Wednesday, 17 December 2014IMS HomepageHome

Process Charts

The charting of work flows, working processes, systems and procedures is a useful way of recording the essential features of a work situation for subsequent analysis.

Process Charts are one of the simpler forms of workflow charting and are still in regular usage but are less common than they once were (see Process Mapping). This is unfortunate since it was the ubiquitous nature of the process chart that made it a common "language" between different groups of people and across different industries.

A variety of process charts has been designed to meet the needs of a particular level or stage of analysis; they can be used at a detailed level (recording activity at a specific work station or workplace), but also at the wider system, process or procedure level.

The different kinds of process chart share a common core set of symbols, though some have additional symbols for specific and specialised process steps. The common symbols (of which there are only five) were first promulgated by the American Society of Mechanical Engineers and have become known as the ASME symbols.

Symbols


OPERATION:
a main step, where the part, material or product is usually modified or changed


INSPECTION:
indicates a check for quality or quantity



TRANSPORT:
the movement of workers, materials or equipment

STORAGE: controlled storage in which material is received into or issued from a store, or an item is retained for reference purposes

DELAY or TEMPORARY STORAGE: indicates a delay in the process, or an object laid aside until required

These symbols are simply linked together in a vertical chart representing the key stages in a process; it is usual to place a commentary in an adjoining column recording contextual/environmental information. e.g. against a Transport symbol would be recorded, start of journey, end of journey, distance and mode of transport.

The simplest form of process chart is known as an outline process chart and records an overview or outline of a process. Only those steps of a process that can be represented by the ASME symbols of operation and inspection are recorded. An outline process chart is often a useful first step to identify key areas of concern before recording (part of) the process in more detail.

In a "full" process chart, where all symbols are used, it is common to chart the process from the "viewpoint" of the material being processed, the worker carrying out the work or, less commonly, a piece of equipment. Thus, the same symbols can be used in different ways. As a simple example, a piece of equipment can be represented on an equipment-type flow process chart as a delay because it is not in use; while a material-type flow process chart of the same process would show the material being transported to the next work station, and a man-type chart could show the operator involved in another operation on another machine.

The chart to be used may be determined by the purpose of the investigation or by the relative costs involved in the process - a highly capital-intensive process may focus more attention on the equipment being used.

Process charts may also be used at a more micro level of analysis. An example is the two-handed process chart which records the motions performed by both hands during a task. The sequence of motion of each hand is charted using the same symbols as before. There are slight changes to the meaning of the symbols, however. The delay symbol is used to indicate that the hand is waiting to carry out its next task. The storage symbol is used to indicate that the hand is holding on to a piece of material or a document. Two-handed process charts are usually drawn on a pre-formatted diagram. Their use has generally been superseded by the analyses involved in the use of low level pre-determined motion times systems.

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