3D Solid Modeling is a Growing Area of CAD

7/30/2019 3D Solid Modeling is a Growing Area of CAD

1/7

3D solid modeling is a growing area of CAD , transforming the way industry uses computers indesign process. A 3D computer model is more realistic and reveals more information. 3D CAD isused to produce 3D computer models so we call 3D CAD a computer modeling tool.

Model Definition

A solid models bears a lot of information. In the case of solid model the surface of modelrepresents the boundary between exterior and interior of the model. Solid modelers normallydefine manifold models only which separates a region into exterior and interior.

Primitive modeling

Many objects can be described mathematically using basic geometric forms. Although most

geometric primitives have unique topologies but differ only in their geometry. A primitivemodeler uses only a limited numbers of geometric primitives to form new topologies this iscalled primitive instancing. Complex topologies can only be formed by combining differentprimitives.

Constructive Solid Geometry Modeling

CSG modeling is a powerful technique that provides more flexibility than primitive modeling.CSG modeling uses Boolean expressions to define relationships between the primitives. Thereare three types of Boolean expressions : Union ( ( (

Boundary Representation Modeling

In B-rep modeling the surfaces or the faces are the basis for defining the solid. A B-rep facerepresents an oriented surface. There are two sides to this surface one is the solid side and theother is the void side. B-rep modelers have the ability of containing both linear and curvededges. The shape of B-rep model is formed by using Euler operations.

Constraint Based Modeling

The process of designing a computer model was thought to be much more irrational thandesigning a real world object , this thought was eliminated when parametric technologiescorporation released Pro/Engineer. Among the key innovations which Pro/engineer havebrought to 3D solid modeling is the idea of having the model defined as a modifiable features.The geometry of each of these features is controlled through modifiable constraints.


2/7

(1) Planning

A critical part of Constraint Based modeling is the planning which is done before the building of model. Careful planning is done so that it is easy to modify the model on later stages if need.

(2) Sources of data

Another important part of Constraint based modeling is the reuse of existing model andinformation if available and utilizing it to form the new model.

(3) Eventual model use

Another critical part of the Constraint based modeling is the process of understanding how themodel data is going to be used once it is created.

(4) Modeling standards

In constraint based modeling certain standards need to be followed. Standard for modelingmay include type of geometry , order of features , order of linking , and how the model is to bedocumented.

Feature analysis

Capturing design intent in a model is a process of defining features and the relation of featureswithin a model. The goal is to make sure that the information extracted from the model for usein other parts of the product development accurately reflects the original purpose of thedesigners and engineers who designed the product. An important of feature analysis is todefine the geometry of the model. The decision of the type of geometry is largly based on ourneeds and requirements.

Feature definition

Defining feature in a model begins with understanding how your modeler allows you to createand edit geometry.

(1) Features from generalized sweeps

Many features in a model can be made through the use of sweeping operations. In a sweepingoperation a closed polygon is used which is called a profile, is drawn on a plane and is moved or


3/7

swept along a defined path for a defined length. Each swept profile can be visualized as a solidobject. Each successive feature after this will modify the existing geometry.

(2) Construction geometry

In defining the location of geometry world coordinate system is used. A work plane is the mostcommon type of construction geometry used to support the creation of part geometry relativeto the world coordinate system. Construction geometry does not represent the final geometrybut instead provides a framework for guiding the construction of geometry.

(3) Sketching the profile

Many features on a part model begin as a profile sketch on a work plane. Once a work plane ischosen view of the work plane has to be selected. There are two types of views to select fromone is pictorial view and the other is normal view. After the selection of view a profile sketchcan be drawn on the work plane.

(4) Constraining the profile

As sketching defines the topology of the profile , Constraining defines the geometry of theprofile therefore it is an important part of profile sketching. The types of constraints can bedivided into two types Explicit and Implicit. When a system applies implicit constraints it will bedetermined in part by a predefined tolerance. On the other hand implicit constraints areapplied by the user to the profile sketch. There are three types of constrained profiles : fullyconstrained , under constrained or over constrained profile.

(5) Completing the feature definition

After the profile is drawn it has to be sweep out to form a 3D form in space. Following are thetypes of sweep : linear sweep , circular sweep , path based sweep , blind sweep , through allsweep , through next sweep , to next sweep.

