There are
numbers of lean manufacturing tools which, when used in proper ways will give
the best results. Once the source of the waste is identified it is easier to
use the suitable lean tool to reduce or eliminate them and try to make waste
free systems. Some of these tools are discussed in this chapter.
1
Cellular Manufacturing
A cell is a combination of people, equipment and
workstations organized in the order of process to flow, to manufacture all or
part of a production unit. Following are the
characteristics of effective cellular manufacturing practice.
1. Should
have one-piece or very small lot of flow.
3.
Is usually arranged in a C or U shape so the
incoming raw materials and outgoing finished goods are easily monitored.
4.
Should
have cross-trained people within the cell for flexibility of operation.
5.
Generally, the cell is arranged in C or U shape
and covers less space than the long assembly lines.
There are lots of benefits
of cellular manufacturing over long assembly lines. Some of
them are as follows.
1.
Reduced work in process inventory because the work
cell is set up to provide a balanced flow from machine to machine.
2.
Reduced direct labor cost because of improved
communication between employees, better material flow, and improved scheduling.
3.
High employee participation is achieved due to
added responsibility of product quality monitored by themselves rather than separate
quality persons.
4.
Increased use of equipment and machinery, because
of better scheduling and faster material flow.
5.
Allows the company higher degrees of flexibility
to accommodate changes in customer demand.
6.
Promotes continuous improvement as problems are
exposed to surface due to low WIP and better communication.
7.
Reduces throughput time and increases velocity for
customer orders from order receipt through production and shipment.
8.
Enhances the employee’s productive capability
through multi-skilled multi-machine operators.
Apart from these tangible benefits, there is the
very important advantage of cellular manufacturing over the linear flow model.
Due to the closed loop arrangement of machines, the operators inside the cell
are familiar with each other’s operations and they understand each other
better. This improves the relation between the operators and helps to improve
productivity. Whereas in long assembly line one operator knows only two operators
(before and after his operation in the line) it seems that operators are
working independently in the line.
2 Continuous
Improvement
Continuous improvement (CI) can be defined
as the planned, organized and systematic process of ongoing, incremental and
company-wide change of existing practices aimed at improving company
performance. Activities and behaviors that facilitate and enable the
development of CI include problem-solving, plan-do-check-act (PDCA) and other
CI tools, policy deployment, cross-functional teams, a formal CI planning and
management group, and formal systems for evaluating CI activities. Successful
CI implementation involves not only the training and development of employees
in the use of tools and processes, but also the establishment of a learning
environment conducive to future continuous learning.
The short description of
PDCA cycle is given below
Plan: Identify an opportunity
and plan for change.
Do: Implement the change on a
small scale.
Check: Use data to analyze the
results of the change and determine whether it made a difference.
Act: If the
change was successful, implement it on a wider scale and continuously assess
the results. If the change did not work, begin the cycle again.
Thus
continuous improvement is an ongoing and never ending process; it measures only
the achievements gained from the application of one process over the existing.
So while selecting the continuous improvement plan one should concentrate on
the area which needs more attention and which adds more value to our products.
There are seven different kinds of continuous improvement tools (Larson, 2003,
p. 46) they can be described as follows. The use of these tools varies from
case to case depending on the requirement of the process to be monitored.
Pareto Diagram: The Pareto diagram is a graphical
overview of the process problems, in ranking order from the most
frequent, down to the least frequent, in descending order from left to right.
Thus, the Pareto diagram illustrates the frequency of fault types. Using a
Pareto, one can decide which fault is the most serious or most frequent
offender.
Fishbone Diagram: A framework used to
identify potential root causes leading to poor quality.
Check
Sheet: A check sheet is a structured, prepared form for collecting
and analyzing data. This is a generic tool that can be adapted for a
wide variety of purposes.
Histogram:
A
graph of variable data providing a pictorial view of the distribution of data
around a desired target value.
Stratification:
A
method of sorting data to identify whether defects are the result of a special
cause, such as an individual employee or specific machine.
Scatter Diagram: A graph
used to display the effect of changes in one input variable on the
output of an operation.
Charting: A graph that tracks the
performance of an operation over time, usually used to monitor the
effectiveness of improvement programs.
3 Just in Time
Just in
time is an integrated set of activities designed to achieve high volume
production using the minimal inventories of raw materials, work in process and
finished goods. Just in time is also based on the logic that nothing will be
produced until it is needed.
