2015 workers and machine performance modeling in manufacturing

Volume 8(4) 185-190 (2015) - 185
J Comput Sci Syst Biol
ISSN: 0974-7230 JCSB, an open access journal
Research Article Open Access
Jilcha et al., J Comput Sci Syst Biol 2015, 8:4
http://dx.doi.org/10.4172/jcsb.1000187
Research Article Open Access
Computer Science
Systems Biology
JournalofComp
uter Science &
S
ystemsBiology
ISSN: 0974-7230
Keywords: PVC pipe product; Arena simulation; Waiting time;
Throughputs; Capacity utilization
Introduction
Industry Performance improvements arising from increased
manufacturing integration continues to be one of the primary
competitive issues in current days. Faced with ever-increasing
challenges such as the globalization, increased world competition, and
increased customer expectations, companies are pursuing strategies
to improve their performance and reduce their costs. Discrete-event
modeling and simulation (DES) is a popular tool in widely varying fields
for identifying and answering questions about the effects of changes
on processes. Recent research into manufacturing systems integration
has identified the need for effective positioning of business objectives
down through the organization and the subsequent measurement of
performance in critical areas as key elements of sustainable competitive
advantage [1-7]. One of the best tools that can indicate the performance
of any company is simulation software. The simulation software can be
divided in to bigger group Simulation Language and Simulators. The
simulation language is programming based using simulation software.
The simulator allows one to build a model of the desired system by
using before- made modeling constructs [8]. In Simulation, language
software the model is developed creating a program syntactically
or graphically using language’s modeling constructs. These types
of simulation software are very flexible tools but the user needs to
know programming concepts and longer modeling times [8,9]. Thus,
simulation can be either discrete event or continuous simulation. In
continuous model, the state of the system can change continuously over
time. In discrete model, though changes can occur only at separated
points in time [10].
During the past decade, the manufacturing industry has undergone
a dynamic transformation. Recently, traditional manufacturers are
inherently subject to high-mix, low volume manufacturing as a
business model [11]. In this paper, discrete event simulation is used to
model workers and machine performance in Ethiopia Plastics Industry.
Highly industries rely on workers and machine performance since
productivity depends on workers and machine availability. A company
will not be able to participate and will not survive in a long-term
perspective if employees do not attribute a high significance to such
organization goals. However, poor workers and machine and machine
performance can be recognized some of the factors are of high load
of work, financial stress, and illness. Therefore, workers and machine
performance, as this function is essential required for huge value to the
organization in maintaining and strengthening its business and revenue
growth [12-16].
Multi-skilling of workers can be achieved by cross-training. Cross-
training is a process in which workers are trained on the tasks, duties,
and responsibilities of multiple tasks in a specific work cell or work area
[14]. Worker assignment and involvement within a labor-intensive cell
is a major role in the performance of the cell [17]. The first model assigns
multi-skilled workers to existing cells while the second model finds the
optimal operator assignment within a cell [15]. The performance of
the workers can be determined from the arena simulation tools to take
an action in line with the other techniques and tools presented in the
previous researches.
The problem observed in this case company is the lack of experts
and variation on processing the PVC pipe in adjusting the heat
treatment and low capacity utilization of the workshop which causes
variation to the specified product. During this, the number of recycled
products is higher per days. The industry can fail to achieve the goal
for efficient and economical production. Capacity includes all resources
such as machineries, workers etc. of the factory.
Therefore, the objective of this paper is to provide industry with a
complete set of tools, techniques and procedures to allow examining of
existing workers and machine performance systems. These techniques
*Corresponding author: Kassu Jilcha, Addis Ababa University, Addis Ababa
Institute of Technology, Addis Ababa, Ethiopia, Tel: +251 913 01774; E-mail:
jkassu@gmail.com
Received May 05, 2015; Accepted May 18, 2015; Published May 20, 2015
Citation: Jilcha K, Berhan E, Sherif H (2015) Workers and Machine Performance
Modeling in Manufacturing System Using Arena Simulation. J Comput Sci Syst Biol
8: 185-190. doi:10.4172/jcsb.1000187
Copyright: © 2015 Jilcha K, et al. This is an open-access article distributed under
the terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and
source are credited.
Abstract
This paper deals with the workers and machine performance measurements in manufacturing system. In
simulating the manufacturing system, discrete event simulation involves the modeling of the system as it improves
throughput time and is particularly useful for modeling queuing systems. In modeling this system, anARENAsimulation
model was developed, verified, and validated to determine the daily production and potential problem areas for the
various request levels in the case company (Ethiopia Plastic Factory). The results obtained show that throughput
time in the existing system is low because of occurrence of bottlenecks, and waiting time identified. Therefore,
some basic proposals have been drawn from the result to raise awareness of the importance of considering human
and machine performance variation in such simulation models. It presents some conceptual ideas for developing a
worker manager for representing worker and machine performance in manufacturing systems simulation models.
The company workers’ and machine performance level is raised by identifying the bottle neck area. They were
recommended to amend the main basic bottle necks identified.
Workers and Machine Performance Modeling in Manufacturing System
Using Arena Simulation
Kassu Jilcha*, Esheitie Berhan and Hannan Sherif
Addis Ababa University, Addis Ababa Institute of Technology, Addis Ababa, Ethiopia

