Advanced Design and Manufacturing Based on STEP

This chapter gives an overview of STEP (Standard for the Exchange of Product model data), assuming that the reader may not be familiar with STEP. The chapter gives a short example of an industrial use of STEP. Then it touches briefly on the history and objectives of STEP, followed by the organization of the Parts of STEP. Next, it goes into technical details of (1) information modelling using EXPRESS and EXPRESS-G, (2) data representation using STEP Part 21 files and other methods, (3) the STEP integrated resources, (4) application protocols (APs), including application activity models (AAMs), application reference models (ARMs), units of functionality (UOFs), application interpreted models (AIMs), application interpreted constructs (AICs), application modules (AMs), and conformance classes, and (5) STEP-NC. The chapter closes with some comments on the future of STEP. The Appendix at the end gives some additional sources of information about STEP.

This chapter begins by describing characteristics a process planning language should have. Then it discusses the extent to which four process planning languages have these characteristics. The first two of these are STEP standard process planning languages (all of AP 240 and part of AP 238). The third is part of ISO 14649. The fourth, called FBICS-ALPS, is a version of the ALPS language adapted for FBICS, a system that does automatic feature-based process planning. Next the chapter summarizes the machining features available in AP 238, ISO 14649, and AP 224. The way in which FBICS does feature-based process planning is presented and a system is described that translates FBICS plans into ISO 14649 plans (which are conceptually identical to AP 238 plans). Finally, the chapter is summarized, and improvements in FBICS needed to make it industrially useful are presented.

Nowadays, the process planning for sequencing NC (numerical control) machining operations is still done manually in principle. In the last decade several approaches for automatic process planning based on Artificial Intelligence (AI) and heuristic algorithms have been developed. Additionally, new technologies such as CAD/CAM (Computer Aided Design/Computer Aided Manufacturing) systems, feature-oriented specifications, and interfaces (e.g., STEP-NC) were introduced. Nevertheless, the process planner still has to modify and acknowledge the generated Workplans manually. In order to overcome this problem, an approach for enabling the automatic preparation of STEP-NC based Workplans with methods known from graph theory is introduced in this chapter. Therefore a STEP-NC Workplan is mapped into a directed graph in a mathematically defined way. Based on that, it is possible to use algorithms to find the shortest path and a Hamiltonian Path (HP) inside this directed graph as optimal sequenced solution under given requirements. Thus, the Workplan will be structured and reordered. Finally, the corresponding NC machining code will be generated and distributed to the machinery. Hence in this chapter, the requirements, the investigation, and the selection of suitable knowledge structuring and processing concepts, the mathematical fundamentals, and the work flow of sequencing a system are investigated. The focus of this chapter is the investigation of heuristic algorithms in order to sequence the STEP-NC machining operations. Finally, a preliminary demonstrator is introduced.

This chapter discusses the realization of direct translation of feature-based CAM files into feature-based CNC part program files. The information infrastructure that allows this to happen is STEP-NC, as described by ISO 14649 Parts 10 and 11. Among the many benefits cited for STEP-NC, the elimination of the costly and inefficient process of post-processing using one standard CNC definition is most commonly cited. However, this chapter argues that a much greater benefit can be found using STEP-NC to resolve the CAM/CNC impedance mismatch where CAM comprehensive process information is reduced into motion primitives. The CAM/CNC impedance mismatch and resulting lack of process information make intelligent machining difficult. Given this perspective, a demonstration system was developed to show that feature-based CNC is possible with STEP-NC, which preserves more feature-based CAM process knowledge to make intelligent machining possible. The demonstration system incorporates: (1) part representation using STEP-NC Part 21 files, (2) reading and analyzing feature-based elements of the STEP-NC, (3) translation into a CNC feature-based representation, and (4) generation of actual CNC programs relying on conversational programming “Canned Cycles”. Cutting and simulation tests have confirmed the advantages of the approach. Overall, the demonstration system shows that a standard information infrastructure such as STEP-NC is essential for advancing manufacturing to enable improvements in efficiency, product quality, life-cycle cost, and time-to-market.

There is no doubt that today manufacturing is more competitive and challenging than ever before in trying to respond to “production on demand”. Due to the complexity of programming there is a need to model their process capability to improve the interoperable manufacturing capability of machines such as turning centres. This chapter focuses on the use of the new standard; ISO 14649 (STEP-NC), to address the process planning and machining of discrete turned components. It explores how ISO 14649 can be used to combine turning and milling operations to support interoperable CNC manufacturing of rotational asymmetric components at a single turning centre. The major contribution of this chapter is the creation of a computational environment for a STEP-NC compliant system for turning operations, namely SCSTO. SCSTO is the experimental part of the research, supported by specification of information models and 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 utilising feature extraction. An important aspect was the need to overcome the complexities of component geometry including milling features so as to have the ability to manufacture turn/mill components.

