1. Define CAD;
Computer aided design can be defined as any design that involves the effective use of computers to create, modify or document an engineering design.
2. CAD system;
The cad system consists of two basic components; they are;
Computer Hardware;
- It consists of graphic workstations,
- Graphic input devices like keyboard, mouse etc., - Graphic output devices like printer and plotters.
Computer Software;
- It consists of operating system for basic operations, - Software package used for geometric modeling,
- Application software for design, analysis and synthesis.
3. Elements of CAD; (or) Various phases of CAD;
The design process in a CAD system consists of 4 stages / phases, they are;
Geometric modeling,
Design analysis and optimization,
Design review and evaluation,
Documentation and drafting.
4. Drawing entities;
A drawing is created using a no. of entities. A large no. of options are provided to draw the entities depending upon the requirements.
Common entities are;
Point, * Line, * Arc, * Ellipse,
Circle, *Polygon, *Spline, *Rectangle, etc.,
5. Drawing Utilities;
Drawing utilities include several functions to have the creation and storage of drawings. Common utilities are;
*Screen size, * Line type, * Scaling * Layers,
*Grid, *Snap,, *Units, , *file utilities, etc.,
6. Editing commands in CAD;
It is necessary to make the corrections and alterations to the entities of a drawing. Editing commands are used for this process.A few editing commands are listed below,
*Erase, *Move, *Array, *Fillet, * Chamfer
*Mirror *Rotate, *Trim, *Copy *Scale, etc.,
7. Geometric modeling;
Geometric modeling involves the use of a CAD system to develop a mathematical description of the geometry of an object.
The mathematical description, called a geometric model is contained in computer memory. These operations include creating new geometric models from basic building blocks available in the system.
8. Geometric modeling techniques;
These are various types of geometric models used in CAD,
Based on the dimensioning, - Two dimensional modeling, - Three dimensional modeling.
Based on the modeling, - Wire frame modeling, - Surface modeling, - Solid modeling.
9. 2D Vs 3D;
2D models are best utilized for design problems, such as flat objects and layouts of building.
3D models are capable of modeling an object in three dimensional according to user instructions.This is helpful in conceptualizing the object since in true 3D models can be displayed in various views and form different angles.
10. Advantages of CAD;
High productivity and reduced lead time,
Accuracy in design,
Better central over the complete project process,
Modifications in design relatively easy,
Simulations of the computer generated model can reduce or eliminate prototype testing,
Effective creation of manufacturing documentation,
Optimized solution can be received,
11. Various 2D transformations;
In computer graphics drawing are created by serious primitives which are represented by the coordinates of their end points.
Certain changes in these drawings can be made by performing some mathematical operations on these coordinates. The basic transformations are Scaling, Rotation, translation, etc..,
12. Applications CAD software package;
The CAD system is applied, wherever we need to draw, design, and any facilities related to that.
Automated industries,
Manufacturing companies,
Aerospace designs,
Civil engineering plans,
Electrical circuits, etc..,
13. CAD software package;
Auto CAD, CATIA, Iron CAD, Pro-E, Turbo CAD, Solid Edge, etc.., 14. Advantages of Wireframe Modeling;
Simple to construct,
Designer needs little training.
It needs less memory space,
It takes less manipulation time,
It is best suitable for manipulation as orthographic, isometric and perspective views.
15. B-rep – Boundry representation;
B-rep construction consists of entering all boundary edge for all surfaces.
This is similar or copying an engineering drawing into the computer, line by line, surface by surface, with one important qualification. The lines must be entered and surfaces oriented in such a way that they create valid volumes.
16. CSG – Constructive Solid Geometry;
CSG technique uses Boolean combinations or primitives solids to build a part.
The Boolean operations are addition (+), subtraction (-), as illustrated in three dimensions.
17. Advantages of Solid Modeling;
It is complete and unambiguous.
Suitable for automated applications like creating part program without much human involvement.
Part - B (16 Marks)
1. Explain the Computer Aided Design in manufacturing?
Computer-aided design (CAD) is the use of computer systems to assist in the creation, modification, analysis, or optimization of a design. CAD software is used to increase the productivity of the designer, improve the quality of design, improve communications through documentation, and to create a database for manufacturing. CAD output is often in the form of electronic files for print, machining, or other manufacturing operations.
