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Chapter: Mechanical : Computer Aided Design : Fundamentals of Computer Graphics

Fundamentals of Computer Graphics

Product cycle- Design process- sequential and concurrent engineering- Computer aided design –CAD system architecture- Computer graphics –co-ordinate systems- 2D and 3D transformations- homogeneous coordinates - Line drawing -Clipping- viewing transformation





Introduction of CAD


In the mid of 1970s, as computer aided design starts to offer more potential than just a skill to replicate manual drafting with electronic drafting, the cost gain for companies to switch to CAD became obvious. The benefit of CAD methods over manual drafting are the capabilities one often takes for established from computer systems; automated creation of Bill of Material, interference checking, auto layout in integrated circuits.



Product cycle


Product cycle integrate processes, people, data, and business and gives a product information for industries and their extended activity. Product cycle is the process of managing the entire lifecycle of a product from starting, through design and manufacture, to repair and removal of manufactured products.


Product cycle methods assist association in managing with the rising difficulty and engineering challenges of developing new products for the worldwide competitive markets.


Product lifecycle management (PLM) can be part of one of the following four fundamentals of a manufacturing information technology structure.


(i)               Customer Relationship Management  (CRM)


(ii)             Supply Chain Management  (SCM)


(iii)          Enterprise resource planning (ERP)


(iv)          Product Planning and Development (PPD).


The core of PLM is in the formation and management of all product information and the technology used to access this data and knowledge. PLM as a discipline appeared from tools such as CAD, CAM and PDM, but can be viewed as the combination of these tools with processes, methods and people through all stages of a product’slife cycle. PLM is not just about software technology but is


also a business approach.



Product Cycle Model


There are several Product cycle models in industry to be considered, one of the possible product


cycle is given below (Fig.1.1.):

Fig.1.1. Product Cycle Model



Step 1: Conceive


Imagine, Specify, Plan, Innovate


The first step is the definition of the product requirements based on company, market and customer. From this requirement, the product's technical data can be defined. In parallel, the early concept design work is performed defining the product with its main functional features. Various media are utilized for these processes, from paper and pencil to clay mock-up to 3D Computer Aided Industrial Design.


Step 2: Design


Describe, Define, Develop, Test, Analyze and Validate


This is where the completed design and development of the product begins, succeeding to prototype testing, through pilot release to final product. It can also involve redesign and ramp for improvement to existing products as well as planned obsolescence. The main tool used for design and development is CAD. This can be simple 2D drawing / drafting or 3D parametric feature based solid/surface modeling.


This step covers many engineering disciplines including: electronic, electrical, mechanical, and civil. Besides the actual making of geometry there is the analysis of the components and assemblies.



Optimization, Validation and Simulation activities are carried out using Computer Aided Engineering (CAE) software. These are used to perform various tasks such as: Computational Fluid Dynamics (CFD); Finite Element Analysis (FEA); and Mechanical Event Simulation (MES). Computer Aided Quality (CAQ) is used for activities such as Dimensional  tolerance analysis. One more task carried out at this step is the sourcing of bought out components with the aid of procurement process.


Step 3: Realize


Manufacture, Make, Build, Procure, Produce, Sell and Deliver


Once the design of the components is complete the method of manufacturing is finalized. This includes CAD operations such as generation of CNC Machining instructions for the product’s component as well as tools to manufacture those components, using integrated Computer Aided Manufacturing (CAM) software.


It includes Production Planning tools for carrying out plant and factory layout and production simulation. Once details components are manufactured their geometrical form and dimensions can be verified against the original data with the use of Computer Aided Inspection Equipment (CAIE). Parallel to the engineering tasks, sales and marketing work take place. This could consist of transferring engineering data to a web based sales configuration.


Step 4: Service

Use, Operate, Maintain, Support, Sustain, Phase-out, Retire, Recycle and Disposal.

The final step of the lifecycle includes managing of information related to service for repair and maintenance, as well as recycling and waste management information. This involves using tools like Maintenance, Repair and Operations Management software.



Design Process


The design process includes series of steps that engineers apply in making functional products and processes. The parts of the process often need to be repeated many times before production of a product can start. The parts that get iterated and the number of such design cycles in any given project can be highly changeable.


