Flexible manufacturing systems emerged in the late 1960s as an alternative to medium-volume, low-variety product manufacturing, i.e., a solution that was capable of fully producing a family of parts automatically. The idea behind this type of system is to be able to adjust the economies of scale of high-volume mass production, within the framework of medium volume production and limited variety. The foregoing is only possible if the economic size of the production batch of the system is equal to 1 or very close to this value, which means that it must be able to perform a model changeover in a time close to zero.
System flexibility is measured in terms of the number of different parts it can process within its operating parameters. There are no manufacturing systems of infinite flexibility, none can be designed to produce anything.
Flexible systems use group technology to identify the families of parts into which the organization's catalog can be divided and to select the particular family that a specific system will be able to manufacture. One of its main characteristics is its ability to respond to changing market demand in a highly efficient manner. Flexible systems, being prepared to produce batches in small quantities and with very low inventories, have the capacity to reprogram very easily, without leaving parts or incomplete products in process.
Flexible manufacturing systems usually require a large economic investment, so their feasibility must be carefully evaluated before making the decision to implement them. You will now review in detail the composition and characteristics of a flexible manufacturing system.To learn more about a flexible system, check out the following video:
MTUAeroEngines. (2022, February 18). Flexible manufacturing system (FMS): Airfoil production with autopilot [Video file]. Retrieved from https://www.youtube.com/watch?v=fdq2-r_o6qs&t=14s
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14.1 FMS definition
A flexible manufacturing system FMS it is a highly automated production system whose operation is based on group technology. Consists of a group of CNC machines unified by an automatic material handling system and controlled by a central computer. They can manufacture many parts belonging to the same family in random order. It is important to note that it is not possible to integrate infinite flexibility into a manufacturing system, therefore, an FMS can produce the parts that make up a family of parts or a limited number of families.
The main task of the central control of an FMS is to dynamically balance, in real time, the load of the machines or cells that make up the system, so that it automatically adapts to changes in production requirements in terms of mix and quantities.
The central control system must be efficient enough to maintain equipment utilization at 80 to 90 percent, because they can operate with little supervision 24 hours a day, seven days a week, depending on certain operating conditions. Thanks to this central control, which has the capacity to coordinate the functions of all the elements of the system, labor requirements are drastically reduced, resulting in savings of 30% to 50% in this aspect. In some cases, the implementation of an FMS has as a goal the achievement of a zero direct labor manufacturing process, in what is called lights-out production.
An FMS is expected to manufacture the different parts randomly, depending on the production requirements, since its main purpose is to obtain the ability to mass produce the parts of the family for which it was designed, in the required quantities, with economic lot sizes as small as the unit. This helps to achieve inventory reductions of 60 to 80 percent, since by producing in very small batches the equipment is in process around 95 percent of the time it spends in the system and prevents the creation of unnecessary inventories.
On the other hand, since the system has the capacity to respond very quickly to changes in customer demand, it is not necessary to create inventories to buffer fluctuations in demand.
Reduced, or virtually no inventory in an FMS also translates into less floor space requirements. This is also aided by the layout of the physical components of the system. In sum, the space requirement of an FMS can be 50 to 60 percent of the space requirement of a traditional system.
Space savings are also influenced by the layout selected for the installation of its elements; however, this selection is decisively conditioned by the devices used by the material handling system, which may consist of automated guided vehicles, material handling robots, gantry robots, or others.
A classification of flexible manufacturing systems considers the following criteria (figure 1).
Figure 1. Criteria for classifying flexible manufacturing systems
14.2 Description of the FMS elements
A flexible manufacturing system is composed of several elements (figure 2).
Figure 2. Example of a flexible manufacturing system layout
Groover, M. (2018). Automation Production System and Computer Integrated Manufacturing (5th ed.). United States: Pearson.
For educational purposes only.
A relevant part is represented by the hardware components, CNC machinery, special purpose machine tools, tooling required for the machines and the work and inspection stations. Other machines that can be included in an FMS are CNC milling machines and lathes, arc and spot-welding robots, CNC metal bending and forming machines, heat treatment furnaces, parts washers, and cleaners for metal mechanical manufacturing systems.
Electronic board manufacturing systems also include adhesive and solder paste dispensers, component setters, curing ovens, wave and reflow soldering machines, board cleaners and various test equipment.
