There are different sets and subsets of value stream mapping (VSM) techniques. These are often techniques individually adapted to specific problems. In general, authors have viewed their creations as answers to their specific problem rather than as generally applicable tools. Hines and Rich identified and characterized a total of seven different value stream mapping tools [13] that served as possible candidates for ameliorating percutaneous transluminal angioplasty (PTA) and stent placement procedures in the university hospital’s interventional radiology department:
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1.
Process (activity) mapping
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2.
Supply chain response matrix
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3.
Production variety funnel
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4.
Quality filter mapping
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5.
Demand amplification mapping/Forrester effect mapping
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6.
Decision point analysis
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7.
Overall (physical) structure mapping (by volume or value)
The industrial origins of these tools (see Table 1) include engineering (1 and 5), action research/logistics (2 and 6), operations management (3), and two relatively contemporary tools (4 and 7). None of the tools was specifically developed for the hospital environment [13].
Table 1 Origin of mapping tools as proposed by Hines and Rich [13] Process activity mapping
Process activity mapping (sometimes also more generally referred to as process mapping) is a technique for streamlining workflow. Process mapping in general refers to activities involved in defining exactly what a business entity does, who is responsible, to what standard a process should be completed, and how the success of a business process can be assessed. After successful process mapping there should be no uncertainty regarding the process.
This technique can be used to eliminate waste, inconsistencies, and irrationalities from the workplace while providing high-quality goods and services easily, quickly, and inexpensively. It is a general approach that includes five stages:
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1.
Study of process flow
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Identification of waste
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Consideration of a better flow pattern
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4.
Consideration of whether the process can be rearranged in a more efficient sequence
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5.
Consideration of whether everything that is being done at each stage is really necessary (and what would happen if superfluous tasks were removed?)
Supply chain response matrix
This tool was first developed and applied in the time compression and logistics industry and is also known by a variety of different names (e.g., time-based process mapping). In the past decades it has gained increasing importance in the globalized textile supply chain industry. This mapping approach seeks to emphasize in a simple diagram the critical lead-time constraints for a particular process. In a horizontal plot the measurements of the product are shown both internally and externally. The vertical plot depicts the average amount of standing inventory at specific points in the supply chain. From supply chain response matrices individual lead times and inventory amounts can be identified and targeted for improvement activity.
Production variety funnel
This approach originates from operations management. The production variety funnel is also called IVAT analysis, which regards internal operations as conforming to I, V, A, or T shapes:
I plants consist of unidirectional, unvarying production of multiple identical items such as a chemical plant.
V plants consist of a limited number of raw materials processed into a wide variety of finished products in a generally diverging pattern. V plants are typical in textiles and metal fabrication industries.
A plants need many raw materials and have a rather limited range of finished products with different streams of raw materials using different facilities; these plants are commonly observed in the aerospace industry or in other major assembly industries.
T plants produce a rather large variety and combination of products from a rather restricted volume of components and resources. Semi-processing parts are often held ready for a wide range of customer-demanded final versions. T plants are characteristic of electronics and household appliance industries.
A graphical delineation using the production variety funnel allows the creator to understand how the company or the specific supply chain operates and how the accompanying complexity can be managed. In addition, production variety funnels can be used in inter-industry research to better understand similarities and differences or to transpose knowledge from one industry (where more research is conducted) to another with rather scarce research.
Quality filter mapping
This mapping technique is a rather new tool designed to identify where quality problems exist within a supply chain. The resulting map depicts three possible types of defects:
The first type is the “product defect.” Product defects are defined as defects in goods produced that are not caught by in-line or end-of-line inspections and are therefore passed on to customers.
The second type of quality defect can be termed “service defect.” Service defects are forwarded to a customer but they are not directly related to the product itself. The defect is rather the result of the accompanying level of service: major service defects can include inappropriate delivery (late or early) and incorrect documentation (e.g., instruction manuals). In general service defects summarize any problems customers may experience that are not due to production faults.
The third type of defect is often called “internal scrap.” Internal scrap refers to defects produced in a company that have been identified by in-line or end-of-line inspection. The inspection methods will vary and can include traditional product inspection, statistical process control, or poka-yoke (ポカヨケ, Japanese; method of preventing errors by putting limits on how an operation can be performed to force the correct completion of the operation).
Each type of defect can be mapped along the supply chain. The rate of defects is usually given on a vertical plot in parts per million (PPM) on an exponential scale.
Demand amplification mapping/Forrester effect mapping
This technique originates from the systems dynamics work of Forrester and Burbidge: The “Forrester effect” was first described in a Harvard Business Review article in 1958 [14]. This effect is linked primarily to delays and poor decision-making concerning information and material flow. The “Burbidge effect” is linked to what is now usually known as the “law of industrial dynamics,” which states:
“ …if demand for products is transmitted along a series of inventories using stock control ordering, then the demand variation will increase with each transfer” [15].
As a result, excess inventory, production, and capacity can generally be detected in unmodified supply chains. Furthermore, it is a known shortcoming of everyday business life that manufacturers are sometimes unable to satisfy retail demand even though on average they may produce more goods than they sell. In a supply chain setting it is therefore known that manufacturers seek to hold—in some cases voluminous—stocks to avoid this dilemma. The use of various mapping techniques loosely based on Forrester and Burbidge’s pioneering work is now quite common to overcome this shortcoming.
This simple analytic tool can be used to demonstrate how demand changes along the supply chain respective to time and procedural steps. This information can then be used for decision-making and further analysis to redesign the value stream configuration, manage and reduce fluctuation, or set up dual-mode solutions, where regular demand can be managed in one way and exceptional or promotional demand can be managed in a separate response pattern.
Decision point analysis
Decision point analysis is of particular use for “T” plants and for supply chains and industries that exhibit similar features. The decision point in the supply chain occurs where actual demand pull gives way to forecast-driven push. At this point, production is no longer related to forecasts.
Gaining an understanding of where in a supply chain this point may be located can be useful for two reasons:
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It is possible to access the processes that operate both downstream and upstream. Thus, one can ensure and control that they are adequately aligned with the relevant pull or push philosophy.
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From a long-term perspective, it is possible to design various “what if” scenarios to view the operation of the value stream if the decision point is moved. This allows a better design of the process itself.
Physical structure mapping
This rather new tool has been developed to elucidate what a particular supply chain looks like at an overview or industry level. This knowledge assists in appreciating industry-specific characteristics of processes in general and their realization in a business entity in particular.
Physical structure maps are widely applied in the automotive industry and are often a combination of two diagrams:
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The first diagram depicts the structure of the industry according to the various ties that exist in both the supplier and the distribution area, with the assembler located in the center. This physical structure map provides an ample industry map that captures most firms involved, with the area of each part of the diagram proportional to the number of firms in each set.
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The second diagram visualizes the industry in a similar way with the same sets of organizations. However, instead of linking the area of the diagram to the number of firms involved, it is directly linked to the value adding (VA) process (or more strictly to the cost-adding process).
Thus, physical structure analysis can be focused at the complete industry or supply chain structure. Analysis may result in a redesign of how the industry itself works. Attempts can be made to eliminate unnecessary activities, simplify or combine necessary but non-value-adding activities, and seek sequence changes that will reduce waste.