One method of the engineering design process focuses on the following common aspects:

Fig.1.2. Design Process

1. Research

A considerable amount of time is used on research, or finding information. Consideration should be given to the available applicable literature, issues and successes linked with avaialbe solutions, and need of marketplaces.

The basis of information should be significant, including existing results. Reverse engineering can be a successful technique if other solutions are available in the market. Added sources of information include the trade journals, available government documents, local libraries, vendor catalogs and personal organizations.

2.  Feasibility assessment


The feasibility study is an analysis and assessment of the possible of a proposed design which is based on detail investigation and research to maintain the process of decision creation. The feasibility assessment helps to focus the scope of the project to spot the best situation. The purpose of a feasibility assessment is to verify whether the project can continue into the design phase.



3.  Conceptualization

A Concept Study is the stage of project planning that includes developing ideas and taking into account the all features of executing those ideas. This stage of a project is done to reduce the likelihood of assess risks, error and evaluate the potential success of the planned project.



4.  Establishing the design requirements


Establishing design requirements is one of the most essential elements in the design practice, and this task is usually performed at the same time as the feasibility analysis. The design requirements control the design of the project all over the engineering design process. A few design


requirements comprise maintainability, hardware and software parameters, availability, and testability.



5.  Preliminary design


The preliminary design fills the gap between the design concept and the detailed design phase. During this task, the system configuration is defined, and schematics, diagrams, and layouts of the


project will offer early project configuration. In detailed design and optimization, the parameters of the part being produced will change, but the preliminary design focuses on creating the common framework to construct the project.


6.  Detailed design


The next phase of preliminary design is the Detailed Design which may includes of procurement also. This phase builds on the already developed preliminary design, aiming to further


develop each phase of the project by total description through drawings, modeling as well as specifications.


The advancement CAD programs have made the detailed design phase more competent. This is because a CAD program can offer optimization, where it can shrink volume without compromising the part's quality. It can also calculate displacement and stress using the FEM to find stresses throughout the part. It is the responsibility of designer to find whether these stresses and displacements are acceptable, so the part is safe.



7.  Production planning and tool design


The production planning and tool design is more than planning how to mass-produce the project and which tools should be used in the manufacturing of the component. Tasks to complete in this stage include material selection, identification of the production processes, finalization of the sequence of operations, and selection of jigs, fixtures, and tooling. This stage also includes testing a working prototype to confirm the created part meets qualification standards.


With the finishing of qualification testing and prototype testing, the design process is completed.



Sequential and Concurrent Engineering

Table 1.1. Sequential Vs Concurrent Engineering


Sequential Engineering

Sequential engineering is the term used to explain the method of production in a linear system. The various steps are done one after another, with all attention and resources focused on that single task.

Sequential  engineering  is  a  system  by  which  a  group  within  an  organization  works sequentially to create new products  and services.

The concurrent engineering is a non-linear product design process during which all stages of manufacturing operate at the same time.

Both process and product design run in serial and take place in the different time.

Process and Product are not matched to attain optimal matching.

Decision making done by only group of  experts.  



Concurrent Engineering

In concurrent engineering, various tasks are handled at the same time, and not essentially in the standard order. This means that info found out later in the course can be added to earlier parts, improving them, and also saving time.

Concurrent engineering is a method by which several groups within an organization work simultaneously to create new products and    services.

The  sequential  engineering  is  a  linear   product design process during which all  stages of manufacturing operate in serial.  

Both product and process design run in parallel and take place in the same time.

Process  and  Product  are  coordinated  to attain optimal matching of requirements for effective quality and delivery.

Decision   making   involves   full   team involvement.


Computer Aided Design


CAD is the intersection of Computer Graphics, Geometric modeling and Design tools (Fig.1.4.). The concepts of computer graphics and geometric modeling and must be used innovatively to serve the design process.


CAD is the function of computer systems to support in the creation, modification, analysis, or optimization of a design.

Fig. 1.4. CAD


CAD software for design uses either vector-based graphics to explain the objects of traditional drafting, or may also develop raster graphics showing the overall look of designed objects. During the manual drafting of engineering drawings, the output of CAD must convey information, like dimensions, materials, processes, and tolerances.


CAD is a significant industrial art used in many purposes, including industrial and architectural design, shipbuilding, automotive, and aerospace industries, and many more. CAD is also extensively used to create computer animation for special effects in movies, and technical manuals, frequently called as Digital Content Creation.


