Quality design of fixture planning for sheet metal assembly

Fixturing plays an important role in enhancing weld quality of the sheet metal assembly process. However, traditional experience-based fixturing schemes and purely optimal fixturing schemes are often sensitive to location fluctuation of the designed locators. In this paper a mathematical representation of deterministic locating and total fixturing for a flexible workpiece is developed first, then a virtual beam model is proposed to evaluate the degree of flexibility of the locating points. A quality design model of fixture planning for sheet metal assembly with resistance spot welding is then developed; both the performance expectation and the variance are considered in the formulation of the objective function; a prescribed factor is used to weight the two objectives. The finite element model based on ANSYS software is set up with a spot weld feature employed and genetic algorithm is used in the optimization process. A simple example and an industrial case illustrate the feasibility of the developed model. This work provides a basis for improving the quality of sheet metal assembly in the design phase.     

Evaluation of system models for an endoscopic fringe projection system

To be able to perform inline inspection of complex geometries, which exhibit for example undercuts or internal structures, a new endoscopic micro fringe projection system has been developed. It is designed to perform areal measurements for tool inspection inside the limited space of metal forming presses by employing flexible image fibers to couple the measurement system’s camera and projector to a compact sensor head. The projector features a laser light source and a digital micro-mirror device to generate high-contrast fringe patterns. To increase the depth of field of the sensor heads, custom gradient-index lenses have been designed as an approximation to the Scheimpflug principle. Challenges arise for both calibration and phase measuring algorithms from the optics, as well as from the reduction in resolution introduced by the fiber bundles. This paper presents an evaluation of two different system models for the endoscopic fringe projection system, which are based on the pinhole camera model and a black box model. An automated calibration process, which gathers the calibration data for two calibration algorithms that are robust to artifacts introduced by the optical path, is demonstrated. Based on a comparison of measurements, differences between the two modeling approaches are discussed. Finally, results of measurements of a demonstrational metal forming tool are shown as an application example.     

Research and development of an accurate 3D shape measurement system based on fringe projection: Model analysis and performance evaluation

In this paper, the research and development of an accurate 3D shape measurement system based on fringe projection is presented. This system utilizes a sliding projection unit to project the desired encoding fringe patterns onto the object and the object shape can be obtained by analyzing the images captured with a camera for each projection. The sliding projection unit uses a high precision grating element fabricated by electron beam lithography to produce the accurate encoding fringe patterns thus to reduce the projection error. And a method based on gray-code and phase-period edge detection is developed to align the grating element with its sliding direction to guarantee the alignment between the projected patterns. The influence of the lens distortion of both the projection unit and the camera is also studied and an improved nonlinear system model is developed based on triangulation. This model gives a more accurate mathematical representation of the shape measurement system and thus improves the system measurement accuracy. The experimental results show that an overall measurement error of 0.04 mm with a variability of ±0.035 mm can be obtained for the developed system.     

Measurement of surface form of Johannesteijsmania altifrons leaf using phase-shift fringe projection

The design of thin-walled structures based on naturally occurring folded structures, such as the Johannesteijsmania altifrons leaf, is relatively unexplored. The main advantage of this particular type of folded leaf is that it is supported by a single main stem, which can be exploited in structural designs if the 3-D surface form is known. Since the leaf can deform if the surface form is measured using conventional contact methods, the non-contact phase-shifting fringe projection method was applied to determine the 3-D surface form of the leaf. The potential of the phase-shifting fringe projection method for reconstructing the 3-D surface of naturally occurring folded structures such as J. altifrons leaf has not been attempted in the past. The objective of this work is to investigate the potential of using this technique to measure the 3-D surface of the life folded leaf in its natural environment. Three fringe patterns were projected onto the leaf with phase-shifts of 0, 2π/3 and 4π/3, captured using a CCD camera and processed to obtain a phase map. The 3-D data of the leaf surface were successfully reconstructed from the phase map using a phase-unwrapping algorithm.     

基于知识的飞机钣金零件工艺性评估方法

在把工艺性分解为可成形性、可加工性、易加工性三项内容的基础上,建立了工艺性评估指标.采用知识的系统化建模方法,构建了飞机钣金零件工艺性评估知识模型,采用数据库方式和程序方式,分别表示出工艺性评估描述性知识和过程性知识,分析了问题定义→知识搜索匹配→修改方案编码匹配→回馈的推理过程.在此基础上,设计了基于知识的评估流程,包括零件信息输入、评估计算,以及不符合工艺性要求零件修改方案的给出.设计了基于Web的飞机钣金零件工艺性评估系统结构,采用Struts框架开发了系统.最后,以某型机四肋前段工艺性评估为例,验证了上述方法的有效性和实用性.     

条纹投射系统深度标定中的数据处理算法分析

条纹投射测量系统深度标定的目的是建立条纹位相和被测物面深度之间的映射关系.标定过程中,不同的数据处理模型和算法对系统最终的测量精度有显著影响.分析比较了标定中几种常用的数据处理方法的特点,包括精确几何模型及其线性化模型,多项式逼近模型,在噪声条件下的误差分布特点,以及节点选择对多项式逼近模型标定精度的影响等.通过数值模拟和实验验证了分析结果的正确性.     

