IE458CAM Computer Aided Manufacturing Part-4 Process Planning Dr. Abdulrahman Al-Ahmari Industrial Engineering Department King Saud University.

IE458 CAMComputer Aided Manufacturing

Part-4Process Planning

Dr. Abdulrahman Al-Ahmari

Industrial Engineering Department

King Saud University

Process Planning Process planning is also called: manufacturing planning, process planning, material processing, process engineering, and machine routing.

Process Planning: is the function within manufacturing facility that establishes which processes and parameters are to be used to convert a part from its initial form to a final form predetermined in an engineering drawing. Process planning can be defined as: the act of preparing detailed work instructions to produce a part.

Design MachineTool

Scheduling and Production Control

Process

Planning

The person who develops the process plan for producing a workpiece is often called the process planner.

 The functions included in process planning are:

  - Raw material preparation

- Processes selection

- Process sequencing

- Machining parameter selection

- Tool path planning

- Machine selection

- Fixture selection

Factors affecting process Plan selection

•Shape

•Tolerance

•Surface finish

• Size

•Material type

• Quantity

•Value of the product

•Urgency

•Manufacturing system itself

•etc.

There are two approaches to carrying out the task of process planning:  1- Manual Process Planning

2- Computer Aided Process Planning (CAPP).:VARIANT

GT based

Computer aids for editing

Parameters selection

GENERATIVE

Some kind of decision logic

Decision tree/table

Artificial Intelligence

Objective-Oriented

Still experience based

AUTOMATIC

Design understanding

Geometric reasoning capability

Manual Process Planning In order to prepare a process plan, a process planner has to have the following

knowledge:1. Ability to interpret an engineering drawing.2. Familiarity with manufacturing processes and practice.3. Familiarity with tooling and fixtures.4. Know what resources are available in the shop.5. Know how to use reference books, such as machinability data

handbooks.6. Ability to do computations on machining time and cost.7. Familiarity with the raw materials.

To prepare a process plan, the following are some steps that have to be taken:

•Study the overall shape of the part, to identify features and all critical dimensions.

•Thoroughly study the drawing. Try to identify all manufacturing features and notes.

•Determine the best raw material shape to use if raw stock is not given.

•Identify datum surfaces. Use information on datum surfaces to determine the setups.

•Select machines for each setup.

•Determine the rough sequence of operations necessary to create all the features for each setup.

•Sequence the operations determined in the previous step. Check whether there is any interference or dependency between operations. Use this information to modify the sequence of operations.

•Select tools for each operation. Try to use the same tool several operations if possible. Keep in mind the trade-off on tool-change time and estimated machining time.

•Select or design fixtures for each setup.

•Evaluate the plan generated thus for and make necessary modifications.

•Select cutting parameters for each operation.

PROCESS PLAN• Also called : operation sheet, route sheet, operation planning summary, or

another similar name.

• The detailed plan contains:

route

processes

process parameters

machine and tool selections

fixtures

• How detail the plan is depends on the application.

• Operation: a process

• Operation Plan (Op-plan): contains the description of an operation, includes tools, machines to be used, process parameters, machining time, etc.

• Op-plan sequence: Summary of a process plan.

Example process plans

Route Sheet

Part No. S1243Part Name: Mounting Bracket

1. Mtl Rm2. Mill02 5 3. Drl01 44. Insp 1

workstation Time(min)

by: T.C. Chang

PROCESS PLAN ACE Inc.

Part No. S0125-FPart Name: HousingOriginal: S.D. Smart Date: 1/1/89Checked: C.S. Good Date: 2/1/89

Material: steel 4340Si

Changes: Date: Approved: T.C. Chang Date: 2/14/89

No. OperationDescription

Workstation Setup Tool Time(Min)

10 Mill bottom surface1 MILL01 see attach#1for illustration

Face mill6 teeth/4" dia

3 setup5 machining

20 Mill top surface MILL01 see attach#1 Face mill6 teeth/4" dia

2 setup6 machining

30 Drill 4 holes DRL02 set on surface1 twist drill1/2" dia2" long

2 setup3 machining

Detailed plan

Rough plan

Study of the Part Drawing The part drawing provides the following features:•Basic form and size of the workpiece.•Outer envelop of the workpiece.•Part features (shapes) to be produced.•Dimensional and geometric tolerances.•Required surface finish (roughness).•Datum surfaces for setup and measurement.•Material of the workpiece.

