Ian Stroud

Reincarnation of G-code based part programs into STEP-NC for turning applications

As STEP-NC emerges as the new CNC control method and a fundamental means for realizing e-manufacturing, old manufacturing information based on the conventional manufacturing standard will become obsolete. In practice, replacement of G-code based part programs into STEP-NC is a huge task. In this paper, methods to interpret G-code based part programs into STEP-NC code are investigated. G-code is a compact, coded set of numbers for axis movements, while STEP-NC is very comprehensive and includes information about features, operations, strategies, cutting tools, and so on. It is thus very challenging to derive such comprehensive information from the low level G-code information. In this paper, we first clarify what should be given and what may be given, and then present algorithms for deriving STEP-NC information, such as geometric features, operations, etc., from the tool movement (G-code) based on expert reasoning. The algorithms are developed for the turning application. The developed algorithms were implemented and tested on G-code part programs used in actual practice.

STL and extensions

Abstract Three approaches to improve the free form fabrication process are discussed: (i) the use of approximation control parameters (ii) the development and use of standard transform language (STL) extensions and (iii) methods to handle exact geometrical models at the rapid prototyping (RP) level. The first two of these are concerned with improving the quality of the data exchanged, the third with improving the quality of the process itself. It is shown that the use of various STL approximation control parameters can improve the quality but does not always result in a good approximation. To improve this situation we propose two versions of an extended STL format with the following advantages: (i) smaller final models are obtained that allow faster geometry processing, (ii) the reconstruction of exact object geometry is possible which permits avoidance of volume distortion for consistent control of slice and layer approximations and (iii) a mechanism is provided that allows attachment of manufacturing information. We describe in pseudo-code and develop an ACIS implementation for the writing of the extended STL format, for the reconstruction of a solid from the extended STL file and for the consistent facetting of an exact model. Slice timing results show significant time reductions for the exact and consistent facetted models over the STL-based facetted models. The main conclusion, though, is that STL should be replaced with a STEP-based data exchange standard.

Container spaces and functional features for top-down 3D layout design

Although there have been many advances in computer-aided modelling techniques and representations of mechanical parts, there are areas where exact modelling is a handicap. One of these is 3D layout design. Here, simpler models are useful for initial design sketches to verify kinematic behaviour and organise product structure before the detailed component design phase begins. A commitment to exact, or close approximational geometry too early can imply a commitment to form before functionality has been finalised. This paper describes a system for top-down 3D layout design based on simple conceptual elements which can be used as a basis for visualisation, discussion, definition of product structure and kinematic functionality in the conceptual design phase before the embodiment or detailing begins. This tool forms a bridge between the abstract nature of the conceptual design phase and the geometric nature of the embodiment phase. The 3D layout module uses design spaces with simple geometry and kinematic connections to represent a product. The design spaces act as containers or envelopes within which the final component design is to be realised. The kinematic connections allow the behaviour of the product to be simulated to gain more information (such as overall component dimensions and areas of potential collisions) for the detailed design phase. In addition the paper describes the design process based on the proposed 3D layout design system and contrasts this with the traditional design process. An industrial case study is presented to illustrate the following advantages of the proposed approach: (i) the design process proceeds faster because unnecessary layout parameter and constraint modifications are avoided since kinematic functionality verification precedes the detail design, (ii) the design process can produce better designs since alternative solution principles can be explored early in the design process. Theoretical issues are discussed concerning kinematic constraint inheritance during design space decomposition and concerning computer support for non-rigid design spaces.

Algorithms and an extended STEP-NC-compliant data model for wire electro discharge machining based on 3D representations

The current paper describes the implementation of the wire electro discharge machining (EDM) algorithms for the STEP-NC project and some possible extensions. Wire EDM uses many working parameters (parameters for spark generation, speed of penetration, etc.) the setting of which needs expert system methods. These expert systems are a coded form of the company knowledge and are based on their experience. The higher information level provided by STEP-NC allows the development of new algorithms to drive the wire. The current way of programming the wire motion is to consider it as a milling tool for 2.5 axis machining operations: the wire trajectory is computed using 2D planar curve offsetting and collision detection algorithms. The use of explicit ruled surfaces allows real 3D offsetting and collision detection. The paper starts by describing the data model and architecture of the demonstration system which was developed during the project. This can be thought of as a simplified process planning phase. The second part of the paper describes algorithms that have been implemented in the STEP-NC environment for prototype software running on the wire EDM NC controller. The final part describes some open questions that remain at the end of the project.

A roadmap for implementing new manufacturing technology based on STEP-NC

Manufacturing is changing. New ideas of control, the maturity of CAM techniques and computer technology have enabled the definition of an advanced machine tool control standard, STEP-NC. STEP-NC is one part of a larger manufacturing picture with links to different manufacturing applications using the STEP suite of standards. STEP-NC is the key to a door behind which there is a rich field of research on manufacturing techniques and opportunities for lean, intelligent and flexible manufacturing. The problem is to pass through that door. Many potential users are waiting for a lead from control developers. Control developers are waiting for market interest. Existing legacy machinery and investment in traditional machining add inertia. Instead of having a clear development path, manufacturing has become something of a Gordian knot waiting to be disentangled. New research projects are addressing these issues as well, but this paper takes a different route in showing how strategic planning can lead to adoption of the new techniques in a phased way, a so-called ‘Roadmap’. The contribution of this paper is the manner in which the overall task of implementation has been subdivided into tasks and phases to achieve the introduction of the new technology.