Citation: Jilcha K, Berhan E, Sherif H (2015) Workers and Machine Performance Modeling in Manufacturing System Using Arena Simulation. J
Comput Sci Syst Biol 8: 185-190. doi:10.4172/jcsb.1000187
Volume 8(4) 185-190 (2015) - 186
helps in applying simulation system model which could be used as
before an existing system is altered or a new system built, to reduce
the chances of failure to meet specifications, to eliminate unforeseen
bottlenecks, to prevent under or over-utilization of resources, and to
optimize system performance.
Material and Methods
The study was conducted by considering different materials
and methods to achieve the goal of this study. The literature reviews
and arena software applications were utilized to come up with good
solution. Simulation, in particular discrete event simulation, has
still not gain industries wide acceptance as decision support tool for
performance evaluation. The researchers have provided the example of
the application of discrete event simulation in evaluating performance
of a production line in the case company. The data was collected from
an Ethiopian Plastic industry production line and the simulation model
is built using arena software simulation. A simulation model provides
a visual animation of the line to see how product will flow through
the line. An ARENA®
simulation model was developed, verified, and
validated to determine the daily production and potential problem
areas for the various production levels in the plastic industry.
Discussion and Results
Production process flow
In general, there are 5 main workshops in Ethiopia plastic industry.
Rawmaterialsintheformofgardenhoseandmasterbatcharesuppliedby
foreign countries like Asia and in domestic like Elsewady Cables Ethiopia
and directed to raw material store for storing and quality checking.
They will be sent to two operating process continuous and injection
section and turn on heat treatment and take the melted plastic with
screw thread then forced into mold. The bundle will be prepared by
hauloof. After the product is finished it will be inspected and then
packaging will be done. Finally; the product will be kept in finishing
storage as shown in Figure 1. The other process is continues (extrusion)
process flow which begins at raw material receiving, and balling unit
machine as indicated by Figure 2.
Data analysis
The collected data through the means of interviews, direct
observation and company document review were analyzed. Fitting
Input Distribution through the input analyzer is used to identify fitted
statistical distribution [18]. It is used to evaluate the distribution’s
Receiving
production
orders
Raw material
Requisition
Properly
mounting mold
Machine
setup
parameters
Full hopper with
raw material
Turn on
heater
Turn on motor
granule plastic
melted and move
screw thread
Open molted and
product take off
Melted
plastic
Finished
product
Packing,
labeling,
stamping
ShippingQuarterly
checked
yes
No
Recycle
Reject
Take corrective action
Figure 1: Injection process flow.
Raw material (garden
hose & master batch
receiving from store)
Mini store
Filter and
stablizer
Mixer
Spine
conveyor
HopperExtruder
machine
Vacuum
tank
Cooling
tank
Numbering stamp
machine tank
Take off
Balling unit
machine
Figure 2: Continuous (extrusion) process flow diagram.