CAD software packages provide the designer with a multi window environment with animation which is regularly used in Digital Content Creation. The animations using wire frame modeling helps the designer to see into the interior of object and to observe the behaviors of the inner components of the assembly during the motion.



CAD Technology


Initially       software  for  CAD  systems  was  developed  with  computer  languages  such


as  FORTRAN but with the development of  object-oriented programming methods this has completely changed. Classic modern parametric attribute based modeler  and freeform surface systems are developing around a number of key  ‘C’modules.

A CAD system can be seen as develop from the interaction of a  Graphical User Interface (GUI) with  NURBS geometry and Boundary representation data through a kernel for  geometric modeling. A geometry constraint engine may also be employed to organize the associative relationships between


components in an assembly.


Unexpected facilities of these relationships have led to a new form of  prototyping called  digital  prototyping. In difference to physical prototypes, which involve manufacturing time in the design. CAD models can be created by a computer after the physical prototype has been scanned using an  CT  scanning device. Based on the nature of the business, digital or physical prototypes can be primarily


selected according to specific requirements.


Currently, no special hardware is required for CAD software. However, some special CAD systems can do graphically and computationally intensive tasks, so a higher end  graphics card, high speed CPUs may be suggested. CAD systems exist for all the major platforms and some packages even


perform multiple platforms.


The  human-machine  interface  is  generally  through  a  mouse but  can  also  be  using  a


digitizing graphics tablet. Handling of the view of the part on the screen is also sometimes done with the help of a Space mouse or Space Ball. Special CAD systems also support stereoscopic glasses for  viewing the 3D objects.




CAD Tools


The CAD tools are mainly using for graphics applications and modeling. Aids such a color, grids, geometric modifiers and group facilitate structural geometric models. Visualization is achieved through shaded components and animation which focus design conceptualization, communication and interference detection. FEM packages provide optimization in shape and structure. Adding tolerances, tolerance analysis and investigating the effect of manufacturing on the design can perform by utilizing CAD tools (Table 1.2).


Table 1.2. CAD Tools Vs Design Process

CAD Tools : Design Process


Geometric modeling, Graphics aids, visualization and manipulation :       Conceptualization


Geometric modeling, Graphics aids, visualization and  Modeling and manipulation, animation, assemblies :          Simulation


Analysis packages, customized programs :          Design Analysis


Structural optimization  : Design Optimization


Dimensioning, tolerance, bill of materials   : Design evaluation


Drafting and detailing, Shaded images       : Communication and Documentation


Uses of CAD


CAD is one of the tools used by designers and engineers and is used in different ways depending on the profession of the customer and the type of software.


CAD is one of the Digital Product Development activities within the  Product Lifecycle  Management practices with other tools, which are either integrated modules or individual, such as:


·        Computer Aided engineering (CAE) and  Finite Element Analysis (FEA)


·        Computer Aided Manufacturing (CAM)


·       Realistic Rendering and Simulation.


·       Product Data Management (PDM).


CAD is also used for the development of photo simulations that are frequently necessary in the preparation of Environmental Impact Reports, in which proposed CAD buildings are superimposed into photographs of existing situation to represent what that conditions will be like, where the proposed services are allowed to be built.


Parameters and constraints can be used to get the size, shape, and other properties of the modeling elements. The features of the CAD system can be used for the several tools for measurement such as yield strength, tensile strength and electrical or electro-magnetic properties.



CAD System Architecture


Computer architecture is a pattern describing how a group of software and hardware technology standards relate to form a computer system. In general, computer architecture refers to how a computer is designed and what technologies it is compatible with. Computer architecture is likened to the art of shaping the needs of the technology, and developing a logical design and standards based on needs.


In CAD, Computer architecture is a set of disciplines that explains the functionality, the organization and the introduction of computer systems; that is, it describes the capabilities of a computer and its programming method in a summary way, and how the internal organization of the system is designed and executed to meet the specified facilities. Computer architecture engages different aspects, including instruction set architecture design, logic design, and implementation. The implementation includes Integrated Circuit Design, Power, and Cooling. Optimization of the design needs expertise with Compilers, Operating Systems and Packaging.



 Instruction set architecture


An instruction set architecture is the interface between the software and hardware and also can be observed as the programmer's view of the machine. Computers do not understand high level languages, if any, language elements that translate directly into a machine's native op codes.


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