Assembly line optimization to Improve Productivity

© Faculty of Mechanical Engineering, Belgrade. All rights reserved FME Transactions (2017) 45, 496-502 496
Received: October 2016, Accepted: December 2016
Correspondence to: Deepak.A
Student of Mechanical Engineering,
Deepak.A, Chennai, India
E-mail: deepak9ad@gmail.com
doi:10.5937/fmet1704496D
A. Deepak
Student
SSN College Of Engineering
Student of Mechanical Engineering
India
R. Srivatsan
Student
Student of Mechanical Engineering
India
V. Samsingh
Assistant Professor
Faculty of Mechanical Engineering
India
A Case Study on Implementation of
Walking Worker Assembly Line to
Improve Productivity and Utilisation of
Resources in a Heavy Duty
Manufacturing Industry
The current industry demands high productivity removing every constraint
inherited during manufacturing a product with limited resources. Re-
configurability and Flexibility to produce multiple components depending
on customer demand is a key factor. This projects aims at optimizing the
productivity of a discrete heavy duty manufacturing company which adopts
a Fixed-Worker-Assembly-Line (FWAL) to manufacture multiple products.
The dynamic nature of heavy duty manufacturing assembly line is
improved by converting FWAL into a Walking-Worker-Assembly-Line
(WWAL). The productivity of proposed WWAL is calculated using
ProModel simulation software and compared with FWAL to ensure
optimization. Better utilization of resources and reduction of WIP is
carried out in WWAL in order to generate an optimized and dynamic
manufacturing unit and establish a common set of rules in converting a
FWAL into WWAL.
Keywords: Simulation, Cycle time, Productivuty, Assembly Line, Heavy
duty manufacturing industry
1. INTRODUCTION
An assembly line is a Manufacturing Tool, first made
by Henry Ford in his manufacturing of automobiles.
An Assembly Line is a progressive system where semi-
finished products from every stage move in line.
Assembly lines are classified into three major types
namely, (i) single model assembly line (ii) multi model
assembly line (iii) mixed model assembly line. The
assembling tasks of a single product are performed by
workers in a single line until it’s manufactured. In a
multi-model assembly line, assembling tasks of various
products are grouped and performed, in order to
manufacture various products. Assembling tasks of
multiple products are performed in batches, in order to
manufacture similar products in mixed model assembly
line [1]. A WWAL is a flexible, dynamic, and
reconfigurable assembly system. Here, the workers are
made to walk in between workstations laid out in
desired layout to carry out the task assigned at each
workstation [2].In fixed worker assembly line, the
worker remains static to carry out the operation
specified and the product moves down the line
according to the process flow [3].Every company aims
to produce more products with lesser workforce. We
need a dynamic manufacturing unit to match the
market demands. A WWAL is an upcoming technique
which employs ultimate utilization of resources. An
analysis of a case study involving conversion of Fixed-
Worker- Assembly-Line (FWAL) to Walking-Worker-
Assembly-Line (WWAL) is employed to draft a
generalized conversion algorithm. We have
emphasised on how the human resource flow and
allocation of work are instrumental in attaining an
optimized WWAL. A Lean Manufacturing company
basically targets the reduction of Work-In-Progress
(WIP) at very stage. WIP is defined as the amount of
work left in the semi finished product. We have studied
how WWAL incorporates better worker utilization and
reduction of WIP [4]. In this paper, we are going to
focus on optimization of manual mechanical
assembling. Conversion of current Fixed Worker
Assembly Line (FWAL) Line to Walking-Worker-
Assembly-Line (WWAL) to generate a lean adopted
manufacturing unit with improved productivity.
2. RELATED WORK
In modern day industries, most of the companies
manufacture a variety of products. We need a dynamic
manufacturing unit to match the production demands.
A FWAL for manufacturing discrete heavy duty
products have numerous disadvantages. The assembly
line is rigid and cannot be re-configured in order to
match the production demands. There is no flexibility
as it is difficult to manufacture a variety of products in
a FWAL. The advantages of a WWAL over FWAL is
studied and analysed to prove that WWAL has
improved flexibility and re-configurability. Flexibility
in an assembly system is the key factor required in any

