7.  Teaching CADCAM and solid modelling to engineers

Y.T. Lee

Abstract

This paper describes the courses in CADCAM and solid modelling for engineering students at Nanyang Technological University. Basically, our students will mainly become users of CADCAM technology and not developers. There are three levels in our courses: what students are taught varies from the use of a CAD system for draughting to the underpinnings of the technology. Solid modelling is emphasized as a means of creating a truly 'complete' object database, from which engineering drawings with multiple views can be generated and for supporting other applications such as mass-properties calculation and interference checking.

Background

Singapore has a vibrant economy with a very strong manufacturing base. Many multi-nationals and local or regional corporations have design and manufacturing facilities in Singapore. Due to the shortage of space and labour and the relatively high and increasing labour cost, the government has placed emphasis on non-labour-intensive and highly automated industries, by giving incentives and assistance for companies to automate. Consequently, there is a need to produce graduates who are trained in automation techniques. In this regard, CADCAM and other computer-based applications feature strongly in the curricula of the local tertiary institutions.

It is worth pointing out that the drive to teach CADCAM technology is currently oriented towards end-users, not developers. The courses we teach, while covering sufficient depth and breadth of theory and fundamentals for a university course, contain a strong emphasis on the application of the technology.

The support from the government in terms of grants and research funds is generous. Hence the laboratories are well equipped, and the students have opportunities to experience the capabilities of a range of modern systems.

This paper will deal with the teaching of solid modelling, contained under the CADCAM umbrella, at both undergraduate and postgraduate level.

The courses at Nanyang Technological University

Solid modelling features as parts of CADCAM-oriented courses at different levels in the School of Mechanical and Production Engineering.

Beginner's level

At the beginner's level, solid modelling is introduced to students as a tool for design. This is done as a part of an engineering graphics course in which students learn the traditional pencil-and-paper techniques as well as the use of a CAD system. The contrast between the two aspects is very quickly brought home: the advantages of CAD are obvious. Solid modelling is a major part of the CAD component, and is used to establish the principle that, in design, it is the three-dimensional model that we should create and not different views of the same object, as in manual drawings and ordinary two-dimensional CAD systems: views are produced from solid models, and not the other way round.

The system used for this course is ProEngineer; it can generate drawings from solid models with associativity between the drawings and the parent solid models. The advantages of solid modelling are quickly apparent, and are exploited in the calculation of geometric properties and interference checking.

Higher levels

Students continue to use solid modelling in projects throughout their undergraduate course. For example, in a second-year engineering design course, they are required to use the solid modelling capabilities in a CAD system for the visualization, evaluation and documentation of a design, including the production of drawings. Further formal teaching on the use of the systems is not part of the course; students are expected to be conversant with the systems, or else to be able to learn the skills by themselves.

A practical course-which is an extended laboratory of 30 hours, on plastic injection moulding-was designed to allow students to exploit a wide range of the capabilities of a CAD system in the design of a product and the corresponding mould inserts, and subsequently to make the product using a moulding machine. The product, with some prescribed restrictions to ensure that it is suitable for moulding, is of the student's own choice, and it is designed using the modelling capabilities of the system. This model is then 'translated' into models of mould inserts (usually two for each product) using Boolean operations provided by the system. NC machine codes are generated directly for machining the inserts, which are then produced on a CNC machine in the School. These inserts are used in a plastic injection moulding machine and the physical components are produced.

In this way the students can appreciate the power of solid modelling in enabling the direct design-to-product process, while exploring the depth of the system by themselves. At the same time, they learn about numerically controlled machines and plastic injection moulding. They also end up with a souvenir.

In these courses, the students are only end-users of CAD and solid modelling, and do not get to know how the various operations are performed or how the objects are represented. Considering that most of these students will be end-users in industry, such exposure is adequate. However, this does not tickle curious minds as to what actually happen behind the well-dressed buttons of modern CAD systems. Students with curiosity about this can satisfy it in a third year course on computer-aided design, where the fundamentals of CAD and solid modelling are taught. This course takes them through the rudiments of computer graphics and introduces the mathematics of curves and surfaces. Solid modelling is a central component, and both CSG and boundary models are treated in depth. The applications of solid modelling, such as mass-properties calculation, assembly and product modelling are also presented. Data exchange and standards such as IGES and STEP, which are important aspects in the use of a CADCAM system, are also covered here.

