Concurrent tolerance charting for component and assembly using “modified tree” approach

The interaction between components in an assembly plays a major role in the performance and reliability of the assembly. However, in conventional design, the dimensions and tolerances of components are usually assigned intuitively to satisfy design constraints. Tolerance analysis is then performed to determine the critical tolerance accumulation that results from the assembly. The tolerances are then modified so that the interaction requirements are satisfied. This approach relies on the experience of the designers and the results may not be an optimum.This paper presents a direct method to determine the working dimensions and tolerances of components that allows control of the assembly interaction. The model is easy to construct and it provides a clear picture of the entire process and assembly links. Using the model, a set of linear equations is formulated directly based on the design constraints and interaction requirements. With appropriate constraints derived in terms of the process capabilities, the desired working dimensions and tolerances can be determined using LINDO, software for solving the linear programming problem. This approach allows the working dimensions and tolerances of all components in an assembly to be determined concurrently.     

An improved tolerance charting technique using an analysis of setup capability

The tolerance charting method enables the calculation of working tolerances in machining process planning. The method has been used as a basic tool for analysing process plans for many decades. Process capability in tolerance charting is modelled using the tolerances of the working dimensions. The literature shows that machining process capability can be analysed from the point of view of surface position errors. During setups, it is possible to perform decomposition into two surface position tolerances: a datum surface position tolerance and a machining surface position tolerance. This type of analysis has the advantage of producing simplified tolerance chains. This paper provides an adaptation of the tolerance charting technique that uses a capability model based on datum and machining surface position tolerance. The results show an improvement in the working tolerance stackup that reduces the capability required for productive resources. As a result, reductions in manufacturing costs can be achieved. The proposal is valid for manual or computer-assisted techniques.     

Determining dimensions for process planning: A backward derivation approach

Computer-aided process planning has shown its great importance in computer integrated manufacturing systems. Dimensioning and tolerancing plays a key role in process planning since the final workpiece must ensure conformance with the dimensions in its blueprint. This paper proposes a simple, efficient approach to derive working dimensions for process planning, based on the tolerance chart technique. The paper first reviews briefly some approaches previously presented, such as the mathematical linear equation approach and the graph tracing approach, it then proposes the backward derivation approach. By setting up the origin of a coordinate system at the left-most surface in a blueprint (B/P), the approach first determines the distances from all the B/P surfaces to the origin by use of the B/P dimensions. Then by updating these dimensions, the final working dimensions are calculated backwards by a simple arithmetical equation.     

工艺尺寸路径图的建立与应用

传统的工艺尺寸链只能够描述工艺尺寸关系而未能提供零件的加工信息,不能体现零件各个要素的加工顺序及其各工序尺寸基准,这无助于工艺路线与尺寸公差的并行设计。用带下标的英文字母表示零件在加工过程中各加工要素,用有向线段表示基准至加工要素之间的工序尺寸,将各个工序尺寸按加工顺序依次用树图的形式画出,得到各要素的形成路径—工艺尺寸路径图。路径图所表达的尺寸关系更加简洁直观、完整,易于建立全相关尺寸模型;从路径图中挖掘出粗基准的一些本质特征,为毛坯尺寸的合理标注提供可靠的理论依据;通过改变路径图中某些要素的位置或顺序,可以实现对工艺路线的改进。通过实例对工艺尺寸路径图进行优化而实现对工艺路线的改进,证明了工艺尺寸路径图对工艺路线的合理制订是行之有效的。     

An industrial implementation of computer-aided tolerance charting

This paper argues that tolerance charting is not relevant for design tolerancing, but that it is an effective tool for process planning. It also argues that the tolerance charting algorithm based on rooted tree graphs, developed by the authors, provides a very general and powerful representation technique for tolerance charting. The technique is explained in detail to show how it can encompass all practical manufacturing processes that affect dimensions. A computer-based implementation of this technique, called CATCH, has been developed and is currently being used by a company in Singapore for process planning.     

Development of an expert system for cold forging of axisymmetric product

This paper deals with an automated computer-aided process planning and die design system by which the designer can determine operation sequences even if they have little experience in process planning and die design for axisymmetric products. An attempt is made to link programs incorporating a number of expert design rules with the process variables obtained by commercial FEM softwares, DEFORM and ANSYS, to form a useful package. The system is composed of four main modules. The process planning and the die design modules consider several factors, such as the complexities of preform geometry, punch and die profiles, specifications of available multi-former, and the availability of standard parts. They can provide a flexible process based on either the reduction in the number of forming sequences by combining the possible two processes in sequence, or the reduction of deviation of the distribution on the level of the required forming loads by controlling the forming ratios. In the die design module optimal design technique and the horizontal split of the die insert were investigated for determining appropriate dimensions of components of the multi-former die set. It is suggested that the proposed method can be beneficial for improving the tool life of the die set in practice.     

