Chapter 2 Literature Review - Faculdade de Engenharia da...
Transcript of Chapter 2 Literature Review - Faculdade de Engenharia da...
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Chapter 2 Literature Review
In this chapter we take a look at what the concept of lean it’s all about. We start by
describing the origins of the lean thinking, a summary of where and how it was created. Then
we take a look at the main principles and concepts of lean manufacturing for a clear
understanding of the project as a whole. Finally, we enlighten the reader through the main
lean tools, procedures and techniques, such as Visual Management, Value Stream Mapping or
Cellular Manufacturing, required for a clear interpretation of the achieved results during the
course of this project.
2.1 - History of Lean Production
The lean production system was born in the automobile industry or, as Peter Drucker
labeled it, “the industry of industries”. The term Lean was introduced for the first time by
James Womack, Daniel Jones and Daniel Roos in their book “The Machine that Changed the
World” based on a five year study observing the differences between mass production, craft
production and lean production in this gigantic industry.
Table 2.1 – Comparisons of Lean Manufacturing with other Production Systems [2, p. 2]
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According to them [3], after World War I, Henry Ford and Alfred Sloan (General Motors)
established the age of mass production as contrast to the centuries of craft production led by
European firms. As a result, the United States dominated the global economy. But, after
World War II, Eiji Toyoda and Taiichi Ohno at the Toyota Motor Company pioneered the real
concept of lean production, making Japan the leading economy country, as other Japanese
companies and industries copied this system.
It all started with a collapse in sales at the Toyota Motor Company that forced them to
dismiss a large part of their work force in 1949. “In thirteen years of effort, the Toyota
Motor Company had, by 1950, produced 2,685 automobiles, compared with the 7,000 the
Rougue was pouring out in a single day”. [3, p. 48] In the effort of turning this around, Eiji
Toyoda, in the spring of 1950, set out on a three-month tour to Ford’s Rouge plant in Detroit,
studying every inch of this factory. Throughout this journey, Eiji noticed that the American
automobile manufacturers used a remarkable system, however this mass system could not be
implemented in Toyota, as their budget was only able to have a few press lines and,
furthermore, the market required a wide variety of vehicles types. As he returned home, he
started to create, along with his production genius, Taiichi Ohno, a similar, but much
improved system, based on a simple die change technique where they discovered that
producing small sets of vehicles was cheaper than producing huge batches, because of the
reduced carrying costs of inventory and making the mistakes much more clear, since they
were not buried by this massive inventory.
Toyota came to call this system the Toyota Production System (TPS), and, ultimately,
Lean Production (term made popular by the two best sellers “The Machine That Changed the
World” and “Lean Thinking” by Womack, Jones and Roos).
2.2 - Toyota Production System
Taiichi Ohno accepted the apparently unmanageable challenge of matching Ford’s
productivity and, along with his team, worked at the shop floor through years of trial and
errors, solving problem after problem, trying to find the antidote to muda and developing a
new production system, the Toyota Production System.
Muda it’s a Japanese word that means ‘waste’. Precisely, it’s any human activity that
absorbs resources and doesn’t create value to the product or service. Both waste and value
will be explained further more in chapter 2.5 - .
For decades Toyota implemented and improved TPS on the shop floor without
documenting the TPS theory. As it matured, it became clear the difficulty of teaching this
theory across other Toyota plants and ultimately suppliers. As a result, Fujio Cho developed
one of the most recognizable symbols in modern manufacturing – The TPS House (Figure 2.1)
[4]
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Figure 2.1 - The TPS House [4]
As in any house, it will only be strong if the roof, the pillars and the foundations are
strong. Therefore, emphasizing the importance of best quality, lowest cost and shortest lead
time (the roof); just-in-time (JIT), produce only what’s needed, that is to produce the right
part, at the right time, at the right amount (left pillar); And jikoda, that means never let a
defect pass into the next station and freeing people from machines [4] (right pillar).
2.3 - Lean Principles
Womack and Jones [5] describe the TPS philosophy as a concept to create value and
eliminate waste. Therefore, five main Lean principles were associated with it, briefly
described below, and those are: Value, Value Stream, Flow, Pull and Perfection.
Value
Express the capacity of accurately specify value from the costumer
perspective, or what he’s willing to pay, for both products and services.
Value Stream
Identify the value stream of specific activities, from raw material to final
goods, required for the development of a product or service, removing non-value-
adding waste along that path.
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Flow
Make the product or service flow without interruptions across the entire
value stream.