The information needed to prepare part drawing for NC include:•The type of coordinate systems offered by the machine tool.•Machine datum systems.•Selection of the program datum (zero).•Machine envelope.•Machine operation capacity (spindle speed, feed, tolerance, and accuracy).

-A-

Datum SelectionA datum is a specific surface, line, plane, or other feature that is assumed to be perfect and is used as a reference point for dimensions or features.A workpiece datum: can be defined as point, line , surface, or cylinder from which dimensions are referenced.The following examples may be used as guidelines for selecting datum surfaces:1.      Important surfaces to the function of the workpiece or he assembly.2.      Reference planes for mating parts of an assembly.3.      Previously machined surfaces.4.      Surfaces that are easy to establish at the machine tool.5.      Surfaces that are parallel to machine movements. A datum can be explicitly or implicitly indicated in the part drawing. A datum is normally called out by an identification symbol such as:

Considerations for Raw MaterialThe features of raw material have a significant effect on:       1.         The amount of material to be removed       2.         The ease of workholding        3.         Machine efficiency The raw material of a part can be prepared from the standard commercially available stock, or it may be a casting or forging in which the rough shape and size have been formed. Commercially available stock appears in the following forms:•Bars (round, square, hexagonal, octagonal, flat, triangular, and half-round)•Plates•Sheets and coils•Pipes and tubes•Structural shapes (beams, angles, tees, zees, and channels)

In preparing raw material from standard stock, the following rules should be followed:

1. Make optimal use of the stock to minimize the amount of removed or wasted material.

2. Premachine datum surfaces with a manually operated machine, if possible, to facilitate the workholding setup.

3. Prepare the raw material drawing.

Part Features Identification and Processes Selection A wide variety of manufacturing processes are used to produce a workpiece. These processes can be classified as:·        Casting processes·        Forming and shaping processes·        Machining processes·        Joining processes·        Finishing processes The machining processes include:·        Drilling (drilling, countering, countersinking, deep-hole drilling, etc.)·        Boring·        Tapping·        Milling (face milling, end milling)·        Turning (facing, straight turning, taper turning, parting, etc.)·        Threading.

Many features must be considered in selecting machining processes. They include:       1.         Part features       2.         Required dimensional and geometric accuracy and tolerance       3.         Required surface finish       4.         Available resources, including NC machines and cutting tools       5.         Cost

Part featuresA part feature is the distinctive geometric form or shape to be produced from

raw material; thus it determines process type, tool types (shapes and size), machine requirements (3-, 4-, or 5-axis), and tool path.

  There are two types of part features:1. Basic features: are those simple forms or shapes that may require only

one machining operation. They include holes, slots, pockets, shoulders, profiles, and angles.

2. Compound features: are those that consist of two or more basic part features. For example, the combined result of two holes with different diameters.

Basic part features and their processes

EXAMPLE: MACHINING PROCESSES SELECTION

Select the machining processes for the part shown in the Figure. Assume that the required dimensional accuracy and surface roughness are within the process capability of drilling and milling operations. The four sides of the raw material have been premachined to the required dimensions.

 Solution Three part features can be identified from the part drawing: •Top flat surface •Outer profile •Three holes The recommended machining processes for these features are •Face-milling the top surface •Rough-milling the outer profile•Finish-milling the outer profile•Center-drilling the three holes •Drilling the three holes

PROCESSES SEQUENCING

 The sequence of operations is determined by the following three considerations:

1. Datum surfaces should be machined first if multiple workholding setups are required. If possible, datum surfaces should be premachined in a manually operated machine to facilitate work-piece locating and clamping. In those cases where two or more holding setups are requi red, rough datum surfaces are preprocessed in a manually operated machine and then used as setup references to produce finished datum surfaces for the final workholding. This ensures the accuracy of the finished part.

