Toyota laid the foundation for development of lean after the Second World War, by introduc-ing the Toyota Production System (TPS). The basis of TPS was Eiji Toyoda’s instruction for his workers to eliminate all waste due to the shortage of materials and money after the war. He defined that everything else than minimum amount of resources (time, space, parts, equipment or material) required for adding value to the product, was waste. The actual development of TPS was done by Taiichi Ohno and his associates, who were working for the Toyota motor company. In the 1990s, manufacturers in the United States (US) and Europe started also im-plementing TPS under the name of just-in-time (JIT). The companies were forced to rational-ize their production to remain competitive against their Japanese competitors. (Pepper and Spedding 2010)
Lean extends the scope of TPS, but the key focus is still in the value stream of a single prod-uct. The target is to eliminate all waste, or muda, in the system. (Womack and Jones 2010)
There are seven forms of waste (Pepper and Spedding 2010):
1. Over-production 2. Defects
3. Unnecessary inventory 4. Inappropriate processing 5. Excessive transportation 6. Waiting
7. Unnecessary motion
In essence lean strives to maximize the flow of products through the process adding value to them. Womack and Jones (2010) define five lean principles of value, value stream, flow, pull and perfection as follows:
1. Value is defined by the customer;
2. The value stream is the set of all the activities that increase the value of the product;
3. Flow is making the transition between the value-creating steps of the value stream as smooth and uniform as possible;
4. Pull refers to pull scheduling in the production, as the production is adjusted according to the demand;
5. Perfection is the goal that is tried to achieve through continuous improvement.
Next some basic lean methods and terms are explained shortly. In addition to the methods pre-sented below, lean utilizes also techniques commonly used in quality management; Fishbone (ishikawa) diagrams, Check sheets, Control charts, Histograms, Pareto charts, Scatter dia-grams and Flowcharts. Kanban boards are also used as a lean tool for visual control. (Söder-quist and Motwani 1999)
VSM
The initial step of implementing lean is mapping the value stream of a product by the methods of value stream mapping (VSM). VSM is used to depict also the flow of information in the system, in addition of the obvious mapping of material and goods. First the current state of the system is mapped and the bottlenecks of the process are pinpointed in the map. To form a val-ue stream map of the desired state of the process possible solutions to the bottlenecks are gath-ered and evaluated by different methods. Traditional form of doing VSM is the “paper and pencil” –approach, where the value stream is sketched just by hand. There is also wide range of software for VSM available in the internet. The strength of these software based approaches is their ability to not only map, but simulate changes in the system. Thus the process developer does not have to go through trial and error when deciding about the possible changes in the system, but he/she can also base the decisions on the simulations.
After systematic VSM, the adoption of other lean tools, like single minute exchange of die (SMED), total productive maintenance (TPM) or 5S may be initialized.
SMED
The total time that is used to change batches in the production is referred as setup- or change-over time. Setup time is waste as it does not add any direct value for the customer. A produc-tion machine, or process, setup activities can be divided into two categories: Internal setup that includes all the activities that have to be completed when the machine, or process, is shut down and External setup that includes all the activities that can be completed while the ma-chine, or process, is running. Single Minute Exchange of Die refers to a setup time reduction technique where as much of the internal setup as possible is converted to external setup.
The basic steps of SMED are (KONE Lean, 2012) :
Document the setup and classify each element as either internal or external.
o Observe if the work element is planned accordingly, if better tooling is required or if the methods used are inadequate.
Change internal setup to external setup whenever possible.
o Focus on elements that stop the process.
Eliminate all possible adjustments required as part of setup routines.
o Quick-lock tooling.
o Mistake proofing.
o Visual control for ensuring correct parameters.
Streamline the external setup.
o Reduce the amount, or even eliminate unnecessary work.
The setup time should be treated just as any other process time and reduced by implementing the following steps:
1. Track the setup time
2. Find the best method of reducing it 3. Standardize the process two different approaches: Preventive Maintenance and Maintenance Prevention.
Preventive maintenance includes both periodic maintenance (done with regular intervals; year-ly, monthyear-ly, etc.) and predictive maintenance that is based on signals or diagnostic techniques that detect deterioration of equipment. Maintenance prevention in the other hand aims to de-sign and construct new equipment in a way that the occurrence of problems is minimized. Al-so improvements done to existing equipment with the same goal is categorized as maintenance prevention.
5S
5S refers to a systematic approach of organizing the work place and keeping it tidy. The name comes from the five steps of its implementation:
1. Sort
- Are the items in the work place:
a) Used frequently b) Used infrequently c) Not needed
2. Stabilize
- Mark a place for every tool and part - Keep everything in their assigned places 3. Shine
- Define person responsible for each areas cleanliness - Keep your area clean
4. Standardize
- Make check lists of the work phases and duties
- Create procedures to prevent equipment from breaking and unnecessary items from accumulating
5. Sustain
- Audit the cleanliness and tidiness - Check-ups
- Signs and posters - Newsletters
5S was originally developed to increase the efficiency of production and was applied on the factory floor level to the actual production lines, but it has been adopted widely also in the of-fices. There is also an extended version of 5S, called 6S, which incorporates safety as the sixth step and according to McClenahen (2006) Lockheed Martin utilizes it in its missile and fire control manufacturing plant in Camden, Arkansas.
Continuous improvement - Kaizen
Continuous improvement is based on the idea of sharing the right and responsibility for every-one to identify, reduce and eliminate waste on their work place. Usually this is realized as a suggestion box and a process for reviewing the received suggestions.
The original idea of Kaizen is to also include the person, or group, that made the suggestion in to the planning and implementation of the suggestion. Also a small task force of employees whose work is affected by the suggestion can be utilized. These task forces are called Kaizen groups.