Pull System
The production is authorized (pulled) by the costumer, as opposite to a push
system where the finished goods are pushed to the costumer.
Perfection
Constantly identify and remove any kind of waste along the value stream to
achieve perfection.
2.4 - Lean Benefits
What can an organization expect as bottom-line results of applying lean thinking to
eliminate waste? Documented results across various industries indicate the results in Table 2.2
can be achieved. [6]
Table 2.2 - Lean Benefits [6, p. 104]
2.5 - 7+2 Non-Value-Added Waste
According to [5], Value can only be defined by the ultimate costumer and it’s created by
the producer, being very hard to accurately define from the producer standpoint. Yet, the
concept of value, which is related to efficiency (doing something at the lowest possible price)
and effectiveness (doing the right things to create the most value for the company), can be
metaphorically defined as quality divided by price. “If you can provide the customer with a
better car without changing price, value has gone up. If you can give the customer a better
car at a lower price, value goes way up.” [7]
All of the activities on an organization can be distributed into two categories: the value-
added activities and the non-value-added activities, being the last one unmistakably related
with waste. In [8], this waste can be subsequently classified in two categories:
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Pure waste
These are expendable activities, for example: unproductive reunions,
dislocations or malfunctions. Corporations are obliged to eliminate this kind of
muda and it can reach up to 65% of the total waste of the organization.
Necessary waste
Although they don’t add value, these activities need to be carried out. As
examples those could be inspection of the arriving raw material or setups. These
can take up to 30% of the total muda.
Together, they represent 95% of the organization’s time, which clearly must be
minimized, otherwise only 5% of the time is used for value-added activities.
But what is waste? What is muda? As said before, muda is a Japanese word for waste.
Taiichi Ohno and Shigeo Shingo, during the development of TPS, defined seven major types of
waste in business or manufacturing processes, listed below, that can be applied not only to a
production line but also to product development, order taking or the office.
1. Overproduction
Overproduction can be viewed as the opposite of JIT and it means producing
items for which there are no orders: produce the wrong part, at the wrong time,
at the wrong amount. This waste was considered, to Ohno, the fundamental
waste, since it causes most of the other wastes. In other words, it produces
unnecessary transportation and storage costs due to the excess of inventory.
2. Waiting Time
This is the unproductive time of a worker, or machine, when he’s just waiting
for something. For example, waiting for the next process step, tool or supply, or
just watching an automated machine finishing a process. It could also be the
waiting time due to the lack of work caused by processing delays, equipment
failure or capacity bottlenecks.
3. Unnecessary transport
Moving work in process (WIP), materials, or even finished goods long
distances is an unnecessary and inefficient transport. This will increase
production costs, the lead time, and can even cause damage to the products
during the course of the movement.
4. Incorrect processing
This concerns the unnecessary steps that are taken in a process, possibly
because of the use of poor tools and product design, causing unneeded motion
and producing defects (waste seven).
5. Excess inventory
The excess of raw materials, WIP or finished goods can cause longer lead
times, damaged goods and delays.
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Extra inventory also hides problems such as production imbalances,
redundancies, defects, paperwork, equipment downtime and long setup times.
Figure 2.2 easily exemplifies this situation through an analogy where water
represents inventory and rocks represent problems. In this case, with a high water
level, the rocks are hidden and the management assumes everything is fine, until
the water drops and the problems are presented. Deliberately forcing the water
level down, all the problems are exposed and can be corrected before they
induce other possible even worse problems.
Figure 2.2 – Inventory hiding problems [7]
6. Unnecessary movement
These are all the needless motion employers have to perform during a
process, such as walking or looking for, reaching for, or stacking parts, tools, etc.
7. Defects
This waste is the production of defected parts or correction, that is, repair,
rework, scrap, replacement and inspection means wasteful handling, time, and
effort.
Liker [4] defined another waste:
8. Unused employee creativity
Not engaging or listening to your employees can cause the loss of ideas, skills,
improvements or learning opportunities.
Yet another waste that I consider relevant not only for the industry, but also to
households, is the waste of energy (also referred in [8]).
9. Energy Consumption
Through time, it became more and more important to rationalize the
consumption of energy, giving great advantages for the consumer and the
environment, being the decrease of energy costs the most attractive benefit for
the consumer. There are numerous ways and techniques for a more efficient
energy use, like the replacement of conventional luminaires with more efficient
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ones, dimensioning a capacitor for the control of the reactive energy, micro
production, cogeneration, etc. It is recommended to do an energy audit to start a
more rationalized use of energy.
