Scheduled maintenance policy for minimum cost – …432958/...Scheduled maintenance policy for...

School of Engineering

Scheduled maintenance policy for

minimum cost

- A case study

Växjö, Spring 2011

Authors: Mohamad Tabikh and Ammar Khattab

Case company: DynaMate IntraLog AB

Scheduled maintenance policy for minimum cost – A case study

Linnaeus University – Spring 2011

2

Organisation/Organization Författare/Authors

Linnaeus University Mohamad Tabikh

School of Engineering Ammar Khattab

Department of Terotechnology (Systemekonomi)

Dokumenttyp/Type of document Handledare/Tutor Examinator/Examiner

Examensarbete/Degree Project Matias T. Hailemariam Imad Alsyouf

Titel och undertitel/Title and subtitle


Sammanfattning/Abstract

This report evaluate the maintenance policies that been applied within specific industrial company,

Taken into considerations all corrective and preventive maintenance costs ,in addition to optimise best

preventive maintenance schedule for minimum cost.

Dynamate Intralog AB was the surveyed company that been encountered high maintenance cost

compatible with less productivity, therefore obtaining maintenance schedule policy for minimum cost

was the best solution for their problem, then by calculating their corrective and preventive

maintenance cost the optimum time was acquired. Finally, the maintenance schedule approve that

organized maintenance based on optimum time enhance the productivity and minimize the company

maintenance cost.

Nyckelord/Keywords

Corrective maintenance, Preventive maintenance, Maintenance Schedule, optimum time

Utgivningsår/Year of issue Språk/Language Antal sidor/Number of pages

2011 English 58

Internet/WWW

http://www.lnu.se



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Acknowledgements

First of all, we would like to take the opportunity to express our gratitude to

everybody who has helped us with this thesis.

In this context, our special thanks refer to our tutor, Matias T. Hailemariam and our

examiners, Imad Alsyouf, Lars Erikson and Anders Ingwald as they have guided and

helped us with our work.

Moreover, we appreciated the cooperation with Dynamate Intralog AB presented by Mr. Gaith that helps us during collecting the data

Finally, we are grateful for our families and friends who have supported us during this period of time, firstly to Bea Cerezo Valera for her constructive comments, then to Idriss, Nurdan, Akif, Nurdos, Hande and Zehra Aksoy.

Växjö, June 2011

Mohamad Tabikh and Ammar Khattab



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Table of contents 1. INTRODUCTION ......................................................................................................................... 8

1.1 Background ......................................................................................................................... 8

1.2 Problem discussion ............................................................................................................. 9

1.3 Problem formulation .......................................................................................................... 9

1.4 Purpose ............................................................................................................................. 10

1.5 Relevance .......................................................................................................................... 10

1.6 Limitations ........................................................................................................................ 10

1.7 Time Frame ....................................................................................................................... 10

2. METHODOLOGY ...................................................................................................................... 12

2.1 Research strategy ............................................................................................................. 12

2.2 Research design ................................................................................................................ 12

2.3 Data collection .................................................................................................................. 13

2.3.1 Semi-structured interviews ......................................................................................... 14

2.3.2 Secondary analysis ..................................................................................................... 14

2.4 Validity and reliability ...................................................................................................... 14

2.5 Generalizing ...................................................................................................................... 15

3. THEORETICAL FRAMEWORK .................................................................................................... 16

3.1 Impact of Maintenance .................................................................................................... 16

3.2 Corrective Maintenance ................................................................................................... 16

3.3 Preventive Maintenance .................................................................................................. 17

3.4 Block policy ....................................................................................................................... 18

3.5 Age policy .......................................................................................................................... 18

3.6 Weibull distribution .......................................................................................................... 19

3.7 Maintenance optimization ............................................................................................... 22

3.8 Schedule maintenance ..................................................................................................... 23

3.9 Life Cycle Cost (LCC) .......................................................................................................... 24

4. EMPIRICAL DATA ..................................................................................................................... 26

4.1 General description .......................................................................................................... 26

4.2 The logistics outsourcing .................................................................................................. 26

4.3 The empty boxes process ................................................................................................. 27

4.4 Robot performance and critical components .................................................................. 28

4.5 Maintenance strategies within Dynamate Intralog AB ................................................... 28



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4.6 Corrective maintenance for essential components ........................................................ 29

4.7 Preventive maintenance for essential components ........................................................ 30

4.7.1 Weekly preventive maintenance ................................................................................ 30

4.7.2 Monthly preventive maintenance .............................................................................. 32

4.8 Corrective and preventive maintenance related cost ..................................................... 33

4.9 Production list for palletizing robot ................................................................................. 34

5. ANALYSIS ................................................................................................................................. 35

5.1 Maintenance cost calculations ......................................................................................... 35

5.2 Distribution for the failure data ....................................................................................... 38

5.3 Optimum time to PM actions ........................................................................................... 39

5.4 Maintenance schedule based on optimum time ............................................................. 41

6. RESULTS ................................................................................................................................... 42

7. CONCLUSION ........................................................................................................................... 43

References ................................................................................................................................... 44

Appendix 1 .................................................................................................................................. 46

Appendix 2 .................................................................................................................................. 47

Appendix 3 .................................................................................................................................. 48

Appendix 4 .................................................................................................................................. 50

Appendix 5 .................................................................................................................................. 51

Appendix 6 .................................................................................................................................. 52

Appendix 7 .................................................................................................................................. 53

Appendix 8 .................................................................................................................................. 54

Appendix 9 .................................................................................................................................. 55

Appendix 10 ................................................................................................................................ 56

Appendix 11 ................................................................................................................................ 57

Appendix 12 ................................................................................................................................ 58



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List of tables, figures and images

List of tables

Table 1. Time Frame .................................................................................................................... 11

Table 2. The value of m ............................................................................................................... 40

Table 3. The optimum time for each component to perform PM .............................................. 40

Table 4. The optimum time to perform PM ................................................................................ 41

List of figures

Figure 1. Maintenance-related time ............................................................................................. 9

Figure 2. Corrective maintenance cycle ...................................................................................... 17

Figure 3. Example of age policy ................................................................................................... 18

Figure 4. Curve shows the total cost with increasing PM actions to an optimal time ................ 22

Figure 5. TPL circulation .............................................................................................................. 27

Figure 6. No. of failures for each critical component during 5190 hours ................................... 38

Figure 7. The time at which the components have failed ........................................................... 39

Figure 8. Current PM Time and Optimum time .......................................................................... 41

List of images

Image 1. The wooden box ........................................................................................................... 27

Image 2. The photocell in palletizing robot................................................................................. 31

Image 3. The brake motor ........................................................................................................... 31

Image 4. The gearbox .................................................................................................................. 32

Image 5. The air bellows ............................................................................................................. 32

Image 6. The control list .............................................................................................................. 33



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List of abbreviations

CBM Condition based monitoring

CM Corrective maintenance

LCC Life Cycle Cost

MLE Maximum Likelihood Estimation

MTTF Mean time to failure

PM Preventive maintenance

TPL Third-party logistics

tp Time interval between PM actions

Cf/Cp Cost ration

Cf Cost of failure

Cp Cost of preventive maintenance



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1. INTRODUCTION

This chapter will present an overview about the report, which includes: Background, problem

discussion, problem formulation, purpose, relevance, limitations and time table.

