Mechanical Desktop Design Process Key Concepts in this Lesson: The design process Part modeling Overview This lesson explains the designer process, and how Mechanical Desktop is used to develop a part

Design is the decision-making process which engineers use in the formulation of plans for the physical realization of machines, systems, and devices for the satisfaction of human needs. A mechanical system is a combination of mechanisms and other components, which transforms, transmits, or utilizes energy, force, or motion for a useful purpose. Mechanical design implies the design of components and systems of a mechanical nature including machines, products, devices, and instruments. The design process consists of seven steps. The process begins with an identification of a need, followed by a definition of a specific project with objectives, conceptual design of the system or project, components design and modeling, assembly, analysis, followed finally by prototype making and testing. The Mechanical Design Process

Seven-step Procedure of Mechanical Design Process Identification of a need Project definition with objectives and a conceptual design of the system or project Conceptual design of the system or project Components design and modeling Assembly Analysis Prototype making and testing

Identification of a Need Designing a system always starts with a need, real or imagined. The system to be designed can be a brand new one or an existing system, which needs to be improved. New systems may be required to perform certain functions previously carried out by human beings, such as assembly, moving objects, etc. Existing systems may need improvements in speed, cost, weight, efficiency, or durability.

Definition of the Project and Objectives The need reveals the general sense of the system to be designed. The project is more specific. It must include all the specifications and objectives for the system that is to be designed. The specifications may consist of input and output quantities, characteristics, and limitations. Typical specifications are dimensional and may include weight limitations, speeds, temperature range, and expected variations in the variables

Conceptual Design of the System Once the objectives of the project have been fully (or at least partially defined), mechanisms and their arrangements to perform the needed functions should be developed. Freehand sketching is of great value in this stage. It can serve two purposes: as a record of designer's ideas and as an aid in discussion with others. A designer should have a broad knowledge of mechanisms, kinematics, machine elements, assembly procedure, etc. During this stage, the designer will make rough calculations and analyses to determine general size and feasibility in terms of the needed amount of space, required types and number of components, how components will be assembled, and the rough size of each component.

Components Design and Modeling A system normally consists of a number of components that form an assembly or sub- assemblies. Components can be of new design parts, existing ones, or commercially available parts. Using 3-D CAD modeling software such as Mechanical Desktop to design the system starts from this stage. New components are created using the CAD program. Existing components can be retrieved from previous files. Components that are in the same family group can be obtained from modifying the existing model files.

Assembly Components are put together to form sub- assemblies or the assembly for performing the intended functions. The assembly operation can be animated with the high- end mechanical design CAD software such as Mechanical Desktop. Interference between mating parts can be readily checked in the assembly mode.

Analysis The analysis step determines whether the performance complies with the specifications. Functionalities, safety, durability, and competitive cost are the main focuses in the analysis stage. As the result of analyses, new designs and new dimensions may be required. The design is a reiterative process in which the designer proceeds through several steps, evaluates the results, and then returns to an earlier stage to modify the design.

Prototype Making and Testing Prototype making and testing are the last stage of the design process. Prototype models are manufactured and tested in the laboratory. It evaluates the final result of the design to determine if the design really satisfies the needs and if it is reliable.

Mechanical Desktop can be used to perform steps 4 (part modeling) and 5 (assembly) of the design procedure.

Part Modeling Using Mechanical Desktop

A part can be regarded as a basic shape with features. The basic shape defines the primitive configuration of the part. Typical shapes are the blocks, channel, I-beam, cylinder, and others. Basic shapes are also referred to as base features. Basic Shapes

A feature is any geometry that augments a basic shape and makes it distinguishable from other parts that could be derived from the same basic shape. In other words, a feature is used to define the detail of the part. Those features that describe the details of the part are also referred to as added features. Figure below shows an example of two parts with different features, which were derived from the same basic shape.Features

Since a variety of parts can be developed from a base shape with differing added features, a logical, generic, five-step modeling approach is used to model parts. Five Step Modeling Approach

Step 1: Part Analysis

Step 2: Sketch Creation

Step 3: Profile the Sketch

Step 4: Basic Shape Creation

Step 5: Add Features

Review Exercises 1. What is design? 2. What is a mechanical system? 3. List the seven steps of the design process, and briefly describe the function of each step. 4. What is a feature? 5. List the five steps of modeling a part using Mechanical Desktop software.

Answers 1. Design is the decision-making process which engineers use in the formulation of plans for the physical realization of machines, systems, and devices for the satisfaction of human needs. 2. A mechanical system is a combination of mechanisms and other components, which transforms, transmits, or utilizes energy, force, or motion for a useful purpose. 3. The design process consists of seven steps. The process begins with an identification of a need, followed by a definition of a specific project with objectives, conceptual design of the system or project, components design and modeling, assembly, analysis, followed finally by prototype making and testing.

Answers Continued 5. Step 1: Part Analysis Step 2: Sketch Creation Step 3: Profile the Sketch Step 4: Basic Shape Creation Step 5: Add Features 4. A feature is any geometry that augments a basic shape and makes it distinguishable from other parts that could be derived from the same basic shape.