典型汽车拉延模设计数据库系统的研究

为缩短汽车覆盖件拉延模开发周期,提出面向拉延模结构设计系统概念及总体结构,利用VBA,建立了典型汽车拉延模设计数据库系统,研究了WTK虚拟环境下VRML与典型汽车拉延模设计CAD数据库系统的集成开发.     

飞机钣金零件制造模型管理方法

分析了飞机钣金零件制造模型的典型状态组成,以框肋零件为例描述了零件制造模型设计态、毛坯态、成形件态和成品件态的内容.在此基础上,针对人员、数据和流程数据管理三要素,建立了基于多态模型的飞机钣金零件制造模型管理方法.对于人员管理,定义了飞机钣金零件制造的人员角色及其主要职责,采用基于规则的权限控制方法;对于数据管理,采用多态模型组织制造模型,以成形件态为例描述了节点数据模型;对于流程管理,以成形件态成形模具所用几何模型的设计为例,建立了流程管理模型.最后,以产品数据管理系统为平台建立了集成应用框架,验证了制造模型管理方法工程化应用的可行性.     

Design for economic manufacture of small sheet metal parts

Arguments are presented for a consideration of the DEM of pressed parts on a basis of equipment and tooling used to produce the parts rather than consider a categorisation based on ‘type’ by industry. It is also suggested that a combination of both generative and variant techniques of process planning, in conjunction with a good classification system and data base, should be used by the designer to develop, store and retrieve the type of information used in cost-optimising the design of pressed parts. This paper outlines the elements of cost involved in the production of pressed parts and presents details of a computer-aided process planning system which will assist the designer to quickly obtain the information necessary to optimise the designs. Typical computer program inputs and outputs are presented together with rules that have emerged in pressing design to reduce the number of tooling stages required and therefore the component manufacturing cost.     

An integrated manufacturing information system for mass sheet metal cutting

In order to reduce manufacturing cost and to improve the operational efficiency, some factories in the sheet-metal-related manufacturing industry centralize the production and management of sheet metal cutting. To support the centralized mass manufacturing paradigm, this paper presents an integrated manufacturing information system to achieve the high utilization of raw sheet material, lower the manufacturing cost, as well as to improve the operational efficiency and production management. The system architecture and some key technologies to implement this system are investigated, based on which, the whole information system is developed. This system integrates the functions of sheet metal part modeling and unfolding, nesting planning, automatic and interactive nesting, cutting process planning, NC-programming, off-line processing simulation and on-line monitoring. The system has been successfully utilized in industry, and an example of its application is described in the paper.     

基于夹具配置的薄板件装配偏差分析模型

为提高当前柔性薄板零件装配偏差分析的效率,提出了一种考虑夹具配置的装配偏差分析模型。通过对柔性薄板的定位装配过程的研究,分析了零件偏差、夹具偏差和装配偏差在各个步骤中的变化过程,建立了N-2-1和3-2-1两种夹具定位规则下的装配前后偏差之间的线性关系;根据装配后夹具定位点的释放模式的不同,建立了过定位释放和完全释放两种模式下的装配偏差分析模型。最后,通过分析实例薄板的装配偏差,表明了该装配偏差分析模型的有效性。     

A parametric study of sheet metal joints for dimensional integrity

The characteristics of joints between parts are one of the most critical issues in variation simulation analysis. This paper presents a parametric study of the dimensional variation characteristics of butt joints and slip joints. These two basic joints encompass the whole domain of joints used in sheet metal assemblies for structural extension. A geometrical model was proposed for predicting the assembly variation in order to take into consideration the possibility of part deformation and tool variation. Butt joints act like rigid bodies in the normal direction. For slip joints, the sensitivity coefficient in the slip direction is a function of tooling variations. The variation from individual part and tooling can be eliminated or substantially reduced if the product structure and assembly process is properly designed. A simple four-part assembly example shows the structure and assembly process. This result provides improved understanding of sheet metal assembly processes and provides a new idea for adaptive product and process design.     

A parametric study of sheet metal joints for dimensional integrity

The characteristics of joints between parts are one of the most critical issues in variation simulation analysis. This paper presents a parametric study of the dimensional variation characteristics of butt joints and slip joints. These two basic joints encompass the whole domain of joints used in sheet metal assemblies for structural extension. A geometrical model was proposed for predicting the assembly variation in order to take into consideration the possibility of part deformation and tool variation. Butt joints act like rigid bodies in the normal direction. For slip joints, the sensitivity coefficient in the slip direction is a function of tooling variations. The variation from individual part and tooling can be eliminated or substantially reduced if the product structure and assembly process is properly designed. A simple four-part assembly example shows the structure and assembly process. This result provides improved understanding of sheet metal assembly processes and provides a new idea for adaptive product and process design.     

