Key Terms

  • Buffer

    Due to variability, the demand flow and the process flow never perfectly synchronize and some sort of buffer is required when matching process output to demand. The only buffers available are:

    • Inventory—transformation occurs before demand
    • Time—transformation occurs after demand
    • Capacity—above the average demand. Extra capacity mitigates the need for inventory and time buffers.
  • Capacity

    The capacity of a process is the maximum output (throughput at the end of the process) as determined by the resource that has the highest long-term utilization.

  • Constraint

    In Project Production Control, a constraint is a predecessor task that must be completed in order for work to flow through the process.

  • Flow

    A Flow is described by a rate. The measure of a flow some unit per unit of time (e.g., barrels per day). The rate of flow is called its throughput.

    A flow can be a set of operations called a process that accomplishes the transformation. A flow can also be a set of individuals creating the demand for the transformed entities.

    Sources: “Factory Physics”, Third Edition, Wallace J. Hopp and Mark L. Spearman, Waveland Press, p 203
  • Inventory

    Inventory is the accumulation of entities that occurs anywhere within and/or between processes (flows).

    Inventory between two or more flows is called stock while inventory within a flow is called work in process or WIP.

  • Kingman’s Equation (VUT equation)

    In queuing theory, a discipline within the mathematical theory of probability, Kingman's formula is an approximation for the mean waiting time in a queue in a system with a single server where arrival times have a general (meaning arbitrary) distribution and service times have a (different) general distribution. It is generally represented as CT = VUT, where CT is Cycle Time, V is a factor representing variability, U is a factor representing utilization, and T represents the mean effective process time.

    Sources: Factory Physics, Third Edition, Wallace J. Hopp and Mark L. Spearman, Page 288
  • Line of Balance

    The "Line of Balance" (LOB) is a graphic device that enables a manager to see at a single glance which of many activities comprising a complex operation are "in balance" - i.e., whether those which should have been completed at the time of the review actually are completed and whether any activities scheduled for future completion are lagging behind schedule. History: LOB was devised by the members of a group headed by George E. Fouch. During 1941, the Goodyear Tire & Rubber Company monitored production with LOB. It was successfully applied to the production planning and scheduling of the huge Navy mobilization program of World War ll. LOB proved to be a valuable tool for expediting production visibility during the Korean hostilities. During this period, defense suppliers used LOB

    Sources: Line of Balance Technology: A graphic method of industrial programming, US Department of Navy, April 1962
  • Little’s Law

    Little's Law defines the relationship between system throughput (TH), cycle time (CT), and work-in-process (WIP). CT = WIP/TH. Cycle time is a dependent variable. WIP is a leading indicator of CT.

    Sources: Factory Physics, Third Edition, Wallace J. Hopp and Mark L. Spearman, Waveland Press, p 239, Queues, Inventories and Maintenance: The Analysis of Operational Systems with Variable Demand and Supply, P. M. Morse, Dover, 2004, p 22, A Proof for the Queuing Formula: L = lW, J. D. C. Little, Operations Research, Volume 9, Issue 3, pp 383-387, Little’s Law as viewed on its 50th Anniversary, J. D. C. Little, Operations Research, Volume 59, Issue 3, pp 536-549
  • Operations Management

    Operations Management is the application of operations science to real-world production, service, and distribution systems. This includes supply chain management as well. Operations management is concerned with the design, control and improvement of any organization’s operations.

  • Operations Research (OR)

    The application of mathematical (quantitative) techniques to the scientific study and analysis of complex systems and optimization problems of organization and coordination of activities in business operations and decision making.

    Historically the discipline emerged as the confluence of several different threads of scientific application. Charles Babbage conducted research into the cost of transportation and sorting of mail which were applied in the UK’s first postal system. To understand the best choice of railway gauge, he conducted studies into dynamical behavior of railway vehicles on a railway network. Military planners during World War 1 were concerned with the scientific planning and organization of logistics of supplies for troops (convoy theory and Lanchester’s laws). The field expanded with the Second World War conferring several problems for US and UK military planners resulting in the development (among other things) of linear and dynamic programming techniques, and other mathematical tools.
    Since then, the field has found application in many areas in transportation, finance, logistics and government.

    Sources: Introduction to Operations Research, F. S. Hillier and G. J. Lieberman, Eight Edition, McGraw- Hill, p3., Maynard’s Industrial Engineering Handbook, Fifth Edition, Kjell B. Zandin (ed.), McGraw-Hill 2001, p G.2
  • Operations Science

    Is the study of the transformation of resources to create and distribute goods and services.

    Operations Science (OS) focuses on the interaction between demand and production and the variability associated with either or both. OS also describes the set of buffers required to synchronize demand with production.

  • Process

    A process is a set of one or more operations designed to transform a set of entities into another form to achieve a particular purpose.

    The process begins with the accumulation of all the needed resources and proceeds through a sequence of operations until completion.

    Examples of processes include production lines, construction projects, hospital operating theaters, insurance claims processing, etc. Also called a Value Stream.

  • Production Control

    Policies, protocols and mechanisms to control transformational processes, the use of resources and variability.

  • Production System

    Any of the methods used in industry to create goods and services from various resources.

    Sources: Encyclopedia Britannica

  • Project Production Management

    The application of Operations Science theories, principles and methods to better understand, control and improve project delivery.

  • Station Cycle Time Formula

    The Station Cycle time formula states that the average cycle time at a station in a production system includes actual Processing Time (PT), as well as Move Time (MT), Setup Time (ST), Queuing Time (QT), Batch Time (BT) (CT=PT + MT + QT + ST + BT) Cycle time for an end-to-end process is CT = PT + MT + SDT + BT + QT where SDT represents the shift differential time.

    Sources: Factory Physics, Third Edition, Wallace J. Hopp and Mark L. Spearman, Waveland Press, p 327
  • Variability

    Variability is the term used to describe any dissimilarity between specific instances of a particular operation or process, particular entity output from an operation, or a particular Demand. The dissimilarity may manifest itself in terms of attributes of the entities/ operations or in the timing of those entities/ operations.

  • Work in Process (WIP)

    Work in process or WIP is the set of entities that are partially transformed within any given process. WIP does not include stock inventory which is composed of completed entities.

    WIP typically accumulates while waiting for available capacity in front of an operation. Stock accumulates between two or more processes (e.g., finished inventory between a process and its demand).