2. Surfaces with larger area have precedence. Larger surfaces tend to be more adaptable to disturbances resulting from machining operations.

3. Feature interference should be avoided. Feature interference occurs when the machining of one feature destroys a requirement for the production of other features. This happens when there is interaction or dependency between machining operations.

EXAMPLE:PROCESSES SEQUENCING

Figure below shows a workpiece in which some features are interrelated. The workpiece has five basic features: a through slot in side C, two angle strips, and two through holes on strip 1 that are perpendicular to side A. The compound features are two tapped holes perpendicular to strip 1. Develop the process sequence for producing the part.

Solution The raw material is cut from a block stock with dimensions 6.25 x 4.25 x 2.25

in. Studying the part features reveals that the two through holes on strip 1 interact with the formation of angle and the slot in side C interacts with the cutting of angle . Machining angle strip 1 first will cause difficulty in drilling the two holes, so the two holes must be produced before angle strip 1. Likewise, making angle strip 2 first will cause difficulty in setting up the workpiece to produce the through slot, so the slot has to be machined before angle strip 2 is made.

 The recommended processes sequence is described below: 1. Setup A for machining side B 2. Setup B for machining sides A and E as well as drilling two holes on Side A3. Setup C for machining sides C and F as well as cutting the slot in side C 4. Setup D for cutting, angle strip 1, drilling two tap holes, and tapping the two

holes 5. Setup E for cutting angle strip 2

Manual Process Planning Examples

Computer Aided Process Planning

Advantages: • It can reduce the skill required of a planner. • It can reduce process-planning time. • It can reduce both process-planning and

manufacturing costs.• It can create more consistent plans.• It can produce more accurate plans.• It can increase productivity.

Two approaches for computer-aided process planning have been pursued:

1. Variant CAPP method2. Generative CAPP method The variant approach uses library retrieval procedures to

find standard plans for similar components. The standard plans are created manually by process planners.

 The generative approach is considered more advanced as

well as more difficult to develop. In a generative process-planning system, process plans are generated automatically for new components without referring to existing plans.

A typical process planning system

Process planning modules and

databases

Process planning is the critical bridge between design and manufacturing (Figure 3). Design information can be translated into manufacturing language only through process planning. Today, both computer-aided design (CAD) and manufacturing (CAM) have been implemented. Integrating, or bridging, these functions requires automated process planning.

Figure 3. Process planning bridges design and manufacturing.

VARIANT PROCESS PLANNING A variant process planning system uses the similarity among components to retrieve existing process plans. A process plan that can be used by a family of components is called a standard plan. A standard plan is stored permanently in the database with a family number as its key. There is no limitation to the detail that a standard plan can contain. However, it must contain at least a sequence of fabrication steps or operations. When a standard plan is retrieved, a certain degree of modification is usually necessary in order to use the plan on a new component.  The retrieval method and the logic in variant systems are predicated on the grouping of parts into families. Common manufacturing methods then can be identified for each family. Such common manufacturing methods are represented by standard plans.  The mechanism of standard plan retrieval is based on part families. A family is represented by a family matrix that includes all possible members.  In general, variant process planning systems have two operational stages: a preparatory stage and a production stage.