1.1 Background

The definition of maintenance may combine the technical and administrative actions

that intended to retain an item or restore it to a state in which it can perform a

required function. Maintenance provides crucial support for heavy and capital-

intensive industry by keeping machinery and equipment in a safe operating condition.

Therefore, maintenance plays a main role in sustaining long-term profitability and

competitiveness for an organization (Aditya and Uday, 2006).

Thus, the market demands on products with higher quality, faster delivery and more

reliable characteristics led to the development of manufacturing systems combining

automation (robotic machines), integration and flexibility. Accordingly this complex

system becoming more vulnerable to various kinds of disturbances, such as

components failure and incidental faults, but maintenance strategies consistent with

high applicable performance may mitigate it. The assimilation of maintenance

management could increase the productive time (availability), reliability, and optimise

performance due to many policies that correlated with high maintainability

techniques. There are two common maintenance strategies dealing with industrial

machinery known as corrective and preventive maintenance, the examples of

corrective maintenance (CM) are configuration of mechanical part and control

equipment when the robot break down (Fix when it’s break). In other hand, preventive

maintenance (PM) can be classified into three categories: time driven, predictive, and

equipment driven. Scheduled maintenance derived from periodic, time intervals of the

system to replace the part. The concept behind it is that wear parts have a fixed

number of cycles to failure which is converted to operating time. By determining the

optimum time to maintain or replace the part with minimum total cost (Mobley,

2004).

Furthermore, maintenance strategy1 cannot be set up farther cost effective analysis

because the economical view tracking the entire process and organization take into

consideration all the direct and hidden cost behind their maintenance strategy. The

total cost of the maintenance (CM and PM) depends on the number of components

replaced during operating period of the system (Chitra, 2003).

1 Maintenance strategy: It is plans which direct the maintenance management towered a desired future

state (Levitt, 2003).



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In order to establish an effective Preventive maintenance (time based), failure data are

required and it does not have to be based on Expert opinions anymore. Using

statistical methods, scheduled maintenance can be optimized, taking into

consideration the three types of maintenance: preventive maintenance, inspection

maintenance and predictive maintenance (Didson, 1994).

1.2 Problem discussion

Many organizations have been failed in implementing PM due to absent of clear

program that should be followed. In addition, many organizations which have program

failed also because of not having activity that ensure the program accomplishment.

(Mobley, 2004) In order to establish an effective programme, failure data are required

to be analysed to calculate the optimum time (Didson, 1994).

There is a survey within industrial sectors covered different production companies

1997 to highlight the maintenance time and in which trend; the present assessment is

shared between planning, prevention and correction. The percentages were

distributed according to how much of their maintenance time was spent on those

factors. Figure 1 show that about half of the maintenance time is spent on corrective

actions and two-fifths on preventive or condition based monitoring (CBM). The

optimum figure for CM is considered to not exceed 30-40 percent and most firms

probably knows this but are still not changing strategies or techniques (Jonsson, 1997).

Figure 1. Maintenance-related time Source: Jonsson, 1997, pp.242

1.3 Problem formulation

The problem can be formulated in this thesis as following:

Is it possible to determine the optimum period to perform PM actions by

analysing a set of failure data?



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1.4 Purpose

The goal of this report is to identify the optimum time that a certain PM actions should

take a place by analyzing the company maintenance policy towards their robot

availability.

1.5 Relevance

In today’s business, a valuable utilization of the machinery (robots) and incorporated

maintenance policies2 are a prerequisite for keep on challenging into the market and

gain profits. Thus, all the efforts regarding to decrease idle time and minimize delivery

delays should be made.

The relevance of this report includes the importance of implementing the right

maintenance policy at the right time in order to avoid unnecessary PM action which

could affect the machine availability.

1.6 Limitations

Maintenance management is wide subject and it’s difficult to consider all the elements

within it, therefore, our focusing will be only on the company applied method. In

addition to, visits limitation to company that narrowing our observations.

1.7 Time Frame

The preliminary work of this thesis started on week nine by deciding the thesis topic

and case company. Afterwards, the authors of this thesis started searching scientific

articles, books, etc. regarding the area of study.

In order to follow up with submission dates, a time plan was developed at the

beginning of week ten. The time frame for the accomplishment of this work is shown

in the following table.

2 Maintenance policy: An identified step used to implement the maintenance actions (Levitt, 2003).



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w.15 w.16 w.17 w.18 w.19 w.20 w.21

Introduction

Methodology

Theory

Empirical findings

Analysis

Results

Conclusions

Review and hand-in

Submission of chapters

1-3

Submission of chapters

1-5

Submission

of final thesis

Table 1. Time Frame



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2. METHODOLOGY

In this chapter different methods had been selected by the authors in order to reveal the

process of the research. The chapter contains the research strategy, the research design, data

collection, validity and reliability, as well as generalizing.

2.1 Research strategy

Ghauri and Grønhaug (2005) classify two different approaches of research by

distinguishing between inductive and deductive approach. These two ways are used by

the researchers in order to identify if their statements are either true or false. If the

statement is established as true, it can be used as the basis for theories. Once the

statement is identified as true or false, it is time to draw the conclusion.

The deductive approach is when the researcher deduces a hypothesis based on what is

known in a specific field, and by collecting data the researcher will reach his or her

findings. Some researchers prefer the inductive approach which is the opposite from

deductive approach. In the inductive approach “theory is the outcome of research”

(Bryman and Bell, 2007, p.14).

According to Saunders et al. (2007), there is another approach which is called

abductive. This approach is the combination of deductive and inductive approaches.

The abductive approach consists on elaborating the theoretical framework in order to

explain a specific case, and later testing this theory on other cases.

An abduction research approach which combines deduction and induction approaches

will be used in this thesis. The deduction approach will be used to collect different

theories, such as life based maintenance, related to the research question in order to

obtain conclusions. The induction approach will be used to verify the conclusions in the

case study of this thesis making new schedule maintenance after applying optimum

time selection methodology.

2.2 Research design

Research design may be classified as exploratory, descriptive and causal. The

exploratory design is used to clarify the research problem by gathering and providing

all the information. In the descriptive design the research problem is known, but focus

on the description of different characteristics of the problem. The causal design is used

to obtain evidence of cause and effect problems (Ghauri and Grønhaug, 2005).