(6) Feature planning strategies

When we talk about the feature planning strategies one of the most important considerationsis whether the profile contains the lines of symmetry or not. This consideration not only assistin the construction of the base feature , but also it will allow the mirror commands to be usedfor duplication. For good modeling practice certain type of features has to be avoided in orderto preserve the integrity of the model geometry.


4/7

Editing part features

The success of the editing of the features depend on the way initial features were planned.

(1) Understanding feature order

Features as they are created are placed at the bottom of the feature tree. If a new feature iscreated then it is place in the feature tree in the correct order. Closely related to this idea is theidea of parent-child relationship between the features. As in a real parent-child relationship thechild feature depends on its parent feature. Deleting the parent feature may result in the loss of child feature. Change in the geometry of the parent feature may change the geometry of childfeature.

(2) Editing feature properties

Within the sketch profile elements of profile can be changed. Normally the elements which arerequired to be changed are the constraints. Dimensional constraints are the easiest to changebut geometric constraints can also be changed. Other parameters that can be changed includetype of sweep path and distance of the sweep.

Duplicating Part Features

The ability to duplicate geometric elements is a powerful ability of all the CAD programs.Constraint based modelers normally allow the user to duplicate at the level of features. Copyingprocess is automated to some degree. A common tool for copying process is Array option.Following are the types of array options: linear array and radial array.

Viewing the part model

The techniques to view a 3D model are based on the projection theory. The primary elementsin creating a projection are the model , the viewer , and the projection plane.

(1) View camera option

The view camera is used to describe the viewing process with respect to 3Dmodels in various

CAD systems. For each view there is a camera and an image plane on to which the model isprojected.

(2) View camera strategy


5/7

The orientation of the view camera with respect to the world coordinate system can varyconsiderably during the process of modeling. Viewpoints should be chosen on the basis of thetask to be performed.

Application of Part Model Data

The part model , and its associated features is a primary module if the product information thatcan be shared with other applications. These applications may be other modules of the 3Dmodeling system . another modeling system .or other related technology. The part modelshould be thought of as part of a larger product database being managed and updated.

(1) Model data associativity

Model data associativity is the process of associating the existing information with the updatedinformation. There are two types of associativities : unidirectional associativity and bidirectional associativity.

(2) Documentation

If the 3D modeling system also has a 2D drafting module then links can be set up between themodel and the views represented in the production drawing. As in 2D CAD the starting point forcreating documentation in a 3d modeling system is to establish paper size and to apply both astandard or custom title block and border. Modelers who know that documentation will be

required can try to constrain the model in ways that will also meet documentation standards.

(3) Assembly modeling

Constructing an assembly begins with bringing in a base component. Each successivecomponent brought in needs to be oriented and located relative to other components in theassembly. Location and orientation is achieved by defining geometric relations betweengeometric elements of a component in the assembly and the elements of components beingbrought in. Geometric elements are mainly defined by two basic tools : Mate and Allign

AnalysisSelecting the right analysis method is as important as determining when or how oftenevaluations should be done . The speed of analysis depends on the scope of the analysis andthe type of analysis performed. Decisions need to be made as to what parts in an assembly andwhat regions of a part need to be analyzed.


6/7

(1) Visual inspection

Visual inspection is an evaluation technique that is quick and easy. The visual inspection mayinvolve making sure all the necessary parts are in assembly model.

(2) Prototyping

Prototyping technique allow physical models to be made directly from a 3D database. Thistechnique can be used for high precision manufacturing. In some cases where prototypes cannot be created the system of virtual reality is used which uses the concept of precision togenerate realistic environments.

(3) Kinematics

Kinematics is an analysis used to calculate the design of a mechanism that is an assembly of multiple parts. The mechanism contains two components : the part models themselves and the joints.

(4) Mass properties analysis

Mass properties analysis is used to obtain additional information With those 3D modelingsystems capable of calculating the volume of a solid, density values can be added to calculate

the overall mass of the solid , in addition to that the centers of gravity and the initial propertiescan also be calculated.

(5) Finite element analysis

The process of creating a model of primitive geometries is called finite element modeling andthe analysis done on it is called finite element analysis.

(6) Ergonomics

Ergonomics examines the interaction between technology and humans.

(7) Computer aided manufacturing

Three dimensional modeling techniques can be combined with computer aided manufacturingcapabilities to ensure that a product design satisfies the desired manufacturabilityrequirements as closely as possible.


7/7

3D Solid Modeling is a Growing Area of CAD

Documents

Transcript of 3D Solid Modeling is a Growing Area of CAD