The Preparatory Stage Preparatory work is required when a company first starts implementing a variant system. During the preparatory stage, existing components are coded, classified, and subsequently grouped into families. The first step is to choose an appropriate coding system. The coding system must cover the entire spectrum of parts produced in the shop. It must be unambiguous and easy to understand. Special features that exist on the parts must be clearly identified by the coding system. An existing coding system may be adopted and then modified for a specific shop. The coding of existing components can be a tedious task. Before it can be done, a thorough study of the inventory of drawings and process plans has to be completed so that an orderly coding task can be conducted. The personnel involved in coding must have a precise understanding of the coding system. They must generate identical code for the same component when they work independently. Inconsistent coding of components results in redundant and erroneous data in the database.  After coding is completed, part families can be formed. The techniques of grouping part families are discussed in GT. A family matrix is then constructed for each part family. Due to the large number of components involved, a computer should be used to help construct family matrices. The next step is to prepare standard process plans for part families. By summarizing the process plans, a set of standard operation plans (OP plans) can be identified. An operation plan contains a sequence of manufacturing operations that are normally performed together in a workstation. An identifier, an OP code, is assigned to each OP plan. A standard process plan is written in terms of OP codes and OP plans. Standard plans are then stored in a database and indexed by family matrices (Figure 4). In many systems, individual process plans are also stored in the database. However, only plans for frequently produced parts are stored. The preparatory stage is a labor-intensive process. It requires a tremendous amount of effort. Whatever is prepared for shop A can be used only for shop A. The system structure and software can be used by other shops, but the database must be prepared uniquely by and for each shop.

Figure 4. The preparatory stage.

The Production Stage The production stage occurs when the system is ready for use. New components now can be planned. An incoming component is first coded. The code is then input to a part- family search routine to find the family to which the component belongs. The family number is then used to retrieve a standard plan. The human planner may modify the standard plan to satisfy the component design. For a frequently produced part, it might be desirable to perform the search by direct code matching. In this case, a process plan (not a standard plan) for an existing part is retrieved. Figure 5 shows the flow of the production stage. Some other functions, such as parameter selection and standard time calculations, can also be added to make the system more complete.

Figure 5. The production stage

Problems associated with the variant approach1. The components to be planned are limited to similar components

previously planned.2. Experienced process planners are still required to modify the standard

plan for the specific component.3. Details of the plan cannot be generated.4. Variant planning cannot be used in an entirely automated

manufacturing system, without additional process planning.

Advantages of the variant approach1. Once a standard plan has been written, a variety of components can be

planned.2. Comparatively simple programming and installation (compared with

generative systems) is required to implement a planning system.3. The system is understandable, and the planner has control of the final

plan.4. It is easy to learn, and easy to use.

Variant CAPP

AN EXAMPLE OF A VARIANT PLANNING SYSTEM An example illustrates the step-by-step construction of a variant process-

planning system. A simplified coding system is used.  The code table is shown in Table 1. Because it is overly simplified for

illustration purposes, this system lacks detail and is not appropriate for actual application. However, it is sufficient to represent the principles of coding for process planning. We call our coding system S-CODE (Simple CODE) and the process-planning system VP (Variant Planning).

 VP is used in a machine shop that produces a variety of small components.

These components range from simple shafts to delicate hydraulic-pump parts. We discuss the construction of VP in the following sequence:

 1. Family formation 2. Database structure 3. Search algorithm 4. Plan editing 5. Process-parameter selection

1. Family Formation In a process-planning system, family formation is based on production parts or, more specifically, their manufacturing features. Components requiring similar processes are grouped into the same family. In GT, different ways to group parts into families are presented. Similar methods can be used for a variant process-planning system. The family matrix must then be represented in a manner that is consistent with the S-CODE. A part-family matrix is a binary matrix similar to a PFA matrix.  We can use Pl

ij to represent a part-family matrix for family l, i= 1, . . . , I, where I is the number of attributes in each code position, and j = 1, J, where J is the number of digits (code length).

In the S-CODE, I is equal to 8 and J is equal to 4. Plij implies that,

for part family l, code position j is allowed to have a value i.  A part-family matrix can be constructed in the following manner.

Let Cklj be the value of code position j for component k in family l, k = 1,

. . . , K (K is the number of components). For k : = 1 to K

For j: = 1 to Ji=Ckl

j

P1ij=1

enddoEnddo

Using this procedure, we can obtain a part-family matrix for family 1 (Figure 6) Thus far, we have a complete set of OP code sequences, OP plans, and a family matrix. The next step is to store them in a computer-interpretable format so that the information can be used later for new components.