Computer-aided design is used in many fields. Its use in designing electronic systems is known as Electronic Design Automation, or EDA. In mechanical design it is known as Mechanical Design Automation (MDA) or computer-aided drafting (CAD), which includes the process of creating a technical drawing with the use of computer software.
CAD software for mechanical design uses either vector-based graphics to depict the objects of traditional drafting, or may also produce raster graphics showing the overall appearance of designed objects. However, it involves more than just shapes. As in the manual drafting of technical and engineering drawings, the output of CAD must convey information, such as materials, processes, dimensions, and tolerances, according to application-specific conventions. CAD may be used to design curves and figures in two-dimensional (2D) space; or curves, surfaces, and solids in three-two-dimensional (3D) space.
CAD may be used to design curves and figures in two-dimensional (2D) space; or curves, surfaces, and solids in three-dimensional (3D) space.
CAD is an important industrial art extensively used in many applications, including automotive, shipbuilding, and aerospace industries, industrial and architectural design, prosthetics, and many more. CAD is also widely used to produce computer animation for special effects in movies, advertising and technical manuals, often called DCC digital content creation. The modern ubiquity and power of computers means that even perfume bottles and shampoo dispensers are designed using techniques unheard of by engineers of the 1960s. Because of its enormous economic importance, CAD has been a major driving force for research in computational geometry, computer graphics (both hardware and software), and discrete differential geometry.
The design of geometric models for object shapes, in particular, is occasionally called computer-aided geometric design (CAGD).
Computer-assisted surgery (CAS)
Computer-aided surgical simulation (CASS)
Computational fluid dynamics (CFD)
Component information system (CIS)
Computer-integrated manufacturing (CIM)
Computer Numerical Controlled (CNC)
Electronic design automation (EDA)
2. Explain the Geometric modeling in CAD?
Geometric modeling is a branch of applied mathematics and computational geometry that studies methods and algorithms for the mathematical description of shapes.
The shapes studied in geometric modeling are mostly two- or three-dimensional, although many of its tools and principles can be applied to sets of any finite dimension.
Today most geometric modeling is done with computers and for computer-based applications. Two-dimensional models are important in computer typography and technical drawing. Three-dimensional models are central to computer-aided design and manufacturing (CAD/CAM), and widely used in many applied technical fields such as civil and mechanical engineering, architecture, geology and medical image processing.
Geometric models are usually distinguished from procedural and object-oriented models, which define the shape implicitly by an opaque algorithm that generates its appearance. They are also contrasted with digital images and volumetric models which represent the shape as a subset of a fine regular partition of space; and with fractal models that give an infinitely recursive definition of the shape.
However, these distinctions are often blurred: for instance, a digital image can be interpreted as a collection of colored squares; and geometric shapes such as circles are defined by implicit mathematical equations. Also, a fractal model yields a parametric or implicit model when its recursive definition is truncated to a finite depth.
3. Explain the Solid modeling technique in CAD?
Solid modeling (or modelling) is a consistent set of principles for mathematical and computer modeling of three-dimensional solids. Solid modeling is distinguished from related areas of geometric modeling and computer graphics by its emphasis on physical fidelity.[1]
Together, the principles of geometric and solid modeling form the foundation of computer-aided design and in general support the creation, exchange, visualization, animation, interrogation, and annotation of digital models of physical objects.
The use of solid modeling techniques allows for the automation of several difficult engineering calculations that are carried out as a part of the design process. Simulation, planning, and verification of processes such as machining and assembly were one of the
main catalysts for the development of solid modeling. More recently, the range of supported manufacturing applications has been greatly expanded to include sheet metal manufacturing, injection molding, welding, pipe routing etc.
Beyond traditional manufacturing, solid modeling techniques serve as the foundation for rapid prototyping, digital data archival and reverse engineering by reconstructing solids from sampled points on physical objects, mechanical analysis using finite elements, motion planning and NC path verification, kinematic and dynamic analysis of mechanisms, and so on. A central problem in all these applications is the ability to effectively represent and manipulate three-dimensional geometry in a fashion that is consistent with the physical behavior of real artifacts. Solid modeling research and development has effectively addressed many of these issues, and continues to be a central focus of computer-aided engineering.
