STEP-compliant CNC system for turning: Data model, architecture, and implementation

STEP-NC, a new data model for CAD-CAM-CNC chain, is expected to encompass the whole scope of e-manufacturing. The new data model formalized as ISO 14649 is under development by ISO TC184 SC1 and SC4 for the replacement of the old standard so-called G&M codes, formalized as ISO 6983 which has been used since the 1950s. As the new data model is being established, development and implementation of STEP-compliant CAD/CAM/CNC system based on the new data model is drawing worldwide attention. Several systems have been reported in such international conventions as the ISO Expert Committee Meeting. Up to the present time, all the STEP-CNC systems are intended for milling operation. In this paper, the authors first present STEP-compliant CNC system for turning system including the data model, followed by a generic architecture and functionality. Implementation results obtained from a prototype system called TurnSTEP have been provided. Based on the results, the authors are convinced of the validity of the STEP-NC data model together with the effectiveness of the STEP-CNC system for turning.     

Design of a STEP compliant system for turning operations

The changing economic climate has made global manufacturing a growing necessity over the last decade, forcing companies from East and West to collaborate beyond geographic boundaries in the design, manufacture and assembly of products. The ISO 10303 and ISO 14649 Standards (STEP and STEP-NC) have been developed to introduce interoperability into manufacturing enterprises so as to meet the challenges of responding to production on demand. This paper describes and illustrates a STEP compliant CAD/CAPP/CAM System for the manufacture of rotational parts on CNC turning centers. The information models to support the proposed system together with the data models defined in the ISO 14649 standard used to create the NC programs are also described. A structured view of a STEP compliant CAD/CAPP/CAM system framework supporting the next generation of intelligent CNC controllers for turn/mill component manufacture is provided. Finally a proposed computational environment for a STEP-NC compliant system for turning operations (SCSTO) is described. SCSTO is the experimental aspect of the research and is supported by information models that and have been constructed using a structured methodology and object-oriented methods. SCSTO was developed to generate a Part 21 file based on machining features to support the interactive generation of process plans utilizing feature extraction. A case study component has been developed to prove the concept of using the milling and turning parts of ISO 14649 to provide a turn-mill CAD/CAPP/CAM environment.     

A STEP-compliant process planning system for CNC turning operations

Over the last 50 years, there have been many significant enhancements in computer aided systems which have influenced the CNC technology. One area that can be considered as a bottleneck to these CNC enhancements, and in particular to interoperability in CNC manufacturing is G&M part programming (ISO 6983). To overcome this bottleneck, the new standard ISO 14649, known as STEP-NC, is being developed to provide detailed information on component design, process planning and machining strategies to manufacture parts for the next generation of intelligent CNCs. This standard forms the basis of a new paradigm shift in the CNC domain to support digital modelling of CNC manufacturing resources. The research in this paper aims to identify major issues and develop new software tools to demonstrate the feasibility of interoperable CNC manufacturing based on STEP-NC. Besides the literature review on recent research and development on STEP-NC, this paper proposes a Process Planning System (PPS) with surface roughness chosen as the process planning objective. PPS consists of five modules: program reader, process planner, STEP-NC CAD viewer, STEP-NC CAM viewer and program writer. The reader is responsible for interpreting the geometry and the manufacturing data from a STEP-NC text file into a stored data list. The process planner uses this data list and enables users to evaluate surface roughness based on a mathematical model. Through the STEP-NC CAD viewer, the part geometry can be shown and via the STEP-NC CAM viewer the toolpath can be verified. Finally, the writer converts the stored STEP-NC data of the system into an updated STEP-NC file. An example case study component is used to demonstrate the PPS and show the interfacing of the STEP-NC data.     

ISO 14649-based nonlinear process planning implementation for complex machining

Increasing attention is being paid to complete machining, i.e., machining of the whole part in a single machine tool, in the metal working industry. For this purpose, complex machine tools equipped with machining components, such as multiple spindles and turrets have been developed by leading machine tool builders. The efficiency of complex machine tools is largely dependent on how the machining components are utilized. The main thrust of this paper is twofold: (1) Proposition of a nonlinear process planning based on the STEP-NC (STEP-compliant data interface for numerical controls) paradigm whose data model is formalized as ISO 14649, and (2) Development of an optimal solution algorithm for process planning for complex machining. The developed algorithm is based on the branch-and-bound approach and heuristics derived from engineering insights. The developed process planning method and optimization algorithm were implemented and tested via the TurnSTEP system developed by our research team. Through the experiments, we are convinced that the new process planning and algorithm can be used as a fundamental means for implementing the third type of STEP-NC [Suh S. TurnSTEP: Tools to create CNC turning programs. In: White paper presented on STEP Implementers’ Forum ISO TC184/SC4 Meeting. 2004], i.e., an Intelligent and Autonomous STEP-NC system for the CAD-CAM-CNC chain supporting e-Manufacturing.     

