undefined | unit 1 fundamentals of 3d modelling

SMD

Unit 1

Fundamentals of 3D Modelling

Q1) Explain the life cycle of a product.

A1) Figure shows the life cycle of a typical product. The product begins with a need which is identified based on customers’ and markets’ demands. The product goes through two main processes from the idea conceptualization to the finished product: The design process and the manufacturing process.

Fig. Typical Product Life Cycle

Design process: The product goes through two main processes from inception to a finished product: the design process and the manufacturing process. Synthesis and analysis are the two main subprocesses of the design process.

Synthesis: The philosophy, functionality, and uniqueness of the product arc all determined during synthesis. During synthesis, a design takes the form of sketches and layout drawings that show the relationship among the various product parts. These sketches and drawings can be created using a CAD/CAM system or simply hand-drawn on paper. They are used during brainstorming discussions among various design teams and for presentation purposes.

Analysis: The analysis subprocess begins with an attempt to put the conceptual design into the context of engineering sciences to evaluate the performance of the expected product. This requires design modeling and simulation. An important aspect of analysis is the "what if' questions that help us to eliminate multiple design choices and find the best solution to each design problem. The outcome of analysis is the design documentation in the form of engineering drawings (also known as blueprints).

Manufacturing Process: The manufacturing process begins with the process planning and ends with the actual product. Process planning is considered the backbone or the manufacturing process since it attempts to determine the most efficient sequence in which to produce the product. A process planner must be aware of the various aspects of manufacturing to plan properly. The planner typically works with the blueprints and may communicate with the design team to clarify or request changes in the design to fit manufacturing requirements. The outcome of the process planning is a production plan, tools procurement, material order, and machine programming. Other special manufacturing needs such as design or jigs and fixtures or inspection gages are planned.

Q2) What is product life cycle management? Explain its need.

A2) Product life cycle Management (PLM) is a system of managing the entire life cycle of the product.

Product lifecycle management (PLM) is the Business Strategy of managing the entire lifecycle of a product from its conception, through design and manufacture, to service and disposal.

It Supports the Extended enterprise (Customers, Design and supply partners). PLM Spans from the Concept to the last stage – the life of a product or plant.

Need of PLM:

The traditional philosophy of product design is based on the principle of minimizing the design and manufacturing cost.

In today’s competitive environment, where market is flooded with large number of identical products, for a success of a product, it is not only important to minimize the design and manufacturing cost but also necessary to minimize the total product life cycle cost.

The product life cycle cost consists of: cost of product inception, design, manufacturing, service and disposal.

This had made it necessary to develop a plan to manage all the phases of product life cycle.

Hence there is the need of PLM to manage the entire life cycle of a product from inception to disposal.

Q3) Define Computer Aided Design. Give its features.

A3) Computer Aided Design:

“The use of computer systems to assist in the creation, modification, synthesis, analysis and optimization of a design of any product, machine or component of machine is defined as Computer Aided Design.”

Features of CAD

CAD enables companies to speed up product development, reduce manufacturing costs, and improve product quality and reliability across a wide range of industries and applications.

Intuitive product development tools give you the capabilities to create, validate, communicate, and manage your product designs and rapidly bring your products to market.

Flexible 3D modeling tools cover the full range of design tasks to quickly develop your product concepts.

Using CAD one can continuously check his/her designs against cost targets with integrated automated manufacturing cost estimation tools.

One can quickly and easily create powerful images and animations to communicate your design intent and functionality.

Verification of operation and performance can be done using CAD while creating your design with fully integrated simulation and analysis tools.

Q4) Give the scope of CAD/CAM

A4) At the core of the CAD and CAM processes is a geometric model of the product under design. Activities of the CAD process include mass properties, finite element analysis, dimensioning. tolerancing, assembly modeling, generating shaded images, and documentation and drafting. Activities of the CAM process include CAPP (Computer Aided Process Planning), NC (numerical control) programming, design of injection mold, CMM (coordinate measuring machine) verification, inspection, assembly via robots, and packaging.

The CAD process and its tools utilize three disciplines: geometric modeling, computer graphics, and design. The CAM process utilizes the disciplines of CAD itself, manufacturing, and automation.

At the core of the CAD and CAM processes is a geometric model of the product under design. Activities of the CAD process include mass properties, finite element analysis, dimensioning, tolerancing, assembly modeling, generating shaded images, and documentation and drafting. Activities of the CAM process include CAPP, NC programming, design of injection molds, CMM verifications, inspection, assembly via robots, and packaging.

The CAD process and its tools utilize three disciplines: geometric modeling, computer graphics, and design. The Cam utilizes the discipline of CAD itself, manufacturing and automation. Figure below shows these disciplines.

Q5) Which CAD tools are used in design process of product cycle?

