*CAD AND CAM INTEGRATION After a part has been designed, it is converted to a finished product by a manufacturing process using CAD-CAM.CAM software includes computer-aided process planning (CAPP) systems in the process planning phase; NC software, for programming numerically controlled machine tools in the production phase;

*CAD AND CAM INTEGRATIONInspection software for use in the inspection phase; and Software for programming robots, for use in the assembly phase.In many CAD and CAM systems the CAD and the CAM are poorly integrated. Therefore stronger integration of CAD and CAM is needed to increase productivity.

*CAD AND CAM INTEGRATIONThe need to automate process planning is the most urgent because that phase is the bridge between design and manufacturing. Thus the primary research efforts at the interface between CAD and CAM have been in the development of computer-aided process planning systems that attempt to automate communication between product engineers and manufacturing engineers.

*PROCESS PLANNINGProcess planning is the function in a manufacturing facility that establishes which processes and parameters are to be used, as well as the machines performing these processes. Alternatively, process planning can be defined as the act of preparing detailed work instructions to machine or assemble a part or parts

*PROCESS PLANNINGThe process plan is sometimes called an operation sheet, route sheet, or operation planning summary. Figure 10.2 illustrates a process plan for producing the part shown in Figure 10.3. In addition to operation sequencing and operation selection, the selection or design of tooling and jigs/fixtures is also a major part of process planning.

*PROCESS PLANNINGFigure: 10.2

*PROCESS PLANNINGFigure: 10.3

*PROCESS PLANNINGMany factors influence the process plan for a part or an assembly. These factors include the part geometry, the required accuracy and surface finish, the quantity to be produced, and the material to be used. For example, a very smooth surface finish may call for a grinding operation, whereas a less fine finish may require a turning operation, for the same part geometry.

*PROCESS PLANNINGSimilarly, small numbers of a part may be produced by a machining process, whereas large numbers may be produced by a forming process using a die.

*MANUAL APPROACH In the manual approach a skilled individual, often a former machinist, examines the drawing of a part and develops the necessary instructions for the process plan. The process plan being generated can be elaborate or simply an aggregation of individual operation descriptions, depending on the shop environment.

*MANUAL APPROACHFor a model shop, where all the machinists are highly skilled the process plan is usually nothing but a list of workstation routes and the details are left to the machinists.To develop process plans for new products. process planners often follow more or less a consistent set of steps. The steps are:Study the overall shape of the part.

*MANUAL APPROACHIdentify datum surfaces and determine setups from this information. Identify part features. Typical features and sub features for machining are illustrated in Figures 10.4 and 10.5, respectively.Group the part features based on the required setups.Order the sequence of the operations.

*TYPICAL MACHINING FEATURES

*TYPICAL MACHINING SUBFEATURES

*MANUAL APPROACHSelect tools for each operation. Select or design fixtures for each setup. Make a final check on the plan. Prepare the final process plan document. We can illustrate manual process planning by following these steps in Example 10.1.Prepare a process plan for the part shown in Figure 10.6. Assume that precut bar stock and only conventional machine tools are used.

*MANUAL APPROACHFigure 10.6

*MANUAL APPROACHANSWERThe part is a rotational component, so a lathe most likely will be used. The datum surfaces S1 and S2 indicated in Figure 10.7 can be machined in one setup in the lathe operation. However, at least two setups are required because of the threaded area. Specifically, part features S1, S2, S3, S4, and S5 can be machined in one setup and S6 and S7 machined in the other setup.

*PART FEATURES TO BE MACHINED7

*MANUAL APPROACHIn addition, the holes S8 cannot be drilled on a lathe, and thus we need one more setup for a drill press. Therefore the following sequence of operations can be used to produce the part.

*MANUAL APPROACHSetup 1Chuck the workpiece.Turn S3 to a 100 mm diameter. Face S 1.Core drill S2.Counter bore S4 and S5. Setup 2Chuck the workpiece on S3. Turn S6 to 50 mm diameter. Undercut the neck.Thread S6. Face S7.

*MANUAL APPROACHSetup 3Locate the workpiece, using S 1 and S2.Mark six holes, S8.Center drill and drill six holes, S8. The elaborate process plans require, selection of tools and parameters.

*VARIANT APPROACHThe variant approach is one of the two approaches used to develop a computer-aided process planning (CAPP). The other approach is the generative approach.The variant approach can be regarded as an advanced manual approach in which the planner's memory retrieval process is aided by the computer.

*VARIANT APPROACHIn this approach the planner's workbook is stored in the computer file. A typical process plan of a similar part can then be retrieved automatically from the computer file. and the retrieved process plan can be edited interactively for the specific part being planned.

*VARIANT APPROACHThus a variant system requires a database containing a standard process plan for each family of parts. Such a plan consists of all instructions that would be included in a process plan for any part in that family. The parts are classified by family, using the group technology concept.

*VARIANT APPROACHIn group technology, each part is assigned a code based on its features, and the parts are grouped into a family according to their codes (Refer to Group Technology).