Volume 8(4) 185-190 (2015) - 187
Model formulation
In modeling design the type of analysis is performed on workers
and machine performance. The products that are selected are the one
those most often produced. They are considered as one of the main
products of Ethiopia Plastic Industry in this case company. The working
period in Ethiopia Plastic Industry is five days and a half day within
eight working hour consideration. This means the working days from
Monday to Friday 8:00 working hours and on Saturday 4:00 working
hours are utilized in the company. The three models for the arena
simulations are workers distribution models, continuous extrusion
models, and injection models as shown in Figures 4-6.
Model verification
Verification assesses the correctness of the formal representation
of the intended model, by inspecting computer code and test runs, and
performing consistency checks on their statistics [20]. More specifically,
verification consists in the main of the following activities:
Inspecting simulation program logic.
✓✓ Performing simulation test runs and inspecting sample path
trajectories. In particular, in a visual simulation environment
(like Arena), the analyst inspects both code printouts as well as
graphics to verify (as best one can) that the underlying program
logic is correct.
✓✓ Performing simple consistency checks, including sanity checks
as well as more sophisticated checks of theoretical relations hips
among predicted statistics.
✓✓ In simulation modeling, each part of model run with different
set of inputs and the obtained outputs were compared by using
throughputs and little’s formula with real outputs.
Model validation
Validation activities are critical to the construction of credible
models. The standard approach to model validation is to collect
data (parameter values, performance metrics, etc.) from the system
under study, and compare them to their model counter parts. These
parameters will prove the validity of the data and simulation.
Number of replication estimation
A good design of simulation replications allows the analyst to
obtain the most statistical information from simulation runs for the
least computational cost. In particular, minimizing the number of
replications and their length is necessary to obtain reliable statistics.
In order to decide the number of replication the model must run some
initial set of replication so that sample average, standard deviation and
confidence interval are computed. This initial set of replication is shown
in Table 4.
parameter and calculates a number of measures of the data. To select
which type of distribution to use, the authors have compared the
square error of each distribution. The larger the square error value, the
further away the fitted distribution is from the actual data. The data was
analyzed by using real recorded time from the operation areas of the
selected product in the case company section. These data supported the
analysis of validation, verification and number of replication estimation
as discussed in the next sections [7].
Model assumption
In Ethiopia Plastics Industry, there are three shifts per day. Workers
distribution through the specified time per shifts can be delayed by
different kind of incidents. The actual working time for whole system
is 8:00 working hours per day. Since it is not expected that a person
will work without some interruptions, the operators may take time for
their personal needs. Assumptions are taken for modeling the variation
of workers performance at time to rest, machine failure, and power
off. The model for one shifts are modeled and analyzed. In the study
only polyvinyl chloride (PVC) pipe line is selected. Raw material is
assumed as a constant input, no interruption of operation is occurred in
continuous and random for injection. The manufacturer working time
is 8:00 working hours per day. Distribution is fitted to input analyzer;
it evaluates the distribution’s parameter and calculates a number of
measures of the data. In order to select which type of distribution is
used, the author has compared the square error of each distribution.
The larger the square error value, the further away the fitted distribution
is from the actual data (19). Therefore the following fit all summary
orders in worker performance distribution from smallest to largest
square error. From the table it can be seen that triangular is the one
with smallest square error and thus it is selected. Line indicates that the
data normal distribution and the blocks are the actual data’s situation
histogram expression when compared to the normal distribution. The
normal distribution is skewed to the right (Tables 1-3, Figure 3 [18,19]).
s/n Process Distribution Square error
1 Raw material requisition 3.5+3 × BETA (0.3847, 0.648) 0.023693
2 Machine set up 4.5+3 × BETA (0.896, 0.979) 0.004202
3 Hopper 3.5+3 × BETA (1.05, 0.7336) 0.012719
4 Turn on heater 5.5+3 × BETA (11.76, 2.47) 0.000290
5
Turn on motor granular plastic
melted move to screw thread
22.5+3 × BETA (11.16, 1.52) 0.001000
6 Melted plastic forced into mold 5.5+GAMM (0.663, 22.87) 0.011748
7 Takeoff 4.5+5 × BETA (0.928, 11.35) 0.019469
8 Package 6.5+4 × BETA (0.996, 1.44) 0.002769
Table 1: PVC pipe process time distribution in injection.
S/n Continuous (extrusion) Distribution Square
1 Workers distribution TRIA (5.5, 6.8, 7.5) 0.00473
Table 2: Workers distribution in continuous (extrusion).
S/n Process Distribution Square error
1 Mixer 9.5+11 × BETA (0.789, 0.848) 0.000365
2 Hopper 4.5+6 × BETA (1.37, 0.815) 0.000534
3 Extruder 1.5+2 × BETA (1.33, 1.42) 0.000121
4 Vacuum 4.5+WEIB (0.873, 1.9) 0.003243
5 Cooling 3.5+4 × BETA (1.52, 0.678) 0.001297
6 Number of stamps TRIA (1.5, 3.2, 4.5) 0.00112
7 Takeoff 2.5+4 × BETA (0.934, 0.903) 0.0001232
8 Balling 9.5+6 × BETA (0.935, 0.836) 0.001245
Table 3: PVC pipe process time distribution in continuous (extrusion).
Figure 3: Input analyzer distribution histogram.

