The importance of engineering design can also be reflected by the additional costs a company may spend to fix some defects and errors occurring to different phases of a product lifecycle. The first‐time correct is an idea goal to make highly diversified products and can only be achieved when CAD tools are capable of eliminating all of the design defects at the design stage. Figure 1.9 shows that, conventionally, the errors with a 75% fixing cost are made at the design stage of products, but the errors fixed at the manufacturing stage or later take around 80% of the fixed cost. It is clear that the earlier an error or defect is identified, the less cost is needed to fix it.
Figure 1.9 Relative costs to fix errors at different phases of product lifecycle.
1.3.3 Types of Design Activities
In this section, the role of CATs in the design aspect is analysed, the nature of engineering designs is discussed, and the potential for using CAT technologies for design problems with different creativity levels is explored. Based on the level of creativity, Designwork (2016) classifies the engineering design problems into types: routine design, redesign, selection design, parametric design, integrated design, and new design (Table 1.2).
Table 1.2 Types of design activities.
| Type | Description | Example |
| Routine design | To perform a design by following existing standards and codes that outline the steps and computations for certain products or systems. | Follow the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Codes to design a pressure vessel. |
| Redesign | To revise an existing design when FRs have been changed in a dynamic environment. | Reprogram a robot when the tag points on the motion trajectory are changed. |
| Selection design | To find a solution by selecting appropriate components from an existing design inventory. | Select standardized fasteners to join two metal plates. |
| Parametric design | To determine design variables in a given conceptual structure for an optimized performance. | Minimize the materials usage of a cylindrical container subject to the given volume. |
| Integrated design | To design and assemble components as an integrated product or system to meet strongly coupled FRs. | Design a robotic configuration for a given task in a modular robot system. |
| New design | To design a product or system from scratch to meet emerging FRs. | Design a patentable product or system. |
Corresponding to the needs to involve computers, human–machine interaction, and human designers, a rougher classification based on the level of creativity and innovation may facilitate further discussion. To this end, the designs can be regrouped as:
1 New design for a design from scratch to conceptual design, detailed design, and assembly design to the final product to meet specified design requirements.
2 Incremental design for a design subjected to given product structures, change individual parts, and functions to meet additional requirements of products.
3 Routine design for a design subjected to given functionalities, topological relations, layouts, and parametrize dimensions for the design of product families.
The level of creativity and innovation can be characterized based on the types of solution space and design variables. Goel (1997) corresponded routine design, innovative design, and new creative design to different combinations of solution space and design variables (Table 1.3).
Table 1.3 Characteristics of solution spaces and design variables.
| Level of creativity | Routine design | Incremental design | New design | |
| Solution space | Structure | Known | Known | Unknown |
| Search procedure | Known | Unknown | Unknown | |
| Design variables | Types | Fixed | Fixed | Changed |
| Ranges | Fixed | Changed | Changed | |
The characteristics of the solution space and design variables determines whether or not an engineering design belongs to a ‘routine’, ‘incremental’, or ‘new’ design. Both humans and computers can compete to accomplish some design activities; however, computers and human designers are good at different things, and it is desirable to synergize the strengths of designers and computers to achieve the effectiveness of engineering designs. Many researchers have discussed the differences between humans and computers. Table 1.4 summarizes the role differences of human beings and computers in engineering design processes.
Table 1.4 Comparison of human designers and computers.
| Human designers | Computers | |
| Strengths | Identifying design needsBrainstorming to think solutions ‘out of the box’Engineering intuition and a big knowledge baseSelecting design variationsThe flexibility to deal with changesQualitative reasoningPsychologically, human decision is more trusted than artificial intelligencePredict trends, patterns, or anomalies, andLearn from experience | Fast speed, reliable, endurance, and consistentCapable of exploring a large number of optionsCarry out long, complex, and laborious calculationsStore and efficiently search large databases andProvide information on design methodologies, heuristic data, and stored expertise |
| Weaknesses | Easily tired and boredCannot do micro manageBiased and inconsistentProne to make errorsNot good at quantified reasoningIncapable of utilizing the data presented in an awkward manner | Difficult to synthesize new rulesLimited knowledge baseNo common sense |
