Journal of

Materials Processing Technology

E L S E V I E R Journal of Materials Processing Technology 61 (1996) 87 92

Integrating CAD/CAM Software for Process Planning Applications

Kurian K. Thomas ', Gary W. Fischer u ~' Technical Center, Case International, 7 South 600 County Line Road, Burr Ridge, IL 60521

Department of Industrial Engineering, The University of Iowa, Iowa City, IA 52242-1527

Abstract

The selection of machining parameters is an important process planning function for manufacturing processes. Typically, machining parameter selection is done manually; although, some software packages are available to assist the process planner with this function.

This paper describes a method for integrating commercial CAD and CAM software packages to provide a process planning tool that can substantially increase productivity and reduce lead-time. The proposed method is based on the concepts of wrappers and neutral data formats. An implementation example is presented to demonstrate the method and the potential for on-line machining parameter selection in an integrated CAD/CAM environment.

Keywords. CAPP, CAD/CAM, CIM, Process Planning, Concurrent Engineering, Machinability Data

1. I n t r o d u c t i o n

Process planning is the critical bridge between design and manufacturing[l]. Design information can be translated into manufacturing language only through process planning. One of the reasons for the decline of industrial productivity growth in the United States could be the lack of recognition and attention given to manufacturing planning[l].

The traditional, manual method of process planning is centered around the "process planner." The process planner typically needs diverse applied knowledge in both design and manufacturing and uses this knowledge, past experience, handbooks and/or various databases to translate the product engineering requirements into detailed manufacturing requirements. But the procedure is tedious, inconsistent and time consuming.

The time spent by a process planner can be broken down into the following categories[2]:

Technical decision making 1 5% Data look-up and calculation 40% Text and document preparation 45%

These statistics reveal that 85% of a process planner's time is spent doing non-decisionmaking and often repetitive activities (work more efficiently done by a computer).

Using computer technology to perform the process planner's non-decisionmaking activities is seen to be a way to not only enormously increase the efficiency of process planning but also give the process planner more time to do technical decisionmaking tasks. Applying computer technology to assist process planning tasks has been the main thrust of most Computer Aided Process Planning (CAPP) systems[1 ]. Some systems even attempt to reduce the 15%

0924-0136/96/$15.00 ~') 1996 Elsevier Science S.A. All rights reserved Pll 0924-0136(96)02470-3

technical decisionmaking part of the process planner's task by using artificial intelligence (AI)-based techniques[3].

CAD/CAM technologies are intended to integrate CAD, CAPP and CAM into one computer environment that allows the user to design, plan and control the manufacturing of products, while automating as many of the activities as possible. CAD/CAM technologies are a natural part of the concurrent engineering paradigm, since they allow the engineer to perform all activities from design through manufacturing within the same computer environment.

Many powerful and sophisticated CAD, CAPP, CAM and CAD/CAM software packages (or systems) are available. Some highlights of these systems include feature based design, 3D solid modeling, automated drafting, 3D machining simulation and automated generation of NC tool paths. The availability of inexpensive computing power combined with fllese features has already made product development activities more productive and efficient. However, these systems also have limitations because of their application- specific nature, their lack of communication linkages, or their inability to share internal data.

This paper describes a method for integrating CAD and CAM software that overcomes some of the current limitations[4]. The main thrust is the CAPP part of CAD/CAM, with specific emphasis on machining and the integration of "off-the-shelf" software to demonstrate the method.

Section 2 of the paper introduces a CAD/CAM concept that describes the integrated environment for design and manufacturing planning. The integration methodology developed through this research is presented in Section 3. Section 4 uses the integrated system to plan machining of an

88 K. K Thomas, G. ~ Fischer~Journal of Materials Processing Technology 61 (1996) 8 ~ 92

example part. Finally, the conclusions of this research are summarized in Section 5.

2. CAD/CAM Concept

The proposed method provides a general way to integrate different packages (written in proprietary code) to create a system that meets the requirements for a particular application. The method is called "Modular Integration of CAD/CAM Software" (MICS), named after the modular organization of the software packages being integrated. The method, illustrated in Fig. 1, is based on wrapper technology[5] and a neutral data format concept[6].

channel. Functions not executed by the integrated CAD/CAM software packages can also be performed by the user through the Control Module.

