Chapter 5 ComputerAided Process Planning CAPP

1
Chapter 5Computer-Aided Process Planning (CAPP)
2
Agenda

• Definition of process planning
• Basic steps in developing a process plan
• The principal process planning approaches

3
Definition of Process Planning

• Process planning serves as an integration
  between and
• Process planning refers to a set of that are
  used to a component or a part so that
  the design specifications are met
• Process planning determines component will be
  manufactured

4
Basic Steps in Developing a Process Plan

• Analysis of part
• Selection of raw
• Determining manufacturing and their
• Selection of tools
• Selection of , devices, and equipment
• Determining machining (cutting speed, feed,
  depth of cut) and manufacturing ( setup
  times, processing time, lead time)

5
Step 1 Analysis of Part Requirements

• The part part features, dimensions, and
  tolerance specifications
• Step 1.1 feature analysis
• Step 1.2 dimensional and tolerance analyses

6
Step 2 Selection of Raw Workpiece

• Attributes
• Shape
• Size (dimensions and weight)
• Material

7
Step 3 Manufacturing Operations and Sequences

• Factors influence the
• Accessibility and setup
• Types of machines and tools available
• Batch size
• Surface roughness and tolerance requirements
• Operations are dependent on one another
• Cutting forces and rigidity of the workpiece-tool
  machine tool
• to evaluate the alternatives
• Quality of product produced
• The efficiency of machining

8
Step 4 Selection of Machine Tools

• Factors
• -related attributes kind of feature desired,
  the dimensions of the workpiece, etc.
• tool-related attributes process capability,
  size, tooling capability, etc.
• -related information production
  quantity and order frequency
• Evaluation
• Input information part tolerances, process
  capability of machine tools, processing cost, raw
  material cost, unit salvage value.
• Note unit processing cost depends on the type
  and size of the machine, production volume of
  parts, workpiece-related information
• Output unit cost of production, manufacturing
  lead time and quality ? select the best machine
• Yijk KijkYojk
  
• Ysjk KsjkYojk
• Xojk KijkXijk KsjkXsjkKijkf(Yijk
  )
• Technological coefficient of scrap Ks
  SC/(1-SC) Sc the fraction of scrap
• Technological coefficient of input Ki 1 Ks

9
Example

• Suppose 500 units of a shaft are to be
  manufactured within 10.003 in. Suppose there are
  three alternative machine tools with the
  information given in the following table. Select
  a machine tool to perform turning operation. The
  other data are Unit raw material cost 10,
  unit salvage value 2, process average
  1.0015in.
• Basic data on types of machine tools
• Type SD unit proc. unit proc.
  setup
• cost ()
  time (m) time (m)
• Turret lathe 0.007 7.00 1.00
  15
• Engine lathe 0.001 10.00 0.90
  30
• Auto. Screw 0.0005 15.00 0.70
  60

10
Solution

• Turret lathe
• Zu11 0.21 and Zl11 0.64 . Thus SC
  0.416830.26109 0.67792
• Technological coefficient of scrap Ks
  SC/(1-SC)2.1048
• Technological coefficient of input Ki 1 Ks
  3.1048
• Number of raw units required Yi KiYo 1552.4
  (units)
• Number of units scrapped Ys KsYo 1052.4
  (units)
• Unit output cost Xo KiXi KsXsKif(Yi)
  48.572
• Manufacturing lead time S tYi 151.1552.4
  1567.4 (min)
• Engine lathe
• Number of units scrapped Ys KsYo 33 (units)
• Unit output cost Xo KiXi KsXsKif(Yi) 21.28
• Manufacturing lead time S tYi 510.06 (min)
• Automatic screw machine
• Number of units scrapped Ys KsYo 1 (units)
• Unit output cost Xo KiXi KsXsKif(Yi) 25.03
• Manufacturing lead time S tYi 410.7 (min)

11
Step 5 Selection of Tools, Workholding Devices,
Inspection Equipment

• The selection of machine tools, cutting tools,
  fixtures and inspection equipment is based
  primarily on
• The , , , , and of parts essentially
  determine the types of workholding devices
  required

12
Step 6 Determining Machining Conditions and
Manufacturing Times

• Input information workpiece material, machine
  tool, cutting tool, etc.
• Output optimal machining conditions cutting
  speed (v, m/min), feed (f, mm/rev), depth of cut
  (d, mm)
• Objective reduce cost and increase production
  rate
• Notations
• c0 cost rate including labor and
  overhead(/min)
• ct tool cost per cutting edge
• t1 non productive time (loading, unloading
  part, idle)(min)
• tc machining time per piece (min/piece)
• td time to change a cutting edge (min)
• tac actual cutting time per piece (min/piece)
• T tool life (min)

13
Minimum Cost per Piece

• Cost per component, Cu nonproductive cost per
  piece machining time cost per piece tool
  changing cost per piece tooling cost per piece
• The feed rate and depth of cut are normally fixed
  to their allowable values, optimum cutting speed
• Optimal tool life

14
Maximum Production Rate

• Time per piece, Tu nonproductive time per piece
  cost of machining time per piece tool
  changing time per piece
• Optimal solution
• Manufacturing lead time major setup time TuQ.
  
• Example 5.2 (reading)

15
The Principal Process Planning Approaches

• The manual -based planning method
• The method
• The CAPP method
• The CAPP method
• process planning

16
The Manual Experience-Based Method

• Basic steps
• Analysis of part requirements
• Selection of raw workpiece
• Determining manufacturing operations and their
  sequences
• Selection of machine tools
• Selection of tools, workholding devices, and
  inspection equipment
• Determining machining conditions and
  manufacturing times processing
• Problems
• Time consuming
• Inconsistent plans
• Take long time and high cost to develop skill of
  a successful planner

17
The CAPP Method

• A multiple of interactions among various
  functions of an organization and dynamic changes
  require to use in process planning (e.g.
  machine break down, design change, etc.)
• Advantages
• Produce accurate and consistent plans
• Reduce cost and lead time
• Reduce skill requirements
• Increase productivity of process planers
• user friendly interface sub-programs cost and
  lead time estimation, work standards.

18
A CAPP Framework
19
The Variant CAPP Method

• A process plan for a new part is created by
  recalling, identifying, and retrieving an for
  a similar part and making for the new
  part
• Process plans are developed for parts
  representing a family of parts ( )
• Steps
• Define the coding scheme classification
• Group the parts into part families
• Develop a standard process plan
• Retrieve and modify the standard plan

20
The Variant CAPP Method

• Advantages
• Reduce time and labor requirements
• Standardized procedures
• Lower development and hardware costs and shorter
  development times
• Disadvantages
• Maintaining consistency in editing is difficult
• Adequately accommodating various combinations of
  factors is difficult
• Dependent on the experience of process planners
• Existing systems CAM-I, MIPLAN

21
The Generative CAPP Method

• Process plans are generated by means of , ,
  , and to perform uniquely the processing
  decisions
• Components
• Geometry-based coding scheme define all
  geometric features.
• Process knowledge in the form of decision logic
  and data perform all activities of process
  planning automatically
• Tools for developing a good manufacturing
  knowledge structure flowcharts, decision trees,
  decision tables, iterative algorithms, expert
  system shells, etc.

22
Knowledge-Based Process Planning

• A computer program that can store the
  manufacturing and use that knowledge to
  the decision process of a human expert
• Problems
• The knowledge representation a real-world
  problem representation scheme by which computer
  can manipulate the information
• The inference mechanism the way in which the
  computer finds the solution. e.g. IF-THEN
• A knowledge-Based System EXPLAN