OPERATIONAL PROBLEMS IN FLEXIBLE MANUFACTURING SYSTEMS: A REVIEW

Gaganpreet KaurDepartment of Mechanical Engineering, ABES Engineering College, Ghaziabad, India

Abstract - A flexible manufacturing system (FMS) is a manufacturing system in which there is certain flexibility that enables the system to adapt the changes and process the specified task, the changes may be preplanned or sudden. In this review paper there is implementation of FMS as Digital factory method for efficient and FMS in the aerospace industry, the necessary number, utilization and sequence of workstations, production quantity of different parts, processing sequence and times are calculated by implementation of the design of an FMS.Further, Scheduling and Control of Flexible Manufacturing Systems is done. Flexible manufacturing systems (FMS) are different from traditional manufacturing systems as FMS's use computers for controlling and handling of parts in an automation system. FMS's have a great potential as well as they are very competitive, due to this fact it worth research in FMS. Then an automation upgrade of the cell is proposed, involving the introduction of an industrial robot for part handling, loading and unloading, and a new automatic surface inspection system (ASIS) for the final part inspection.

INTRODUCTIONDue to their numerous advantages such as low stock quantity, high productivity, high product quality, low production lead time, fast response to customer demand, low labor cost, etc., flexible manufacturing systems are favored in more and more establishments with each passing day. There is an arrangement of different machines in a flexible manufacturing system (FMS) which are linked to each other with the aid of a certain transport system. The parts are loaded and handled in various ways. All the handling, loading/unloading, transporting is correct, speedy and automatic. There is a main computer which controls both machines and transport system. The fundamental components of FMS are:

1. Workstations

2. Automated Material Handling and Storage system.

3. Computer Control System

Bottleneck model is a simple and intuitive deterministic approach that can describe the FMS performance mathematically. The purpose of the analysis is to determine necessary number of servers at each workstation to fulfill production rates by calculating the work loads of all stations.

In Scheduling and Control of FMS, fixed automation generally used in transfer lines which is eliminated by computer control system which distinguishes FMS from other.

LITERATURE REVIEWSome surveys of the literature reviews have also been conducted . However, in these literature reviews focus is on the specific approaches, for example: scheduling problems. In this review

paper, reviews are made on articles which have a broader methodological approach while considering the issues related to various operations.

FMS can have economic production of a wider diversity of parts likened to others in low volumes. FMS's has various advantages such as rapid turn around, supreme quality, gentle inventory costs, normal labor costs, etc. because of which it is extensively recognized in the manufacturing area and its various fields.

There are numerous research complications which were raised by industrial fraternity and hence they can broadly be classified into two problem area which are:

1.Design problems and;

2. Operational problems.

This paper gives an summary of the published literature on the operation problems of FMS.

We review this paper form various points and then impression of procedure used in resolving the issue is discussed.

Based on the methodology that were generally followed, FMS operations literature can be divided into these three approaches:

1. Control theoretic approach

2. Simulation based approach

3. Artificial intelligence (AI) based approach

1. Control theoretic approach Akella (1984) pronounce and overview the presentation and dealing of a simulated model of an real facility and this is often done using this policy which is hierarchical. When the parts are to be manufactured to succeed in the worth of a particular demand which may vary with time a FMS is taken into account . The simulation results that were calculated of Akella et al. shows that a better output and low add progress are often produced by using the methodology of hierarchical scheduling. it had been observed that it can track the requirements of the system to a way closer extent while handling disturbances thanks to failure of the machine. It also can be observed that, as are often seen, for production of a specific part mix the closed-loop system control policy is employed to tailored. Also the buffer capacity and therefore the few other constraints aren't taken into consideration while tooling of the FMS. For determining the part flow, the control scheme is employed for locating solutions of an optimization model.

2. Simulation based approach Normally, for the evaluation of dispatching rules simulation is employed as a tool. In 1989, concurrent simulation is proposed for completing the scheduling of production. therein scheme, a modern state of the FMS was obtained as multiple simulators of a production

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two hours, whereas the EDM machine is stopped for five min to change the worn electrodes after 6 produced units. To demonstrate the assembly capacity of the manufacturing cell. a hard and fast cycle time were used for the manual operations .The simulation process was managed with a step size of 4.26 hrs. for a time limit of 1 year, and required 40 seconds to be accomplish. The simulation process of the physical cells indicate that it's unable to supply required annual volume. Appreciations to extensive period of loading/unloading and high setup times required when two subsequent different part numbers are being processed on an identical machine.