FME Transactions VOL. 45, No 4, 2017 ▪ 497
scenario and approximately 40% of capital cost is
assigned to assembly unit and upto 50% in a manual
assembly unit and optimizing an assembly line is a key
factor that influences the efficiency of a manufacturing
unit. Improvement on ergonomics in a WWAL to
prevent injuries and enhance working conditions and
optimize production. Comparison between FWAL and
WWAL is studied and the parameters that define them
are interpreted. Three phases for designing a WWAL,
modelling, simulation and optimization are derived and
a simulation study to prove WWAL works better than
FWAL. There exists an optimized WWAL which is not
optimized and doesn’t integrate human resource
performances and ergonomics to enhance productivity.
Fluctuating current market demands flexible and
reconfigurable assembly system. Disadvantages
resulting from non-integrated design approaches in
WWAL can include: greater operating costs
economically and ergonomically and a duplication of
design efforts. A frame work to design a WWAL is
listed and two major steps in designing the framework
are structural design level which involves determining
the physical assembly line layout and operational
design level which optimises the staff workers for the
system and the specified skill levels for responding to
the demand. Integration of flexible workforce and
framework of layouts yields an optimized WWAL [5].
The manning of human resource in an assembly line
improves flexibility. In a WWAL, there are fewer
workers than workstations on the line. This dynamic,
flexible and re-configurable system is called walking
worker assembly line (WWAL). The workers travel to
different workstations to perform the assigned task in
order to manufacture the products. When there is
congestion of workers with more task time at a
particular workstation, it is called as bottle neck
workstation. A Mathematical model is generated
considering the ergonomic analysis and the constraints
in a WWAL [6]. The assembly line systems and the
variability in an assembly line are defined and the line
balancing problems and worker classifications are
studied as a linear layout of WWAL is interpreted and
studied thoroughly incorporated in a case study in
automobile assembly operations with 40 workstations
and 4 buffers by simulation. The designed WWAL is
implemented using Siemens software which aims at
optimizing productivity of manual assembly line [7].
Methodology adopted to generate an optimized
production line are, as-in-study-product selection-time
method, Analysis-assembly line balancing-operational
analysis, System evaluation-performance evaluation of
product selection using ABC classification (selection
based on importance), part process matrix (selection
using product parts requirement). Different layout
types in an assembly line are interpreted and motion
economy principles are to be considered while
optimizing an assembly line. The 3-step productivity is
applied in a mobile phone package industry. Single
stage parallel line’ and Five stage serial line
‘configurations are produced and simulated using
Witness simulation software [9]. The tools and system
adopted in designing a manufacturing unit for
ergonomics and time optimization in a Railway coach
manufacturing scenario is designed into 3 phases,
assembly line sequencing using Delima Quest
software, an index to evaluate designs and flow value
analysis, workplace assembly and ergonomics analysis
using human modelling software Jack5.0, find
bottlenecks, JIT, in current network, make
improvements either in ‘arrangement of work stations
‘along line production or in complete product
utilization [8].
3. PROCESS PARAMETERS FOR CONVERSION
OF FWAL INTO WWAL
The conversion requirement and the way of conversion
is explained in Fig.1 process flow chart, where we have
embraced enhancement of critical parameters of an
assembling unit and achieve an optimized lean adopted
assembling unit.
1. The current FWAL is scrutinized in order to find the
scope for optimization and the constraints to be
satisfied are determined.
2.Data collection is done in order to determine the
productivity of FWAL.
3.Conversion of FWAL into WWAL is
achieved by grouping operating tasks that are either
similar or that share a common inventory or both.
Figure 1. Process flow diagram for generalised conversion

