Associate Professor
Department of Industrial, Welding and Systems Engineering
The Ohio State University
210 Baker Systems Engineering
1971 Neil Avenue
Columbus, OH 43210
Phone: (614) 688-4685
Email: irani.4@osu.edu
URL: http://www-iwse.eng.ohio-state.edu/ISEFACULTY/IRANI/IRANI.htm
Production Flow Analysis:
Production Flow Analysis (PFA) is a comprehensive method for material flow analysis, part family formation, design of manufacturing cells, and facility layout design that was developed in the early 70.s. PFAST (Production Flow Analysis and Simplification Toolkit) is a software tool that has automated the manual methods of Production Flow Analysis (PFA). In a typical application, Production Flow Analysis (PFA) is implemented in four stages - Factory Flow Analysis (FFA), Group Analysis (GA), Line Analysis (LA) and Tooling Analysis (TA). Each stage in PFA seeks to eliminate delays in production flows and operational wastes in a progressively smaller area of the factory. In Factory Flow Analysis (FFA), the flows between shops (or buildings) on the factory site are evaluated to eliminate wastes due to transportation, communication delays, use of large containers to store WIP and use of bulk-handling material handling equipment to move the large containers over large distances. In Group Analysis (GA), the flows between machines in each shop within the factory are evaluated to implement manufacturing cells to produce families of parts with identical (or similar) routings. In Line Analysis (LA), the flows between machines in each cell are evaluated. A layout for the cell is designed for efficient inter-machine material handling, multi-machine tending by individual operators and minimum wasted motions by operators. In Tooling Analysis (TA), the flows at each machine in a cell are evaluated to optimize the workstation layout for ergonomics of machine operation and rapid execution of setup activities, such as machine loading/unloading, tool changes, fixture changes, tool kitting and storage, parts inspection and cleanup.
Download white paper on Production Flow Analysis and PFAST.
Motivation for developing PFAST:
The fundamental motivation for the design and development of PFAST is the concept of Group Technology (GT) which seeks to identify and group together similar parts to take advantage of their similarities in manufacturing and design. GT has been practiced around the world for many years as part of good engineering practice and scientific management. Originally, GT was defined as "a method of manufacturing piece parts by the classification of these parts into groups and subsequently applying to each group similar technological operations" (Mitrofanov, 1966). A modern definition of GT is "the realization that many problems are similar, and that by grouping them, a single solution can be found to a set of problems, thus saving time and effort" (Shunk, 1987). This definition captures the true essence of GT that the population of entities or activities in a manufacturing system, or sub-system, can be replaced by a smaller number of families. However, the most general definition of GT is that "it is a manufacturing philosophy which identifies and exploits the underlying proximity of parts and manufacturing processes" (Ham, 1985). Part families are at the core of best practices, such as Variety Reduction, Standardization, Design For Flow, Flexibility, Agility and Reconfigurability, which are essential for "supercharging" the implementation of Lean Thinking in high-variety low-volume manufacturing facilities.
What is the relationship between GT and Cellular Manufacturing (CM)? CM is an application of the GT concept specifically for factory reconfiguration and layout design. Cellular Manufacturing Systems (CMS) have been erroneously promoted as the only layout alternative to replace the process layouts that are widely observed in job shops. This is because process layouts give a jobshop owner a false sense of mix and volume flexibility. Whereas, cellular layouts give a jobshop owner limited operational benefits of flow line production only for certain segments of his/her total product mix and customer base. CM involves processing a collection of similar parts on a dedicated group of machines or manufacturing processes. A Manufacturing Cell can be defined as "an independent group of functionally dissimilar machines, located together on the floor, dedicated to the manufacture of a family of similar parts". A Part Family can be defined as "a collection of parts which are similar either because of geometric shape and size or because similar processing steps are required to manufacture them". Usually, in a Cellular Manufacturing System (CMS), it is preferable that a cell be dedicated to a single part family, that each part family be produced completely within its cell, and that the different cells have minimum interaction with each other.
How PFAST facilitates Lean Thinking in Jobshops (JobshopLean):
PFAST facilitates the execution of two key steps in the 5-step Lean Thinking Process in jobshops and other high-variety low-volume facilities:
Step #2: Identify the Value Stream [PFAST facilitates this step by identifying product families in a product mix that could contain anywhere between 500 to 5000+ different manufacturing routings]
Step #3: Make the remaining value-creating steps in the Value Stream flow [PFAST facilitates this step by helping to design product-focused (or cellular) and POUS (Point Of Use Storage) facility layouts using manufacturing routings for components and Bills of Routings for assemblies, respectively]
To date, PFAST has facilitated the implementation of Lean Thinking in machining, pipe fabrication, forging, woodworking, cable manufacturing, electronic assembly and welding jobshops. In fact, PFAST makes it possible for any jobshop-type manufacturer (repair, welding/fabrication, foundry, machining, forging, etc.) in the high-variety low-volume sectors of industry to implement JobshopLean (JSLean). Recently, exploratory projects have been initiated to use PFAST to evaluate and re-design service facilities, such as offices, hospitals, warehouses and corporate buildings.