Table 1. S-CODE

Figure 6. A part-family matrix

2 Database Structure

 The VP system contains only a small amount of information as compared to an industrial application, where thousands of components and process plans usually have to be stored and retrieved. Because of the large amount of information, database systems play an important role in variant process planning. A database is no more than a group of cross-referenced data files. The database contains all the necessary information for an application and can be accessed to by several different programs for specific applications. There are three approaches to construct a database: hierarchical, network, and relational. Although the concept and structure for these approaches are very different, they can serve the same purpose.

 For commercial programming, there are several available database management systems, such as CODASYL, ORACLE, ACCESS, dBASE, and Lotus 1-2-3. These systems are high-level languages for database construction and manipulation. Of course, a database can always be written using procedural languages such as COBOL, FORTRAN, and C. No matter what approach and language are used, the basic structure of the database is the same.

The hierarchical approach is used to construct the database in the design of the VP system. Figure 7 shows the hierarchy of the data. Each family is accessed by its family member. A standard plan is associated with each family and is represented by an OP-code sequence. In the sequence, each OP code has an associated OP plan stored on a lower level. Data for each level are stored in a file; therefore, VP requires three files:

1. A family-matrix file,

2. A standard-plan file, and

3. An OP file. Figure 7. A data hierarchy

The family name and family matrix are stored as a record in the database. A forward pointer is used to link the next record and another pointer is used to locate the associated standard plan in the standard-plan file. We can assign two words for the family name: two words for pointers, and I x J (8 x 4) words for the family matrix. A total of 36 (8 x 4 + 4) words are required for each record. Figure 8 illustrates the structure of a family-matrix file. Because the OP-code sequence has a variable length, the structure for a standard- plan file must include variable record lengths. In the file, a director is used to locate OP- code sequences. The rest of the file is divided into segments, with each storing up to five OP codes. The last word is used to indicate the continuation of the sequence. Expansion, deletion, and modification of a record are made possible by pointers in the directory and the continuation flag.  The OP-plan file has a structure similar to the standard-plan file except that it maintains link pointers to the standard-plan file. Because records in the standard-plan file have a one-to-many relationship with those in the OP-plan file, it is necessary to keep "where-it-comes-from pointers" in the OP-plan file. This organization makes file maintenance easier. Figure 9 shows the overall structure of the VP database. The storage of families 1 and 2 is shown in Figure 10.

Figure 8. Data record content

Figure 9. A database structure.

Figure 10. VP system data

3 Search Procedure Once the preparatory stage has been completed, the variant planning system is ready for production. The basic idea of a variant system is to retrieve process plans for similar components. The search for a process plan is based on the search of a part family to which the component belongs. When the part family is found, the associated standard plan can be easily retrieved. A family-matrix search can be seen as the matching of the family matrix with a given code. Family matrices can be considered as masks. Whenever a code can pass through mask testing successfully, the family is found. The search procedure can be described as follows:

This search procedure can be demonstrated by an example. The mounting bracket shown in Figure 11 will be planned using the VP system. Based on the S-CODE in Table 1, a code (6514) can be developed for the component. (To make VP even more effective, we could develop an interactive coding system for component coding. This interactive system could eliminate the use of the manual table. C1=6, C2=5, C3=1 , and C4=4). Referring to Figure 10, we can start the family search. Figure 12 shows the step-by-step search procedure. The search results in the retrieval of a standard plan represented by an OP-code sequence. This standard plan normally requires some modification before it can be used. OP plans can be retrieved and substituted for OP codes in the OP-code sequence. Manual modification of the final process plan is also needed.

Figure 11. The component to be planned: workpiece.

