LEAN PRODUCTION

A business system that requires less resource to make products with fewer defects to precise customer desires.

A business system for organizing and managing product development, operations, suppliers, and customer relations that requires less human effort, less space, less capital, less material, and less time to make products with fewer defects to precise customer desires, compared with the previous system of Mass Production.

Lean Production was pioneered by Toyota after World War II and, as of 1990, typically required half the human effort, half the manufacturing space and capital investment for a given amount of capacity, and a fraction of the development and lead time of Mass Production Systems – while making products in wider variety at lower volumes with many fewer defects.

Lean Production Methods

1. Pull System (Kanban): A method of production control in which downstream activities signal their needs to upstream activities. Pull System strives to eliminate overproduction and is one of the three major components of a complete just-in-time production system.

In Pull System, a downstream operation, whether within the same facility or in a separate facility, provides information to the upstream operation, often via a kanban card, about what part or material is needed, the quantity needed, and when and where it is needed. Nothing is produced by the upstream supplier process until the downstream customer process signals a need. This is the opposite of Push System.

2. Production Smoothing (Heijunka): Leveling the type and quantity of production over a fixed period of time. This enables production to efficiently meet customer demands while avoiding batching and results in minimum inventories, capital costs, manpower, and production lead time through the whole value stream.

With regard to leveling production by type of item, suppose that a shirt company offers Models A, B, C, and D to the public and that weekly demand for shirts is five of Model A, three of Model B, and two each of Models C and D. A mass producer, seeking economies of scale and wishing to minimize changeovers between products, would probably build these products in the weekly sequence AAAAABBBCCDD.

A lean producer, mindful of the effect of sending large, infrequent batches of orders upstream to suppliers, would strive to build in the repeating sequence AABCDAABCDAB, making appropriate production system improvements, such as reducing changeover times. This sequence would be adjusted periodically according to changing customer orders.

3. Continuous Flow (One-Piece Flow): Making and moving one piece at a time.

Producing and moving one item at a time (or a small and consistent batch of items) through a series of processing steps as continuously as possible, with each step making just what is requested by the next step.

Continuous flow can be achieved in a number of ways, ranging from moving assembly lines to manual cells. It also is called “One-Piece Flow”, “Single-Piece Flow”, and “Make One, Move One”.

4. Flexible Production (Shojinka): Shojinka means “flexible manpower line” and the ability to adjust the line to meet production requirements with any number of workers and demand changes. It is sometimes called “labor linearity” in English to refer to the capability of an assembly line to be balanced even when production volume fluctuates up or down.

The location of processing steps for a product immediately adjacent to each other so that parts, documents, etc., can be processed in very nearly continuous flow, either one at a time or in small batch sizes that are maintained through the complete sequence of processing steps.

A U shape is common because it minimizes walking distance and allows different combinations of work tasks for operators. This is an important consideration in Lean Production because the number of operators in a cell will change with changes in demand. A U shape also facilitates performance of the first and last steps in the process by the same operator, which is helpful in maintaining work pace and smooth flow.

5. Otonomation (Jidoka): Providing machines and operators the ability to detect when an abnormal condition has occurred and immediately stop work. This enables operations to build in quality at each process and to separate men and machines for more efficient work. Jidoka is one of the two pillars of the Toyota Production System along with Just-In-Time (JIT).

Jidoka highlights the causes of problems because work stops immediately when a problem first occurs. This leads to improvements in the processes that build in quality by eliminating the root causes of defects.

Jidoka sometimes is called autonomation, meaning automation with human intelligence. This is because it gives equipment the ability to distinguish good parts from bad autonomously, without being monitored by an operator. This eliminates the need for operators to continuously watch machines and leads in turn to large productivity gains because one operator can handle several machines, often termed multiprocess handling.

6. Total Productive Maintenance (TPM): A set of techniques to ensure that every machine in a production process always is able to perform its required tasks.

The approach is termed total in three senses. First, it requires the total participation of all employees, not only maintenance personnel but line managers, manufacturing engineers, quality experts, and operators. Second, it seeks total productivity of equipment by focusing on all of the six major losses that plague equipment: downtime, changeover time, minor stops, speed losses, scrap, and rework. Third, it addresses the total life cycle of equipment to revise maintenance practices, activities, and improvements in relation to where equipment is in its life cycle.

7. Single Minute Exchange of Die (SMED): A process for changing over production equipment from one part number to another in as little time as possible. SMED refers to the target of reducing changeover times to a single digit, or less than 10 minutes.

Shigeo Shingo’s key insights about setup reduction, which were developed in the 1950s and 1960s, were separating internal setup operations – which can be done only when a machine is stopped (such as inserting a new die) – from external operations that can be performed while the machine is running (such as transporting the new die to the machine), and then converting internal setup operations to external operations.

8. Continuous Improvement (Kaizen): Continuous improvement of an entire value stream or an individual process to create more value with less waste.

There are two levels of Kaizen:

Value Stream Mapping is an excellent tool for identifying an entire value stream and determining where Flow and Process Kaizen are appropriate.

(Resource: Lean Production, Ayperi Serdaroglu Okur; Lean Lexicon)