Unified representation of fixtures: clamping,locating and supporting elements in CNC manufacture

A CNC machining operation is the outcome of the application of the integrated capabilities of various resources within the CNC machining centre. Part fixtures, clamping and other location mechanisms are essential subsets of CNC machining resources. Today, various fixturing techniques and attachments available in the market allow manufacturers to enhance their production capability without buying expensive machine tools. This technology-rich fixturing domain is detached while representing and exchanging machine tool resource information for making manufacturing decisions. The research work in this article utilises the STEP-NC compliant unified manufacturing resource model (UMRM) for representing fixtures in conjunction with the parent CNC machining centre. Thus, UMRM is enhanced in this context to represent various fixtures such as universal vises, chucks, pallets and auxiliary rotary tables among others. The major contribution of this article is the application of the extension of the UMRM approach for representing fixturing domain, which allows generic modelling of fixtures and loading devices in addition to machine workpiece and process modelling. This would enable the stage of automated process planning and manufacturing. The universal approach in representing resource information allows the data to be utilised for making a wide variety of manufacturing decisions.     

Virtual prototyping and manufacturing planning by using tri-dexel models and haptic force feedback

This paper presents a new method of using the tri-dexel volumetric models and a haptics force feedback for virtual prototyping and manufacturing planning. In the proposed method, the initial polyhedral surface model is converted to a tri-dexel volumetric model by using a depth-peeling dexelization algorithm. In the virtual prototyping process, the tri-dexel volumetric model is updated by the swept volume of a moving cutter via a haptic force feedback interface device. A collision detection algorithm is proposed for the virtual sculpting and the pencil-cut planning with real-time haptic force feedback to the users. Tool paths are generated for machining the virtual sculpted parts via the simulation and verification on a virtual CNC machine tool before they are actually machined. Computer implementation and practical examples are also presented in this paper. The proposed method enables the haptic-aided virtual prototyping and manufacturing planning of complex surface parts.     

Virtual prototyping and manufacturing planning by using tri-dexel models and haptic force feedback

This paper presents a new method of using the tri-dexel volumetric models and a haptics force feedback for virtual prototyping and manufacturing planning. In the proposed method, the initial polyhedral surface model is converted to a tri-dexel volumetric model by using a depth-peeling dexelization algorithm. In the virtual prototyping process, the tri-dexel volumetric model is updated by the swept volume of a moving cutter via a haptic force feedback interface device. A collision detection algorithm is proposed for the virtual sculpting and the pencil-cut planning with real-time haptic force feedback to the users. Tool paths are generated for machining the virtual sculpted parts via the simulation and verification on a virtual CNC machine tool before they are actually machined. Computer implementation and practical examples are also presented in this paper. The proposed method enables the haptic-aided virtual prototyping and manufacturing planning of complex surface parts.     

Optimization of machining datum selection and machining tolerance allocation with genetic algorithms

In machining process planning, selection of machining datum and allocation of machining tolerances are crucial as they directly affect the part quality and machining efficiency. This study explores the feasibility to build a mathematical model for computer aided process planning (CAPP) to find the optimal machining datum set and machining tolerances simultaneously for rotational parts. Tolerance chart and an efficient dimension chain tracing method are utilized to establish the relationship between machining datums and tolerances. A mixed-discrete nonlinear optimization model is formulated with the manufacturing cost as the objective function and blueprint tolerances and machine tool capabilities as constraints. A directed random search method, genetic algorithm (GA), is used to find optimum solutions. The computational results indicate that the proposed methodology is capable and robust in finding the optimal machining datum set and tolerances. The proposed model and solution procedure can be used as a building block for computer automated process planning.     

Improving productivity of a multi-product machining line at a motorcycle manufacturing plant

This paper introduces a case study to improve productivity of a multi-product transmission case machining line at a motorcycle manufacturing plant. First, the manufacturing process is introduced to characterise the production flow. Through structural modelling, such a process is simplified through aggregations and transformed into a two-stage Bernoulli line model with split dedicated machines and finite buffers. Using Markov chain analysis, the system throughput can be estimated. The results are validated by plant data. To improve system productivity, through numerical experiments, we investigate the impacts of increasing machine efficiency, varying demands and implementing different loading policies. Such a study provides a quantitative tool for plant engineers and managers to improve production operations.     

