Assembly is a hierarchical process. It involves the construction of subassemblies and their assembly with other subassemblies and components. A product is split in subassemblies at the design stage as it is not practical to handle the design of the whole product. Splitting the assemblies into subassemblies has the advantage of modularity in design, manufacturing and assembly. Most complex assemblies tend to include a number of subassemblies. There exist methods to extract assembly mate information but identifying subassemblies within the assembly remains a challenge. There is a need to identify subassemblies automatically without human interference. This paper aims at detecting the subassemblies by making use of Application Programming Interface (API) of the computer aided design (CAD) software.

1. International Journal of Applied Engineering Research, ISSN 0973-4562, Vol. 8, No. 19 (2013)
© Research India Publications; http://www.ripublication.com/ijaer.htm
[Page No. 2529]
Automatic Identification of Sub Assembly in an Assembly
Arun Tom Mathew, Ishan Kossambe, Aniket Kavlekar and Nikhil Karve
School of Mechanical Engineering, VIT University, Vellore, Tamilnadu, India
E-mail: arun.mathew@vit.ac.in
Abstract
Assembly is a hierarchical process. It involves the
construction of subassemblies and their assembly with other
subassemblies and components. A product is split in
subassemblies at the design stage as it is not practical to
handle the design of the whole product. Splitting the
assemblies into subassemblies has the advantage of modularity
in design, manufacturing and assembly. Most complex
assemblies tend to include a number of subassemblies. There
exist methods to extract assembly mate information but
identifying subassemblies within the assembly remains a
challenge. There is a need to identify subassemblies
automatically without human interference. This paper aims at
detecting the subassemblies by making use of Application
Programming Interface (API) of the computer aided design
(CAD) software.
Keywords: Subassemblies, API, Solidworks.
1. Introduction
Assembly sequence planning is the most important decision in
any project. The amount of information contained in a small
assembly is very large. As the numbers of parts in an assembly
increases the situation becomes more and more complex. It is
very essential to discretize these parts in smaller
subassemblies which then can be assembled together to form
the final assembly. For accurate final assembly the method
chosen to detect these subassemblies and assembling them
correctly plays a vital role. A planning engineer studies the
assembly geometry, draws the hierarchical tree and finally
after a lot of iterations and discussion comes with an assembly
plan. Still this plan may not prove to be optimum and is
subjected to changes as the assembly process starts. This is an
area of assembly planning where a lot of research is going on
over the years. But still there are lot of challenges in deciding
over the assembly sequence. A lot of work is being done to
reduce the cost involved in assembly activity.
Assembly costs account for 10–30% of total industrial
product labor costs [4], and as much as 50% of product
manufacturing cost [6, 7]. One way of achieving this is to
improve assembly planning. The objective of the assembly
planner is to find out different ways in which the project can
be assembled and evaluating them to come out finally with
most efficient method. In fast growing world the products are
changing in months. Due to competition in the global market,
companies keep on modifying their product. Also the
manufacturing methods are changing at a rapid pace. As a
result of these changes, it is desirable to automate the planning
activity. The order in which the parts are assembled greatly
affects the efficiency of the assembly process.
Detecting the presence of a subassembly in an assembly
can make a difference while assembling complex components.
Assembling the final project by knowing the subassembly
offers several benefits. By dividing the main assembly into
subassemblies reduces the number of parts to be handled,
thereby smoothens the assembly process. For identifying
subassemblies, the entire assembly has to be studied properly
and all the interdependencies of parts in the assembly have to
be found out. With recent development in CAD all the parts or
subassemblies are modeled using CAD packages, therefore the
geometric and their topological information are available in
the computer database. The model should provide a
representation of parts and relationships such as contacts,
degree of freedom among parts of assembly. For accurate
detection of assemblies, all these information is necessary.
Once this information is extracted, it will be easier to find the
interdependencies between the parts. These can be then
represented in the form of liaison diagram. Liaison is nothing
but the mating features between the individual parts. In this
paper using the Automatic Programmable Interface (API) of
the CAD software the required information is extracted and
then used to detect subassemblies in an assembly.
2. Literature Review
Assembly sequence planning is highly complicated problem.
There is no fixed method by which this problem can be
solved. Also it is bounded by lot of constraints. As the
numbers of parts forming the assembly increases, the ways in
which it can be assembled also increases exponentially.
Assembly tree can be used to represent a product in
hierarchical form. If a product is first divided into
substructures, which are also continually divided into small
substructures, the number of assembly sequences for the
product can then be decreased by a large amount. One of the
key issues in sub-assembly detection is the representation
model of the geometrical and technological relationship
between the components of a product. Zussman et al. [9],
proposed a method in which components joined together are
grouped as possible subassemblies. A relational graph was
used, which relates an object to its attributes, and assembly
features of the object to assembly features of the other objects.
The kinematics relationship between the objects is represented
by an object graph. By grouping components into pairs that
have a kinematics relationship, subassemblies are detected
from the object graph. These relationships remain unchanged
during the disassembly process and the subassembly is
considered as a single component in the generation of
assembly sequences. The feasible assembly sequences are then

