床身式铣床几何精度检验与调整

正1.主轴箱垂直移动的直线度(1)定义与公差范围主轴箱垂直移动的直线度是指检验立柱垂直导轨和主轴箱垂直导轨各自的直线度及两导轨的配合状况。如图1所示,此项精度在机床横向(a项)垂直平面及机床纵向(b项)垂直平面两个平面内检验。在300mm测量长度上,a、b两项公差为0.025mm。此项精度超差会影响被加工表面的直线度。     

精密机床加工误差灵敏度分析与公差设计

加工精度是衡量精密机床加工性能的重要指标,当前针对提高加工精度的研究主要围绕误差补偿展开,缺少根据加工件的精度要求而进行机床运动轴公差设计的研究。从公差设计的角度出发,通过机床空间运动误差建模、蒙特卡洛法模拟,实现最小二乘法评价零件加工精度;利用正交试验方法,得到某项精度要求与机床运动轴误差的公差带的多组对应数据,通过多元线性回归,进行灵敏度分析;同时基于自适应遗传算法,给出了运动轴误差的公差设计方法,保证所设计的公差带在装配工艺上的可行性。通过对某精密卧式坐标镗床29项误差公差带设计,验证了该方法的可行性。     

导轨修理与安装中的一些问题

由于机修工作接触面广、技术复杂,而机修队伍又分散,因而在许多问题上往往存在不同的理解。本文就导轨修理与安装问题谈一些看法,供讨论。 一、关于导轨精度检测 导轨修理的目的就是为了恢复精度,所以必须正确理解机床精度标准中关于导轨精度的含义和所采用检验方法的原理。 1.不直度的线值公差与角值公差 为控制溜板(或工作台)移动轨迹的不直度,在我国的机床精度标准中,对溜板长度与其行程的比值较小的机床采用线值公差,而对此比值较大的机床则采用角值公差。譬如在《JB 2314-78,普通车床精度》、《JB 2499-78,六角车床精度》、《(GC)3-…     

利用钢球定位测量圆跳动公差

一、概述对图1所示零件圆跳动公差的测量,一般按照基准孔的尺寸精度,设计制造相应的圆柱(锥)导向芯轴或可胀式芯轴来测量。用圆柱(锥)导向芯轴时,由于基准孔有一定的尺寸公差,芯轴与基准孔之间有间隙,所以     

基于Pro/E的复杂箱体三维数控加工前处理方法研究

制造企业越来越多地使用3D软件进行设计与制造,设计工程师通常使用零件的基本尺寸与公差标注信息来描述箱体类零件模型,大多数箱体类零件需要在数控机床上加工,数控机床加工零件的精度取决于机床精度,其走刀位置都是走到公差中心点,这就需要数控编程工程师对模型的加工尺寸进行相应的转换.本文使用VB API对Pro/E进行二次开发,提取箱体模型的基本尺寸和公差信息,通过计算得出满足数控加工要求的尺寸值,并利用这些尺寸值驱动生成新模型,从而完成数控加工编程的自动前处理.避免了尺寸转换的遗漏和错误,提高了生产效率,减少了加工废品率.     

机床导轨的设计计算

一、前言导轨是每台机床不可缺少的部件,它的制造精度直接影响加工零件的精度。导轨的耐磨性是影响机床精度保持性和使用寿命的关键因素之一。因而导轨的制造精度和耐磨性成为机床好坏的重要指标。在毛主席革命路线指引下,我国机床行业的广大工人和技术人员,在党的领导下,对机床导轨的设计和制造进行了许多工作,取得了可喜的成果。     

关于锥度量规磨削的探讨

锥度量规是机床主轴加工过程中的关键检具，随着机床性能、精度、速度的进一步提高，对锥度量规制造提出了更高的要求，同时，对锥度量规磨削提出了更高的尺寸及形位公差精度的要求。     

