What Is a Flexible Manufacturing Production Line?

Basic Composition of a Flexible Manufacturing Line

When a mechanical part requires many operations, manufacturers often arrange the processing equipment in sequence and connect it with transfer and auxiliary devices. The resulting machining production line completes a defined process for one or more similar products. Its equipment is selected and arranged around the process route and operations used by most or all of those products. This organization requires reasonable stability in product design and process and can be used for batch or mass production.

Manufacturing lines include paced flow lines and automated lines. An automated line adds a control system that automatically manages workpiece transfer, indexing, positioning, clamping, and auxiliary-device actions according to a predefined program.

Line structure and complexity depend on the workpiece, process requirements, process sequence, production rate, and automation level. Regardless of complexity, a line normally contains five basic elements: processing equipment, tooling and fixtures, a material-transfer system, auxiliary systems, and a control system.

Types of Flexible Manufacturing Lines

1. Classification by workpiece shape and motion
   1. Rotating-workpiece lines. These lines machine shafts, disks, and rings while the workpiece rotates. Typical operations include turning or grinding internal and external diameters, grooves, threads, and end faces.
   2. Nonrotating-workpiece lines. These lines machine housings and miscellaneous parts that normally remain stationary. Typical operations include drilling, counterboring, boring, reaming, face milling, and slot milling.
2. Classification by product variety
   1. Single-product lines. Highly productive special-purpose machines, tooling, transfer equipment, and auxiliary equipment are arranged along a fixed process route. Workpieces move from one station to the next for machining, inspection, and cleaning. Quality and efficiency are high, but investment and specialization are also high, making conversion difficult. These lines suit mass production.
   2. Adjustable group-product lines. Adjustable special-purpose equipment is designed through group technology and arranged around a group process. These lines provide high efficiency and automation for families of structurally and technologically similar products. They suit batch production and can be rebuilt or reorganized when products change.
3. Classification by process equipment
   1. General-purpose machine-tool lines. These lines have short build times and low cost and are often used for small and medium rotating parts such as disks, shafts, sleeves, and gears.
   2. Modular machine-tool lines. Connected modular machines offer relatively short design and build cycles, reliable operation, and good economic performance in mass production.
   3. Special-purpose machine-tool lines. These have long design and build cycles and high investment. They suit unusually structured or complex workpieces and stable high-volume products.
   4. Flexible manufacturing lines. Multifunction CNC machines and machining centers are integrated with material handling and computer control. Rotary tables and automatic tool changers allow each machine to complete multiple faces and operations in fewer setups, reducing location error. These lines suit complex, accurate parts in small and medium batches and can respond quickly to market changes, but they require high investment and technical capability.
      
4. Classification by equipment connection
   1. Rigid lines. With no intermediate storage, each part moves directly from one station to the next. Machining and transfer must follow a strict takt, and one machine failure stops the entire line. Machines and auxiliary devices therefore require high stability and reliability.
   2. Buffered flexible lines. Storage can be placed between adjacent machines or groups of machines. If one machine stops, the others can continue for a limited time. Buffers can also balance stations with different cycle times.
5. Classification by workpiece transfer
   1. Direct-transfer lines. The transfer device acts directly on a surface of the workpiece. Parts enter at the beginning of the line and leave at the end after processing.
   2. Pallet-fixture lines. Each workpiece is mounted on a traveling fixture that moves through the stations on the main conveyor. After machining, a return conveyor carries the fixture back to the start.

Design Principles

1. Meet the production program while allowing growth; technical and economic analysis should normally support recovery of line investment within five years.
2. Ensure that every product drawing requirement is achieved.
3. Provide suitable adjustability for batch size and expected production duration.
4. Use stable, reliable processes and equipment with low initial, operating, and maintenance costs.
5. Reduce labor intensity and improve working conditions.
6. Minimize floor space while preserving safe, convenient operation, observation, and maintenance.
7. Support resource conservation, environmental protection, and clean production.

Design Content and Sequence

1. Define the line process plan and prepare operation and machining diagrams.
2. Select general-purpose equipment and design any special-purpose machines.
3. Define the logistics method and design transfer devices.
4. Select and design auxiliary devices.
5. Design the overall line layout.
6. Prepare the overall dimensional connection drawing.
7. Design the line control system.
8. Prepare operating instructions and maintenance precautions.