A5) The various CAD tools that are used to perform various steps in design process is given below:

Sketching tools (2D operations):

CAD system offers many sketching commands/tools, which allow us to create various 2D shapes using geometrical entities such as lines, circles, arcs, fillets, rectangles and chamfers. All CAD systems offer these sketching tools.

2. Modelling tools (3D operations)

We take the sketches that we create and apply various 3D operations to them to obtain various features and surfaces which we call CAD models. CAD system offer many 3D operation for both solid and surfaces such as extrusion, revolve, cut, holes, ribs, chamfers, fillets, sweeps and lofts. These commands can be selected using the menu-bar or toolbar approach. It is important to know that 3D operations may require more than one sketch I order to completely define the feature or surface.

3. Viewing command

Once the object is created using 3D operations, or while in the process of creating models and sketches, CAD system allow us to view those models in many different ways. Most of the viewing operations on CAD system can be classified into three groups: view orientation, view modes, and view manipulations.

View orientation includes standard views such as front, top, right, and isometric. They basically align the object on screen in a way that displays selected views.

View modes allow us to change the display of the model to different types such as wireframe, hidden, or shaded.

View manipulation allow us to dynamically rotate, pan, and zoom the model to gain better control over its viewing.

4. Productivity tools

All CAD system provide certain productivity tools/features that reduce the time required to create a model and also increase the accuracy of the model. Examples of such productivity tools are geometric modifiers, geometric arrays and grids.

5. Management tools

CAD system provide management tools so that a user can group together the entities of similar nature, which in turn assists in editing, visualization, and efficient access to CAD models. Some management tools that CAD system offer are layers and colors.

6. Editing tools

When one needs to retrieve the model later by opening its file to resume its modelling by performing new CAD/CAM operations.These operations include either editing the existing model definition or adding new entities to it.

7. Coordinate system and sketch plane tools

Coordinate system and sketch plane are the most important concepts in a CAD system. They are used to input, store and display model geometry and graphics. The three coordinate systems that achieve these tasks are Model coordinate system, working coordinate system, and screen coordinate system.

Q6) Explain different types of software modules

A6) There are considerable numbers of applications for the various existing CAD/CAM systems. For example, there are mechanical, electrical, and architectural CAD and CAM products. An inspection of these various systems reveals that they have a generic structure and common modules. Awareness of such structure and modules enables users to better understand system functions for both evaluation and training purposes.

The major available modules are:

The operating system (OS) module provides functions for interacting with the operating system. This module provides a portable way of using operating system dependent functionality. This model helps the CAD/CAM system or software to interact with the operating system of the computer.

The geometric module is the heart of a CAD/CAM system. It provides users with functions to perform geometric modeling and construction. Editing and manipulation of existing geometry, drafting and documentation. The typical modeling operations that users can engage in arc model creation, cleanup, documentation, and printing/plotting. Shaded images can be generated as part of model documentation.

The applications module varies from one software system to another. However, there are common applications shared by most CAD/CAM systems. Mechanical applications include mass property calculations, assembly analysis, tolerance analysis and synthesis, sheet metal design, finite element modeling and analysis, mechanisms analysis, animation techniques, and simulation and analysis of plastic injection molding. Manufacturing applications include CAPP, NC, CIM, robot simulation, and group technology.

The programming module allows users to customize systems by programming them to fit certain design and manufacturing tasks. A CAD/CAM system requires advanced knowledge of the system architecture, its database format, and a high-level programming language such as C, C++, Java, Scheme, or others.

The communications module is crucial if integration is to be achieved between the CAD/CAM system, other computer systems, and manufacturing facilities. It is common to network the system to transfer the CAD database of a model for analysis purposes or to transfer its CAM database to the shop floor for production. This module also serves the purpose of translating databases between CAD/CAM systems using graphics standards such as IGES and STEP.

The collaborative module is emerging as an outcome of the widespread of the World Wide Web and the Internet. This module supports collaborative design. Various design teams in different geographical locations can work concurrently on the same part, assembly, or drawing file in real time over the Web. One team can make changes that other teams can view and accept or reject.

Q7) Explain feature and sketch-based modelling approach

A7) Now-a-days, feature based modelling is most widely used approach of creating 3D model.

Feature is defined as the combination of shape and operation to build the parts.

Shape is a 2D sketch.

Operation is an activity that converts the sketch into a 3D shape.

Steps in Feature and sketch based modelling are

Create sketches (shapes)

First step is to create the shapes or sketches. A shape is a 2D profile or a cross-section.

ii. Create features

Apply feature operations to the sketches created in previous step. Different feature operations are extrude, revolve, sweep, loft, etc.

iii. Combine features

Different features are combined to form a 3D model.

Most of the CAD softwares like Solidworks, CATIA, etc uses this approach to create a 3D model.

Q8) Explain 2 ½ extrusions and axisymmetric geometric models

A8)

2 ½ Extrusions

2 ½ extrusion models are those who have uniform cross section and thickness in a direction perpendicular to the plane of the cross section.