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As the purpose of this thesis is to determine the exact optimum period to perform PM

actions, the causal method will be used. The authors will confront the cause-and-effect

problems by determining which policy is the most suitable for the robot.

Moreover, Bryman & Bell (2007) assert that a research design provides a structure for

the collection and analysis of data and there are five different types: experimental

design, cross-sectional or social survey design, longitudinal design, case study design

and comparative design.

Case study design “is concerned with the complexity and particular nature of the case

in question”. A case study can be: a single organization, a single location, a person, or a

single event (Bryman & Bell, 2007, p.62).

In this thesis a case study design will be applied because the data will be collected from

an industrial company located in Sweden. For this reason this design is the most

suitable for the thesis in order to obtain appropriate data and develops analytic and

problem solving skills. Furthermore, this kind of research requires a tangible approach

whilst connected to failures and statistical distributions, although it allows for

exploration of solutions for complex issues and applying new knowledge. The case

study here enables us to observe the current situation and monitoring all the factors

surrounded by it.

2.3 Data collection

There are two methods for collecting data, qualitative and quantitative. Qualitative

method is the collection and analysis of data by words; whereas quantitative method is

through statistics and mathematics i.e. researchers employ measurement (Bryman and

Bell, 2007). In addition, Creswell (2009) states that the combination of quantitative and

qualitative approaches leads to mixed methods research. Employing both methods

provides an extensive understanding of research problems.

This thesis is a result of both qualitative and quantitative research, as the authors

investigate and evaluate maintenance policy in the industrial sector using data which is

verbally coded as well as statistics in order to provide cost effective solutions to the

case study. Therefore both methods are suitable in order to create a deeper

understanding about our topic.

For this paper, data was collected through interviews with different employees at the

company and by analyzing statistics and documents that have been collected by the

case study. The methods that will be applied in this thesis in order to get the most

significant data are detailed below.



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2.3.1 Semi-structured interviews

Bryman and Bell (2007, p.213) state that a semi-structured interview “refers to a

context in which the interviewer has a series of questions that are in the general form

of an interview schedule but is able to vary the sequence of questions”. Interviewers

have the opportunity to ask further questions depending on the interviewees’

answers. When a researcher is collecting data by conducting semi-structure interviews,

he or she has to control the situation, ask the most important questions and be able to

adapt to the situation (Ghauri and Grønhaug, 2005).

The authors of this paper will interview several workers in the company with the

purpose of obtaining expert information about maintenance actions. The interviews

will consist of ten questions of different types such as open and closed questions. See

appendix (1). Thus, we will reduce the duration of the interview as well as making it

easier for interviewees to answer. The questions will be accurate in order to reach our

purpose. These questions mostly been formulated based on recent observations and

meeting with production and logistics manager, in addition to recent data collected

from last year of robot effectiveness such as availability, productivity and reliability

(failure data).

2.3.2 Secondary analysis

According to Bryman and Bell (2007), secondary analysis involves the analysis of data

by researches who have not participated in the compilation of the data. Other

researchers such as companies or other kinds of organizations have collected them for

their own purposes. Secondary analysis entails the analysis of quantitative as well as

qualitative data.

In this thesis will be performed a secondary analysis of a large amount of information

that our case study have collected for several years and thereby will reveal relevant

knowledge on our thesis.

2.4 Validity and reliability

There are different important criteria in order to evaluate a research. On the one hand

there is validity and on the other hand reliability. Validity is “concerned with the

integrity of the conclusions that are generated from a piece of research” (Bryman and

Bell, 2007, p.41). Moreover, reliability is “concerned with the question of whether the

results of a study are repeatable” (Bryman and Bell, 2007, p.40). Reliability is

connected with quantitative research since it is relevant to know whether if a measure

is stable or not (Bryman and Bell, 2007).



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This thesis will provide the validity of the data by collecting accurate and relevant

information from various articles and books in order to find the most appropriate

theories for our thesis. Furthermore, the questions for the interview will be formulated

in a careful way to get the best relevant answers. Therefore the ways that been

performed for designing the questions taken into considerations the internal, external

and content validity. To provide reliability, the authors will interview different

operators and group leaders in order to know how the maintenance affects the robot.

The questions are related to every part of the process with the aim of achieving a

wider perspective.

2.5 Generalizing

Generalization of results involves that the researcher create a representative sample in

order to generalize the results to other groups or cases beyond than the one of the

research (Bryman and Bell, 2007). The qualitative method as well as quantitative can

be generalized, some of the reasons may be the situation of the case study or the type

of the research (Saunders et al., 2007).

The Generalizability of the results can be guaranteed from the implemented

researching approaches and specific methods adapted only in company’s applied same

maintenance strategies and have almost similar cost ratios. Hence, these factors may

rely on optimum time method in order to perform preventive maintenance schedule.

By the way, we cannot generalize the following results statements because of various

systems adaptation and different element may involve the optimum time model

evaluation.

Consequently, may this method encountered an internal and external blocks through

implementation stage such as human errors or learning curve minimization, especially

this way based on high corrective cost over preventive cost, and in such companies a

certain corrective action still benefiting more than life based maintenance.



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3. THEORETICAL FRAMEWORK

This chapter contains theories about maintenance management in order to provide a clear

picture of the theories which will be used in the research.

3.1 Impact of Maintenance

Maintenance has been always considered as extra unnecessary actions which mean

cost for managers nevertheless; it is an existence cost that could be hidden.

Maintenance forms a portion from the total operating plant. Recently Maintenance

has been highlighted due to it is impact in industrial field (Mobley, 2004).

Nowadays organizations are not only satisfied with keep machines in good conditions

further, maintenance actions could be planned and totally efficient. Maintenance

sometimes could be critical aspect in an organization it could turn unnecessary cost

into profits. In united state over than $600 billion has been spent on critical plant

systems although it has been increased to $800 billion by 10 years (Mobley, 2004).

3.2 Corrective Maintenance

Corrective maintenance or breakdown maintenance, which attempt to minimize the

severity of equipment failures once they occur, and this tactic focuses on maintenance

procedures that bring equipment back to production in the shortest time. Such

alternatives include standby machines, spare parts inventories, and worker

reassignments. Furthermore, corrective maintenance plays a vital role in maintenance

management whilst the failures occurrences could not be allocated and prevented.

Hence, there are many corrective maintenance techniques to eliminate the severity of

machine malfunction; those techniques include increases service crews, inventory

buffers, and machine redundancy (Sheu and Krajewski, 1994). The evaluation of

corrective maintenance requirements based on tangible data developed from previous

system faults and repair experience with an item, controlling the current corrective

maintenance activity, and prediction of future corrective maintenance requirements

through statistical analysis of repair history that categorized by quantitative

methodologies. The classic corrective maintenance cycle runs from the point of failure

detection through verification of restoration, as shown in Figure 2 (Langford, 2007).



