What Is Computer-Aided Process Planning (CAPP)?

In this section we introduce the topic of CAPP, and review important components of this technology. Chang and Wysk (1985) define process planning as “machining processes and parameters that are to be used to convert (machine) a workpiece from its initial form to a final form predetermined from an engineering drawing.” Implicit in their definition is the selection of machining resources (machine and cutting tools), the specification of setups and fixturing, and the generation of operation

sequences and numerical control (NC) code. Traditionally, the task of process planning is performed by a human process planner with acquired expertise in machining practices who determines from a part’s engineering drawings what the machining requirements are.

Manual process planning has many drawbacks. In particular, it is a slow, repetitive task that is  prone to error. With industry’s emphasis on automation for improved productivity and quality, computerized CAD and computer-aided manufacturing (CAM) systems which generate the data for driving computer numerical control (CNC) machine tools, are the state-of-the-art. Manual process planning in this context is a bottleneck to the information flow between design and manufacturing.

CAPP is the use of computerized software and hardware systems for automating the process planning task. The objective is to increase productivity and quality by improving the speed and accuracy of process planning through automation of as many manual tasks as possible. CAPP will increase automation and promote integration among the following tasks:

1. Recognition of machining features and the construction of their associated machining volumes from a geometric CAD model of the part and workpiece

2. Mapping machining volumes to machining operations

3. Assigning operations to cutting tools

4. Determining setups and fixturing

5. Selecting suitable machine tools

6. Generating cost-effective machining sequences

7. Determining the machining parameters for each operation

8. Generating cutter location data and finally NC machine code

Traditionally, CAPP has been approached in two ways. These two approaches are variant process planning and generative process planning. In the following section we discuss these and other issues in a review of work in this field.

THE

MECHANICAL

SYSTEMS

DESIGN

HANDBOOK

Modeling, Measurement,

and Control

OSITA D. I. NWOKAH

YILDIRIM HURMUZLU

Southern Methodist University

Dallas, Texas

CRC PRESS

Boca Raton London New York Washington, D.C.

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