The origins and methods of LEAN


What is Lean?

The origin of lean stems from Toyota Production System. Taiichi Ohno in his book 'Toyota Production System: Beyond Large-Scale Production', described the most important objective of Toyota System as "increase production efficiency by consistently and thoroughly eliminating waste". The revolution and evolution of this system is now referred to as lean production.

Dave Stockton and Riham Khalil in Lean Business Environment lecture note De Montfort University, has defined lean as "the process or activities to improve a processing system, making the process efficient and improving in quality, cost and on-time delivery". Also John Bicheno in Cause and Effect Lean described "lean thinking as a philosophy and not a system or technique".

Hence, lean generally encompasses the attitude/culture to improve on processes using appropriate tools and technique to specify value, identify improvement possibilities, implement them and continuously seek perfection through continuous improvement.

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The lean idea/thinking demands the prevention and elimination of wastes and achievement of high efficiency. 'Muda', a Japanese word which refers to waste includes processes, activities and resources which do not contribute value to the customer's demands both in manufacturing and in service. These wastes are:

Overproduction: This refers to the production of excess products. Production should aim at only producing the exact quantity and quality just at the time needed.

Over processing: This is the use of inappropriate processing method - machine or schedule. For instance, the excess scheduling of processes that do not add value to product in the production line.

Waiting: This can come in form of non-utilization such as blocking, waiting, stoppages (break down or maintenance), and change over C/O.

Transportation: This refers to movement of materials from one place to the other. It can be internal within the shop floor (long distances within layout) or external from supplier (Local or international).

Unnecessary Motion: This refers to human motion as well as machines. For instance, bending, stretching, movement of the hands (double handling), walking and around.

Inventory: This can be in form Work in Progress (WIP), excess materials from the suppliers not in use, lying on the store. This affects cash flow, and consumes space as well. Just in Time (JIT) manufacturing reduces inventory

Defects: This refers to the products not meeting the standardised quality set for the production. They can be reworked or scrap. It affects cost.



Scheduling refers to a phase of stage in project management that involves splitting of the project into various tasks, outlining them with estimated time and resources required in other complete the project. Uncoordinated schedule can likely introduce waste 'Muda' in the manufacturing process which can come in form of underutilization of workforce and unnecessary increase in project lead time.


William J. Stevenson "Production Operations Management"; - Sixth Edition; pp. 801.

"Chris received new word processing software for her birthday. She also received a check, with which she intends to purchase a new computer. Chris's college instructor has assigned a paper due next week. Chris has decided that she will prepare the paper on the new computer. She has made a list of the activities she will need to do and their estimated times"


People Involved:

- Chris

1.3.2 Using Flow chart:

As the schedule of the activities in the above case study is uncoordinated, Flow chart - which is on the seven quality tools, can be implemented in lean thinking. This tool has been chosen in other to map out and understand the process flow of the activities as Chris will want to apply them in other to achieve quality result in the preparation of the paper and also at when due - on time delivery. The chart is shown in Fig

Lean thinking and the use of the quality tool - flow chart has enabld the coordiantion of the activies in a logical sequence.


As mentioned previously, lean is all about continuous improvement and flow. The above flow chart can be rearranged implementing lean to show a more logcial sequence that has a better flow or the activities in a regular form.

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As a continuous improvement, a flow has been achieved for continuity from choosing a topic (Ch) until the paper is submitted (Sub).

The total time of the project in hours = Time for (G + H + A + D + I + B + F + E + C)

= 2.0 + 1.0 + 0.8 + 0.6 + 2.0 + 0.4 + 3.0 + 0.5 + 0.2

= 10.5 Hours

Furthermore on improvement, the value added activities can be identified and differentiated from the non-value added activities.

Having identified the non-value added activities, the time for these activities can be reduced in other to reduce the total lead time of the project.

If activity E is reduced from 2.0 hours to 1.6 hours and the activity G reduced from 0.5 hours to 0.3 hours, then the total lead time of the project becomes 9.9 hours.

Hence % reduction in total time = 10.5 - 9.9 x 100 = 5.7%


1.4.1 Network Diagram:

Network diagram can be used to represent the schedule sequence, making activity 'A' to run in parallel with activity 'D'. From Critical path analysis, the total lead time is further reduced.

:. Since G - H - D - I - B - F - E - C has the longer total time of completion, it is the critical path, and therefore the total lead time is dependent on the critical path. Hence the total lead time has been reduced to 9.1 hours from 9.9 hours.

% age reduction from the previous time = 9.9 - 9.1 x 100 = 8.08%



Implementing sustained lean with continuous improvement using appropriate process flow sequence, reduction of time spent on non-value added activities and proper activity scheduling with network diagram has reduced the total time by 10.5%. This will facilitate on time delivery which is a performance measure of successful lean implementation.



