Advanced CAD Modeling

The ability to use a variety of CAD tools is one of the most basic competences expected of a modern engineer. It represents a language and a tool, and is used to communicate with other engineers anywhere in the world. While the basic CAD operations are fairly easy to learn, understanding the functioning of CAD tools requires more detailed knowledge of mathematical and computer laws behind the individual CAD operations. In this chapter the reader will learn about the mathematical laws of CAD curves and surfaces that are the key to understanding freeform modelling. It begins with a computer description of the curves in space, which is followed by various procedures for creating freeform surfaces based on these curves. The chapter ends with an explanation of several definitions and descriptions of the transitions, i.e., the continuity between the curves and the surfaces. Understanding the latter is becoming increasingly important for the automotive, aerospace and consumer-goods industries, as properly executed transitions between surfaces have a significant effect on the strength, aerodynamic, ergonomic and aesthetic properties of a product. At the same time, these topics are often not covered by many regular engineering curricula due to a lack of time or because their importance is overlooked. As a result, engineers only deal with them when they face a concrete challenge for the first time—which is often on their first job.

As a rule any CAD modelling should eventually result in a solid model or a system of solid models with all their functional and aesthetic details. Achieving this goal requires the user to understand modelling with features, solid models and the basic principles of the Boolean algebra of solid CAD bodies. As such, this is an essential part of surface modelling, too. Surface modelling is a valuable tool, providing an experienced CAD designer with a faster and better execution of complex CAD shapes. However, experienced CAD designers will not abandon working with features and solid bodies. Instead, based on their own knowledge, experience and the expected results, they will choose the most appropriate approach—the best tool for creating individual steps and details, while navigating through all their skills. This chapter presents the importance of such navigation for the example of a Kaplan turbine blade. This is an example of a product where one part has a fairly complex but very important surface, defining the efficiency of the hydro power plant, while the other end has a geometrically regular shape, allowing accurate and flexible assembly with the turbine rotor. The fastest possible, good-quality results require concurrent decisions about whether to execute individual steps by means of features or surfaces. This chapter explains the process of creating surfaces, creating solid bodies from surfaces, and combining solid bodies in order to come to the end product.

The objective of this chapter is to present the use of 2D graphics (sketches, drawings, photographs, 2D documents) for the creation of 3D models. The application of 2D graphics is common and also immensely useful for reconstructing existing technical products, as well as for the development of new products in cooperation with industrial designers. This chapter also shows how to modify surfaces freely—creating freeform surfaces in order to achieve specific design effects. Although the free forming of surfaces is not related exclusively to surface modelling—planes, as well as solid bodies can be free formed, too—and for the reasons of presenting the procedure and the technological work clearly, free transformation is explained on a surface body in this case. In the example, shown here, a 2D designer sketch is used to create a lamp shade, i.e., a shell element that can be created most easily by means of surface modelling. This chapter also shows how to uniformly divide a continuous plane or surface into several separate surface segments, while preserving their geometric continuity. The suggested procedure can be used for different purposes in design and engineering, including modifying the visual surface properties of a product, or in order to set limited stress areas in numerical simulations.

Using a combination of surfaces and their transformations, one advantage of surface modelling is the ability to be able to create such CAD geometries that would not be possible only by combining the basic features of solid modelling. Using the example of a mass-market product—a hand blender—a number of procedures for working with surfaces are presented that can lead to a final target shape. Choosing a particular step depends on the functional and technical views, as well as the mathematical rules of CAD surface modelling. The choice of the model is not random, as modelling end products for mass-market products belongs to the most demanding design tasks, as it requires fulfilling a variety of working and design functions, many compromises, a great deal of experience and work, all at the same time. Here, it is important to understand the logical, mathematical properties of curves, surfaces and operations for working with them. Thus, this chapter brings the theory from the first chapter of this book into practice.

Product development should begin by fulfilling the product’s primary functions during the concept stage, whereas its auxiliary functions are added later, during the detailed design. Nowadays, nearly all products with an external shape that is related with the human or natural environment are developed in such a way that the product shape is developed as a single uniform body, which is later cut/split into individual components of the same system. In this chapter the activities will continue on the model created in the case study started in the previous chapter. The chapter will explain how to cut up a uniform solid CAD model into several bodies and how to create joining edges and make a new assembly with the newly created bodies. Later, one such created hand-blender casing’s components serves as an example of creating a mould cavity with one tool cavity for injecting a polymer product. This case study presents additional commands to use with surfaces, features for creating design elements that are characteristic of the products made by polymer injection moulding, and creating parting curves and planes, up to the point of creating a tool cavity.