498 ▪ VOL. 45, No 4, 2017 FME Transactions
4.The number of workstations will depend on the
number of products to be manufactured. The grouped
tasks are assigned to respective workstations according
to the process flow. The allocation of machines
depends on demand level and operation time.
5.The workstations are placed in a desired layout such
that, the layout that suits the production plant and other
constraints that are incorporated.
6.The workers are made to walk in the layout designed
to perform the assigned task at their respective
workstations. The directional of work flow and the
path network for resources to move are defined.
7.Bottle neck analysis of WWAL is employed in order
to determine the effectiveness of the proposed system.
8.Bottle neck analysis yields whether a station is idle or
congested using equation 1. A positive value yields to
work station idle time whereas, a negative value yields
an in-process waiting time.
( ) ( ){ }1x x xx x x X x X
Ot Wt Ot +∈ ∈ ∈
+ −∑ ∑ ∑ (1)
9.Optimization analysis of WWAL espouses a lean
adopted manufacturing unit as it eliminates the buffer
zones and reduces WIP.
10. The number of workers will be less than the
number of workstations.
11.Situational analysis of WWAL using appropriate
software to enhance optimization results. Simulational
analysis helps us achieve desired precise results [9].
4. OPTIMIZATION BY WWAL
4.1 Assessment of Current Scenario (FWAL)
The discrete heavy duty manufacturing company
embraces a Fixed Worker Assembly Line, where the
workers stay in a place to assemble a single product, until
it being completely manufactured. The machines
manufactured here are majorly grouped into two
categories namely, Frequency Machines (FM) and
Profitable Machines (PM). There are further, automatic
and manual operating machine types in each group which
are to be assembled. The constraints in the production
system are obtained and assessed. Further the Buffer
zones involved in the system are evaluated and optimized.
4.1.1 Constraints
The following are the constraints predefined and
adopted throughout the project:
1. A minimum of two workers are necessary to
assembly part of the machine
2. A minimum of two workers are necessary to
carry parts from inventory to working area.
3. We aren’t optimizing task buffer time now as
it requires further ergonomic study.
4.1.2. Buffer
Buffer includes all the activities and tasks that add up
to the cycle time and decrease the productivity. There
are two types of buffer in current manufacturing
system namely task buffer and stage buffer.
(i)Task buffer: The buffer time involved in every
activity incorporated while assembling is defined as the
task buffer.
Table 1. Notations for buffer activity
Activity Notation Buffer activity
base buffer Tba, Tbb
leg tapping changeover &
painting
bed buffer Tma, Tmb x bed and y bed changeover
cutting arm
buffer
Tca,, Tcb,
Tcc, Tca
changeover from block to
base assembly
z bed buffer Tza feed movement screws
cover assembly
buffer
Tca unit screws of varied size
coolant buffer Twau lower steel rod attachments
door buffer Tda door nuts and screws pickup
coolant tank
buffer
Tcta tank pick up and setting
bearing buffer Tbh varied size tools
bearing
housing buffer
Tbha varied tools for fixing
automatic
buffer
Tabh, Tabw varied tools and attachments
(ii)Stage buffer: These include the tool change and
changeover time from one activity to another, for
example from base assembly tools to x-y bed tools.
4.2 Data Collection
Collection of data is an important part in case study
analysis while proposing an optimized production
system. The collected data are grouped into the
following tabular columns for analysis.
Table 2. Task buffer time (mins)
Activity
Task
buffer
PM
M
PMA
FMA/
M
FMA/
M2
FMA/
M3
Base Tba 6 6 4 2 2
Tbb 5 5 4 - -
x-y-bed Tma 5 5 4 2 2
Tmb 5 5 4 2 -
Cutting Tca 4 4 4 2 2
Tcb 3 3 4 - -
Tcc 5 5 - - -
Tcd 2 2 - - -
Z-Bed Tza 7 20 4 2 2
Cover
Assembly
Tca 2 2 4 2 2
Coolant Twau 2 2 4 2 -
Door Tda 2 2 4 2 -
Tank Tcta 2 2 4 2 -
Bell Tbh 2 2 2 2 -
Bearing Tbha 2 2 2 - -
Auto Tabh 10 10 3 4 2
Tabw 10 10 - - -
Index: PM-profit machines, FM-frequency
machines, A-automatic machines, M-manual machines.