Batch size refers to the number of parts of a product processed in a processing work station at a particular cycle time of the station. Processing of a particular batch size is usually completed before intake of another batch. The batch size of a work station relates directly to the cycle time of the station hence has an influence on the lead time of production coming to completion.


Velarde, G. J., Saloni, D. E., van Dyk, H., and Giunta, M. (2009). Process flow improvement proposal using lean manufacturing philosophy and simulation technique on a modular home manufacturer. Lean Construction Journal pp 82 - 83

"The manufacturing processes of every module begin with the production of the base (foundation), the walls, and the tops simultaneously. By doing this the company assures that the walls and tops will be ready to assemble when the process needs to take place. The plumbing operations starts with the module base and after the walls and the tops are assembled; part of the plumbing is finished. The electrical part of the process begins after the walls are in place and ends after the top assembly is finished. After all the plumbing and the electrical operations are finished, the exterior work begins. The interior drywall operations then take place including all the waiting times due to several steps in drying and sanding. Final quality control is performed at the very end of the final finishing step.

A complete time study was done with follow up of different modules throughout the entire facility. Also additional system performance information was obtained from historical production information from the company data"

Fig : Current State Value Stream Map of the manufacturing facility of the Modular homes


2.3.1 Evaluation of the Current Value stream Map (VSM):

The existing manufacturing process work stations are nine in number.

The current value added time is calculated thus: summation of all the cycle time (C/T) of the individual process work station:

90 + 90 + 45 + 60 + 120 + 205 + 240 + 320 + 300 = 1470 mins

The queuing time is calculated in hours and the C/T is calculated in mins.

The current total lead time of project calculated thus: summation of all the C/T of the processes and the queuing time of the WIP inventory:

90 + 60 + 90 + 60 + 45 + 60 + 60 + 120 + 205 + 240 + 320 + 60 + 300 = 1710 mins

The takt time of the manufacturing = Real production line = 1470

Customer Demand 4.5

= 326.7 mins

Observation of WIP inventory queuing.

Very large batch sizes at the ending line of the production.

2.3.2 People involved:

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- Production Management, - Production, - Suppliers, - Customer, - Team heads of the processes, - The process Operators.

2.3.4 Lean Proposal for the Future State VSM:

The major observation from the current state VSM reveals large batch size down the line of production at the Drywall and Final finish stations. This has led to long lead time for the production.

Hence, the following improvements have been proposed implementing lean thinking to achieve a better Future state VSM.

Reduction of the batch size in the following process stations: Electric, Exterior, Drywall and Final finish. The batch sizes were reduced to nine (9) each and this also consequently reduced the production lead time.

Introduction of Kanban for the suppliers. The suppliers can be done daily; this will enhance the information flow and coordination between the organisation and the supplier. The Kanban will also initiate necessary pattern of schedule and delivery for the production supervisor's control.

The reduction and elimination of the WIP inventory queuing along the process flow and introduction of supermarket Kanban for the station so that there will reduced unnecessary daily motion to the production supervisor.

A pull system FIFO is also introduced to enhance a continuous flow material through the work station.

Introduction of Kanban between the production supervisor and the despatch in other to keep accurate record of the completed productions in other to have on-time delivery.

After the Implementation of lean with continuous improvement of the Current VSM, the improvement of the Future VSM can be seen in the table and graph below:

Table: Improvement on the Current VSM showing the Future VSM of the Manufacturing facility of Modular homes.

Chart : Improvement on Process lead time of the Current VSM showing the Future VSM of the Manufacturing facility of Modular homes.

Table : Overall Percentage improvement measure Current Vs Future VSM of the Manufacturing facility of the modular homes


Implementing lean with continuous improvement using VSM tool has achieved improvement in the manufacturing. Introduction of the pull system and elimination of the WIP inventory will facilitate proper continuous flow of materials. The C/T reduction from the reduced batch sizes has also reduced the total lead time of production.

Another achievement of the large batch size reduction is the quick observation of defect during the inspection. So the rework level and scrap quantity is reduced. The lean waste of defects is eliminated.



Multiple handling can be defined as a system in a manufacturing where there are more than one products/parts to produce or there are more than one material resource handled during the manufacturing process. Having a lean thinking, wastes such as defects, unnecessary motion and inventory maybe associated with manufacturing with multiple handling. Implementing sustained lean thinking will bring solution.


