by Dale Baker
Figure 4.3
A design can be an arrangement of shapes and lines that forms a decorative pattern. This is the type of design that we will consider in this chapter.
A process by which a design for an object or a structure is created is called a design process. All design processes have similarities. They all involve creativity. They all involve making decisions. However, engineering design tends to require a more extensive and specialized knowledge of technology, math, and science than other types of design.
Engineering Design
Teams undertake several different types of engineering design projects. Most projects involve modifying or enhancing an existing product or process; these projects are described as incremental design. Sometimes a new product is developed from scratch. Such a project would be a new design. Both types of projects use the design process.
The purpose of most design projects is to develop an object, structure, or process that meets the needs of customers and stakeholders. A customer is someone who will use the designed object; customers usually pay for the product. A stakeholder is someone who has an interest in the product. Customers are stakeholders; other stakeholders may include government agencies, companies, and individuals. For example, stakeholders for a new automobile design might include the individuals who will purchase it, the mechanics who will maintain and repair it, the Environmental Protection Agency that will monitor its emissions, and the oil companies that will supply its fuel.
Design problems are almost always open ended—they rarely have a single correct solution. Instead, there are usually several solutions that will satisfy the desired needs. One of the challenges of design is to choose from the vast number of possible solutions. Indeed, engineered products may be very complex, and the design of such products may require that a design team make hundreds or thousands of decisions. Without a clearly defined process to follow, the team may not develop designs that meet the needs of customers or other stakeholders; the team may make poor decisions or lose sight of the important attributes of the product. Thus, it is important to use a structured design process. Structured design processes offer several advantages. They provide a framework in which the team decision-making is made explicit and the decision process can be well documented. They also reduce the likelihood that important issues will be forgotten or overlooked.
In this section, we describe “the engineering design process,” which may give the impression that there is only one correct process. In reality, many processes have been successfully applied to engineering design. The design process discussed in this section may not always be the best for a given project or problem. The design process should not be applied blindly, but should be adapted to fit the circumstances of the design team and the particular project. The design process should also be subjected to a continuous improvement process so that the design team’s performance improves over time.
The engineering design process may not result in a viable design for several reasons:
Incorrect or unrealistic assumptions.
A lack of understanding of the desired needs or underlying problems to be solved.
Errors in design specifications or representations (e.g. models and drawings).
Inadequate testing of prototypes.
Poor design choices.
Sometimes, poor design decisions made early in the process will make it impossible to develop a design that successfully meets customers' needs.
A Design Process
In this section we present a typical engineering design process. Other descriptions of the design process may break the process into somewhat different steps and may use somewhat different terms to describe the steps, but most design processes are similar to this one. An example of how this design process could be applied is in The Design Process in Action section.
Figure 4.4
A design process.
Our basic engineering design process includes the steps shown in Figure 4. Note that Figure 4 shows each step being completed before the next step begins; this process is sequential. In many real-life situations, the design team may revisit a step several times to create the final design. We now describe the steps in more detail.
Define the problem. In the problem definition step, the needs of potential customers are investigated; potential competitors are identified and their market positions are characterized; constraints imposed by government regulations or technological limitations are identified; and constraints on the design effort such as available personnel, time, and money are established. The problem definition process results in a clear understanding of the scope of the design project and the resources available to solve the design problem. This understanding is often expressed in a problem statement. This understanding is also expressed in the form of criteria and constraints.
Identify criteria and constraints. Criteria and constraints are used to evaluate the quality of a design. Constraints describe conditions that must be met by the design and design process; a design must meet all constraints. Criteria are measurable values that can be used to compare several designs and determine which is better.
Generate ideas. Once criteria and constraints are identified, the design team generates ideas for designs. These ideas come from many different sources; these include existing products (including competitors’ products), brainstorming and other creative activities, and market and technical research. Ideas are combined to generate potential designs; at this stage, designs are concepts without a significant level of detail.
Explore possibilities. After potential designs are generated, they are explored to understand their characteristics and likely advantages and disadvantages.
