A fixture repeatability and reproducibility measure to predict the quality of machined parts

The production of high quality parts in a flexible manufacturing system is obtained by careful monitoring and control of various operating inputs such as manufacturing processes, fixtures, and gauges that are required to produce these parts. This research focuses on the performance of machining fixtures and develops a measure called the Fixture Repeatability and Reproducibility Measure (FR-R) to evaluate the performance of machining fixtures. This FR-R measure quantifies the variability of a part dimension that is contributed by the fixture under static loading conditions. This measure was used to evaluate the performance of two different fixtures that were utilized to produce two different parts. One part was machined only in parallel planes after location and clamping on the fixture. The second part, of a different geometry, was located and clamped in a different fixture, and then machined in mutually perpendicular planes. An investigation of data for the first part revealed that the FR-R detected the existence of fixture malfunctions. After the fixture was repaired, fresh measurements and further analysis with this FR-R measure revealed inherent problems in the manufacturing process that were addressed by redesigning the part and fixture for the next generation of product. The FR-R measure on the second part confirmed that the current performance of the fixture was satisfactory and matched the historical performance of the fixture. The conclusion was made that this FR-R measure was not only viable, but also desirable. For example, this measure facilitated pre-production evaluation of machining fixtures. Further, the FR-R measure is generated by using an off-line coordinate measuring machine to evaluate fixtures; thus minimizing the use of expensive production machines to do the same job. Finally, this measure showed that it could be used to monitor fixture performance during production, and prevent the production of scrap parts. In summary, this FR-R measure could be used to predict the quality of machined parts in a flexible manufacturing environment.     

Optimal cutter selection for complex three-axis NC mould machining

Proper cutter selection can reduce NC machining time greatly. Most researchers select cutters based on tool path generation, which is very time consuming, and only a very limited number of cutters can be selected. A new cutter selection methodology for complex mould machining based on an efficient interference detection algorithm is introduced. With this approach, the feasible regions for the candidate cutters are first identified without tool path generation. The machining times for different cutter combinations are then estimated based on the areas of the feasible regions and the cutter feed rates. The set of cutters that can machine the workpiece with minimum time is selected as the optimal candidate cutters. Since no tool path needs to be generated before cutter selection, the cutters can be selected efficiently, and the number of the cutters that can be used in NC machining can be quite large. The system has been tested with several industrial parts and it can select optimal cutters effectively and efficiently.     

实体数控仿真刀具扫掠体的构造

实体数控仿真具有重要意义，刀具扫掠体构造是实体数控铣削仿真的重要环节．分析了刃具轮廓、刀具运动形式和加工指令对构造刀具扫掠体的影响．基于ACIS平台研究了刀具扫掠体的构造，提出了动态构造刀具扫掠体算法，给出了该算法的流程图．并将其应用到正在研制和开发的实体数控铣削仿真系统中，给出了2．5D实体数控铣削仿真的应用实例。     

Setup planning for machining the features of prismatic parts

This paper focus on the development of a formalized procedure for automatic generation of feasible setups and then to select an optimal setup plan for machining the features of a given prismatic part. The proposed work simultaneously considers the basic concepts of setup planning from both machining and fixturing viewpoints in order to formulate feasible setup plans. The tasks that are performed are: (a) identifying groups of features that can be machined in a single setup, (b) determining a suitable work piece orientation, i.e. the suitable datum planes for each setup, (c) determining all the feasible setup plans to machine the given set of features of prismatic parts, and (d) evaluating the feasible setup plans on the basis of technological (available tolerance) and economical conditions (total setup time). For the proposed work the authors have introduced four new concepts namely, ‘surface fit for location’, ‘primary group’ ‘secondary group’, and ‘eligible group’. The first concept plays an important role in the identification of suitable faces of the part for positioning, clamping and supporting. The other three help in clustering of features, which can be converted in to candidate setups.     

