Saturday, April 19, 2014

Standard Operation and Standard Operation Sheets in Toyota Production System

Industrial Engineers, F.W. Taylor, Frank Gilbreth, Harrington Emerson and subsequently H.B. Maynard emphasized the need to employ standard operating procedures in Production and Distribution systems. In Toyota Motors, Taiichi Ohno implemented standard operations with the additional responsibility given to supervisors to ensure that there is improvement in standard operations periodically. The idea that operators and supervisors have to be involved more in operation improvement activities was advocated by Alan Mogensen, an industrial engineer and he named it work simplification. During second world war, American agencies created a training within industry system that emphasized improvement activities to be undertaken by supervisors. Japanese managers and engineers have absorbed all these ideas and Taiichi Ohno and other managers in Toyota Motors came out with world class implementation of IE principles and techniques.

We understand about IE in Japan through the books of Shigeo Shingo and Taiichi Ohno.

Standard Operation and Standard Operation Sheets

Taiichi Ohno wrote:

Standard work sheets and the information contained in them are important elements of the Toyota production system. Standard worksheet must be written in a manner that workers understand it.

In Toyota, standard work sheet is the basis for examining the resources used by an operation and eliminating waste (excess usage of resources), for improving machining processes and tools, installing autonomous systems, analyzing the need for transportation and methods of transportation, and for optimizing the work-in-progress at various steps in the process or operation. Standard work sheet will be updated by steps taken to prevent the recurrence of defects, operational mistakes, accidents and all ideas suggested by operators. Standard work sheet provides the basis for current execution and also for process and operation improvement.

The standard work sheet provides for effective and efficient combination of materials, workers and machines. This combination is termed as work combination in Toyota.

Standard worksheet contains three elements.
1. Work sequence
2. Cycle time
3. Standard inventory

The term work sequence in an operation refers to the various tasks carried out in an operation. It includes the worker picking the item, transporting it to the machine if required, mounting it on the machine, doing the operation, removing it from the machine etc. The job of supervisor, section chief or group foreman is to train workers. When the standard work sheet or work sequence is very clear, it should take only three days to train a new worker (say trained in general machining work) and workers quickly learn to avoid rework involved in producing defective parts.

Cycle time is the time allowed to make one piece or unit. It is actually standard time in the usual terminology. When there is difference between the actual time taken and the standard time, in most cases, it is due to  differences in operation motion and sequence. So a standard work sheet helps the supervisor to first check whether the operator is following the sequence and motions specified.

The concept of tact time is different and number of worker allotted to a group depends on the tact time. If the tact time is less more workers are allotted to a work cell and if tact time is more less number of workers are allotted to a work cell. But standard time for various operations performed by a work cell remain the same.

Standard inventory refers to the inventory kept before and after an operation. This inventory is kept to absorb fluctuations in output by the earlier operations or it could be the lot size inventory. Toyota production system is based on low inventory every where and therefore, the standard inventory has to be adhered to more rigorously.

Three Temporal Aspects of Standard Operations.

Shigeo Shingo describes the past, present and future aspects of standard operations.

Standard operation implies optimization of work conditions by analyzing

What is produced
Who - persons, machines, tools,and jigs
How - Method - machine speeds and feeds, man's movements
Where - Layout of the equipment and man - Work Station Design
When - Standard time, and Schedule

The Toyota production system insists that standard operation sheets are written by production people only. This refers to the past. This gives the engineer, supervisor, and workers of the shop an occasion to see what they are doing and facilitates operations improvement. So, from the idea that industrial engineer prepares the standard operation sheet, the responsibility is shifted to the production people. Industrial engineer may still make his contribution, but the final operation sheet is prepared and implemented by the production people only. It gets periodically improved even without the involvement of industrial engineers.

New workers are trained by using standard operation sheets. The workers keep referring to the sheet until they are familiar with the technique. So, there has to be a standard operation sheet by the side of the machine using which new workers are trained.

The Toyota system demands that all work is done within standard time and supervisor is charged with the responsibility. He has to train the worker. He has to determine the nonstandard motions responsible for the extra time. Thus the standard operation sheet helps in correcting deviations.

Also supervisor is responsible for improvements. A supervisor who has not improved the standard procedures in his area of work would feel embarassed in the Toyota culture.

The above is the explanation for the past, present and future of standard operation sheets by Shigeo Shingo.

Types of Standard Operating Charts

The standard operations system is more elaborate in TPS than normally described in traditional IE texts.

Capacity charts by part
For a part, the order of operations, operation names, machine numbers on which it can be processed, basic operation time, tool changing time, etc. are given.

Standard task combination
This sheet will describe the order in which individual worker's operations takes place.

Task manual
Task manuals described procedures for each element of the operation. For example, for machine operation, tool changing, set changes, etc.

Task instruction manual
It provides instructions for trainers who provide training to operators

Standard operating sheet
These sheets indicate order of tasks in an operation, cycle time, operation inventory, safety and quality instructions.

Source: Shigeo Shingo - A Study of the Toyota Production System from Industrial Engineering Point of View.

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