机器视觉的薄片零件尺寸检测系统

对基于机器视觉的薄片零件尺寸检测系统进行研究。针对计算机硬盘弹性臂薄片零件的尺寸检测,采用线阵工业相机扫描获取待检零件图像,根据扫描特性提出了标定算法,同时提出了一种轮廓矢量化算法。将经过滤波、标定、二值化、边缘提取和细化的图像进行轮廓矢量化得到待检零件的尺寸参数,并与从设计图DXF文件中读取的零件的相应尺寸参数进行对比,判断零件制造质量。实测结果表明,检测系统的轮廓矢量化精度达到1 pixel,检测精度达到1 μm,平均每个零件的检测时间为1 s,该检测系统是可行的。     

柔性薄壁件装配公差的分析

产品设计过程中需要根据零件公差计尊其装配公差，但是传统的方法均假定零件在装配过程中不发生变形。针对金属薄壁件刚性小，易变形等特点，利用根据数论方法产生的伪随机点对薄壁件的装配公差进行有限元计算。计算结果表明：该方法的计算量远小于Monte Carlo法。并利用正交实验分析方法分析了零件公差对装配误差的影响。     

Characterisation of a measurement system for reproducible friction testing on sheet metal under plane strain

The testing equipment can compromise the quantification of the friction on sheet metal. This paper focuses on a systematic analysis of the testing equipment as a measurement system of the friction phenomena. It is shown that the mechanical response of the system may be responsible for significant variations on the quantification of frictional effects. Historical and inter-laboratory testing data show that, upon proper design of the measurement system, friction can be quantified, reproduced, and replicated with a significant degree of accuracy. This paper discusses the requirements and the controls of the test needed to maintain the uncertainty at its minimum level. The results show the feasibility of characterising friction in order to study the effects of the sheet, lubricant, and forming tools. This study is based on tests where cyclic bending under tension resulted in significant stretching and thinning of the sheet, but with the width remaining approximately constant. Friction research under other sheet forming modes may, however, benefit from the significance of the findings presented here.     

Towards an intelligent approach for CMM inspection planning of prismatic parts

This paper presents a model of prismatic parts (PPs) inspection planning on CMMs, in terms of an intelligent concept of inspection planning. The developed model is composed of Inspection Feature Construction, Sampling Strategy, Probe Accessibility Analysis, Automated Collision-Free Generation, and Probe Path Planning. In this model, the simulation of a measuring probe path is based on three algorithms: Algorithm for Measurement Points Distribution, Algorithm for Collision Avoidance, and Algorithm for Probe Path Planning. The simulation output is a measuring protocol for CMM UMM500. An experiment was performed on two PPs that have been produced for the purpose of this research. The inspection results show that all tolerances for both PPs are within the specified limits. The proposed model presents a novel approach for the automatic inspection and a basis for the development of an integrated, intelligent concept of inspection planning. The advantages of this approach imply the reduction of preparation time due to an automatic generation of a measuring protocol, a possibility for the optimisation of measuring probe path, i.e. the reduction of a time needed for the actual measurement and analysis of a workpiece, and an automatic configuration of measuring probes.     

Shape error measurement using ray-tracing and fringe scanning methods: projection of grating displayed on a liquid crystal panel

We present an improved Hartmann test, which has high spatial resolution with respect to the measuring points, for measuring projection mirrors. In the method, grid lines with a sinusoidal transmittance distribution are displayed on a liquid crystal panel and illuminated with a collimated laser beam. The beam transmitted through the liquid crystal panel reflects off the mirror surface being tested and reaches a screen. A charge-coupled device camera detects the projected images, which contain information about the inclination of the surface being tested. Any error in the shape of the mirror surface is identified by integrating the inclination. To increase the spatial resolution, the fringe scanning method is performed by shifting the grid lines on the liquid crystal panel. The grid lines are optimized for the shape of the mirror being tested. Because the grid lines are displayed by an electrical method, the shifting operation is easy and rapid, and furthermore, the displacement can be done precisely. The shape error of an off-axis parabolic mirror made of plastic is measured by the proposed method.     

板材FMS的修正分层控制结构研究

研究板材柔性制造系统 (FMS)控制系统结构。在比较了几种典型控制系统结构之后 ,采用修正分层结构作为板材FMS的控制系统框架 ;文章详细研究了板材FMS的物理组成以及修正分层控制系统结构形式及其实现方式。     

A fast full-field 3D measurement system for BGA coplanarity inspection

Ball-Grid-Array (BGA) has become one of the most popular packaging techniques in the electronics industry. Coplanarity inspection of BGA solder balls is critical for process and quality control in BGA manufacturing. Currently, the 3D measurement systems for BGA coplanarity inspection are mainly based on laser scanning techniques. However, they suffer from low inspection speed due to the physical line-scanning process. In this paper, a fast and cost-effective 3D measurement system for coplanarity inspection of BGA solder balls is proposed. The proposed system uses an LCD-based phase measuring technique to perform full-field 3D measurement of BGA solder balls with high accuracy. Experiments have shown that the coplanarity measurement of BGA solder balls is very efficient and effective with the proposed system. The measurement repeatability is in the micrometer range. The processing time of the proposed 3D measurement system for an image of 640×480 pixels is less than 2 s on a typical personal computer.