Figure 2. Example of a flexible manufacturing system layout
Groover, M. (2018). Automation Production System and Computer Integrated Manufacturing (5th ed.). United States: Pearson.
For educational purposes only.
Another significant part of an FMS is the material handling system. This type of system is divided into two blocks: the primary system and the secondary system.
The primary material handling system is used to move parts between the FMS machine tools and must be compatible with the control system so that it can provide independent movement between the machine tools of parts that are placed on specially designed pallets or containers to accommodate the parts.
The primary system must be able to allow temporary storage or parking of parts, allow access to the machine tools for maintenance activities on the machine tools, and finally, interface with the secondary material handling system.
The secondary material handling system is used to deliver parts to each machine tool within the FMS. Like the primary, it must be able to communicate with the system control and allow the temporary storage of parts. The secondary system orients and aligns the parts properly by feeding them to the corresponding machines and must be able to interface with the primary system.
The primary material handling systems of an FMS can be designed based on automated guided vehicles or fixed-route conveyors with the necessary mobility characteristics to serve the FMS.
Photo of an AGV (Automatic Guided Vehicle)
KUKA. (2022). Automatic Guided Vehicle. Retrieved from https://www.kuka.com/es-es/productos-servicios/movilidad/plataformas-m%c3%b3viles/kmp-1500
For educational purposes only.
Secondary systems can be somewhat more complex in configuration and consist of carousels, vibratory feeders, and robotic material handling arms.
The next element within an FMS is the computer control system. It consists of the hardware parts: computers, monitors, data acquisition elements and interfaces, and its intangible components: the CNC numerical control programs, the traffic management programs of the material handling systems, the machine tooling information and production management programs, and the general control software of the FMS system.
The following is a chart of typical functions of an FMS control system (Groover, 2018).
Function |
Description |
Programming of parts by NC |
Numerical control programming for parts manufactured by the system. |
Production control |
Parts information, machine loading and other planning functions. |
Distribution of CNC programs |
The necessary programs are distributed to the appropriate machines. |
Workpiece control |
Control of the status of the parts in the system, operations already performed on a part and operations to be performed. |
Tool management |
Inventory control and status of tools, transport of tools to and from the system. |
Control of material handling systems |
Programming and control of primary and secondary material handling systems. |
System administration |
Creation of system performance reports (system utilization level, production quota, quality level, among others). |
Classification of flexible manufacturing systems
Each FMS is specifically designed for a specific application, family, and process; therefore, FMS are custom engineered and unique systems. They can be classified as follows (figure 3).
Figure 3. FMS classifications
Groover, M. (2018). Automation Production System and Computer Integrated Manufacturing (5th ed.). United States: Pearson.
For educational purposes only.
14.3 FMS implementation
Before considering the implementation of a flexible system, it is necessary to evaluate that there is an intermediate demand for parts and that these parts have enough similarities to form a family of parts. If what you have in the system are products with a high production volume and very few variations in their design, then a less flexible production system, such as a transfer line, is appropriate. Once it has been decided that an FMS is in the best interest of the organization, then the economic evaluation of the new system will be carried out.
The economic evaluation of the project includes a complete analysis of the cost of the implementation and the determination of the potential benefits expected to be achieved. Typically, millions of dollars are at stake and the factors that go into the analysis are the cost of capital, energy, materials and labor, the expected demand for the parts or products involved and an analysis of possible future variations in production. A vitally important consideration is the time and effort that the organization will have to expend to install, start-up and refine the system. There is a tendency to think that FMS systems are suitable only for large manufacturing organizations because of the large amount of capital involved in their implementation.
On the other hand, the size or capacity must be carefully considered, since these systems must be designed to operate constantly, and to achieve an adequate recovery of the invested capital. To ensure this aspect, system load scheduling must be critical, as the machines must not fail to operate and work inefficiently.
FMS programming is of the dynamic type and capable of determining both the routing of parts and their priority in the system, responding to changes in the instantaneous demand of the parts to be processed. The characteristic of FMS is to be able to process parts with an economical batch of unit size, so it is said that there is no time wasted in changing models, however, the quality performance of the systems must be monitored on each part produced, both in the characteristics of the parts and in the condition of the system tools.
It is necessary to consider that an organization's need for flexibility is not always met by a flexible manufacturing system. Sometimes it is convenient to leave this characteristic defined in terms of the conformation of the production mix, (combination of parts that the system can perform at the same time), the adaptability to changes in design, instantaneous demand, parts processing route or the ease/difficulty of performing a model change on a given machine.