Computer Numerical Control (CNC) stone cutting technology with circular sawblades has been used to machine stone construction parts such as flagstones, rebates, mouldings, columns, balusters, etc., from dimensional ashlars. There are major differences between conventional metal cutting and stone cutting processes using circular sawblades, not to mention the fact that each process is governed by specific technology parameters. Circular sawblade machines used for stone cutting can be quite complex, with five or more axes. In some cases, they are automated using CNC systems with the same programming technology as the CNC machines for metal cutting. The need to increase productivity, quality and effectiveness in stone cutting has challenged the stone processing industry to make technological adaptations of successful concepts applied in other industries. While the STEP-NC standard has shown its benefits for conventional metal cutting, the main issue discussed in this chapter is whether STEP-NC can also bring benefits to the stone cutting sector, where new trends in regard to outsourcing, collaboration and even shop-floor integration have not traditionally been major business issues. A secondary issue is about how standards could accommodate sawblade stone cutting technology. In an attempt to address both of these issues, the chapter reviews some particularities of sawblade stone machining processes and proposes an extended STEP-NC compliant model.

To implement STEP-Compliant CNC, the implementing platform is very important. How to design open, STEP-Compliant CNC software and hardware platform becomes a hot research topic. A lot of research was focused on the STEP-NC data pre-processing of the STEPCompliant CNC, but how to design flexible, open structure software and hardware platform for STEP-Compliant CNC implementing was not described in detail. In this chapter, the requirements of STEP-Compliant CNC system are analysed. Based on these requirements, an engine based platform is given as the software platform according to the reactive characteristic of the CNC system. In this platform, the software structure is designed as the Decision Unit (DU), Function Description Data (FDD) and System Engine (SE). The intelligent control rules and algorithms are designed in DU. The control rules of the NC functions are designed as the FDD, which works like a dictionary. FDD can use the resource of DU with specially designed Dynamic Link Library (DLL). SE is built upon this dictionary. When the system started, SE gives response to the stimuli according to the description of FDD. It can call the decision making functions through the description of FDD. Statechart method is used for the modelling of control rules, an FDD generator being designed to convert the modelling data of control rules to FDD. With this method, FDD can be easily derived. For this flexible software architecture, a corresponding flexible hardware platform is also designed. In this chapter, an Ethernet based industrial fieldbus is used for the hardware platform. The implementing details are given. With this design methodology, system upgrading can be easily done by simply regenerating of FDD and hardware reconfiguration.

Machining process optimization is the selection of machining parameters for a given process to achieve the maximum material removal rates within the process and machine limitations. Since the majority of those limitations directly relate to the cutting forces generated during the machining process, accurately calculating these cutting forces is not only critical to the optimization effort but also to the preservation of the equipment used in process. Calculation of the cutting forces requires knowing the cross-sectional geometry of each tool path over the course of the machining process. Although this geometrical information is available when three-dimensional (3D) modelling is applied in modern CAM systems, there has been no direct means to extract this information for use in the cutting force calculation and process optimization, until the recent work on ISO 10303 AP 238 (STEP-NC). This application protocol provides a new data model to transfer product data from CAM systems to computerized numerical controllers (CNC). It also contains the necessary data structure to implement the tool path geometry information into the process optimization. This protocol offers an unprecedented opportunity to control and manage the machining process based on explicit in-process information contained in the model that was previously unavailable. In this chapter, the fundamentals of cutting force calculation are explained, the tool path cross-sectional geometry in machining operations and its parameterization in ISO 10303 AP 238 are illustrated, the basic principles of force based optimization are described, along with a depiction of the optimization implementation plans. All of this demonstrates the vital role ISO 10303 AP 238 plays in machining process optimization.

