The Flexible Manufacturing System (FMS) is composed of a unified information control system, a material storage and transportation system, and a collection of processing equipment that is digitally controlled.
The Flexible Manufacturing System (FMS) is an automated production system that can adapt to the changing of machined components. It consists of a series of interconnected machines, linked by automated loading and unloading devices and controlled by computer systems. Raw materials and finished parts are loaded and unloaded on the part transfer system, which carries the components from one machine to another in a seamless sequence. Each machine in the FMS receives operational instructions and automatically loads and unloads the necessary tools without the need for manual intervention.
Development
In 1967, the British company Molins introduced the “System 24”, based on Williamson’s concept of Flexible Manufacturing Systems (FMS). It consisted of six multi-process CNC machines with a modular structure and aimed to achieve 24/7 continuous processing without supervision. However, the project was not fully realized due to economic and technical challenges.
The same year, White Sunstone of the United States developed the Omniline I system, which consisted of eight machining centers and two multi-axis drilling machines. The workpieces were placed in a jig on a pallet, transported and processed through the machine tools in a fixed sequence, making it suitable for small to high-volume production. This flexible automation device was similar to a traditional production line and was referred to as a flexible automatic line.
FMS was also developed in other countries such as Japan, the former Soviet Union, and Germany. In 1976, Japan’s FANUC showcased a Flexible Manufacturing Unit (FMC) consisting of a machining center and industrial robots, providing a key equipment for FMS development. The FMC typically comprised of 12 CNC machine tools and material transfer devices, with a separate workpiece storage station and unit control system that could automatically load and unload workpieces and even detect them. It was suitable for multi-variety small batch production applications.
Over time, FMS has evolved both technically and quantitatively. In practical applications, the FMS typically consists of 3-5 devices, but there are also larger systems in use. In 1982, Japan’s FANUC built an automated motor processing shop consisting of 60 FMCs (including 50 industrial robots) and a three-dimensional warehouse, along with two automatic guided trolleys for transporting blanks and workpieces. This unmanned, 24/7 workshop was a crucial step towards a fully automated, computer-integrated factory.
Despite some limitations, the economical FMS, which was not fully automated, helped popularize the design and technical achievements of FMS.
Process basis
The basis of FMS is a group of technologies that determine the production process based on the group of processing objects. It selects the appropriate CNC machining equipment and the storage and transportation system for workpieces, tools, and other materials, which is controlled by a computer. This enables the automatic adjustment and efficient batch production of a variety of workpieces within a certain range, providing “flexibility” to change products to meet market demand.
FMS also integrates both manufacturing and partial production management functions, which improves production efficiency. Its process range is expanding to include blank manufacturing, machining, assembly, and quality inspection. Most FMS systems that are put into use are used for cutting and also for stamping and welding.
System composition
Processing Equipment: The main processing equipment used in FMS are machining centers and CNC lathes. The machining centers are used to machine box and plate parts while CNC lathes are used to machine shaft and disk parts. In the production of medium and large batches of small varieties, a machining center with a replaceable headstock is often used for higher efficiency.
Storage and Handling: The storage and handling system deals with blanks, workpieces, tools, fixtures, gauges, and chips. The materials can be stored in a flat tray warehouse or a large storage warehouse. Blanks are loaded onto the fixture on a pallet by the worker and stored in a designated area of the automated warehouse. They are then sent to the designated station by the automated handling system according to the instructions of the material management computer.
The fixed-track trolley and transfer raceway are suitable for arranging the FMS equipment in the order of the process. The order of automatically guiding the trolley conveyance is independent of the equipment arrangement position, providing greater flexibility. Industrial robots can transport and load workpieces from 1-4 machines to a limited extent. For larger workpieces, an automatic pallet changer (APC) is often used. Robots that travel on the track can also be used for the transfer and loading and unloading of the workpiece.
Tools can be removed one by one from the magazine or replaced with spare sub-tools. The jaws of the lathe chuck, special clamps, and the headstock of the special machining center can also be replaced automatically. The chip handling and handling system is necessary to ensure continuous FMS operation. The economical structural solution is chosen based on the chip shape, removal amount, and processing requirements.
Information control
The FMS information control system typically adopts a hierarchical control structure. The first level consists of the computer numerical control (CNC) device for each processing equipment, which controls each processing process. The second level is a group control computer, which distributes the production plan and numerical control commands from the third-level computer to the CNC devices of the first level and reports their operational status information to the higher computer.
The third level is the main computer (control computer) of the FMS, which formulates production operation plans, manages the FMS operation status, and manages various data. The fourth level is the management computer for the entire plant.
Specialized application software, in addition to the system software that supports computer operations, is crucial for implementing FMS functionality. This software generally includes control software (for controlling machine tools, material storage and transportation systems, inspection devices, and monitoring systems), planning management software (for scheduling management, quality management, inventory management, tooling management, etc.), and data management software (for simulation, retrieval, and various databases).
To ensure the continuous automatic operation of the FMS, monitoring of the tool and cutting process is essential. Possible methods are:
- Measuring the current power output or torque of the spindle motor of the machine tool;
- Using a sensor to detect tool breakage;
- Directly measuring the change in the cutting edge size of the tool or the size of the workpiece working surface with a contact probe;
- Keeping track of the cutting time of the tool for tool life management.
In addition, contact probes can be used to measure machine tool thermal deformation and workpiece mounting errors and make compensations accordingly.
System type
Flexible manufacturing refers to a manufacturing system that can adapt to changes in processing objects with computer support. There are three types of flexible manufacturing systems:
- Flexible Manufacturing Unit: This consists of one or several CNC machine tools or machining centers that can automatically change tools and fixtures as needed to machine different workpieces. It is suitable for processing parts with complex shapes, simple processing steps, long processing time, and small batch size. It has high equipment flexibility but low flexibility for personnel and processing.
- Flexible Manufacturing System: This is a production system consisting of a CNC machine tool or machining center and a material conveying device that is automatically controlled by an electronic computer. It can handle a variety of processing without stopping the machine and is suitable for machining parts with complex shapes, many processing steps, and large batch sizes. The system is flexible in processing and material handling, but the flexibility of personnel is still low.
- Flexible Automatic Production Line: This is a production line consisting of adjustable machine tools (mostly dedicated machine tools) combined with automatic transport devices. It can process large quantities of different gauge parts. A flexible automatic production line with low flexibility is close to an automatic production line for mass production, while one with high flexibility is close to a flexible manufacturing system for small batch and multi-variety production.
