What Is a Flexible Manufacturing System? Types, Features, and Structure

Traditional high-volume automation is rigid. It delivers excellent productivity for a few stable products but cannot respond efficiently to small batches and high product variety. Flexible automated equipment and manufacturing systems were developed to meet that need.

Flexible Production Equipment

The basic equipment in a flexible manufacturing system includes CNC machine tools, robots, automated guided vehicles, and automated storage.

A CNC machine is controlled by a computer or dedicated electronic controller. The machining sequence, process parameters, and machine motions are encoded in a numerical-control program and entered into the CNC, which directs the machine automatically. A position-feedback loop is often added to form a closed-loop system and improve accuracy. Effective users still need process planning, cutting-parameter selection, correct tooling and fixturing, tool measurement, machine knowledge, and programming skills.

1. Classification by Process

1. General CNC machines. CNC lathes, mills, boring machines, drills, grinders, gear shapers, and gear hobbing machines perform the same basic processes as their conventional equivalents but automatically produce complex shapes.
2. Machining centers with automatic tool changing. A machining center adds a magazine holding roughly 10 to 100 tools and an automatic tool changer. After one setup, it can automatically mill or turn, bore, drill, and ream the workpiece.
3. Multi-axis CNC machines. These machines control a larger number of axes, commonly three to five.

2. Classification by Toolpath

1. Point-to-point control. The controller moves accurately from one position to another without cutting during the move. Coordinate boring and CNC drilling machines are typical examples.
2. Point-to-point linear control. The controller manages both endpoint position and the straight path between points, normally along a machine axis. Cutting can occur along one coordinate axis, and more auxiliary functions are available.
3. Contour control. Continuous-path control coordinates two or more axes and controls speed and position throughout the cut, allowing complex shapes. Typical machines include CNC lathes, grinders, mills, and machining centers.

A contouring machining center such as the FHN100T typically includes X-, Y-, and Z-axis motion units, a rotary table for multi-face machining, an automatic tool changer (ATC), and a CNC controller.

Its control system uses sequence control together with touch sensing, management, and adaptive functions. T codes select tools, S codes command spindle speed, and the rotary table provides indexing.

Touch-sensing functions can automatically center a tool from the spindle datum, detect tool breakage and stop the machine, reduce air-cut time by moving at twice the cutting feed until contact, correct X/Y/Z reference planes to compensate for thermal and part-size variation, and measure hole diameter so the system can adjust the tool automatically.

Management functions compare preset tool life with actual use, substitute a standby tool automatically, and monitor operating information for fault diagnosis.

Adaptive control (AC) uses detectors on the axis-feed and spindle motors to monitor load. A load within the set range is normal. If it falls below the range, feed can increase to shorten cycle time; if it rises above the range, feed decreases to protect the tool.

Flexible Manufacturing Systems: Features, Types, and Structure

A flexible manufacturing system (FMS) integrates an information-control system, material storage and handling, and a group of CNC machines. Based on group technology, it defines processes for a family of workpieces, selects compatible machines and logistics, and uses computer control to produce different parts efficiently in batches while changing product mix as demand changes.

Features and Application Range

An FMS normally contains several CNC machines and machining centers, automatic loading and unloading, storage, and material transfer under centralized computer control. Compared with rigid automation, it provides:

• High flexibility for related parts with different process requirements.
• High automation, including unattended operation.
• High equipment utilization because setup and other auxiliary time are reduced.
• High productivity.
• Lower direct labor cost and improved economic return.

An FMS can support one-off and small-batch work as well as medium- and high-volume mixed production, combining flexibility, quality, and efficiency.

Types of FMS

1. Flexible manufacturing cell (FMC). A computer-controlled CNC machine or machining center is combined with a circular or oval pallet conveyor or an industrial robot. It can change workpieces without stopping and is the basic unit of a larger FMS.
2. Flexible manufacturing system. Two or more CNC machines, machining centers, or cells are connected by rail-guided or autonomous vehicles or robots, automatic pallet or robot loading, automated storage, and integrated computer planning, scheduling, and monitoring.
3. Flexible manufacturing line. Several machining centers or CNC machines, some partly specialized, are arranged in process order. The line may have a production takt, but it can be adjusted quickly to product changes and retains FMS functionality.

System Composition and Control

An FMS contains logistics and information systems, each made up of several subsystems. Its main processing equipment is normally two to six vertical or horizontal milling-boring centers and turning centers. Conveyors, guided or autonomous vehicles, and industrial robots can form linear, loop, or networked transfer systems. Storage may use an automated high-bay warehouse and stacker crane or floor storage and pallet stations.

A pallet acts as a traveling fixture. It carries the part fixture and workpiece as one unit, is moved by the handling system, and is positioned and clamped automatically on the machine table. Pallet stations can also provide temporary storage and buffering. Separate stores may hold blanks, finished parts, tools, and fixtures. Cleaning, deburring, measurement, and inspection stations can be included as needed.

The control system connects several computers and equipment controllers through a network in a hierarchical architecture. Its work covers four areas:

1. Process planning. Define processes from product requirements and adapt them dynamically to schedule changes.
2. Production planning and scheduling. Maintain balanced production and high equipment utilization.
3. Workstation and equipment control. Coordinate machine tools, material transfer and storage, measuring machines, cleaning equipment, robots, and other devices.
4. Condition monitoring and quality assurance. Monitor and control the system so that it operates safely, reliably, normally, and with stable quality.