Striving for a total integration of CAD, CAPP, CAM and CNC

Over the last 50 years, conventional programming of the numerical controlled (NC) machine tools has been based on a data model stipulated by ISO 6983, or otherwise known as G-codes. It was designed to sequentially pass instructions to the controls of machine tools with little, if any, intelligence. It has been realized that this standard has led to serious impediments for the fulfilment of total CAD/CAM integration. The forthcoming ISO 14649 defines a new interface for exchange of information between CAD/CAM systems and NC machine tools. ISO 14649 is strictly harmonized with ISO 10303 (STEP), hence the name STEP-NC meaning an extended STEP for numerical control. There has been substantial amount of research being carried out concerning STEP-NC, in particular EU and USA; its benefits and potentials are revealing and appealing. The manufacturing industry may have to embrace itself with a revolutionary change even more dramatic than that of introduction of numerical control about half a century ago.     

Standard process monitoring and traceability programming in collaborative CAD/CAM/CNC manufacturing scenarios

The paper focuses on collaborative STEP-based CAD/CAM/CNC supply chains to program and automate machining process data monitoring and traceability activities. A traceability interface (traceability nc_functions) is defined for the new CNC programming standard ISO STEP-NC. CAM systems will be able to program monitoring and data access activities by inserting traceability nc_function calls in CNC programs. On the shop floor, controllers will automatically interpret these nc_functions to access process data while machining and will relate data records with the corresponding machining operations in a STEP-NC part program. With both types of information—process data and standard machining program (STEP-NC part program)—spread and technologically heterogeneous engineering systems will have full knowledge about what has happened in production. Traceability data access automation will assure data reliability. The paper describes a traceability scenario where standards such as MTConnect and ISA-95 support, rather than interfere with, the STEP-NC traceability proposal.     

An advanced STEP-NC controller for intelligent machining processes

Major improvements in high speed machining technologies are not followed by suitable evolutions of the programming standard ISO 6983, also called G-code. New STEP-NC standard aims at performing high level intelligent NC programming adapted to modern machining issues. The integration of manufacturing level in the numerical chain CAD–CAM–Simulation–CNC allows the implementation of a unique file gathering of all the needed information of a part that is directly machined without post-processing. In this paper, the authors show the new possibilities in terms of the following criteria: integrating simulation and optimization of the machining parameters, providing feedback to CNC controller, allowing modifications of the geometry and machining parameters on the CNC, computing new algorithms for tool-paths generation, adaptation to machine structure and characteristics, etc. A STEP-NC interface has been developed for CNC machine tools. It enables parts machining from a STEP-NC file and integrates several new possibilities and opens the way of intelligent high level programming including the machine model and an adaptation to machining real conditions.     

An innovative software architecture to improve information flow from CAM to CNC

Over the years, machine tool evolution has allowed faster equipment, using new configurations, to manufacture parts that were almost impossible to machine in the past. Despite this tremendous evolution in machine and control technologies, the metalworking industry is still using the old ISO 6983 G-Codes programming interface to control the motion of these machines. This programming interface is not the most flexible or most appropriate for use by new open-architecture machine controllers and object-oriented high-level machining interfaces such as ISO 14649 (STEP-NC). This work proposes an innovative language, the ‘Base Numerical Control Language (BNCL),’ which is based on a low-level simple instruction set-like approach. The architecture is designed around two concepts: the BNCL virtual machine, which acts as a virtual microprocessor, and the BNCL virtual hardware, which is an abstraction of the machine tool. The language is characterised by its simplicity and flexibility, two qualities that are critical in a market in which the capabilities and performance of machines are constantly improving. The proposed architectural concepts are validated through various computer simulation and physical tests, including performance throughput, trajectory driving, and CNC controller extension capabilities.     

STEP-NC compliant process planning as an enabler for adaptive global manufacturing

Manufacturing firms are seeking more efficient methods of CNC manufacture. ISO14649 informally known as STEP-NC has been proposed as a high-level hierarchical manufacturing information model as a replacement for the low-level machining instructions of ISO6983 and RS274D. In this paper, the applicability of STEP-NC as an enabler for creating an adaptive global manufacturing system is examined. The overall framework of the system is presented followed by an outline of its information requirements. Suitability of STEP-NC to support each requirement is then studied with the necessary additions highlighted. Finally, a test component is used in conjunction with a prototype of the advanced global manufacturing system to demonstrate the applicability of the STEP-NC standard to support manufacturing information in such a system.     

