UNIT-III Group Technology and Computer Aided Process Planning

Group Technology GT is a manufacturing philosophy to increase production effectively by grouping a variety of parts having similarities of shape, dimension and/or process route https://www.youtube.com/watch?v=48szrhv-DzM

Part families Collection of parts which are similar either because of geometric shape and size (or) because similar processing steps are required in the manufacturing. Design Part Family Grouped the parts similar in their design (shape & geometry) characteristics Manufacturing Part Family Grouped the Parts similar in their manufacturing characteristics ( Mfg. Process)

Methods for part family formation Visual inspection Parts classification and coding system Production flow analysis

Visual Inspection It involves looking of parts, photos of parts (or) drawings of parts and arranging them into similar groups

Parts Classification and Coding System Coding is a systematic process of establishing an alphanumeric value for parts based on selected part families Most difficult , most time- consuming , most sophisticated and widely used methods It will vary from one company to another company

Coding System Structure Hierarchical Code Attribute Code Decision tree codes

Hierarchical Code (Monocode) The interpretation of each successive symbol depends on the value of the proceeding symbols.

Hierarchical Code

Example-Spur gear

Merits and Demerits It Provides large amount of information relatively small no. of digits Defining the meanings for each digit in a hierarchical system is difficult

Attribute Code (Polycode) The interpretation of each symbol in the sequence does not depend on the value of preceding symbols Each digit in this code represents information in its own right and does not directly qualify the information provided by the other digits

Example-Spur Gear

Merits and Demerits Polycodes are compact and easy to use Its lacks in detail as compared to monocode

Decision tree codes (Hybrid Code) Hybrid code Captures the best features of the hierarchical and polycode structures It combines both design and manufacturing attributes

Decision tree codes (Hybrid Code)

Reasons for using a coding scheme Design retrieval Automated process planning Machine cell design

Selection of a Coding System Objective-of the classification system Robustness- Capability of handling all parts Expandability- Ability to cope up with future demands Automation- for computer use Efficiency- the code efficiency, the no. of digits required to code a typical part, should be evaluated. Cost- including initial, modifying, interfacing and operational costs Simplicity – ease of use training

Coding Systems Opitz Classification systems MICLASS Systems DCLASS System KK-3 System CODE System CUTPLAN System RNC System Part Analog System Brisch System COFORM

Opitz Classification systems

Production flow analysis (PFA) Identifying part families and associated machine groupings that uses the information contained on production route sheets rather on part drawings

Steps involved in Production flow analysis Data collection- (part no. o/p sequence) Sorting of process routings- (Group technology- Arranging of Process Types) Preparation of PFA chart-Tabulation of a Process of a machine. Cluster Analysis

Steps involved in Production flow analysis

Facility Design using Group Technology Line (or product) Layout Functional (or Process ) Layout, and Group (or combination ) layout

Line (or product) Layout Machines are arranged in the sequence as required by the product

Functional (or process) Layout Keeping similar machines/operations at one location

Group (or Combination) Layout Combination of Product layout and process layout https://www.youtube.com/watch?v=VnOFJHkp_UQ

Cellular Manufacturing (CM) Cellular Manufacturing, production work stations and equipment are arranged in a sequence that supports a smooth flow of materials and components through the production process with minimal transport or delay.

Process Planning The product design for the each product developed in design department. To convert the product design into product , a manufacturing plan is required. The activity of developing such a plan is called Process Planning “An Act of preparing a detailed processing documentation for the manufacture of a piece part or assembly”

Document Process Planning Clear in detail about the particular product in form of route and operation sheet

Approaches of Process Planning 1.Manual Process Planning 2.Computer Aided Process Planning i) Retrieval CAPP System ii) Generative CAPP System

Manual Process Planning Merits: Its very much suited for small scale industries It requires low investment costs Demerits: Its time consuming Required skill process planner It increases paper work

Computer Aided Process Planning (CAPP) CAPP- Use of computers in the process planning, one can reduce the routine clerical work of manufacturing engineers Benefits: Process rationalization and standardization Productivity improvement Product cost reduction Elimination of human error Reduction in time Reduced clerical effort and paper work Faster respond to engineering changes

Computer Aided Process Planning (CAPP)

Variant (or) Retrieval CAPP Systems A process plan for a new part is created by identifying and retrieving an existing plan for a similar part, followed by the retrieving an existing plan for a similar part, followed by the necessary modifications to necessary modifications to adapt it to the new part.

Variant (or) Retrieval CAPP Systems Variant approach is commonly implemented with GT coding system. Here, the parts are segmented into groups based on similarity and each group has a master plan.

Advantages Once a standard plan has been written, a variety of components can be planned. Programming and installation are comparatively simple. It is easy to learn and easy to use.

Disadvantages The components to be planned are limited to previously planned similar components. Experienced process planners are still required to modify the standard plan for the specific component. Variant planning cannot be used in an entirely automated manufacturing system, without additional process planning.

Generative CAPP System In a generative approach, a process plan for each component is created from scratch without human intervention. These systems are designed to automatically synthesize process information to develop a process plan for a part. (Computer Automatically generates a unique operation/route sheet whenever the part is ordered)

Generative CAPP System Generative CAPP systems contain the logic to use manufacturing data bases, knowledge bases and suitable part description schemes to generate a process plan for a particular part.

Advantages and Disadvantages Consistent process plans can be generated rapidly. New components can be planned as easily as existing components. It has potential for integrating with an automated manufacturing facility to provide detailed control information. The generative approach is complex and very difficult to develop