In their final year, undergraduates are required to do a substantial project lasting for the whole year. A student who has special interests in an area can choose to pursue a related project. In recent years, colleagues and I have run a number of projects dealing with different aspects of CAD and solid modelling.

Master's degree in computer-integrated manufacturing

Nanyang University offers a master's degree course in computer-integrated manufacturing (CIM) which centres on the use of computers in supporting and integrating manufacturing activities. Subjects include management aspects of using computer technology, factory automation, knowledge-based systems, computer networking, simulation, database technology, concurrent engineering and, of course, computer-aided design and manufacturing.

This is a part-time course (with classes held two evenings a week) designed for working engineers, and the students are drawn from the local population of engineering and computing graduates. These students, although they are all graduates working in relevant industries, have varied backgrounds, sometimes at different ends of the CIM spectrum. Some are established production engineers who have had little contact with computers; some are computer-technology graduates to whom design and manufacturing sounds like double Dutch. All have the common aim of learning how computers can be used in the manufacturing environment.

One of the key objectives of the course is that the contents ought to be relevant to local industries. It is also necessary to keep the relevance of a subject within the CIM framework in view, where the integration of the subject with other CIM activities is a central issue. (It is all too easy for a specialist lecturer to sink into the depths of his or her pet topic and lose the larger view.) It is difficult to design a course at the graduate level that can satisfy these objectives while making sure that all the students are taken along.

So far, our presentation of computer-aided design has always concentrated on the fundamentals, treating geometric modelling in depth. This includes the basic data-structures and algorithms for solid modelling. Recent concepts of feature-based and constraint-based design are also introduced. We emphasize applications of CAD, and algorithms and system architectures for supporting different applications are also covered. Each student is given the opportunity to use a CAD system if they have not already used one in their job.

Some comments on references

CAD and solid modelling is still evolving, and so the material we deliver is constantly being updated. There are books on the subject that can serve as good references; they include Mortenson's Geometric Modeling (John Wiley, 1985), Hoffmann's Geometric and Solid Modeling: an Introduction (Morgan Kaufmann, 1989) and Zeid's CADCAM : Theory and Practice (McGraw-Hill, 1991). The first two of these books concentrate on geometric and solid modelling, and the third is a comprehensive treatment of different aspects of CADCAM, including geometric and solid modelling, although the topics do not seem to be well integrated.

While these books cover the established aspects of modelling technology well, newer concepts like feature-based and constraint-based modelling are not included. To support the teaching of the subject with an up-to-date flavour, new books that treat these topics in depth are needed.

Other books have appeared recently, such as CADCAM: from Principles to Practice by McMahon and Browne (Addison Wesley, 1993) and Computer Graphics and Geometric Modelling for Engineers by Anand (John Wiley, 1993), designed to serve undergraduate-level courses. But these do not have sufficient depth in geometric and solid modelling.

Supporting facilities

The Singapore government is strong in supporting its two universities and funds are available to equip the laboratories with modern facilities, both software and hardware. The School of Mechanical and Production Engineering at Nanyang Technological University has a CADCAM Laboratory with 60 workstations, sufficient to handle a population of over 450 students per class per year. The software that we are currently running on these workstations for teaching is ProEngineer. But Unigraphics, IDEAS, and several other systems are also available. Allied with these are finite-element analysis software packages such as ANSYS, PAFEC and MARC. The laboratory also houses 30 PCs running systems such as AutoCAD, CADKey, and Algo. Other modelling and CADCAM systems are available at other sites in the University. The kernel modeller ACIS is also available.

The machines in the CADCAM Laboratory support research activities as well as teaching. (That includes their use to design rigs and so on). However, research into the underlying techniques of geometric and solid modelling are carried out in this laboratory, too. The School also has a CNC laboratory equipped with two machining centres, several numerically controlled lathes and turning machines, and two EDM machines. 

Conclusion

This paper has outlined the teaching of solid modelling in the School of Mechanical and Production Engineering at NTU, Singapore. Invariably, the formal courses have solid modelling under the larger umbrella of CADCAM. This is a correct approach: after all, that is where engineers will encounter solid modelling. Hence the teaching of solid modelling is strongly intertwined with the teaching of CADCAM. Courses for students who are mostly prospective end-users do not go into the technical details of the technology, but courses directed at more specialized students do. It is our opinion that modern CADCAM systems are quite well designed and sufficiently user-friendly, and it is straightforward for students to gain proficiency by using them on their own. Hence we introduce our students to a system in the first year; subsequently, they have to use and learn more about it by themselves.

Back to index