A novel methodology for cross-technology interoperability in CNC machining

In CNC part programmes, the lack of standardisation for representing part geometry and semantics of manufacturing operations leads to the necessity for existence of a unique part programme for each machine. Generating multiple programmes for producing the same part is not a value adding activity and is very time consuming. This wasteful activity can be eliminated if users are given the ability to write an NC program for a specific machine and robustly convert the program to syntax suitable for another CNC machine with a different structure. This, cross-technology interoperability, would enable for parts manufactured on old CNC machines using legacy code to be manufactured on new CNC machines by automatically converting the programmes. Every NC programme is written based on various categories of information such as: cutting tool specifications, process planning knowledge and machine tool information. This paper presents an approach for cross-technology interoperability by refining high-level process information (i.e., geometric features on the part and embedded manufacturing resource data) from NC programmes. These refined items of information stored in compliance with the ISO14649 (STEP-NC) standard may then be combined with new manufacturing resource information to generate NC code in a format that is compatible with machines based on different technologies. The authors provide a framework for this process of identification, semantic interpretation and re-integration of information. The focus of this paper is on asymmetric rotational components as the initial application area. To demonstrate the proposed cross-technology interoperability approach, a C-axis CNC turn–mill machine and a 4 axis CNC machining centre have been used with a simple test component.     

Dealing with feature interactions for prismatic parts in STEP-NC

Determining the precedence of machining features is a critical issue in feature-based process planning. It becomes more complex when geometric interaction occurs between machining features. STEP-NC, the extension of STEP (ISO 10303) standard developed for CNC controllers, is a feature-based data model. It represents all the geometric and topological product data minus feature interactions. In this paper, machining precedence of interactive and non-interactive STEP-NC features is discussed. Local and global precedence of machining features are defined on the basis of geometric constraints, such as geometric interaction of features and feature approach face and technological constraint such as access direction of the cutting tool. A software tool has been developed to visualize the STEP-NC part model and to generate the graphs of feature interaction and feature precedence. The output can be then used to augment the STEP-NC data in order to generate the optimal sequence of operations.     

Realization of STEP-NC enabled machining

A STEP-compliant CNC machine tool that demonstrated a G-code free machining scenario is presented. The aim of this research is to showcase the advantages of, and evaluate, STEP-NC—a new NC data model—by implementing it in a legacy CNC system. The work consists of two parts: retrofitting an existing CNC machine and the development of a STEP-compliant NC Converter called STEPcNC. The CompuCam's motion control system is used for retrofitting the machine, which is programmable using its own motion control language—6K Motion Control language and capable of interfacing with other CAPP/CAM programs through languages such as Visual Basic, Visual C++ and Delphi. STEPcNC can understand and process STEP-NC codes, and interface with the CNC controller through a Human Machine Interface. It makes use of STEP-NC information such as “Workplan”, “Workingstep”, machining strategy, machining features and cutting tools that is present in a STEP-NC file. Hence, the system is truly feature-based. The Application Interpreted Model of STEP-NC has been used.     

数控G代码转换为STEP文件方法的研究*

为了解决ISO10303和ISO14649标准的数控代码兼容性问题,基于可拓理论中的基元理论,建立了表达ISO6983标准中数控G代码知识的信息模型——复合元RG-function。根据STEP标准的要求,给出了G代码信息模型的EXPRESS语言描述模型,并在此基础上实现对G代码描述模型的实例化,从而生成STEP文件。构建了数控G代码向STEP文件转换的系统模型,介绍了其主要组成模块,并重点讨论了中间文件生成模块的算法流程。     

工件坐标系编程的译码程序设计

数控系统对零件加工程序段中的坐标值译码最为复杂,采用C语言开发了数控系统中的译码程序,实现了工件坐标系下的编程译码,为今后实现更多编程方法提供了方便。     

An assessment of the current state of product data technologies

Industrial organizations can benefit from the exchange or sharing of digital product data across the borders of disciplines, organizations and vendor-specific solutions. A number of international standards have been developed to make this possible. Of these, ISO 10303 (STEP), ISO/PAS 16739 (IAI/IFC) and ISO 15926 are the most prominent. The first release of STEP was published in 1994, the first release of IAI/IFC in 1997, and ISO 15926 in 2003. Today, many years after their introduction, it must be concluded that the industrial uptake of these standards has been poor. It must be concluded further that, with the current generation of PDT standards, the loss of data or meaning can hardly be avoided. Data exchange between heterogeneous applications is not really supported. In industrial practice, product data are still exchanged in native file formats, less ‘intelligent’ electronic standards, or-even worse-via paper media. The anticipated benefits of PDT standards are not yet reaped by industry. This article discusses the causes of poor performance and poor industrial uptake, with the aim to encourage the development of new strategies and technologies.     

