CAD/CAM Education in Hong Kong 171

N.L. Hickerson Head, Computer Centre, Hong Kong Polytechnic

This paper is concerned with the application of computer • methods to mechanical design in Hong Kong and the education of engineers to meet the need for manpower in this field. In particular, the development of CAD/CAM at the Hong Kong Polytechnic is described. The initial system adopted to meet teaching and research needs includes the capabilities of geometric modelling, finite element analysis, drafting, and kinematic analysis. The educational pro- gram also includes practical work with robots, computer numerically controlled machines, and computer applications to factory management.

Keywords: Computer aided design, computer aided manufac- turing, geometric modelling, drafting, education, finite element analysis, numerical control, robotics.

1. Introduction

The application of C A D / C A M methods by Hong Kong industry has developed slowly until recent times. The reasons for this are several, and include the judgement that manpower was less costly than the hardware and software needed to implement C A D / C A M . Also, in certain fields of engineering, original design activity by local agen- cies was relatively low in volume. These factors are changing, and cofipled with the declining cost of computer hardware, there is now a growing inter- est in the use of C A D / C A M in almost every aspect of engineering and architecture. One sup- plier of computer systems is currently installing an average of three C A D / C A M systems in Hong Kong every two months, and most of the major vendors of C A D / C A M facilities are now in oper- ation here.

In order to equip future Hong Kong engineers with education in C A D / C A M methods, syllabuses of the engineering departments of local institu- tions of higher education include • the study of C A D / C A M methods. This paper describes the development of C A D / C A M at the Hong Kong Polytechnic, particularly in the areas of mechani- cal design and manufacturing.

2. Approach to CAD

Norris Hiekerson has served as the Head of the Computer Centre at Hong Kong Polytechnic since 1979. Previ- ously he was a Principal Lecturer in the Civil and Structural Engineering Department, having joined the Poly- technic in 1973. Mr Hickerson holds degrees in civil engineering from Vanderbilt University, The University of Illinois and Columbia University.

North-Holland Robotics 1 (1985) 171-175

In concept, an information flow as illustrated in Fig. 1 was considered for the provision of a CAD system. All elements for a completely integrated system are not yet in place, but steady progress is being made. Specific functions required for the C A D system are the following.

2.1. Geometric Modelling

Geometric modelling is one of the essential features of a CAD system. Using such a system, a designer can create the shape of a machine part on a graphics display screen. The pictorial model is converted by the computer system into mathemati- cal form, and is stored for future use. The model may be recalled and manipulated by the designer.

0167-8493/85/$3.30 © 1985, Elsevier Science Publishers B.V. (North-Holland)

172 N.L. Hickerson / CAD in Mechanical Design

DESIGMER I

/ ILLUSTRATIDM &

FILMS

FLFIM OF IMFORMATIOM IN A CAD SYSTEM

I

GRAPHICS I ~

TECHMICAL LISTIMGS DESCRIPTIONS

Fig, 1. CAD information flow diagram.

The model may be rotated, cross sections may be displayed, and detail views may be shown.

A modelling system may be two-dimensional or three-dimensional. Both facilities are needed for a general mechanical design system. Also, some two-dimensional CAD software packages provide a pseudo three-dimensional capability, in which perspective or isometric views are created from the data from two-dimensional views.

Three-dimensional modelling software often uses a wire-frame type of representation, in which the form of a part is created with connected line segments. Wire frame systems are often inade- quate to model a solid object, and more refined representation is possible with 3D surface model- ling or solid modelling methods.

2.2. Analysis

Another major task of a CAD system is stress analysis. Finite element solutions for this type of problem has been in use for many years. Programs such as PAFEC, ANSYS, SAP, NASTRAN, and STRUDL provide standard analysis features, in- cluding dynamic and thermal effects. Also, many

• CAD systems provide automatic mass property calculations, such as volume, first moments, and centre of mass.

A requirement for an analysis system is the availability of adequate pre- and post-processors. Originally, the input to a finite element program called for large amounts of numerical data, such as node coordinates and section properties. For a sizeable problem, this could be very difficult to check. More than one engineer has felt the frustra- tion of having a lengthy computer run proving to be useless because of data errors. Fig. 2 shows a finite element• mesh generated by a typical pre- processor. Also, the output from a large finite element analysis is normally a ream of computer paper, with row u p o n row of figures representing displacements and stresses. This is often difficult to interpret.

Pre- and post-processors for most finite element packages are available which help to avoid errors in input data, and facilitate the interpretation of output. Color display can be a help in this regard, for the identification of areas of stress concentra- tion, etc.

