基于仿真分析的BT40主轴系统公差设计与优化

公差设计质量直接影响产品的性能和制造成本。为提高主轴系统公差设计的质量和效率,提出了一种基于建模仿真的公差设计与优化方法。模拟BT40主轴系统的结构和装配过程,首先在CETOL6σ软件中建立主轴系统的数字化公差模型,利用该模型分析各主要公差对系统输出精度的贡献度和敏感度。然后以类比法公差设计作为原始方案,仿真检验其设计效果。最后以公差贡献度和敏感度为依据,对原有公差设计方案进行修正及优化。结果表明:优化后的方案显著提高了主轴系统的输出精度。     

Study of an assembly tolerance allocation model based on Monte Carlo simulation

The traditional design methods of assembly tolerance allocation are usually based on engineers' experience, or the worst on worst tolerance analysis (WOW) method, or the root sum square tolerance analysis (RSS) method. However, the above-mentioned methods, whilst used frequently in the analysis of a single-dimensional chain, are not suitable for the analysis of geometrical tolerance and multi-dimensional chains. Also, the relationship between tolerance and manufacturing cost is not considered and a suitable tolerance allocation based on minimum manufacturing cost can not be obtained. Some research works have applied linear or non-linear programming methods to optimize the tolerance allocation of each part in an assembly. However, the convergence of the solution is not ensured. The purpose of this study is to provide an integrated approach, including tolerance design, manufacturing cost analysis and multiple chains consideration, using the Monte Carlo method to optimize the tolerance allocation with minimum cost. The Monte Carlo method, a statistical simulation method, was used to simulate the dimension variance of each part and each dimensional chain. The contribution percentage of each part on each dimensional chain was calculated. Tolerance cost was chosen as an object function and the tolerance allocation model as a constraint condition, the optimum tolerances of each part being obtained by the iteration method. Results of computer simulation for several examples were compared with published data for demonstrating the feasibility of the proposed method. It can be concluded that the tolerance-allocation model combined with a tolerance-cost relationship can provide a very practical and useful approach for design engineers.     

基于现值质量损失的并行公差技术研究

在并行设计环境中,用多变量质量损失函数在连续复利条件下把产品质量特征的退化作为一个连续的现金流量函数进行建模,从而建立了多重质量特征产品的质量损失现值与其相关工序参数的函数关系。在此基础上,把质量损失的现值和产品随时间退化的影响集成到总的装配成本模型中,建立了并行公差设计的优化模型。产品的并行优化设计与工序公差,通过使总的装配成本最小化获得。一个圆锥齿轮装配的并行优化分配设计与工序公差实例验证了该模型在实践中的有效性。     

Allocation of assembly tolerances to minimize costs

The cost and quality of an assembly depend on the processes used to manufacture its components. The specific processes and process settings are often dictated by the tolerances on the components. One long-standing challenge is allocating the assembly tolerance to components. Many methods have been proposed, most of which endeavor to minimize cost. We propose a tolerance allocation method that minimizes cost by jointly considering process variation and tolerance specifications. A cost model including processing cost, scrap cost, and quality loss is employed. The cost is minimized by a heuristic strategy. An overrunning clutch assembly case study is used to evaluate the method.     

高精度管材拉拔过程计算机模拟研究

高精度管材是一种内表面质量要求很高,内径尺寸允许偏差很小的管材。研究了高精度管材拉拔模具形式对管材生产的影响。开发了一种新型芯棒,利用MSC.MARC有限元仿真软件,模拟高精度管材的拉拔过程,分析了新型芯棒对高精度管材尺寸精度的影响规律,为研究和生产提供有效的帮助。     

THE TOLERANCE DESIGN MANUFACTURE AND RELIABILITY

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Tolerancing for manufacturing via cost minimization

The purpose of dimensioning and tolerancing for process planning is to determine the dimensions and tolerances that are to be produced at each stage in the manufacture of a component in order that the design dimensions and tolerances specified on the engineering drawing of the component are satisfied. Three proposed objective functions for cost minimization are developed in this paper according to various situations. When cost information is available average cost per acceptable unit produced in minimized, otherwise ratio of number of components to be machined to output is minimized. If residual tolerances exist sum of manufactured tolerances are maximized by assigning weights according to their process capabilities. Combining these objective functions a computerized optimization program has been developed which determines the optimum set of dimensions and tolerances which satisfies the specified design dimensions and tolerances and the permissible machining allowances, with the cost of producing all dimensions to the respective tolerances to be minimal.