Volume 8(4) 185-190 (2015) - 188
Figure 4: Workers distribution model.
Figure 5: Continuous extrusion model.
Figure 6: Injection model.

Volume 8(4) 185-190 (2015) - 189
For PVC pipe continuous extrusion production line initial
replication (no) is 6 and the initial half width (ho) is 21.40. Assuming
that the h= 0.25, taking 95% Confidence Level.
DF= n-1= 6-1= 5
2
2
2
1,1 / 2
s
n t n a
h
≅ − −
2
2
2
3.97
n 6 1,1 0.05 / 2
0.25
t≅ − −

2 2
2
2 2
3.97 3.97
n 0.025,5 (2571)2* 1,666
0.22 0.25
t≅ ≅ =

By considering this equation the number of replications is 1,666
Conclusion
In this study worker and machine performance in manufacturing
system using simulation has been used. The simulation is done by using
Arena software. The performance measure used is throughput and it is
directly related to waiting time; work in process, resource or capacity
utilization. Simulation models were built for the continuous (extrusion)
and injection workshops separately and finally a model is prepared
for the purpose of conducting the computer based simulation. The
problems identified are the throughput time from the existing system is
low because of occurrence of bottlenecks, and waiting time identified.
Workers agent should be assigned on the machinery and workers
performance to focus on each operating system due that the number
of recycle products can be reduced. Otherwise, the company continues
like this for a long time and it will be difficult for them to compete in
today’s market. Therefore, to improve the existing performance of the
company, resource utilization improvement is a mandatory.
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Workshop Replication Number out (hr) Total time (hr) WIP per (hr)
Continues (extrusion )
1 1.903 0.4014 0.7691
2 1.909 0.4484 0.8588
3 1.904 0.4697 0.8977
4 1898 0.4014 0.6691
5 1899 0.7484 0.8588
6 1.904 0.5497 0.9977
Mean 1,902.83
Half width 21.40
Standard deviation 3.970
Injection mold
1 2.424 9.5589 26.134
2 2.453 7.3193 19.4321
3 2.447 8.2891 23.0371
4 2.460 6.5589 22.897
5 2.452 7.2165 15.465
6 2.448 8.4356 25.786
Mean 2,447.33
Half width 34.84
Workers shift time
1 150 2.9167 0.4404
2 151 2.9167 0.4413
3 151 2.196 0.4420
4 151 2.134 0.4303
5 151.40 2.5674 0.4405
6 151.33 2.214 0.412
Mean 150.95
Half width 1.08
Table 4: Number of replication.

Volume 8(4) 185-190 (2015) - 190
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Citation: Jilcha K, Berhan E, Sherif H (2015) Workers and Machine
Performance Modeling in Manufacturing System Using Arena Simulation. J

2015 workers and machine performance modeling in manufacturing

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