Flexible manufacturing system (FMS) for automating machine tools
A flexible manufacturing system (FMS) makes it possible to automate production with machine tools and thus enable unmanned production and increase the production capacity and utilization rate of the machine tools. With an FMS, you can manufacture several types of parts simultaneously, and adjust the due dates on the fly. This enables short lead times and small batch sizes, while preserving the benefits of mass production.
Free tied-up capital, cut personnel costs, and improve quality at the same time
Efficient materials management and logistics together with advanced production planning features make it possible to run production with only a little presetting and fewer operating personnel, yet still improve quality as there are fewer human factors affecting the production. The system saves factory floor space as materials, fixtures, and pallets are stored within the FMS.
Video: FMS in three minutes
Operation principle of the FMS
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Machining cycles are based on job sequences assigned to a machining pallet. A job sequence defines the loading jobs, machining jobs, and unloading jobs for a machining cycle, as well as the order the jobs are performed in. The specific fixture to be used for clamping the part and the part ID after the machining cycle are also specified in the job sequence. The operator can create and edit job sequences and save them as master data. The job sequences of a part comprise the operation plan for the part. Manufacturing orders are created based on registered operation plans. Manufacturing is scheduled according to the due date in the manufacturing order and the availability of raw material and fixtures defined in the operation plan. |
 The workflow of the flexible manufacturing system. |
Total control of production
The advanced FMS control system allows total control of production since information about production orders, machining queues, and resources (raw materials, NC programs, and preset tools) is all in the same system. The FMS control system has interfaces to ERP (Enterprise Resource Planning) systems as well as to CAD/CAM systems, which make it possible to exchange both production and part data between the FMS and other systems. Advanced FMS systems can include a tool storage system and software for central management of tool and presetting data for the machine tools connected to the system.
An attractive investment option for companies of different sizes
The configurability and flexibility of an FMS make it an attractive investment option for various types of companies, from small subcontracting companies to large enterprises. The smallest FMS systems are a replacement for pallet pools, whereas large systems can be considered a factory within a factory. Fastems manufactures FMS systems ranging from small, single-machine tool systems up to large factory-wide systems. Fastems' smallest FMS is called the Flexible pallet container (FPC). The medium-sized solution is called the Flexible pallet magazine (FPM) and the largest system is called the Multi-level system (MLS).
Three main parts of a flexible manufacturing system
Generally, a flexible manufacturing system consists of three main parts: the machine tools, an automatic transfer system with storage, and a control system that is responsible for the overall process control. Machine tools are generally horizontal machining centers that provide the highest machine flexibility but also vertical machining centers can be used. A machining center can use a large variety of tools for machining the parts. A horizontal machining center can also perform turning operations. This kind of a machine tool can machine a wide variety of parts. However, the most important thing is the fact that a machining center has a common mechanical interface to all workpieces. The machining pallet is a job carrier that can carry one or more machining jobs for different parts to the machine tool without setup. This feature enables processing of a wide variety of jobs. This is sometimes called chaotic production.
The most common transfer system is a rail-guided vehicle (RGV) that can handle machining pallets. Other types of transfer systems can also be used, for example automated guided vehicles (AGV) or conveyor systems. Standard industrial robots are also gaining popularity. Fastems uses rail-guided stacker cranes in its FPC, FPM, and MLS systems and Fanuc industrial robots in robot cells (RPC).
The role of the control system is to keep automatic production running based on embedded algorithms, parameters, and production orders. The FMS control system is the master controller and the machine controllers are slaves. The FMS control system also enables unmanned production ranging from a few hours to several days.
Operation
In an FMS system, the loading station operator clamps parts to the fixtures on machining pallets. Depending on the parts to be manufactured, this manual work can be automated by using, for example, an industrial robot and hydraulically-operated machining fixtures.
The right method of scheduling
The FMS control system has to decide which jobs to dispatch each time a machine tool or loading station becomes idle. This decision-making is the key task of the control system. There is no single ideal solution on how to do this. The right method depends on many things, such as job queue statuses, production orders and their priorities, availability of machining resources (parts, tools), operator availability, supervising preference, and overall production profile.
The problem is that by favoring one target (for example machine utilization) one can easily neglect another (for example, keeping part priorities). In some cases, simulation can be used to find the overall optimum for a period of time (for example 8 hours) and then implement the result as a static schedule. However, this method requires that nothing unexpected happens (tool breakage, machine breakage, etc.). Normally, this cannot be guaranteed and, therefore, the normal way of scheduling is based on a reactive principle, that is, the decision about the next action is made at the last possible moment.
When to talk about a flexible manufacturing system
In everyday business communication, the term FMS is easily used when a machine is automated with, for example, an industrial robot. This is fine, provided that the system really has the main flexibility property: the possibility to run parallel production without manual setup. However, this is usually not the case and robot cells are operated by running production lots one after another. One might think that this has nothing to do with industrial practices and is merely a polemic and an academic question. Of course, firm orthodoxy leads nowhere and we could also use the term FMS for a robotics system capable of automatic setup change between production lots. However, the right way of using the term FMS helps the customer understand what the system is actually capable of and what it cannot do.