Figure 12. The search procedure

4. Plan Editing and Parameter Selection  Before a process plan can be released to the shop, some modification of the standard plan is necessary, and process parameters must be added to the plan. There are two types of plan editing: one is the editing of the standard plan itself in the database, and the other is the editing of the plan for the component. Editing a standard plan implies that a permanent change in the stored plan be made. This editing must be handled very carefully because the effectiveness of a standard plan affects the process plans generated for the entire family of components. Aside from the technical considerations of file maintenance, the structure of the database must be flexible enough for expansion and additions and deletions of data records. As a result, the pointer system in V'P may even prove to be efficient.  Editing a process plan for a component requires the same expertise as editing a standard plan. However, it is a temporary change and, therefore does not affect any other component in the family. During the editing process, the standard plan has to be modified to suit the specific needs of the given component. Some operations or entire OP records have to be removed and others must be changed. Additional operations also may be required to satisfy the design. A text editor is usually used at this stage.

 A complete process plan includes not only operations, but also process parameters. As discussed in (process engineering), process parameters can be found in machining data handbooks or can be calculated using optimization techniques. The first approach is easier and more appropriate for the VP systems.

 Figure 13 shows the structure for the parameter file. Data in the file are linked so that we can go through the tree to find the feed and speed for an operation. For example, MILL02 for the mounting bracket in Figure 11 uses a face-milling process. The workpiece material is cast iron (BHN = 180). The depth of cut for roughing is 0.25 in. and a 0.5-in.-diameter cutter is used. Using pointers, we can then locate from this information a velocity (V = 55 sfm) and a feed (f = 0.001 ipr).

This parameter file can be integrated into VP to select process parameters automatically. Information such as depth of cut and cutter diameter can be retrieved directly from the OP plan for each operation. The same approach is also appropriate for standard time selection.

With this example, we have completed our discussion of the variant process- planning approach.

Figure 13. A process parameter file

The Generative CAPP Method

Generative process planning can be defined as a system that synthesizes process information in

order to create a process plan for a new component automatically.

Feature withlocation

(position andorientation)

Processknowledge

base

Fixturingknowledge

base

Eitherfeaturebaseddesigndata

Or regularmodeller withfeatureextractor

Processselection

Fixturingmethod

Testselection

Cuttingparameters

Cutterpath

NC machine

Rawmaterialselection

Raw materialselection

Toolingknowledge

base

Merchantabilitydatabase

Routeplanner

The generative

process planning system

ADVANTAGES OF THE GENERATIVE APPROACH

1. Generate consistent process plans rapidly;2. New components can be planned as easily as existing

components;3. It has potential for integrating with an automated

manufacturing facility to provide detailed control information.

Successful implementation of this approach requires the following key developments:

• Process planning knowledge must be identified and captured.

• The part to be produced must be clearly and precisely defined in a computer-readable format.

• The captured process planning knowledge and the part description data must be incorporated into a unified

manufacturing database.

Major components of Generative CAPP

(i) part description

(ii) manufacturing databases

(iii) decision making logic and algorithms

PRODUCT REPRESENTATION

Geometrical informationPart shapeDesign features

Technological informationTolerancesSurface quality (surface finish, surface integrity)Special manufacturing notesEtc.

"Feature information"Manufacturing featurese.g. slots, holes, pockets, etc.

INPUT REPRESENTATION SELECTION

• How much information is needed?• Data format required.• Ease of use for the planning.• Interface with other functions, such as, part

programming, design, etc.• Easy recognition of manufacturing features.• Easy extraction of planning information from

the representation.

WHAT INPUT REPRESENTATIONS

• GT CODE• Line drawing• Special language• Symbolic representation• Solid model

– CSG– B-Rep– others?

• Feature based model

SPECIAL LANGUAGEAUTAP

10 CYLINDER/3,1/11 DFIT/K,5/12 CHAMFER/.2,2.6/20 CYLINDER/2.5,1.2/21 LTOL/+0.001,-0.001/

3

11.2

2.5

.2x2.6

K5

+.001-.001

CIMS/PRO REPRESENTATION

a1

a2 a3

a4

a5

a6

t

X

Y Z

sweep

direction

GARI REPRESENTATION

0 3.0

2.5

0 1.