A wrapper can be one of two types[5]: an application wrapper and a tool wrapper, depending on whether the wrapper is used by an application or by a tool. The basic purpose of the wrapper is to function as a translator (for commands and data) between the proprietary CAD/CAM software and the overall CAD/CAM system. Information going into the CAD/CAM software is first translated by the wrapper from the system's neutral format to the proprietary format of the specific software. Likewise, data sent from the CAD/CAM software is translated into the neutral format.

{• kb, er

Module

CAPP [

Fig. 1. Modular Integration of CAD/CAM Software (MICS).

The system presented in Fig. 1 represents a hypothetical system that covers all major CAD/CAM functions and consists of four main components:

I. Central Database - - stores any data that needs to be transferred, in a neutral format, between the CAD/CAM software packages in the system.

2. Control Module - - provides the user interface to organize and monitor the execution of activities in the system; additionally, it could automate the scheduling and execution of the activities.

3. Application software packages and their wrappers the system has nine such modules: the CAD Module, the CAM Module and seven modules within CAPP that perform the individual process planning functions.

4. Communication Channel - - connects the Central Database, the Control Module and CAD/CAM software modules into one system.

Through the Control Module, the user issues a command to the one of the CAD/CAM software modules, such as the CAD ]nodule, to execute a particular function. Any external data required by that module is taken from the Central Database, converted to the internal format of the CAD software package, and the function is executed. Upon completion of the function, results, and/or data required by other modules, are converted to the neutral format and sent to the Central Database for storage. The CAM Module performs the CAM functions of CAD/CAM, such as management and control of manufacturing activities on the shop floor[6].

MICS promotes a "plug-in" type modular concept. Various CAD/CAM software packages can be plugged into the CAD/CAM system using wrappers and the communication

I

I Connection to the CAD/CAM System

Wrapper

Machining Parameter Selection Software

i

Machining Parameter Selection Module

Fig. 2. Structure of a CAD/CAM software module in MICS.

Fig. 2 shows an example structure for the Machining Parameter Selection Module in the CAD/CAM system presented in Fig. 1. The module consists of three components: the Wrapper, the Local Database and the Machining Parameter Selection Software. The Machining Parameter Selection Software is a commercial software package that performs the machining parameter selection function. The Local Database stores data relevant to the Machining Parameter Selection Module in a format that the Machining Parameter Selection Software understands. The local database can be physically separate or an integral part of the software. The representation shown is used only to stress the importance of local data stored in the software's proprietary format.

The Machining Parameter Selection Software communicates with the CAD/CAM System through the Wrapper. All the commands issued by the Control Module are interpreted by the Wrapper and converted into a language/format that the software understands. Outgoing controls from the software are also interpreted before being sent to the Control Module. Data management and transfer between the Local Database and the Central Database is controlled via the Wrapper, which allows local data to be stored in a proprietary format while central data can be maintained in a neutral format. Physically, the Wrapper is a set of computer programs that perform these data transfer and communication functions. Although Fig. 2 shows a

K.K. Thomas. G. g'i Fischer~Journal of Materials Processing Technology 61 (1996) 8~92 89

CAD/CAM software package that performs a single process planning function, the same framework can be applied for integrating software that performs any other CAD/CAM function(s).

3. Integrat ion M e t h o d o l o g y

hnplementat ion of the MICS concept is achieved by applying it to the integration of two commercial CAD/CAM software packages, considered to be representative of the s tate-of- the-market products: Pro /ENGINEER ® (Pro/El and ToolPro TM Grade Application Advisor (ToolPro). Together, these packages create a critical subset of the overall CAD/CAM system described in the previous section. The integrated system is called the Pro/E-ToolPro CAD~CAM System (or PTCS). In the integrated PTCS environment, ToolPro automates the machining parameter selection function witliin the Pro/E process planning function.

3.1 Process Planning in Pro/E

Before describing the proposed CAD/CAM implementation, the fnnctionality of Pro/E and ToolPro will be briefly reviewed. Process planning in Pro/E is performed through P r o / M A N U F A C T U R I N G TM (Pro/MAN) module. Fig. 3 illustrates the process planning operation in Pro/MAN.

I [

FIXTURE SET1 IPS

Pro/MANUFACTURING

DESIGN MODEL ] ] WORKPIECE ]

~qD,-] MANUMFoACTURING ] ' ~ I MACHINE TOOLS

S E.I~[ Up OPERATION

DEFINE NC SEQUENCES ] 1]

PRODUCE

FILES tAPT) MODEL

1 POST-PROCESS

t I DRIVE NC

MACHINE TOOL

Fig. 3. The manufacturing process in Pro/'MAN[7].