This system takes into account machining cost, scrap and where in the production process it occurs, manufactured dimensions and their distributions, allocated tolerances and process capabilities.     

Concurrent optimization of design and machining tolerances using the genetic algorithms method

The allocation of design and machining tolerances has a significant effect on both manufacturing cost and quality. This paper presents a procedure to concurrently allocate both design and machining tolerances based on optimum total machining cost. The non-linear multi-variable optimization problem formulated is solved using the genetic algorithms method. Two design examples involving concurrent allocation of both design and machining tolerances are presented to demonstrate the effectiveness of the method.     

多质量特性产品的参数与容差并行设计优化

对具有多质量特性的产品（或过程）进行了参数与容差并行设计，通过平衡参数设计阶段所带来的质量损失，和缩小设计参数容差所增加的成本，提出了总成本函数，考虑了设计参数的波动及整个过程的经济性。并通过实例进行了分析，结果表明，与传统的参数设计方法相比，并行设计得到的响应的方差与总成本都显著地降低。     

Early cost estimation for tolerance verification

This paper presents a methodology for estimating the verification cost of geometric tolerances at the design stage, which is useful for optimizing the tolerance specifications of mechanical products. The tolerance verification cost may be seen as the sum of the measurement and uncertainty costs. The measurement cost depends on the adopted device and on the measurement time. The uncertainty cost is related to type A (declaring a conforming part non-conforming) and type B (declaring a non-conforming part conforming) errors: these errors are strongly influenced by the measurement procedure, which depends on the measurement device and determines the measurement time. The methodology is illustrated and validated using simulation and industrial case studies.     

单排多型芯结构公差累积分析

为了解决单排多型芯模具结构中模具型芯存在的公差累积过大的问题,通过分析单排多型芯模具固定孔和型芯的尺寸特点,提出了两种优化模具结构设计、合理设计型芯和固定孔的公差分配的方法。有效降低模具零件的加工难度,提高模具生产时的稳定性。     

An accuracy analysis of the peg-and-hole assembly problem

A peg-and-hole assembly may adopt clearance, transition or interference fits depending on the functional requirements of the particular design. The international standards that are used for the specification of the nature of a fit refer, nevertheless, only to dimensional deviations. They do not consider the actual geometry of the assembly components. Geometrical tolerances are assigned in addition to the dimensional tolerances whereas, for certain applications, the latter may also include some provision for them. Maximum and minimum functional clearances, dimensional and geometrical tolerances of a peg-and-hole assembly consist of a system where values of the first two variables are design-imposed and the dimensional/geometrical tolerance values have to be suitably allocated. This tolerance allocation cannot, however, be effected by a straightforward approach. The unknown variables are more than the available clearance/tolerance relationships and in the current engineering practice, the problem solution is usually based on experimental/empirical data and/or general tolerance assignment guidelines. The paper addresses this problem through a systematic analysis of the accuracy requirements of a peg-and-hole clearance fit assembly. The analysis is then followed by the development of a methodology for the evaluation of the dimensional and geometrical tolerances of the assembly components. The presented algorithm is further applied and discussed in a case study.     

The application of tool deflection knowledge in process planning to meet geometric tolerances

Machine tool deflections due to cutting forces can result in dimensional errors on workpieces. The problem is most severe when flexible tools such as end mills are used. When dimensioned features are specified with tolerances, process planning should examine the compromise between achieving high productivity rates and meeting dimensions within the specified tolerances. The use of geometric dimensioning and tolerancing permits interaction between size and position and makes bonus tolerances available. The errors occurring in end milling are first examined and modelled using regression methods. A procedure is proposed for selecting optimal feed rates that ensure that tolerances can be met. The process is demonstrated in machining a slot using the down milling mode. The use of a tolerance analysis chart clarifies the results of the test in relation to the tolerance standards. The need to consider the transient errors at the exit of the cut is demonstrated.     

Human and robot allocation method for hybrid assembly systems

Manufacturing companies today need to increase both changeability and efficiency of production systems in order to strengthen their competitiveness. Hybrid assembly systems have evolved as solutions to counter this issue. In this system, humans and robots cooperate to perform assembly tasks; the system has the advantage of maximizing robot efficiency and human flexibility. This paper proposes a method for planning human and robot allocation in hybrid assembly systems. The method enables us to select the initial human and robot allocation, that minimizes the expected total production cost including robot investment and labor cost taking into consideration possible scenarios of future changes in product models and production volumes.     