2. International Journal of Applied Engineering Research, ISSN 0973-4562, Vol. 8, No. 19 (2013)
© Research India Publications; http://www.ripublication.com/ijaer.htm
[Page No. 2530]
generated from this object graph containing the subassemblies
and individual components. Dini and Santochi [3] proposed a
procedure based on mathematical conditions applied on three
matrices namely interference matrix, contact matrix and
connection matrix to automatically detect the presence of the
subassembly. Ong and Wong [5] detected the subassemblies
automatically by making use of the product model. The
product model which comprised of components and
subassemblies was passed through a developed program to
generate the subassembly sequence. This work was verified by
making use of inference and connectivity graphs. Zhang et al.
[8] describes algorithm to generate optimal assembly modules
for the reduction of dimensional variation in automobile body
assembly planning and suggested an adaptive strategy for
product and process design. A mathematical model was
developed which is easily managed by computer program, to
describe the precedence knowledge and detect all the possible
sub-assemblies and feasible sequences through mathematical
calculations, and solve the ‘‘combinatorial explosion’’
problem.
From the above mentioned literature, it is inferred that
most of the subassembly detection is done by mathematical
computation methods. Not much work is done in automation
of sub-assembly detection without human intervention. This
automation can be achieved by using the API (Application
Programming Interface) that links visual basic with
SolidWorks (CAD modelling package).
3. Methodology
The aim of this paper is to ease the assembly process by
finding the possible sub-assemblies in any given assembly.
Our objective is to identify subassemblies automatically and
reduce human interference in deciding it. To accomplish this
objective, an algorithm is generated which automatically
detects the possible sub-assemblies in the given assembly. The
steps followed in the research are as follows:
1. Generation of database
2. Development of the algorithm
3. Implementation with an example
3.1 Generation of Database
For a given assembly, all the mating relations need to be
extracted and stored in a database. This data is used to identify
the sub-assemblies. In any assembly all the components have
relations with each other; depending on these relations the
assembly sequence is decided. The assembly module
automatically extracts all the mating relations present in the
assembly. It basically reads the feature tree of the assembly
and gets all the mates which are given between various parts
in the assembly. The mating data extracted consists of all the
information needed like type of mate, which parts are mated
together etc. Using the algorithm explained by A. Mathew
[1,2], a code is written in visual basic which extracts all Mate
Information and a database is created as shown in Fig. 1. This
database is the basis for finding the possible sub-assemblies.
Fig. 1: Database.
3.2 Development of the Algorithm
An algorithm is developed and executed using Visual Basic
for Applications in order to detect the possible sub-assemblies.
An assembly consists of ‘n’ number of parts. In most of the
assemblies there exists a sub-assembly having ‘i’ parts. A sub
assembly is valid if one of these ‘i’ parts has mating relation
with any one of the ‘n-i’ parts. Initially the relationships
between parts in the assembly, list of parts and Assembly view
are extracted using the Generate Database and stored in a
database. The required information is extracted and passed
through the algorithm which reads the information and stores
it in the form of an array and then compares with each part to
detect a possible sub-assembly. The algorithm is illustrated in
the Flow Chart in Fig. 2

