, and rapid construction. As a result, this system provides a feasible and useful scheme for many enterprises to construct their own reverse measuring system based on existing equipment to aid in rapid product development and extend the function of existing equipment.

A special CAD/CAM software for electro-discharge machining of shrouded turbine blisks

In this paper, a special-purpose CAD/CAM software package, BliskCad/Cam, based on a commercial CAD/CAM software Unigraphics is developed to reduce difficulties in CNC-EDM of the shrouded turbine blisks. The software package consists of five modules such as electrode design, path searching, and machining simulation module. Functions of BliskCad/Cam include parametrical reconstruction of 3-D model of the blisk, intelligent design of complex shaped electrode, automatic generation of NC codes, search of interference-free tool path for multi-axis NC-EDM and machining simulation, etc. Experimental verification is conducted by using BliskCad/Cam and the results show that it satisfies the requirements, and can realize precision machining and reduce accessorial time remarkably.

Fast Bezier interpolator with real-time lookahead function for high-accuracy machining

This study presents a real-time fast Bezier interpolation method that solves linearly segmented contour problems that occur during milling using conventional CNC machines. Depending on the length and the CSB criterion, these linearized segments can be regarded as noise, continuous short blocks (CSBs), or G01 blocks. The CSB criterion proposed in this paper is employed to identify CSBs during the NC code interpreting stage. The CSBs are fitted into cubic Bezier curves and interpolated to produce smoother contours in real-time machining. Two different NC programs possessing a large number of short blocks were tested on our PC-based real-time control system. Simulations and experimental results demonstrate that the proposed fast Bezier interpolator (FBI) with real-time lookahead function provides satisfactory performance.

Research on Sawing and Milling Features and NC Programming of Plastic Door and Window

In this paper, the structure of plastic door and window and the characteristics of sawing and milling machining PVC profile are introduced, and on the basis of analyzing the relationship between function and kerfs of the window parts, the feature model of machining window profile is constructed, hereby making the geometry modeling and defining the essential elements of design feature make the process of automatic NC code generation simplified and its reliability strengthened.

Design of a generic five-axis postprocessor based on generalized kinematics model of machine tool

This paper presents a generic five-axis postprocessor system for various five-axis machine tools. The generalized kinematics model of common five-axis machines is constructed by combining two rotational degrees of freedom on the fixture table and two rotational degrees of freedom on the spindle. The complete analytical equations for NC data are obtained through homogeneous coordinate transformation matrix and inverse kinematics. The derived five-axis NC code expression is a general form suitable for all kinds of five-axis machine tools with three orthogonal linear axes and two orthogonal rotational axes. A window-based postprocessor software written by Borland C++ Builder and OpenGL has been developed according to the presented algorithm. The wireframe model of the configured five-axis machine tool can be promptly shown and rotated/zoomed dynamically on the screen to assist the user to input relevant parameters correctly and efficiently. Through the implementation of the developed postprocessor and the verification by the solid cutting simulation software as well as the real machining experiment, the effectiveness of the proposed scheme was confirmed.

Precise bi-arc curve fitting algorithm for machining an aspheric surface

With the rapid development of the information/image system and aero-space industries, high quality optic aspheric surface lenses play an increasingly important role for completion of the functionalities. Aspheric lenses are non-spherical surfaces having rotation symmetry about the lens axis. The aspheric lens has various shapes according to its application and often requires tens nanometer order form accuracy since surface roughness and form accuracy play essential roles in the functional performance of the optical products. Interpolation of the aspherical surface path must precisely meet the allowable tolerance. Linear interpolation of the aspheric surface path for CNC machining generates an enormous amount of NC code to satisfy the extremely small tolerance, and produces scallops on the machined surface due to the acceleration and deceleration of the tool during every linear motion. Alternatively, interpolations with bi-arcs are used. In this paper, in order to minimize the error induced by the cutting tool path and to shorten the calculation time of interpolation, a precise -arc interpolation method is proposed. The developed algorithm of bi-arc interpolation meets the given tolerance precisely. This is guaranteed by an analytical proof and error maps. Another advantage is its ability to calculate about five times faster than the existing arc interpolation, since iterative calculations for the maximum error can be omitted. The developed algorithm has been used for the precise aspheric machining.

Machining Simulation and Experimental Research of Complex Surface Parts Based on the PMAC

In order to machine the complex free surface, in this paper, NC interpolation of any complex surface is realized used the recursive reconstruction algorithm. The interpolating errors of this algorithm are controllable, and its applicability is relatively wide. Then, these NC codes of the complex human’s free surface are obtained with data exchange of the manufacturing module in the software UG, and machining simulation is obtained used NC codes. Finally, these NC codes are entered into the NC micro-machine tool, which is controlled by the PMAC and developed by ourselves, and the experimental research of the human’s free surface has been finished on this machine tool. The experimental results show that the NC interpolation accuracy of this recursive reconstruction algorithm is very high, and the machining simulation and machining experiments of the complex human’s surface are completely consistent. The study result shows that the complex surface molding is smooth and continuous, and the machined surface is satisfactory.

STEP-NC and function blocks for interoperable manufacturing

Interoperable manufacturing systems help manufacturing companies stay competitive in the environment of frequent and unpredictable market changes. An important part of a manufacturing system is computer numerically controlled (CNC) machine tools. Over the years, G-codes have been extensively used by CNC machine tools and are now considered as a bottleneck for making these machines adaptable and interoperable. Two new technologies emerged in recent years: Standard for the Exchange of Product data for Numerical Control (STEP-NC) and function blocks. The STEP-NC data model represents a common standard for NC programming, making the goal of a generic NC code generation facility a reality. Function blocks are an emerging IEC standard for distributed industrial processes and control systems. They can be used for CNC controls to encapsulate machining data, such as machining features and their needed algorithms. This paper introduces the above two new standards and the technologies that are developed based on the standards. The main body is devoted to analyze the standards from the functionality viewpoint. These functionalities include, bidirectional information flow in computer-aided design/computer-aided manufacturing, data sharing over the Internet, the use of feature-based machining concept, modularity and reusability, intelligent and autonomous CNC, and portability among resources. Some implementations are also presented to showcase how the standards are used to develop technologies for interoperable machining. Note to Practitioners-Modern computer numerically controlled (CNC) machine tools are limited in functions because their controllers rely on G-codes for communications. G-code is considered a "dumb" language as it only documents instructional and procedural data, leaving most of the design information behind. G-code programs are also hardware dependent, denying modern CNC machine tools desired interoperability and portability. In recent years, two new standards emerged, STEP-NC and function blocks. They may hold the key to empowering CNC machine tools with richer information which, in turn, gives CNC machine tools the ability to "think" intelligently and to be interoperable. This paper introduces these two standards, the technologies that have been developed based on the standards and some prototype systems using the standards and technologies. The intention is not to highlight any achieved research outcome. Instead, the focus is on informing the research and practical world about these new standards, analyzing them from the viewpoint of supporting interoperable CNC machine tools, and offering some futuristic views about these standards and technologies. While these standards are still in their infancy, research activities and prototype systems are already coming thick and fast. There seems to be a "healthy" mixture of participants working in the field. They range from the manufacturers of all systems related to the data interface (i.e., CAM systems, controls, and machine tools), to the users and academic institutions.