Assembly PROCEDURE

1. UNIT IV
ASSEMBLY OF PARTS
Syllabus
Assembly modelling, interference of positions and orientation, tolerance
analysis, mass property calculations, mechanism simulation and interference
checking.

2. Assembly modelling
• An assembly is a collection of independent parts.
• Assembly modeling is a technique applied by CAD and product visualization
software systems to utilize multiple files that shows components within a
product.
• Assembly model must include the spatial position and hierarchical
relationship among the parts and the assembly (attachment) relationship
(mating conditions) between parts.

7. Assembly tree
• The most natural way to represent the hierarchical relationship between the
various parts of an assembly is an assembly tree.
• An assembly is subdivided in to several subassemblies at different levels.
• The leaves of the tree represent individual parts or subassemblies.

8. Assembly tree

11. Assembly planning
• Assembly planning is a key to creating successful assemblies.
• An assembly should be parametric and flexible, it means that the
relationship between the assembly parts should be easy to change
and update.
• When a designer changes some of the assembly parameters, the
others should update accordingly.

12. • Before create an assembly, we should consider the following issues
• Identify the dependencies between the components of an assembly
• Identify the dependencies between the features of each part
• Analyze the order of assembling the parts.

13. Three assembly approaches
• Bottom – up assembly approach
• Top – down assembly approach
• Combination of both

14. Bottom – up assembly approach
• In this approach, we create the individual parts independently, insert them
into an assembly, and use the mating conditions to locate and orient them in
the assembly as required by the assembly design.

17. Top – down assembly approach
• The top down approach, while good for any size assembly, is ideal for large
assemblies consisting of ten of thousands of components.
• In this approach begins with an assembly layout sketch. The layout serves as
the behind the scenes backbone of the assembly.

19. Mating Conditions
• Coincident
• Concentric
• Tangent
• Coplanar
• Parallel faces
• Perpendicular faces

25. Interference of position and orientation
• The interference of the position and orientation of a part in an assembly
from mating conditions requires computing its 4x4 homogeneous
transformation matrix from these conditions.
• This matrix relates the parts local coordinate system (part MCS) to the
assembly’s global coordinate system (assembly MCS).

26. • The simplest method for specifying the location and orientation of each part
in an assembly is to provide the 4x4 homogeneous transformation matrix
[T].