Development of an integrated model for process planning and parameter selection for machining processes

The concept of ‘do it right the first time’ in the machining industry not only expects the best quality products but also at the best possible cost. The cost of machining depends on intelligent process planning and selection of machining parameters such as speed, feed, and depth of cut. The problem of machining parameter selection has received great attention by researchers and many techniques have been developed. A review of these techniques reveals that the selection of the machine and cutting tool is done before the process of cutting parameter selection and process sequencing, and often the selection is based on experience. The current research is an attempt to develop an integrated model (ExIMPro: Expert system based Integrated model for Machining Processes) which finds the sequence of operations with set of machines, tools, and other process parameters to minimise the cost of machining for a cylindrical part. This system consists of existing expert system Machining Parameter SELection (MPSEL) for machine and tool selection and a Microsoft Excel® and Visual Basic® based parameter selection model. The present model focuses on turning and cylindrical grinding operations but other processes can be incorporated with little modification to the software.     

Structured approach to the design of a production data analysis facility Part 2: Implementation and evaluation

This paper reports research into a novel machining, inspection and analysis facility directed towards a small manufacturing enterprise. A major feature of the facility is the ability to produce rapid manufacturing control through feedback data generated from the seamless integration of machining, inspection and production data analysis activities in order to influence the regeneration of NC part programs. The major contribution of the paper explores the implementation and evaluation of a prototype production data analysis facility that consists of four constituents: machine and inspection planning, production code generation, comparative tolerance analysis, and manufacturing data analysis, the execution of which is supported by the use of order and manufacturing information models. An integrated multifunctional prototype production data analysis software tool has been developed for a limited number of manufacturing features for 2½D prismatic components. This prototype software tool has been tested and is critically reviewed with future work.     

Optimal selection of cutting parameters in multi-tool milling operations using a genetic algorithm

In the milling of large monolithic structural components for aircraft, 70–80% of the total cut volume is removed using high-speed roughing operations. In order to achieve the economic objective (i.e. optimal part quality in minimal machining time) of this process, it is necessary to determine the optimal cutting conditions while respecting the multiple constraints (functional and technological) imposed by the machine, the tool and the part geometry. This work presents a physical model called GA-MPO (genetic algorithm based milling parameter optimisation system) for the prediction of the optimal cutting parameters (namely, axial depth of cut (a _p), radial immersion (a _e), feed rate (f _t) and spindle speed (n)) in the multi-tool milling of prismatic parts. By submitting a preliminary milling process plan (i.e. CL data file) generated by CAM (computer-aided manufacturing) software, the developed system provides an optimal combination of process parameters (for each machining feature), respecting the machine–tool–part functional/technological constraints. The obtained prediction accuracy and enhanced functional capabilities of the developed system demonstrate its improved performance over other models available in the literature.     

The CAM as the centre of gravity of the five-axis high speed milling of complex parts

The use of multi-axis high-speed milling has increased in different industrial sectors such as automotive, aeronautical, and the manufacturing of complex moulds. This trend can be observed at the latest technical fairs and the catalogues of the main machine tool manufacturers. Furthermore, for machining impossible shapes, multi-axis machining introduces two main advantages. First it gives the option of performing all operations in only one set-up of the raw block, which can be a prismatic block or a near-to-net shape form. Second it offers the capability of setting the cutting speed, depth of cut and feed to optimize tool life and part quality.

However, multi-axis milling is a very complex process that requires special care in the CNC program preparation in the CAM stage, which is critical for a successful process. Thus, the use of a virtual machining simulation utility is highly recommended. Collisions, over-cuts, interferences and dangerous machine movements can be predicted and avoided. On the other hand, continuous variation of the tool can be used to optimize cutting parameters such as cutting forces. Final result is the minimization of tool deflection due to the cutting forces and, in this way, the precision and roughness of finished parts are improved.

In this paper a reliable method for multi-axis HSM is presented. This methodology is based on two aspects. First a cutting force estimation in order to get minimum cutting force tool-paths. Second a complete virtual simulation to ensure a collision-free tool-path. A final objective is to generate reliable CNC programs. In this manner, the CAM becomes the centre of gravity of the machining planning procedure.

The methodology has been applied to the machining of two plastic moulds in hardened steel (32 HRC), a 7075-T6 aluminium honeycomb part for aeronautical purposes and a 65 HRC AISI 1.2379 part. Times, tolerances and surface roughness have been measured to check the success of the purposed methodology.     