A hint-based machining feature recognition system for 2.5D parts

The recognition of machining features in a part with arbitrary feature interactions is a difficult task. In this paper a hint-based machining feature recognition system for 2.5D parts with arbitrary feature interactions is presented. A pre-processor is used to screen out invalid 2.5D parts automatically and calculate the possible machining directions. The feature recognition starts with identifying the traces of features present in the part. Once a hint is found, geometrical reasoning is then used to compute other parameters to complete a maximally extended feature instance. The system handles hole, linear slot and circular slot features in the first pass. Various possibilities, like through or blind hole, through or blind slot, floorless or multi-floor slots are instantiated after their testing and repairing. The system then, likewise, handles floor-based and floorless pockets, in the second pass. The recognition process is tightly coupled with the machining environment to ensure machinability of the recognized features. A prototype of the system is implemented in visual C++ and ACIS® 3D modelling toolkit.     

Design model generation for reverse engineering using multi-sensors

Reverse engineering is the process of creating a design model and a manufacturing database for an existing part or prototype. The applications of reverse engineering are in redesigning of existing partstools or prototype parts where the CAD model of the part is not available. Reverse engineering, for the most part, is performed as an interactive process where the designer identifies the surface features from digitized data and then models the surfaces accordingly. This paper presents the algorithms and implementation results for a reverse engineering system which is intended to automatically create CAD representations of part prototypes. An integrated sensory system combining contact and non-contact sensors has been developed to digitize parts surfaces. The sensory system fuses data from machine vision and a coordinate measuring machine (CMM) in order to automatically digitize the part surface. Machine vision is used to capture the orthographic views of the part. The images of these orthographic views are processed and vectorized to create five views of the part in the form of an engineering drawing. The system utilizes the generated orthographic projections to automatically drive the CMM to capture a grid of point coordinates from the part surface. The CMM digitization process is guided by the segmentation provided from the orthographic views. The segmented data from the part surface is input to the surface modeling module of the system where parametric surfaces are fitted through the digitized points. The surfaces are then extended and intersected using the Hermite approximation method to develop the 3-D CAD model of the part. Accuracy and automation is achieved by combining global shape information obtained from part images with the accurate point data acquired by a CMM. Algorithms for surface segmentation, part digitization, surface extension, and surface intersection modeling are described in this paper.     

Tool path generation for five-axis machining of blisks with barrel cutters

A barrel cutter has a cutting segment with a large radius on its profile, and this arc segment allows the cutter to tilt away from the part surface, avoiding the collisions of the tool with the part. Therefore, barrel cutters are suitable for five-axis blisk machining. However, the barrel cutters are more challenging for CAM software to generate paths. A method of generating collision-free and large-machining width flank milling paths with smooth axes movements for blisk machining with barrel cutters is proposed. Local gouge between the tool flute surface and the blade to be machined is considered, and the collisions of the blisk with the non-cutting parts of the tool, i.e. tool shank and holder, are also detected. The machined part geometry is the complement of the cutter’s swept envelope from the stock. Accordingly, the swept profile of the cutter at each cutter contact point is employed to evaluate the machining width naturally. Thereafter, a multi-criteria tool path generation model is established, and it is converted into a single-objective optimization with the weighted sum method. An algorithm based on the Differential Evolution algorithm is developed to solve this model. The numerical example illustrates the effectiveness of the proposed method.     

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.     

An efficient algorithm for automatic machining sequence planning in milling operations

Machining sequence planning can be considered as one of the most important functions of manufacturing process planning. However, less attention has been paid to automation of this function in contemporary computer-aided process planning systems. This paper describes an efficient algorithm for automatic machining sequence planning in 2.5D milling operations. It is programmed in LISP and forms the machining sequence planning module of a CIM system. This module is integrated with a feature-based design system that determines required machining operations and parameters for each machining operation. This information is then sent to the machining sequence planning module for determining proper machining sequence plans for producing the part. The algorithm generates feasible machining sequences based on the bilateral precedence between machining operations. The algorithm results in minimized tool changes.     