The processing time of the manufacturing cell is 6224.30 hours throughout, corresponding to 260 corresponding days. The result of the simulation specifies that grinding machine was holding up of the system even though the volume is not saturated, as it is working at 78.5 % of the total throughput time. This is due to the fact that there is high percentage of time which corresponds to block state. In which a resource is waiting for the operator for the loading & unloading of the components of the cell. Thus, the manufacturing system need to be arranged differently to meet the expected volumes. The flexibility of the manufacturing cell was improved with the introduction of the handling robots which works in a different manner and they also help in achieving the expected volume. Thanks to the higher payload capacity of the robots as compared to human labors.

CONCLUSION

The main pros of a flexible manufacturing system in dealing manufacturing resources like time and contribution in order to produce a new product, are its high flexibility. There are so many applications of FMS but the finest application is found in manufacture of small groups of products largely from mass production. From the review paper we come to the conclusion that the performance or efficiency of manufacturing system increases by using FMS. More specifically, efficiency of system was increased by idle times of workstations. Also MLT, labour costs, product costs decreased. The system utilization was 95.3% after using FMS which is 35% growth from its actual (previous) conditions.

In future we've to figure in investigating the various methodologies use in practical arena, which will help to form the control systems more friendly for the user, and also in developing the system more compact. The issues of FMS control are so difficult and time taking. Aside from struggling to get the simplest answers to problem formulations, research might be done on FMS control and collaborating scheduling where there's input within the circle by human. For various researchers flexible manufacturing system is sort of different thing. The substitute processes aspect is merely emphasized. It's the time to figure forward to additional development of the control structures which are compact and which can consider the complicated interaction of various resources in Flexible Manufacturing System: robots, fixtures, tools, pallets, CNC machines. So with the assistance of hierarchical or heterarchical schemes this might be done. There are few papers which are published employing a approach of simulation, but normally they're did not provide the solid modelling of FMS.The approach which use the Digital factory increasing the flexibility and efficiency of fabricating cell of aerospace industry. This approach of Digital factory is figure on the utilization of methods which are digital and include tools like simulation, computer game and 3-dimension modelling to work out the manufacturing system

firm were initialized. But after some period of your time these simulators stopped. then for the simplest way for using them, these simulators were analyzed as a terminating simulations. as compared to the mathematical formulation of the operational problems of FMS simulation are often considered as more conformable. With the utilization of simulation, there's no need of using any needless assumptions as there's not any concern for feasibility. Also these simulation models are often as real together needs it to be.

3. Artificial intelligence based approach

For solving problems associated with FMS AI (AI) is widely used because it suits the conditions. Also FMS was developed for solving problems which involves an outsized search space and with the assistance of human expertise we will find fast solutions of the given problems. Hall (1984) proposed use of FMS for the method determination, the sequencing of knowledge and for scheduling. But did not describe the system or results obtained. Sauce and Collinot also described a system which was object oriented for the representation of FMS which create daily off line timetables using numerous constraints and therefore the factors of flexibility.

The approach of the digital factory is essentially to use digital methods & tools for the stimulation,3D modeling and computer game so as to examine the complex manufacturing system and to extend the efficiency. The Purpose of the project is to skin a extensive area for the fiscal robots within the field of planned importance and for the event of the industry. The target is to develop an environment having high level of automation of smart robot cells which are capable to process products categorized by different shape dimension and material. The aerospace industries widely use the economic robots for handling the department of loading/unloading of the machine components and therefore the surface of the finished part by using Automatic Surface Inspection System (ASIS). There was a case study done on three different part which are the three turbine vanes of an engine. Machines which were utilized in the cell were

1 Makino G7 grinding machine

1 Zeiss Duramax CMM

1 Machine Cleaning

2 Agie Form 300 EDM machines.

Firstly, the aim was to examine the efficiency of the manufacturing cells in order that the results are often compared after the inspection. Discrete Event Simulation (DES) may be a tool which helps to review different conditions for variable changes within the Manufacturing machine system and analysis is completed.

A DES model was initially setup with the expectations having the subsequent production times: 17 shifts per week, 7.5 hours per shift, 48 weeks per annum . A worker was appointed to the manufacturing cell: to take care of mounting and dismounting, loading/unloading parts on the machines with the assistance of tools, to hold out setup processes, and to perform operations for the upkeep and inspection of the ultimate parts. During the time of loading and unloading, as during the setup of the new parts, the manufacturing cells were given the trades which have experience in handling these sort of large component and therefore this kind of equipment available within the plant. There are maintenance operations which are administered regularly on the grinding machine and therefore the EDM machines were used for the simulation model. After processing of the 48 parts, the grinding machine is at a standstill for

Operational Problems In Flexible Manufacturing Systems: A Review

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Vision & Quest, Vol. 7, No. 2, July-Dec. 2017ISSN: 0975-8410

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