Throughput perspective

The throughput perspective deals with the alleviation of system constraints to ensure maximum rate of production. The system can be viewed as a chain of interdependent links that work together toward a common goal. Overall performance of the chain is governed by the strength of the weakest link. Therefore, improvement activities that do not focus on the weakest link are considered to be wasteful. This is important to understand because organisations consist of complex systems with an almost infinite number of improvement opportunities, which must be executed with a limited amount of resources; resources must therefore be focused on the fundamental opportunities.

The chain analogy provides inherent prioritisation of the fundamental opportunities, because the weakest link must always be the focus of improvement activities. This link is known as the constraint and is responsible for the prevention of maximum process throughput. The constraint can either be external or internal, but external constraints such as the vendor or market are not within the scope of this roadmap; internal constraints are located in the organisation because of operations with limited capacities that govern flow. Throughput is therefore defined in this perspective as the rate of production, and does not consider sales as defined in the value perspective.

Phase 1: Constraint exploitation

The system has one immediate constraint that must be identified and exploited in order to streamline operations and improve throughput. Various basic techniques can be utilised for constraint identification, but the most effective technique is to find the operation with the longest cycle time; this is the operation with the lowest throughput.

Exploitation activities can be initiated once the constraint is identified; standardised work, visual management, and the 5-S movement provided the foundation for these activities. The constraint must be made transparent so that people know where to focus their attention. Exploitation activities must only use available resources and people in order to decrease the workload or increase the throughput of the constraint.

Decrease the workload of the constraint through the elimination of insignificant work, or work that can be performed by other operations; even if these operations are less efficient, the workload of the constraint is reduced to increase throughput. Then make sure that the input to the constraint is free of defects, and also that the output of the constraint is within conformance; quality is discussed in detail in the next perspective.

Chapter 6 The theory of perspective Industrial Engineering Page 154 Increase the throughput of the constraint with more efficient practices. The simplest approach is to ensure that the most productive and skilled person is assigned to the constraint. Also train several people in the skills required for constraint operation to guarantee a functional constraint even when some people are absent. Furthermore, continue to execute standardised work, visual management, and the 5-S movement.

Phase 2: Process flow

Process flow is important to support the constraint and to encourage additional waste elimination activities. Operations must therefore be connected in terms of physical location and information so that work can be passed from one operation to the next without wasteful activities such as transport and delays. However, these connections lead to operations that are more dependent on each other; so when one operation shuts down, the next also shuts down. This creates a certain amount of discomfort, but it also creates a process in which people are forced to think and solve problems.

Process flow should run on an unbalanced schedule. The purpose is to ensure that other operations support the constraint with their additional capacity. This means that scheduled work must be performed as fast as possible when orders are received. Once an operation is completed the operator can clean the work area, help other team members, or execute other improvement activities. Some people attempt to balance resources to takt time, which is the minimum rate of production required to meet customer demand, but the problem with this approach is that every operation in the process can become the constraint if there is variation in the process, demand or products. Take note that resource utilisation must be optimised, and not maximised.

Phase 3: Kanban pull system

The kanban pull system is used to control the flow of work through the process based on customer consumption. This system produces what is needed, based on a signal (kanban) that connects information between operations. The purpose of the kanban pull system is to replenish buffers between operations with the same amount of work that was removed. These buffers are used to protect the process from variation and minimise overproduction, which is often used to compensate for problems that might surface when flow is created. Inventory buffers are therefore a waste, which must be removed once a predictable degree of variation is reached and the process is stable.

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