2.6 - Continuous Improvement
In Japanese, Continuous Improvement is known as Kaizen, which literally means change
(kai) for the better (zen), term that has come to be accepted as one of the key concepts of
management when the book by Masaaki Imai “Kaizen: The Key to Japan’s Competitive
Success” was published in 1986.
The word Kaizen implies improvement that involves everyone – both managers and
workers - and entails relatively little expense. The kaizen philosophy assumes that our way of
life – be it our working life, our social life, or our home life – should focus on constant-
improvement efforts. This concept is so natural and obvious to many Japanese that they
don’t even realize they possess it! [9]
There are three major components that involve continuous improvement. [8] The first
one encourages people to make mistakes, what can be seen as counterintuitive. Many
organizations punish mistakes and tend to label who made them as ‘losers’ or ‘incapables’.
This creates a fear of failing that deprive us of continuously try and improve. In fact, one
should understand why do those mistakes happen and avoid that they are repeated.
The second component encourages and rewards people to identify problems and solve
them. This is based on the principle that the one that better knows a process is the one who
makes it. A top manager will not have the same acknowledge of a manufacturing process as
the machine operator of that process.
To finish, the third component asks people to identify ways of making things better, that
is, encourages them to constantly overcome themselves. This is a way of proactive
empowerment.
Continuous Improvement is an ongoing and never ending process and there are different
kinds of continuous improvement tools, for example the PDCA Cycle, Standardization or the
5W1H.
2.6.1 - PDCA Cycle
The PDCA cycle has its origins in the Shewhart Cycle by Dr. Walter A. Shewhart in 1939.
Figure XX presents the Shewhart Cycle and the contrast with the precious straight line, as Dr.
Shewhart itself wrote “In fact these three steps must go in a circle instead of in a straight
line as shown in fig. 10 [in this case Figure 2.3]. It may be helpful to think of the three steps
in the mass production process as steps in the scientific method. In this sense, specification,
production, and inspection correspond respectively to making a hypothesis, carrying out an
experiment, and testing the hypothesis. The three steps constitute a dynamic scientific
process of acquiring knowledge.” [10, pp. 44-45]
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Figure 2.3 – Shewhart Cycle, 1939 [10]
In 1951, Dr. W. Edwards Deming modified this cycle at the Japanese Union of Scientists
and Engineers (JUSE), adding a fourth step to the cycle and stressing the importance of
constant interaction among design, production, sales and research and that the four steps
should be rotated constantly, with quality of product and service as the aim. The Japanese
called this the “Deming Wheel” [11]
Figure 2.4 – Deming Wheel [11]
Directly from the 1950 version, Deming reintroduces the Shewhart Cycle in 1986, stating:
“Any step may need guidance of statistical methodology for economy, speed, and protection
from faulty conclusions from failure to test and measure the effects of interactions.” [11]
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Figure 2.5 – The Shewhart Cycle, 1986 [12]
Again, in 1993, Deming modified the Shewhart cycle and called it the Shewhart cycle for
learning and improvement, or the PSDA Cycle. “A flow diagram for learning and for
improvement of a product or of a process” [13]
Figure 2.6 – PDSA Cycle [13, p. 132]
Although, it this cycle is well known as the PDCA (Plan, Do, Check and Act), Deming
stated in the Moen, Nolan, and Provost manuscript, “… be sure to call it PDSA, not the
corruption PDCA.” He warned Western audiences that Plan, Do, Check and Act version is
inaccurate because the English word “check” means “to hold back”. [11]
In short, the PDSA cycle has four steps:
Plan – Definition of a problem and identify an opportunity and plan for change
Do – Implement the change on a small scale
Study – Analyze the results of the change and study its modifications
Act – If the change was successful, adopt the change and continuously study the
results. If the change was not successful, run the cycle again.
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2.6.2 - Standardization
A standardized work or process is a much easier work to teach, improve, document, audit
and transfer. Thus, all efforts in this direction are welcome unless they constrain the creative
processes of people. [8]
With standardized work there’s no space for improvised tasks that may destroy plans and
day-to-day budgets. In other words, everyone does the same process in the same way and if
someone identifies a better, faster and efficient method for this process, this method is
made a standard. In every cycle of the PDCA, it should be noted the knowledge and good
practices promoting standardization, transforming the PDCA cycle into the SDCA (standard,
do, check, act).
2.6.3 - 5W1H
5W1H was originated from a poem wrote by Rudyard Kipling, thus being also known as the
Kipling Method, which started:
I Keep six honest serving-men:
(They taught me all I knew)
Their names are What and Where and When
And How and Why and Who.