Table 3. Tasks Operating Time (PM&FM) (mins)
PM/FM PMM PMA FMA/M FMA/M FMA/M
1
2
Base
x-y-bed
2
2
3
3
4
4
5
5
1
1
3
4
Cutting
z-bed
2
2
3
9
4
4
5
5
1
1
5
6
Cover
assembly
Coolant
2
2
3
3
4
4
5
5
1
1
7
8
Door
Tank
2
2
3
3
4
4
5
5
1
1
9
10
Bearing
Auto
2
2
3
3
4
4
5
5
1
1
4.3 Calculation of Current Productivity: Statistical
Analysis
The following section deals with the analysis and
simulation of WWAL for the system.
4.3.1. Operation time: The amount of time that is needed
for the two workers to perform the tasks assigned.
4.3.2. Cycle time: The amount of time required to
assemble a product completely including every
possible buffer. In this case study, one cycle of
production yields five machines.
Formulae used:
( ), xx X
T B n T∈
= ∑ (2)
( ) 1, x xx X
S B n T − +∈
= ∑ (3)
( ), x xx X
O T n E∈
= ∑ (4)
( ) 1
,
X X X XT T OT
C T n
β
− ++ +
=
∑ ∑ ∑ (5)
( ) ( ) ( )( ), , , , , , /C T n M T O T x T B n S B C T β= + + + + (6)
4.4 Task Grouping
Grouping of similar tasks is the next step in conversion.
For instance the base production of all machines is
grouped. In this case, we have five machines whose
assembling tasks are similar. There are ten assembling
tasks for each machine to be grouped.
4.5 Workstation Installation & Allocation of Work
The next major step is creating workstations in which
the grouped tasks are to be carried out. We are creating
five workstations as five machines are to be manu–
factured. The grouped tasks are assigned to specified
workstations.
4.5.1 Human Resources Available For Machines
Which are to be Distributor
The available human resources to be considered in our
production model are:
Mechanical Assembly : 2
Sub Assembly : 4
Every workstation involves assembly activity of a
single machine and allocation of work is defined by
resource flow. The allocations of machine order are
based on demand level and operation time.
4.6 Proposed Layout
The workstations are placed in a U-Shaped layout as
demonstrated in Fig.2, in the production floor. The five
machines are placed in five workstations in the U-
Shaped layout. The number of workers will be less
than the number of workstations [10]. The workers are
made to walk in between these workstations to perform
the tasks assigned. As the distance between the
workstations is uniform and small, it assists a visual
feedback system. A visual feedback system is when
workers in a workstation can seek help from workers
of nearer workstations and consvey information in case
of an emergency or failure. D is the distance between
the workstations and V is the speed of workers. The D
value is calculated to be 0.32 m and V to be 2m/s.
Figure 2. Workstation layout of WWAL
4.7 Bottle Neck Analysis
Congestion of workers before the workstation is called
as bottle neck. Bottle neck analysis yields workstation
3 as bottle neck workstation as there is a task that
involves 9 min of assembling that makes the workers
of previous workstation to wait and downtime
production at the bottle neck workstation. Bottle neck
analysis yields whether a station is idle or congested
[11].
4.8 Resource Flow
Workers are made to walk in between multiple U-
Shaped workstations and perform the allocated tasks.
Workers are made to walk unidirectional unless an
emergency situation is called. Two workers begin the
operation at first workstation, on their completion they
move to the next workstation. The next two workers
enter that workstation now to complete the next
procedural task progressively. Speed of workers is
assumed to be 2m/s.
4.9 Optimization Analysis
Lean adopted manufacturing unit is generated as it
eliminates the stage buffers and reduction of WIP at every
workstation. We are manufacturing five machines which
are majorly classified into two types. Ten tasks are carried
out in order to generate a completely manu–factured
component. For every machine assembling, minor
arrangements have to be made in order to perform the
next machine’s task which includes ‘machine setting’ and
‘tool change’. The total of ten stage buffer zones for every
component and fifty stage buffer zones for all 5 machines

