Effect of Testing Normality on Estimating Process Capability Indices

Process capability indices are used to measure whether a manufacturing process meets the specifications. The studies of these indices are usually based on the assumption that the process follows a normal distribution. These include the indices C_p, C_pk, C_pm, and C_pmk. When the investigator is uncertain whether the process follows a normal distribution, a test of normality may be used to resolve the uncertainty. If the test accepts the null hypothesis that the process follows a normal distribution, the investigator uses C_p, C_pk, C_pm, or C_pmk. If the test rejects the null hypothesis, the investigator uses indices under non-normal distributions. Therefore the test of normality is a preliminary test that determines the form of the distribution and the index to use. In this paper we study the effect of the preliminary test of normality on the estimation of the four process capability indices mentioned above.     

简化的测量过程统计控制方法

休哈特控制图平均值控制界限的设置对于计量标准或测量设备来说有很大的局限性,根据计量标准或测量设备的特点,提出简化的测量过程统计控制方法,该方法省去了标准偏差或极差控制图。根据标准偏差试验结果的大小,提出了子组最少测量次数的确定方法,平均值控制界限以各组平均值算得的标准偏差来设置,平均值控制图异常的判断准则简化为3种判据,进而大大减少了实施统计控制的工作量,便于推广应用。     

On the Efficiency of Runs Rules Schemes for Process Monitoring

There are two main types of variations, namely, common and special causes leading to in‐control and out‐of‐control states, respectively. Control charts are popular tools used to differentiate between these two states of a process. Implementation of runs rules schemes with control charts is an attractive approach for process monitoring. This study is designed to describe the methodology of runs rules schemes and discuss their implementation for different types of control charts. We have considered memory‐less charts, namely, , S, and R charts for our study purposes. It is examined that the efficiency gain depends on the number of decision points utilized to implement a given rule. Moreover, superiority of runs rules schemes may vary for different types of location and dispersion charts. An application example using a dataset is also included in the study for practical considerations. Copyright © 2015 John Wiley & Sons, Ltd.     

基于成本控制的小批量生产工序能力指数研究

传统的工序能力指数分析方法仅仅从统计质量管理的角度对过程能力进行分析,而忽略了所加工产品的不同批量、不同价值、不同加工工序成本的影响。对国内外多品种、小批量的工序能力指数研究现状进行了回顾,在对工序能力指数的点估计及置信区间进行分析的基础上,提出了基于成本控制的多品种、小批量生产方式下确定工序能力指数的方法,从而达到降低生产加工过程成本的目的。     

AR(1)型自相关过程的过程能力分析方法研究

传统上进行过程能力分析是基于过程观测数据统计独立这一基本假设,而实际工作中,过程数据并不是总能满足彼此统计独立的假设前提.介绍了过程观测值符合AR(1)型自相关模型时,计算过程能力指数的方法.用一个具体案例进行分析,结果表明:数据间存在正相关时,传统方法高估了过程能力指数,而利用笔者介绍的方法可以得到正确的结论.     

Tolerance design for the fit between bore and shaft for precision assemblies with significant error-scaling problems

An inspection procedure may be necessary when a process does not have the capability to produce parts that meet specifications. After inspection, the accepted parts then have a probability density function which is truncated. In a previous paper, the authors presented a method for the computation of tolerances for the fit between a bore and a shaft, based on the construction of a probabilistic model of the fit, using truncated probability density functions for the bore and shaft. In this paper, a method of design is presented for the computation of tolerances for the bore and shaft that are necessary to satisfy the tolerance of the fit and at the same time minimize the probability of rejection for the processes that produce the bore and shaft. Application is made to the situation where the variations in the dimensions of the parts may be large compared with their nominal dimension or the fit requirement of the assembly. Such a situation will be denoted as the error-scaling problem.     

Process True Capability Evaluation with the Consideration of Measurement System Variability and Expected Quality Loss

Process capability indices are widely computed under the assumption that the measurement system is free from errors. However, measurement variability is unavoidable and has a significant impact in process capability evaluation. From an economic point of view, Taguchi loss function is an effective tool to measure the quality loss of a product characteristic deviated from target value that is extensively used without taking into account the effect of the measurement system. This paper investigates the influence of measurement system variability on the process capability analysis through the calculation of process capability indices. A new quality loss function, integrating the measurement system errors, is developed to compute the optimal true process capability regarding to the expected mean value of the Taguchi loss function and the loss resulting from the control of the true process capability. Copyright © 2016 John Wiley & Sons, Ltd.     

Comparisons of Some Exponentially Weighted Moving Average Control Charts for Monitoring the Process Mean and Variance

An exponentially weighted moving average (EWMA) control chart for monitoring the process mean μ may be slow to detect large shifts in μ when the EWMA tuning parameter λ is small. An additional problem, sometimes called the inertia problem, is that the EWMA statistic may be in a disadvantageous position on the wrong side of the target when a shift in μ occurs, which may significantly delay detection of a shift in μ. Options for improving the performance of the EWMA chart include using the EWMA chart in combination with a Shewhart chart or in combination with an EWMA chart based on squared deviations from target. The EWMA chart based on squared deviations from target is designed to detect increases in the process standard deviation σ, but it is also very effective for detecting large shifts inμ. Capizzi and Masarotto recently proposed the option of an adaptive EWMA control chart in which λ is a function of the data. With the adaptive feature, the EWMA chart behaves like a standard EWMA chart when the current observation is close to the previous EWMA statistic, and like a Shewhart chart otherwise. Here we extend the use of the adaptive feature to EWMA charts based on squared deviations from target, and also consider an alternate way of defining the adaptive feature. We discuss performance measures that we believe are appropriate for assessing the effects of inertia, and compare the performance of various charts and combinations of charts. Standard practice is to simultaneously monitor both μ and σ, so we consider control chart performance when the objective is to detect small or large changes in μ or increases in σ. We find that combinations of EWMA control charts that include a chart based on squared deviations from target give good overall performance whether or not these charts have the adaptive feature.     

