Pierce nuts clinch it over weld nuts for Dyson

When Dyson's designers set about coming up with a better washing machine, amongst the many products chosen were Profil clinch nuts to secure the adjustable feet on its base plate

In just a short period of time, domestic appliance manufacturer, Dyson has established a justified reputation for outstanding product performance and design innovation.

Its dual cyclone vacuum cleaner range has taken the market by storm.

So, when the company's founder, James Dyson asked his designers to come up with a better washing machine, nothing was left to chance - from the fundamental principles involved; which resulted in the new model's unique, contra-rotating drums - right down to the choice of Profil clinch nuts to secure the adjustable feet on its base plate.

Wiltshire-based Dyson employs around 2,000 staff at its Malmesbury headquarters and manufacturing site.

The modern plant houses the company's research and design facilities, as well as production lines for the established dual cyclone cleaner range and recently-introduced CR01 contra-rotating drum washing machine.

Four man-years and one million hours have gone into the development and engineering of this new product - not to mention the equivalent of 20 years normal usage into its testing.

It should therefore be no surprise that the finished washer both outcleans, and offers twice the throughput of its nearest rivals.

According to Andrea Coggins, the design engineer responsible development of the CR01's structural cabinet: "Stringent targets were established for every aspect of the machine's performance.

The same principle was also applied to the components used in its construction; including the internal side panels and base plate." Manufactured from pressed 1 mm sheet metal, these components are at the structural heart of the unit.

"In addition to being able to withstand the rigours of vibration, they also have to exhibit excellent corrosion resistance," Coggins explains, "which is why we decided to produce them from Zintec material." Another important function of the base plate is its provision of mounting points for the appliance's adjustable feet, which are employed to level the machine and ensure its stability in use.

When loaded, CR01 washers have an all-up weight of around 100 kg.

Accordingly, the unit's feet mountings - and rear mounted rollers - are called upon to withstand significant static and dynamic loads.

Not only that, but the fastening application is further constrained in terms of: a limited space envelope and the need for a near-flush finish; as well as the perpetual requirement for low installed costs and simple assembly methods.

The search for a suitable way to mount the feet pointed the Dyson team to investigate a number of assembly options.

Among the first to be considered, and discounted, was the use of weld nuts.

"Although a welded fastener offered a solution in principle, it would have necessitated us changing from the Zintec material we had already specified, to a mild steel pressing - with an unacceptable reduction in corrosion resistance," says Coggins.

"This led us to evaluate various rivet nut alternatives and ultimately resulted in the identification of pierce nuts as our preferred option.

"Our investigations indicated that this fastening method is widely employed throughout the automotive sector.

However, we were surprised that only one supplier, Profil, was able to offer a truly comprehensive range of products, backed by a track record of applications engineering experience." A further key requirement for the mounting points is that the screw-in feet must not 'chatter' or lose their adjustment as a result of machine vibration.

To overcome this, Profil recommended the specification of its RSF type pierce nuts, complete with standard nylon thread inserts - a solution that has subsequently proved entirely satisfactory in operation.

The first stage of the installation sequence is undertaken by loading the pre-formed Zintec base plates into a jig at a dedicated press station.

The Profil pierce nuts are then located by hand and subsequently pressed into position using purpose-design swaging tools.

"The mechanical forming operation results in very secure fastenings," notes Coggins, "which display extremely high resistance to pull out and torque loads." Following extensive prototype and pre-production runs using soft tooling, the CR01 went into full production during the fourth quarter of 2000.

To date, the fastening method has proved the ideal choice.

"Not only does Profil provide the best all round solution to our needs," says Coggins, "but it also offers us the option of further process automation - along with corresponding unit cost reductions - as we ramp up production to meet increases in customer demand.".

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