Development of an expert system for cold forging of axisymmetric product

This paper deals with an automated computer-aided process planning and die design system by which the designer can determine operation sequences even if they have little experience in process planning and die design for axisymmetric products. An attempt is made to link programs incorporating a number of expert design rules with the process variables obtained by commercial FEM softwares, DEFORM and ANSYS, to form a useful package. The system is composed of four main modules. The process planning and the die design modules consider several factors, such as the complexities of preform geometry, punch and die profiles, specifications of available multi-former, and the availability of standard parts. They can provide a flexible process based on either the reduction in the number of forming sequences by combining the possible two processes in sequence, or the reduction of deviation of the distribution on the level of the required forming loads by controlling the forming ratios. In the die design module optimal design technique and the horizontal split of the die insert were investigated for determining appropriate dimensions of components of the multi-former die set. It is suggested that the proposed method can be beneficial for improving the tool life of the die set in practice.     

Optimized sequential design of two-dimensional tolerances

Tolerancing has great impact on the cost and quality of a product. Previous research essentially focussed on one-dimensional tolerancing where sized tolerances accumulate only in one direction. When sized and angular tolerances are considered simultaneously, tolerances accumulate, however, in two different directions in the given view plane. We utilize related tolerance zones to illustrate the accumulation processes of sized and angular tolerances. The orientational tolerances are converted into the equivalent sized or angular tolerances in terms of their engineering semantics. We establish the sequential linear optimization models to maximize the 2D sized, angular, and orientational working tolerances of a 3D machined part based on the process capabilities. At any completion stage of operations, we measure the processed sized dimensions and then substitute them into the dimensional chains to dynamically re-calculate the mean working dimensions for remaining operations. We also re-evaluate the working tolerances for remaining operations using sequential optimization models. This approach can release the working tolerances, reduce manufacturing costs, and enhance the acceptance rate of machined parts when we manufacture the complex, low-volume, and high-value-added parts. The approach is finally illustrated with a practical example.     

A novel approach for benchmarking and assessing the performance of state estimators

State estimation is a widely adopted soft sensing technique that incorporates predictions from an accurate model of the process and measurements to provide reliable estimates of unmeasured variables. The reliability of such estimators is threatened by measurement related challenges and model inaccuracies. In this article, a method for benchmarking of state estimation techniques is proposed. This method can be used to quantify the performance and hence reliability of an estimator. The Hurst exponents of a posteriori filtering errors are analyzed to characterize a benchmark (minimum mean squared error) estimator, similar to the minimum variance control benchmark developed for control loops. A distance metric is then used to quantify the extent of deviation of an estimator from the benchmark. The proposed technique is developed for linear systems and extended to non-linear systems with single as well as multiple measurable variables. Simulation studies are carried out with Kalman based as well as Monte Carlo based estimators whose computational details are significantly different. Results reveal that the technique serves as a tool that can quantify the performance and assess the reliability of a state estimator. The strengths and limitations of the proposed technique are discussed with guidelines on applications and deployment of the technique in a real life system.     

A Matrix Method for Calculating Working Dimensions and Offsets for Tolerance Charting

This paper presents a new matrix method for calculating working dimensions and offsets for tolerance charts. The method is part of a more general datum hierarchy tree technique for tolerance planning and control. The matrix method is suitable for both manual and computer-aided computation. It has been implemented in an industrial program, CATCH, and a prototype artificial intelligence (AI) program for process planning. The method has been successfully taught to engineering students in New Zealand and Finland. Worked examples are provided to illustrate the method. The examples show how to calculate working dimensions without offsets, and how to calculate an offset working dimension and an offset resultant dimension.     

基于小波包与关联维数的阀片故障诊断

结合了小波包降噪和关联维数对某往复压缩机阀片故障做了定量识别。实测阀片在正常和磨损两种工况下的振动信号,用小波包对信号进行降噪处理后,用改进的关联维数算法分别计算两个信号的关联维数。实例表明:小波包降噪能明显地滤除噪声,阀片在正常和磨损两种工况下的关联维数明显不同,关联维数可作为阀片故障特征的定量提取。     

有限变工况特征迁移学习方法及其在高速列车轴箱 轴承故障诊断中的应用

以高速列车轴箱轴承为研究对象,提出了一种适用于有限数量变工况下的轴承故障诊断方法。该方法以有监督的学习模式构造自编码器,将不同工况下特征值集向参考工况下特征集做映射迁移,从而减弱由工况变化引起的轴承故障特征值改变的影响。再将迁移后的特征集输入由参考工况特征集预训练的基于卷积神经网络的故障诊断模型,实现变工况下轴承故障的诊断。凯斯西储大学轴承公开数据集和高速列车轴箱轴承数据集的试验结果表明,经监督式自编码器特征迁移后的轴承故障识别准确率有了较大提升,该方法能够较好的实现有限工况下的特征序列的迁移,解决工况变化带来的故障特征的畸变问题。     

