Industries Group
Dissertation for Master Degree
Autumn 2013
Abstract
The approach of a production system depends on the low downtime of the equipment and the process. Maintenance and repairs and quality control play an essential role in achieving this goal. In addition, with the passage of time, the quality of the equipment decreases and a transition of quality may occur from the state under control to the state out of control, which is characterized by the increase in the return rate of the product and the tendency to failure. This thesis presents an integrated model to integrate optimization of maintenance intervals and preventive maintenance and control parameters. Two types of maintenance and repair policies are considered. Minimal corrective maintenance that repairs the state and conditions of the equipment without affecting their life and preventive maintenance and repairs that puts the equipment between as good as new and as bad as old. The proposed model can determine the optimal value of each of the four decision variables. That is, the sample size (n), sampling interval time (h), control limit coefficient (k), and preventive maintenance intervals (), which minimizes the total cost of the integration case per unit of time. A numerical example is shown to explain the effect of cost parameters in the policy of integrating quality control and preventive maintenance from an economic point of view. The sensitivity of different parameters has also been tested.
Keywords: Preventive maintenance and repairs, process quality policy, statistical quality control, Integrated model, cost minimization
Chapter one
Research overview
Introduction
The problem of scheduling in production has always been one of the important and developable topics for engineers and researchers. A lot of work has been done on this topic so far and many researchers have proposed models to optimize scheduling in production. More specifically, the problem of scheduling in production in single machine systems has been one of the sub-topics in production scheduling. Meanwhile, topics such as preventive maintenance and repairs (PM), and corrective maintenance and repairs (CM) are also included in the subject literature. Issues such as the time to perform maintenance operations and preventive and corrective repairs become the concern of researchers. When is the best time to perform maintenance and repairs on the car.
On the other hand, the issue of quality control of products produced by machines is also considered by quality controllers. Issues such as whether the product produced by the system had the quality we expected and met our expectations and target values. Whether the system is under control or not. If the system is out of control, what was the reason? And how to bring the system back under control and actually find a way to solve the problem that caused our system to go from under control to out of control.
Determining the optimal parameters of the control chart to minimize the costs resulting from the quality control of the produced product and the design of the control chart is another thing that production managers should consider in the discussion of quality control.
The importance of These two issues, i.e. maintenance and repairs and quality control in production, are undeniable, and not considering these two aspects in production will cause many problems that will harm the production work and cause Depreciation of the machine, rising costs, lowering the quality of the produced product, increasing the return rate of the product, customer dissatisfaction and so on. will be.
Statement of the problem
As it was said, the two issues of maintenance and repairs and quality control are of particular importance in the discussion of production, and not paying attention to these two aspects in the work of production can have many negative consequences.
For this purpose, many models have been presented and developed about these two problems.The purpose of these models in the discussion of maintenance and repairs is to obtain a time interval to apply preventive or corrective maintenance and repairs During the process, the costs resulting from these maintenance and repairs, such as the cost of machine idleness, the cost of repair labor, etc. minimize And in the discussion of quality control, determining the parameters of the control chart optimally so as to minimize the costs caused by the control.
But recent studies have shown that these two aspects have significant relationships and dependencies with each other, and because of these relationships and dependencies, it is better to consider these two aspects together. In fact, considering these two aspects independently and separately, considering the relationship between them, it is not a reasonable thing and it does not result in optimal results for us. Many integrated models have been presented by researchers in recent years, and in most of these models, integrating maintenance and repairs, production scheduling, and quality control improves the production process compared to when these three aspects are considered independently. This comparison has been made in most articles about integrated models and it is concluded that integrating and integrating these three aspects is better than when they are considered independently and separately, and the costs are lower in the integrated and integrated state than in the independent and separated state.
In this thesis, an integrated model is presented that considers the two aspects of maintenance and repairs and quality control in one system. done is In this model, all the features of maintenance and repairs and quality control have been written in the form of a model in an integrated manner and it has been solved.
In fact, an integrated model is proposed to integrate optimization of maintenance intervals and preventive maintenance and control parameters. Two types of maintenance and repair policies are considered. Minimal corrective repair that repairs the state and condition of the equipment without affecting their life and preventive maintenance and repairs that puts the equipment between as good as new and as bad as old. The proposed model can determine the optimal value of each of the four decision variables. That is, sample size (n), sampling interval time (h), control limit coefficient (k), and preventive maintenance intervals (), which minimizes the total expected cost of integration per unit time. A numerical example is shown to explain the impact of cost parameters in the policy of combining quality control and preventive maintenance from an economic point of view.
The working system in this thesis is a single-machine system with one component that produces one type of product. produces In fact, the presented model examines the optimal time intervals for preventive maintenance and repairs on this machine, as well as the optimal quality control parameters to check the quality of the produced product, in such a way that the costs of maintenance and repairs and quality control are minimized. The approach of a production system is dependent on the lack of equipment and process downtime. Maintenance and repairs and quality control play an essential role in achieving this goal. In addition, with the passage of time, the quality of the equipment decreases, and a quality transition from the controlled state to the out-of-control state may occur, which is characterized by an increase in the product return rate and the tendency to failure.
Scheduling of maintenance and repairs and quality process is a part of operational policies that is the result of the performance of any production system. Despite the common effects between these decisions, which are not very important, model-based approaches are provided to optimize them in a simulated manner. For example, most production scheduling models do not consider the impact of machine availability due to breakdowns or maintenance activities. Similarly, maintenance and repair planning models rarely consider the effect of maintenance and repairs on customer delivery time and requirements.