*VARIANT APPROACHA process plan is developed in the variant approach as follows. The process planning task for a new part starts with coding, which is equivalent to describing the part using the group technology concept. Then the part is assigned to the proper family according to its code.

*VARIANT APPROACHThe standard process plan for this family can then be retrieved from the computer.This plan contains general instructions for handling all the parts in the family, so some editing may be required for the specific part of interest. The editing can easily be performed with the editing capabilities provided in the variant systems.

*VARIANT APPROACHOften very little editing is required because the new plan is simply a variation of the standard process plan. Consequently, considerable time is saved in preparing the plan, and the resulting plans are much more consistent than those prepared manually. If the part being planned cannot be assigned to an existing family of parts, the planner can develop a new standard process plan interactively.

*GENERATIVE APPROACHIn the generative approach, a process plan is generated automatically from engineering specifications of the finished part. The first step in generating a process plan for a new part using a generative system is to enter the engineering specifications into the system. Ideally, these specifications would be read directly from a CAD database.

*GENERATIVE APPROACHFor this to occur, the generative CAPP system must have the ability to recognize the machining features of a part, such as a hole, slot, pocket, etc.However, the design features used in the feature-based modeling system may still have to be converted to the proper machining features. Some design features have one-to-one correspondence with machining features, but many require a complicated process.

*GENERATIVE APPROACHIn addition, feature information alone does not provide all the information necessary for process planning. For example, most CAD models do not contain tolerance and materials information, which must be provided manually. These are some of the reasons why a truly automatic generative process planning system has not yet been developed.

*GENERATIVE APPROACHInstead, a manual approach to coding the engineering specifications of the part is often used. The coding scheme utilized must define all the geometric features and their associated details, such as locations, tolerances, and sizes. The coded data are accompanied by textual information. Additionally, the shape of the raw stock must be provided.

*GENERATIVE APPROACHThe second step is to transform the coded data and accompanying textual information into a detailed process plan. During this phase, the best sequence of operations and the detailed conditions for each operation must be determined. These conditions include tooling, fixtures, gauges, clamping, feeds, and speeds.

*GENERATIVE APPROACHA large database and complex built-in decision logic would certainly be required to generate a process plan for an arbitrarily complex parts at this level of detail. As a result, the generative approach has been restricted to special classes of parts that have a relatively limited set of part features.

*COMPUTER-AIDED PROCESS PLANNING SYSTEMS

Most existing computer-aided process planning systems (e.g., CAM-1 CAPP, Ml PLAN, MITURN, MIAPP, ACUDATA/UNIVATION, CINTURN, and COMCAPPV) are based on the variant approach. However, some systems (eg. CPPP. AUTAP, APPAS, GENPLAN, CAR, MetCAPP, and ICEM-PART) based on the generative approach have been reported recently in the literature.

*CAM-1 CAPP system The CAM-1 CAPP system was developed from CAM-1 in 1976. CAM-1 CAPP is a database management system written in FORTRAN; It provides a structure for a database, retrieval logic, and interactive editing capability. The coding scheme for part classification and the output format are added by the user.

*CAM-1 CAPP systemThus a coding scheme tailored to the user's specific environment is allowed if the code is not longer than 36 digits. For example, Lockheed-Georgia used a modified Opitz code for its CAPP system. The CAM-1 CAPP coding scheme also allows the user to use any existing GT system.

*CAM-1 CAPP systemA graphical description of the CAM-1 CAPP system is shown in Figure 10.8.

*CAM-1 CAPP systemFor each family of parts, a standard process plan is maintained in a standard sequence file. The detailed description of each op code is stored in the operation plan file. In each family matrix file, the matrix defines which parts belong to that family from the codes assigned to the parts by the coding system.

*CAM-1 CAPP systemOne such matrix is illustrated in Figure 10.9. The columns represent the positions of the digits in the group technology code, and the rows represent the digits that can be assigned to any one position for the code. In this case, the group technology code comprises five positions, and each position can have a value of 0-9.

*CAM-1 CAPP systemFigure 10.9: A part family matrix

1234501x2xx3xx4x5xx6xx78 x9

*CAM-1 CAPP systemThe matrix in Figure 10.9 shows that the parts represented by the codes 31632, 32646, and 35638, for example, belong to the same family.

*CAM-1 CAPP systemA process plan is generated by a CAM-1 CAPP system in four main steps, as illustrated in Figure 10.8.Step 1: After the part being planned has been classified by family, a search for the part family is performed by the system, using the stored part family matrix and the code of the part.

*CAM-1 CAPP systemStep 2: The planner inputs the header information to identify the process plan being generated. The header information includes the part number, material, planner, part name, and revision. Step 3: The operation sequence required to manufacture a part, sometimes called a routing, is generated. Sample op codes are shown in Figure 10.10.