This is a well-known quality management technique that is based on six trigger questions:
What? Why? Where? When? Who? and How?. These are useful in collecting information to
ensure the fulfillment of a certain action plan, diagnose a problem and design solutions. It
can be generically view in two ways, with the change of the end question:
To find the root problem cause:
o What is the problem?
o Why does it occur?
o Where is it located?
o When does it occur?
o Who is involved?
o How did it appear?
To find a solution to a problem:
o What will be done?
o Why is it being done?
o Where will it be done?
o When will it be done?
o Who will be responsible for it?
o How will it be implemented?
Lately it has been included the how much question, transforming the 5W1H in 5W2H, as in
“How much does it cost to have this problem?” or “How much does it cost to implement this
solution?”
2.7 - Lean Tools and Techniques
In this subchapter we explain how the main lean tools and techniques, used during this
project, are performed, providing a clear perception of how we achieved some
values/results. We start by elucidation the reader about Visual Management including the 5S
program, its importance and implementation method. Carrying out with an insight about the
Value Stream Mapping (VSM), how to draw one and its main principles, also referring to the
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ABC Analysis, a tool that clarifies which of a company’s products are the most important to
management (an important task to start the a VSM). We finish this with a perception of the
characteristics and benefits of cellular manufacturing and how to balance a line.
2.7.1 - Visual Management
Work must be rigorously standardized (by the work team, not only some remote industrial
engineering group) and that employees and machines must be taught to monitor their own
work. This matters need to be coupled with visual controls, ranging from the 5Ss (where all
debris and unnecessary items are removed and every tool has a clearly marked storage place
visible from the work area) to status indicators (often in the form of andon1 boards), and
from a clearly posted, up-to-date standard work charts to display of key measurable and
financial information on the costs of the process. The precise techniques will vary with the
application, but the key principle does not: Everyone involved must be able to see and must
understand every aspect of the operation and its status all times. [5]
The main role of visual management, or visual documentation, is to convert a personal or
centralized knowledge workplace into some kind of knowledge data base or a public
knowledge workplace (Figure 2.7), creating a work environment that is self-explaining, self-
oriented and self-improving.
Figure 2.7 – The role of visual documentation: converting the workplace into a knowledge field [14, p.
67]
2.7.2 - 5S Technique
A vital component of visual management is the 5S organization system. One of the most
known and applied tool of Lean, has its origins in Japan in the early 70s. The main purpose of
its practices is to provide a more efficient, safe and organized workstation, leading to a
reduction of waste and the improvement of workers and processes performances.
The name of this technique comes from the initial letter of five Japanese words – Seiri,
Seiton, Seiso, Seiketsu and Shitsuke, each one leading to an order of implementation:
1 Andon is a manufacturing term denoting a system to notify all the stakeholders of a quality or process problem
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1. Seiri (sort)
Separate the useful from de useless. That is to sort through items and keep
only what is needed to perform value-added-activities and dispose of what is not.
A method to do this is the red-tagging. This consists in marking the rarely
used items with a red tag (Figure 2.8), identifying them as an item to remove from
the workplace. This can be done according to the next table.
Table 2.3 – Red tag classification
Red tag Usage Frequency Where to place
Daily Workstation
Once a week Work area
✓ Once a month Storage place
✓ Once a year Warehouse
✓ Obsolete Sell/Eliminate
Figure 2.8 – Red tag example
2. Seiton (orderliness)
“A place for everything and everything in its place” is the phrase that truly
describes this step. There must be well-defined place for everything and check
that everything is in its place. The most frequently used gear need to be placed
at hand (avoiding unnecessary movement for the worker), and visual help
(identifying labels) should be on the gear and at the place where they must be
placed.
3. Seiso (cleanliness)
Cleaning the workstation anticipates failure conditions that could hurt the
product’s quality or cause machine failure.
4. Seiketsu (standardize)
Define a standard regulation for order and cleanliness in the workplace. In
other words, develop systems and procedures, with visual controls for example,
to maintain and monitor the previous S’s.
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5. Shitsuke (self-discipline)
Maintain a stabilized workplace in an ongoing process of continuous
improvement.