Terry Hill, "Manufacturing Strategy - Text and Cases" Second edition ISBN 0-333-76222-3 pp 470

Outline of Manufacturing Process in SANTAL (SA)

"Santal (SA) is a subsidiary of the Albi Group, a French-based conglomerate with manufacturing plants throughout Europe and North America involving aerospace parts and automotive parts production.

Santal has three major moulding processes for the manufacturing of the machine parts for both aerospace and automotive. These moulding processes are compression, injection, and transfer moulding. Represented below is the manufacturing data on the sample of aerospace parts and automotive products.


3.3.1 Histogram:

The problem reported in this case is that of multiple handling of different parts of products using different manufacturing processes. Hence being lean thinking, the large data sets has been summarised in a graphical form using the histogram. Comparison is also made as regards type of process used and the quantity of product.

From the histogram, all aerospace products are manufactured by

compression moulding with a total of = 1500 tonnes.

The total output of products from automotive products equals 3535 tonnes accounting;

compression moulding = 1635 tonnes

Transfer moulding = 1190 tonnes

Injection moulding = 710 tonnes


The differences in volumes of manufacturing outputs have been shown aerospace and automotive parts as well as the moulding processes within the automotive products. Lean is implemented here by splitting the plant layout into two having differently, the automotive section and the aerospace section.

3.4.1 Facility Layout:

Aerospace Section:

There is a single compression moulding processing in this section. Hence a Process-oriented Layout is implemented.

This reduces the internal transportation within the sector as processes have close proximity

There is a better utilisation of the machines.

This will facilitate flexibility which is moving people where and when there are needed.

There will also be equipment flexibility in allocation of tasks.

Automotive Section:

There are different moulding processes here and this section has relative low-volume and high-volume end. Hence a Group Technology/Cellular Layout is implemented. This will comprise the thre moulding process and hence the following are achieve:

Team attitude which is involvement and commitment to work.

Increase in flexibility as everyone in the team is involved and skills can be moved from one place to another.

Visibility in the layout will be established such that one can see what is happening and help out in case of problem anywhere.


The 'Muda' in the form of underutilisation will be reduced. After implementing lean, there will also be good utilisation of space and internal transportation reduced while the lean is continuously sustained.



In lean manufacturing, a frequent machine breakdown constitutes waste of lead time in the production, large amount of rework and sometimes the increased cost of production.

Don Tapping et al in 'Value Stream Management, pp 40' has illustrated 'Cost plus versus price minus' in the cost reduction principle as being more efficient in lean thinking to maximise profit in terms of cost.

Elimination of waste associated with frequent machine breakdowns using lean is illustrated in the case study below.


"Personal experience at Mek-Mak Printing Press Umuahia Nigeria. The company's business is full press printing. The process flow starts from design artwork, through colour separation, Lithography, impression and packaging. The impression machine breaks down frequently and there are large paper destroyed during each breakdown in the process"


4.3.1 People Involved:

In creative problem solving improvement process, the problem needs a strategic decision level approach and being an involvement thing, it has to be a team brainstorming exercise which includes:

- Production managers, - Production supervisors, - Operators, and - Suppliers.

Firstly, the five 'w' in lean problem solving is applied,

What is the Problem? - There is frequent machine breakdown in the impression work station

When does it happen? - It occurs during morning shifts

Who is responsible? - The impression printing operator.

Where does it happen? - At the impression stage of the printing.


4.3.2 Cause and Effect Diagram (Ishikawa Diagram):

This is a process improvement tool which has been used to highlight where the problem is, discover and create a list of possible causes of the problem.

After the brain storming, it has been discovered that the main causes of the problem relates to:

The switching of shift from night to morning and

Type of thickness of material used in the morning shift.

4.3.3 The 5 Why's?

Furthermore the 5 Why's are used to determine the root cause of the problem.

The main cause is the Shifts switch from Night to Morning


Because the operator in the morning shift used paper.


Because it is the material he saw on shop floor


Because he assumed the paper on shop floor is required to continue the job.


He is not aware card was used on machine at the last night's shift and he did not adjust the machine setting.


He did not see any record of previous night's job on machine.

The root cause has been identified as the lack of visual management in the company and also at the work stations.


The following VCS are implemented and visualised properly for everybody to see clearly:

Process Control: This is the overall processing from customer at order and back to customer at delivery.

Work Control: This is scheduling and flow of material visualized in other to keep the operators informed.

Equipment, Fixture and Tool Control: This informs the operators what equipment is needed.

5'S is implemented to sort out materials not needed on shop floor, arrange, clean and sweep the workstation. It is continuously sustained in the process.


Untidy workstation can constitute distractions in the workstation. But the use of the VCS which is a powerful lean tool and 5'S created a continuous improved visual management, hence mistakes of not adjust machine which leads to frequent breakdown is prevented.