Pro/MAN provides the tools to plan and simulate numerical control manufacturing processes. The process planning begins after the part design model has been created. A manufacturing model, which is an assembly of the part design geometry and the workpiece geometry, is created in Pro/MAN. The workpiece in Pro/E is a model that represents the raw stock that is machined to get the finished part.

The CL data file, which eventually is translated into the code that runs a specific CNC machine, can be created either automatically or in a lnanual, interactive mode, then stored. The CL data file as the name suggests, is an ASCII file of the cutter location information for all the NC sequences in an operation set up in Pro/MAN. Tool change data, speed and fee&ate data are also inchtded in the CL data file.

3.2 Parameter Selection in ToolPro

ToolPro, developed by Kennametal Inc., follows the planning process illustrated in Fig. 4[8]. ToolPro helps the user select the best cutting tool and machining parameters for single point turning operations. Fig. 5 illustrates the ToolPro output screen and a sample recommendation.

SELECT MATERIAL TYPE ]

t I SELECT

TYPE OF CUT

[ GRADE RECOMMENDATION I V

ENTER 1. Depth of cut 2. Length of cut 3. Diameter of workpiece

COMPLETE RECOMMENDATION I

Fig. 4. The ToolPro planning process.

The material type needed for an operation can be selected from ToolPro's material database comprising ten different kinds of materials ranging from carbon steels to nonrnetallic materials, such as glass, ceramics and plastics.

K KENNAM[!TAL (R)

Uncoated Tungsten Carbide K313

[ I

~1 i~:i~i:~: ~:~:~l Suggested Range ]ii!~:~ ~i ii I -,3 i!iiiiiii i~i!i~ •

Cutting Speed (sfm)

FI - Material F2 - Cut Type F6 - Next Grade F7 - Metric

Material: Aluminum [ Hardness: 50 - 150 BHN

Type of Cut: Semi-Finishing to Roughing I Actual DOC: O. 10[I inches Cutting Speed [ Diameter: 1.5ll0 inches 2"~8 sfm [ Length: 2.250 nches Feedn~te

(I.015 ipr Spindle Speed

3152 rpm Feed

46.229 ipm Metal Removal

21.789 cu in/rail Power

5.0 hi Time in Cnt

0.(15 rain Applicable Grades

KC730 K313 KTI25

F3 - D. O. (7. F4 - Diameter F5 - Length [=8 - Files F9 - Print FI0 - Help

Fig. 5. ToolPro output screen.

ToolPro 's turning operations are classified into six types of cuts; the classification is based on a depth of cut range for each cut type. For example, Heavy Roughing is classified as a turning operation with a depth of cut between 0.250 and 0.500 inch. The user specifies the length of cut, the diameter of

90 K.K. Thomas, G.W. Fischer~Journal of Materials Processing Technology 61 (1996) 87-92

the workpiece and the depth of cut value, which has to be within the range of the selected type of cut.

From the ToolPro output, the user evaluates the tool grade recommendations and their associated operating relationships between feedrate (inches per revolution) vs. cutting speed (surface feet per minute) according to the graph displayed on the screen (see Fig. 5). The user can move the cursor in the graphical region to select the most appropriate combination of feedrate and cutting speed for the selected tool, or change to another tool and repeat the process. Hence, the user can manually try out many machining scenarios, while partially automating the process parameter selection function.

Based on the user input values and previous selections made by tile user, additional machining parameters and data are calculated by ToolPro: spindle speed (rpm), feed (inches per minute), metal removal rate (cubic inches per minute), power (horsepower), and time in cut (minutes). These output values along with the earlier outputs constitute a complete recommendation data set for each tool grade. Other text data such as user comments can also be added to the recommendation.

ToolPro has a file manager, where recommendation data is stored for future retrieval, and a utility called "gcxport" that can be used to convert tile data to an ASCII formatted file. Each recommendation data set is saved as a record and twelve records can be saved at one time in ToolPro.

