Journal of Quality Engineering and Management

Abstract Any statistical method designed to detect process changes over time is within the scope of statistical process control. Among the most widely used tools for statistical process control, the control chart is the most important and powerful tool for statistical process control. Here it is important to understand that statistical process control charts are not complete in relation to process control in two respects. They do not have non-random causes and their elimination. In this paper, we introduce robust control diagrams for time-series data to detect reasoned deviations. We collect daily diagrams and draw solid control charts and standard control charts for time series data. Statistical analysis of this design was performed using SPSS16 software and finally by comparing Solid control diagram With standard control diagram for time series data, we conclude that the stable control diagram has a better performance than the standard control diagram. 

Abstract In usual quality control methods, the quality of a process or product is evaluated by monitoring one or more quality characteristics using the corresponding distribution of one or more variables. Recently, in many cases, quality is defined through the relationship called profile between one or more response and independent variables as a supplanting way. In order to monitor linear profiles in this study, the EWMAR control chart and its normal distribution are used to detect various changes in the intercept, slope and standard deviation. To improve the performance of the chart, run rules are used here. Then, in order to validate the proposed control chart, its performance is examined based on the average length of the sequence (ARL) criteria in the out-of-control for increasing changes, decreasing changes and simultaneous changes in intercept and slope and standard deviation. The results show that the proposed method has a much better performance in incremental and decreasing shifts than other charts. Also, the proposed scheme performs better than other run rules. 
 
 

Abstract In this paper, a novel multi objective mathematical programing model is developed which focuses on enhancement of quality of design via optimizing the layout of components in multicomponent systems. The objectives include maximization of accessibility to components, optimization of distance between members based on their positive/negative interaction, maximal maintenance space inclusion around components and minimization of total volume of the system. The structure of the variables and constraints of the model is novel and assorts the formulation of the objectives. As a case study, the model is used to optimize the layout of components of a laser range finder. First, the model is converted to a single objective one via the weighting method and by using the eigenvalue approach. Then, the obtained model is solved via Lingo. Results demonstrate that the solution is close to the ideal solution by 82.7%. Moreover, accessibility (the most important objective) and maintenance distance requirement correspond 100% to their ideal value. 

Abstract  This article examines the receipt of ISO 9001 certification on the return on assets in the life cycle of listed companies and compares it with counterparts without quality control. To measure the value of the company, the criteria of return on assets and MTB ratio were used. The statistical population of the study is the production companies listed on the stock exchange during the research period from 2012 to 2018. For the analysis of multivariate regression equations, the panel data method was tested with a fixed and random effects approach. The results of this study showed that obtaining ISO has been able to have a significant effect on the value of the company during the growth period. However, no significant relationship has been observed on the value of the company during the maturity period. It can be inferred that companies that are in the growth stage can significantly increase the value of their company by using the ISO 9001 quality management certification. 
 
 

Abstract  The present paper focuses on the utilization of simulation approach for modelling the problem in the presence of different factors of uncertainty, as well as response surface methodology on the simulation results in sequencing problem of a 3-machine robotic manufacturing cell under S6 cycle, where produces multiple parts. The process supports by a single gripper robot to load/unload products and also displacement within the system. This study considers machine’s failure and repair such that machine’s probability density function of failure and repair time in this robotic cell follows exponential distribution. Minimizing both S6 cycle time and operational cost and maximizing throughput in this cell are the optimization’s main objectives. The simulation results of numerical examples indicate that this approach improves significantly the time of obtaining the optimal solution in comparison with the previous mathematical modelling.   

Abstract This research provides a solution for modeling the availability of Feed Water System (FWS) of Heat Recovery Steam Generator (HRSG) in MAPNA Boiler and Equipment Engineering and Manufacturing Company with the aim of determining the system equipment suppliers in such a way that the total cost in the construction and operation of the system is minimized. The Feed Water System is one of the most sensitive parts of boilers; because its failure causes the boiler to stop and incurs irreparable costs to the system. The system may be in three capacities: full capacity, half load, and stop, each of which may impose costs on the system. For modeling, possible states are first written for the system and then the system configuration is plotted using the reliability block diagram and P&ID. Then the results of modeling with Markov chain method are placed in a mathematical optimization model. After solving the model, the optimal strategy in selecting equipment suppliers will be determined.