图解法的原理及其在制订工艺过程中的应用

制订零件加工艺过程时需要确定工序次序和各工序的加工尺寸。而用尺寸链法来解则常常是相当困难的。本文首先简单介绍图解法,然后讨论了它与尺寸链的关系和它在制订工艺过程中的应用。     

基于机器视觉的FDM-3D快速成型异常工况监控系统

针对FDM-3D打印过程中存在的各类打印故障,提出了一种基于机器视觉的FDM-3D快速成型异常工况监控系统,该系统能够完成自动识别和报警等功能,实现无人值守状态下的智能监控。首先,基于视觉提取实际打印目标的轮廓;然后,基于计算机图形学获取stl文件中待打印物体的理论轮廓,并将其与实际打印目标的轮廓做对比;最后,开发一个基于网络的自动报警系统。实验结果表明,该监控系统能够对零件垮塌或打印机喷头堵塞等状况实现实时在线的评价。基于图像识别的监控方法能够与3D打印目标的造型实时匹配,该方法可以扩展到多种不同类型的打印机。     

Dimension measurement of hot large forgings with a novel time-of-flight system

The dimension measurement of hot large forgings is necessary for process control and product quality. However, the conventional technique in forging plants leads to a high scrap rate of raw materials. In order to reduce the waste and increase the productivity, this paper presents a novel measurement technique based on the pulsed time-of-flight (TOF) laser radar to measure the dimensions of hot large forgings. The system consists of a TOF, a scanning device of the two-degree-of-freedom (2-dof) spherical parallel mechanism (SPM), and two motors. Then, its measuring principle and the SPM are described. A special data-processing method is developed to extract the dimensions and the shape of a large forging by scanning for a few times. The laboratory experiments indicate that the shape and dimensions such as the diameter and length can be achieved by virtue of the TOF system. The dimension measurement in a forging plant is also conducted to verify the effectiveness of the presented system.     

基于C8051F005单片机和MEMS加速度传感器ADXL311的倾角仪

提出了一种基于C8051F005单片机和ADXL311双轴加速度传感器的数字式倾角仪的设计方法,并介绍了其软硬件的实现。该倾角仪的工作原理是依次在0°、90°、180°3个不同位置,由C8051F005单片机A/D转换进行定标,然后将处理后的数据送外部设备显示。该倾角仪首次使用需先进行标定,改善因在不同工作环境下所产生的角度误差,与传统的倾角仪相比具有很高的灵敏度,满足各种不同场合下测量精度的要求。     

Part segmentation by superquadric fitting-a new approach towards automatic design of cooling system for plastic injection mould

The cooling system of an injection mould plays an important role in determining the productivity of the moulding process and the quality of the moulded part. Previous research has mainly focused on the analysis and optimization of cooling systems, but techniques that can be used for the automatic design of cooling systems have not been well investigated. In a previous project, we developed an automatic system that can generate preliminary designs for cooling systems. A key component of that automatic system is an algorithm that segments a part with a complex shape into simpler shape portions to facilitate the subsequent design synthesis process. This segmentation method, based on a feature recognition technique, has limited geometric coverage. In this research, a new method of part segmentation with an extended geometric coverage is developed. This method first estimates the regions where segmentation boundaries exist, and then refines the regions until they can be used to segment the part into separate portions. When this new part segmentation algorithm is integrated into an automatic design system, the system can generate cooling system designs for a larger class of plastic parts.     

Selection of machining datum and allocation of tolerance through tolerance charting technique

Tolerance charting is an effective tool to determine the optimal allocation of working dimensions and working tolerances such that the blueprint dimensions and tolerances can be achieved to accomplish the cost objectives.The selection of machining datum and allocation of tolerances are critical in any machining process planning as they directly affect any setup methods/machine tools selection and machining time.This paper mainly focuses on the selection of optimum machining datums and machining tolerances simultaneously in process planning.A dynamic tolerance charting constraint scheme is developed and implemented in the optimization procedure.An optimization model is formulated for selecting machining datum and tolerances and implemented with an algorithm namely Elitist Non-Dominated Sorting Genetic Algorithm(NSGA-II).The computational results indicate that the proposed methodology is capable and robust in finding the optimal machining datum set and tolerances.     

两工位数控专用电机壳铣钻床研制

依据用户需求和被加工件规格提出产品规划,采用现代设计方法进行两工序、两工位工作原理与工艺方案设计及系统功能原理方案设计,确立机电液一体化控制的总体结构方案,阐述该设备机械系统执行部分的创新结构及主要技术特征。