A few control points of a B-spline are not enough for an accurate description of the geometry between the selected points that is supposed to follow physical laws. With a good understanding of the physical laws that you want to describe, and by reducing the distances between the interpolation points, it is possible to approach closely to the exact curve; however, at the expense of increasing the volume of the required data and computation time, while this will still be only an approximation of the exact function. Thus, in many cases it is faster, easier and most of all, more accurate, with less required data, to describe a curve using an exact physical or mathematical equation. This is possible with modern modellers. In this chapter we demonstrate how to describe the geometry with exact physical equations. Two case studies show how to control 2D and 3D curves, both in explicit and parametric forms. Furthermore, modern modellers allow the attachment of equation parameters and variables to the existing CAD geometry or dimensions.

Reverse engineering has been practised since the beginning of technology. Fundamentally, it is about the identification of existing technical and natural solutions, and their reconstruction into new, identical or even improved technical solutions. Over the years it has flourished systematically, thanks to the development of new and technologically increasingly advanced and economically affordable measuring procedures, which allows the accurate reconstruction of not only technical principles but also detailed shapes and dimensions. This chapter explains the position of reverse engineering in the modern design and development process. It also introduces the main measuring methods for capturing data on the geometry of physical objects. These methods are divided into groups, depending on how they work and the physical laws on which they are based. We also present the main advantages and disadvantages of particular groups of methods, and recommendations for their application where the best results can be achieved.

This chapter deals with acquiring information about the shape of products by means of contact measuring devices. The objective of such measurements usually involves remanufacturing or changing the 3D models of an object, and controlling the geometric accuracy of the product, compared to its 3D model. Several types of measuring devices, sensors and their functioning are presented. As an example, a physical product—an automotive cooling thermostat—is measured and a unique new model is created on the basis of the measured data. We present the correct use of a mechanical measurement arm to capture data on the geometry of an example product. The acquired data then serve as a basis for modelling a complementary part that is intended to retrofit the existing measured component.

Reconstructing complex surfaces and geometries is generally performed with the use of optical measuring systems that allow the capture of large volumes of data in short periods of time. For the most part these are laser measuring systems, as they allow simple and fairly reliable blocking of the external effects on measuring. Understanding laser measuring systems and their functioning is recommended for the high-quality scanning of 3D shapes of physical objects and their CAD reconstruction from the captured data. This chapter deals in detail with the laws of laser triangulation: we present the basics of determining points by means of optical triangulation, the basics of laser light and its effect on measuring, as well as possible problems when measuring due to the natural properties of the laser beam; we present the most frequent limitations of 3D laser measurements and the reasons for measuring errors. This chapter also presents some methods for assessing the quality of measurements. It ends with an explanation of the effect of the optical properties of surfaces on measuring.

Using practical examples, this chapter presents in detail the procedures for reconstructing CAD models from point clouds. These procedures differ depending on the product’s geometry. We present a procedure for reconstructing the objects where geometrically simple building blocks—surfaces—prevail, as well as two procedures for reconstructing objects with prevailing freeform shapes. The first one involves creating a CAD model that is based on the contours that follow the captured point cloud, while in the other one, the cloud is used to create a closed—watertight—mesh of four-edged freeform patches. The chapter explains working with points, and creating a triangular mesh, used as a basis for reconstructing the shape of an object into a CAD model. The geometric approach explains the steps of attaching the basic geometric surfaces to a triangular mesh, then trimming and combining them into a solid model. The first freeform surface approach provides advice for setting the contours that will yield the best possible CAD model. We also explained in which cases to adopt the approach of reconstructing freeform models. The second freeform-surface approach provides recommendations for proper work with freeform patches in order to achieve a correct description of the surface and the optimum patch density.

This last chapter covers the details of fillets, i.e., the transitions between surfaces. Adding fillets and other aesthetic details is usually recommended just before the end of the modelling process. This strategy is mainly due to better control of the main function and shape of the product, which also includes changing and modifying the product at some later stage, if necessary. It makes the computer model more robust to changes and the design is more stable. On a variety of examples this chapter presents different geometry-transition problems and possible solutions for creating better-quality fillets and other design solutions. In order to present as many different solutions as possible, there is no single large case study. Instead, there are several small examples of different models with suggested problems in need of a solution. In this way many explicit problems and approaches can be clearly exposed and solutions demonstrated. As a conclusion to this chapter, a few guidelines are presented, assisting in creating high-quality 3D models. The recommendations refer to SolidWorks, but they also apply to most other up-to-date modellers.