In most modern manufacturing systems, products are often the output of some multistage processes. In these processes, the stages are dependent on each other, where the output quality of each stage depends also on the output quality of the previous stages. This PROPERTY is called the CASCADE PROPERTY. Although there are many studies in multistage process monitoring, there are fewer works on profile monitoring in multistage processes, especially on the variability monitoring of a multistage profile in Phase-I for which no research is found in the literature. In this paper, a new methodology is proposed to monitor the standard deviation involved in a simple linear profile designed in Phase I to monitor multistage processes with the CASCADE PROPERTY. To this aim, an autoregressive correlation model between the stages is considered first.Then, the effect of the CASCADE PROPERTY on the performances of three types ofT2 control charts in Phase I with shifts in standard deviation is investigated. As we show that this effect is significant, aU statistic is next used to remove the CASCADE effect, based on which the investigated control charts are modified. Simulation studies reveal good performances of the modified control charts.

A simple semi-phenomenological model, which accurately predicts the dependence of threshold current for temperature of Resonant-phonon three well quantum CASCADE laser based on vertical transitions is offered. We found that, the longitude optical phonon scattering of thermally excited electrons is the most important limiting factor for thermal performance of high frequency THz QCLs. In low frequency region, parasitic current increases the threshold current. Based on our model the use of materials with higher longitude optical phonon energy such as InGaAs/GaAsSb and decreasing the lower laser level lifetime can increase the maximum performance temperature. Our observations may can be used to understand the notion of the effects of thermal electrons on reduction of laser performance.

The unstable flow with rotating-stall-like (RS) effects in a rotor-CASCADE of an axial compressor was numerically investigated. The RS was captured with the reduction in mass flow rate and increasing of exit static pressure with respect to design operating condition of the single rotor. The oscillatory velocity traces during the stall propagation showed that the RS vortices repeat periodically, and the mass flow rate was highly affected by the blockage areas made by stall vortices. The results also showed that large scale vortices highly affects on the generation and growth of the new vortices. An unsteady two-dimensional finite-volume solver was employed for the numerical study which was developed based on Van Leer’s flux splitting algorithm in conjunction with TVD limiters and the κ-ε turbulence model was also employed. The good agreement of the computed mass flow rate with the experimental results validates the numerical study.

The manufacturing operations often involve multistage processes where the process capability of each stage is affected by the process capability of its precedent processes. This PROPERTY is known as the CASCADE PROPERTY. The purpose of this paper is to estimate the process capability of the second stage of two-stage process while the CASCADE PROPERTY impact is removed using residuals analysis. To this end, a method is proposed to determine the specification limits of the residuals based on the specification limits of the quality characteristics in the first and second stages. The Cp, Cpk and Spk indices are used to calculate the capability of the second stage in the two-stage process. The results of simulation study show the satisfactory performance of the proposed method in estimating the pure process capability of the second stage.

If the quality of a process is described using a linear functional relationship betweenthe response variable and independent variables, such a relationship is called the profile. Today, with the development of manufacturing technologies, multistage processes have found a special position in manufacturing companies and industriesIn the present paper, we consider a multistage process with AR(1) auto-correlatedsimple linear profile in each stage and address the effect of both auto-correlationand CASCADE PROPERTY on the efficiency of common monitoring procedures. Toeliminate the effect of auto-correlation, we used a transformation method as a remedial measure at first. Then, an approach based on the U statistic is applied toeliminate the CASCADE effect. Next, a modified T 2 control chart is proposed to monitor the process in the second stage. The performance of the proposed controchart is evaluated in terms of the average run length criterion. The simulationstudies show that the proposed control chart perform satisfactorily.