X

Y3.0

F1

F2

F3

(F1 (type face) (direction xp) (quality 120))(F2 (type face) (direction yp) (quality 64))(F3 (type face) (direction ym) (quality rough))(H1 (type countersunk-hole) (diameter 1.0) (countersink-diameter 3.0) (starting-from F2) (opening-into F3))(distance H1 F1 3.0)(countersink-depth F2 H1 0.5)

Feature Recognition• CAPP systems do not understand the 3-D geometry

of the designed parts from CAD systems in terms of their engineering meaning related to manufacturing and assembly.

• FeaturesFeatures Generic shapes of objects with which engineers associate certain attributes and knowledge useful in reasoning or describing the products.

A generic part feature recognition system should be able to

• Extract design information of a part drawn from a CAD database

• Identify all surfaces of the part

• Recognize, reason about, and/or interpret these surfaces in terms of part features

Feature recognition is important not only for CAPP but also for classification and coding (Recall variant process planning !!)

Graph-Based ApproachAttributed Adjacency Graph (AAG)AAG is a graph G = (N,A,T)

Where N = {nodes} , A = {arcs}, T = {attributes}

f1

f2 f1 f20

node attribute arc

Attributed Adjacency Graph (AAG): Definition (See page 180)

Step

Slot

Three-side pocket

Four-side pocket

Pocket (blind hole)

Through Hole

EXAMPLE 5.4ft is easy for a human to see that the part shown in Figure 5. 14a has a slot mid a pocket feature. In this example, however, we simulate the computer to apply the

feature recognition algorithm discussed earlier. We therefore want to solve the following:

(a) Develop the AAG of the object.(b) Give the matrix representation of the AAG.

(c) Recognize the features in this object.

Pocket Slot

Solution(a) First, we have to label each surface of the part. Given that the part is labeled as shown in

Figure 5.l4a. we develop the AAG as shown in Figure 5,14b from the definition of AAG. By the definition of AAG we mean that each surface of this part is represented by a node and

each edge by an arc with attribute I or 0.(b) For the purpose of inputting the AAG graph into the computer, we have to convert the

graph to matrix form. The matrix representation of AAG is given as follows:

Zeros mean “Feature”

Remove the rows and columns without “0” elements…

00

0

00

000

F2 F3 F4 F5F

1F2F3F4

00

F12 F13

F11F12

Pocket

Slot

(b) For the purpose of inputting the AAG graph into the computer, we have to convert the graph to matrix form. The matrix representation of AAG is given as follows:

DIFFICULTIES OF FEATURE RECOGNITION

• Potentially large number of features.

• Features are domain and user specific.

• Lack of a theory in features.

• Input geometric model specific. Based on incomplete models.

• Computational complexity of the algorithms.

• Existing algorithms are limited to simple features.

Decision Logic

• The major function of the decision logic is to match the process capabilities with the design function.– Decision tables.– Decision trees.– Artificial intelligence.

Decision TablesA decision table is a tabular method for expressing the actions that should

follow if certain conditions exist. This technique permits the representation of many logical if-then expressions in a compact,

structured manner.

Figure 6.13 illustrates the four major components of a decision table:Decision conditions: are expressed as condition stubs and entries. The condition stubs are the criteria that the decision maker wants to apply

in the decision process. The condition entries are the responses for each condition stub.

Actions: are to be taken when the specified conditions are satisfied. The components are action stubs and action entries. The stubs denote all

actions that can be taken, and the entries designate the specific actions to be taken for specific conditions.

Each column of entries is called a rule and is numbered so that it is easily identified. The number of possible rules in a decision table is related to

the number of condition stubs. In general, there are 2N possible rules, where N represents the number of condition stubs.

FIGURE 6.13 Components of a

decision table.

Example decision table.