A model to determine the optimal parameters for sustainable-energy machining in a multi-pass turning operation

This study presents a model for the optimization of machining parameters for the minimum energy consumption in a multi-pass turning operation. The model takes into account finishing and roughing passes separately for the energy optimization followed by the dual optimization of the energy functions for a combination of one finishing pass and multiple roughing passes to finish a desired diameter on a cylindrical workpiece. The parametric constraints, tool-life constraints and operational constraints are enforced in the model before optimizing the energy function using non-linear programming. The model is applied to an example case for the optimization. The effects of total-depth-to-be-removed, material removal rate and tool replacement time are evaluated on the optimal parameters for sustainable machining.

Strategy features for communicating aesthetic shapes for manufacturing

The STEP effort and the STEP-NC project have produced a great deal of work on features for mechanical parts and how to manufacture parts based on these. However, there is at present less information about how to manufacture aesthetic products with less well-defined features. The aim of the present paper is to describe an approach to communication and machining features in stone products. The work was done as part of a project, LITHO-PRO, which had the main aim of developing machining for dry high-speed milling of stone and industrial ceramics. As part of this project the EPFL worked on CAD and CAM functions for aesthetic products. Since the main aim of the project was to develop a new machine and machining process, it was decided that the STEP-NC philosophy was appropriate for communication. However, the stone products are usually aesthetic rather than functional so the feature set defined in the STEP AP-224 document could not be used directly. The aim of the paper is to present an approach to feature definition in terms of manufacturing strategies which is an extension to the classical, mechanical engineering features already determined as part of STEP.

A green productivity based process planning system for a machining process

In the metal cutting industry, manufacturers have strived to increase energy efficiency and to reduce environmental burdens through the use of dust collectors and waste disposers. It is more beneficial and efficient to apply the front-of-pipe technology that prevents the sources of pollutants and minimises energy use through the redesign of products and the change of process planning and machining operations. In particular, process planning for the environment, called eco-process planning, is central to increasing energy efficiency and reducing environmental burdens because process planning decisions greatly influence machining performance. At present, greenability, a term used to indicate environmental friendliness, has been little considered as a major concern in the process planning stage because process planning decisions have focused on improving productivity aspects that include speed, cost and quality. Thus, it is essential to develop an eco-process planning approach that enables the harmonisation and enhancement of greenability performance while improving productivity performance, termed green productivity (GP). This paper presents the development of a GP-based process planning algorithm that enables the derivation of process parameters for improving GP in machining operations. The core mechanism of the algorithm is the realisation of the process improvement cycle that measures GP performance by the collection of machining data, quantifies this performance by categorical representation and predicts the performance through prediction models. To show the feasibility and applicability of the proposed algorithm, we have conducted an experiment and implemented a prototype system for a turning machining process.

Process-oriented Life Cycle Assessment framework for environmentally conscious manufacturing

Environmental concern requires manufacturers to extend the domain of their control and responsibility across the product’s life cycle. Much of the research has concentrated on assessment of environmental performance through the application of the Life Cycle Assessment (LCA) framework that provides a technical methodology to help identification of environmental impacts of product systems. However, the current LCA framework does not incorporate dynamic and diverse characteristics of manufacturing processes. As a result, the LCA’s referential data will largely deviate from the real ones to an extent that the purpose of LCA is not meaningful. In other words, the current and fixed referential data-based method is not suitable to specify the impact categories related to manufacturing processes. From the perspective of decision making related with environmental impact during manufacturing, the current LCA method carried out in the off-line is hard to apply. As a result, performance index, such as greenability, a major performance index for environment conscious manufacturing cannot be implemented in the real practice. This paper presents the development of a framework (called process-oriented LCA) to realize environmental conscious manufacturing incorporating both greenability and productivity. To show the applicability and validity of this framework, experiments and analysis have been conducted and a prototype system has been implemented for a turning machining process.

STEP-NC machine tool data model and its applications

The machine tool data model of STEP-NC (ISO 14649) was conceived as a necessary extension to the original STEP-NC set of standards to make efficient control possible. The intention of this paper is to describe the background to the data model as well as related research work building on a higher level of information than can currently be found in the control information. The development of STEP-NC controllers promises improved manufacturing and resource use. However, even with legacy controllers there are advantages in using STEP-NC as an intermediate representation. This paper describes how the data model for describing machine capability was developed and what can be delivered by using this standard data model for machine tool. A machine tool selection algorithm is developed in order to validate the data model. Technical issues were derived from developing a system for process planning based on STEP-NC. Machine tools are selected automatically by the comparison with machine capability, work space and tolerance with the proposed data model. This function can contribute reconfigurable manufacturing systems and distributed and multi-controller-based manufacturing environment.