Lean manufacturing (LM) may be viewed as a systematic approach to identify and eliminate the waste (non-value added activities) through continuous improvement and synchronizing the production process to such an extent that flow of the product can be possible at the pull of the customer with emphasized focus on perfection (quality) in the pursuit of manufacturing excellence. Lean has been originally created and defined as the elimination of muda (waste) in the book The Machine that Changed the World by Womack, Jones, and Roos (Womack et al. 1990). Toyota production system evolved from the base of Ford manufacturing system with major emphasis on elimination of wastes and happens to be successfully used for improving system effectiveness.
In the lean philosophy, value is determined by the end customer. It means identifying what the customer is willing to pay for, what creates value for him. The whole process of producing and delivering a product should be examined and optimized from the customers point of view. So once value is defined, we can explore the value stream, being all activities both value-added and non-value added that are currently required to bring the product from raw material to end product to the customer. (Rother and Shook 1999).
Next, wasteful steps have to be eliminated and flow can be introduced in the remaining value-added processes. The concept of flow is to make parts ideally one piece at a time from raw materials to finished goods and to move them one by one to the next workstation with no waiting time in between. Pull is the notion of producing at the rate of the demand of the customer. Perfection is achieved when people within the organization realize that the continuous improvement process of eliminating waste and reducing mistakes while offering what the customer actually wants becomes possible (Womack and Jones 1996; McDonald et al. 2000).
Lean focuses on the big picture or improvements in the entire business process as opposed to incremental improvements. It is the business process system that can significantly improve a companys profitability. Lean concepts improve operating performance by focusing on the continuous flow of products, materials or services through the value stream. To achieve this, the various forms of waste must be identified and eliminated. Waste can include any activity, step or process that does not add value for the customer.
In order to improve efficiency, effectiveness and profitability, focus relentlessly on eliminating all aspects of the manufacturing process that add no value from your customers perspective. The core idea of lean
manufacturing is actually quite simple relentlessly work on eliminating waste. There are eight major forms of waste described as following Table 1: Table 1 Eight wastes of manufacturing
Lean has a very extensive collection of tools and concepts. Surveying the most important of these, understanding both what they are and how they can help is an excellent way to get started. There are a lot of great ideas to explore in lean. The following Figure 1 shows some of the common Lean Tools.
Figure 1. Lean Tools
In the following, few more Essentials Lean Tools or key concepts are given, which are associated with lean manufacturing. 1) 5S
3) Bottleneck Analysis
4) Continuous Flow
5) Gemba (The Real Place)
6) Heijunka (Level Scheduling)
7) Hoshin Kanri (Policy Deployment)
8) Jidoka (Autonomation)
9) Just-In-Time (JIT)
10) Kaizen (Continuous Improvement)
11) Kanban (Pull System)
12) KPI (Key Performance Indicator)
13) Overall Equipment Effectiveness (OEE)
14) PDCA (Plan, Do, Check, Act)
15) Poka-Yoke (Error Proofing)
16) Root Cause Analysis
17) Single Minute Exchange of Die (SMED)
18) Six Big Losses
19) SMART Goals
20) Standardized Work
21) Takt Time
22) Total Productive Maintenance (TPM)
23) Toyota Production System (TPS)
24) Value Stream Mapping
25) Visual Factory
Tools (methodologies) that are part of Lean are addressed in literature. In (McDonald et al. 2000; Rahn 2001), the pull technique of only producing what is required when it is required is used in the improved phases. The results are less rework and scrap, lower work-in-process, reduced lead time, increased throughput rate and higher service level. Other tools such as standard work (Cudney and Fargher 2001), quick changeover (Van Goubergen and Van Landeghem 2001; 2002), 5S (Henderson and Larco 2000), etc. can be referred to the works in the reference.
III. Value Stream Mapping
Value Stream Mapping is a method used for business process and product
improvement, which originated with the development of the Lean business philosophy. The value stream Mapping is the collection of all of the value-added and non value-added activities that generate the product or service that is required to meet the customers needs. A value stream map illustrates the flow of materials and information as the product or service moves through the process.
In contrast to the well-defined and rich set of lean tools and methods (Henderson and Larco 2000), as promoted by the Lean Enterprise Institute, there exist very few implementation methods. In recent years, value stream mapping (VSM) has emerged as the preferred way to implement lean. Value stream mapping is a mapping tool that is used to describe supply chain networks. It maps not only material flows but also information flows that signal and control the material flows. The material flow path of the product is traced back from the final operation in its routing to the storage location for raw material. This visual representation facilitates the process of lean implementation by helping to identify the value-added steps in a value stream, and eliminating the non-value added steps/waste (muda) (Rother and Shook 1999). Despite its success, VSM has some drawbacks:
(1) VSM is a ³paper and pencil³ based technique used primarily to document value streams. It is composed by physically ³walking ³ along the flow and recording what happens on the floor. This will limit both the level of detail and the number of different versions that we can handle.