2.3. Drafting

Computer assisted drafting provides for the au- tomatic production of engineering drawings from information stored in the computer about the geo-

N.L. Hickerson / CAD in Mechanical Design 173

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AUTO SCALING XV=I YV=2 ZV=3 D iST=6.14 XF=3.98 YF=4.86 ZF=1.44

WIND=2 AUTO SCALING XV=-I YV=I ZV=I OIST=G.74 XF=4.08 YF=4.67 ZF=1.42 HIDDEN

W I N D = 3 AUTO SCALING XV=.7 YV=.3 ZV=I DIST=18.5 XF=4.17

Fig. 2. Finite element node network.

POLYTECHMIC CAD

COMPUTER CENTRE

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CALCEIMP 948 3XGIGI TERMINALS TEKTRONIX 4014 TEKTRONIX 4107 SIGMA 6014 SUMMAGRAPHICS

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FACILITIES

VAX 11/750 8 MBYTE MEMORY 2X67 MBYTE DISKS 2X300 MBYTE DISKS 800/1600 BPI MAGNETIC TAPE UNIT

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Fig. 3. CAD laboratory configuration at HKP.

174 N.L. Hickerson / CAD in Mechanical Design

metric model. In fact, drafting is often the first function to be automated in a design office which adopts CAD. Functions required of a computer drafting system are the following: • Scaling, so that drawings or stored elements of a

drawing may be produced to any scale. • Symbol library; a library of commonly used

symbols and details which may be created once and stored for future use.

• Overlays; the capability to create and store various overlays that may be recalled for future u s e .

• Capability to enter text for drawing annotation. • Copy function, to allow repetition for repro-

ducing any part of a drawing already created on another area of the drawing.

• Deletion, so that lines or areas of a drawing may be erased.

• Automatic cross hatching. • Automatic calculation of distances and subse-

quent dimensioning. • Automatic calculation of enclosed areas. • Geometric functions, such as rotation of views

and moving a line to a parallel position. • The system should support digitizer input. A schematic diagram of CAD facilities installed at

the Hong Kong Polytechnic is shown in Fig. 3. Another CAD capability needed for mechanical

design which is still to be added to the system is the facility for Kinematic analysis. This provides the ability to solve complicated mechanism prob- lems, so'me of the systems available giving an animated view of the motion.

3. CAM Development

The functions of CAM systems which have been implemented, or are planned for adoption in the case of the Hong Kong Polytechnic are de- scribed below.

3.1. Numer i ca l Control

Numerically controlled machines have been used in the teaching work of the Hong Kong Polytechnic for several years. Such machines are in use in the Polytechnic's Industrial Centre and the Department of Production and Industrial En- gineering.

Numerical control (NC) implies the technique of controlling a machine tool with coded informa- tion to make a part. Instructions are written in a

CAD/CAM SYSTEM HARDWARE CONFIGURATION

DISK STORAGE I (300 MB)

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INSTAVIEW C COLDUR ~DRKSTATION

BRIDGEPORT NC MILL/DRILL

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L ~_A P E DRIVE f

PRDGRAMMABLE I COMMUNICATION UNIT

i I MITSUI SEIKI CNC MACHINING CENTRE

Fig. 4. Elite CAD/CAM laboratory configuration, HKP Dept. of Production and Industrial Engineering.

N.L. Hickerson / CAD in Mechanical Design 175

programming language such a APT, and are usu- ally stored on magnetic or paper tapes. These are used to control the machine tool.

Computer Numerical Control (CNC) refers to a system in which the computer is connected directly to the machine tool being controlled.

3.2. Robotics

Principles of robotics are now included in the educational program for engineering students at the Polytechnic. Robots are used to perform a variety of materials handling tasks in the C A D / C A M system, and are used to select and position tools and work pieces for the NC machine tools.

At present, robots are usually programmed by an operator physically leading the robot through the desired operations, the so-called " teach mode". Work is now in progress to develop systems where instructions to the robot are issued directly by the computer, and simulation programs are available which will display the positions of the robot as its various instructions are executed.

3.3. Factory Management

The operations of the CAM functions of a manufacturing facility are coordinated with fac- tory management methods. The computer may be used to perform such management tasks as inven- tory control and the scheduling of resources. The technology is leading to ever-increasing automa- tion of manufacturing processes.

A diagram of the C A D / C A M laboratory of the Hong Kong Polytechnic's Department of Produc- tion and Industrial Engineering is shown in Fig. 4.

4. Conclusion

The use of C A D / C A M methods in Hong Kong is still at an early stage. There are, however, strong motivations to adopt modern manufacturing methods. While computers are no panacea, the use of C A D / C A M is increasing as local organizations find profitable applications. It is incumbent upon educational institutions to be a community re- source in this new area of technology.