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Figure 2. Corrective maintenance cycle

Source: Langford, 2007, pp.60

3.3 Preventive Maintenance

Preventive maintenance is a very wide concept there is no specific accurate definition,

but it can be generalized as all actions that should be taken on the machine in order to

minimize the occurrence of unexpected downtime (Duffuaa et al., 1998).

Mean time to failure (MTTF) or the bathtub curve shows that there is a high probability

of occurrence of failure in the first phase which is the installation phase. After a period

of time the machine goes into the Normal phase where it supposes to work as it

designed. Then the cost of maintain the machine goes higher and higher with time

because of wear out. In preventive maintenance machine repaired according to

schedules based on MTTF statistically (Mobley, 2004).

Implementing the preventive maintenance could be varies, since it is a wide subject

which has more than one edge. Some of the preventive maintenance practices do not

exceed what the manual of the machine says. On the other hand it could be a



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comprehensive preventive maintenance starting with replacing a component and

ending with minor adjustment of a minor component. Depending on the type of the

machine and the type of the component, the production system, and many other

factors play a role in implementing preventive maintenance (Mobley, 2004).

3.4 Block policy

Maintenance policies are a set of protocols that followed in order to reduce the

number of unexpected stoppages. Performing PM actions at certain point of time

regardless of component’s condition defined as a Block policy. Block policy aims to

maintain the component so that the failure could be avoided as much as possible that

may lead to a catastrophic failure (Thomas.H.Savit, 1993).

A fixed time intervals is identified for PM actions to take a place, these actions are

scheduled and is being implemented periodically. This policy wins normally when the

cost of preventive maintenance is lower comparing with other PM cost polices.

Moving towered from fixed intervals that are scheduled to a dynamic scheduling for

those intervals based on operating hours, defined as age policy (Sherwin, 2010).

3.5 Age policy

This policy is defined as perform a preventive maintenance at tp (time interval between

PM actions) hours of continuous operating. tp could be finite or infinite, in case of

infinite tp no preventive maintenance scheduled. On the other hand, when failure

occurs before tp PM take a place and rescheduling for the next PM actions must be

done.

Figure 3. Example of age policy Source: Duffuaa el at., 1998, pp.60



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Figure above shows two operating cycle for a component, first cycle component has

been operating till tp and scheduled PM took a place. Next cycle component has been

fail prior tp, that case PM actions has been rescheduled for the next cycle. The

objective of this model is that tp is being optimum and PM actions (replacement, break

down maintenance) are performed with minimum cost per unit time (Duffuaa et al.,

1998).

The cost of PM actions and break down maintenance are associated with the Total

expected cost per cycle which is:

Where R(tp) is the probability that the component will survives till tp (Duffuaa el at.,

1998).

3.6 Weibull distribution

In probability and statistics Weibull distribution is the most commonly used model in

modern reliability engineering. Weibull used in statistical analysis due its flexibility and

ability to deal with small sample size in order to evaluate lifetime of a system,

component. It was named after Waloddi Weibull. Weibull and lognormal are called the

lifetime distribution because they tends better in representing the measurement of

product life. Weibull distribution is mostly applicable in manufacturing industries and

can be applied in a variety of forms of parameters (Murthy et al., 2004).

Exponential function is a special case from Weibull distribution. It is widely used to

represent the lifetime for a set of data and also a modelling trend with decreasing or

increasing failure rate the probability density function f(t) for Weibull distribution is

give as:

f(t) = β/ηβ(t-ɣ)

β-1exp[-(t-ɣ/η)

β]

And

R(t) = exp[-(t-ɣ/η)β]

Where: γ = Location parameter

β = Shape parameter

η = Scale parameter



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The Weibull distribution model gives an insight of how the distribution will look like. By using the three parameters mentioned above as an input. Obtaining a graph from those inputs could be possible which will show the probability that a certain component will fail at a certain point in time. The two parameters are obtained by setting γ=0 which give:

f(t) = β/ηβ(t)

β-1exp-(t/η)

β

Weibull distribution one-parameter occurs when the value of shape parameter β is being determined or assumed. The one-parameter Weibull p.d.f is obtained by setting γ = 0 and assumed β = k = constant.

f(t) = k/ηβ(t)

k – 1exp-(t/η)

k

The first parameter that is used is called the Location parameter denoted by γ (Gamma). This determines where the graph will start and in most cases it always assumed to be zero showing that it is the minimum time to failure. When gamma parameter is set to be zero, this is called the two-parameter Weibull distribution.

The shape parameter is the second parameter usually denoted by β. This parameter determines the shape of the graph and known as the Weibull slope. The β parameter is the function of the hazard rates (Murthy et al., 2004).

β=1, constant hazard rate and Fit to exponential function.

β<1, Decreasing hazard rate. β>1, Increasing hazard rate. β=3.5, fit to normal distribution.

With some values of (β), the equation will reduce to other distribution model. For example if β=1, the p.d.f of the three-parameter, Weibull will reduce to the two-parameter exponential distribution with the probability density function f(t) given as:

The different slope will approach the value of η at different F(t) depending on time. The last parameter in Weibull distribution is called the scale parameter denoted by η. The scale parameter is the point at which 63.2% of the products have failed. The higher the number of η value, the more the graph is stretched over period of time (Murthy et al., 2004).



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Parameters estimation methods

According to Dodson (1994), there are four most commonly used methods to estimate

Weibull parameters:

- Maximum Likelihood estimation

MLE refers to Maximum Likelihood Estimation, one of the most widely statistics

method to estimate Weibulls’ parameters. Based on maximize the value that maximize

the probability of a data. Let X1,X2,…..Xn be independent random variables which are

the representations for the probability density function f(x,Ɵ).

The Likelihood function is being maximized by a natural logarithm in order to simplify

the calculations.

- Moment estimation

This method is used in estimation parameters by matching the moment of the sample

to the moment defined by distribution. In case of Weibull two parameters, first and

second moment for a sample data would be variance and mean which equal to:

And

- Probability and Hazard plotting

Both of them are a graphical method used in order to estimate the Weibull

parameters. The cumulative distributions are being linearized by a logarithmic

transformation. Median rank is being used in probability approach. Furthermore if it

would be a manual approach it would require special papers. But due to high

technique in computers, linearization can easily be done.



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3.7 Maintenance optimization

Figure 4. Curve shows the total cost with increasing PM actions to an optimal time Source: Levitt , 2003, pp.12

Figure above shows the minimum overall cost with increasing PM costs to an optimum

time. Notice that cost becomes stabilized with time since PM actions going no more

effective.

L is the time interval which the total cost is the minimum.

Implementing a maintenance policy does not mean avoiding extra cost all the time.

Defining the right time interval in order to PM actions take a place is exactly what all

organizations looking for. With time PM costs increased and become ineffective then,

it would preferable to have breakdown instead of running ineffective PM actions. This

caused by age of the system wearing out (Levitt, 2003).

