Optimization of clearance variation in selective assembly for components with multiple characteristics

Quality is an important aspect of any manufacturing process. Only high quality products can survive in the market. The consumer not only wants quality, precision and trouble-free products, but also wants them at attractive prices. When a product consists of two or more components, the quality of that product depends upon the quality of the mating parts. The mating parts may be manufactured using different machines and processes with different standard deviations. Therefore, the dimensional distributions of the mating parts are not similar. This results in clearance or interference between the mating parts. In some high precision assemblies, it may not be possible to have closer assembly clearance variation with interchangeable system. Selective assembly meets the above requisite and gives an enhanced solution. Selective assembly is a method of obtaining high precision assemblies from relatively low precision components. In this paper, a new selective assembly method is proposed to minimize the clearance variation and surplus parts for a complex assembly which consists of the components viz. piston, piston ring. In this assembly, each component will have more than one quality characteristic contributing for the assembly, for e.g., piston diameter will assemble with cylinder inner diameter; piston groove diameter will assemble with piston ring inner diameter, etc. In selective assembly each quality characteristic will fall in different groups. Non-dominated sorting genetic algorithm (NSGA) is used to find the best combination to obtain the minimum clearance variation in this assembly.     

The influence of assembly clearance on the deformation and stress of an assembly structure through FEA simulation

In order to facilitate parts assembly in a product structure, different clearances are provided in mating parts. The aim of this research is to investigate role of certain clearances in an assembly structure. These clearances are not part of tolerance stack but still can impart significant impact on product functional performance. Their influence on the product functional parameters like different stresses and deformation is studied in this research. A structure from automotive spot welding equipment is considered for this study. The effect of these clearances is determined using finite element analysis (FEA) simulations for process model of the product. It is found that some clearances are more critical for certain parameters. The results show that the product design can be improved by taking such clearances into consideration during design phase.     

双锥密封径向间隙及筒体端设计研究进展部

双锥密封是高压容器常用的一种密封结构。虽然GB 150－1998《钢制压力容器》规定了双锥密封的设计方法,但如何正确合理地设计双锥密封,一直受到持续关注,尤其是双锥环内圆柱面与端盖支承面之间径向间隙和筒体端部的结构设计与其强度校核。为了进一步研究径向间隙的取值和完善筒体端部的强度计算,评述了双锥密封径向间隙和双锥密封筒体端部结构强度校核的研究状况,指出对双锥密封需要进一步考虑的因素。     

基于焊装工艺相似的白车身零件实例检索

为充分利用前人的成功工艺经验,提出了一种基于焊装工艺相似的白车身零件实例检索的方法。考虑零件的主特征、辅助特征及特征之间的约束关系,建立了零件特征信息模型。从焊装工艺相似的角度,分3个阶段计算了零件间的相似度。第一阶段计算零件间主、辅特征的形状相似度和关系相似度,过滤掉形状不相似的零件;第二阶段计算零件间的几何尺寸的相似度,再次过滤掉尺寸相差较大的零件;第三阶段计算零件间的材料种类和材料厚度的相似度,获得工艺最相似的零件。通过具体的实例验证了该方法的有效性。     

Angular coordinate transformations during complex dimensional analysis of parts and assembly units in CALS technologies

Methods for the calculation of angular and linear dimensional chains in six-coordinate space are considered. Formulas for the evaluation of angular errors and mathematical expressions showing the influence of these errors on the linear positions of dimensional chain members are obtained in the projection form suitable for use in CAD, CAM, and CAPP systems for CALS technologies.     

泵类零件配合和形位公差的选用探讨

从实际应用中阐述了泵类零件设计时选择表面配合和形位公差的原则；着重介绍了形位公差的项目、基准选取以及公差值的确定方法。     

Dynamic analysis and load-sharing characteristic of multiple pinion drives in tunnel boring machine

A dynamic model of multi-gear drive in a tunnel boring machine is demonstrated in this study in which the effects of inertia on the driving mechanism and cutter head are considered. With the nonlinear coupling factors between the ring gear and multiple pinions considered, a dynamic analysis of multiple pinion drives is conducted, and their load-sharing characteristic is proposed. The load-sharing coefficients at different rotating cutter head speeds and input torques are determined and are found to reach up to 1.2–1.3. A simulated experimental platform of multiple pinion drives is performed, and subsequent torque distributions are measured under step load in the driving shaft of pinions. An imbalance in torque distribution of pinions is verified, and the load-sharing coefficients in each pinion can reach 1.262. Torque load fluctuation is regarded as system noise that can directly be coupled into the control system in the control strategy.     

多品种中小批量类型企业生产计划控制方法的实证研究

组织有秩序的生产与满足市场多变的要求,是多品种、中小批量生产企业进行生产计划控制管理的两难选择。以胜利柴油机厂为例,说明将理论与该企业实际相结合,通过生产计划控制流程再造,在生产制造系统信息数据准确化、标准化和集成化的基础上,以全厂中心仓库为枢纽,对产品零、部件实行品种、定额月滚动控制,可以获得较好的效果,并为进一步实施MRPⅡ打下基础。     

The impact of production mix variations and models varieties on the parts-feeding policy selection in a JIT assembly system

One of the significant challenges in operating a mix-model assembly system is the feeding of parts to the productive units. In order to avoid production loss, assembly systems require uninterrupted availability of components to feed workstations. On the other hand, the feeding of assembly components has to be performed in a way that minimises the related costs. In the past, the feeding system most widely used was so-called ‘line storage’ in which the components were stored along the assembly stations in large quantities and were periodically refilled by the central warehouse. Following just-in-time principles, nowadays, assembly system feeding is undertaken by supermarkets, as in decentralised storage areas close to the assembly lines. From such kinds of warehousing, a growing number of manufacturers are adopting two other feeding strategies: the kanban system, which continuously refills the assembly stations through the pull kanban system, or the kitting system, in which kits of components are prepared and delivered following the product through the assembly stations. This paper aims to quantitatively analyse and compare these two recent feeding strategies, considering the production mix variation and the assembled models variety influence. Moreover, kanban-kitting feeding policy and the related optimization issues are considered as hybrid. The findings from an industrial case study and a simulation analysis are also reported. Finally, a decision-making tool that defines a series of ‘convenience areas’ for the different feeding policies is provided.     

Experimental and CFD study on the mass flow-rate characteristic of gas through orifice-type restrictor in aerostatic bearings

This paper describes the experimental and CFD study on the mass flow-rate characteristic through an orifice-type restrictor in aerostatic bearings. In the conventional design of gas-lubricated aerostatic bearings, the mass flow-rate of gas through an orifice-type restrictor is generally derived from a well-known mathematical model, which is originally developed to describe the mass flow-rate property through an ideal nozzle. It is reasonable to doubt if there is any difference between the property of mass flow-rate through an orifice and that through a nozzle. In this paper, therefore, a series of simulations and experiments are carried out and the results show that the mass flow-rate characteristic through an orifice is different from that through a nozzle. Consequently, the conventional model to determine the mass flow-rate through an orifice-type restrictor in aerostatic bearings may have to be updated to the proposed new model for more precise design and modelling of the gas-lubricated aerostatic bearings.