01-01-2013, 04:57 PM
Engineering Drawing and CAD.
The design process:
Almost everything around us has been created by, or is influenced by, engineers:
Buildings, vehicles, roads, railways, food growing and processing, books, medical care,
recreation, etc.
All of these have either been conceived and created from scratch or have evolved from
existing ideas. Either way, an engineering design process will have been followed, in
one form or another. The Design as a generic tool module provides an interesting a
comprehensive introduction to engineering and design, so a detailed discussion of the
design process will not be included here.
The design model.
The concept of the designer working with a model of a design is fundamental to the
design process.
The design model is a representation of the design. This model could be anything from
a few ideas in the designers head, through to rough sketches and notes, calculations,
sets of detailed formal engineering drawings, computer generated 3D representations,
physical prototypes, etc.
The design model would be used by the designer to record and develop ideas and to
provide a basis to evaluate the design.
Larger design projects are undertaken by more than one engineer. Design models are
used to communicate and demonstrate ideas between all those concerned with the
product design, development, manufacture and use.
Orthographic projection.
We have discussed both the role of the design model in the design process and the
importance of the representation of the form or shape in this role.
Now we will consider in detail the methods designers use to represent the form of their
designs.
Back in the 18th century a French mathematician and
engineer, Gaspard Monge (1746-1818), was involved
with the design of military armory. He developed a
system, using two planes of projection at right angles
to each other, for graphical description of solid objects.
Pictorial Drawing.
Orthographic projection is used as an unambiguous and accurate way of providing
information, primarily for manufacturing and detail design. This form of representation
can however make it difficult to visualise objects. Pictorial views can be created to give a
more three dimensional impression of the object. There are three types of pictorial
projections commonly used, as shown below.
Third angle projection.
The construction method used is the same. The difference between first and third angle
projection when creating or reading really lies with the positions of the views. For the
same component, an orthographic projection drawing with the same front, side and plan
views would look like Figure 2.2b below.
Part modelling:
You can create 3D solid part models of your
designs, such as this conrod. The dimensions that
define the model are related to each other and can
be changed and controlled. So, if you change one
dimension, others will change with it. Software that
allows this is refereed to as parametric. For example, change the center distance of the
bores of this conrod and the whole model will stretch out.
You can also assign material properties, analyse mass properties, control the colour and
texture of the appearance, create photo realistic images with lighting, shadows and
perspective.