The area denoted by X is all organizations interest in which the total cost during this

time interval would be the minimum. As mentioned before, determining this time

interval is the biggest challenge. Dodson (1994) asserts that minimizing the total cost

per unit time in order to find the optimum time according to the following equation:

Where: Cp is the cost of preventive maintenance.

Cr is the cost of failure.

T is the time between preventive maintenance actions.



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Instead of minimizing the previous equation every time by usual numerical routine,

Dodson (1994) has developed a table that can easily used and applicable by following

assumptions:

- Time to failure follows Weibull distribution.

- Preventive maintenance is performed at time = T with cost equal to Cp.

- If a failure occur before time = T cost of failure is incurred.

- The last and the most important condition is when the component is being

maintained it is return into its’ initial state “As good as new”.

The optimum time between preventive maintenance actions can be easily calculated

by the following formula:

Where: m is the cost ration Cf/Cp.

is the shape parameter.

is the location parameter.

3.8 Schedule maintenance

When preventive maintenance is being mentioned, a number of fixed PM actions done every month, quarter or season are coming to our minds. Actually PM actions are based on two main aspects procedure and discipline.

Procedure is that the right actions are being carefully taken at the right time. Discipline is that all actions are planned and under control. Discipline is the check aspect for PM actions; hence it could not be overlooked. Failing of implementing a scheduled maintenance for some organization mainly comes from discipline aspect, which is being ignored. Scheduled maintenance is one step forward of improving PM actions to be in accurate need of it (Mobley, 2004).

According to Mobley (2004), there are six main elements for accurate procedure:

Listing of components plus the intervals that they should received a preventive maintenance.

A schedule for a year that breaks down by month.

Person responsibility to do the work.

Updating the records for the actions that had done, and when next action due to.

Do any corrective action when it is needed.



24

Some PM actions could take a place every interval weather it is necessary or not,

hence, unnecessary stoppage may occurs. Since scheduled maintenance aim to reduce

unplanned stoppages, scheduled maintenance should be based on real actual need of

PM actions.

3.9 Life Cycle Cost (LCC)

Life Cycle Cost is a method to calculate the total cost of a structure during its lifetime.

A system will not be considered as an economical when the maintenance costs are

high. From an economic perspective, the purpose of cost optimization is decreasing

the total life cycle cost (Sarma and Adeli, 2002). LCC analysis is applied with the aim of

selecting the most cost effective approach from different alternatives in order to reach

the lowest long-term cost (Negrea et al., 2007).

According to Negrea et al. (2007, p.217), the LCC includes the following steps:

1. Define the problem which requires LC

2. Alternatives and acquisition/sustaining costs

3. Prepare cost breakdown structure

4. Select analytical cost model

5. Collect cost estimates as well as cost models

6. Make cost profiles for each year of study

7. Make break, even charts for alternatives

8. Pareto charts of vital few cost contributors

9. Analysis of high costs

10. Study risks of high cost items

11. Select preferred course of action using LCC

Furthermore, Liu et al. (2010) state that the value of LCC can be obtained by

calculating the equation below.

CLCC = CI + CO + CM + CF + CD

Where CI is the investment costs, CO is the operation costs, CM is the maintenance

costs, CF is the failure costs and CD is the disposal costs. But only analyzing the LCC one

by one is not enough since the impact of the system will be ignored. It is necessary to

include the cost of externalities (Cexter), which results in the following equation.

CLCC = CI + CO + CM + CF + CD + Cexter



25

LCC can be discounted using the present value method at a certain interest rate (i)

after n years, in the present time. The following equation shows the present value of

LCC:

PC LCC = F C LCC / (1 + i)n

Where F C LCC is the future value of LCC and is equal to CLCC calculated above, and PC LCC is

the present value of LCC discounted.



26

4. EMPIRICAL DATA

In this chapter, a description of case company, the production process is presented. Moreover,

data gathered from the interviews and observations are included through this part.

4.1 General description

Dynamate Intralog AB is a Swedish company established in 2000, the company is

located in Oskarshamn city and it includes 60 employees in total that distributed into

managers, technicians and workshop workers. The company main roles are

categorized into three functions: providing warehousing, transportation and

production support services.

Dynamate Intralog AB considered Daughter Company of heavy industrial firm known

as Scania that placed in Södertalje; Scania objectives are to deliver optimised heavy

trucks, buses, and engines. Thus, obtaining logistical services from Dynamate Intralog

AB are critical issues among Scania’s production system because of intensive workload

within manufacturing and assembling lines.

4.2 The logistics outsourcing

Dynamate Intralog AB is a third-party logistics (TPL) provider that transports on-

demand the containers that required in Scania’s production line, and those containers

contain boxes filled up with truck elements such as electronic items, steering wheels,

doors, and so on.

After supplier delivered containers to Dynamate Intralog AB, the unloaded process

start taken place by workers in which they sort the boxes according to their marked

labels and then shifted to warehouse area by forklifts for later supply. On other hand,

Scania send their empty boxes by trucks to Dynamate in order to store them after

robots processing them, and these procedures related to limited and overloaded

materials in Scania’s facility. The figure below shows TPL circulation between supplier,

Scania and Dynamate.



27

Figure 5. TPL circulation

Proceeding from the figure, Dynamate highlighted a core value through TPL circulation,

for that reason Dynamate was our interest of study and we are going to present the

empty boxes process in details after it arrives to company and then to robots.

4.3 The empty boxes process

The container arrived to Dynamate Intralog AB from Scania filled by empty boxes (30),

the workers unloading following container and transported through conveyor belt

towards the workstation whilst fork-lifts waiting to carry those empty boxes to

palletizing robot. Then the wooden boxes have been checked by taken lids away to be

ensured that boxes don’t contain any forgotten items by Scania inspectors. The next

step is to organize all boxes upon the production line and let the chain driver take

them into the main robot function which is splitting the box elements into pallet and

collar. This action done by robot arm (Kragplockaren) by folding the collar and place it

in collars area for packaging and transportation purposes, then pallet moved to pallets

region for same goal. This picture shows how the wooden box looks like:

Collar

Pallet

Image 1. The wooden box

Dynamate

Intralog

AB

Scania

Supplier



28

According to Mrs. Norberg (Maintenance Technician of Dynamate Intralog AB), she

defined empty boxes process as simple and complicated system; its simple while all

steps are clear and there is no delay between different operations, and its very

complicated in case of components failure occurred to palletizing robot that stop the

whole production line. The company refers their time and money loses to machine

wear-out, therefore they are depending quite much in maintenance strategies, and in

such a case the corrective and preventive policy have been applied. The problem still in

high rate and need more integrated and flexible maintenance approach in order to

minimize time and money loses.

