The Engineering Design Process

Engineering design is one of the processes normally associated with the entire business or enterprise. from receipt of the order or product idea. 10 maintenance of the product. and all stages in between (Figure 2.6). The design process requires input from such areas as customer needs. materials. capital, energy. time requirements. and human knowledge and skills. Two important societal concerns that an engineer must take into account are legal and environmelltal issues. Every business must operate within the law that governs their business. When designing. it is important that the engineer understand that legal issues may affect the designed product. Safety laws related to automobiles are an example of how government legislation can affect a design. Governmcnt regulations related to the cnvironment may also havc a bearing on the final outcome of the design. For cxamplc. the cmission requircments on an automobile cngine havc a great effect on the final design. An cxample of human knowledgc input is an cngineer's knowledge of graphics. mathematics. and the sciences. Such knowledge is used by the engineer to analyze and solve prohlems. An engineering design involves hoth a process and a product. A process is a series of continuous actions ending in a panicular result. A product is anything produced as a result of some process. As the design of a product or process is developed. the design team applies engineering principles, follows budgetary constraints. and takes into account legal and social issues. For example, when a building is designed. engineering principles arc used to analyze the structure for loads: determine the structure's cost. based on the materials 10 be used. the size of the structure. and aesthetic considemtions; and create a design that adhcres to the local laws. Graphics is an extremely important pan of the engineering design process. which uses graphics as a tool to visualize possible solutions and to document the design for communications purposes. Graphics or geometric modeling using CAD is used to visualize, analyze, d(X~ument. and produce a product or process. In fact. geometric modeling it,<;elf could be considere a process. geometric modeling produces final design solutions, as well as inputs to the production process, in the form of wrnputer databases. As a product. geometric modeling is a result of the engineering design process. 

The Engineering Design Process
Bertoline-Wiebe-Miller:
Fundamentals of Graphics Communication,3/e
The McGraw-Hill Companies,2001
 

Sectional views

There are some instances when parts have complex internal geometries and one needs to know information about the inside as well as the outside of the artefact. In such cases, it is possible to include a section as one of the orthographic views. A typical section is shown in Figure 2.16. This is a drawing of a cover that is secured to another part by five bolts. These five bolts pass through the five holes in the edge of the flange. There is an internal chamber and some form of pressurised system is connected to the cover by the central threaded hole. The engineering drawing in Figure 2.16 is in third angle projection. The top drawing is incomplete. It is only half the full flange. This is because the part is symmetrical on either side of the horizontal centre line, hence the 'equals' signs at either end. This means that, in the observer's eye, a mirror image of the part should be placed below the centre line. Note that the view projected (beneath) from this plan view is not a side view but a section through the centre. In museums, it is normal practice to cut or section complex parts like engines to show the internal workings. Parts that are sectioned are invariably painted red (or any other bright colour!). In engineering drawing terms, the equivalent of painting something red is to use cross-hatching lines which, in the case of Figure 2.16, are placed at 45 ~ The ISO rules concerning the form and layout of such section lines is given in Chapter 3. The method of indicating the fact that a section has been taken on the view, from which the section is projected, is shown in the plan view of the flange. Here, the centre line has two thicker lines at either end with arrows showing the direction of viewing. Against the arrows are the capital letters W, and it is along these lines and in the direction of arrows that the sectional view is taken. The third angle projection view beneath is a section along the line AA, hence it is given the title 'Section AN. This method of showing the section position with a thickened line and arrows is explained further in the following chapter on ISO rules. Other examples of sections are given in the assembly drawing of a small hand vice (see Figure 1.11) and the detailed drawing of the movable jaw of the vice (see Figure 1.12). In the case of the movable jaw detailed drawing in Figure 1.12, the front view is shown on the top-left and the right-hand side drawing view is a right-hand section through the centre line. In this instance there are no section lines or arrows to indicate that it is a section through the centre. However, in this case, it should be obvious that the section is through the centre and therefore it is not necessary to include the arrows. However, this is not the case for the inverted planned view, which is a complicated half-section with two section plane levels on the left-hand side and a conventional inverted plan (unsectioned) view on the right-hand side. Because this is a complicated inverted plan view, the section line and arrows are shown to guide the viewer. Note that the crosshatched lines on the two different left-hand planes are staggered slightly. A different type of section is shown in the assembly drawing in Figure 1.11. Here the movable jaw (part number 3), the hardened insert (part number 2), the bush (part number 4), the bush screw (part number 5) and part of the jaw clamp screw (part number 6) are shown in section. This is what is termed a 'local' section because the whole side view is not in section but a part of it. The various parts in the section are cross-hatched with lines at different slopes and different spacings. The section limits are shown by the zig-zag line on the movable jaw and a wavy line on the jaw clamp screw. Another type of section is shown on the tommy bar of the assembly drawing. This is a small circle with cross-hatching inside. This is called a 'revolved section' and it shows that, at this particular point along the tommy bar, the cross-sectional shape is circular. In this instance the cross-sectional shape would be the same at any point along the tommy so it doesn't really matter where the section appears. The ISO standards dealing with sectional views are ISO 128-40:2001 and ISO 128-44:2001. 

