Computer Aided Computer Aided Process Planning Process Planning

(CAPP)(CAPP)

What is Process PlanningWhat is Process Planning??

Process planning acts as a bridge Process planning acts as a bridge between design and manufacturing between design and manufacturing by translating design specifications by translating design specifications into manufacturing process detailsinto manufacturing process details

Process PlanProcess Plan

Refers to a set of instructions that are Refers to a set of instructions that are used to used to

make a component or a part so that the make a component or a part so that the design make a component or a part so design make a component or a part so that the design specifications are metthat the design specifications are met

„ „ Determines how a component will be Determines how a component will be manufacturedmanufactured

„ „ „ „ Is a major determinant of Is a major determinant of manufacturing cost and profitability of manufacturing cost and profitability of products products

Basic Steps in Developing a Basic Steps in Developing a Process PlanProcess Plan

1.1. Analysis of part requirementsAnalysis of part requirements2.2. Selection of raw work piece Selection of raw work piece 3.3. Determining manufacturing operations and their Determining manufacturing operations and their

sequencesequence4.4. Selection of machine toolsSelection of machine tools5.5. Selection of tools, work-holding devices, and Selection of tools, work-holding devices, and

inspection equipmentinspection equipment6.6. Determining machining conditions (cutting Determining machining conditions (cutting

speedspeedfeed, depth of cut) and manufacturing times (setup feed, depth of cut) and manufacturing times (setup time, processing time, and lead times)time, processing time, and lead times)

Process Planning Process Planning ApproachesApproaches

„ „ Manual SystemsManual Systems „ „ Computer AidsComputer Aids „ „ Variant SystemsVariant Systems „ „ Experimental Generative SystemsExperimental Generative Systems

Manually Prepared Process Manually Prepared Process PlanningPlanning

„ „ A skilled individual examines a part drawing A skilled individual examines a part drawing to develop the necessary instructions for the to develop the necessary instructions for the process planprocess plan

„ „ Requires knowledge of the manufacturing Requires knowledge of the manufacturing capabilities of the factory (many times capabilities of the factory (many times undocumented) [„ Machine and process undocumented) [„ Machine and process capabilities, tooling, materials, standard capabilities, tooling, materials, standard practices, and associated costs]practices, and associated costs]

„ „ Widely used, time consuming, plans Widely used, time consuming, plans developed over a period of time may not be developed over a period of time may not be consistent nor objectiveconsistent nor objective

„ „ Excessive time and cost may be required to Excessive time and cost may be required to develop develop

necessary skills for successful plannersnecessary skills for successful planners

Computer ApplicationComputer Application “Computer-aided” is a key factor in the integration o� “Computer-aided” is a key factor in the integration o� CAD and CAMCAD and CAM The use of computers in process planning can:� The use of computers in process planning can:� Systematically produce accurate and consistent � Systematically produce accurate and consistent �

process plprocess pl Reduce the cost and lead time of process planning� Reduce the cost and lead time of process planning� Reduce skill requirements of process planners� Reduce skill requirements of process planners� Increase productivity of process planners� Increase productivity of process planners� Interface application programs such as work � Interface application programs such as work �

standards, cost estimation and lead time estimationstandards, cost estimation and lead time estimation Consistently optimize process routings� Consistently optimize process routings� Reduce preproduction lead times� Reduce preproduction lead times� Increase responsiveness to engineering changes� Increase responsiveness to engineering changes�

Variant CAPP MethodologyVariant CAPP Methodology „ „ Recall, identify, and retrieve and existing plan Recall, identify, and retrieve and existing plan

for a similar part and make necessary for a similar part and make necessary modifications similar part and make necessary modifications similar part and make necessary modificationsmodifications

„ „ Interactive environment between the planner Interactive environment between the planner and the Computer and the Computer

Process planning for a new part starts with coding Process planning for a new part starts with coding and classifying the part into a similar family and classifying the part into a similar family

Requires the establishment and maintaining of a Requires the establishment and maintaining of a database of standard process plans that contains database of standard process plans that contains operations, tools, notes, etc.operations, tools, notes, etc.