Modern manufacturing requires a flexible numerical chain of industrial products, in particular the relationships between CAD/CAM solutions and CNC. No longer can CNC controllers restrain their tasks at the execution of inflexible orders and choices made at earlier stages of the numerical chain. Thus, in a STEP-compliant environment, the CNC controller possesses a broad decision-making power to optimize the NC programming according to the machining equipment properties. The NC programming environment then has to face new challenges. In the first part of the chapter, an implementation method leading to STEP-NC advanced manufacturing is proposed. This approach is divided into three successive sceneries of STEP-NC deployment for progressive improvements. Industrial concerns can also use STEP-compliant applications with their current machining equipment. In the second part of the chapter, the STEP-NC Platform for Advanced and Intelligent Programming (SPAIM) developed at IRCCyN is presented. This platform controls current industrial machine tools directly from STEP-NC files, which benefits from this new data model. It also includes new tool-paths programming methods, such as pattern strategies for trochoidal milling and plunging tool-paths. The platform demonstrates the benefits of STEP-NC for industry and also forms a basis for future STEP-NC related research and validation.

In the early twenty-first century, manufacturing companies face increased productivity pressures and requirements for greater product variability. One of their biggest challenges is to make, while cooperating with multiple design and supply chain partners, the first part “correct and fast”. This requirement leads to the need for a data exchange standard that allows disparate entities and their associated devices in a manufacturing system to share data seamlessly in a common format. This will enable, in the future digital factory foundation, the development and use of a “Smart and Ubiquitous NC machining workstation” that represents the brain and knowledge repository of the manufacturing system, based on high bandwidth information, real-time networking, and the ability to be adaptive (self-learning and flexible). The foundation of the Smart NC Machining Workstation is a STEP-compliant NC system connected to a Manufacturing Information Pipeline and distributed hubs for data acquisition from compliant devices as well as for agent-based communication with legacy data. This structure will support a self-learning decision controller providing intelligent science-based algorithms for automatic and optimised tool-path generation and on-line corrective software, preventive maintenance, hardware diagnostics based on statistical process control. Standardisation of the whole process will be achieved through the use of STEP and related standards to form an interoperable and adaptable solution across varied equipment and devices. Only such a standardised and digitised product-process-resource description will enable the transformation from resource-based to knowledge-based, networked and adaptive manufacturing.

Manufacturing firms continuously strive to improve existing methods or develop new ideas to reduce production costs and lead times in order to provide quality assured parts rapidly to customers. Maintaining control over the processes involved in manufacturing is therefore vital. The manufacturing process chain includes product design, machining and measurement processes as well as the interpretation of measurement results. However, these process chain elements are currently regarded as separate islands of information. In the large majority of current manufacturing companies the machining and inspection processes are not integrated. This limits the process control capability in terms of modifying the machining process parameters. In-process modification of machining parameters such as the work coordinate system (WCS) offsets, tool diameter and length, etc. can lead to improvements in the quality of manufactured parts and also control the rejection rates for parts produced in batches. In this chapter, literature related to statistical process control and manufacturing data analysis are presented together with a commercial process control solution, namely the Renishaw Productivity+. The authors envisage the use of STEP-NC standards as one of the ways to integrate machining and inspection processes for CNC machine tools. Based on the standards a process control information model for CNC manufacturing has been specified. The final part of the chapter describes a standardised process control system together with a computational prototype based on this system and its application with a simple piece.

Manufacturing enterprises of all sizes, from small subcontractors and job shops to transnational aerospace and automotive giants, rely on a vast array of resources to generate added value and accomplish their business goals. These resources are comprised of human resource, knowledge resources and technological resources. Achieving business goals requires relevant, timely and well-calculated decision-making. A decision making process requires a model of the decision domain to be constructed with the necessary fidelity to achieve acceptable results and to determine the best course of action in the problem context. A reliable representation of manufacturing resources is therefore necessary for making correct decisions along the manufacturing chain. In this chapter a STEP-NC compliant methodology for representing technological manufacturing resources is presented. This modelling approach is based on mechanical elements that constitute machine tools and other manufacturing hardware together with their kinematic links and is developed with a focus on supporting process planning decisions. Models for various types of machines are presented at the end of the chapter to highlight the flexibility of this approach in modelling manufacturing resources.

To realize the articulate link between design and manufacturing, it is necessary to realize interoperable digital tools which represent the semantics of information independently of any implementations. In manufacturing, the interoperable CNC machining systems can be characterized as being capable of (1) seamless information flow without any errors related to the quality of the shape information, (2) feature-based machining, and (3) autonomous CNC. In this research, modelling and implementation of the Digital Semantic Machining Model that fulfils the above requirements are proposed. The Digital Semantic Machining Model is based on STEP-technology, which includes representation and quality inspection of shape data, feature model and feature recognition process model, and feature-based CNC machining process model.

