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ComputerAided_Design_Engineering_amp_Manufactur.pdf

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TABLE 5.4 (continued) Data Structure for Representing the Machine Tools<br />

S. No. Name Type Width Dec Description<br />

29 ACC3 C 4 Accessory available with the machine tool as a code<br />

(pointer).<br />

30 ACC4 C 4 Accessory available with the machine tool as a code<br />

(pointer).<br />

31 REMARKS C 50 Remarks if any.<br />

(b) Cutting tools: Along with the pocket and machining operation, the cutting tools used in a<br />

machining operation can be represented by tool codes. Recall that the cutting tools are<br />

modeled in Data-GIFTS. Given a cutting tool code, one can obtain other details from MRIR.<br />

(c) Cutting process parameters: The parameters (speed, feed, and depth of cut) can be represented<br />

along with the pocket geometry, machining operation, and cutting tools.<br />

5.13 Macro-GIFTS: Macro-Planning Module<br />

In earlier sections, the implementation of Turbo-Model for achieving PDIR and Data-GIFTS for achieving<br />

MRIR is explained. The model of PPIR as employed in GIFTS is also explained. The function of the<br />

planning modules of GIFTS is to take PDIR and MRIR as inputs and generate PPIR as output as shown<br />

in Figure 5.12. The following sections outline how this is achieved in GIFTS.<br />

The planning functions of CAPP can be broadly divided into: (a) macro planning and (b) micro<br />

planning. Macro-planning deals with upstream planning issues and hence is concerned with planning<br />

at the part level. Micro planning, also called operation planning, is mainly concerned with the details of<br />

specific manufacturing operations. The selection of cutting tools and process parameters falls under the<br />

scope of microplanning.<br />

Macro-GIFTS, the macro-planning module of GIFTS, is responsible for operation selection, machine<br />

tool selection, setup planning, and operation sequencing.<br />

Operation Selection<br />

One of the most critical issues involved in process planning is the identification of the various operations<br />

required for manufacturing the part. This choice is more difficult because there are too many possibilities<br />

and the planner has to come up with the optimum choice commensurate with the requirements. Hence<br />

it is necessary to combine the product geometry and technology, along with the machining resources<br />

capability, to arrive at a possible operation for a given feature or pocket.<br />

There are a number of approaches suggested in the literature. The approaches will also have to be based<br />

on the product geometries. We will therefore divide the operation selection into the following categories:<br />

• Cylindrical surfaces (external and internal)<br />

• Plane surfaces<br />

• Hole making processes<br />

• Sculptured surfaces<br />

• Pocket clearance<br />

Each of these categories has its separate methods and algorithms for the purpose of identifying the<br />

machinable volumes and the corresponding operation selection and sequencing methods. One major<br />

assumption we will be making is that the product data base is organized in the form of features. This<br />

helps in making the machinable volume identification an easier task. Even if the original product is in<br />

other forms, a feature recognition module can be added in between to make use of the following

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