Integrating humans and automation increases plant productivity

Mitsubishi Electric has increased production efficiency at its Kani manufacturing facility by introducing a human element to previously automated assembly lines. Reintegrating a human element led to an 84% reduction in space, increased productivity and helped the factory react to changes in product demand.

The Kani factory, which is part of the company’s Nagoya Works in Japan, produces motor starters and contactors, and has 14,000 variations and possible configurations in its product range. Demand from customers for greater choice had diluted the volumes of each particular product, despite overall product quantities increasing.

Automation is not always the answer

In the past, the Kani factory had totally automated assembly lines which were ideal for mass production with few product variations where high yields could be realised at high speed. However, many individual components were required to be in stock and ready for the manufacturing process, without which the lines would not be able to run for any appreciable length of time.

Many assembly lines had been optimised to produce a limited range of products, and these would stand still when components ran out. It became difficult and uneconomical for the factory to produce small batches.

The company used the e-F@ctory concept and the e-F@ctory Alliance, CLPA and other collaborative engineering groups to address the issue.

After looking at the root cause of inconsistencies by analysing data, Mitsubishi Electric found that natural, normal, organic growth in the production process had inadvertently led to inefficiencies. It re-evaluated the need for 100% automated lines and realised that restoring some human elements could potentially reduce manufacturing anomalies.

Further observations revealed that the automated parts feeding of some larger components not only created a bottleneck, but led to the parts feeders consuming large volumes of space which could, under specific conditions, result in minor damage to the components.

Conversely, the automation of some tasks appeared possible through a combination of technologies. An example was the misalignment of certain screws during the assembly process. The automation system, unaware of the misalignment, would try to insert the screw and cause damage to the entrance of the hole.

Two technologies helped to overcome this problem: the automatic alignment of robots and combining rotational drives for inserting the screws using torque sensors. The hole can now be located easily and aligned correctly, and the torque sensor confirms the absence of misalignment and that the screw is tightened to the correct level. The increased use of vision systems, checking for correct assembly and alignment, has also helped increase the number of right-first-time products.

A further idea was to etch a matrix code on the body of each product and track it through the various stages. As the product arrives at a workstation, its code is read and the appropriate processes and parts applied. At the end of the manufacturing cycle, each product has a traceable manufacturing history, making it possible to track the history of individual issues.

Improving efficiency

By redesigning the process and reintegrating the human element, a single line that occupied 280 m² has been reduced to a cell of 44.1 m². This 84% reduction in space means that the productivity of each square metre of production hall has been increased through greater utilisation.

Although a single new cell cannot produce the same volume and speed of units as the original fully automated line, it is now possible to deploy up to 6.3 cells in the same space. This means total productivity density is much higher due to three key factors: a wider variety of products can be manufactured in smaller batches, one stoppage does not halt the whole of production and the total number of production lines has increased.

According to the company, the end result is effective optimisation of both machine and human resources, production process and space.

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