The CNC (Computerized & Numerically controlled) machine centre is a basic element of FMS. There is an automatic tool changer and pallet changer systems in CNC. There is automatic transfer of tools, identification of pallets and their changing. Even tool identification and correction is automatic. Inspection is automatic. Pallet pool contains pallets stored in front of the machine. Pallets are handled by Pallet handling System called Rail Guided vehicle (RGV) or Automatic Rail Guided Vehicle (ARGV). There are pallet and tool preparation areas.
Hierarchy of Hardware
Host computer is at the top of the hierarchy. It maintains data-base of parts, fixtures, pallets, machines, scheduling. This computer can be linked to a plant-wide PPC-system and also to CAD system.
The middle-level hierarchy consists of a cell controller. At the bottom level, there are control systems of individual machines, material handling system, tool pre-setter and peripheral devices for data exchange.
There is networking among these elements.
Functions of hardware
Host Computer: Decides detailed production schedule in the light of production requirements. Transfer shift-wise production to the cell controller. Generate MIS reports.
Cell Controller: Executes shift-wise production schedule after receiving it from the host computer. It does so by interacting with the individual elements. Carries tool management.
1. Increased machine utilization.
2. Reduced WIP.
3. Reduction in finished goods.
4. Reduction in number of machines and operating personnel.
The quantification of the above factors will make it possible to appreciate the savings by FMS, and may make us inclined to justify its high installation cost.
Technology of FMS
The ever changing environment has put a premium on flexibility. A manufacturing method today has to satisfy a variety of conflicting targets. Therefore, though flexibility is called for, it should not affect productivity. Flexible manufacturing system overcomes the limitations of conventional batch manufacturing system. It employs computer and numerical control techniques. It was first installed in England in 1968. Since then, it has been adopted by many countries. Mostly, it is applied in electronics assembly, IC manufacturing and metal cutting.
Steel-collar workers or robots are a common feature of automated factories. More and more manufacturing functions are being integrated to computers (CIM: Computer Integrated Manufacturing). Product specifications, designing, machine control, material handling, production process control are some such functions. A common data-base is used. It includes computer aided deign (CAD), computer aided manufacturing (CAM), robotics and material requirement planning (MRP). Data generated may include NC machine tools—CNC or DNC machines and robots
Structurally, FMS consists of a set of machine tools performing production operations, linked up material handling system. The overall control is exercised by a central computer. The Flexible Manufacturing System (FMS), as it is aptly called, consists of a large number of tools whose functioning is coordinated through a computer program. In fact, the same programs also integrates different aspects of the machining process, material handling and job scheduling into a seamless system that can respond quickly to any change I the demand for the final product.
We have traveled from automatic mechanisms to numeric control (NC). CNC uses mini-computers. NC machines use magnetic tape whereas CNC machines are on-line to a computer. DNC machines use a central computer to control several CNC machines. CNC machines can produce a specific part or group of parts. Such grouping is called a cell. Each cell has a computer which interfaces with the CNC. The operation of several such cells is coordinated by a central computer through the aid of a material handling system. In the FMS, scheduling decisions are made on the actual state of the system. FMS is put into different categories depending upon the number of CNC machines and their arrangements.
The three sub-system of FMS are—machining, assembly and fabrication. The CAD/ CAM system are integrated to FMS. The sub-system may be connected to storage/retrieval system (AS/RS) . It allows flexible routing of parts. The integration of AS/RS to FMS is through a material handling system, which could be an automatic guided vehicle (AGV) or robot or conveyor. Most FMS literature emphasizes machining only. Flexible assembly system (FAS) and flexible fabrication system (FFS) have developed independently. All three have the potential for application of flexible technology.
Bharat Forge’s Machine Components Division (MCD) uses an FMS to respond quickly to demand fluctuations. Flexible Manufacturing System will not work unless material handing systems are automated.