Making CNC machine tools more open, interoperable and intelligent—a review of the technologies
Introduction
From the start of craft production in the 1800s to the pioneering mass production of the early 1900s there have been a number of revolutionary changes to manufacturing system's configurations. The most recognised traditional configuration of manufacturing systems was the dedicated transfer (machine) line, which enabled mass production at high efficiency and low cost. With the need of the 1970s and 1980s to produce a wider range of parts, “flexible” manufacturing was developed to meet these needs for the production of smaller batches of different parts. These systems used groups of computer numerically controlled (CNC) machines that could be reprogrammed to make different parts combined with automated transport systems and storage. These CNC machines became the central elements in the systems such as flexible transfer lines, flexible manufacturing systems (FMS) and flexible manufacturing cells (FMC).
However, the amount of flexibility existing in these systems was still believed to be limited. In order to prepare manufacturing companies to face increasingly frequent and unpredictable market changes with confidence, interoperable and more open manufacturing systems are needed. In the process of designing and operating interoperable and open manufacturing systems there is a need to distinguish from among system-level issues, component-level (i.e. machine and control) issues, and ramp-up time reduction issues [1], [2]. Most of the research effort has been spared on the issues at the system level, some at the component level and little on the ramp-up time reduction issues. At the component level, research work has primarily centred around the control issues concerning machine tools, with the aim to provide enabling CNC technologies for modular and open-architecture control [3], [4].
CNC machine tools are the main components in any manufacturing system. There are demands and new opportunities to empower the current CNC machines with the much-needed features such as interoperability, adaptability, agility and reconfigurability. To this end, there are two major issues that need to be addressed namely product data compatibility/interoperability and adaptable CNC machines. Up till now little research has been carried out in this field, but due to the developments of the new CNC data model known as STEP-NC, there has been a surge of research activities in trying to address the above-mentioned issues. This paper reports on these research activities and tries to address the issues of interoperability and adaptability for CNC machine tools.
Section snippets
Impediments of current CNC technologies
Today's CNC machine designs are well developed with capabilities such as multi-axis control, error compensation and multi-process manufacture (e.g. combined mill/turn/laser and grinding machines). In the mean time, these capabilities have made the programming task increasingly more difficult and machine tools themselves less adaptable. Some effort has been made to alleviate this problem, in particularly the trend towards open architecture control, based on OSACA [5] and open modular
The STEP-NC standard
Today a new standard namely ISO 14649 [11], [12], [13], [14], [15], [16] recognised informally as STEP-NC is being developed by vendors, users and academic institutes world wide to provide a data model for a new breed of intelligent CNCs. The data model represents a common standard specifically aimed at NC programming, making the goal of a standardised CNC controller and NC code generation facility a reality. Currently two versions of STEP-NC are being developed by ISO. The first is the
STEP-NC international community
In the second half of the 1990s, an effort from the international community backed by ISO started the major change in the concept of NC programming, through an international intelligent manufacturing systems (IMS) programme [26]. The programme was co-ordinated across four worldwide regions each with individual projects namely Europe, Korea, Switzerland and the USA. The major co-ordinators of the programme are Siemens (EU), CADCAMation (Switzerland), STEP Tools (USA) and ERC-ACI (Korea).
STEP-NC
STEP-NC for more open and interoperable machine tools
There are four types of research work related to STEP-NC: (1) conventional CNC control using STEP-NC; (2) new STEP-NC enabled control; (3) STEP-NC enabled intelligent control; and (4) collaborative STEP-NC enabled machining. The degree of adaptability increases from Type 1 to Type 4. It is to be noted that STEP-NC together with STEP is now forming a common data model for representing complete product information. Its far-reaching effect lies in a total integration of CAD, CAPP, CAM and CNC with
Portable STEP-NC tool–path
On 3rd February 2005, the OMAC STEP-NC Working Group hosted an STEP-NC Forum in Orlando, FL, USA. The main purpose of the demonstration is two-fold: (a) to demonstrate how STEP-NC information can support portable machining on five-axis machining centres; and (b) to see if STEP-NC tool–path description capabilities can be used to streamline the data flow between existing CAD/CAM systems and machining centres. The AIM (AP-238) version of STEP-NC was adopted, and its CC1 (conformance class 1)
Challenges and opportunities
Though some early research work has shown that STEP-NC can be an enabling tool for developing more open, interoperable and intelligent CNC machine tools, to gain acceptability by the NC community and particularly the CNC programmers and operators, a number of challenges still lie ahead. These challenges also present ample opportunities for various parties such as NC machine tool manufacturers, CNC controller manufacturers and commercial CAD/CAPP/CAM vendors.
Conclusions
Modern CNC machine tools, though capable in functionalities, lack adaptability, portability and intelligence. This is due to the fact that a 50-year-old language is still employed by these machine tools. NC programs following this format are only meant for execution on a specific machine tool. They cannot be reinterpreted by a CAM system or a SFP system for a different machine tool. Automatic generation of a 100% optimised NC program is not possible as design information and know-how about the
Xun W. Xu received a BSc and MSc from Shenyang Jianzhu University and Dalian University of Technology, PR China in 1982 and 1988, respectively. In 1996, he received a PhD from the Department of Mechanical Engineering, University of Manchester Institute of Science and Technology (UMIST), UK. He is now a senior lecturer at the Department of Mechanical Engineering, the University of Auckland, New Zealand. Dr. Xu is a member of ASME and IPENZ. In addition to his teaching and research activities at
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2021, Expert Systems with ApplicationsCitation Excerpt :The advent of more modern systems has introduced flexible manufacturing, which dominated the 1970s and 1980s and enabled the low-batch production of a wide range of parts. Flexible manufacturing was mostly realized thanks to CNC machines, which became a critical manufacturing resource at this time due to their capability of being reprogrammed to produce different parts (Xu & Newman, 2006). Consequently, CNC machines with multi-axis and multi-process workstation configurations were developed to support the high-speed manufacturing of precision parts such as complex aerospace components (Newman et al., 2008), allowing existing control to be narrowed down to tool size and machine command status.
Xun W. Xu received a BSc and MSc from Shenyang Jianzhu University and Dalian University of Technology, PR China in 1982 and 1988, respectively. In 1996, he received a PhD from the Department of Mechanical Engineering, University of Manchester Institute of Science and Technology (UMIST), UK. He is now a senior lecturer at the Department of Mechanical Engineering, the University of Auckland, New Zealand. Dr. Xu is a member of ASME and IPENZ. In addition to his teaching and research activities at the University of Auckland, Dr. Xu has been actively engaged in various industrial consultancy work. He heads the Manufacturing Systems Laboratory and the CAD/CAM Laboratory in the University of Auckland. His main interests lie in the areas of CAD/CAPP/CAM, STEP, and STEP-NC.
Stephen T. Newman gained BSc honours degree in production technology and management in 1982 from the University of Aston, Birmingham, on a sandwich degree sponsored by Land Rover Ltd. Having worked at Land Rover for 4 years he joined Loughborough University as a research associate and gained his PhD in 1990. In 1989, he was appointed, as a lecturer in manufacturing engineering, promoted to senior lecturer in 1997 and Reader in computer-aided manufacturing in 2000. In January 2006, he joined the University of Bath as a professor in the area of Innovative Manufacturing. He has 20 years of experience in European and National R & D programmes being involved in Eureka Factory, EU Framework V and framework VI programmes together with numerous national EPSRC research programmes.