FLEXIBLE MANUFACTURING SYSTEM LAYOUT AND SCHEDULING, Lecture notes of Computer Integrated Manufacturing

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Chapter- 3

FLEXIBLE

MANUFACTURING

SYSTEM LAYOUT AND

SCHEDULING

FLEXIBLE MANUFACTURING SYSTEM LAYOUT AND

 - CHAPTER - 

• 3.1 Introduction SCHEDULING
• 3.2 Introduction to Flexible Manufacturing System
  • 3.2.1 Types of FMS
  • 3.2.2 Elements of Flexible Manufacturing System
    • System 3.2.3 Hard ware components of Flexible Manufacturing
• 3.3 Layout Configurations of Flexible Manufacturing System
  • 3.3.1 Line layout
  • 3.3.2 Loop layout
  • 3.3.3 Ladder type layout
  • 3.3.4 Carousel layout
  • 3.3.5 Robot centered cell
  • 3.3.6 The open field layout
• 3.4 Scheduling of Flexible Manufacturing System
  • 3.4.1 Introduction to FMS scheduling
  • 3.4.2 Functions of scheduling
  • 3.4.3 Objectives of scheduling
  • 3.4.4 Elements of scheduling
  • 3.4.5. Principles of scheduling
• 3.5 Scheduling priority rules
• 3.6 Benefits of FMS

3.2 INTRODUCTION TO FLEXIBLE MANUFACTURING SYSTEM

“Manufacturing Industries are facing vigorous threats by inflation in market needs, corporate lifestyle and globalization. Hence, in current situation, Industries which are responding rapidly to market fluctuations with more competitiveness will have great capabilities in producing products with high quality and low cost. In the view of manufacturers, production cost is not at all a significant factor which affects them. But, some of the factors which are important to the manufacturer are flexibility, quality, efficient delivery and customer satisfaction.” “Hence, with the help of automation, robotics and other innovative concepts such as just-in-time (JIT), Production planning and control (PPC), enterprise resource planning (ERP) etc., manufacturers are very keen to attain these factors.” “Flexible manufacturing is a theory which permits production systems to perform under high modified production needs. The problems such as minimum inventories and market-response time to bump into customer needs, response to adjust as per the deviations in the market. In order to sweep market by reducing the cost of products and services will be mandatory to various companies to shift over to flexible manufacturing systems. FMSs as a possible way to overcome the said issues while making reliable and good quality and cost effective yields. Flexible manufacturing system has advanced as a tool to bridge the gap

between high mechanized line and CNC Machines with efficient mid- volume production of a various part mix with low setup time, low work- in-process, low inventory, short manufacturing lead time, high machine utilization and high quality [ 74 ]. FMS is especially attractive for medium and low-capacity industries such as automotive, aeronautical, steel and electronics.” “”Flexible manufacturing system incorporates the following concepts and skills in an automated production system [ 75 ].

1. Flexible automation
2. Group technology
3. Computer numerical control machine tools
4. Automated material handling between machines” 3.2.1 TYPES OF FMS “Flexible manufacturing systems can be separated into various types subject to their natures:” 1. DEPENDING UPON KINDS OF OPERATION “Flexible manufacturing system can be illustrious subject to the kinds of operation performed:” a. “Processing operation. It performs some activities on a given job. Such activities convert the job from one shape to another continuous up to the final product. It enhances significance by

handling system and automatically by a distributed computer system. It also includes non-processing work stations that support production but do not directly participate in it e.g., part / pallet washing stations, co-ordinate measuring machines. These features significantly differentiate it from Flexible manufacturing cell (FMC).” N um be r^ of m ac hi ne s^ (M ) Annual Production(Z), Flexibility (F), cost incurred(C) Flexible manufacturing System Flexible manufacturing cell Single machine cell Fig. 3.1: Comparison for three categories of FMS In this research, authors focused on Flexible manufacturing system

3. BASED ON LEVEL OF FLEXIBILITY “FMS is further classified based on the level of flexibility related to the manufacturing system. Two categories are depicted here:” a. Dedicated FMS. “ It is made to produce a certain variety of part styles. The product design is considered fixed. So, the system can be designed with a certain amount of process specialization to make the operation more efficient.”

b. Random order FMS. “ It is able to handle the substantial variations in part configurations. To accommodate these variations, a random order FMS must be more flexible than the dedicated FMS. A random order FMS is capable of processing parts that have a higher degree of complexity. Thus, to deal with these kinds of complexity, sophisticated computer control system is used for this FMS type .” In this research, authors consider Random order FMS Fl ex ib ilit y( F )^ , p ar t^ va ri et y^ (p ) Production rate(Z), annual volume(V) Random order of FMS Dedicated FMS Fig. 3.2: differences between dedicated and random-order FMS types 3.2.2 ELEMENTS OF FLEXIBLE MANUFACTURING SYSTEM “A flexible manufacturing system consists of two subsystems:”  Physical subsystem  Control subsystem Physical subsystem includes the following elements:

3.3 LAYOUT CONFIGURATIONS OF FLEXIBLE MANUFACTURING

SYSTEM

“Flexible manufacturing system brings rewards in actual manufacture of products as the process is designed for several products to be run on different machines within a manufacturing facility which allows for greater growth and stability with more diversity in the output. A Flexible manufacturing system is designed to provide an effective operation sequence to fulfill the production requirements and reasonably allocate the resources [ 19 ]. The objectives of the system are to shorten the throughput time and reduce the resource requirements which include avoiding deadlock in material flow, decreasing in- process inventory , balancing the workload of all machines and make good use of the bottleneck devices [ 77 ].” 3.3.1 Line layout “An Automated guided vehicle is most efficient when the movement is in straight-lines along the AGV path in a single-row machine layout. Machines are arranged only on one side of AGV path [ 78 ], and in double row machine layout, machines are arranged on both sides. A possible arrangement of this layout is shown in fig-3.3 [ 79 ].”

