V. Read the text and arrange the following items of an outline.

a) Types of systems implemented in CAD

b) 3D solid modelling

c) The development of the graphical user interface prototype in the early 1940s

d) The creation of final product

e) CAD application

TEXT A

Designers have long used computers for their calculations. Initial developments were carried out in the 1960s within the aircraft and automotive industries in the area of 3D surface construction and NC¹ programming, most of it independent of one another and often not publicly published until much later. Some of the mathematical description work on curves was developed in the early 1940s by Isaac Jacob Schoenberg. Effectively, it was a prototype of graphical user interface, an indispensable feature of modern CAD.

Computer-aided design (CAD) is the use of a wide range of computerbased tools that assist engineers, architects and other design professions in their design activities. It is the main geometry authoring tool which involves both software and sometimes special purpose hardware. Current packages range from 2D vector drafting systems to 3D solid and surface modelers. CAD is used in many ways depending on the profession of the user and the type of software in question. Each of the different types of CAD systems requires the operator to think differently about how he will use them and he must design their virtual components in a different manner for each.

There are many producers of 2D systems, including a number of free and open source programs. These provide an approach to the drawing process without all the fuss over scale and placement on the drawing sheet that accompanied hand drafting, since these can be adjusted as required during the creation of the final draft.

3D wireframe is basically an intention of 2D drafting. Each line has to be manually inserted into the drawing. The final product has no mass properties associated with it and cannot have features directly added to it, such as holes. The operator approaches these in a similar fashion to 2D systems, although many 3D systems allow using the wireframe model to make the final engineering views.

3D “dumb” solids (programs incorporating this technology include AutoCAD and Cadney 19) are created in a similar fashion to the way you would create the real world object. Each object and feature, after creation, is what it is. If the operator wants to change it, he must add material to it, subtract “material” from it or delete the object or the feature and start over. Due to this, it doesn`t matter how the initial operator creates his components, as long as the final product is represented correctly. If future modifications are to be made, the method used to make the original part will not, in most cases, affect the procedure used to make new modifications. Draft views can easily be generated from the models. Assemblies generally don`t include tools to easily allow motion, or identify interference between components.

3D parametric solid modelling² requires the operator to use what is usually referred to as “design intent”. The objects and features created are adjustable. Parametric solids require the operator to consider the consequences of his actions carefully. What may be simplest today could be worst case tomorrow.

CAD implementations have evolved dramatically. Advances in programming and computer hardware, notably solid modelling in the 1980s, have allowed more versatile applications of computers in design activities.

Notes:

¹NC ( numerical control) – числовое управление;

² Solid modelling – объемное моделирование.

Date: 2016-01-14; view: 1204