Flow means producing without (or with minimal) batches, waiting, or wasted motion, in other words flow means that each individual product keeps moving either in the literal sense or in the sense of being continuously worked on.

The concept of flow has origins that predate TPS.

Henry Ford utilised scientific management theory to implement production lines and one-piece production in 1910.

Ford identified that there were two basic ways to build an automobile: one was to keep the automobiles stationary whilst moving the assembly workers around; the other was to keep the assembly workers stationary whilst the automobiles where moved around.

Keniche Sekine (1990, pp3-4) former head of the TPS consulting group describes the situation when Ford discovered the benefit of moving the automobiles around:

Recognizing how bulky and heavy automobiles were, Ford initially thought it better to follow the first concept (keeping cars stationary).

However, one day while looking for ways to eliminate waste from assembly processes, Ford noticed the following:

§ Waste in the scattered movement of workers

§ Waste in searching for, comparing and finding objects

§ Waste in conveying objects

After noticing these types of waste, Ford though long and hard about how he could eliminate them.

Finally, he hit upon the idea of mounting cars on a row of cars that could be pulled along by a rope and winch.

Right away he issued the following instruction to his employees:

1. Set up a large winch and a large thick rope to pull the automobiles along during assembly.

2. Since the factory was about 80m long, divide the assembly line into 15 one hour processes. This would allow the rope to pull all of the automobiles to the next process once per hour.

3. Distribute the assembly parts to their corresponding processes before they are needed.

4. Assign three or four workers to each process and work out the balance of labour by observing the assembly line.”

The experiment proved a big success. Sekine (1990) reports that assembly time per vehicle was reduced from 13 hours to just 5 hours from following the preceding 4 steps.

Ford had established a simple methodology for creating production flow, and almost 100 years later these for steps are evident in conventional techniques used to create production flow.

These techniques are detailed below

Production flow is a worthy prize for any manufacturer and to achieve it a number of things need to be in place.

Broadly speaking Womack et.al (2003) identifies the pre- requisites to achieve flow as:-

• A clear understanding of your customer requirement so that the production process can be organised to specifically achieve them.

• Production team with responsibility for adding value to the same product should be co-located, and move away from traditional production silos.

• Production equipment should be fit for purpose and well maintained to allow operation with minimal waste.

• Production processes should be standardised to ensure even, consistent paced work without production operators becoming overburdened, or operating in conditions of waste.

• Production employees should attempt to identify and eliminate all waste in production.

• Pull systems should be introduced to ensure that process only produces a good that the subsequent process needs.

• Visual management systems should be implemented so that production process abnormalities and the consequent countermeasure can be easily identified.

Additionally Muhlemann, Oakland & Lockyer (1992) identify the further requirements of:

§ Constant demand is required as flow systems are designed to achieve a specified output, if the output changes the lay out of the system will need to be changed in order to avoid the cost of inventory, or failure to meet customer requirements.

§ Standardised tasks need to be present to ensure that process variability is minimised and the production line can meet customer demand with minimum levels of waste.

§ Material inputs to the system must be on time and to the required quality, as disruption will cause the system to fail.

Flow allows the entire production process to be regulated by the natural laws of supply and demand.

It works by customer demand stimulating the production of a stock-keeping unit.

In turn the production of a stock-keeping unit stimulates the production and delivery of all the required components…and so on.

The result is that the right parts and materials are produced at the right time and delivered exactly when they are required; in the exact amounts they are needed. Production is ‘pulled’ by the customer rather than being ‘pushed’ by the capabilities (or limitations) of the production system itself, as detailed in this History of Lean article.

Traditionally the physical manifestation of flow production process is the moving production line.

However using a technique called ‘line balancing’ we can get the benefits of a flow line in a fixed assembly position. Sekine (1992) terms fixed assembly manufacture ‘gypsy production’ as the product remains in one place whilst workers move around it.

Line balancing means adjusting the spread of work evenly between people to the rate of customer demand.

In summary, flow production methodologies are not new, but do require a number of things to be in place before they can be implemented.

Reprinted with the kind permission of Barry Williams (MBA)