CFRP柔性件保形加工中的变形控制

碳纤维增强树脂基复合材料(CFRP)柔性件的保形加工是航空航天高端装备制造的重要环节,柔性件的可靠装夹是控制加工变形、降低加工尺寸偏差的前提。首先,在理论分析的基础上,明确了柔性件装夹中夹紧及摩擦约束基本条件,提出了基于悬臂梁理论的“随形-就近”吸盘分布原则。进而,使用“ISIGHTABAQUS”联合仿真方法,实现了不同装夹条件及等效切削力作用下CFRP柔性件变形的仿真分析,分析表明：真空吸盘的弹性变形易加大装夹变形,应采用弹性真空吸盘与刚性定位吸盘组合的方式;定位吸盘数量为8、12或16,并“随形-就近”分布时,真空吸盘数量及分布对柔性件变形的影响可忽略。最后,仿真与实验分析了考虑定位几何量偏差时的加工尺寸偏差,仿真与实验结果规律基本一致,优化装夹后的加工尺寸偏差最大降幅达57.7μm (35%);综上,CFRP柔性件保形加工中变形引起的加工尺寸偏差不容忽略,在“随形-就近”、“定位与真空吸盘组合”原则下优化装夹可以大幅降低变形引起的尺寸偏差。     

基于旋转工件轮廓智能输入系统二维视图的三维重构技术

为了解决虚拟三坐标测量软件对军工涉密项目中零件检测路径规划问题,提出了一种基于二维视图的三维重构技术,设计了旋转工件轮廓二维视图的智能输入系统;操作人员根据提示输入图纸上旋转体母线的关键信息;系统软件对输入信息进行连续性、交叉性和封闭性判断,以构成正确轮廓母线;环绕旋转轴旋转母线重构出三维实体模型,按照标准IGES文件格式输出,从而实现二维视图的三维实体重构、生成的IGES文件提供给坐标测量机系统软件,可实现坐标测量机的自动化测量．联合运用该输入系统与虚拟三坐标测量机,解决了军事涉密项目中零件检测的路径动态规划问题     

Computer-aided optimization of multi-pass turning operations for continuous forms on CNC lathes

The Computer Numerical Control (CNC) machine is one of the most effective production facilities used in manufacturing industry. Determining the optimal machining parameters is essential in the machining process planning since the machining parameters significantly affect production cost and quality of machined parts. Previous studies involving machining optimization of turning operations concentrated primarily on developing machining models for bar components. Machined parts on the CNC lathes, however, typically have continuous forms. In this study, we formulate an optimization model for turned parts with continuous forms. Also, a stochastic optimization method based on the simulated annealing algorithm and the pattern search is applied to solve this machining optimization problem. Finally, the applications of the developed machining model and the proposed optimization algorithm are established through the numerical examples.     

用三坐标数控铣床加工空间曲面时的圆弧插值算法

论述了在三坐标数控铣床上采用球头铣刀铣削空间复杂形面时圆弧插值的计算方法.把刀具中心等距曲线轨迹的计算归结为计算零件轮廓上点的坐标,确定了加工空间等距曲线时插值点的计算流程图.利用圆弧插值算法推导出了坐标增量计算公式,此公式可应用到数控装置修正刀具的半径,从而提高零件廓形的加工精度.此算法也可应用到端铣刀加工时圆弧插值的计算.     