LOAD STATION SLO T- SLO T- SLO T- SL OT

- SLO T- SLO T- SLO T- SL OT - SLO T- UNLOAD STATION CONVEYOR Fig. 3.3: Line layout 3.3.2 Loop layout “The loop layout uses conveyor systems that allow unidirectional flow of parts around the loop. A secondary material handling system is provided at a workstation which permits the flow of parts without any obstruction. A possible arrangement of this layout is shown in fig-3. [ 80 ].” S^1 S^9 S^7 S^3 S^5 JOB LOA^ UNDING LOADING S^2 S^8 S^4 S^6 starting of work part completed work part Fig. 3.4: Loop layout

3.3.5 Robot centered cell “If a handling robot is used in a Flexible manufacturing system cell , the machines are laid out in a circle, such a layout is called circular layout. A possible arrangement of this layout is shown in fig-3.7[ 1 ].” Fig. 3.7: Robot centered cell 3.3.6 The open field layout “The open field layout is also an adoption of the loop configuration. The open field layout consists of loops and ladders organized to achieve the desired processing requirements. This is used for the processing of a large family of parts. The number of different machines may be limited,

and the parts are routed to different workstations depending on availability of machines. A possible arrangement of this layout is shown in fig-3.8[ 11 ].” Fig. 3.8: Open Field Layout 3.4 SCHEDULING OF FLEXIBLE MANUFACTURING SYSTEM 3.4.1 Introduction to FMS scheduling “Scheduling is a method of totaling start and finish time data to the job sequencing dictated in the sequencing process. Sequencing process in turn, is defined as getting the order in which jobs are processed on a machine. The sequence thus obtained determines the schedule, since authors assume each job is started on the machine as soon as the job has finished all predecessor operations and the machine has completed all earlier jobs in the sequences. This is referred to as a

performance criteria minimizing the make span or the mean order lateness and tardiness are usually considered.” “Under both types of scheduling problems, three different scheduling and control decisions are taken while managing day-to-day operations. i. When to load a part into FMS? ii. Which type of part to be loaded into FMS? iii. Dispatching of part.” “For the first decision, factors such as system congestion and part fixture availability are considered. The second decision concerns choosing the type of part to enter the FMS at the loading station when it is time for a new part to enter the system, considering such factors as part characteristics and machine workload conditions. The dispatching decision is depend on routing parts through the FMS at the time of actual production, and also sequencing parts at the individual machines in an FMS.” 3.4.2 Functions of scheduling To design an effective production scheduling system, the following functions must be carried out in most systematic and efficient manner [ 2 ].

1. Assigning different jobs to different facilities after considering the feasibility of allocation (loading).

2. Establishing a set of rules of priorities to sequence the activities on the facilities.(sequencing)
3. Dispatching job orders as per the schedule to initiate loading of jobs to facilities. Reviewing the status of jobs i.e., monitoring the achievement and the scheduling or changing the priorities of the jobs to rectify the deviation. 3.4.3 Objectives of scheduling “The objectives of FMS scheduling [ 84 ].
4. Achieving high efficiency of the operations by optimally utilizing machines and equipment.
5. Maintaining low inventories in process and raw materials.
6. Maintaining short flow time of products. The objectives often become conflicting to each other and as such the scheduling process involves a trade – off conflicting objectives such that proper balance is obtained.”” 3.4.4 Elements of scheduling “Scheduling determines the timings and order of the operations to optimize the use of resources to meet production requirements. The following are the elements of scheduling [ 85 ]. a. Job arrival patterns b. Number and variety of machines /operations

3.5 Scheduling priority rules “A sample set of priority rules are presented below” In this work, there are six kinds of rules for operation selecting from the given allowed set. (1) Short Processing Time (SPT) ,  Process the operation with minimum processing time. (2) Most Work Remaining (MWR) ,  Process the operation among the tasks with the maximum total processing time. (3) Random Selecting Rule ,  Select an operation from the giving allowed set with a random way. (4) Long Processing Time (LPT) ,  Process the operation with maximal processing time. (5) Most Operation Remaining (MOR) ,  Process the operation among the tasks with most remaining operation. (6) Earliest due date Rule(EDD)rule ,  The earliest due date rule minimises the maximum job lateness, or job tardiness, but unfortunately it tends to need more tasks and increased the mean tardiness The author made an attempt on a few priority rules such as Most Work Remaining (MWR), Short Processing Time

(SPT), Random Selecting Rule in this task of scheduling for optimum arrangement of machines in FMS layout 3 .6 Benefits of FMS Flexible manufacturing system benefits are listed as follows:  Reduction of inventories throughout the complete chain of manufacturing including work-in-progress  Reduction of lead time by 40%  Improved machine utilization by 30%  Reduction of labour times by 30%  Reduction of direct and indirect labour costs  Increased management control over the entire manufacturing process  Substantially reduced scrap levels.  The ability to adapt quickly to new work pieces. Summary SN SS“As the work reported on flexible manufacturing system layout optimization, using scheduling as a constraint is very scanty, the researcher is motivated in selecting this problems as his research work.”