Select a design concept. Potential designs are evaluated relative to the constraints and criteria, and one or more is selected to be designed in detail and prototyped. This selection is made using a structured process that requires the constraints to be met and chooses the best design according to the criteria.
Develop a detailed design. The selected design is developed in more detail. The design architecture is established by identifying physical and functional chunks. Shapes and dimensions are determined, materials and fabrication processes are selected, and product components are identified. The design is developed in enough detail that prototypes and models of the design can be made.
Create models and prototypes. One or more prototypes are typically implemented to characterize various aspects of the design. Prototypes may be physical models of the design in which dimensions, materials, and fabrication processes emulate important aspects of the design. Increasingly, prototypes are implemented using computer modeling software that simulates mechanical, electrical, and other characteristics of the product.
Test and evaluate. Prototypes are tested to see whether the design meets all constraints and performs acceptably relative to the criteria.
Refine the design. Testing and evaluation may reveal weaknesses of the design or indicate ways in which the design may be improved. At this point, the design may be refined to better meet the criteria and constraints. Sometimes, testing and evaluation show that a design will not work, so that a different design concept must be selected; in this case, the process goes back to the “Select a design concept” step.
Implementation. Depending on the context, the design is produced or constructed.
Communicate process and results. The activities and results of the design process are documented. This documentation is communicated to the appropriate stakeholders in the design.
The design process in Figure 4 is often called a sequential process because each step follows the previous one in direct sequence. This model does not account for the iterative nature of many actual design projects; as designs are developed, prototyped, and evaluated, their strengths and weaknesses are better understood and changes are made to the design on the basis of this improved understanding. After changing the design, the process of prototyping and evaluating is repeated. The design process in which the processe
s are iterated is often called a spiral design process. A spiral design process is illustrated in Figure 5.
Figure 4.5
A spiral design process. Changes are made in the design, and then the improved design is evaluated.
The advantage of using a spiral design process is that the end design is often much better than the initial design. The significant disadvantage of the spiral design process is that time and resources are required for each loop in the spiral; if these are not planned for, the project may easily be late and over budget.
Review Questions
Multiple Choice
The following questions will help you assess your understanding of the Discovering Engineering section. There may be one, two, three, or even four correct answers to each question. To demonstrate your understanding, you should find all of the correct answers.
Which attributes describe the engineering design process? Creativity
Specialized knowledge of math and science
Decision making
Specialized knowledge of technology
Incremental design means that the design process is slow
an existing product or process is modified
design is done in pieces
an existing product or process is enhanced
The design process may not produce a good product because the team was made up of different kinds of engineers
materials were delivered too late to use
the engineers focused on attributes of the product
prototypes were not tested adequately
Which of these is used to evaluate the quality of a design? The number of prototypes tested
The spiral design process
Criteria and constraints
The size of the engineering firm
What is the first step in the design process? Explore possibilities
Define the problem
Select a design
Generate ideas
What is the last step in the design process? Communicate process and results
Test and evaluate
Refine the design
Implement
A good design does not have constraints
is not limited by criteria
meets constraints
develops criteria and constraints
Free Response Questions
Why are planning and evaluation as important as creativity in the design process?
What is the difference between engineering design and other types of design (architectural, fashion, etc.)?
Review Answers
The Design Process
a,b,c,d
b,d
d
c
b
a
c
The Design Process in Action
In this section, we go through an example of a team using the design process. This section provides more detail about the steps of the sequential design process.
Case Study
To provide concrete examples throughout this section, we will use a design case study. In this case study, we will follow the design process used by an intrepid team of engineers who work at a small manufacturing company to develop a product that solves some of the problems with current commuting options. At the beginning of their project, the team chose a suitable engineering name for their project: the sustainable commuter vehicle, or SCV for short.
According to the United States Department of Transportation, in 2000, over three-fourths of the trips made to and from work were made by individuals traveling alone in a car, sport utility vehicle, or truck. In some ways, jumping in the car and going is the hallmark of modern American life. Americans prize the convenience and comfort of the modern automobile, even though it creates some serious problems.