The implementation of a flexible manufacturing system is a very specialized task, since they are designed from an integral architecture between hardware and software, that is to say, both systems are designed in a complementary way, which makes it difficult to later include elements different from the original concept. It can be said that both hardware and software within the FMS are "proprietary systems”. This means that the boundaries between components and functionalities are not clearly defined, which makes it difficult to identify them, and they are closely linked. FMS have fixed hardware and software, and although the software is programmable, this type of architecture does not allow changes to be made easily. Therefore, flexible manufacturing systems are limited in terms of upgrading, adding new components, adapting, or changing their production capacity.
An FMS can be characterized in conceptual terms of its components. The first point that is essential to know is the type and family of products to be manufactured. With this data it is possible to determine the process required for its manufacture and therefore establish the equipment to be involved in this process, as well as the necessary tooling for the manufacture of the specific family of parts.
The next necessary information refers to the production volume to be covered by the FMS, from the expected volume or demand it is possible to calculate the number of machines of each type needed to form the system. Currently, FMS are composed of between two and a maximum of ten machines or workstations, with more than ten, their programming becomes prohibitively complicated.
The next point in the integration of a flexible system is the selection of material handling systems. Automatically guided vehicle systems or fixed path conveyors with some implicit flexibilities are available for the primary system and conveyors, carousels, and robotic arms for the secondary system. The material handling part should also include the design of the containers in which the parts are accommodated for transport.
Finally, there is the design of the control system, which must be custom-made, and which incorporates all the necessary operating features and monitoring functions. The control system is the center of flexibility in this type of solution.
Applications and benefits of a flexible manufacturing system
Flexible manufacturing systems are an expression of world-class manufacturing. They involve and group technological developments in several areas: industrial robotics, computer numerical control, technological groups, cellular manufacturing, systems for production planning and control, automatic systems for storage and transport of materials, process automation, among others.
FMS are considered as the union of several flexible manufacturing cells (FMC). Compared to cells, which only manufacture a part of a product and are mostly simple parts, FMS can generate more complex products. Their field of application is quite extensive; they are currently found in multiple manufacturing applications in the automotive and metal mechanics industries, in the manufacture of white goods (washing machines, stoves, refrigerators) or household appliances (microwave ovens, toasters, blenders), in the manufacture of electronic components such as computers and printers, and in the manufacture of medical devices.
FMS can work for any industry, but its greatest advantage is obtained when the product demand is flexible in terms of design and production variety and can even mix different products on the same production line.
Benefits of flexible manufacturing systems
According to Groover (2018), some advantages derived from the implementation of FMS are as follows:
According to Groover (2018), FMSs positively impact material handling systems. Some of the benefits that can be mentioned are the following:
In some situations, an upgrade or rethinking of the FMS may need to be considered. Criteria that may suggest the need for a modification may include the following:
FMS have emerged as a solution to the problems faced by manufacturing organizations immersed in a global market, under intense financial pressure and demanding ever greater variety in the products it consumes.
FMS rely on group technology to classify the parts that a system will be able to manufacture into families. The main components of a flexible manufacturing system are the CNC machines and workstations, the material handling systems, and the central control system. Since flexible systems are designed and manufactured as a whole, both hardware and software are so closely linked, making it very difficult to make any modifications to a system of this nature.
To date, FMS still require a large financial investment, which makes them primarily suitable for companies with sufficient capital to sustain such a large expenditure. An FMS must be designed with great precision, since its utilization will always be maximum, even if the production batch is very small; moreover, modifying them once built is a complex and costly task.
On the other hand, among its advantages are the reduction of raw material and work-in-process inventories, the reduction of space required for parts manufacturing, the simplification of direct labor and the increase in the quality of the parts produced.Make sure that you:
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Through a search for information and classification, the student will describe the main components of a flexible manufacturing system applied in real situations.
Objective
To learn the main components and practice the concepts related to flexible manufacturing systems or FMS.
Instructions
Individually
Figure 1. Robot-centered manufacturing cell
Groover, M. (2018). Automation Production System and Computer Integrated Manufacturing (5th ed.). United States: Pearson.
For educational purposes only.
Deliverable(s)
A document with the development of the activity.Description
It applies the concepts related to FMS and deepens the knowledge of this technology from its emergence to the present day. In addition, answer a quiz with review questions.
Instructions
Individually