Process control in CNC manufacturing for discrete components: A STEP-NC compliant framework

With today's highly competitive global manufacturing marketplace, the pressure for right-first-time manufacture has never been so high. New emerging data standards combined with machine data collection methods, such as in-process verification lead the way to a complete paradigm shift from the traditional manufacturing and inspection to intelligent networked process control. Low-level G and M codes offer very limited information on machine capabilities or work piece characteristics which consequently, results in no information being available on manufacturing processes, inspection plans and work piece attributes in terms of tolerances, etc. and design features to computer numerically controlled (CNC) machines. One solution to the aforementioned problems is using STEP-NC (ISO 14649) suite of standards, which aim to provide higher-level information for process control. In this paper, the authors provide a definition for process control in CNC manufacturing and identify the challenges in achieving process control in current CNC manufacturing scenario. The paper then introduces a STEP-compliant framework that makes use of self-learning algorithms that enable the manufacturing system to learn from previous data and results in eliminating the errors and consistently producing quality products. The framework relies on knowledge discovery methods such as data mining encapsulated in a process analyser to derive rules for corrective measures to control the manufacturing process. The design for the knowledge-based process analyser and the various process control mechanisms conclude the paper.     

Advanced CNC system with in-process feed-rate optimisation

Tight quality requirements and stringent customer demands are the main thrust behind the development of new generation machine tool controllers that are more universal, adaptable and interoperable. The development of some international standards such as STEP and STEP-NC presents a vision for intelligent CNC machining. Implementation of STEP-NC enabled Machine Condition Monitoring (MCM) is presented in this paper. The system allows optimisation during machining in order to shorten machining time and increase product quality. In the system, an optiSTEP-NC, an AECopt controller and a Knowledge-Based Evaluation (KBE) module have been developed. The aim of the optiSTEP-NC system is to perform initial feed-rate optimisation based on STEP-NC data to assist process planners in assigning appropriate machining parameters. AECopt acts as a connector between the process planner and machining environment with the intention to provide adaptive and automatic in-process machining optimisation. KBE based-MTConnect is responsible for obtaining machining know-how. Optimisation is performed before, during or after machining operations, based on the data collected and monitored such as machining vibration, acceleration and jerk, cutting power and feed-rate.     

新一代几何造型系统—GEMS4.0

ＧＥＭＳ４．０是清华大学ＣＡＤ中心在工作站上用Ｃ语言开发的新一代几何造型系统。和９０年代初问世的第三代几何造型系统相比，它具有如下特点：基于线框，表面，实体和特征表示的非流形造型；具有参数化设计，变量几何，尺寸驱动；扫描面，自由曲面和雕塑面用非均匀有理Ｂ样条（ＮＵＲＢＳ）表示，几何数据及属性的文件传送和数据库存取基于国际标准ＳＴＥＰ；基于窗口环境，面向对象的事件驱动和数据表格驱动的系统结构有利于开     

Strategic advantages of interoperability for global manufacturing using CNC technology

In the domain of manufacturing, computer numerically controllers (CNC) technology is a major contributor to the production capacity of the enterprises. The advances in CNC technology coupled with enhancements in computing systems have provided the basis to re-examine the way in which computer-aided systems (CAx) can be used to enable global manufacturing. Interoperability of the various components of the CAx chain is therefore a major prerequisite for manufacturing enterprises for becoming strategically agile and consequently globally competitive. Being interoperable, resources can be utilized interchangeably in a plug-and-produce manner. Over the last 8 years the eminence of a STEP standard for machining entitled STEP-NC (numerical control) has become a well-known vehicle for research to improve the level of information availability at the CNC machine tool. In this paper, the authors introduce the background to the evolution of CNC manufacturing over the last 50 years and the current standards available for programming. A review of the literature in interoperable CNC manufacturing is then provided relating to milling, turn–mill and other NC processes. The major part of the paper provides a strategic view of how interoperability can be implemented across the CAx chain with a range of standards used to regulate the flow of information. Finally, the paper outlines the advantages and major issues for future developments in interoperability, identifying future key requirements and limiting factors.     

一个开放可扩展的SDAI实现系统

STEP标准数据存取界面－SDAI为应用程序提供了独立于数据存储的STEP数据访问界面，SDAI允许访问不同的数据存储系统，有不同的实现语言联编方式，如果对每一种实用语言和数据存储系统单独实现SDAI，其工作量将是巨大的，该文选择系数据库作为SDAI数据存储系统，C语言作为实现语言，实现系统独立于不同的关系数据库系统，并且为不同语言的联编提供了一个统一的开发平台，提高了系统的开放性和可扩展性，为STEP在企业信息集成中的应用提供了核心操作，STEP建模语言EXPRESS，关系数据库，SDAI实现语言在模式表示上的不匹配是系统实现要解决的主要问题，该文从数据字典，STEP数据的字储与访问等方面阐明了系统实现时没模式之间的匹配过程。