exist in current scenario. The proposed system consists of
five workstations where five machines to be assembled
are placed. The five machines share common tasks but
different tools and minor arrangements in their settings.
The similar task of every product is carried out in five
stations by the walking workers, in their first run and the
next similar task in their next run and goes on
progressively. This ensures elimination of stage buffer
zones and minimizes it into ten stage buffer zones from
fifty in the proposed scenario as the tool changes and
minor arrangement settings are required only when
dissimilar tasks are carried out.
4.10 Simulation Model Of Proposed System
Simulation of the proposed system is incorporated to
demonstrate the optimization of worker utilization and
increase in productivity. We have used ProModel
software to carry out the simulation.
1. Build Menu allows access to define the major
elements namely: Locations, Entities, Arrivals,
Processing, and Resources.
2. Eleven locations are created in which the WS
locations are where the operations are carried out
whose capacities are one and five barrel locations with
infinite capacity and inventory locations are defined.
3. Five entities which are the five machines to be
manufactured are defined.
4. Arrival cycle is defined as shown in Fig.3, for the
entities to enter the location in scheduled order.
5. Arrival cycle is defined as shown in Fig4, an called
in the arrivals menu.
6. Path network of the resource worker is defined.
Here, the ‘distance between the workstations’,
’unidirectional flow of resources’, and ‘non-passing
type’ path are defined as dshown in Fig5.
7. Index: One worker does the activity of two.
Two resources are defined as shown in Fig.6, where
one worker operate in a single workstation as the
capacity of workstations are limited to one.
8. Processing routing is defined and the barrel locations
are indicated in order to store the ten assembling tasks
and then route to exit. Fig.7, shows the processing
logic defined for execution of assembling tasks.
-Operations defined are, (i) USE<Worker> FOR<x
mins> (ii) WAIT<x hr>
-Move logic used, (i) MOVE WITH<Worker>FOR<x
mins>THEN FREE
Figure 3. Arrival cycle defined for the entities to flow in.
Figure 4. Arrivals process where it calls the defined arrival
cyce for structured entity flow
Figure 5. Path Network defined for workers to move in and
the direction of flow to ensure proper worker allocation
and walking time calculation.
Figure 6. Resources to be moved in the path network are
defined and called here.
Figure 7. Processing step is where you define the flow of
operation for execution.
5. RESULTS AND DISCUSSIONS
In our case study, one cycle of production yields five
machines. The total number of working days for an
employee in the company is for 261 days and the
number of working hours per day is 8 hours.