A demo of PFAST is now available for download at http://cast.cse.ohio-state.edu/pfast/. This demo is capable of processing an input data file with 50 routings (max). Ten pre-formatted Example datasets have been included with this demo version so that anybody who is interested can quickly run PFAST and study the various outputs that this "starter" version of PFAST produces. If you wish to analyze your own product mix, you will need to prepare and format your data as per the sheets included in the Template.xls file that is included with the examples. Please provide us your comments via the Feedback and Bugs pages at http://cast.cse.ohio-state.edu/pfast/.
How PFA complements Value Stream Mapping (VSM) and Extended Value Stream Mapping (EVSM):
Learning To See (ISBN: 0-9667843-0-8) and Seeing The Whole (ISBN: 0-9667843-5-9) are two pioneering books published by the Lean Enterprise Institute (www.lean.org). Both books describe a manual method - Value Stream Mapping - of mapping material and information flows at the factory level and the enterprise level, respectively. A Value Stream Map is a paper-and-pencil representation of every process in the material and information flow of a product within a single factory. Similarly, an Extended Value Stream Map is a paper-and-pencil representation of every process in the material and information flow of a product involving multiple factories (or firms) along the entire value stream from raw materials to end customer.
Based on my experience, I will unequivocally state that VSM fails miserably when it is required to segment and map large numbers of interacting value streams, especially in the case of families of parts with diverse routings and shared resources. Similarly, EVSM fails miserably when it is required to map the complete BOM (Bill Of Materials) for a product that has a material flow network spanning numerous suppliers, cities, even continents.
PFA can easily be used to map, identify and eliminate wastes and delays in the Value Stream of a complete product by analyzing its material flow network at various levels, as follows:
- Company (or Inter-Factory) Flow Analysis: The maximum delays occur when the components and subassemblies that constitute a final product assembly in the Enterprise must move across a network of Factories at geographically dispersed locations. Each Factory is usually supported by a large network of Suppliers at geographically dispersed locations.
- Factory Flow Analysis (FFA): Within each Factory, the longest delays occur when the components and subassemblies must flow between several Shops (or Departments) located on the Factory site.
- Group Analysis (GA): Within each Shop (or Department) in a Factory, especially if the Shop (or Department) has a Process (or Functional) layout, then the batch-and-queue flows of components and subassemblies within that Shop will cause significant flow delays.
- Line Analysis (LA): Within each Cell in each Shop (or Department), if the Cell is poorly designed, that could further delay the timely completion of the components and subassemblies that are produced in that Cell.
- Tooling Analysis (TA): At each Machine within each Cell in each Shop (or Department), an un-ergonomic layout of the Machine's footprint, combined with manual machine loading/unloading, long setups and non-standardized work, could further delay the timely completion of components and subassemblies that are produced on that Machine.
For Further Reading:
For more details on Production Flow Analysis, please reference the following book: Burbidge, John L. (1989) Production Flow Analysis for Planning Group Technology. Oxford University Press. ISBN 0-19-859183-7. In addition, there is a white paper that can be downloaded from the Home page at http://cast.cse.ohio-state.edu/pfast/.
For more details on the use of PFAST to design hybrid cellular layouts for jobshops, please reference the following book: Irani, S. A. and Huang, H. (2005). Hybrid Cellular Layouts: New Ideas for Design of Flexible and Lean Layouts for Jobshops available at www.zipedu.com/HCL.html.
For more details on the use of PFAST to do Product-Process Matrix Analysis, please reference "Value Stream Mapping for Jobshops" posted at www.lean.org/Community/Resources/ThinkersCorner.cfm). In addition, please read the section "The Product Family Matrix: Homework before Value Stream Mapping" in the article "Creating the Future State" posted at www.lean.org/Community/Registered/LEIFeatures.cfm.
For white papers and articles that describe actual industry projects on JobshopLean that were facilitated by PFAST, please visit the Success Stories page at http://cast.cse.ohio-state.edu/pfast/.
For more details on the architecture, algorithms and complete range of industrial applications of PFAST, please visit www-iwse.eng.ohio-state.edu/ISEFaculty/IRANI/IRANI.htm. In addition, please read the Overview of Applications on the Deployment Services page at http://cast.cse.ohio-state.edu/pfast/.