Group Technology in Manufacturing

Advanced Machining Concepts

• Group Technology (GT) exploits similarities in parts to use similar processes and tooling.
• It can be implemented manually, as cellular manufacturing, or automated, as a flexible manufacturing system.

Group Technology Defined

• Manufacturing approach where similar parts are identified and grouped together.
• It takes advantage of similarities in design and production.
• Similar parts are classified into part families.
• Similar processing is done for each family.
• Improved efficiency is achieved by organizing production stations into cells specializing in producing certain part families.

Part Family

• A group of parts with similarities in geometric shape, size, or manufacturing processes.
• Part families are a central feature of group technology.
• There are typically always differences among parts in a family
• However the similarities are close enough that the parts can be grouped into the same family

Ways to Identify Part Families

• Visual Inspection: Grouping parts into families based on judgment using the parts or photos.
• Production Flow Analysis: Classifying parts using information in route sheets.
• Parts Classification and Coding: Identifying part similarities and differences using a coding scheme.

Parts Classification and Coding

• Systems can be based on part design attributes, manufacturing attributes, or both.

Part Design Attributes

• Major Dimensions
• Basic external shape
• Basic internal shape
• Length/diameter ratio
• Material type
• Part function
• Tolerances
• Surface finish

Part Manufacturing Attributes

• Major process.
• Operation sequence.
• Batch size.
• Annual production.
• Machine tools.
• Cutting tools.
• Material type.

Features and Corresponding Operations

• External cylinder corresponds to Turning
• Face of cylinder corresponds to Facing
• Smooth Surface corresponds to External cylindrical grinding
• Axial Hole corresponds to Drilling
• Internal Threads corresponds to Tapping
• Cylindrical Step corresponds to Turning
• Counterbore corresponds to Counterboring

Machine Cell Designs

• Single machine.
• Multiple machines with manual handling.
• Multiple machines with mechanized handling.
• Flexible manufacturing cell.
• Flexible manufacturing system.

Benefits of Group Technology

• Standardized tooling, fixtures, and setups are encouraged.
• Material handling is reduced, with parts moving within a machine cell instead of the entire factory.
• Process planning and production scheduling are simplified.
• Work-in-process and manufacturing lead time are reduced.
• Higher worker satisfaction in a GT Cell.
• Higher quality work.

Problems in Group Technology

• Identifying Part Families can be a substantial task if the plant makes makes many different parts
• Rearranging Machines into cells requires plants, it takes plan and the machines aren't producing during the changeover

Flexible Manufacturing System

• It's an automated GT machine cell.
• Includes processing stations (usually CNC machine tools).
• Features an automated material handling and storage system.
• It's typically controlled by an integrated computer system.
• Relies on the principles of GT.
• An FMS is usually capable of producing a single part family or a limited range of part families but is not unlimited.

Tests of Flexibility

• Can it process different part styles in a non-batch mode?
• Can it accept changes in production schedule?
• Can it respond gracefully to equipment malfunctions and breakdowns?
• Can it accommodate the introduction of new part designs?

Is the Robotic Work Cell Flexible?

• Can it machine different part configurations in a mix rather than in batches?
• Can the production schedule and part mix be changed?
• Can it operate if one machine breaks down and can its work be temporarily reassigned to the other machine during repairs?
• Can NC part programs for new part designs be written off-line and then downloaded for execution?

FMS Components

• Hardware components.
• Software and control functions.
• Human labor.

Hardware Components

• Workstations CNC machines in a machining type system.
• Material handling system for moving parts between stations.
• Central control computer to coordinate activities for smooth operation.

Five Types of FMS Layouts

• In-line
• Loop
• Ladder
• Open field
• Robot-centered cell
• The basic layout of the FMS is established by the material handling system

Typical Computer Functions in a FMS

NC part programming

• Developing NC programs for new parts.

Production control

• Managing product mix and machine scheduling.
• Performing other planning functions.

NC program download

• Downloading part programs to individual stations.

More Computer Functions in a FMS

Machine control

• Individual workstations require controls, usually CNC

Workpart control

• Monitor status of each workpart in the system
• Monitor status of pallet fixtures
• Instructions on loading/unloading pallet fixtures

Transport control

• Control of work handling system

Tool management

• Managing tool inventory and status.
• Tool changing and resharpening.
• Transporting tools to and from grinding.

System management

• Compiling management reports on performance, such as utilization and production rates.

Duties Performed by Human Labor

• Loading/unloading parts.
• Changing/setting cutting tools.
• Equipment maintenance/repair.
• NC part programming.
• Programming/operating the computer system.
• Overall system management.

FMS Applications

• Common applications include machining, assembly, inspection, sheet metal processing, and forging.

Typical FMS Benefits

• Higher machine utilization due to better work handling, off-line setups, and improved scheduling.
• Reduced work-in-process because of continuous production.
• Lower manufacturing lead times.
• Greater flexibility in production scheduling.

This text discusses Group Technology (GT), a manufacturing approach that exploits similarities in parts to use similar processes and tooling. GT can be implemented manually, as cellular manufacturing, or automated, as a flexible manufacturing system. Part families, groups of parts with similar characteristics, are central to GT.