No. of machines produced per year= No. of working
hours in a year/ C.T (n)
There is a reduction of cycle time considerably in the
proposed WWAL as shown in Fig8, which compares the
cycle time of current model and proposed model. The
buffer zones involved in both the models are compared
in Fig.9, which shows the dynamic nature of WWAL
and reduced buffer time that enhances productivity and
assists a dynamic assembling unit.
Table 4. Calculation results (fatigue value β=0.97)
Statistical
Parameters
FWAL
(min)
Simulated
parameters
WWAL
(min)
Task Buffer 248 Task Buffer 248
Stage Buffer 550 Stage Buffer 246
Operation Time 266 Operation Time 266
Worker waiting
time
15.6
Moving Time 243
Table 5. comparison results
Productivity FWAL WWAL
C.T (n) 18.27 hrs 16.6 hrs
Number of machines 570 625
Figure 8. Graphical representation for comparing the cycle
times between FWAL and WWAL.
Figure 9. Graphical representation of all buffer times in
FWAL and WWAL
6. CONCLUSION
The proposed WWAL model can serve as an aid to the
heavy duty manufacturing industries by reducing cycle
time and improving the productivity. This model can
be further implemented in other types of manufacturing
industries that employ bulky conveyors for production.
The algorithm elucidated above in this research paper
for converting Fixed Worker Assembly Line to
Walking Worker Assembly Line was verified with the
help of a virtual model simulated using Promodel
software.
As future research, the impact of ergonomic factors
and working condition parameters that will keep
varying when the workers keep moving between every
workstation in the assembly line can be analyzed and
the perfomance of the Walking Worker Assembly Line
can be enhanced further.
REFERENCES
[1] Panavi Yerasi, Productivity Improvement of
annual Assembly Line, Submitted to the Office of
Graduate Studies of Texas A&M University in
partial fulfillment of the requirements for the
degree of MASTER OF SCIENCE
[2] Atiya Al-Zuheri, Lee Luong, Dr. Ke Xing, A
Framework Supporting The Design Of Walking
Worker Assembly Line Towards Improving
Productivity And Ergonomics Performance, Atiya
Al-Zuheri et al Int. Journal of Engineering
Research and Applications www.ijera.com ISSN :
2248-9622, Vol. 4, Issue 3( Version 1), March
2014, pp.514-523.
[3] Q Wang, GW Owen, AR Milenham Comparison
between fixed- and walking-worker assembly lines
Article in Proceedings of the Institution of
Mechanical Engineers Part B Journal of Engineering
Manufacture 219(11):845-848 · April 2005
[4] H. T. Papadopoulos, M. I. Vidalis, Minimizing
WORK-IN-PROCESS inventory in reliable produ–
ction lines, International Journal of Production
Economics, Volume 70, Issue 2, 21 March 2001,
Pages 185-197.
[5] Atiya Al-Zuheri, Lee Luong, Dr. Ke Xing, An
Integrated Design Support Methodology for
Walking Worker Assembly Lines, Proceedings of
the International MultiConference of Engineers
and Computer Scientists 2010 Vol e, IMECS
2010, March17-19,2010, Hong Kong
[6] Atiya Al-Zuheri, Ke Xing and Lee Luong
,Mathematical modelling for process design of
walking worker assembly line in productivity and
ergonomics, ARTICLE in International Journal
Of Industrial And Systems Engineering February
2013 DOI: 10.1504/IJISE.2013.052923.
[7] Afshin Amini Malaki, A Study of the Effects of
Operational Time Variability in Assembly Lines
with Linear Walking Workers This thesis work has
been carried out at the School of Engineering in
Jönköping University within the subject area of
Production Systems. The work is part of two years
Master of Science program
[8] A.Marzano, K.gyapong-kodua, S.Ratchev, Virtual
Ergonomics and Time Optimization of a Railway
Coch, 45th
CIRP Conference on Manufacturing
Systems 2012
[9] Atiya Al-Zuheri, Lee Luong, Dr. Ke Xing, The
Role of Randomness of a Manual Assembly Line

with Walking Workers on Model Validation, 45th
CIRP Conference on Manufacturing Systems 2012
[10]Ronnachai Sirovetnuku, Parames Chutima, The
Impact of walking Time in U-Shaped Assembly
Linen Worker allocation problems, Engineering
Journal, Vol 14, No.2 2010
[11]Lemessi M, Rehbein S, Rehn G. Semi-automatic
simulation-based bottleneck detection approach.
[12]Proceedings of the 2012 Winter Simulation
Conference 2012.
СТУДИЈА СЛУЧАЈА ФЛЕКСИБИЛНЕ
МОНТАЖНЕ ЛИНИЈЕ У ЦИЉУ
ПОБОЉШАЊА ПРОДУКТИВНОСТИ И
ИСКОРИШЋЕЊА РЕСУРСА У ТЕШКОЈ
ИНДУСТРИЈИ
А. Деепак, Р. Сриватсан, В. Самсингх
Један од захтева данашње индустрије је висока
продуктивност која елиминише сва ограничења
производње која намећу ограничени ресурси.
Кључни фактори су реконфигурабилност и
флексибилност процеса производње сложених
делова према захтевима купаца. Циљ пројекта је
оптимизација продуктивности одређене компаније
која се бави производњом машина и која има систем
нефлексибилне монтажне линије, тј. без кретања
радника поред траке. Динамика монтажне линије за
производњу машина се повећала преласком на
флексибилни систем. Продуктивност је израчуната
помоћу ProModel софтвера и извршено је поређење
са нефлексибилним системом да би се обезбедила
оптимизација. Код флексибилног система
постигнута је боља искоришћеност ресурса и
редукција трајања радног процеса како би се
произвела и оптимизирала производња компоненте
и установио низ правила за прелазак са
нефлексибилне на флексибилну монтажну линију.

Assembly line optimization to Improve Productivity

More Related Content

What's hot (20)

Similar to Assembly line optimization to Improve Productivity (20)

Recently uploaded (20)

Assembly line optimization to Improve Productivity