Virtual hybrid-FDM system to enhance surface finish

Many rapid prototyping systems which produce prototypes by layer-by-layer material deposition are now commercially available. The layer-by-layer deposition process leads to a stepped surface known as staircase. Staircase formation is a geometric constraint of the layered manufacturing, which can not be eliminated. The presence of staircase on the surface of a prototype detracts from the surface finish and hence restricts functionality of prototypes. It is realized that there is a need to make modifications in RP (rapid prototyping) systems so that prototypes with better surface finish can be produced without incurring high production costs. A virtual hybrid fused deposition modelling system (hybrid-FDM) is proposed in the present work that uses both layer-by-layer deposition and machining. In this system, CAD model is sliced adaptively using limited centre line average (Ra) value as a criterion (Pandey et al. 2003a). Hot cutter machining/ploughing (HCM) (Pandey et al. 2003b) is recommended to machine the build edges (staircase) of ABS material. Numerically controlled x-y traversing mechanism is proposed as an attachment to move hot cutters along the periphery of slices to machine build edges. In this paper, geometrical designs of cutters are proposed. A process planning system to decide the number of layers to be deposited and then machined in order to access intricate features of a part is implemented. The developed system simulates surface roughness, before and after hot cutter machining. An experimental study is carried out by machining the build edges of an axisymmetric FDM part on lathe machine to form a basis for a hybrid-FDM system.     

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.     

大型结构件数控加工在位计量检测技术研究

在位计量检测以加工机床为硬件载体,实现加工、测量一体化,对提高产品质量和生产效率有重要意义。介绍了数控加工在位计量检测系统的组成与方案的实现过程,对系统的性能进行了现场试验,结果表明大型结构件数控加工在位计量检测系统可对大型数控加工零件工艺过程中的尺寸和形位误差进行准确在位测量,大大缩短了大型数控加工件的定位时间,有效提高了一次装夹加工的效率和合格率,避免了工件的二次装夹,降低了生产成本,为数字化装配提供有力保证。     

基于CAE某发动机加强板成形模具的设计

对某发动机加强板零件进行分析,通过计算及运用相关软件确定其展开尺寸.对弯曲成形模具凹、凸模工作部分运用CAE技术进行设计,并用Mastercam软件来模拟加工,加工时合理选择铣刀与参数设置,可得到较为理想的走刀路线.这样可获得凹、凸模的详细加工过程平面录像,同时可设计出模具的总装图及零件图.     

The Perrego algorithm: a flexible machine-component grouping algorithm based on group technology techniques

The Perrego algorithm, which forms machining cells based upon the weighted importance of the parts which they produce, is presented. Classification and coding (C&C) and production flow analysis (PFA) were synthesized into one single algorithm using similarity coefficients and a cluster identification algorithm to combine the two methods. The resulting unique algorithm's advantage is the utilization of morphological information, such as manufacturing production quantity requirements, with the technological attributes of the parts: cells were formed with minimal amounts of parts travelling between cells. The algorithm also considers the economics of machine duplication for forming independent cells.     

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.     

Design of delayed reconfigurable manufacturing system based on part family grouping and machine selection

To improve the convertibility of reconfigurable manufacturing system (RMS), the concept of delayed reconfigurable manufacturing system (D-RMS) was proposed. RMS and D-RMS are both constructed around part family. However, D-RMS may suffer from ultra-long system problem with unacceptable idle machines using generic RMS part families. Besides, considering the complex basic system structure of D-RMS, machine selection of D-RMS should be addressed, including dedicated machine, flexible machine, and reconfigurable machine. Therefore, a system design method for D-RMS based on part family grouping and machine selection is proposed. Firstly, a part family grouping method is proposed for D-RMS that groups the parts with more former common operations into the same part family. The concept of longest relative position common operation subsequence (LPCS) is proposed. The similarity coefficient among the parts is calculated based on LPCS. The reciprocal value of the operation position of LPCS is adopted as the characteristic value. The average linkage clustering (ALC) algorithm is used to cluster the parts. Secondly, a machine selection method is proposed to complete the system design of D-RMS, including machine selection rules and the dividing point decision model. Finally, a case study is given to implement and verify the proposed system design method for D-RMS. The results show that the proposed system design method is effective, which can group parts with more former common operations into the same part family and select appropriate machine types.