Value stream mapping for effective lean manufacturing.

Vujica Herzog, Natasa ; Polajnar, Andrej ; Kostanjevec, Tomaz 等

1. INTRODUCTION

Lean manufacturing (LM) was developed by Taiichi Ohno at Toyota Motor Company in the 1950s. The publication of the book The Machine that Changed the World (Womack et al, 1990) started the diffusion of lean manufacturing practices first of all in automotive industry and later in all other industries from agriculture to aerospace.

Womack et al. (1990) defined 'Lean' as the elimination of waste and for this reason the main goal of lean manufacturing is the elimination of everything that does not add value to the product or service.

Although lean manufacturing have been around for a long time its use is again increasing recently. Lean manufacturing is nowadays frequently mentioned together with another quality improvement tools such as Six-sigma or Theory of constrains. The new approach believes that for an organization to label itself as strictly a Lean or e.g. Six-Sigma is a mistake. Being a company that is dedicated to continuous improvement and employs the best tool available for a given application is better. Continuous improvement has been around forever and is a part of any industry. The performance of the changes may be slightly different depending on the industry but the objectives are the same--to do what we do better, cheaper and faster.

In the paper the use of a very simple but also very valuable tool called VSM will be presented. VSM can help us to understand how the work site currently operates, design a lean flow and plan how to get there.

2. LITERATURE REVIEW

2.1 Lean manufacturing and its tools

In their book Lean Thinking (1996), James P. Womack and Daniel T. Jones defined a set of five basic principles that characterize a lean enterprise:

* Define 'value' from the perspective of the customer.

* Identify the 'value streams' and eliminate 'waste' from them.

* Create 'Pull'.

* Introduce 'Pull'.

* Strive to 'Perfection'.

The brief description of the most common lean tools includes:

* Cellular manufacturing: Organizes the entire process for a particular product or similar products into a group or cell, including all the necessary machines, equipment and operators. Resources within cells are arranged to easily facilitate all operations.

* Just-in-time (JIT): A system where a customer initiates demand and demand is then transmitted backward from the final assembly all the way to raw material, thus 'pulling' all requirements just when they are required.

* Kanbans: A signalling system for implementing JIT production.

* Total preventive maintenance (TPM). Workers carry out regular equipment maintenance to detect any anomalies. The focus is changed from fixing breakdowns to preventing them. Since operators are the closest to the machines, they are included in maintenance and monitoring activities in order to prevent and provide warning of malfunctions.

* Setup time reduction: Continuously try to reduce the setup time on the machine.

* Total quality management (TQM): A system of continuous improvement employing participative management that is centred on the needs of customers. Key components are employee involvement and training, problem-solving teams, statistical methods, long-term goals, and recognition that inefficiencies are produced by the system, not people.

* 5S: Focuses on effective work place organization and standardized work procedures.

2.2 Overview of VSM

A value stream is a collection of all actions (value-added as well as non-value-added) that are required to bring a product through the main flows, starting with raw material and ending with the customer (Rother and Shook, 1999; Abdulmalek and Rajgopal, 2007). These actions consider the flow of both information and materials within the overall supply chain. The ultimate goal of VSM is to identify all types of waste in the value stream and to take steps to try and eliminate them. While researchers have developed a number of tools to optimize individual operations within a supply chain, most of these tools fall short in linking and visualizing the nature of the material and information flow throughout the company's entire supply chain. Taking the value stream viewpoint means working on the big picture and not individual processes. VSM creates a common basis for the production process, thus facilitation more thoughtful decisions to improve the value stream (McDonald et al., 2002).

VSM is a pencil and paper tool or computer added tool, which is created using a predefined set of standardized icons (Fig.1). The first step is to choose a particular product or product family as the target for improvement. The next step is to draw a current state map that is essentially a snapshot capturing how things are currently being done. This is accomplished while walking along the actual process, and provides one with a basis for analyzing the system and identifying its weaknesses. The third step in VSM is to create the future state map, which is a picture of how the system should look after the inefficiencies in it have been removed. Creating a future state map is done by answering a set of questions on issues related to efficiency, and on technical implementation related to the use of lean tools. This map then becomes the basis for making the necessary changes to the system.

[FIGURE 1 OMITTED]

3. CURRENT AND FUTURE STATE MAP

VSM enables us to easily create, share and manage our processes. Current state mapping process can be summarized in the following items:

* Select a Product Family

* Form a Team

* Understand Customer Demand

* Map the Process Flow

* Map the Material Flow

* Map the Information Flow

* Understand Waste

* Identify and Eliminate Waste

[FIGURE 2 OMITTED]

The process of defining and describing the future state map starts with developing the current state map, where target areas for improvement start to show up. When designing the future state map the following topics should be considered:

* Key Questions

* Future State Icons and Examples

* Map the Future State Process Flow

* Map the Future State Material Flow

* Map the Future State Information Flow

* Outline a Plan

* Metrics

[FIGURE 3 OMITTED]

4. DISCUSSION

In creating the ideal future state map we try to identify lean manufacturing tools to drive the identified problems down, while looking at the schedule across the entire value stream. Inventory and lead time may be viewed as two related issues since the more inventories, the longer any item must for its turn and thus, the longer the lead time. We follow a systematic procedure where we try to answer a series of structured questions. In lean manufacturing understanding, identifying and elimination of waste is the key for success. Waste is anything that does not directly add value to the final product or contribute to the products transformation. There are seven basic types of waste known as COMMWIP what stands for Correction, Overproduction, Material Movement, Motion, Waiting, Inventory and Processing.

5. CONCLUSION

The presented VSM is one of the most effective and powerful tool that should be used at every improvement process in the company. It makes the flow of material and information visible and helps us to sort out what to keep and what eliminate and as such can be jointly used with any other quality improvement tool or methodology.

The future research could focus on simulation based VSM generators and thus make the decision processes about LM easier and more evident.

6. REFERENCES

Abdulmalek, F.A.; Rajgopal, J. (2007). Analyzing the benefits of lean manufacturing and value stream mapping via simulation: A process sector case study, International journal of production economics, 107, 223-236.

McDonald, T.; Van Aken, E.M. & Rentes, A.F. (2002). Utilizing simulation to enhance value stream mapping: a manufacturing case application. International Journal of Logistics: Research and Applications 5 (2), 213-232.

Rother, M.; Shook, J. (1999). Learning to see: Value Stream Mapping to Add Value and Eliminate Muda, The Lean Enterprise Institute, Inc., Brookline, MA.

Womack, J.P.; Jones, D.T. & Ross, D. (1990), The Machine that changed the World. Macmillan Publishing Company, Canada.

Womack, J.P.; Jones, D.T. (1996), Lean thinking, Simon & Schuster, New York.