复合进给电解加工机床控制系统设计与测试

为解决航空制造领域复杂零件的加工难题，针对研制的复合进给电解加工机床，开发了基于PC（ personal computer，个人计算机）和PMAC（programmable multi-axles controller，可编程多轴控制器）运动控制卡的开放式数控系统。基于虚拟仪器技术及其开发环境LabVIEW平台，遵循模块化设计思路，采用ActiveX自动化技术和CLF (call library function，调用库函数)节点设计了复合进给电解加工机床控制系统的人机交互界面，通过调用PMAC运动控制卡中的服务程序PmacServer，实现上位机与PMAC运动控制卡之间的功能交互。为了验证该控制系统的可靠性和运行稳定性，使用激光干涉仪进行了实验测试。实验结果显示，该控制系统响应迅速，运行稳定，人机交互界面易于操作；机床运动误差控制在-5~5 μm内，重复定位误差小于2.3 μm，能够满足航空发动机叶片的电解加工精度要求。研究结果在电解加工领域具有重要工程应用价值，可以为新一代高性能电解加工机床的设计提供参考。     

Improving visual inspection using binocular rivalry

In this study, we solve the non-identical parallel CNC machine scheduling problem. We have two objectives: minimizing the manufacturing cost (comprising machining, non-machining and tooling costs) and minimizing the total weighted tardiness. The tooling constraints affect the non-machining times as well as the machining conditions, such as cutting speed and feed rate, which in turn specify the machining times and tool lives. We propose a two-stage algorithm to find optimal machining conditions and to determine machine allocation, tool allocation and part scheduling decisions. The proposed algorithm generates different schedules according to the relative importance of the objectives.     

Optimisation of machining parameters by criterion of maximum productivity

The optimisation of machining parameters for machine tools using the criterion of maximum productivity rate is not a new problem – many unresolved issues remain. The intensification of machining processes leads to changes in the productivity rate; analytically defining optimal machining parameters for the maximum productivity rate in real-world manufacturing processes is, therefore, an important problem that needs to be addressed. This paper aims to formulate a mathematical model for the optimisation of cutting processes on machine tools based on the criterion of maximum productivity rate. The mathematical model is based on technological data, machining and reliability parameters of the machine tool units. Several practical applications are discussed.     

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.     

基于改进干扰观测器的虚拟轴机床滑模控制研究

圆弧齿轮加工用虚拟轴机床伺服系统存在的不确定性会影响系统的性能,从而降低圆弧齿轮的加工精度;同时,滑模控制中抖动现象会影响控制的精度和稳定性.为提高虚拟轴机床的加工精度和抑制滑模控制中的抖动现象,提出了基于改进观测器的滑模变结构控制算法来控制虚拟轴机床的伺服电机,算法中采用该干扰观测器对系统中的不确定性进行观测,利用饱和函数代替符号函数来抑制滑模控制中的抖动现象.推导了基于改进观测器的滑模变结构控制律,并证明了所设计控制器的稳定性;为验证算法的有效性,在MATLAB中进行了仿真,仿真结果表明:所提出的算法能够有效地观测系统中存在的不确定性因素,并抑制滑模控制中的抖动现象,系统具有较强的位置跟踪性能和抗干扰能力.     

Development and pilot testing for virtual manufacturing tools with intelligent attributes

The use of synthetic and surrogate tools in training robots and planning events within virtual environments has tremendous potential in making the programming of complex machines simple and easy. For example, by designating tasks off-line with the virtual tools, attributes such as process planning and collision avoidance can be automatically and efficiently incorporated. In our research we have experimented with the use of attribute laden virtual tools in various tasks such as robotic-based grinding and welding processes. Such attribute laden virtual tools aid human operators in path planning as well as in making decisions about the process itself. In this paper we have tested our concepts of virtual tools and the use of attributes such as physical, reflex and command actions. Four sets of experiments were conducted with human subjects. Two kinds of virtual tools were used in these experiments, one with guide plane attributes and the other without them. One set of experiments using the head mounted display interface, tested human performance and evaluated the effect of the learning process in using the virtual tools. Results showed that there was marked improvement in task execution time using the tools laden with guide plane attributes over the unencumbered virtual tools. This paper discusses various future applications of these virtual tools in manufacturing. It is observed that unlike non-haptic visual interfaces, where no physical feed back is available to the user, attribute laden tools could provide a much easier interface to robots.     