4. Explain the Wire-frame modeling technique in CAD?
A wire-frame model is a visual presentation of a three-dimensional (3D) or physical object used in 3D computer graphics. It is created by specifying each edge of the physical object where two mathematically continuous smooth surfaces meet, or by connecting an object's constituent vertices using straight lines or curves. The object is projected onto a display screen by drawing lines at the location of each edge. The term wire frame comes from designers using metal wire to represent the three-dimensional shape of solid objects.
3D wire frame allows to construct and manipulate solids and solid surfaces. The 3D solid modeling technique efficiently draws higher quality representations of solids than the conventional line drawing.
Using a wire-frame model allows visualization of the underlying design structure of a 3D model. Traditional two-dimensional views and drawings can be created by appropriate rotation of the object and selection of hidden line removal via cutting planes.
Since wire-frame renderings are relatively simple and fast to calculate, they are often used in cases where a high screen frame rate is needed (for instance, when working with a particularly complex 3D model, or in real-time systems that model exterior phenomena).
When greater graphical detail is desired, surface textures can be added automatically after completion of the initial rendering of the wire frame. This allows the designer to quickly review chansolids or rotate the object to new desired views without long delays associated with more realistic rendering.
The wire frame format is also well suited and widely used in programming tool paths for direct numerical control (DNC) machine tools.
Hand-drawn wire-frame-like illustrations date back as far as the Italian Renaissance.[1] Wire-frame models were also used extensively in video games to represent 3D objects during the 1980s and early 1990s when properly filled 3D objects would have been too complex to calculate and draw with the computers of the time. Wire-frame models are also used as the input for computer-aided manufacturing (CAM).
There are mainly three types of 3D CAD models. Wire frame is one of them and it is the most abstract and least realistic. Other types of 3D CAD models are surface and solid.
This method of modelling consists of only lines, points and curves defining the edges of an object
5. Write the differences between the Solids vs. Surface Modeling? What and why you need to know?
Computer aided design (CAD) isn’t like a car in that you can use it pretty well even if you don’t know how it works. It pays to know what happening ‘under the hood’ when using CAD. It is important to know about surface and solids modeling because it does affect the way you model, and it is important to know if you are switching platforms. It is also very important to know about for rapid prototyping.
Surfaces and solids are the underlying math that defines the geometry of the forms you create. There are three ways to define 3D geometry: solids, surfaces and wireframes.
Wireframes don’t play much of a role in CAD, but primarily in digital content creation (DCC) and gaming.
The easiest way to understand the difference between surface and solids modeling is to think of a water balloon; the water in the balloon would be solids modeling, while the latex skin would be surface modeling. Need more of an explanation? No problem.
Solids modeling
Solids modeling is defining an object with geometric mass. Solids modeling programs usually create models by creating a base solid and adding or subtracting from it with subsequent features. Features such as extrudes, extrude cuts, revolves, radii, chamfers, etc.
Examples of solids modeling programs are Solidworks, CATIA, and ProEngineer. It was originally developed for machine design, and is used heavily for engineering with large part assemblies, digital testing and rapid prototyping.
Surface modeling
Surface modeling is defining an object’s exterior with an infinitesimally thin skin.
This skin is created by lofts, sweeps, and NURBS curves - i.e. sculptured surfaces with lots of curvature. The surfaces are either defined by poles or guide curves. A surface is considered a solid only when it is completely enclosed. It is used to make technical surfaces (e.g. air plane wing) or aesthetic surfaces (e.g. car’s hood).
It was developed for the aerospace and automotive industries in the late 70s.
Rhinoceros 3D and Alias Studio Tools are examples of a surface modeling programs. It is generally considered more difficult than solids modeling, but the models are more robust because the programs aren’t generally feature based. Later changes have to modify the existing geometry as opposed to just editing the original feature, which is more difficult but keeps the model from collapsing when one feature interferes with another.
6. Write the functions of various Edit and Inquiry commands in CAD?
Editing an entity or group of entities in Autocad requires the entity or the group to be selected. There are three ways of doing this :
1) Autocad can be set to allow the user to select the objects first, and then accept commands to process them. This is called noun/verb selection. This mode of operation can be enabled/disabled using the DDSELECT command which opens up a dialogue box.