Optimization of Grinding Process Through Design of Experiment (DOE)—A Comparative Study

Grinding is one of the most important processes for producing discrete components with high precision, and it accounts for about 20% to 30% of the total expenditure on machining operations in industrialized nations. So, it becomes imperative that the grinding process with its parameters must be understood properly to have good control over the quality, productivity, and cost aspects of the process. Many experimental investigations reveal that depth of cut, wheel speed, and work speed are the major influential parameters that affect the quality of the ground part. Determination of optimum parameters lies in the proper selection and introduction of suitable design of experiments (DOEs) at the earliest stage of the process and product development cycles. This paper compares and contrasts factorial design with Taguchi's design of experiments used in the determination of optimum grinding conditions. Optimum grinding conditions and grinding cycle time were estimated for each DOE and results were compared and analyzed. ANOVA analysis was carried out for the interpretation and for obtaining insight into the process as a whole.     

Neuro-Knowledge-Based Expert System (NKBES) for Optimal Scheming of Die Casting Process

We develop a neuro-knowledge-based expert system (NKBES) frame in this work. The system mainly concerns with decision of gating system and die casting machine based on a neuro-inference engine launched under the MATLAB software environment. For enhancement of reasoning agility, an error back-propagation neural network was applied. A rapidly convergent adaptive learning rate (ALR) and a momentum-based error back-propagation algorithm was used to conduct neuro-reasoning. The working effect of the system was compared to a conventional expert system that is based on a two-way (forward and backward) chaining inference mechanism. As the reference, the present paper provided the neural networks sum-squared error (S5E) and ALR vs iterative epoch curves of process planning case mentioned above. The study suggests that the neuro-modeling optimization application to die casting process design has good feasibility, and based on that a novel and effective intelligent expert system can be launched at low cost.     

Double Punch Test to control the energy dissipation in tension of FRC (Barcelona test)

Current testing methods used to measure tensile properties of Fiber Reinforced Concrete (FRC) are mainly based on bending test of beam specimens. They normally show a considerable scatter that makes difficult the quality control, as in particular when such properties are intended to estimate the strength of structural members. In order to improve the material assessment procedure, the Double Punch Test (DPT) has been recovered for the quality control of the tension behaviour of FRC. Former experimental research showed the feasibility of the test and a reduction of the scatter in the values of the tensile strength and of the toughness. This paper describes the results of an experimental program carried out using both DPT and bending test on FRC with different type of fibers, concretes and fiber contents. In addition, a correlation between both tests is proposed. Its application to steel and polyolefin FRC specimens shows very good results.     

光学设计软件（ADTF4）的设计

本文针对已实用化的光学设计软件系统ADTF4，阐述在设计中对几个主要技术问题的分析与处理，如：基于切比雪夫数值积分的质量函数、新型自变量的变化尺度，质量函数相关的识别与查处、线性检查与步长控制以及边界约束等。     

Development of Run-To-Run (R2R) controller for the multiple-input multiple-output (MIMO) system using fuzzy control theories

Run-to-Run (R2R) control has been extensively applied in semiconductor manufacturing. In particular, del Castillo, E. and Rajagopal, R., A multivariate double EWMA process adjustment scheme for drifting processes. IIE Trans., 2002, 34, 1055–1068, investigated double multivariate exponentially weighted moving average (MEWMA) controller for the multiple-input multiple-output (MIMO) system in an attempt to adjust and maintain the linear dynamic process outputs on target. Multivariate fuzzy control, inherently different from conventional MEWMA-based control, is another promising alternative that consists of fuzzy logic and set concept. Providing the fuzzy control can structure an appropriate membership function for the R2R MIMO system, thus it can be shown a practically useful control tool in comparison to MEWMA control. In this paper, fuzzy logic is utilized to design the multivariate fuzzy controller for the type of R2R applications based primarily on the min-max-gravity method advocated by Gupta, M.M., Kiszka, J.B. and Trojan, G.M., Multivariable structure of fuzzy control systems. IEEE Trans. Sys., Man Cybern., 1986, 16, 638–656. Under a variety of disturbance models, the proposed multivariate fuzzy controller can produce quite competitive control performance when compared to MEWMA control.     

CaO-MgO-Al_2O_3-SiO_2-P_2O_5-F系微晶玻璃初晶相Ca_5(PO_4)_3F析晶过程的研究

本文应用透射电镜:选区电子衍射和微区成份分析并结合扫描电镜形貌观察,深入研究了 CaO-MgO-Al_2O_3-SiO_2-P_2O_5-F 系可切削生物微晶玻璃初晶相 Ca_5(PO_4)_3F 的析晶机理。研究表明,玻璃首先发生二液分离,形成了能够析出初晶相 Ca_5(PO_4)_3F 晶体的富 P~(5+)、Ca~(2+)、Mg~(2+)、Ti~(4+)的液滴相。在进一步的热处理中,液滴相发生整体核化,并逐步形成由大量细小晶粒镶嵌生长构成的球形 Ca_5(PO_4)_3F 聚集体。随着热处理温度的提高,这些球形 Ca_5(PO_4)_3F 聚集体逐渐转变为广泛分布于微晶玻璃另一主晶相氟金云母中的六方短柱状 Ca_5(PO_4)_3F 微小晶体。