Vehicles create % of greenhouse gas emissions in the United States and appear to be a significant contributor to future climate change. Carbon dioxide is one of the principle greenhouse gasses emitted by vehicles.
A typical American household spends more money on driving costs than it spends on food.
In most major metropolitan areas, “rush hour” (congested traffic conditions similar to those in Figure 6) now lasts six to seven hours a day.
Traffic congestion costs $63.1 billion per year. Each year, commuters stuck in traffic jams waste 2.3 billion gallons of fuel, not to mention their time or frustration.
Figure 4.6
Rush hour traffic in Washington, D.C. Heavy traffic and long delays, as well as the associated air pollution and fuel consumption, are major problems for communities.
Is there a way to solve some of these problems without completely giving up the comfort and convenience that we have come to expect?
Activity
To increase understanding of the issues faced by the engineering team, complete one or more of the following exercises that involve problems associated with commuting.
Research the issues associated with commuting in your area. These issues might include traffic congestion, accidents, and pollution.
Do you know anybody who commutes regularly to work alone in their automobile? Talk to them about the benefits and drawbacks associated with this.
Find information on transportation planning in your area. How much money is spent developing new roadways? How much money is spent upgrading and maintaining existing roads? Is the current road network effective?
What problems do environmental activists in your area see with the current commuting infrastructure?
With your understanding, write a paragraph describing the commuter problem from the perspectives of the commuter, the city planner, and the environmental activist.
Activity
Spend an hour working with a team of classmates to develop a design solution to the commuter problem. Write a paragraph that describes what your team did during the hour. Then consider the following questions:
Did your team find a solution? If not, why not?
What processes did your team use to find solutions?
How good is your solution? How do you know whether it is good or not?
How well did you document your design process?
In this section, we will describe the (fictional) design process used by the SCV team to address the commuting problem.
Define the Problem
Problem definition is one of the most critical steps in the design process. Since the design team trying to solve this problem will expend a significant effort, it is very important that the problem being addressed is actually the problem that is important to potential customers. It is also important that the problem be clearly defined and understood by the design team.
Many techniques can be used to clearly define and understand the problem (see Fogler and LeBlanc, 1995). These techniques include
gathering information from customers and other stakeholders,
finding expert information (either in person or through books or other sources),
doing a root cause analysis to identify what the real problem is.
The SCV design team began by gathering information about the issues associated with vehicular commuting and traffic congestion. They found and read several government reports. They interviewed various stakeholders in the commuting problem; these included people who commute to and from work in their car each day, officials from state and local departments of transportation, and representatives of environmental groups. They also used their own experience as commuters.
Activity
Using your understanding of the issues associated with commuting, develop a problem statement to describe the problem that the design team should solve.
On the basis of the research that they performed, the design team defined their design problem to be “Design a commuter vehicle that is environmentally friendly, acceptable to a typical commuter, and compatible with existing transportation infrastructure.”
The design team also expanded this problem statement to make it more informative as follows. Environmenta
lly friendly means that the vehicle produces as little pollution and greenhouse gases as possible and uses sources of renewable energy. Acceptable to the commuter means that the vehicle is convenient (does not require the commuter to wait), comfortable, and affordable. Compatible with existing infrastructure means that the vehicle does not require changing roads, bridges, etc., and does not require the development of a new fuel distribution system.
Identify Criteria and Constraints
The problem statement is used as a starting point to develop an understanding of the characteristics of a good solution. These characteristics are described in terms of constraints and criteria. A constraint is a limitation or condition that must be satisfied by a design. A criterion is a standard or attribute of a design that can be measured. The constraints and criteria are used in subsequent steps of the design process to determine which of many possible designs should be implemented.
Activity
Using your problem statement or the one developed by the design team, develop criteria and constraints that could be applied to decide whether a potential commuter vehicle design is good or not.
From the problem statement, the SCV design team identified criteria and constraints that would apply to their design. They identified the following constraint:
