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Chapter: Mechanical : Computer Aided Design : Assembly of Parts

Assembly modeling

Assembly modeling is a technique applied by CAD and product visualization software systems to utilize multiple files that shows components within a product.


Assembly modeling


Assembly modeling is a technique applied by CAD and product visualization software systems to utilize multiple files that shows components within a product. The components within an assembly are called as solid / surface models.


The designer usually has approach to models that others are functioning on concurrently. For example, different people may be creating one machine that has different components. New parts are extra to an assembly model as they are generated. Every designer has approach to the assembly model, during a work in progress, and while working in their own components. The design development is noticeable to everyone participated. Based on the system, it might be essential for the users to obtain the most recent versions saved of every individual component to update the assembly.


The personal data files defining the 3D geometry of personal components are assembled together via a number of sub assembly levels to generate an assembly explaining the complete product. Every CAD methods support the bottom-up construction. A few systems, through associative copying of geometry between components allow top-down construction. Components can be situated within the assembly applying absolute coordinate position methods.


Mating conditions are defines of the relative location of mechanism between each other; for example axis position of two holes or distance between two faces. The final place of all objects based on these relationships is computing using a geometry constraint engine built into the CAD package.


The significance of assembly modeling in obtaining the full advantages of Product Life-cycle Management has directed to ongoing benefits in this technology. These contain the benefit of lightweight data structures that accept visualization of and interaction with huge amounts of data related to product, interface between PDM systems and active digital mock up method that combine the skill to visualize the assembly mock up with the skill to design and redesign with measure, analyze and simulate.



1. Assembly Concepts


When components are additional to an assembly, parent and child relationships are created. These relationships are displayed by graphically as an assembly tree. Parts are parametrically connected by position constraints. These constraints have data about how a part should be placed within the assembly hierarchy and how it should respond if other components are edited.


Functioning within the framework of an assembly is prepared easier by accepting to apply more commands to other parts and sub-assemblies. These contain the Annotation Text, Inquire, Point, Datum Plane and Pattern Component commands. Bigger assembly performance is improved by removing unwanted redraws and improved display management while zooming.


Assembly models have additional data than simply the sum of their components. With assembly modeling interference verifies between parts and assembly specific data such as mass properties.

Fig.4.1. Assembly of parts



2. Bottom up Assembly design


In a ‘bottom up’assembly design, complex assemblies are divided into minor subassemblies and parts. Every part is considered as individual part by one or more designers. The parts can be archived in a library in one or more 3D Files. This is the high effective way to generate and manage


complex assemblies.


Every part is included into the active part making a component request and thus an assembly. The component will be the child of the active part and then it will be the active part. Hence an instance


of the actual part is applied; it revises automatically if the archived part is edited by activating.



Bottom up Hierarchy:


The ‘bottom up’assembly design hierarchy of the basic assembly is shown in figure 4.2. All the parts exist prior to Part1. When Part1 is generated, it becomes the active. It would utilize the menu


sequence to add Bracket and it becomes the active part.



Insert > Component




Assembly Design Tool Bar >



As per example shown in figure 4.2., ‘Bracket’is a child of Part1. The dashed line represents that  ‘Bracket’exists in the   3D file Parts  Z3. The dotted line represents that ‘Bracket’is inserted into Part-1.  After Bracket is   added, Part1 is redefined. Bolt and Washer are  then  added  the  same process and Part-1 is reactivated again.

Fig.4.2. Bottom up Design –Part 1



Module of subassembly is added similar as Bracket’,‘Bolt’,and Washer’again becoming a


child of Part-1. But, because Module Subassembly already has the two items Seal and Module, they are added and continue as its children.


Sequence of operations (Fig. 4.2.):

§    File-1 has 1 part.


§    Part-1 has 4 components.


§    Module Subassembly has 2 components.


§    All of the items are illustrations of the original parts that reside in the ZW3D file Parts Z3.


§    If File-1 is eliminated from the active assembly before it is saved and Part1 are removed. The original parts placed in the file Parts Z3 are not changed.

§    If File-1 is saved and Part1 is also saved.


§    If File-1 is erased and Part1 is also erased.




3.Top down Assembly Design


In a ‘topdown’assembly design all parts are classically designed by the similar person within a single part. 3D assembly handles ‘top down’method by allowing to design and creation of a component while work in the active part. Hence, the active part will be an assembly part.


The part becomes a child of the active part and then it will be the active part. The part, when generated, is an instance of a base part which will be a root object located in the active file. Every part is activated and modified as needed. The ‘top down’assembly design has its benefits. If the project is terminated or to go in a different new direction, removing the file will remove the part and all of its components.



Top down Hierarchy


The ‘top down’assembly method is shown in a figure 4.3 and one of the components exist prior to Part-1. When Part-1 is generated, it will be the active part. The following command sequence to generate Bracket and create it the active part.


Assembly Design Tool Bar >

Fig.4.3. Top down Design –Part 1



Bracket is a child of Part-1. The dashed line illustrates that by default when Bracket is generated; it is attached to File-1. The dotted line illustrates that Bracket is attached into Part-1. When Bracket is executed Part1 is reactivated. Bolt and Washer are then generated using the similar process and Part-1 is reactivated again.


Subassembly Module is generated like the Bracket, Bolt, and Washer again will be a child of Part1. But, Module Subassembly remains active when seal is developed. Seal will be the active part and by default also exists in File-1 but is inserted into Module Subassembly hence it was active at the time of  seal was  created.  Subassembly Module  is  then reactivated and Module is  generated  like


a Seal.



Sequence of operations (Fig 4.3):


·       File-1 has 7.


·       Part-1 contains 4 components, which are illustrations of the basic parts located in File-1.



·        Subassembly Module contains 2 components which are also illustrations of the basic parts located in File-1.


·       If File-1 is saved it has all of its original parts.


·       If File-1 is erased, it and all of its basic parts are erased.


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