Conquering six sigma

Zero defects is the target of temperature control maker Ranco. Adele Kimber reports on the quest for quality

To the casual visitor, Ranco Control’s Plymouth facility might seem a typical example of British manufacturing. The plant makes a well established product – a temperature control for refrigerators – and has a mix of production lines, some highly automated but others labour intensive.

Nevertheless, when Ranco’s parent, the engineering giant Siebe, announced a global quality improvement programme late last year, the plant was highlighted as one of just three of its 150 operations world-wide that are examples of world class manufacturing and quality programmes.

Ranco is an illustration of the ultimate manufacturing standards Siebe wants to reach across the whole group. On some of its lines Ranco reaches the six sigma quality standard – defined as three or fewer defects per million.

Siebe has placed that six sigma level as the quality target for the whole group.

The six sigma method – named after the statistical symbol for standard deviation – establishes a system by which to measure products, services and processes, and improve quality.

The philosophy focuses on the idea that quality is free: the more you work towards zero defect production, the higher the return on investment.

It teaches the user a way of collecting and analysing data, and by combining the mean and standard deviation, a calculation of the sigma value of a process.

The higher the sigma value the better. When a process is said to be six sigma it is best-in-class, and such a level would yield only three defects in every million. When something is reckoned to be four sigma, it is average, yielding around 6,200 defects per million.

At Ranco Europe, managing director Sergio Frangi says the quality initiative will help the company move forward, but argues that the philosophy is already in place. Six sigma will offer a set of processes with which to understand the company’s quality standards more clearly and to understand what more can be achieved.

`It will help to teach us how to improve the details. It is an electron microscope instead of an eye glass,’ says Frangi.

He stresses that the technique by which it has been able to reach the six sigma standard on some of its lines are straightforward.

`We know that we are quite close to six sigma in many of our operations but the last part is the most difficult,’ he says.

The K Control is Ranco’s best known product, used mainly for temperature control in domestic refrigerators, as well as in cars and air-conditioning units. More than 25 million are produced each year and it has over 50% market share in Europe, and around 35% world-wide. More than 287 million have been produced since it was introduced in 1978.

In the UK, Ranco produces between 75,000 and 95,000 controls a day, and exports more than three-quarters of them. Most of the customers are global manufacturers, including Electrolux, Volvo and Bosch.

The K control is a capillary temperature control which uses a CFC-free vapour-filled sensor. As the temperature increases the fill expands; changes in pressure cause a bellows to expand or contract, actuating a lever system to trigger a switch. The switch activates or de-activates the compressor within the refrigerator.

Frangi says the manufacture of most of the elements for the K Control is between 100 and 50ppm defects.

`If things go unexpectedly wrong, the rate goes up,’ he says.

But the integrity of the control rests largely with the performance of the bellows, and the manufacture of the bellows capsule already operates at the six sigma level.

An automated welding technique for the capsule devised by Ranco has removed almost all quality problems and four automated K bellows manufacturing lines have been installed at Plymouth.

`Zero failure rate of the bellows is crucial. The K controls are tested to one million cycles and have never failed – the compressor in a domestic refrigerator withstands on average about 700,000 on-off cycles during its life,’ says Frangi.

Quality standards set by customers have played a significant part in Ranco’s approach to quality. UK general manager Pat Hayne is proud of its quality awards – all at the top level – from customers such as Ford, Electrolux and Hotpoint.

`Each of the customers has a very different approach to quality standards and they want to us to be able to meet their own specific criteria,’ he says. `We have a long history of high quality standards, and that is not isolated to production.’

A quality steering committee, made up of plant managers, production manager, quality manager and personnel and training manager, meets bi-monthly to set strategy and procedures for total quality.

A huge range of products on offer means that manufacturing must be flexible. Kits are made to order and very little is kept in stock. There are 10 models for domestic refrigerators available, but 2,800 variations, and they are offered in batch sizes of 100 to 100,000.

Manufacturing cells are dedicated to different models, with up to 50 cells working on controls for Electrolux. The aim is to give people working in the cells responsibility for the quality of the products which they produce.

`With the cell approach we can make hundreds of models just as easily as bigger batches – but there is some extra cost in the small batches and we have to be careful with smaller customers,’ says Hayne.

Frangi says an important element of Ranco’s approach to quality starts when automated machinery for its production lines are designed and built.

Much of the design and engineering of its manufacturing processes are carried out at Ranco’s Italian base in Lamazzo.

Higher labour costs in Italy mean that the Italian plant is more highly automated than those in the UK and technology is transferred to Plymouth once tried and tested in Italy, and once a realistic payback is possible.

But automation is not always a guarantee of high quality standards. `With increased automation, the risk of systematic mistakes is bigger, but you can put it right much more easily,’ he says.

`Continuous improvement is built in to everything we do. Last year, for example, defects from a brazing operation went up. Two ideas from Italian and British engineers were used to solve the problems and reduce the failure rate,’ says Frangi.

Transferable quality standards are important to Ranco, as its customers increasingly operate on a global basis. A recent deal with Electrolux, worth £40m over three years, means controls will be manufactured around the world to a common standard.

`We have invested a lot in automation in the last few years to reduce costs and improve quality. We ensure that we design our machines in such a way that manufacturing facilities can be set up anywhere,’ he says.

The challenge for Ranco is to push more of its production to the six sigma level. `It is very difficult to drive the final defects from the last system – from five and a half to six sigma,’ says Hayne.

`Six sigma sets a clear target for quality and gives us a positive measurement of what we are achieving,’ he says.