STEP-NC is a new model for data transfer and exchange between CAD/CAM and CNC that allows specifying machining processes rather than tool motions with respect to the machine axes. This chapter presents a novel procedure for the design of decentralized STEP-NC compliant manufacturing solutions. Considering the problem of dispatching and managing a network of STEP-NC compliant machines, a three-tier architecture is proposed to perform remote machining requests. The architecture is composed of a dispatcher, a series of managers dislocated in manufacturing units, and agents interfacing with the STEP-NC compliant intelligent CNC machines. An ad hoc STEP-NC Network Management Protocol describes the exchange of messages between tiers. To prove the effectiveness of the decentralized manufacturing architecture, this chapter shows its application in a test-bed and describes how to evaluate the performance of the designed solution.

In response to the current rapidly changing manufacturing environment, product modelling technology has been widely researched to provide information for supporting the development of customised products. Traditional product modelling technologies are unable to support the information exchange and share in various stages of product development processes that could be taking place in a distributed manufacturing environment. This has caused many problems such as information loss, data format incompatibility and reduced efficiency and effectiveness of product data applications. This has consequently created bottlenecks for the integration of product development processes. In this chapter, a Generic Product Modelling Framework (GPMF) is proposed to overcome the problems of information exchange and sharing. This framework uses the Standard for the Exchange Product Model Data (STEP) as a foundation, and consists of four functional components: an EXPRESS Data Model namely EDM, a STEP–based modelling environment, a “five-phase” modelling method, and three EDM data exchange and sharing methods. The case study shows that the product models built based on the GPMF are capable of integrating information in product design, manufacturing and assembly. The GPMF is compatible, comprehensive, and flexible, and it is able to support information exchange and sharing.

The ISO STEP suite of standards is quite vast and covers many domains. One such domain of interest is Product Data Management (PDM), which deals with product metadata and related business objects along with several engineering and business processes. The schemas that deal with PDM are spread over several Application Protocols of STEP, and have been collected together informally as STEP PDM Schema. In recent times, other standards development organizations, such as the Object Management Group (OMG), have taken up the task of developing standardized services that involve PDM information models and related processes. These services exploit the fast growing web services over the Internet. These services are also built upon the STEP standards, among other things. This chapter describes the PDM domain covered by STEP and how it is influencing other standards such as the OMG PLM Services.

This chapter explores the suitability of STEP to enable Product Lifecycle Management (PLM). It summarizes the relevant standards and discusses their potential to support PLM. After evaluating that STEP is best suited to support PLM, the chapter focuses on engineering change management an activity that is typical of PLM. In order to capture the change evaluation data, STEP-compliant extensions to the existing engineering change data model are proposed. A physical STEP file derived from the proposed information model to capture and represent an example engineering change is demonstrated. The chapter closes by identifying issues internal to ISO 10303 that potentially hinder lifecycle-wide exchange and reuse of product information.

Heterogeneous objects refer to objects with spatially different material compositions or structures. Tremendous research efforts have been devoted to modelling heterogeneous objects and many heterogeneous object representations have been proposed. Regardless of the diversity of these CAD models, there are needs to transport and exchange the included geometry, topology as well as material distribution between CAD modellers, CAE tools and CAM facilities. In literature and practical applications there have been lots of STEP (STandard for the Exchange of Product model data) based tools and implementations for the exchange of the geometric/topological data. However, there has been only limited research on the data exchange of material distributions. This chapter focuses on an XML implementation for data exchange of heterogeneous CAD models. The proposed heterogeneous CAD model is described by Extensible Markup Language and detailed approaches to represent the voxel based, explicit function based and heterogeneous feature tree based models are described. The idea is to introduce self-descriptive, customised tags/vocabularies to fit the specific needs of material modelling. The structure of the heterogeneous CAD model is specified with XML schemas and related data validations can accordingly be checked to ensure the model correctness. A prototype CAD module is developed to construct XML-based heterogeneous material model, and the XML model is then exported to SolidWorks to test the validity of the proposed approach. Results show the proposed XML based model can facilitate the data exchanges of heterogeneous material distributions.

Software tools enabling enterprises to plan manufacturing processes efficiently can be turnkey solutions for gaining advantages in global competition. Nevertheless, existing CAM systems complementing each other in functionality are often not interoperable without supplementary technical and organisational effort. Open computer-based manufacturing, which is introduced in this chapter, is an approach to solving the problems of software inhomogeneity along the CAD-CAM-NC chain via a common platform. With an extension of the STEP standards for CAM related data and functional interfaces, this framework is able to embed software modules which encapsulate specific functionalities. Possible realisation can rely on known techniques from service-oriented architecture. The developed platform can be used, for example, in coupled simulation systems or process data acquisition, which can improve NC planning processes.