Value stream mapping
Value-stream mapping is a lean-management method for analyzing the current state and designing a future state for the series of events that take a product or service from its beginning through to the customer. A value stream focus on areas of a firm that add value to a product or service, whereas a value chain refers to all of the activities within a company. At Toyota, it is known as "material- and information-flow mapping".
Purpose of value stream mapping
The purpose of value stream mapping is to identify and remove or reduce "waste" in value streams, thereby increasing the efficiency of a given value stream. Waste removal is intended to increase productivity by creating leaner operations which in turn make waste and quality problems easier to identify.
Types of waste
Daniel T. Jones (1995) identifies seven commonly accepted types of waste. These terms are updated from the Toyota production system (TPS)'s original nomenclature:
- Faster-than-necessary pace: creating too much of a good or service that damages production flow, quality, and productivity. Previously referred to as overproduction, and leads to storage and lead time waste.
- Waiting: any time goods are not being transported or worked on.
- Conveyance: the process by which goods are moved around. Previously referred to as transport, and includes double-handling and excessive movement.
- Processing: an overly complex solution for a simple procedure. Previously referred to as inappropriate processing, and includes unsafe production. This typically leads to poor layout and communication, and unnecessary motion.
- Excess Stock: an overabundance of inventory which results in greater lead times, increased difficulty identifying problems, and significant storage costs. Previously referred to as unnecessary inventory.
- Unnecessary motion: ergonomic waste that requires employees to use excess energy such as picking up objects, bending, or stretching. Previously referred to as unnecessary movements, and usually avoidable.
- Correction of mistakes: any cost associated with defects or the resources required to correct them.
Waste removal operations
Monden (1994) identifies three types of operations:
- Non-value adding operations (NVA): actions that should be eliminated, such as waiting.
- Necessary but non-value adding (NNVA): actions that are wasteful but necessary under current operating procedures
- Value-adding (VA): conversion of processing of raw materials via manual labor.
Using the method
Value-stream mapping has supporting methods that are often used in Lean environments to analyze and design flows at the system level (across multiple processes).
Although value-stream mapping is often associated with manufacturing, it is also used in logistics, supply chain, service related industries, healthcare, software development, product development, and administrative and office processes.
In a build-to-the-standard form, Shigeo Shingo suggests that the value-adding steps be drawn across the centre of the map and the non–value-adding steps be represented in vertical lines at right angles to the value stream. Thus, the activities become easily separated into the value stream, which is the focus of one type of attention, and the 'waste' steps, another type. He calls the value stream the process and the non-value streams the operations. The thinking here is that the non–value-adding steps are often preparatory or tidying up to the value-adding step and are closely associated with the person or machine/workstation that executes that value-adding step. Therefore, each vertical line is the 'story' of a person or workstation whilst the horizontal line represents the 'story' of the product being created.
In software engineering
The success of Lean in manufacturing and production has led to an interest in its adoption in software development. However, it was noted that the current literature on adoption of Lean in software development had a disconnect between the high-level principles and the concrete practices related to lean and agile software development. The literature had also a limited focus on wastes that were literally mapped from the categories identified for manufacturing. This was ignoring the transformation that lean thinking has itself undergone and moved away from the focus on "removal of waste" to "creating and delivering value". The use of value stream mapping as suggested by the pioneer authors of the field Womack and Jones was identified as the missing link in the current literature on lean in software development.
Value-stream mapping analyzes both material (artifact) and information flow. The following two resources exemplify the use of VSM to do it in the context of software process improvement in industrial settings:
- "Artifact analysis": analysis of software artifacts like requirements, use case, change request or defect report through the development process
- "Information flow analysis": analysis of information flows in the development process
Associated analysis methods
Hines and Rich (1997) defined seven value stream mapping tools they are:
- Process activity mapping: the initial step of constructing a map which consists of a study of process flows, waste identification, and business process re-engineering.
- Supply chain response matrix: identifying critical bottlenecks for processes in a simple diagram.
- Production variety funnel: helps draw connections to other industries that may have solutions to existing problems.
- Quality filter mapping: locates product and service defects in the supply chain.
- Demand amplification mapping: identifies delays and material flow decision making errors. Also known as Forrester effect mapping.
- Decision point analysis: determines inflection points for push-and-pull demand in the supply chain.
- Physical structure mapping: combined model that overviews supply chain from an industry level.
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