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| Value Stream Mapping
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| Introduction |
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Powerful yet simple, no other tool can outline and distinguish the true value of a product as VSM can. Business cases, payback periods, and other management tools do not necessarily add value to products. However, understanding the proper flow of that product and maximizing value throughout the stream can eliminate many costly errors. The beauty of value-stream mapping is found in its usefulness and simplic-ity. VSM helps answer the question: How do we continuously improve in a capable, sustainable manner? VSM is a map that outlines the current and future state of a production system, allowing users to under-stand where they are and what wasteful acts need to be eliminated. The user then applies lean manufac-turing principals to transition into the future state.
Promoted and instituted by Toyota Production Systems, VSM immigrated into North America in the 1990s. VSM is a pencil-and-paper tool that helps users see and understand the flow of material and information as products make their way through the value stream. The value stream includes the value-adding and non value-adding activities that are required to bring a product from raw material through delivery to the customer. In other words, VSM is an outline of a products manufacturing life cycle that identifies each step throughout the production process.
The overall goal of VSM is to move from batch and push to one-piece flow and pull through the entire value stream. The ultimate goal is to design and introduce a lean value stream that optimizes the flow of the entire system - from information, to material, to finished goods arriving at the customer's door. Lead-time, inventory, and over-production are therefore reduced; throughput, efficiency, and quality are im-proved.
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| The current state |
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Where do we begin this mapping and how does it work? Developing the map requires the user to draw a series of icons, each representing a different stage in the value stream. There are three distinct icon types: material flow, information, and general icons. Material flow icons represent stops in the manufacturing process (machines, assembly stations), outside sources (factories), inventories, push arrows, truck shipments, etc. Information lines are used to connect material flow icons to form a complete and united production sys-tem. The lines represent all types of information flow, including manual, electronic, kanbans, go-see scheduling, and load levelling
Now that the current state of the value stream has been mapped, waste throughout the stream must be identified and eliminated to shorten lead-time and improve the value-added percentage - in other words, to transform the production system from a batch and push into a one-piece flow and pull.
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| The future state |
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The future-state map is easy to develop but requires determination and persistence to implement. This said, the development of the future-state map is critical to provide a blueprint to the ideal state of lean. There is a method to developing the future state.
The first step requires the calculation of takt time. Takt time is the number of units required by the cus-tomer per unit of time. To calculate takt time, use the following formula: takt time = (net operating time / period) / (customer requirements / period). Note that takt time is not cycle time. However, for a lean proc-ess, cycle time plus a small efficiency standard should equal takt time.
The importance of takt time lies in the goal of producing one unit just in time to replace a unit used by the customer - in other words, a cycle time based on one-piece flow. If cycle time exceeds takt time, the process will generate WIP, waiting, excess motion, damage, and other waste. Again, changes inside de-partments, machine cells, and warehouses most likely will be required to promote one-piece flow and ensure that takt time is met.
Reducing cycle time and creating one-piece flow leads into the next future state question: Where can the production system use continuous flow? An example of continuous flow is an automated assembly line. The automation forces one-piece, continuous flow. True, the line most likely can be stopped - since continuous flow does not imply 100 percent efficiency - but the nature of the automation forces line support and engineers to balance the operation and ensure continuous flow.
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