2) The commands can be given first, and the objects can be specified when the user is prompted for them.
3) The SELECT command can be used to select a specific selection set, which can be referred to in subsequent editing operations.
Editing with grips :
Selected objects can be edited by manipulating grips that appear on the selected entity. The Grips mode can be enabled with the DDGRIPS command which opens up a dialogue box.
The editing operations possible using grips are : Stretch, Move, Rotate, Scale and Mirror
7. Erasing unwanted objects and retrieving accidentally removed ones :
The ERASE command permanently removes specified objects. To erase only the drawn object, enter "L" at the 'select oblects' prompt.
8. The OOPS command restores only the most recently erased objects.
9. Copying and Moving :
The commands available are :
MOVE, COPY, ROTATE, SCALE, MIRROR, STRETCH and ARRAY
The MOVE and COPY commands are for recreating the object at another place.
The COPY command retains a copy in the original place while the MOVE command does not.
10. The SCALE command allows the size of objects to be changed. It scales the object about a reference point, by expanding/shrinking it equally in all directions.
SCALE can be used to rescale an entire drawing in one go.
11. The ARRAY command creates multiple copies of entities in a rectangular or polar pattern. To change the orientation of the array, use SNAP Rotate command or SNAPANG system variable.
12. Changes, Cuts and Constructions : These commands allow you to change properties of objects (like color, layer,etc.) and modify objects by trimming /extending their ends, and cutting sections out of them. They can also be used to draw fillet arcs, chamfer lines, parallel lines, offset curves, and construction markers.
The available commands are :
CHANGE, DDEDIT, BREAK, TRIM, EXTEND, FILLET, CHAMFER, OFFSET, DIVIDE, and MEASURE
The CHANGE command is used to change the following : color, elevation, layer, linetype, thickness
Characteristics other than the above can also be changed by specifying a point instead of choosing one of the above properties. Then this "change point" is used to modify the object depending on whether the object is a line or a circle, etc. The "change point"
method works for multiple entities also.
Variations of the CHANGE command are : DDCHPROP and CHPROP
The DDEDIT command allows editing of both text and attribute definitions. The command can be used either in paper space or in model space, whichever is active when the command is issued. It cannot be used on text attributes that are part of a block.
The BREAK command erases part of a line, trace, circle, arc or 2D polyline The end points of the part are specified by the user.
The TRIM command is used to trim objects such that they end exactly at cutting edges defined by other intersecting objects.
The EXTEND command is the complement of the TRIM command because it lets you extend an object till it meets another object.
The FILLET command connects two lines, arcs or circles by means of a smoothly fitted arc of specified radius.
The CHAMFER command is similar : it trims two intersecting lines a specified distance from the intersection and connects the trimmed ends with a new line segment.
The OFFSET command constructs an entity parallel to the specified one, either through a given point or at a given distance.
The DIVIDE command lets you divide an entity into several equal-length parts, placing markers along the object at the dividing points.
The MEASURE command is similar to the DIVIDE command : it measures an entity and places markers at specified intervals.
Polyline, Mesh, and Block Editing :
There are two basic commands for this : PEDIT and EXPLODE. PEDIT is used to edit 2D and 3D polylines, and 3D polygon meshes.
The EXPLODE command breaks up a complex entity as follows :
A Block or associative Dimension is replaced with copies of simple entities comprising the Block or Dimension. Polylines are replaced with simple and arcs; 3D polygon meshes with 3D faces and polyface meshes with 3D faces, lines and points.
Undoing commands :
U command : causes the most recent command to be undone.
REDO command : reverses the effect of the most recent U command.
UNDO command : can undo several commands simultaneously.
Inquiry commands are commands which allow the user to inquire into locations and relationships into entities.
Inquiry commands available in Autocad are :
LIST : lists data for an entity.
DBLIST : lists data for every entity in the drawing.
ID : gives co-ordinates of a point specified in the graphics window.
DIST : measures angle and distance between two points.
AREA : finds are of specified enclosure.
AREA : finds are of specified enclosure.