CAD Model AssemblyTechniques Investigation

Introduction

Computer-Aided Design (CAD) activities are

an integral part of the product design and

development process. With a number of CAD

model assembly techniques available, choosing

the best technique based on the complexity of

the model is very critical in order to save time

and effort. The goal of this research is to

investigate the effectiveness of different

approaches used to assemble a CAD model.

The basics

There are a number of techniques available to assemble

a product in a CAD package. Each technique serves the

main purpose, which is to assemble the product but

these packages do not reason about parts in the way

engineers think while assembling the product. So if

 proper technique is used depending on the part

complexity, the assembly time can be reduced

considerably.

Models of different part counts, ranging from 5 to

greater than 50 are being designed using SolidWorks.

The models are then assembled using a number of

approaches, including the Bottom-up approach and Top-

down approach and their effectiveness is being

investigated based on model complexity level.

The bottom-up assembly approach

The bottom-up assembly design approach is the

traditional and the most widely preferred approach for

assembly design. In this assembly design approach,

all components are created as separate part

documents. They are then placed and referenced in

the assembly as external components.

In this type of approach, the components are created

in the part mode. After all the components are created,

a new assembly module can be started and the

components can be inserted in it using the tools

 provided in the Assembly mode. After inserting the

components, the design can assembled using the

assembly mates.

The main advantage of this assembly design approach

is that the view of the part is not restricted because

there is only a single part in the current file.

Therefore, this approach allows to concentrate on the

complex individual features.

This technique is practical to model parts that are

already designed, or parts which do not change their

shape and dimension based on change in design or

shape of other parts.

A V10 engine assembled using the bottom-up

assembly approach

Conclusions

The research concludes that the top-down

technique, while a little more difficult to do and

requiring more work when creating the model, is

 better for designing products from scratch where

the assembly will need to go through many changes

 before reaching its final configuration. The

technique can not only save a significant amount of

time, but can also assure compatibility of

components of an assembly with a greater degree

of certainty than the bottom up design.

Samrat Baweja

Department of Mechanical Engineering, Northeastern University

References

[1] Dassault Systèmes SolidWorks Help Manual,

Assemblies > Design Methods (Bottom-up and

Top-down Design).

[2] Automated CAD Assembly and its Application

in DOME, Sinha, Prabhat K., MIT, June 2002

Investigation of the effectiveness of various CAD model assembly techniques

The top-down assembly approach

Top-down assembly technique, also known in

SolidWorks as "in-context", is used to create

assemblies where parts are modeled inside the

assembly. The parts are related to driving entities

inside the assembly which control the shape, features,

dimensions and position of those parts, in a way that

changes introduced to the driving entities drive the

configuration of all the in-context modeled parts and

therefore the entire assembly.

Creating a properly structured Top-down assembly

requires more analysis and work as compared to

creating a Bottom-up assembly. However, the

advantage that the top-down modeling possesses is

that very little work and time is required when design

changes occur, since all parts and components will

automatically update to new shapes, dimensions,

 position, etc. as new input parameters are entered into

the driving entities at the assembly level.

This technique allows the creation of re-usable

flexible models so that they can meet t he design

intent and quickly adapt to changes needed during the

design cycle or during the entire product life cycle.

A multi-link model assembled using the top-down

assembly approach