4.4 Robot performance and critical components

During the interview with Mr. Weli Zubair (Production and Logistic Manager of

Dynamate Intralog AB), he states various kind of failures types encountered the

machine components and he mentioned frequent stoppages because of these

breakdowns. Furthermore, the observations show many disturbances blocking the

robot efficiency in terms of time (availability), consequently the overall equipment

effectiveness declined by limiting the operational time. Hence studying robot critical

components are important to optimize system reliability and conducting best

maintenance practices. According to Mr. Weli Zubair, components can be ranked and

listed as following:

Photocell, gearbox, brake motor, guide rails, chain, turntable, and robot arm; the

system performance proportionally affected by these components availability. Those

elements are going to be clarified in details in later parts.

4.5 Maintenance strategies within Dynamate Intralog AB

Proceeding from Mrs. Norberg statement about maintenance importance in their daily

work and how may reduce the declined production, they been conducted a preventive

maintenance schedule beside a corrective actions policy while failure suddenly occurs

and need to be replaced or fixed instantly. For that reason, weekly and monthly

preventive maintenance procedures have been accomplished through various ways of

problem solving by maintenance technicians and the instruction list have to be

followed by all robot workers even though they are not maintenance engineers. In

addition to all these preventive and corrective actions, the time and money loses still

gradually arising and affects production capacity negatively wherein the accuracy in

scheduling maintenance may enhance those factors positively.



29

4.6 Corrective maintenance for essential components

During our visit to the company, we have tried to collect data as much as it’s possible

about robot critical components and its stoppage time for approximately two year

interval. As we mentioned above, the critical components selection based on interview

with production manager that listed by him, consistency with his daily experience. First

component was the photocell and its reflexes, this item exposed to internal and

external errors done by human through accidental crash, or by environmental issues

and not dismissed the electrical contact, in which all situations led to non processing

system and breakdowns to other mechanical parts. Thus, photocell needs a certain

type of corrective maintenance known as replacement by new, and this route

considering money and time consumption, for instance every hour spent in corrective

maintenance its costs 450 SEK and new photocell costs 1500 SEK.

Sequentially, detecting the photocell been broken or non-functioning takes around 30

minutes and 1 hour to be fixed or replaced although the spare parts reserved in

storage and buffer areas, but the consequences from broken photocell involve other

hindrance operations and components to be responding. For example, whilst photocell

not running perfectly the whole process flows through production line deactivated and

passed wooden box may damaged because of mistiming robotic movement, and in

such a case if this wooden box damage and stuck in the robot arm need around 1 hour

to remove it. The dataset about photocell divided into number of failures and their

times to failure been collected through interview and it will be presented in appendix

(3).

Second component is brake motor incurred mechanical failure such friction between

brake cylinder and vanes caused by unstable screws that being running for long term,

plus the erosion appeared on the surface of brake metal. Accordingly, this kind of

failure evaluated as real problem because of time needed to repair the fault and in

case of replacement by new one. In both cases it goes along 3 days to reactivate the

production engine back because of outsourcing demand for brake motor elements as

well as importing maintenance engineers who has capabilities dealing with complex

repair. Nevertheless, detecting the failure takes around 1 hour to be located. Dataset

been gathered and generated based on times to failure and number of failures. See

appendix (4).

Third component is gearbox, its very fundamental components and hard to allocate

the failure immediately might took 2 hours to detect, and in some cases the oil leakage

from the gearbox gives a deterministic sign to stop the robot and recurred the minor

failure before entering the major stoppage that long 2-4 days until the robot reactivate

again. This long period due to gearbox parts outsourcing or buying a new one, that



30

type of failure affect other components indeed. Dataset about this component can be

found in appendix (5).

Fourth component known as air bellows, the failure here surrounded by rusty

conditions because of corrosion basis, and that can be known through air leakages.

This is the hardest failure to detect because the system still processing and long farther

in same state down to suddenly breakdown. That’s taking almost 5 hours to detect the

failure and need 4-6 hours to restore the functional circumstances. Data set about this

component shown in appendix (6).

Finally, control list component has over-flooded fat problem suit a sliding collars and

that’s actually a serious problem been observed tangibly through our visit, also the

wear-out and corrosion appeared clearly. When this problem occurred the robot arm

stop working however attempted to reinstall again, and required the worker to stop

machine then try to remove the collar manually and put it in collar area then restart

the machine. This mission takes 5-10 minute to reuse the robot arm, but main problem

was control list and here the maintenance technician has to come and repair or

replace the control list. The time needed split into two branches either item is

available in storages and this operation to repair required 2-3 hours or they have to

wait at least 2 days to receive such a component. Data set of this component shown in

appendix (7).

4.7 Preventive maintenance for essential components

Mrs. Norberg focused on preventive maintenance practices within Dynamate Intralog

AB; she splits the preventive maintenance schedule into two periods, weekly and

monthly. She has talked about other component entailed by this scheduled

maintenance but she gave us information about the critical component that been

ranked by Mr. Weli Zubair.

4.7.1 Weekly preventive maintenance

Photocells and reflexes have to be cleaned every Thursday by a cloth for safety reason;

otherwise any smash may prohibit signalling waves from access reflexes. The worker

has to follow the cleaning instruction step by step and not endanger photocell

positioning mode. This operation doesn’t require long time and high effort, perhaps

takes 20 minutes approximately and the machine does not need to stop. Moreover,

the worker has to replace the photocell almost every two and a half weeks, which may

take up to 1 hour of inactivated robot through replacement operation.



31

Image 2. The photocell in palletizing robot

Brake motor has to check every Thursday by measuring the distance between the vane

and brake cylinder, the measurement has to shown 0, 2 mm through using feeler

gauge otherwise the screws around the vane must adjust the difference between

them. This operation longs from 15 minutes – 1 hour but the whole machine being

stopped. The replacement screws take place every 2 weeks and the whole robot being

stopped for almost 1 hour, and the screws cost 100 SEK.

Image 3. The brake motor

Photocell

Vane



32

4.7.2 Monthly preventive maintenance

Gearbox undergoes among monthly check to notice the oil leakage and to check if

there is chaotic sound release from it, in such a case the mechanical technicians has to

monitor such a situation. The robot still working during this kind of observations and

inspections, but in extreme cases the machine has to stopped, for example the sound

test showed unusual resonance waves. The inspection takes 30 minutes, besides the

oiling for 20 minutes.

Image 4. The gearbox

Air bellows checked monthly by monitoring the air outlet paths if there is no air

leakage through those channels besides checking the cracks that would happen

throughout chemical reactions, for instance corrosion and erosion. The inspection

longs 30-50 minutes by stopping the machine.

Image 5. The air bellows

Control list criticality considered because of its role importance, the control list has to

be checked from surface cracked or lubricant troubles, for that reason the machine has

to be stopped form 30 minutes- 1 hour and dried from over-flood fat, then pour new

viscosity oil.