„ „ Requires recall and editing capabilityRequires recall and editing capability

Variant CAPPVariant CAPP

Variant CAPPVariant CAPP

Variant CAPPVariant CAPPAdvantages:Advantages: „ „ Efficient processing and evaluation of complicated Efficient processing and evaluation of complicated

activities and decisionsactivities and decisions „ „ Standardized proceduresStandardized procedures „ „ Lower development and hardware costsLower development and hardware costs „ „ Shorter development timesShorter development timesDisadvantages:Disadvantages: Inconsistency in editing „Inconsistency in editing „ „ „ Quality is dependent on knowledge and skill of Quality is dependent on knowledge and skill of

plannerplanner „ „ Optimization of variables such as material, Optimization of variables such as material,

geometry, size, precision, quality, alternative geometry, size, precision, quality, alternative processing sequences, and machine loading is difficultprocessing sequences, and machine loading is difficult

Generative CAPP Generative CAPP MethodologyMethodology

„ „ Process plans are automatically generated by means Process plans are automatically generated by means of decision logic, formulas, technology algorithms, and of decision logic, formulas, technology algorithms, and textual and geometry-based datatextual and geometry-based data

„ „ Truly universal system not yet developedTruly universal system not yet developed „ „ There are essentially two major components:There are essentially two major components: „ „ Geometry-basedGeometry-based -- define all geometric features for -- define all geometric features for

all process related surfaces together with feature all process related surfaces together with feature dimensions, locations and tolerances and the surface dimensions, locations and tolerances and the surface finish desired on the locations, and tolerances and the finish desired on the locations, and tolerances and the surface finish desired on the features.surface finish desired on the features.

„ „ Knowledge-basedKnowledge-based -- the automatic matching of part -- the automatic matching of part geometry requirements with the manufacturing geometry requirements with the manufacturing capabilities using process knowledge in the form of capabilities using process knowledge in the form of decision logic and data.decision logic and data.

Sources of Mfg KnowledgeSources of Mfg Knowledge „ „ Acquisition and documentation of Acquisition and documentation of

manufacturing knowledge is not a one-time manufacturing knowledge is not a one-time activity but a recurring process -- the backbone activity but a recurring process -- the backbone of process planningof process planning

„ „ Decision tables are a convenient way to Decision tables are a convenient way to document manufacturing knowledge (Boolean-document manufacturing knowledge (Boolean-type values such as true, false, do not care, etc. type values such as true, false, do not care, etc. or continuous values)or continuous values)

„ „ Decision table elements include:Decision table elements include: ConditionsConditions - state the goal to achieve - state the goal to achieve „ „ ActionsActions - state the operations to perform - state the operations to perform „ „ Rules Rules - establish the relationship between - establish the relationship between

conditions and actionsconditions and actions

Building Decision TablesBuilding Decision Tables „ „ A decision table is partitioned (conditions and A decision table is partitioned (conditions and

decisions) by vertical and horizontal linesdecisions) by vertical and horizontal lines „ „ The portion of the table above the horizontal The portion of the table above the horizontal

lines specifies the condition, and the portion lines specifies the condition, and the portion below those lines indicates the actionbelow those lines indicates the action

„ „ The portion to the left of the vertical lines The portion to the left of the vertical lines contains the stub (or tag), and the portion to the contains the stub (or tag), and the portion to the right, the entries.right, the entries.

„ „ Decision rules are identified by columns in the Decision rules are identified by columns in the entry part of the decisionentry part of the decision

Building Decision Tables: Building Decision Tables: ExampleExample

Construct a decision table for the � Construct a decision table for the �weekend decision that can be weekend decision that can be described as follows:described as follows:

“If it is raining, I will go to the arcade � “If it is raining, I will go to the arcade �and play video games”and play video games”

“If it is not raining and hot, I will go � “If it is not raining and hot, I will go �to the beach”to the beach”

“If it is not raining and cool, I will go � “If it is not raining and cool, I will go �on a picnic with a friend”on a picnic with a friend”

Building Decision Tables: Building Decision Tables: Example SolutionExample Solution