Just-in-time
manufacturing is a Japanese management philosophy applied in manufacturing. It
involves having the right items with the right quality and quantity in the
right place at the right time. The ability to manage inventory (which often
accounts
for as
much as 80 percent of product cost) to coincide with market demand or changing
product specifications can substantially boost profits and improve a
manufacturer’s competitive position by reducing inventories and waste. In
general, Just in Time (JIT) helps to optimize company resources like capital,
equipment, and labor. The goal of JIT is the total elimination of waste in the
manufacturing process. Although JIT system is applied mostly to manufacturing
environment, the concepts are not limited to this area of business only. The
philosophy of JIT is a continuous improvement that puts emphasis on prevention
rather than correction, and demands a companywide focus on quality. The
requirement of JIT is that equipment, resources and labor are made available
only in the amount required and at the time required to do the work. It is
based on producing only the necessary units in the necessary quantities at the
necessary time by bringing production rates exactly in line with market demand.
In short, JIT means making what the market wants, when it wants, by using a
minimum of facilities, equipment, materials, and human resources.
JIT principles are based
on the following
·
It is commonly used to describe the stockless
production manufacturing approach, where only the right parts are completed at
the right time.
·
It
is not a destination but a journey.
·
Reducing
inventory, improving quality and controlling cost.
·
A
“Pull System” where the parts are produced only w hen they are required.
Pull and Push System
In push
system, when work is finished at a workstation, the output is pushed to the
next station; or, in the case of the final operation, it is pushed on to the
final inventory. In this system, work is pushed on as it is completed, with no
regard for whether the next station is ready for the work or not. In this way,
the WIP is unbalanced in all operations throughout the shop floor.
|
Description
|
Push System
|
Pull System
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Signal to produce
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Schedule or plan
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Customer signal
|
|
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More
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||
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Timing of signal
|
Advance of the need
|
At the time of the need
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Planning horizon
|
Fairly long
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Very short
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Leveling of
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No
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Generally yes
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Demand
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||
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Too much inventory, no
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Does not planned ahead,
missed
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Negatives about
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visual control, long and
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customer demand at the
|
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the system
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planned lead times, requires
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beginning of product life cycle,
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more information
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too much inventory at the last
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Non repetitive, batch,
short
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Repetitive, high volume
|
|
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Best for
|
product lifecycle, long lead
|
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manufacturing and stable demand
|
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||
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time purchasing
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Problem visibility
|
Not visible
|
Visible
|
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Stress to improve
|
Little
|
Much
|
|
|
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|
|
The push system is also known as the Materials
Requirements Planning (MRP) system. This system is based on the planning
department setting up a long-term production schedule, which is then dissected
to give a detailed schedule for making or buying parts. This detailed schedule
then pushes the production people to make a part and push it forward to the
next station. The major weakness of this system is that it relies on guessing
the future customer demand to develop the schedule that production is based on
and guessing the time it takes to produce each part. Overestimation and
under-estimation may lead to excess inventory or part shortages, respectively.
Whereas in pull system; each work station pulls
the output from the preceding station as it is needed. Output from the final
operation is pulled by customer demand or the master schedule.
Thus in pull system work is moved in response to demand from the next stage in
the process. The Kanban system is used to monitor the effective pull process.
Table 1 helps to differentiate Pull and Push system.
4 Total Productive
Maintenance
Machine
breakdown is one of the major headaches for people related to production. The
reliability of the equipment on the shop floor is very important because if any
one of the machines is down the entire shop floor productivity may be nil. The
tool that takes care of these sudden breakdowns and awakes maintenance as well
as production workers to minimize these unplanned breakdowns is called total
productive maintenance. Total Productive Maintenance (TPM) is a maintenance
program, which involves a newly defined concept for maintaining plants and
equipment. The goal of the TPM program is to increase production, increase
employee morale and job satisfaction.
TPM is
set of tools, which when implemented in an organization as a whole gives the best
utilization of machines with least disruption of production. The set of tools
are called pillars of TPM and they are shortly described here and illustrated
in a TPM diagram
5S
The first
pillar of TPM is called 5S, which organize and cleans work place; this helps to
make problems visible and attracts the attentions of everyone. Brief
description of 5S elements are as follows:
Sort: The first step in making
things cleaned up and organized.
Set In Order: Organize, identify and
arrange everything in a work area.
Shine: Regular cleaning and
maintenance.
Standardize: Make it easy to maintain,
simplify and standardize.
Sustain: Maintain what has been
achieved.
Autonomous maintenance
This is
about the involvement of production workers in the day to day general
maintenance of machines like cleaning, lubricating etc. which saves the time of
skilled maintenance person at the same time the production workers are made
more responsible to their machines.
Kaizen
Kaizen is
for small improvements, but carried out on a continual basis and involve all
people in the organization. Kaizen requires no or little investment. The
principle behind is that “a very large number of small improvements are more
effective in an organizational environment than a few improvements of large
value.” This pillar is aimed at reducing losses in the workplace that affect
our efficiencies (Kumar, 2008, p. 220).
Planned maintenance
It
addresses the proactive approach of maintenance activities. This involves four
types of maintenance namely preventive maintenance, breakdown maintenance,
corrective maintenance, and maintenance prevention.