Object-oriented modelling of manufacturing information system for collaborative design

Object-oriented technology has been widely acclaimed as offering a revolution in computing that is resolving a myriad of problems inherent in developing and managing organisational information processing capabilities. Although its foundations arose in computer programming languages, object-oriented technology has implications for a wide range of business computing activities including: programming, analysis and design, information management, and information sharing. The problematic issues in the development of manufacturing software systems are related to the various characteristics of manufacturing systems, which are wide, dynamic and complex. Design for manufacturing (DFM) is the integrated practice of designing components while considering their manufacturability, and its benefits are widely acknowledged in the industry. A model has been developed using object oriented technology, after analysing the fundamental elements necessary for modelling manufacturing and process planning framework used in collaborative design and manufacturing in machine tool manufacturing. The main components of this model are: process planning model (PPM), manufacturing activity model (MAM), manufacturing resource model (MRM) and manufacturing cost and time model. We are using ontologies in conjunction with specific conceptual models, which can contribute to improve the interoperability between these models. The performance of this model is shown by means of one real world case. The developed manufacturing information based design tool integrated with an intelligence design system can be used for collaborative design and manufacturing, which will support machine tool designers’ to achieve cost effective and timely design.     

A polychromatic sets approach to the conceptual design of machine tools

Currently very few computer-aided conceptual design systems are available to support the initial development of a machine tool and its structure (concept, calculation, design) and the verification of the prototype. In recent years, polychromatic sets have emerged as a promising approach for mathematical modelling. The theory, techniques, and approaches of polychromatic sets are capable of playing an important role in the conceptual design of a variety of products including machine tools. In this paper, the concept of polychromatic sets is introduced, and a polychromatic sets approach for the conceptual design of machine tools is proposed. The usefulness of the proposed method is illustrated by a conceptual design example of a machining centre of drilling, milling, and boring. Applying the proposed approach to machine tools helps to make right decisions in the conceptual design stage. Due to its powerful mathematical modelling capability, the polychromatic sets technique proposed in this paper may possibly be extended and applied to design evaluation problems encountered in other design tasks in manufacturing systems including process planning.     

Implementation of a CNC NURBS curve interpolator based on control of speed and precision

An efficient real-time Non-Uniform Rational B-Spline (NURBS) curve interpolator for high-speed and high-accuracy curve machining is developed and implemented, which considers the confined contour error, acceleration/deceleration (ACC/DEC) planning and the machine dynamic response simultaneously. A practical method is proposed to adjust the feed rate to the curvature radius of NURBS curves to achieve higher machining precision. However, at the sharp corner of the curves, the feed rate fluctuation might result in large impacts to machine tools. The offline pre-interpolation for sharp corners is presented. The feed rate is reduced in advance according with the machine's acceleration capability as well as satisfying the confined contour error. The velocity profile can be chosen dynamically to meet the requirements of the machining process by means of flexible ACC/DEC planning. In addition, a new strategy based on the geometrical properties of NURBS curves is suggested to predict the deceleration point. Therefore, the process of acceleration and deceleration is so smooth that it can satisfy the need of the machining process. This NURBS interpolator has been validated on a CNC system, which greatly improves machining accuracy for both position and velocity control.     

Real-time cutting simulation system of a milling operation for autonomous and intelligent machine tools

The conceptual architecture of autonomous and intelligent machine tools has been proposed not only to generate flexibly the process and operation plan but also to utilize the machine tools and cutting tools' performance while satisfying the requirements of the products and avoiding unexpected machining trouble. In order to realize the autonomous milling, machining strategy such as tool paths and cutting conditions must be decided, not in advance like current NC machining, but in a real-time manner. The objective of this research is to develop a real time machining optimization with machining simulation. Consequently, a cutting simulation system called a virtual machining simulator has been developed for this purpose. This simulator can calculate the changing geometry of the workpiece and estimate the instantaneous cutting force, torque, etc using the physical model. This estimated information enables the system to decide the suitable cutting conditions according to the machinability evaluated. In this paper, the machining status is evaluated and the cutting conditions are modified in real time so that the requirement of the machining operation is satisfied by referring to the physical model. The reliable and safe machining operation is carried out by maintaining the cutting force and torque desired value.     

A CAPP framework with optimized process parameters for rotational components

Process planning, as a critical stage integrating the design and manufacturing phase in a manufacturing environment, has been automated to meet the needs for higher productivity and lower production cost. Being an input to various systems such as scheduling and routing, process planning results are of great importance in the manufacturing stage. Though feature extraction and sequence optimization have been given much attention, the process parameters are rarely dealt with. This paper focuses on the development of a new generative computer aided process planning (CAPP) framework for rotational components. The developed framework includes modules for feature extraction based on CAD application programming interfaces, determination of the optimum sequence and generation of optimum process parameters. The optimization of the machining operations is achieved using the evolutionary technique. The approach resulted in the reduction and prediction of machining time and cost. The framework is demonstrated with a case study.