导轨测量中的角值误差和线值误差——对《钳工必读》导轨不直度测算方法的异议

如何正确测量与评价机床导轨的精度与质量,是机床制造和机床维修工作中必须解决的问题.角值公差与线值公差是导轨测量中经常用到的工程技术术语,虽然在机床精度标准中,它们都称为导轨不直度,但两者的定义、标注形式、测量手段、计算取值方法都全然不同;两者在数值上也不存在任何换算关系.这点必须清楚无误,不容有任何混淆.但在我厂的维修工作者中,因概念不清、观点混乱而争论不休者却不乏其人.甚至在我厂的精度检验单技术文件中,也经常出现标注错误的情况.更严重的是,在天津机械工业局1983年再版的《钳工必读》这样典型的工人技术等级标准自学丛书普及读物中,对于用水平仪测量导轨水平不直度的方法,也出现明显的错误,更在广大钳工中引起错误的看法和测量计算的错误.因而有必要在此提出讨论,以辨明正误.     

一般公差的合理应用

一般公差即线性尺寸的末往公差，是指在车间普通工艺条件下，机床设备一般加工能力可保证的线性尺寸公差。主要适用于金属切削加工的线性尺寸。对一般冲压件的加工尺寸、非金属材料和其他工艺方法加工的尺寸可参照使用。当然，有关工艺方法的本注公差有专项国家标准作了规定，如：冲压件未注公差为GB／T15055一94；铸件尺寸公差为GB6414－86；钢质模锻件公差为GB12362－90；锤上自由锻件公差为GB15826－1995等。采用一般公差是指在该尺寸后面不注出极限偏差，主要适用于低精度的配合尺寸，在正常车间精度保证的条件下，一般可不检验。采…     

轴一套类零件配合尺寸公差最优设计的研究

公差设计的优劣不仅直接影响产品零件装配精度的实现,而且对产品制造成本亦将产生重大影响。文章对轴－套类零件制造（加工与装配） 成本的各因素进行了分析,提出了达到装配精度要求的最优装配方法的判定准则,建立了生产成本最低的轴－套类零件最优公差设计的数学模型,并用实例验证了该模型在实际中的正确性与有效性。     

A cost-tolerance analytical approach for design and manufacturing

Tolerance assignment in mechanical engineering product design and manufacturing is critical both for product quality and performance as well as for its manufacturing cost. Simple design rules, industry available comparative experimental data, tables, charts, and personal expertise are currently used for cost optimum tolerancing. Such a methodology is not very practical, requires considerable time and effort and is not always suitable for a CAD/CAM environment. To face these limitations, a new model for the manufacturing cost-tolerance function has been developed and is presented in the paper. It may well be used for direct-tolerance optimisation applications and it is shown that it produces results that are in satisfactory agreement with existing cost-tolerance data. Its use is further analysed and demonstrated in solving linear manufacturing tolerance transfer problems.     

制造系统中的公差与成本

公差设计是产品设计中的重要组成部分。公差设计的优劣,对产品制造加工过程有直接影响。文章详细分析了产品公差设计的类型和过程及产品成本的各项因素,提出了公差—成本关系的基本模型,为基于成本最低的公差设计优化提供了基础理论依据。     

公差优化中的制造成本估算

以公差优化为目标进行制造成本估算是对公差———成本关系进行建模的基础问题。文章分析比较了传统的制造成本的计算方法,提出了已知制造系统状态时对公差———制造成 本关系的建模 方法———多参数公式法,详细阐述了该方法的使用环境以及提出该方法的必要性及合理性,并以实例对其可用性进行了说明和验证。     

Simultaneous process mean and process tolerance determination with asymmetrical loss function

Process design involves process mean and process tolerance determination. Process mean determination is finding the best settings for product quality, without affecting manufacturing cost. However, process tolerance determination is a manufacturing process selection which generally affects manufacturing cost and product quality. In this study, asymmetric quality loss is considered in measuring product quality, and tolerance cost is adopted in representing manufacturing cost. To reflect the combined effect of process mean and process tolerance completely, failure cost is added to the category of manufacturing cost. Then, based on the sum of these three costs, a simultaneous optimization of process mean and process tolerance is determined for process planning in the early stages of development.     

