Computer Aided Process Planning (CAPP)

What is Process Planning? Process planning acts as a bridge between design and manufacturing by translating design specifications into manufacturing process details Process planning acts as a bridge between design and manufacturing by translating design specifications into manufacturing process details

Process Plan Refers to a set of instructions that are used to 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 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 „ Determines how a component will be manufactured „ „ Is a major determinant of manufacturing cost and profitability of products „ „ Is a major determinant of manufacturing cost and profitability of products

Basic Steps in Developing a Process Plan 1. Analysis of part requirements 2. Selection of raw work piece 3. Determining manufacturing operations and their sequence 4. Selection of machine tools 5. Selection of tools, work-holding devices, and inspection equipment 6. Determining machining conditions (cutting speed feed, depth of cut) and manufacturing times (setup time, processing time, and lead times)

Process Planning Approaches „ Manual Systems „ Manual Systems „ Computer Aids „ Computer Aids „ Variant Systems „ Variant Systems „ Experimental Generative Systems „ Experimental Generative Systems

Manually Prepared Process Planning „ A skilled individual examines a part drawing to develop the necessary instructions for the process plan „ 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] „ 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 „ 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 „ Excessive time and cost may be required to develop necessary skills for successful planners necessary skills for successful planners

Computer Application „ “Computer-aided” is a key factor in the integration o „ “Computer-aided” is a key factor in the integration o CAD and CAM CAD and CAM „ The use of computers in process planning can: „ The use of computers in process planning can: „ Systematically produce accurate and consistent process pl „ Systematically produce accurate and consistent process 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 standards, cost estimation and lead time estimation „ Interface application programs such as work standards, 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 Methodology „ Recall, identify, and retrieve and existing plan for a similar part and make necessary modifications similar part and make necessary modifications „ 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 „ 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 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 the establishment and maintaining of a database of standard process plans that contains operations, tools, notes, etc. „ Requires recall and editing capability „ Requires recall and editing capability

Variant CAPP

Advantages: „ Efficient processing and evaluation of complicated activities and decisions „ Efficient processing and evaluation of complicated activities and decisions „ Standardized procedures „ Standardized procedures „ Lower development and hardware costs „ Lower development and hardware costs „ Shorter development times „ Shorter development timesDisadvantages: Inconsistency in editing „ Inconsistency in editing „ „ Quality is dependent on knowledge and skill of planner „ 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 „ Optimization of variables such as material, geometry, size, precision, quality, alternative processing sequences, and machine loading is difficult

Generative CAPP Methodology „ Process plans are automatically generated by means of decision logic, formulas, technology algorithms, and textual and geometry-based data „ 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 „ Truly universal system not yet developed „ There are essentially two major components: „ 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. „ 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. „ Knowledge-based -- the automatic matching of part geometry requirements with the manufacturing capabilities using process knowledge in the form of decision logic and data.

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 „ 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 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: „ Decision table elements include: Conditions - state the goal to achieve Conditions - state the goal to achieve „ Actions - state the operations to perform „ Actions - state the operations to perform „ Rules - establish the relationship between conditions and actions „ Rules - establish the relationship between conditions and actions

Building Decision Tables „ A decision table is partitioned (conditions and decisions) by vertical and horizontal lines „ 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 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. „ 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 „ Decision rules are identified by columns in the entry part of the decision

Building Decision Tables: Example „ Construct a decision table for the weekend decision that can be described as follows: „ 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 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 hot, I will go to the beach” „ “If it is not raining and cool, I will go on a picnic with a friend” „ “If it is not raining and cool, I will go on a picnic with a friend”

Building Decision Tables: Example Solution

Types of Decision Tables

Main Considerations in Decision Tables Construction

Decision table for the selection of machines of turning operations

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.

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

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 values: 2 number of conditions If all conditions are simply Y/N values: 2 number of conditions If 1 condition with 3 values and 3 with 2: 3 1 * 2 3 = 24 If 1 condition with 3 values and 3 with 2: 3 1 * 2 3 = 24 Or, use the Values column and multiply each value down the column, eg. 3*2*2*2=24 Or, use the Values column and multiply each value down the column, eg. 3*2*2*2=24

Step 3: Fill columns Example: A decision table is constructed for three conditions as shown in the table: Conditions and actionsRules Customer ordered from fall catalogYYYYNNNN Customer ordered from Christmas catalogYYNNYYNN Customer ordered from specialty catalogYNYNYNYN Send out this year’s Christmas catalogXXXX Send out the new specialty catalogXX Send out both catalogsXX

Step 5: Combine Rules Rules 2,4,6 and 8 can be combined because they all have two common things: 1. The action is to send out this year’s catalog. 2. 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.

Step 5: Combine Rules Rules Conditions and actions Customer ordered from fall catalogYYYYNNNN Customer ordered from Christmas catalog YYNNYYNN Customer ordered from specialty catalog YNYNYNYN Send out this year’s Christmas catalogXXXX Send out the new specialty catalogXX Send out both catalogsXX

Step 5: Combine Rules Rules Conditions and actions Customer ordered from fall catalog Customer ordered from Christmas catalog Y-N-Y-N- Customer ordered from specialty catalogYNYNYNYN Send out this year’s Christmas catalogXXXX Send out the new specialty catalogXX Send out both catalogsXX

Step 5: Combine Rules Rules Conditions and actions123 Customer ordered from fall catalog--- Customer ordered from Christmas catalog Y-N Customer ordered from specialty catalogYNY Send out this year’s Christmas catalogX Send out the new specialty catalogX Send out both catalogsX

Step 7: Rearrange the table Conditions and actionsRules 123 Customer ordered from fall catalog--- Customer ordered from Christmas catalogY-N Customer ordered from specialty catalogYNY Send out this year’s Christmas catalogX Send out the new specialty catalogX Send out both catalogsX

Advantages of decision tables Tables help analyst to ensure completeness. Tables help analyst to ensure completeness. It easy to check for possible errors, impossible situations, contradictions and redundancies. It easy to check for possible errors, impossible situations, contradictions and redundancies. Can be taken as input and provide computer program code as output. Can be taken as input and provide computer program code as output.