Practical 3 Auto

8/3/2019 Practical 3 Auto

1/5

Practical-3

Aim: Study of computer aided process planning.

Definition: Computer-aided process planning (CAPP) is the use of computer technology to aid in the process

planning of a part or product, in manufacturing. CAPP is the link between CAD and CAM in that it

provides for the planning of the process to be used in producing a designed part.

Process planning can be defined as an act of preparing processing documentation for the manufacturing

of a piece, part or an assembly. When process planning is done using a computer: Computer Aided Process Planning

About Process Planning:

Products and their components are designed to perform certain specific functions. Every product hassome design specifications which ensures its functionally aspects. The task of manufacturing is to

produce components such that they meet design specifications. Process planning acts as a bridgebetween design and manufacturing by translating design specification into manufacturing process

details. It refers to set of instructions that are used to make a components or a part so that the

design specifications are meet, therefore it is major determinant of manufacturing cost and

profitability of products. Process planning answers the question regarding required information andactivities involve in transforming raw materials into a finished product. The process starts with the

selection of raw material and ends with the completion of part. The development of process plan

involves mainly a set of following activities:

(1) Analysis of part requirements (2) Selection of work piece(3) Selection of manufacturing operations (4) Selection of machine tools

(5) Selection of tools. Tool holding devices and other equipments(6) Selection of manufacturing conditions (7) Determination of manufacturing items

Traditional process plan:

It is also known as manual Process Plan. The manual experience-based process planning is most widely

used. It is mainly based on a manufacturing engineer's experience and knowledge of production

facilities, equipment, their capabilities, processes, and tooling.

The major problem with this approach is that it is time consuming and developed plans may not be

consistent and optimum. The feasibility of developed process plan is dependant on many factors such asavailability of machine tools, scheduling and machine allocation etc. Computer aided process planning is

developed to overcome this problems to some extent.

1


2/5

Introduction to Computer aided process planning:

Process planning is concerned with determining the sequence of individual manufacturing

operations needed to produce a given part or product. The resulting operation sequence is documented on

a form typically referred to as a route sheet containing a listing of the production operations andassociated machine tools for a work part or assembly. Process planning in manufacturing also refers to

the planning of use of blanks, spare parts, packaging material, user instructions (manuals) etc.

The term "Computer-Aided Production Planning" is used in different context on different parts

of the production process; to some extent CAPP overlaps with the term "PIC" (Production and Inventory

Control).

Process planning translates design information into the process steps and instructions to

efficiently and effectively manufacture products. As the design process is supported by many computer-

aided tools, computer-aided process planning (CAPP) has evolved to simplify and improve process planning

and achieve more effective use of manufacturing resources.

Process planning encompasses the activities and functions to prepare a detailed set of plans and

instructions to produce a part. The planning begins with engineering drawings, specifications, parts or

material lists and a forecast of demand. The results of the planning are:

1. Routings which specify operations, operation sequences, work centers, standards, tooling

and fixtures. This routing becomes a major input to the manufacturing resource planning

system to define operations for production activity control purposes and define required

resources for capacity requirements planning purposes.2. Process plans which typically provide more detailed, step-by-step work instructions including

dimensions related to individual operations, machining parameters, set-up instructions, and

quality assurance checkpoints.

3. Fabrication and assembly drawings to support manufacture (as opposed to engineering

drawings to define the part).

Keneth Crow stated that "Manual process planning is based on a manufacturing engineer's experience and

knowledge of production facilities, equipment, their capabilities, processes, and tooling. Process planning is

very time-consuming and the results vary based on the person doing the planning".

According to Engelke, the need for CAPP is greater with an increased number of different types of parts

being manufactured, and with a more complex manufacturing process.

Computer-aided process planning initially evolved as a means to electronically store a process plan once it

was created, retrieve it, modify it for a new part and print the plan. Other capabilities were table-driven

2


3/5

cost and standard estimating systems, for sales representatives to create customer quotations and

estimate delivery time.

As mentioned in figure, the primary purpose of process planning is to translate the design requirements

into manufacturing process details. This suggests a system in which design information is processed by the

process planning system to generate manufacturing process details. CAPP integrates and optimizes system

performance into the inter-organizational flow. For example, when one changes the design, it must be able

to fall back on CAPP module to generate manufacturing process and cost estimates for these design

changes. Similarly, in case of machine breakdown on the shop floor, CAPP must generate the alternative

actions so that most economical solution can be adopted in the given situation. A typical CAPP frame-work is

shown in figure.

When compared with manual experience-based process planning, CAPP offers following advantages:

(1) Systematic development of accurate and consistent process plans.

(2) Reduction of cost and lead time of process planning.

(3) Reduced skill requirements of process planners.(4) Increased productivity of process planners.

(5) Higher level application programs such as cost and manufacturing lead time

estimation and work standards can be interfaced.

3


4/5

Types of Computer aided process planning:

(1) The Variant CAPP method:

In variant CAPP approach, a process plan for a new part is created by recalling,

identifying and retrieving an existing plan for a similar part and making necessary modifications for thenew part. Sometimes, the process plans are developed for parts representing a family of parts called

'master parts'. The similarities in design attributes and manufacturing methods are exploited for thepurpose of formation of part families. A number of methods have been developed for part family formation

using coding and classification schemes of group technology (GT), similarity-coefficient based algorithms

and mathematical programming models.

The variant process planning approach can be realized as a four step process;

1. Definition of coding scheme

2. Grouping parts into part families3. Development of a standard process plan

4. Retrieval and modification of standard process plan

A number of variant process planning schemes have been developed and are in use.

One of the most widely used CAPP system is CAM-I developed by McDonnell-Douglas Automation Company.

This system can be used to generate process plan for rotational, prismatic and sheet-metal parts.

(2) The Generative CAPP method:

The next stage of evolution is towards generative CAPP. In the generative CAPP,process plans are generated by means of decision logic, formulas, technology algorithms and geometry

based data to perform uniquely many processing decisions for converting part from raw material to

finished state.

There are two major components of generative CAPP; geometry based coding

scheme and process knowledge in form of decision logic data. The geometry based coding scheme defines

all geometric features for process related surfaces together with feature dimensions, locations, tolerances

and the surface finish desired on the features. The level of detail is much greater in a generative systemthan a variant system. For example, details such as rough and finished states of the parts and process

capability of machine tools to transform these parts to the desired states are provided. Process knowledgein form of in the form of decision logic and data matches the part geometry requirements with the

manufacturing capabilities using knowledge base. It includes selection of processes, machine tools, jigs or

fixtures, tools, inspection equipments and sequencing operations.

Development of manufacturing knowledge base is backbone of generative CAPP. The

tools that are widely used in development of this database are flow-charts, decision tables, decision trees,

iterative algorithms, concept of unit machined surfaces, pattern recognition techniques and artificialintelligence techniques such as expert system shells.

4


5/5

Benefits of computer aided process planning:

Reduced process planning and production lead-times.

Faster response to engineering changes in the product.

Greater process plan accuracy and consistency.

Inclusion of up-to-date information in a central database.

Improved cost estimating procedures and fewer calculation errors.

More complete and detailed process plans.

Improved production scheduling and capacity utilization.

Improved ability to introduce new manufacturing technology and rapidly update processplans to utilize the improved technology.

5

Practical 3 Auto

Documents

Transcript of Practical 3 Auto