An unfortunate consequence of this technique is that many companies confuse 5S with
lean production itself. They implement the 5S, do workshops about it, and in the end, they
don’t get time or costs reductions and quality doesn’t improve. It must be noted that 5S is
not to organize and label materials, tools and create a shiny environment, it is a support to
lean systems for a smooth flow to takt time. [4]
2.7.3 - Spaghetti Diagram
From a lean perspective, the first thing you should do in approaching any process is to
map the value stream following the circuitous path of material (or paper information)
through your process. The best way to do this is to walk the actual path of the process, draw
it on a layout of the plan and calculate the time and distance traveled - this is called the
“spaghetti diagram”. [4]
Although spaghetti diagrams are a simple way to analyze the product flow, they do not
contain the level of information that we can find in the Value Stream Mapping (VSM).
2.7.4 - Value Stream Mapping
Value Stream Mapping (VSM), or “Material and Information Flow Mapping” as it was known
at Toyota, is a technique originally developed by Toyota and then popularized by the book
“Learning to See” by Rother and Shook.
In their book they define Value Stream Mapping as “a pencil and paper tool that helps you
to see and understand the flow of material and information as a product makes its way
through the value stream. What we mean by value-stream mapping is simple: Follow a
product’s production path from customer to supplier, and carefully draw a visual
representation of every process in the material and information flow. Then ask a set of key
questions and draw a future-state map of how value should flow.” [15]
When constructing a VSM, the flow of information is outlined in the superior part of the
map, starting from the right to the left, whereas the flow of materials is drew in the inferior
part of the map, starting from the left to the right. It is also essential to insert the stock
points with the time they stay waiting for the next process of the flow and below each
process their respective cycle time (see the next illustration). With this, we can easily
determine the product lead time and processing time, or value added time.
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Figure 2.9 – Current State VSM Example [16]
In the previous image we can note different symbols and icons. These symbols represent a
common, simple and intuitive language that promotes an easy comprehension of the map for
everyone. Their meanings are presented in the next picture.
Figure 2.10 – VSM Symbols [15]
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Succinctly, the method to develop a VSM is to start by selecting a product or product
family to map. Then draw a current state map (or AS-IS state) with a clear view of the
current value stream with the flow of materials and information. After carefully analyzing the
current state map and determining what wastes are influencing the lead time, which
activities are and aren’t creating value to the product, it’s time to develop an improvement
plan and draw the future state map (or TO-BE state). Figure XX represents a future state map
of the previous VSM (figure xx).
Figure 2.11 – Future State VSM Example [16]
In this map it should be clear a reduction of the lead time and an improvement in the
processes synchronization. Last but not least one must constantly improve towards
perfection, implementing a continuous improvement policy.
As mentioned, when developing a VSM a question arises – what’s the product, or service,
that we should map? The answer is to choose the one that has the most impact on the
company’s development or the one that has more gaining potential with the implementation
of continuous improvement tools. [8] Consequently, we have the ABC Analysis.
2.7.5 - ABC Analysis
The ABC Analysis consists in categorizing items so that the most important will receive
management attention. [17]
In this analysis, the products are grouped in three categories in order of their estimated
importance (A, B and C), based on the Pareto principle. This principle, also known as the 80-
20 rule, states that the majority of the situations are dominated by a few vital elements, for
example, “80% of your sales come from 20% of your products”.
Considering the annual turnover of a company as a selection parameter, one could
categorize the products as the following example:
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Class A items – 75 to 80% of the turnover, from 15 to 20% of products
Class B items – 10 to 15% of the turnover, from 20 to 25% of products
Class C items – 5 to 10% of the turnover, from 60 to 65% of products
Figure 2.12 exemplifies a typical ABC curve, identifying the three categories of products
and the respected value on production.
Figure 2.12 – Typical ABC Curve
There are no fixed percentages to each class. Different ratios can be applied based on
different objectives and criteria. Yet, they’re categorized through very important to
marginally important products, where:
Class A
These items are the most important ones for the company. Hence, there
should be a tight and rigorous control, quick deliveries/supplies and should be
kept a safety stock.
Class B
These items are less important than class A items, therefore must be the
same concerns as with class A, but with lower incidence.
Class C
These are marginally important items. There shouldn’t be such much
attention and time wasted on these items, since they don’t bring a big impact to
the company’s development.
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2.7.6 - Cellular Manufacturing
The ‘conventional bundle’ and ‘straight line’ systems are the most common approaches to
work organization and often referred to as the ‘line system’ or ‘progressive bundle’ system.
In these methods of working, cut pieces are bundled and distributed to workers to perform
predominantly short-cycle tasks. Having completed their tasks, operators would re-bundle
these pieces and then pass them onto other operators to complete another short-cycle task.