Engineering Drawing for Manufacture
by Brian Griffiths
Publisher: Elsevier Science & Technology Books

Why are first and third angle projections so named?

The terms first angle projection and third angle projection may seem like complicated terms but the reason for their naming is connected with geometry. Figure 2.15 shows four angles given by the planes OA, OB, OC and OD. When a part is placed in any of the four quadrants, its outline can be projected onto any of the vertical or horizontal planes. These projections are produced by viewing the parts either from the right-hand side or from above as shown by the arrows in the diagram. In first angle projection the arrows project the shape of the parts onto the planes OA and OB. When the two planes are opened up to 180 ~ as shown in the small diagrams in Figure 2.15, the two views will be in first angle projection arrangement. When the part in the third quadrant is viewed from the righthand side and from above, the view will be projected forwards onto the faces OC and OD. When the planes are opened up to 180 ~ the views will be in third angle projection arrangement, as shown in thesmall diagrams in Figure 2.15. If parts were to be placed in the second and fourth quadrant, the views projected onto the faces when opened out would be incoherent and invalid because they cannot be projected from one another. It is for this reason that there is no such thing as second angle projection or fourth angle projection. There are several ISO standards dealing with views in first and third angle projection. These standards are" ISO 128"1982, ISO 128-30:2001 and ISO 128-34:2001. 
Engineering Drawing for Manufacture
by Brian Griffiths
Publisher: Elsevier Science & Technology Books
 

Design Aesthetic

Design is the process of conceiving or inventing ideas mentally and communicating those ideas to others in a form that is easily understood. Most often the communications tool is graphics. Design is used for two primary purposes: personal expression, and product or proccss dcvelopment (Figure 2.1). Design for personal expression. usually associated with art. is divided into concrete (realistic) and abstract dcsign and is uften a source uf beauty and intercst (Figure 2.2). Whcn a design servcs some useful purpose. such asthe shape of a ncw automobile wheel. it is classified as a design for product or process development (Figllre 2.3). Aesthetic design is concerned with the look and feel of a product. Industrial designers specialize in the aesthetic qualities of products. as well as other clements related to human-machine functionality. Functional design is concerned with the function of a product or process. Airflow over an automobile is an example of a fllnctional design element. Most engineers are con~~erned with functional elements (Figure 2.4). Many products will have both aesthetic and functional design elements. requiring the engineers and designers to work as a ieam to produce a product or system thaI is both runctional and aeslhetically pleasing (Figure 2.5). 

The Engineering Design Process
Bertoline-Wiebe-Miller:
Fundamentals of Graphics Communication,3/e
The McGraw-Hill Companies,200