*CAM-1 CAPP systemFigure 10.10 Sample op codes10RAWMTL 20 SAWBAR30CNCLATH 40 INSP 50 HTRT60 SAND

*CAM-1 CAPP system70 HOB 80 NCLATH 90 DEBUR 100 CNCGRIND 110 SLURRY 120 INSP 130 LASERMK 140 PKG

*CAM-1 CAPP systemStep 4: Next the text describing the work performed at each operation is created and/or edited. Figure 10.11 illustrates the operation plan for an op code CNCLATH. Once an operation plan has been completed for each operation, the operation plans of all the op codes are merged to form the complete process plan.

*Figure 10.11 Example of an operation plan

*MIPLAN and MultiCAPP MIPLAN and MultiCAPP were developed in conjunction with the Organization for Industrial Research, Inc. Both are variant systems that use the MICLASS coding system for part description. Process plan retrieval is based on part code, part number, family matrix, and code range.

*MIPLAN and Multi-CAPPPart code input results in retrieval of similar parts, and each process plan displayed can be subsequently edited by the planner. These systems are similar to the CAM-1 CAPP system with MICLASS embedded as part of the system.

*MetCAPP MetCAPP is a typical CAPP system based on the generative approach. MetCAPP generates a process plans as follows: First, the feature extraction module in MetCAPP extracts the feature information from a geometric model created by a CAD system.

*MetCAPPOnce the machining features have been identified, it uses the inference rules stored in the knowledge base to determine the machining methods and their orders. MetCAPP can be classified as a knowledge-based generative CAPP system. It can also estimate the machining cost and time from the generated process plans.

*MetCAPPCurrently, MetCAPP has the inference rules and the necessary data for milling, turning, and hole making processes in its knowledge base.

*ICEM-PARTICEM-PART was originally developed at the Laboratory of Production and Design Engineering of University of Twente in Holland and then later commercialized by ICEM. It is a generative CAPP system, mainly used for machining 21/2 dimensional prismatic parts.

*ICEM-PARTICEM-PART generates a process plan as follows. First, it reads a geometric model in either ACIS format or STEP AP203/AP214 format and extracts the machining features. Then it selects the setup, cutter, and machine tool automatically and suggests the optimal order of processing. It also generates the NC tool paths for each machining feature. ICEM-PART is an example of CAD/CAPP/CAM integration.

*GROUP TECHNOLOGY Grouping similar parts into a family with a proper coding system is an essential step for computer-aided process planning. The concept of group technology enables this classification. One of the definitions of group technology (GT) can be stated as follows:

*GROUP TECHNOLOGYGroup technology is the realization that many problems are similar, and that by grouping similar problems, a single solution can be found to a set of problems thus saving time and effort. [Solaja and Urosevic, 1973]

*GROUP TECHNOLOGYThe objective of group technology is to form a database of similar parts, design. and process and use that database to establish a common procedure for designing and manufacturing those parts. The parts are assigned to a part family based on similarities in design, such as shape, or processes, such as milling and drilling operations.

*GROUP TECHNOLOGYGroup technology can support the development of efficient plant layouts by having each cell layout handle each part family. This simplifies the flow patterns of materials in a plant, which leads to reductions in transfer times of materials between machines, materials handling, and part manufacturing lead time.

*GROUP TECHNOLOGYSince similar parts are being produced on the same machines, machine setup times are reduced, and special tooling may be taken advantage of. Process planners can review the process plan for a similar part with a similar GT code and modify it to generate the process plan for the new part, instead of starting from scratch for each new part to be planned.

*Classification and CodingClassification of a part involves placing the part in a group, or family, based on the existence or absence of similar attributes. Coding of a part involves assigning symbols to the part; these symbols should reflect the attributes or features of the part.

*Classification and CodingIf the coding and classification system is to be used successfully in manufacturing, it must identify attributes such as tolerances, machinability of materials, processes, and machine tool requirements. There are three different types of code structure in GT coding system: hierarchical (mono-code), chain (polycode), and hybrid.

*Classification and CodingIn hierarchical codes, or monocodes, each code number has a different meaning, depending on the preceding characters.Figure 10.12 illustrates the hierarchical codes for a 54xxx family, which is a frame of a facsimile machine.

*Classification and CodingFigure 10.12: Example of a hierarchical code

*Classification and CodingIn this example, the fourth digit of 541 xx indicates the type of plastic resin. but the same digit of 542xx indicates the existence of the ribs in the part. The hierarchical structure has the advantage of representing a large amount of information with very few codes. However, identifying the meaning of a digit is difficult because the entire hierarchy has to be traced.

*POLYCODEIn polycode each digit is independent of all others, including the preceding digits, with each digit carrying self-contained information about the part. Thus polycodes are easy to construct and modify, as needed. Their primary drawback is that they can carry much less information than a monocode of the same length.

*HYBRID STRUCTURE In the hybrid structure, some digits are arranged hierarchically and others are fixed. In other words, it is a mixture of the hierarchical and chain structures. Most classification and coding systems used in industry are based on a hybrid structure in order to exploit the advantages of both structures.

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