Extrude command is used to create 2 ½ extrusion models with a uniform thickness.

To create this type of models, a 2D sketch is required. This 2D sketch is the cross section of the desired model. Another input required to create this kind of model is a extrusion vector. The extrusion vector is always perpendicular to the plane of sketch. 2D sketch is extruded in a direction of extrusion vector, hence called as 2 ½ extrusions.

First step, we create the cross section in a sketch plane. Second, we extrude the cross section if the model has uniform thickness.

2 ½ D extrusion models

2. Axisymmetric models

Axisymmetric models are the models which are symmetric about its axis.

These are also the type of 2 ½ D models.

Revolve feature is used to create such kind of models. The input to create these models are a 2D sketch and axis of symmetry (revolution vector). Sketch and axis are in same plane. Sketch can be revolved for different angles to revolve. 360o revolve gives a full revolved sketch as shown below.

First, we create a sketch in the sketch plane with axis to revolve.

Second, we use revolve command and revolve the sketch about the axis for the required angle of revolution to create 2 ½ D axisymmetric model.

Q9) Give three types of geometric modelling

A9)

3D modeling is the process of developing graphics and images that appear to have three dimensions. It is of three types

Solid Modelling System

Surface Modelling System

Wireframe Models

Wireframe Modelling

Developed in 1960s and referred as “a stick figure” or “an edge representation”

The word “wireframe” is related to the fact that one may imagine a wire that is bent to follow the object edges to generate a model.

Model consists entirely of points, lines, arcs and circles, conics, and curves.

In 3D wireframe model, an object is not recorded as a solid. Instead the vertices that define the boundary of the object, or the intersections of the edges of the object boundary are recorded as a collection of points and their connectivity.

2. Surface Modelling

A surface model is a set of faces.

A surface model consists of wireframe entities that form the basis to create surface entities the basis to create surface entities.

In general, a wireframe model can be extracted from a surface model by deleting or blanking all surface entities surface model by deleting or blanking all surface entities

Shape design and representation of complex objects such as car, ship, and airplane bodies as well as casting

Used to be separated, shape model are now incorporated into solid models.

Surface models define only the geometry, no topology

3. Solid Modelling

The solid modeling technique is based upon the "half-space" concept.

The boundary of the model separates the interior and exterior of the modeled object.

The object is defined by the volume space contained within the defined boundary of the object.

In general speaking, a closed boundary is needed to define a solid object.

Informationally complete, valid, and unambiguous representation (Spatial addressability)– points in space to be classified relative to the object, if it is inside outside or on the object.

Store both geometric and topological information; can verify whether two objects occupy the same space.

Improves the quality of design improves visualization and has improved the quality of design, improves visualization, and has potential for functional automation and integration.

Q10) Write a note on VRML web-based viewing

A10)

The internet has affected CAD/CAM as it has many other fields. One noticeable change is that we can view CAD models in a web browser without having the CAD systems that have created them up and running. This is a significant advantage, especially for marketing engineers and mobile designers. A marketing engineer may need to share product 3D shaded views with a group of customers. Or a CAD designer may want to present a CAD model to a group of engineers in a meeting.

VRML (Virtual Reality Modeling Language) enables us to display CAD models in a Web browser. Moreover, we can manipulate these models. For example, we can rotate a 3D view in the browser window to look at other invisible sides of it.

We need to use CAD system to generate a VRML file before we can use the VRML plug-in. While the CAD system is running, save the CAD file in VRML format to generate a VRML file. Simply click this sequence:

File – Save As—select the VRML filename. The VRML file extension is .wrl.

We need a browser window to open the .wrl file to view it. While the VRML file is open in the browser window, we manipulate it using the buttons offered by the plug-in.

VRML is a standard file format for three-dimensional graphics data, whereas CGM and DWF are two-dimensional formats. Although VRML has limitations, such as loss of accuracy and large file sizes, most geometric modeling system vendors have opted to go with the VRML output capability because of VRML's support for three-dimensional work. Some even go a step further, providing the ability to put the VRML model into a Web page and add information such as text and hyperlinks to the page. Just as in Hypertext Markup Language (HTML) hypertext links-now used to link to other World Wide Web (WWW or the Web) data VRML files contain URLs that can point to any other type of file on the Web, including other VRML files. When VRML files are read by a viewer, a navigable three-dimensional model appears. Hot spots (links to other URLs) are identified by a graphical change in the cursor, much like the user encounters on HTML pages [Beazley 1996]. Clicking the mouse on a hot spot loads the file associated with the hot spot. By clicking on the different parts of a model, for instance, a user can open a window that displays information written by another member of the design team. When clicking on a different corner of the image, the user can read technical characteristics about the model and can see concerns posted by someone else on the team.

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