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Computer Aided Process Planning (CAPP)

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Computer Aided Process Planning ... and inspection equipment Determining machining conditions (cutting speed feed, depth of cut) and manufacturing times ... – PowerPoint PPT presentation

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Title: Computer Aided Process Planning (CAPP)


1
Computer Aided Process Planning (CAPP)
2
What is Process Planning?
  • Process planning acts as a bridge between design
    and manufacturing by translating design
    specifications into manufacturing process details

3
Process Plan
  • Refers to a set of instructions that are used to
  • make a component or a part so that the design
    make a component or a part so that the design
    specifications are met
  • ? Determines how a component will be manufactured
  • ? ? Is a major determinant of manufacturing cost
    and profitability of products

4
Basic Steps in Developing a Process Plan
  • Analysis of part requirements
  • Selection of raw work piece
  • Determining manufacturing operations and their
    sequence
  • Selection of machine tools
  • Selection of tools, work-holding devices, and
    inspection equipment
  • Determining machining conditions (cutting speed
  • feed, depth of cut) and manufacturing times
    (setup
  • time, processing time, and lead times)

5
Process Planning Approaches
  • ? Manual Systems
  • ? Computer Aids
  • ? Variant Systems
  • ? Experimental Generative Systems

6
Manually Prepared Process Planning
  • ? A skilled individual examines a part drawing to
    develop the necessary instructions for the
    process plan
  • ? Requires knowledge of the manufacturing
    capabilities of the factory (many times
    undocumented) ? Machine and process
    capabilities, tooling, materials, standard
    practices, and associated costs
  • ? Widely used, time consuming, plans developed
    over a period of time may not be consistent nor
    objective
  • ? Excessive time and cost may be required to
    develop
  • necessary skills for successful planners

7
Computer Application
  • ? Computer-aided is a key factor in the
    integration o
  • CAD and CAM
  • ? The use of computers in process planning can
  • ? Systematically produce accurate and consistent
    process pl
  • ? Reduce the cost and lead time of process
    planning
  • ? Reduce skill requirements of process planners
  • ? Increase productivity of process planners
  • ? Interface application programs such as work
    standards, cost estimation and lead time
    estimation
  • ? Consistently optimize process routings
  • ? Reduce preproduction lead times
  • ? Increase responsiveness to engineering changes

8
Variant CAPP Methodology
  • ? Recall, identify, and retrieve and existing
    plan for a similar part and make necessary
    modifications similar part and make necessary
    modifications
  • ? Interactive environment between the planner and
    the Computer
  • Process planning for a new part starts with
    coding and classifying the part into a similar
    family
  • Requires the establishment and maintaining of a
    database of standard process plans that contains
    operations, tools, notes, etc.
  • ? Requires recall and editing capability

9
Variant CAPP
10
Variant CAPP
11
Variant CAPP
  • Advantages
  • ? Efficient processing and evaluation of
    complicated activities and decisions
  • ? Standardized procedures
  • ? Lower development and hardware costs
  • ? Shorter development times
  • Disadvantages
  • Inconsistency in editing ?
  • ? Quality is dependent on knowledge and skill of
    planner
  • ? Optimization of variables such as material,
    geometry, size, precision, quality, alternative
    processing sequences, and machine loading is
    difficult

12
Generative CAPP Methodology
  • ? Process plans are automatically generated by
    means of decision logic, formulas, technology
    algorithms, and textual and geometry-based data
  • ? Truly universal system not yet developed
  • ? There are essentially two major components
  • ? Geometry-based -- define all geometric features
    for all process related surfaces together with
    feature dimensions, locations and tolerances and
    the surface finish desired on the locations, and
    tolerances and the surface finish desired on the
    features.
  • ? Knowledge-based -- the automatic matching of
    part geometry requirements with the manufacturing
    capabilities using process knowledge in the form
    of decision logic and data.

