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7.15 - Computer Aided Process Planning & Estimating Systems (CAPPES)


The process plan (manufacturing layout or process routing) is a key document holding manufacturing information. The use of Computer Aided Process Planning (CAPP) in parallel with the CAD process enables this document to become a ‘live’ store of manufacturing data.

Traditional Process Planning Characteristics

Traditional process planning has the following characteristics which lead to a long lead times, inconsistency and unnecessary overheads.

  • High manual & clerical content
  • Repetition of similar or identical decisions in many routine tasks
  • Depends on experience and judgement of planning engineer
  • Knowledge ‘locked up’ in planning engineers heads and their ‘black books’

CAPP Characteristics

CAPP has the following characteristics, with the benefits of shorter lead times and reduced costs.

  • Use of standard routings
  • Frees planners from clerical effort
  • Enables optimisation of manufacturing systems designs via techniques such as:
    • Group Technology,
    • Rank Order Clustering,
    • Process Flow Analysis and
    • From-To-Charting
    • Shorter lead times
  • Process rationalisation
  • Increased productivity of process planners
  • Ability to interface with other application programs
  • Best practice is used in every plan

Types of CAPP System

There are three types CAPP systems:

Basic Systems

These CAPP systems are, in essence, word processors dedicated to a standard manufacturing flowcharting layout format. The main advantages of this system over manual, purely paper based systems, is the speed with which layouts can be modified or corrected. This has an associated reduction in clerical effort. Standard FMEA spreadsheet grids integrate well with such systems.

Variant or Retrieval Systems

These CAPP systems generally have the following characteristics:

  • Part classification and coding
  • Standard process plan for each part family.
  • New components coded and appropriate standard process plan accessed with editing as necessary
  • Machine routings may be the same, but specific operations may vary
  • Complete plan must document operations as well as sequence of machines

The diagram shows the logic of a typical variant CAPP system.

Generative Systems

This type of CAPP system generally has the following features:

  • Computer creates an individual process plan automatically with operator
  • Employs a set of algorithms/decision tables to progress through technical and logical decisions towards a final manufacturing layout
  • Requires comprehensive component descriptions to be input
  • Concept of Expert Systems employing Artificial Intelligence

The five main elements of a CAPP system are:

  • Component, product and tooling classification, grouping and coding system (e.g. Opitz)
  • Computer aided process analysis and specification
  • Time standards
  • Manufacturing engineering database, files, logic processor, standard form for process flow routing, tool kit lists, manufacturing operation sheets and quality profile support/diagnostics data
  • Distributed communication system serving business and cell management, manufacturing development and operations engineering functions and product costing functions.


This description of CAPP systems is somewhat dated and needs a modern technology update as they can now be directly linked to CAD via solid modelling capabilities. Also they shorten the cycle – time of provision of cost estimates to design engineers. See Process Selection – guide 6.16