3.3 Integration qf ToolPro and Pro/E

As mentioned earlier, one of the steps in defining an NC sequence in the Pro/MAN session is the selection of machining parameters. Pro/E does provide the user with an interface through which values can be manually entered by the user. For turning NC sequences, the most important of the machining parameters are the following:

1. Feedrate, in inches per revolution (ipr) or inches per minute (ipm) referred to as "cut feed."

2. Depth of cut, in inches called 7"step_depth" in Pro /MAN.

3. Spindle speed, in revolutions per minute (rpm) - - referred to as " sp ind lespeed ."

From the previous discussion, it is obvious that the best of both worlds is attained when by using ToolPro to select the machining parameters for the turning sequences that are defined in Pro/MAN. Fortunately, Pro/E provides an interface called Pro /DEVELOW M (Pro/DEVELOP) that allows the user to interface user-defined applications, such as ToolPro, with Pro/E modules.

3.4 Using Pro~DEVELOP T M

Pro/DEVELOP consists of a library of C functions that provide a supported interface to Pro/E and direct access to the Pro/E database. Using Pro/DEVELOP involves writing a C language program that makes calls to the supplied library of functions and performs other functions to access and manipulate the ToolPro file data[4]. Such a program can then use tile standard Pro/E menus and message tools, as well as directly access tile Pro/E database[7].

3.5 Development O[ PTCS

The design that was actually implemented to integrate Pro/E and ToolPro is somewhat different from the MICS concept (see Fig. 6). The implemented design consists of four

components. There is only one Wrapper for both CAD/CAM software packages and the Wrapper is combined with the Control Module into a single module. The Central Database is connected to the CAD/CAM system through the Wrapper and Control Module.

Since PTCS is not a complex CAD/CAM system, a separate wrapper for each software package is not justified. A single wrapper is sufficient to handle the communication and data transfer between the two software packages. For the same reason, a separate control module also is not required for this application. The Wrapper and Control Module perform the following four functions.

1. Control the execution of each CAD/CAM software package.

2. Handle the data manipulation between the neutral data format of the Central Database and the proprietary format of each application.

3. Control data transfer to and from the Central Database. 4. Provide an interface for the user to operate the

CAD/CAM system and enter input data.

Wrapper and

Control Module

I Pro/E [ I ToolPro Software Software Fig. 6. Implemented design of PTCS.

Pro/E is UNIX-based and ToolPro is a PC-based software package that works on the DOS operating system. To overcome the incompatible operating system problem, ToolPro was installed on SoftPC, a software emulation of an IBM PC-AT compatible personal computer. SoftPC works on the UNIX operating system and allows direct execution of DOS applications on UNIX. Bringing both CAD/CAM software packages (Pro/E and ToolPro) to the same HP/UX operating platform created a common ground for the execution of commands and the transfer of data.

The file manipulation program takes a comma delimited ToolPro output data file (ASCII format); reads in the depth of cut in inches, feedrate in ipr/ipm and spindle speed in rpm; and writes out an ASCII formatted Pro/E machining parameter file, inserting these parameter values at the appropriate locations in the Pro/E file. The file manipulation program is written in the "awk" programming language. Awk was chosen for this purpose because it is a UNIX utility that is well suited for file manipulation tasks.

The autoexec.bat program is set up on the DOS operating system through SoftPC. The Pro/DEVELOP program only executes SoftPC, not ToolPro. When the SoftPC environment is started up, the autoexec,bat program is automatically

K.K. Thomas. G.W. Fischer~Journal of Materials Processing Technology 61 (1996) 87-92 91

executed, which in turn starts up ToolPro and sets up the user at the starting point of the program. When the user completes the ToolPro exercise and exits, autoexec.bat starts up the gexport utility to convert the TooIPro recommendation into an ASCII formatted file.

The Central Database for this application has a very simple structure. The output from ToolPro containing data required by Pro/E is a comma delimited, ASCII formatted file. The input to Pro/E is also an ASCII formatted file. Therefore, the Central Database for this CAD/CAM system is made up of two ASCII formatted files: the Pro/E machining parameter file and the ToolPro output data file.

4. Using PTCS

PTCS was installed on a HP/UX workstation at the Center for Computer Aided Design (CCAD) network at The University of Iowa. However, most of its usage was through the Iowa Computer Aided Engineering Network (ICAEN) at the College of Engineering by remote access to the CCAD network.

At the start point of the PTCS procedure, it is assumed that the following Pro/E activities have been performed: a manufacturing model has been created, the manufacturing database and an operation have been set up, and a turn type NC sequence is being defined.

The design and manufacture of a Gear Shifter Knob is used as an example to demonstrate the capability of PTCS[4]. The product design is done in Pro/E (see Fig. 7) and the process planning uses PTCS.