Outlet path



33

Image 6. The control list

4.8 Corrective and preventive maintenance related cost

The data have been obtained about corrective maintenance cost covered the following

categories; labour and new item cost. (The stoppage time cost will be discussed in

analysis part).

According to appendix (3) the photocell shows 43 number of failures through 5190

hours, the labour cost as mentioned before was 450 SEK and replacement cost is 1500

SEK.

Then, Brake motor appendix (4) shows 3 number of failures during 5109 hours, the

labour cost approximately 500 SEK and parts cost about 2000-6000 SEK for instance

vane or cylinder damage, but in case of replace it with new item cost 8000 SEK. After

that, the gearbox repair may cost approximately 6000 SEK and can be less when its

minor fix such as small parts within the gearbox, labour cost at least 500 SEK, the

number of failures doesn’t occurs so often which is only 2 times see appendix (5). On

other hand, the air bellows take place quite much in failure number it reach 6 times,

and the labour cost 500 SEK beside the repair and replacement costs that ranging from

1000 SEK- 5000 SEK. At last, control list required more attention because of its

importance related to robot arm, the labour cost is 450 SEK and the replacement or

repair cost ranging from 1000 SEK- 4000 SEK.

The preventive cost classified into time spent in preventive maintenance in terms of

money and the stoppage time cost that are going to be considered in analysis part as

well.

Preventive maintenance cost for photocell within 1 week is 75 SEK and no need for

machine stoppage by cleaning the dirt upon photocell. In paradox with brake motor

Control list



34

that need to stop the whole robot to make preventive maintenance and it costs up to

500 SEK. The gearbox required only vision inspection to be surely about functioning

conditions, and does not required any spending cost in this activity, because it might

be included through daily work instructions. The air bellows require 225 SEK even as

considered monthly and it’s very sensitive to be checked correctly. Finally the

preventive maintenance cost for control list component may range around 500 SEK

divided into labour and lubricant cost.

4.9 Production list for palletizing robot

Mr. Weli Zubair provided us by data about production list during week 6, this

information contains total number of the boxes that been produced among this week,

the stoppage time and operational time been given. He informed us about company

maximum production value and it was 89 boxes during 1 hour and the current

situation show opposite or bad production rate because of external disturbances and

internal failures. Appendix (2) represent 1067 boxes been produced in one shift during

(week 6) which is reflect negatively to company ultimate goal.



35

5. ANALYSIS

This chapter comprising the data that have been collected about maintenance practices and

their correlations to costs, the assumptions been conducted in this part to obtain systematic

calculations.

5.1 Maintenance cost calculations

As we mentioned before the data been gathered within 5190 hours interval of time,

the assumption here related to production unit whereas each box equal to 1 SEK, and

the dataset record 43, 3, 2, 6 and 7 failures number of components respectively.

The total maintenance cost contains of two main factors which are corrective and

preventive maintenance cost, so the calculations will take each component one by

one, starting with photocell, the formulas consists of the following combinations:

(1) Photocell

Corrective cost: Labour cost /h + Stoppage time cost + Replacement item cost

Labour cost /h = 450 SEK

Stoppage time/ one failure number = 2.5 hours

New photocell cost 1500 SEK

Labour cost during 5190 hours = 450×2.5×43 = 48,375 SEK

New photocells cost through 5190 hours = 1500×43 = 64,500 SEK

Stoppage time = 2.5×43 = 107, 5 hours and in terms of money, as the assumption

induce the time variable by each box cost 1 SEK, then Stoppage time cost = 89×1×107,5

= 9,567.5 SEK

Therefore, Corrective cost = 48,375+64,500+9,567.5 = 122,442.5 SEK

Preventive cost: Labour cost + Stoppage time cost+ Replacement item cost

Labour cost during 5190 hours = 150×5190\60 = 12,975 SEK

Replacement item cost = 1500×35= 52,500 SEK

Stoppage time = 34.6 hours, which mean = 89×1×34.6= 3,079.4 SEK

Therefore, preventive cost = 12,975+ 52,500+3,079.4= 68,554.4 SEK



36

(2) Brake motor



Stoppage time/ one failure number = 30 hours

New parts cost 6000 SEK

Labour cost during 5190 hours = 450×30×3 = 40,500 SEK

New parts cost through 5190 hours= 6000×3 = 18,000 SEK

Stoppage time = 30×3= 90 hours, then Stoppage time cost = 89×1×90= 8,010 SEK

Therefore, Corrective cost = 40,500+18,000+8,010 = 66,510 SEK


Labour cost during 5190 hours = 450×5190\60 = 38,925 SEK

Replacement item cost = 100×5190\120= 4,325 SEK

Stoppage time = 173 hours, which mean = 89×1×173= 15,397 SEK

Therefore, preventive cost =38,925 +4,325 +15,397 = 58,647 SEK

(3) Gearbox








Therefore, Corrective cost =27,000 +12,000 +4,800 = 43,800 SEK



37


Labour cost during 5190 hours = 56.25×5190\60 = 4,865.625 SEK

Replacement item cost = 0 SEK

Stoppage time = 28.6 hours, then Stoppage time cost = 89×1×28.6= 2,551.3 SEK

Therefore, preventive cost = 4,865.625 + 2,551.3 = 7416.9 SEK

(4) Air bellows










Labour cost during 5190 hours = 56.25×5190\60 = 4,865.625 SEK

Replacement item cost = 0 SEK

Stoppage time = 72 hours, then Stoppage time cost = 89×1×72= 6,408 SEK

Therefore, preventive cost = 4,865.625 + 6,408= 11,273.625 SEK

(5) Control list






38







Labour cost during 5190 hours = 112.5×86.5=9,731.25 SEK

Lubricant cost = 500 SEK

Stoppage time = 21.625 hours, then Stoppage time cost = 89×1×21.625= 1,924.6 SEK

Therefore, preventive cost = 9,731.25 +500+1,924.6 = 10,233.1746 SEK

5.2 Distribution for the failure data

Figure 6. No. of failures for each critical component during 5190 hours

A graph above gives a holistic view about the failures that occurred during 5190

operating hours. While X axis represent the components and Y axis represents the

numbers of failure. From the graph it is so obvious that photo cell has the most

frequent failure comparing with the rest of the components.



39

Figure 7. The time at which the components have failed

A graph above shows failure time for critical components. X axis represents the

number of failures while Y axis represents the time at which the component has been

failed. Failures have been registered over a 5190 operating hours. It is obviously shown

that Guide ways for example has registered three failures during these operating

hours. Those failures registered in different hours.

Due to large Number of failures for the ‘photo cell’ component it has been taken out of

the graph in order to clarify the other components.

5.3 Optimum time to PM actions

In order to find the optimum time for each components, we need to use the following

equation 3.7. Under the following assumptions:

- The component as good as new after performing the maintenance actions.

- Cf is incurred if the component fail before time=T.

- Preventive maintenance is performed with Cp on a component at time =T.