(2) In real world situations, many companies are of a high variety, low volume type, meaning that many value streams are composed of many tens or hundreds of industrial parts and products. This adds a level of complication (and variability) that cannot be addressed by normal methods.
(3) Revealing as a VSM map can be (see Figure 1 and 2 as examples), many people fail to ³see³ how it translates into reality. So, the value stream map risks ending up as a nice poster, without much further use.
IV. SIMULATION AS PART OF VSM
(1) Simulation as a Cost Saving Tool
The use of a simulation model can help managers see the effects before a big implementation: the impact of layout changes, resource reallocation, etc. on the key performance indicators before and after lean transformation without huge investment (Van Landeghem and Debuf 1997, Rahn 2001).
(2) Simulation as a Training Tool
In most companies, especially when they are small, new concepts are hard to introduce. Simulation has proven to be a powerful eye-opener (Van Landeghem and Debuf 1997; Van Landeghem 1998; Whitman et al. 2001). By combining simulation with the visual map of VSM, we aim to achieve faster adoption and less resistance to change from the workforce. V. THE EXAMPLE
A mythical train manufacturer produces multiple products (general trains, fast speed trains, freight trains, etc.). We choose a core product family, general trains that exist in 3 different sizes large, medium, and small. After drawing its value stream maps (current state and future state), we build the simulation models representing these two maps. This example exists as a physical simulation game (VanbLandeghem and Dams 1995). By using the same example, we will compare in future experiments with simulation approaches.
There are two scenarios being simulated. The two supply chain networks that we simulate are shown in Figure 2 and 3. The first scenario or the current state is a MRP (Material Requirements Planning) based production system. There is a production control-planning centre, which generates the time schedule specifying the time (when) and the amount (how much) of materials, parts, and components that should be ordered or produced. The manufacturing processes (the rectangles in Figure 2) consist of material purchasing from suppliers, cutting strips, cutting A/B type strips, cabin assembly, chassis assembly, final assembly and shipping to customers. A typical characteristic of this kind of production system is the inventory storage points in between (the triangles in Figure 2).
Then, this last workstation starts fabricating the final product at the pace of takt time which is defined as the available production time divided by the rate of customer demand (Womack and Jones 1996; Rother and Shook 1999). When the parts are taken away from the supermarkets, this is the signal for the upstream workstations to produce new parts to supplement the parts taken away from the supermarkets. This upstream workstation then pulls from the next further upstream workstation, and so on all the way back to the original release of materials. Some features in the model are supermarkets, manufacturing cells (The layout of machines of different types performing different operations in a tight sequence, typically in a U-shape, to permit single-piece-flow and flexible deployment of human effort by means of multi-machine working (Rother and Shook 1999).), etc
Figure 2 Scenario 1 (Current State) A Push System
This review paper has provided a basic overview of the Lean Manufacturing tools and techniques. A more complete review and benefits of lean shows in Table 2. Modern Engineering is given closed look towards all the engineering processes like design, manufacturing, supplying and servicing of equipments and machines to the end customers. The faster and robust processes have always been boon of the industry; to cater the ever-changing taste and demand of customers. Prevailing volatile market condition compels the Industry to implement the various lean tools to meet the fierce competition erupted out of global competition, changing customer demands, pressure on time to market etc. Thus, industry may select VSM to as a viable alternative to enhance their competitive edge. To combat the above situations, Indian manufacturers are all have to implement the Lean Manufacturing System in a big way to join with the global users. VII. References
Askin R G & Goldberg J B, Design and Analysis of Lean Production Systems (John Wiley and Sons, New York) 2002, 352-406. Ohno T, Toyota Production System (Productivity Press, Portland) 1988, 75-80. 4Monden Y, Toyota Production System An Integrated Approach to Just-in-Time (Engineering and Management Press, Georgia) 1993, 80-102. Groover M P, Automation, Production Systems and Computer-Aided-Manufacturing(Prentice-Hall., New Jersey) 1980, 402-460. McDonald T, Van Aken E M & Rentes A F, Utilizing simulation to enhance value stream mapping: A manufacturing case application, Int J Logist Res Appl, 5(2002) 213-232 Simchi L & Kaminsky D P, Designing and Managing the Supply Chain: Concepts, Strategies and Case Studies (McGraw-Hill, New York) 2000, 280-312. Cudney, E.A. and J. Fargher.
2001. Using Standard Work in Lean Manufacturing, IIE Annual Conference.
Rahn, R. 2001. Lean manufacturing using Computer Aided Simulation, IIE Annual Conference.
Yang-Hua Lian, Hendrik Van Landeghem, An Application of Simulation and Value Stream Mapping in Lean Manufacturing