5" dlOmeler, 4" long Alu+inum bar sto~k

~ork+in'proc¢$1 ( r e l ~ l t of +~e ++th© +pcratio++

MANE: IK . r ia+ E. Tfiemos TITLE: ]Gear Shifter Kmob DATE: 19/22¢~$ Ma~ler's The~i l , Univ. of 1ola

ProI[ momu[o</.rln 9 model

Fig. 8. Pro/E manufacturing model.

parameter selection. The output of the process planning operation for the Gear Shifter Knob is a Pro/E CL data file.

Manufacturing the Gear Shifter Knob from the aluminum bar stock involves six main operations, as noted in Fig. 9. Operation 1 and Operation 2 are set up as a single "Pro/MAN operation" consisting of two NC sequences: an Area-Turning NC sequence that performs the rough turning machining operation and a Profile-Turning NC sequence that performs the finish turning machining operation.

I I1LF: GeQr Sh,Fl~r Knob

D~Tr: gi221°S M¢~Icrr+ T~esi$, u~iq. 01 ego

ALL °IIAEMSION$ ARE IN lACHES M~I[RIAL ALUMINUM DJM[N~IOMAL TOLERANCE tl'O.O01 SUR[AEE ROUGHN[S5: 7S mlcroes

I S ~ R 30

1'3 ~ g~[W

R ?9 R/0

RIGHT $10[ VIEW

Fig. 7. Pro/E part drawing of the Gear Shifter Knob.

The Gear Shifter Knob is 2.21 inches long and its largest cross-section has a diameter of 1.4 inches. Its small end has a threaded hole 0.4 inch in diameter and 0.5 inch deep, used to fasten it to the gear shifter lever. The material is aluminum and the workpiece is a bar stock 1.5 inches in diameter and 4 inches long. The Gear Shifter Knob (machined part) is machined from the aluminum bar stock (workpiece), as noted in the Pro/E rendering of the manufacturing model in Fig. 8.

The complete process planning operation is outlined, but the main focus is on the machining parameter selection function and the use of ToolPro in the PTCS environment. The specific PTCS steps are explained only for machining

OPERATION SHEET

Part Name: Gear Shifter Knob Material: Aluminum

Operation Description Machine Rough turning to shape and 2-axis, Left Handed CNC approximate size Lathe Finish turning to exact size and 2-axis, Left Handed CNC required surface finish Lathe

Band Saw

N o ,

1

2

3

4 5

6

Sawing off the gear shifter knob from the machined part Grindin~ the sawed end Drilling the hole on the small end of the part Threadin~ the hole

Grinder CNC Drilling Machine

CNC Drilling Machine

Fig. 9. Operation sheet for the Gear Shifter Knob.

The machining parameters are selected using ToolPro in the PTCS environment. ToolPro is started by selecting the customized "ToolPro" menu button from the standard "Mfg Params" menu of Pro/E. Fig. 10 shows the complete recommendation generated by ToolPro for the first operation.

Using YoolPro, appropriate values are selected for the Pro/E cut_feed, step_depth and spindle_speed parameters, based on the machine tool power constraints and machining time. Although the tool grade recommended is K313, K68 is the tool grade actually used. Since both grades are similar and K68 was available in the department's CNC Machining Laboratory, the K68 was selected instead of the K313.

Subsequent steps in PTCS transfer the ToolPro recommendation data into a user-specified Pro/E machining parameter file. This file is then opened in Pro/E with the selected values replacing the parameters that otherwise have a reference value o f - l . Other parameters are changed as

92 K.K. Thomas. G. VK Fischer~Journal of Materials Processing Technology 61 (1996) 87-92

appropriate. One important parameter that has to be defined is "roughstock allow." As the name suggests, it is the stock allowance that remains at the end of the rough machining operation. This parameter specifies the depth of cut for the subsequent, single pass Profile-Turning NC sequence. It is manually set to a value of 0.008 inch.

GRADE APPLICATION ADVISOR - REVISION !.2 Recommendation

Material: Aluminum

Type of Cut: Semi-Finishing: to Rou,zhin~

Depth of Cut: 0.100 inch Diameter: 1.500 inches Length: 2.250 inches

Grade: K313 Speed: 1238 sfm

Feed: 0.015 ipr Spindle Speed: 3152 rpm

Feed: 46.229 ipm Metal Removah 21.789 cu in/rain Power: 5.0 hp

Time in Cut: 0.05 rain

Fig. 10. Recommendation for the Area-Turning sequence.

