Computer-aided design/Principles and terminology

Part of:

• Engineering and Technology
• Mechanical Engineering; Production and Design Engineering
• Computer Aided Design Course

Introduction

Computer aided design is a complex process.

There are many specialized tools that can speed up your design, minimize errors and improve your results.

In this lesson, we will:

• Familiarize you with terms used in CAD industry.
• Give the general idea of design process stages.
• Teach about available software tools and their general purpose.

Terminology

Read about frequently used CAD/CAE/CAM terms on Wikipedia:

• CAD (MCAD - mechanical, ECAD -electronic and electrical, AEC - Architecture, engineering and construction ...) Computer-aided design (CAD) is the use of a wide range of computer-based tools that assist engineers, architects and other design professionals in their design activities. The term CADD is sometimes used and it stands for Computer-aided Drafting and Design.
• CAE, CAx Computer-aided engineering is the use of information technology for supporting engineers in tasks such as analysis, simulation, design, manufacture, planning, diagnosis and repair.
• CAM Computer-aided manufacturing is the use of software tools that assist engineers, in the manufacture of product components.
• GD&T GD&T, also refered to as geometric dimensioning and tolerancing, is a symbolic language used on engineering drawings and computer generated three-dimensional solid models (CAD) for explicitly describing nominal geometry and its allowable variation.
• PLM Product lifecycle management (PLM) is the process of managing the entire lifecycle of a product from its conception, through design and manufacture, to service and disposal. In the PLM process engineers use different CAD/CAE/CAM tools.

Follow the links to get acquainted with other terms and abbreviations used in the CAD/CAE/CAM industry.

Design process

Scheme of Design Process (gif)

Scheme of Design Process (svg)

On the charts (gif and svg versions) you can see the generalized design, validation and manufacturing process.

Each stage requires specific knowledge and skills, and often requires the use of specific software.

Need or Idea

Usually the design process starts with a defined need. The need can be defined by market research, by the requirements of a larger body of work (for example airplane part). Sometimes, but more rarely than you may think, the design process is begun with a new idea or invention.

At any rate, a needs analysis should precede any decision to undertake a project. This includes defining the need in a highly detailed way, in writing. This is similar to the requirements specification process in software engineering.

Research

Professionals tend to research available solutions before beginning their work. There is no need to "reinvent the wheel".

You should study existing solutions and concepts, evaluating their weaknesses and strengths. Your research should also cover available parts that you can use as a part of your design. It is obvious, that Internet and search engines like Google are very helpful for this task. There are also many libraries of standardized parts which you can import into your project.

Concept

Based on your research, start with a high level concept. You should specify the main principles and major parts. For example you can consider Diesel or Stirling engines for stationary electric generators.

Draft

You can choose to create a draft by pen and paper. Some prefer to use simple vector graphics programs, others even simple CAD (for example SmartSketch), yet others prefer to start directly in their main CAD system.

Model Design

2D and 3D modeling in CAD. The designer creates a model with details, and this is the key part of the design process, and often the most time consuming. This will be described in greater detail in further lessons.

Part Libraries

Standard parts, or parts created by other team members, can be used in your model (you don't have to reinvent the wheel). Files representing a part can be downloaded from the Internet, or local networks. They are also distributed on CD ROMs or together with CAD as and extension (library). By putting these predefined parts into your project, you ensure that they are correct and save a lot of time and effort. When working on a large project, this becomes a requirement to ensure the parts operate together, swap out equivalent parts, and coordinate distributed teams' work. This was, a standard part can be inserted into the project by one team member, and used by all.

Assembly modeling

Parts are assembled into a machine or mechanism. Parts are put together using mating conditions such as alignment of the axis of two holes. More about how to do this in further lessons.

Analysis

Specialized programs (CAE -- Computer Aided Engineering) aid you in analysis of 3D model robustness and performance. Many software tools are used for this task. Most notably FEM (Finite Element Method) and Kinematics. Some CAD programs include these tools built in.

Engineering Drawings

From your 3D models, you generate a set of engineering drawings for manufacturing. These drawings are then distributed to the departments and individuals responsible for producing that work. Also these drawings must be toleranced for proper manufacturing.

Tool Design

You can use CAM software to simulate, optimize and prepare manufacturing. Generated NC (Numeric Control) code is then executed by manufacturing machines like lathes or milling cutters.

Planning

Critical Path Method, Gannt chart and other methods and tools are used by project managers to plan and optimize manufacturing. Project management and ERP systems are used.

Presentation

You should create photo realistic images and/or animations to present your design. This allows you to get customer feedback even before the product is actually manufactured. You can also consider using rapid prototyping techniques to present a physical 3D model.

Major CAD/CAE/CAM software companies develop and sell tools that cover the whole cycle. These complex software tools support change management, teamwork, versioning and resource planning.

Tasks to do

1. Play the role of an engineer who has to select an appropriate software package for manufacturing.
2. Select a manufacturer of a specific consumer product. Choose a company that you know, or find one on the Internet (preferably one with well-described products and manufacturing processes).
3. Find at least two (2) appropriate CAD/CAE/CAM packages suitable for your selected manufacturer. These software tools should support all the major design process stages (modeling, analysis, tool design, and presentation). Tools for teamwork, project management and planning is a plus.
4. Compare and contrast your selected tools in terms of functionality, their added value, and price. (Use a weighted evaluation methodology to determine which included CAD/CAM/CAE software functions are most valuable/appropriate to your chosen manufacturer.)

Outcomes

Your focused research of CAD/CAE/CAM industry gives you an overview about available tools and their producers. You have also become familiar with industry lingo and terminology.

After successfully accomplishing this task you will be able to initialize the CAD/CAE/CAM software selection process for a specific industry.

Learning Assignment

Write a Paper (approxiamately 2 pages) with:

1. Description of one of your chosen manufacturers.
2. Discuss the manufacturer's business critical needs and requirements.
3. Compare and contrast at least two software tools that meet these needs and requirements.
4. Provide a weighted evaluation of your selected software tools (their major functions and features). Hint: Use tables.

You will need:

• Word processor like OpenOffice Writer
• Internet access and browser

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