Lean manufacturing refers to a company's ongoing, systematic effort to eliminate the sources of waste in a production process. This article briefly notes the origins of lean manufacturing and summarizes eight causes of waste in the production process. It discusses five important lean manufacturing tools and examines how eight manufacturers are incorporating these tools into their production processes. Finally, the article lists seven advantages and seven disadvantages of lean manufacturing.
Keywords Cellular Manufacturing; Just-in-Time (JIT); Kaizen; Kanban; Lean Manufacturing; Manufacture
Manufacturing: Lean Manufacturing
Lean manufacturing refers to a company's ongoing, systematic effort to eliminate the sources of waste in a production process.
The seeds of lean manufacturing in mass production were planted as early as the 18th century, when a French gunmaker, Honore Blanc, implemented the time and resource-saving practice of using interchangeable parts for the assembly of guns. (Lienhard, 1999). However, Toyota Motor Company is generally considered to have spearheaded modern lean manufacturing by implementing the just-in-time (JIT) inventory system on a full-scale basis in 1938 (Toyota).
The Major Causes of Waste in the Production Process
Syddell (2005) notes that Brad Perkins, senior director, auto and industrial, for Oracle Asia Pacific, indicates that while there are many minor causes of waste in the production process, the major causes can be grouped into eight areas:
- Over Production
- Unnecessary Motion
- Processing Failures
Over production waste refers to the practice of making something for which there is no customer. (This was a very common practice before widespread adoption of lean manufacturing principles and is called "stockpiling." Many manufacturers still over produce as a safety measure. See also "Inventory" in this section.)
Waiting waste results from searching for tools, or from waiting for machine setup, materials or information. (Whenever production workers are idle due to waiting for necessary parts, equipment, or information, the efficiency of the production process is compromised.)
Conveyance waste involves the unnecessary moving of parts or information. (See also "Unnecessary Motion" in this section.)
Processing waste occurs when more work is done to an item than is required by the customer's specifications, or when data must be entered into multiple locations.
Inventory waste happens when assets are used to stock parts or products that have not been ordered by a customer. (The practice of building up inventory of products or parts is also known as "stockpiling.")
Waste from unnecessary motion includes time spent from performing extra movements, like walking to get the parts needed for assembly. (Unnecessary motion is similar to conveyance waste, but generally applies to workers while conveyance waste applies to extra movements of parts and data.)
Waste from processing failure refers to any time spent reworking defective components or products.
Space is wasted when more real estate is used than is required. Extra space also means more utilities and overhead required to manage the space.
Lean Manufacturing Tools
Of course, any technique or tool that reduces waste in a production process — whether it's developed in-house, copied from another company, or purchased from a supplier or consultant — can be considered part of a lean manufacturing strategy. However, the following five tools for reducing waste are commonly associated with lean manufacturing:
- Cellular Manufacturing
- Just-in-time (JIT)
The first lean manufacturing tool is cellular manufacturing. This strategy involves the arrangement of production work stations and equipment in a sequence that supports a smooth flow of materials and components through the production process with minimal transport or delay. Cellular manufacturing minimizes the time required to manufacture a single product by moving the product through the entire production process one-piece at a time, at a rate determined by a customer's needs. Cellular manufacturing is in direct contrast to batch-and-queue (also known as large-lot) production which involves processing multiple parts before sending them on to the next machine or process (United States Environmental Protection Agency, 2006).
The second lean manufacturing tool is JIT. The practice of JIT refers to the supplying of parts or items at the time that they are needed and not before. JIT can apply to parts or items supplied to the manufacturer or to the items that the manufacturer produces for its customers. In either scenario, JIT directly contrasts with the practice of building up inventory by stockpiling items.
The third lean manufacturing tool is kaizen. Kaizen is a Japanese term that refers to the process of continuous improvement, often in small, incremental steps. To be effective, kaizen must involve the entire workforce in its philosophy and practice.
The fourth lean manufacturing tool is kanban. Kanban is an integral part of the JIT production process; it is an information tool that specifies exactly which parts or items are needed during the production process and exactly when they are needed.
The last lean manufacturing tool is poka-yoke. Poka-yoke refers to error-proofing the production process during the design phase to eliminate faulty products altogether, or if that is not possible, to detect defects at the earliest possible moment in the production process.
In this section, we will examine how specific companies are incorporating the following five lean manufacturing tools to reduce waste in the production process and also see how one company has taken a unique approach to teaching the principles of lean manufacturing.
1. Cellular Manufacturing
- 2. Just-in-time (JIT)
- 3. Kaizen
- 4. Kanban
- 5. Poka-yoke
Cellular Manufacturing: Advance Turning
Advance Turning & Manufacturing Inc., a Michigan-based manufacturer to the aerospace and medical industries, has a high mix of job orders with low part volumes: it ships 1600 jobs monthly with an average volume of 70 pieces per job. To maintain a competitive edge in its marketplace, Advance Turning shifted from a production process that moved parts through multiple machines and operators to a one-piece-flow production process that utilizes 20 work cells to make parts one at a time until they are completed and ready for shipment. The cellular system allows cell operators the flexibility to run jobs with similar setup requirements and thus completely avoid breaking down the machine setups. Since the work cell arrangement incorporates in-process part checks by the work cell operators, Advance Turning has reduced the amount of scrap material and extra parts generated (Bates, 2006).
Just-in-Time (JIT): Hayward Industries Inc., General Motors Corp.,
JIT inventory systems are a hallmark of lean manufacturing. To be effective though, JIT depends upon implementation by both manufacturers and their suppliers. If the supplier can't provide the manufacturer with the parts and materials on a just-in-time basis, then the manufacturer is held up and may not be able to supply the customers on the as-needed basis dictated by a successful JIT strategy. This is particularly important if a natural or other disaster occurs to upset the delivery of items from supplier to manufacturer.
Katz (2007) provides examples of how three manufacturers — Hayward Industries...
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