[18]
These systems have led to several familiar problems. Each function tends to act as a
“silo” and hands its output “over the wall” to the next function. They are characterized by
departmental barriers and parochialism, and generally slow progress of work though the
system. Much of the job lead time consists of non-value-adding times devoted to move, wait,
information collection, etc. [19]
Group technology (or cellular) layouts allocates dissimilar machines into cells to work on
products that have similar shapes and processing requirements. The overall objective is to
gain the benefits of product layout in job-shop kinds of production. These benefits include:
[7]
Better human relations. Cells consist of a few workers who form a small work
team; a team turns out complete units of work.
Improved operator expertise. Workers see only a limited number of different
parts in a finite production cycle, so repetition means quick learning.
Less in-process inventory and material handling. A cell combines several
production stages, so fewer parts travel through the shop
Faster production setup. Fewer jobs mean reduced tooling and hence faster
tooling changes
There are relatively few formalized ‘standards’ of teamworking in the apparel context.
The Toyota Sewing System (TSS) is one of them (see Figure 2.13). [19]
Figure 2.13 – The Toyota Sewing System [18]
Some characteristics of the TSS are: [18]
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Operatives stand to allow easy movement between work stations. Ideally, an
operative should not stay standing in the same position as they will move
between work stations.
The module is usually U-shaped. This aids communication between operatives.
Operators work on single garments.
Each operator performs approximately 2-4 operations, depending on the product.
Work flow is sequential.
Operators’ skills overlap.
2.8 - Line Balancing
In the following subdivisions we’ll be explaining the basics for balancing an assembly line,
concepts also essential for the balancing a production cell. In particular, we’ll briefly discuss
the concepts of takt time, cycle time and their relation, and the key steps for balancing an
assembly line.
2.8.1 - Takt time
Takt time, also known as the production pace, is the rate at which customers require
finished units. [15] In other words, it sets the desired time between units of production
output, synchronized to costumer demand.
It stems from the German word ‘takt’ that means pace, beat or musical meter and can be
determined by dividing the productive time available per day and the required demand also
per day.
(2.1)
Note that takt time represents the actual customer demand rate so you must not subtract
time for unplanned machine downtime or other unforeseen internal problems, only the
scheduled downtime for maintenance or planned breaks.
2.8.2 - Cycle time
Cycle time is how frequently a finished unit actually comes off the end of your line or
pacemaker cell. [20] In this case, it includes all types of delays occurred while completing a
job, as exemplified in the next formula:
[21] (2.2)
Cycle time and takt time should be balanced in parallel, with approximated time.
Without this precaution the production may result in a late delivery and customer
dissatisfaction (when cycle time is greater than takt time) or cause excess inventory or use of
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resources (when cycle time is shorter than takt time), like the use of extra operators (Figure
2.14).
Figure 2.14 – Cycling much faster than takt time may require more people [20]
Comparing takt time and cycle time is the easiest way to answer the simple but critical
questions: “How frequently does the customer need one piece?” and “How frequently do we
actually make one piece at our pacemaker process?”.
2.8.3 - Line balancing process
The process of balancing an assembly line involves three major steps: determine the takt
time, calculate the theoretical minimum number of workstations and assign specific assembly
tasks to each workstation. These steps can be performed has described below:
1. Takt Time
We can determine the takt time by dividing the productive time available
and the required demand per day, as previously described.
2. Minimum number of workstations
This can be calculated as the total tasks duration time divided by the
takt time. The total tasks duration time is the sum of all tasks times that
it takes to make the product in analysis.
(2.3)
3. Assign tasks to workstations
Assign tasks, one at a time, to the first workstation until the sum of the task
times is equal to the workstation cycle time, or no other tasks are feasible
because of time or sequence restrictions. Repeat the process for Workstation 2,
Workstation 3, and so on until all tasks are assigned. [7]
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One can also determine the maximum number of production and measure the
efficiency of an assembly line as follows:
(2.4)
(2.5)
References
[1] ATP - Associação Têxtil e Vestuário de Portugal, [Online]. Available: http://www.atp.pt/gca/index.php?id=18. [Acedido em March 2012].
[2] M. Houshmand e B. Jamshidnezhad, “Conceptual Design Of Lean Production Systems Through an Axiomatic Approach,” em Proceedings of ICAD2002 Second International Conference on Axiomatic Desig, Cambridge, MA, 2002.
[3] J. P. Womack, D. T. Jones e D. Roos, The Machine That Changed The World, New York: Rawson Associates, 1990.
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