The ToolPro option is next used to define the machining parameters for the Profile-Turning NC sequence (Operation 2) and the complete recommendation generated by ToolPro is shown in Fig. 1 l. The steps and the logic followed are very similar to those for an Area-Turning NC sequence. The rough_stock_allow parameter is not defined for Profile- Turning NC sequences for reasons explained, previously.

the importance of process planning in the engineering effort, the research reported in this paper focused on the CAPP part of CAD/CAM.

MICS uses the concepts of wrappers and neutral data formats to provide a structured, yet loosely defined method to integrate off-the-shelf CAD/CAM software packages into a system. Since there is only one user interface to the CAD/CAM system, consistency in its use is maintained. Further, MICS supports the concurrent engineering paradigm by providing a common computer environment for the different CAD/CAM functions.

PTCS, a system that integrates Pro/E and ToolPro, implements the MICS method to automate the machining parameter selection function within the Pro/E process planning function. Using PTCS, machining parameters can be selected based on material, machine power, and machining time considerations. The operation of PTCS was demonstrated using the Gear Shifter Knob example.

As expected, both MICS and PTCS have advantages and limitations. Some advantages include direct integration of commercial CAD and CAM software packages, single user interface, and support of iterative design analysis to achieve a more optimal design. Some limitations include possible duplication of data storage, longer processing time than for a specialized CAD/CAM system, and limitations of commercial packages to support integration. However, the proposed implementation does provide an approach for increasing the productivity of machining process planning and other CAD/CAM system applications that can ultimately lead to an integrated concurrent engineering environment.

GRADE APPLICATION ADVISOR - REVISION 1.2 Recommendation

Material: Aluminum

Type of Cut: Finishin~

Depth of Cut: 0.008 inch Dianmter: 1.500 inches Length: 2.250 inches

Grade: K313 Speed: 1749 sfm

Feed: 0.002 ipr Spindle Speed: 4453 rpm

Feed: 7.422 ipm Metal Removal: 0.28 cu inlmin Power: 0.1 hp

Time in Cut: 0,30 rain

Fig. 11. Recommendation for the Profile-Turning sequence.

The end result of process planning in Pro/E is a CL data file that is later post-processed into the machine-specific NC code. The process plan for the Gear Shitter Knob consists of six operations, of which, the first two are setup using PTCS. Pro/E stores each NC sequence as a feature, one for the Area- Turning NC sequence and one for the Profile-Turning NC sequence[4].

5. Conclusions

There are a number of powerful, commercial CAD/CAM software packages in the market today. However, few of today's CAD/CAM software packages can interface with one another and work in a cooperative environment.

Through this research, a method for integrating commercial CAD/CAM software, called MICS, was developed. Because of

References

[1] Chang, T. C. and Wysk, R. A., An Introduction to Automated Process Planning Systems, Prentice-Hall, Inc., Englewood Cliffs, NJ, 1985.

[2] Logan, F. A., Logan Associates, U.K., "Planning-The Vital Link Between Design and Production," Reprinted in CAPP Computer Aided Process Planning, Computer and Automated Systems, Association of SME, Dearborn, MI, 1985.

[3] Chang, Y. C., Expert Process Planning.for Mant~facturing, Addison-Wesley Publishing Company, Menlo Park, CA, 1990.

[4] Thomas, K.K., "Integrating Commercial CAD/CAM Software for Process Planning Applications," M.S. Thesis, Department of Industrial Engineering, The University of Iowa, Iowa City, IA (1995).

[5] Wu, J. K., Choong, F. N., Kvidera, D. A., Jiang, X., Hsieh, L. J., McGee, B. and Sangareddi, K., "Application Wrappers in a Simulation-based Concurrent Engineering Environment," Technical Report, Center for Simulation and Design Optimization of Mechanical Systems, College of Engineering, The University of Iowa, Iowa City, IA (1994).

[6] Rembold, U., Nnaji, B. O. and Storr, A., Computer Integrated Manufacturing and Engineering, Addison- Wesley Publishing Company, Inc., New York, NY,1993.

[7] Parametric Technology Corporation, Waltham, MA, Pro~ENGINEER ® User's Guide, 1995. Kennametal lnc., Latrobe, PA, Grade Application Advisor User's Manual, ToolPro TM Software Series, 1989.