Types of Decision TablesTypes of Decision Tables

Main Considerations in Main Considerations in Decision Tables Decision Tables

ConstructionConstruction

Main Considerations in Main Considerations in Decision Tables Decision Tables

ConstructionConstruction

Main Considerations in Main Considerations in Decision Tables Decision Tables

ConstructionConstruction

Main Considerations in Main Considerations in Decision Tables Decision Tables

ConstructionConstruction

Decision table for the selection Decision table for the selection of machines of turning of machines of turning

operationsoperations

Steps to Create a decision Steps to Create a decision tabletable

1.1. List all conditions in the decision tableList all conditions in the decision table

2.2. Calculate the number of possible Calculate the number of possible combinationscombinations

3.3. Fill columns with all possible combinationsFill columns with all possible combinations

4.4. Insert X where rules suggest certain Insert X where rules suggest certain actionsactions

5.5. Combine rules where it is apparent that an Combine rules where it is apparent that an alternative does not make a difference in alternative does not make a difference in the outcome the outcome

6.6. Check the table for any impossible Check the table for any impossible situation, contradictions and redundancies.situation, contradictions and redundancies.

7.7. Rearrange the table to be more Rearrange the table to be more understandable. understandable.

Step 1: List all conditionsStep 1: List all conditions

Causes Values 1 2 3 4 5 6 7 8Cause 1 Y, N Y Y Y Y N N N NCause 2 Y, N Y Y N N Y Y N NCause 3 Y, N Y N Y N Y N Y NEffectsEffect 1 X X XEffect 2 X X X

Combinations Hints:Hints: Write down the Write down the

values the values the condition/cause can condition/cause can assumeassume

Cluster related Cluster related causescauses

Put the most Put the most dominating cause dominating cause firstfirst

Put multi valued Put multi valued causes lastcauses last

Step 2: Calculate Step 2: Calculate combinationscombinations

Number of Values to the power of the number of conditions with these values

If all conditions are simply Y/N values:If all conditions are simply Y/N values:22number of conditionsnumber of conditions

If 1 condition with 3 values and 3 with If 1 condition with 3 values and 3 with 2:2:3311 * 2 * 233 = 24 = 24

Or, use the Values column and Or, use the Values column and multiply each value down the column, multiply each value down the column, eg. 3*2*2*2=24eg. 3*2*2*2=24

Step 3: Fill columnsStep 3: Fill columnsExample: A decision table is constructed for three conditions as shown in the table:

Conditions and actions 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 year’s Christmas catalog

X X X X

Send out the new specialty catalog X X

Send out both catalogs X X

Step 5: Combine RulesStep 5: Combine RulesRules 2,4,6 and 8 can be combined Rules 2,4,6 and 8 can be combined

because they all have two common because they all have two common things:things:

1.1.The action is to send out this year’s The action is to send out this year’s catalog.catalog.

2.2.The alternative for C3 is always NThe alternative for C3 is always N

It does not matter what the alternatives It does not matter what the alternatives are for C1 & C2, SO we put dashes [-]are for C1 & C2, SO we put dashes [-]

Rules 1 and 5 can be combined, likewise, Rules 1 and 5 can be combined, likewise, rules 3 and 7 can be combined.rules 3 and 7 can be combined.

Step 5: Combine RulesStep 5: Combine 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 year’s Christmas catalog

X X X X

Send out the new specialty catalog

X X

Send out both catalogs X X

Step 5: Combine RulesStep 5: Combine 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 year’s Christmas catalog

X X X X

Send out the new specialty catalog X X

Send out both catalogs X X

Step 5: Combine RulesStep 5: Combine 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 year’s Christmas catalog

X

Send out the new specialty catalog X

Send out both catalogs X

Step 7: Rearrange the tableStep 7: Rearrange the table

Conditions and actions 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 year’s Christmas catalog X

Send out the new specialty catalog X

Send out both catalogs X

Advantages of decision Advantages of decision tablestables

Tables help analyst to ensure Tables help analyst to ensure completeness.completeness.

It easy to check for possible errors, It easy to check for possible errors, impossible situations, contradictions impossible situations, contradictions and redundancies.and redundancies.

Can be taken as input and provide Can be taken as input and provide computer program code as output.computer program code as output.