FLEXIBLE MANUFACTURING SYSTEM

 Introduction A flexible manufacturing system (FMS) is a manufacturing system in which there is some amount of flexibility to react in the case of changes, whether predicted or unpredicted. This flexibility can be divided into two categories: ١.  Machine flexibility, covers the system's ability to be changed to produce new product types, and ability to change the order of operations executed on a part, and ٢. Routing flexibility, this consists of the ability to use multiple machines to perform the same operation on a part, as well as the system’s ability to absorb large-scale changes, such as in volume, capacity, or capability. Most FMS systems consist of three main systems.  ١. The work machines which are often using computerized machines, ٢. Material handling system to optimize parts flow, and  ٣. The central control computer which controls material movements and machine flow.  An Industrial Flexible Manufacturing System (FMS) consists of robots, Computer-controlled Machines, Numerical controlled machines (CNC), instrumentation devices, computers, sensors, and other stand-alone systems such as inspection machines

FMS is actually an automated set of numerically controlled machine tools and material handling systems, capable of performing a wide range manufacturing operations with quick tooling and instruction changeovers.

 Flexibility is an attribute that allows a mixed model manufacturing system to cope up with a certain level of variations in part or product style, without having any interruption in production due to changeovers between models. Flexibility measures the ability to adapt “to a wide range of possible environment”. To be flexible, a manufacturing system must posses the following capabilities:

 Identification of the different production units to perform the correct operation

  Quick changeover of operating instructions to the computer controlled production machines

 Quick changeover of physical setups of fixtures, tools and other working units These capabilities are often difficult to engineer through manually operated manufacturing systems. So, an automated system assisted with sensor system is required to accomplish the needs and requirements of contemporary business milieu. Flexible manufacturing system has come up as a viable mean to achieve these prerequisites. The term flexible manufacturing system, or FMS, refers to a highly automated GT machine cell, consisting of a group of computer numerical control (CNC) machine tools and supporting workstations, interconnected by an automated material handling and storage system, and all controlled by a distributed computer system. The reason, the FMS is called flexible, is that it is capable of processing a variety of different part styles simultaneously with the quick tooling and instruction changeovers. Also, quantities of productions can be adjusted easily to changing demand patterns. 

The different types of flexibility that are exhibited by manufacturing systems are given below:

1. Machine Flexibility. It is the capability to adapt a given machine in the system to a wide range of production operations and part styles. The greater the range of operations and part styles the greater will be the machine flexibility. The various factors on which machine flexibility depends are:

•      Setup or changeover time

•      Ease with which part-programs can be downloaded to machines

•      Tool storage capacity of machines

•      Skill and versatility of workers in the systems 

2.      Production Flexibility. It is the range of part styles that can be produced on the systems. The range of part styles that can be produced by a manufacturing system at moderate cost and time is determined by the process envelope. It depends on following factors:

•      Machine flexibility of individual stations

•      Range of machine flexibilities of all stations in the system

3.      Mix Flexibility. It is defined as the ability to change the product mix while maintaining the same total production quantity that is, producing the same parts only in different proportions. It is also known as process flexibility. Mix flexibility provides protection against market variability by accommodating changes in product mix due to the use of shared resources. However, high mix variations may result in requirements for a greater number of tools, fixtures, and other resources. Mixed flexibility depends on factors such as:

•      Similarity of parts in the mix

•      Machine flexibility

•      Relative work content times of parts produced 

4.      Product Flexibility. It refers to ability to change over to a new set of products economically and quickly in response to the changing market requirements. The change over time includes the time for designing, planning, tooling, and fixturing of new products introduced in the manufacturing line-up. It depends upon following factors:

•      Relatedness of new part design with the existing part family 

•      Off-line part program preparation 

•      Machine flexibility

5.      Routing Flexibility. It can define as capacity to produce parts on alternative workstation in case of equipment breakdowns, tool failure, and other interruptions at any particular station. It helps in increasing throughput, in the presence of external changes such as product mix, engineering changes, or new product introductions.  Following are the factors which decides routing flexibility:

•      Similarity of parts in the mix

•      Similarity of workstations 

•      Common tooling

6.      Volume Flexibility. It is the ability of the system to vary the production volumes of different products to accommodate changes in demand while remaining profitable.  It can also be termed as capacity flexibility. Factors affecting the volume flexibility are:

•      Level of manual labor performing production 

•      Amount invested in capital equipment 

7.      Expansion Flexibility. It is defined as the ease with which the system can be expanded to foster total production volume. Expansion flexibility depends on following factors: 

•      Cost incurred in adding new workstations and trained workers 

•      Easiness in expansion of layout  

•      Type of part handling system used

Since flexibility is inversely proportional to the sensitivity to change, a measure of flexibility must quantify the term “penalty of change (POC)”, which is defined as follows:

POC = penalty x probability

Here, penalty is equal to the amount upto which the system is penalized for changes made against the system constraints, with the given probability. 

Lower the value of POC obtained, higher will be the flexibility of the system.