It is aimed
towards customer delight through the highest quality and defect free
manufacturing. In this system, one has to take care of parts which affect
product quality and try to eliminate or modify them to give customer superior
quality.
Training
Employees
should be trained such that they can analyze the root cause of the problem.
General know how of the problem is not sufficient rather they should be able to
know why the problem is occurring and how to eliminate it. For this employee
need continuous training, ultimately; the entire employee should be
multi-skilled and should solve the problem in their area by themselves.
Office TPM
This tool
is about increasing the efficiencies in office (administrative) activities.
This tool works the problems like communication issues, data retrieval
processes, management information systems, office equipment losses, up to date
information about inventories etc.
Safety Health and
Environment
In this
area, the focus is to create a safe workplace and a surrounding area that would
not be damaged by our process or procedures. This pillar will play an active
role in each of the other pillars on a regular basis. Safe work environment
means accident free, fire less and it should not damage the health of workers.
5 Work
Standardization
A very
important principle of waste reduction is the standardization of work.
Standardized work basically ensures that each job is organized and carried out
in the same manner; irrespective of the people working on it. In this way if
the work is standardized the same quality output will be received even if the
worker is changed in process. At Toyota, every worker follows the same
processing steps all the time. This
includes
the time needed to finish a job, the order of steps to follow for each job, and
the parts on hand. By doing this one ensures that line balancing is achieved,
unwanted work in process inventory is minimized and non value added activities
are reduced. A tool that is used to standardize work is called takt time.
6 Waste Reduction
Techniques
Some of
the waste reduction tools include zero defects, setup time reduction, and line
balancing. The goal of zero defects is to ensure that products are fault free
all the way, through continuous improvement of the manufacturing process
(Karlsson and Ahlstrom 1996). Human beings almost invariably will make errors.
When errors are made and are not caught then defective parts will appear at the
end of the process. However, if the errors can be prevented before they happen
then defective parts can be avoided. One of the tools that the zero defect
principle uses is Poka Yoke. Poka-Yoke, which was developed by Shingo, is an
autonomous defect control system that is put on a machine that inspects all
parts to make sure that there are zero defects. The goal of Poka-Yoke is to
observe the defective parts at the source, detect the cause of the defect, and
to avoid moving the defective part to the next workstation.
Single
Minute Exchange of Die (SMED) is another technique of waste reduction. During
1950’s Ohno devised this system; and was able to reduce the die changing time
from 1 day to three minutes (Womack, Jones and Ross, 1990). The basic idea of
SMED is to reduce the setup time on a machine. There are two types of setups:
internal and external. Internal setup activities are those that can be carried
out only when the machine is stopped while external setup activities are those
that can be done during machining. The idea is to move as many activities as
possible from internal to external (Feld, 2000). Once all activities are
identified than the next step is to try to simplify these activities (e.g.
standardize setup, use fewer bolts). By reducing the setup time many benefits
can be realized. First, die-changing specialists are not needed. Second, inventory
can be reduced by producing small batches and more variety of product mix can
be run.
Line
balancing is considered a great weapon against waste, especially the wasted
time of workers. The idea is to make every workstation produce the right volume
of work that is sent to upstream workstations without any stoppage (Mid-America
Manufacturing Technology Center Press Release, 2000). This will guarantee that
each workstation is working in a synchronized manner, neither faster nor slower
than other workstations.
7 Value Stream mapping
Value
Stream Mapping (VSM) is a technique that was originally developed by Toyota and
then popularized by the book, Learning to See (The Lean Enterprise Institute,
1998), by Rother and Shook. VSM is used to find waste in the value stream of a
product. Once waste is identified, then it is easier to make plan to eliminate
it. The purpose of VSM is process improvement at the system level. Value stream
maps show the process in a normal flow format. However, in addition to the
information normally found on a process flow diagram, value stream maps show
the information flow necessary to plan and meet the customer’s normal demands.
Other process information includes cycle times, inventories, changeover times,
staffing and modes of transportation etc. VSMs can be made for the entire
business process or part of it depending upon necessity. The key benefit to
value stream mapping is that it focuses on the entire value stream to find
system wastes and try to eliminate the pitfall.
Generally, the value stream maps are of three types. Present State Value Stream
Map (PSVSM) tells about the current situation, Future State Value Stream Map
(FSVSM) can be obtained by removing wastes (which can be eliminated in the
short time like three to six months) from PSVSM and Ideal State Value Stream
Mapping (ISVSM) is obtained by removing all the wastes from the stream. The VSM
is designed to be a tool for highlighting activities. In lean terminology they
are called kaizen activities, for waste reduction. Once the wastes are
highlighted, the purpose of a VSM is to communicate the opportunities so they
may be prioritized and acted upon. Hence, the prioritization and action must
follow the VSM, otherwise it is just a waste like other wastes.
Lean Manufacturing Tools are used in production and manufacturing process improvements under the Lean manufacturing system.
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