Compatibility of tolerancing

Tolerances are assigned to a mechanical engineering design either on the basis of functional and/or manufacturing requirements (toleranced dimensions, geometrical tolerances) or on the basis of the general categories—fine, medium, coarse—of the international standards or the designer's knowledge and experience (untoleranced dimensions). Conventional dimensions of the currently applicable dimensioning rules and implicit dimensions, including those attributed to geometrical tolerances, thus create four groups of tolerances which may or may not be compatible. In addition, any tolerance compromise, however tedious and difficult, not achieved systematically may well lead to accuracies which cannot be produced by the available machine tools. In the paper, a systematic approach to the above problems is presented. A methodology is demonstrated for the verification of the tolerance compatibility and for the assignment of compatible, producible and cost optimum tolerances.     

Study on the tolerance allocation optimization by fuzzy-set weight-center evaluation method

The tolerance allocation optimization method by fuzzy-set weight-center evaluation is used to derive the manufacturing difficulty coefficient, through quantifying the manufacturing condition factors which all affect the manufacturing cost, including the forming means of the blank, element size, machining surface features, operator’s skills, and material’s machinability. The coefficient is then converted into a weight factor used in the inversed square model representing the relationship between the cost and tolerance, a cost-objective function model based on optimal tolerance allocation according to the manufacturing conditions is thus established for optimizing and allocating the tolerances. Integrating this model into computer-aided-tolerance-allocation makes it more convenient, accurate, and feasible.     

Optimum manufacturing tolerance to selective assembly technique for different assembly specifications by using genetic algorithm

Tolerance on parts dimension plays a vital role as the quality of the product depends on sub components tolerance. Thus, precision products that are manufactured reflect at high manufacturing cost. To overcome this situation, sub components of an assembly may be manufactured with wider tolerance, measured (using latest technologies like image processing) and grouped in partition and corresponding group components may be mated randomly. This present work is to obtain an optimum manufacturing tolerance to selective assembly technique using GA and to obtain maximum number of closer assembly specification products from wider tolerance sub components. A two components product (fan shaft assembly) is considered as an example problem, in which the subcomponents are manufactured with wide tolerance and partitioned into three to ten groups. A combination of best groups is obtained for the various assembly specifications with different manufacturing tolerances. The proposed method resulted nearly 965 assemblies produced out of one thousand parts with 15.86% of savings in manufacturing cost.     

Optimal Process Tolerance Balancing Based on Process Capabilities

An optimal approach for process tolerance balancing is presented. The new approach is based on process capabilities and is to be used in the stage of process planning. A nonlinear programming model is used to simultaneously optimise process tolerances of required operations. In the optimisation model, the objective function is to minimise the total manufacturing cost with different weighting factors. Using the estimated standard deviations of the dimensions and the manufacturing cost-tolerance functions, the constraint equations for the process tolerance chains and the manufacturing capability indices are established, together with a model for the economical tolerance bounds of machine tools. A practical example was used to verify the usefulness of the proposed approach. The results of the comparative study show that the proposed approach is more advantageous in relaxing tolerance requirements and in reducing scrap rates generally, compared with the existing methods. ID="A1"Correspondance and offprint requests to: Dr Y. Gao, Department of Mechanical Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong. E-mail: meygao@ust.hk     

Tolerance design optimization of machine elements using genetic algorithm

An important problem that faces design engineers is how to assign tolerance limits. In practical applications, tolerances are most often assigned as an informal compromise between functionality, quality and manufacturing cost. Frequently, the compromise is obtained iteratively by trial and error. A more scientific approach is often desirable for better performance. In this paper, a genetic algorithm (GA) is used for the design of tolerances of machine elements to obtain the global optimal solution. The objective is to design the optimum tolerances of the individual components to achieve the required assembly tolerance, zero percentage rejection of the components and minimum cost of manufacturing. The proposed procedure using GA is described in this paper for two tolerance design optimization problems: gear train and overrunning clutch assemblies. Results are compared with conventional techniques and the performances are analyzed.