When “Lean Thinking” – the blockbuster volume on “How to Implement Lean” reached the bookstores, the undertone in the book in principle was “just do it”. The authors of “Lean Thinking” (Womack and Jones, 2003), were quick to notice that this “just do it” approach had its flaws.
As in any transformation process, sticking to a prescribed formula is no easy feat. In their step-by-step transformation process description in chapter 11 of “Lean Thinking” (Womack and Jones, 2003), most overlooked is step 4: “Map the entire value stream for all of your product families”.
In “Learning to see” (Rother and Shook, 1999) the authors, Mike Rother and John Shook picked-up on exactly this weak point of “Lean Thinking” and presented a guidebook on mapping the value stream. Subsequently, comprehensive VSM reference books that were published picked-up on this rationale, including the recommendable standard work “Mapping the Total Value Stream” (Nash and Poling, 2008).
Value Stream Mapping, abbreviated VSM, is a technique used to define and optimize the various steps involved in completing a product or a service from start to finish. The application of VSM is also referred to as visualization of all steps in a work process. If done properly a value stream map not only takes into account the product’s inherent activities but also supports information flow and management processes.
Fundamentally there is a minimum of two mapping sequences: the current state and the ideal state mapping. Often the ideal state may be considered improbable, thus a future (in-between) state of a particular value stream may be mapped as well.
The VSM process is ideally conducted in the following order:
- Process selection: Ideally VSM is done on a suitable “aggregation” level, i.e., by product/product family, distribution channel or other particular business segmentation. Mapping everything that is going on in a business generally is not very helpful, such maps are overly complicated. Besides the physical flow mapping, most crucially the information flow has to be mapped. Commonly recommended is to commence with the physical flow first, beginning with the distribution of the final product and working upstream to the start of the process. However, as practical examples have taught me, depicting the information flow is often much more challenging and crucial overall to the business. As VSM combines the information flow into the physical goods flow process map I would recommend that one starts mapping with the important, interlinking information flow elements, as this defines the breadth and depth of a process to a great extent.
- Data collection: A further challenge in any mapping process is the collection of process data. Data quality and accuracy are crucial in order to derive significance in the determination of process and resource constraints.
As with any tool or technique VSM has undoubted advantages as well as disadvantages. VSM is not a catch-all multi-purpose tool that solves all process problems. It must be said that any issue not connected to the material or information flow is unlikely to benefit from a value stream map.
VSM is suited to relate manufacturing processes to its supply chains and distribution channels. It also allows the integration of material and information flows. In this context, it links production control and scheduling functions, i.e. production planning and shop floor control using operating parameters such as cycle and changeover timings. This information stems from routings or actual time recordings and forms the basis for the implementation of time-based capacity modeling by designing the production system based on the complete end-to-end flow time for a product family.
Further, it provides a company with a “blueprint” for strategic planning to deploy the principles of Lean Thinking for their transformation into a Lean Enterprise.
Limitations of Value Stream Mapping
So far so good, but Value Stream Mapping done in isolation will not produce meaningful results in a variety of scenarios. VSM might fail outright in scenarios with multiple products with no identical material flow maps. It also lacks economic measures for “value” (ex. profit, throughput, operating costs and inventory expenses). It is further inadequate in the display of the facility layout and its spatial structure.
Furthermore, it is unable to show the impact on WIP, order throughput and operating expenses of inefficient material flows in the facility, i.e., backtracking, crisscross flows, “non-sequential flows, large inter-operation travel distances and how that impacts inter-operation material handling delays, the sequence in which batches enter the queue formed at each processing step in a stream, container sizes, trip frequencies between operations, queuing delays, sequencing rules for multiple orders and capacity constraints” (Irani and Zhou, 2018).
When dealing with complex, multi-tier product BoMs with multi-level operation process charts Value Stream Mapping becomes confusing. A further limitation is a bias on high volume, low variety manufacturing systems – systems that typically favor assembly line setups, which are geared for continuous flow. In conjunction with this, it fails to consider the allocations and utilization of shop floor space, for WIP storage, material handling and production support.
Further recommended reading on this subject:
- Irani, S. and Zhou, J. 2018. Value Stream Mapping of a Complete Product. Columbus, OH 43210: The Ohio State University
- Nash, M. and Poling, S. 2008. Mapping the total value stream. Boca Raton: CRC Press
- Rother, M. and Shook, J. 2009. Learning to see. Brookline, Massachusetts, USA: The Lean Enterprise Institute
- Womack, J. and Jones, D. 2003. Lean thinking. 2nd ed. New York, N.Y.: Free Press