13
Sources of Mfg Knowledge
  • ? Acquisition and documentation of manufacturing
    knowledge is not a one-time activity but a
    recurring process -- the backbone of process
    planning
  • ? Decision tables are a convenient way to
    document manufacturing knowledge (Boolean-type
    values such as true, false, do not care, etc. or
    continuous values)
  • ? Decision table elements include
  • Conditions - state the goal to achieve
  • ? Actions - state the operations to perform
  • ? Rules - establish the relationship between
    conditions and actions

14
Building Decision Tables
  • ? A decision table is partitioned (conditions and
    decisions) by vertical and horizontal lines
  • ? The portion of the table above the horizontal
    lines specifies the condition, and the portion
    below those lines indicates the action
  • ? The portion to the left of the vertical lines
    contains the stub (or tag), and the portion to
    the right, the entries.
  • ? Decision rules are identified by columns in the
    entry part of the decision

15
Building Decision Tables Example
  • ? Construct a decision table for the weekend
    decision that can be described as follows
  • ? If it is raining, I will go to the arcade and
    play video games
  • ? If it is not raining and hot, I will go to the
    beach
  • ? If it is not raining and cool, I will go on a
    picnic with a friend

16
Building Decision Tables Example Solution
17
Types of Decision Tables
18
Main Considerations in Decision Tables
Construction
19
Main Considerations in Decision Tables
Construction
20
Main Considerations in Decision Tables
Construction
21
Main Considerations in Decision Tables
Construction
22
Decision table for the selection of machines of
turning operations
23
Steps to Create a decision table
  1. List all conditions in the decision table
  2. Calculate the number of possible combinations
  3. Fill columns with all possible combinations
  4. Insert X where rules suggest certain actions
  5. Combine rules where it is apparent that an
    alternative does not make a difference in the
    outcome
  6. Check the table for any impossible situation,
    contradictions and redundancies.
  7. Rearrange the table to be more understandable.

24
Step 1 List all conditions
  • Hints
  • Write down the values the condition/cause can
    assume
  • Cluster related causes
  • Put the most dominating cause first
  • Put multi valued causes last

25
Step 2 Calculate combinations
Number of Values to the power of the number of
conditions with these values
  • If all conditions are simply Y/N values2number
    of conditions
  • If 1 condition with 3 values and 3 with 231
    23 24
  • Or, use the Values column and multiply each value
    down the column, eg. 322224

26
Step 3 Fill columns
Example A decision table is constructed for
three conditions as shown in the table
Conditions and actions Rules Rules Rules Rules Rules Rules Rules Rules
1 2 3 4 5 6 7 8
Customer ordered from fall catalog Y Y Y Y N N N N
Customer ordered from Christmas catalog Y Y N N Y Y N N
Customer ordered from specialty catalog Y N Y N Y N Y N
Send out this years Christmas catalog X X X X
Send out the new specialty catalog X X
Send out both catalogs X X
27
Step 5 Combine Rules
  • Rules 2,4,6 and 8 can be combined because they
    all have two common things
  • The action is to send out this years catalog.
  • The alternative for C3 is always N
  • It does not matter what the alternatives are for
    C1 C2, SO we put dashes -
  • Rules 1 and 5 can be combined, likewise, rules 3
    and 7 can be combined.

28
Step 5 Combine Rules
Rules Rules Rules Rules Rules Rules Rules Rules
Conditions and actions 1 2 3 4 5 6 7 8
Customer ordered from fall catalog Y Y Y Y N N N N
Customer ordered from Christmas catalog Y Y N N Y Y N N
Customer ordered from specialty catalog Y N Y N Y N Y N
Send out this years Christmas catalog X X X X
Send out the new specialty catalog X X
Send out both catalogs X X
29
Step 5 Combine Rules
Rules Rules Rules Rules Rules Rules Rules Rules
Conditions and actions 1 2 3 4 5 6 7 8
Customer ordered from fall catalog - - - - - - - -
Customer ordered from Christmas catalog Y - N - Y - N -
Customer ordered from specialty catalog Y N Y N Y N Y N
Send out this years Christmas catalog X X X X
Send out the new specialty catalog X X
Send out both catalogs X X
30
Step 5 Combine Rules
Rules Rules Rules Rules Rules Rules Rules Rules
Conditions and actions 1 2 3
Customer ordered from fall catalog - - -
Customer ordered from Christmas catalog Y - N
Customer ordered from specialty catalog Y N Y
Send out this years Christmas catalog X
Send out the new specialty catalog X
Send out both catalogs X
31
Step 7 Rearrange the table
Conditions and actions Rules Rules Rules
1 2 3
Customer ordered from fall catalog - - -
Customer ordered from Christmas catalog Y - N
Customer ordered from specialty catalog Y N Y
Send out this years Christmas catalog X
Send out the new specialty catalog X
Send out both catalogs X
32
Advantages of decision tables
  • Tables help analyst to ensure completeness.
  • It easy to check for possible errors, impossible
    situations, contradictions and redundancies.
  • Can be taken as input and provide computer
    program code as output.
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