- Time to fail follows a Weibull distribution.

T= (m.η) + γ

Gamma is zero here for all components, thus value of m can be easily found from the

table appendix (8).



40

Table 2. The value of m Source: Dodson, 1994

Finding the value of m, substitute it with equation 1 we have the optimum time to

replace, maintain the component. Table 4 bellow shows the optimum time for each

component. For the value of B see appendixes (9, 10, 11, and 12).

Cc/Cp

Ration cost

β

η

m γ Opti T

= (m.η) +

γ

Photocells and

reflexes

1.786063

9.3 121.8 2.229 0 97.8054

brake Motor 1.134073

1.36

4178 2.229

0 9312.762

Gear Box 5.905432

1.26 4667 0.574

0 2678.858

Air Bellows 4.486046

1.48 4048 0.746

0 3019.808

Control list 4.30062

2.75 4570 0.521 0 2380.97

Table 3. The optimum time for each component to perform PM



41

5.4 Maintenance schedule based on optimum time

Maintenance scheduling could be done based on the calculating the optimum time. Graph

bellow shows if we could run PM actions for more than one component at the same time in

order to minimize the total PM costs. Notice Photo cell has been taken out with respect to

scale.

Figure 8. Current PM Time and Optimum time

It is obvious that there are some unnecessary PM actions which mean extra

unnecessary cost. PM could be rescheduled and implemented in groups for multiple

components.

Table 4. The optimum time to perform PM

Components Time to perform PM

Photocells and reflexes 97.8054

Break Motor 9312.762

Gear Box 2678.858

Air Bellows 3019.808

Control List 2380.97



42

6. RESULTS

In this chapter the final result of the thesis analysis presented. With respect to the data

collected from the company.

As results, critical components have been determined based on an interview with the

production manager. Those components are photocells and reflexes, Break motor,

Gear box, Air bellows, and Control list. Failure data for these components have been

followed a Weibull distribution. In addition estimating the value of beta and eata for

each component are essential to calculate the optimum time.

The optimum time for the critical components have been determined to let PM actions

take a place. Optimum hours are 98, 9313, 2679, 3020 and 2381 hours for photocells

and reflexes, Break motor, Gear box, Air bellows, and Control list respectively.

Based on the calculation, schedule for those critical components has been made,

aiming to reduce the total number of PM actions. A group of actions has been

scheduled together as table 4.

The number of PM actions could be reduced by knowing the exact time, therefore

unnecessary cost could be avoided. In the previous table, a PM could be performed

after 2200 operating hours for Control list and Gear Box. Instead of apply PM every

900 hours. It is obvious that two round of PM unnecessary. There for those costs could

be avoided, the total cost for PM actions for the whole components would be

Cost of PM for Component x1, 2,…n * Number of PM

Cost of PM After scheduling 87570.7 sek which is definitely less than the current one since the total no. of planned stoppages has been reduced.



43

7. CONCLUSION

In this chapter the conclusion of our thesis which answer the problem formulation, criticism to

our thesis and suggestions

Company experience is one method to identify the critical components. Using FMECA

for example could make the analysis more accurate. Recording the failures of the

machine is one step forward to enhance the availability of it. Analyse a historical data

is the second step to improve the maintenance policy.

In order to avoid extra unnecessary cost Optimum time has been scheduled; PM

actions should be implemented at the right time that could effective. By determining

the optimum time a group of PM actions could be implemented at once.

The main aim for scheduling the PM actions is to identify the right time interval that

should the PM actions performed. Based on analysis and knowing the behaviour of the

system or component. Readability and availability of the data play big role in the result

part and sometimes could affect a critical decision that the organization should make.

Subsequently, the reasons behind the failure types are the core of analyzing the data

by Weibull, and the way that trends through dealt with certain reasons of faults and

not the all causes. Thus, FMEA is an integrated reliability analysis tool in order to cover

all the critical failures and their consequences in the system. For instance the external

factors may enhance the failure occurrence and the environment indeed, therefore, to

manage better solutions these factors have to be considered.

Recommendations

The company needs to enhance their workers to have enough knowledge about those

components and have best maintenance practices manual to monitor all the machine

elements in case of stoppage and breakdowns.

Furthermore, the inspection is very fundamental for avoiding system idle and

malfunctions components later on, hence may condition based maintenance be

suitable to be investigate in future.



44

References

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46

Appendix 1

QUESTIONNAIRE

1- What is the logistic connection between Dynamate and Scania along the supply

chain?

2- Is there any lead-time or barriers through production process flow?

3- Is the problem classified into following categorizations:

a- Logistic b- Machinery and Maintenance c- Human resources

4- What is the production process according to robot main functions?

5- Is the robot stoppage time related to:

a- Failure components b- company policy such as just in time c- other

reasons

6- Is the declined production whilst the robot deactivates involved critical

components Breakdowns and what are these components?

7- What are the maintenance strategies and policies towards these components,

and if there any analysis tools dealing with?

8- Is there any human factors and untrained worker may affect negatively the

palletizing robotic system?

9- How much money and time were spending in corrective maintenance respect

to failure components?

10- How much money and time were spending in preventive maintenance and if it

been scheduled?



47

Appendix 2

This table present the boxes number that been produced in week 6

Number of boxes that been produced

Disturbance time or stoppages/minutes

First day of work is 22 from 26 boxes

70 minutes

Second day of work is 26 from 35 boxes

120 minutes

Third day of work is 26 from 39 boxes

60 minutes

Fourth day of work is 23 from 34 boxes

40 minutes



48

Appendix 3

Component No. of failures during 5190 hours

Photo cell 43

Failure No. at T, hour

1 119

2 224

3 355

4 455

5 590

6 719

7 835

8 964

9 1085

10 1218

11 1332

12 1459

13 1581

14 1689

15 1818

16 1914

17 2031

18 2156

19 2291

20 2381

21 2521

22 2612

23 2701

24 2820

25 2917

26 3049

27 3161

28 3285

29 3418

30 3546

31 3654



49

32 3745

33 3885

34 3990

35 4085

36 4196

37 4303

38 4420

39 4519

40 4640

41 4734

42 4847

43 4976



50

Appendix 4


Brake Motor 3

Failure No. at T

1 2407

2 3641

3 4753

Table of failures for Brake motor during 5190



51

Appendix 5


Gear Box 2

Failure No. at T

1 3588

2 4799

Table shows the failure time for Gear box



52

Appendix 6


Gear Box 2

Failure No. at T

1 3588

2 4799

Table shows the failure time for Gear box



53

Appendix 7


Control List 7

Failure No. at T

1 2700

2 2923

3 3444

4

4133

5 4456

6 4878

7 5045



54

Appendix 8



55

Appendix 9

Break Motor



56

Appendix 10

Gear Box



57

Appendix 11

Air bellows



58

Appendix 12

Control List

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