The Six Sigma strategy and the Lean Six Sigma strategy

Lean Manufacturing employs a range of powerful tools to eliminate waste, shorten time cycle, decrease cost and increase quality. Tools can range from simple to relatively complex ones. The basic tools of Lean are Process mapping, Value Stream Mapping, Spaghetti diagrams and Kaizen events as shown in figure 4 (Carreira et. al., 2006).
Figure 4- The Lean Manufacturing tools

Process mapping, provides a visual presentation of the process, step by step as shown in appendix A, figure 10. It presents the sequence of steps, from start to end, and aids in understanding the current status of the process. Process mapping helps management to identify the steps that are value added or non-value added (Gopalakrishnan, 2010).

Process mapping uses flowchart with many symbols including box, diamond, arrow, triangle, big D, ovals and circles. The box is the most commonly used symbol in the flowchart, and it represents an activity. It can include a word within it. The diamond represents an inspection, review, or decision, and demonstrates two possible outcomes: pass or fail. The arrow represents transport and direction of the flow. Triangles represent storage or filling; within the triangles words can be included. The big “D” represents delay such as bottlenecks, equipment breakdowns, batching and waiting for information. Ovals represent start and end of the process map, and circles represent a reference to another process.

Process mapping can be done at three levels of detail: Macro, Functional activity and Task procedure. Macro is the least detailed and includes two to seven steps. The Macro flowchart is applied at the beginning of a process improvement project, and, where the main parts of a process need to be illustrated (Refer to appendix A, figure 11).

Functional activity flowchart, also called deployment flowchart, contains moderate level of detail. It includes the job title, rather than department title, of people working in the process, as well as the activities or work performed by each individual (Refer to appendix A, figure 12).

Task procedure flowchart is the most detailed of all, and is usually used in situations where new activities are created, or where the problem keeps showing up at a certain box (Refer to appendix A, figure 13). It is also used for training or certification purposes like validating and testing procedures (Madison, 2005).

Another tool of Lean Manufacturing is Value Stream Mapping (VSM), which shows all the value added and non-value added actions currently required, to bring a product or service through the main flow’s essentials, i.e. in logical steps from start to end (Rother et. al., 2008).

However, the main purpose of VSM is to understand the value flow, which involves the design flow; from concept to launch, and production flow; from raw material to customer demand (Gopalakrishnan, 2010).
Spaghetti diagram is a simple yet powerful Lean Manufacturing tool used to visualize the work flow movement and transportation of a process. It is called Spaghetti diagram because the lines in the diagram resemble spaghetti lines as shown in appendix A, figure 14 (Sarkar, 2007). Spaghetti diagram helps to establish the layout of the process, by identifying, the path that a specific part or product travels, and also, the distance between documents, items, materials, or people. The purpose of this tool is to spot opportunities to reduce waste, and also decrease the distance traveled in the process, in order to increase the efficiency (Vincent, 2006).

Kaizen event is the most important tool of Lean Manufacturing. It is a focused set of actions, for applying or driving, one or more of the goals of an area in the manufacturing process. This tool will be further discussed in the Lean Six Sigma section (tools and techniques) (Wilson, 2010).

3.3.2 Advantages and Disadvantages of Lean Manufacturing
There are many advantages to implementation of the Lean approach; some of these advantages are discussed below:
Ӣ Lean Manufacturing maximizes customer value, as the project moves through its phases, and minimizes waste of materials and carbon dioxide emissions. It also leads to better products and more efficient production.
Ӣ The process reduces time of production, which means more products are made in less time, with minimal cost and fewer defects.
Ӣ It requires less human effort. Also, since the materials arrive on time, fewer or no on-site storage is needed.
Ӣ Lean construction enables more efficient construction; less space is occupied due to off-site assembly of items such as structural insulated panels, pre-cast concrete, structure steel, raised-access floors, movable walls, etc.
Ӣ Lean construction also reduces and manages any variability and vagueness in the project plan. It transforms a project from project definition into design proper by creating, identifying, and evaluating links between purposes, concepts and criteria required for improvement of Lean production in construction.
Other advantages of Lean Manufacturing, based on the ”˜nine principles’ mentioned previously, are highlighted below (cited from Bosch Rexroth Corporation (2007)):
”¢ In ”˜Continuous Flow’, using manual push or gravity conveyors, instead of belt conveyors, can minimize the complexity, and in turn can make them easy to service and reduce time. Also, it is easy to move workstations within a work cell since they are simply connected end-to-end.
”¢ Other benefits of ”˜Continuous Flow’ include elimination of non-value added movements and inventory.
”¢ The curved corners of U-shaped work cell in ”˜Continuous Flow’ can encourage batch process by acting as a mini storage area. This problem can be solved using ball roller transfer (as shown in appendix A, figure 15), to facilitate movement through the corners of the U-shape.
”¢ ”˜Lean Machines’ can provide a continuous improvement environment, due to quick production changeover, and customizable production. It also saves cost, and the environment, by using reconfigurable and reusable material in the machines.
”¢ ”˜Workplace Organization’ reduces wasted motion and interrupted work piece flow, by avoiding loss or misplacement of tools through separate tool holders for each workstation’s tools. It also minimizes the downtime, and improves quality, by using simple, easy to reposition and reusable information boards at the workplace.
”¢ ”˜Part Presentation’ reduces wasted motion, provides easy reconfiguration, and quick changeover. It also results in uninterrupted production, since gravity feed conveyors, bins fits and case lifters focus on continuous production, with minimum number of interruptions.
”¢ ”˜Reconfigurability’ in Lean Manufacturing provides uninterrupted work piece flow, and quick changeover that minimizes downtime, and therefore less production time is lost.
”¢ ”˜Quality’ allows immediate feedback on quality as workers inspect parts, and rapid change of quality gages, as assembled product or process changes. It also encourages changeover, eliminates rework areas, and provides platform for continuous improvement.
”¢ In Lean Manufacturing, ”˜Maintainability’ means easy source of replacing parts, quick service, and also minimum down time.
”¢ Easy serviceability, optimum ergonomic design, and minimum down time, are the benefits of ”˜Ease of access’, which is one of the Lean Manufacturing principles.
”¢ The principle of ”˜Ergonomics’ in Lean Manufacturing can result in better working environment, including lower employee turnover and fewer work-related injuries.
Even though Lean Manufacturing is mostly a beneficial process, there are a few disadvantages, which are listed below:
Ӣ Any disruptions to the plan can lead to difficulties in the next stages of construction, or even prevent the project from continuing. Such difficulties can increase the cost of the project.
Ӣ Significant loss of production can take place in case of an unforeseen setback in material delivery (Alarcon, 1997).