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Fig. 2: Algorithm.
ALGORITHM
EXTRACT THE MATE
INFORMATION AND NUMBER OF
PARTS
A
DON’T COUNT
DON’T SAVE
DOES
PART i HAS
A MATE
WITH PART
DOES PART j
HAS A MATE
WITH THE i
UNSAVED
PART
COUNT
PART i AND
SAVED j PARTS
IS NOT A SUB
ASSEMBLY
REPEATTILLj≤NUMBEROFPARTSSAVEDREPEATTILLi≤NUMBEROFPARTS
NO
NO
NO
COUNT=1
SUB ASSEMBLY

4. International Journal of Applied Engineering Research, ISSN 0973-4562, Vol. 8, No. 19 (2013)
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4. Implementation with an Example
For modeling the assembly, the commercial CAD package,
SolidWorks is used. The benefit of using SolidWorks is it
includes an entire API with functions that can be called from
Visual Basic. Another advantage of using SolidWorks is that it
shares the same solid modeling engine as Catia and several
other systems like the Unigraphics and Pro/Engineer. These
CAD systems are used in large applications.
Crank hook assembly is taken as a case study and on this
assembly the above algorithm is implemented. The Crank
hook assembly consists of 14 components namely cover plate,
distance bolt ,nutm20,cross,head ,hook, thrust bearing-dust
cover ,nut ,split pin, lock plate, hex screw, pulley pin, pulley,
bush. The assembled and exploded view is shown in Fig. 4
and Fig. 5 respectively. These parts are created separately in
SolidWorks and saved as “.sldprt” files. Each part is called
and then assembled using various mating conditions like
perpendicular, coincident, parallel, concentric, angle, distance
and tangent. This assembly is saved as “.sldasm” file. The
mating relations are extracted using AME algorithm [1] and
stored in database as shown in Fig. 1. The algorithm for Sub-
assembly detection is executed which uses the information
from the database and detects the possible sub-assemblies. In
this case two sub-assemblies are found as shown in Fig. 6.
Sub-assembly 1 consists of thrust bearing and dust cover; and
sub-assembly 2 consists of pulley, bush1 and bush2. The Sub-
assembly detection application developed is shown in Fig. 6.
The system used to run the program is Intel core i5 3rd
generation 2.6 Hz. Processor, with 4 GB RAM. The results
obtained are analyzed in the below section.
Fig. 3: Crane Hook Assembly.
Table 1: List of Parts In The Assembly.
Sl. No PART
1 PULLEY
2 COVER PLATE
3 BUSH
4 DISTANCE BOLT
5 NUT
6 DUST COVER
7 THRUST BEARING
8 HOOK
9 CROSS HEAD BLOCK
10 LOCK PLATE
11 HEX SCREW
12 NUT M20
13 PULLEY PIN
14 SPLIT PIN
Fig. 4: Crane Hook Assembly.
Fig. 5: Crane Hook Exploded View.

5. International Journal of Applied Engineering Research, ISSN 0973-4562, Vol. 8, No. 19 (2013)
© Research India Publications; http://www.ripublication.com/ijaer.htm
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Fig. 6: Sub Assembly Detection Form.
5. Conclusion
The algorithm detects the possible sub-assemblies for a given
assembly. The example taken in this paper has 14 parts,
whereas in industries assemblies consist of much number of
parts. The liaison information provides relationships between
parts which is useful in assembly sequence planning. Although
many modeling packages provide information about the solid
models, the information regarding to the relationships between
parts in the assembly is not explicitly available. In this paper,
using relationship liaison diagram, the possible subassembly
present in an assembly can be detected. The methodology
described first extracts the assembly information, processes it
and then generates liaisons. The generated liaisons are further
processed using the algorithm developed and detects the sub-
assembly. The process described in this paper is fully
automated, simplifies the process of extracting geometrical
constraints for any given assembly considering the relation-
ships between components of a CAD model using the
Automated Programmable Interface of the CAD software. The
main constraint in this approach is that the designer should
model the assembly components and define the mating
conditions while assembling the product properly. This
considerably reduces the time for sequencing, assembly time,
making it more manageable as the number of parts while
carrying out the assembly is reduced as we are working with
sub assembly and remaining parts thereby considerably cutting
down on assembly cost and time.
References
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Using API to Generate Liaison Relationships from an
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