What makes up a “Design?”

A product design (noun) includes aspects that are physical or tangible and easily observed as well as characteristics that are inferred. The overall product look, what components are used and their sizes and materials are usually easily observable. However, the purpose of each component, the justification for why it was manufactured in a certain way, and the overall vision or strategy of the product producer must be inferred using good engineering analysis. Consider reverse engineering. In reverse engineering, an existing product performance and physical features are measured. However, simply knowing all the dimensions of every part in a new car doesn’t enable someone to make an exact copy of that car. The hard work of reverse engineering is understanding the intangibles. What are the functions, why did the designers choose certain dimensions, materials, and processes, etc.? Answer these questions requires detailed analysis and the end result is often an answer with some underlying uncertainty. In a forward design, process the same works in the opposite direction but the same challenges exist. Defining the functions, behaviors, strategy and vision are the difficult first step. When done correctly, specification of the physical architecture and component specification is straight forward.

Tangibles – Systems, Subsystems and Assemblies, Components

Product design is the process of creating a solution that meets the needs and expectations of the customers and the stakeholders. It involves designing and validating systems, assemblies or subsystems, and components that work together to deliver the desired functionality and performance.

A system is a set of interrelated subsystems or assemblies that form a whole and perform a specific function. For example, a car is a system that consists of various subsystems such as the engine, the transmission, the brakes, etc. A system design defines the overall architecture and specifications of the system, such as its inputs, outputs, interfaces, constraints, and requirements.

An assembly or a subsystem is a group of components that work together to perform a sub-function within the system. For example, the engine is a subsystem that converts fuel into mechanical power. An assembly design defines the structure and configuration of the assembly or subsystem, such as its dimensions, materials, connections, tolerances, and testing methods.

A component is a single part or element that performs a specific task within the assembly or subsystem. For example, a piston is a component that moves up and down inside the cylinder of the engine. A component design defines the shape and properties of the component, such as its geometry, surface finish, strength, durability, and manufacturability. While mostly outside the scope of a mechanical design focus text, software can also be implemented at the component or assembly level.

By designing and validating systems, assemblies or subsystems, and components in a systematic and iterative way, product designers can create solutions that meet the needs and expectations of the stakeholders. The process of product design moves from the system level to the component level. Components are synthesized into assemblies and assemblies into systems. This process is described in the chapter on detailed design.

Function, Behavior, Performance, and Strategy/Vision

A function is the purpose or goal of a product design. It describes what the product is intended (by designers) to do or achieve for the user or the environment. A function can be expressed as a verb and a noun, such as “to store books” or “to filter water”. A product design can have one or more functions, depending on its complexity and scope. Additionally, a product has both high-level functions (a car transports people) and numerous sub functions (safely secure passengers, cool passengers).

A function is an essential aspect of product design, as it guides the design process and influences the form, materials, features, and aesthetics of the product. A function also helps to evaluate the effectiveness and efficiency of a product design, by comparing the intended function with the actual performance and user feedback. We will revisit functions and functions structures in Chapter 5 on conceptual design development.

As function describes the intended actions of a product, behavior is a description of the actual actions of components and products. Behavior is the physical phenomena needed to express a function. For example, the function of converting electrical energy into rotational mechanical energy is an idea that can be expressed as the electromotive force. Behavior can be described using equations relating parameters. Such as converting electrical voltage and current (electrical power) to torque and rotational speed (mechanical power). Components implement one or more behaviors in order to express a desired function. A DC motor implements the function of conversion of electrical power to mechanical power using the physical principle of the electromotive force. One of the major challenges of design is that components don’t exhibit only a single behavior. A DC motor also exhibits vibration and heat. These are not usually the primary desired functions, however, designers must consider them as well. Functions of heat transfer and vibration management also must be expressed through behavior and ultimately lead to specification of components such as housings and heat sinks. This leads to a few important principles:

1. Functions, Behaviors, and Components (sometimes called structures) are closely tied together in the design process. A choice in any domain affects others.
2. The same function can be implemented with many different behaviors and components, selecting one solution too early in design process unnecessarily constrains the available design choices later.
3. The decision process for function, behavior and component are cyclical. Meaning that new additional functionality is often needed when a behavior or component is specified.

The concept of performance or quality was discussed in the previous section. To reiterate here, the choice to what level of behavioral performance (fuel efficiency for example) and which areas of performance to focus on define your technical competitive strategy. As you will see when we discuss developing specifications, setting these targets is essential for developing competitive products.

Design Strategy and Product Vision

Finally, we will consider the role of design strategy or, more elegantly, product vision. This intangibles concept affects the design decisions and thus the final outcome of the product design process. In the product marketplace, there are often many different manufacturers for the same general product. The sum of what differentiates them is their different design strategies. When designing a product, you will make many choices considering functionality, behaviors, components and levels or performance. What should guide that process is your product vision.