From solid modelling to skin model shapes: Shifting paradigms in computer-aided tolerancing

Product design requires the consideration of geometric models and representations that reflect shape deviations and support tolerance management issues. Computer-Aided Tolerancing (CAT) systems have been developed as simulation tools for modelling the effects of tolerances on digital product simulation. However, geometric variations cannot be addressed efficiently with regard to form deviations. This paper investigates the concepts of Skin Model Shapes, which provide a finite describability and the digital representation of the Skin Model concept, and their unified discrete geometry representation. New contributions to tolerance representation and analysis are presented. Applications and perspectives for CAT systems are highlighted as well.     

A correlation between deviations in circularity, cylindricity, roughness and size tolerances

It is often necessary to prescribe size and form tolerances when specific workpiece accuracy is demanded. On the basis of published data and investigations carried out by the author a correlation has been developed between deviations in form for circularity and cylindricity, and International Organization for Standardization (ISO) tolerances. The range of application is for nominal sizes up to 10 000 mm and for tolerance grades 4–16. This correlation can help constructors and workshop workers to choose the size of form tolerances for circularity and cylindricity when a certain workpiece accuracy is demanded. The proposed correlation is verified by measurements of the fitting of workpieces for industrial production and the evaluation of measuring data.     

Quantitative circularity tolerance analysis and design for 2D precision assemblies

Circular, cylindrical, or spherical features are fundamental geometric features in engineering. As precision requirement becomes more stringent, it is not sufficient to consider only size tolerance of circular and cylindrical parts. However, currently there is no quantitative and systematic way of assigning circularity and cylindricity tolerances. This paper investigates how to specify circularity tolerance quantitatively for 2D assemblies. Statistical matrices to quantify positioning error of two perfectly circular mating parts subject to size tolerance for both clearance and transition fit conditions are first developed. The analysis is then extended to nonideal profiles whose profile errors are assumed to deviate from a best-fit circle according to a normal distribution. The assumption of the normal distribution is then removed for more general results via computer simulation. For this purpose, an experimentally verified profile model is used to generate realistic profiles as those produced by various machining processes. Numerous pairs of these realistic profiles are then assembled virtually using Monte Carlo simulation to quantify their positioning errors. The simulation results and the analytical results are compared for cross-checking. Finally, systematic design procedures are proposed to assign circularity tolerance by prescribing a fit condition with a desirable process capability. By the nature of circularity tolerance, this paper addresses a 2D assembly. The result of this 2D analysis can be a foundation for more complicated 3D problems, such as assigning cylindricity tolerance.     

基于Matlab的公差稳健设计

本文认为产品寿命周期定义中应增加一个市场开拓阶段，认为产品全寿命周期成本应当包含生产成本、品牌成本和使用成本三大主要部分。利用质量损失回收提出基于成本的公差稳健设计原则，然后应用Matlab工具求解公差设计模型，设计结果具有稳健性和简便性。     

行波管零件挤压成形质量影响因素分析

以电子行业中铣床加工的行波管零件作为研究对象,其加工形状复杂、尺寸小、形位公差要求高、加工难度较大,生产成本较高。针对这些要求和问题,设计了两种冷挤压成形方案,并利用Deform软件对成形过程进行了数值模拟,依据仿真结果采用了有四周约束的凹模,同时分析了上模加载速度、摩擦系数和保压时间对最终产品质量的影响。最终以尺寸相对偏差为评价指标,通过正交实验得到了行波管零件挤压成形最佳工艺参数组合:上模加载速度为60 mm·s^-1、摩擦系数为0.08、保压时间为3 min。并据此参数进行实验验证,得到了成形效果良好的行波管零件。研究结果对类似产品在生产中的工艺改进具有一定的指导意义。     

Integrated Inspection and Machining for Maximum Conformance to Design Tolerances

Designers' intent for the form, fit and function of products is expressed by design tolerances the conformance to which is the main objective of manufacturing processes. A methodology for maximizing the adherence to the specified tolerances using an integrated machining and inspection system is presented. Considering the desired tolerance envelope of the part, an error decomposition technique is developed to model machining errors caused by the systematic and non-systematic errors in the machine tool. The model is used to adaptively plan the final machining cuts, based on inspection feedback, to enhance the geometric accuracy of the final product and is illustrated by an example. This approach reduces scrap and rework and their associated costs.