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For ‘spring’ think custom, not commodity

03 June 2010

While most engineers think of springs as high volume commodity items, customised products are available from progressive spring makers with the right technologies, expertise and willingness to adapt, as this Dorset based company has demonstrated

William Hughes has acquired its spring-making process knowledge over a period of 200 years, so when it comes to satisfying the particular requirements of individual customers, the company has a long pedigree to call upon. Today, specialists at its high-tech facility in Stalbridge maintain a close liaison with industry leading customers, developing innovative bespoke products – often on short lead-times – to solve an otherwise intractable problem.

A recent example involved a German automotive client, who needed to fast track a spring for seats fitted to a new two-door model. The front seat positions were deemed too difficult to adjust in order to provide access to the rear, and with the new model already in production, this oversight demanded immediate attention.

The automotive client’s tier one seat supplier approached William Hughes with a request for a customised spring within a four-week timeframe. Adding to the challenge, there were a number of constraints imposed by the customer, as Peter Korzilius, business product and development manager at William Hughes explains.

“The special spring had to be unseen, unheard and operate smoothly, avoiding catch points, and we could only use the existing holes and edges available within the seat structure mechanism. Furthermore, the solution had to comply with strict health and safety regulations regarding spring assembly procedures. This can be a potential hot potato for less experienced spring makers.”

Engineers from William Hughes invested a lot of time in the design office at the seat maker, where parameters such as extension force, track length, fitting space and mounting points could be assessed. Using high tensile wire less than 1mm in diameter, a special extension spring was designed to fit with minimum effort into the car seat structure without any modification to existing parts, thus ensuring continuity of production.

The spring features a black plastic coating to help suppress noise and pass the required BSR (buzz, squeak, rattle) test. The paint is applied at William Hughes’ plant in Stalbridge, where it is subject to dip-spin and oven cure. Finally, the entire length of the extension spring is covered in a thin plastic sleeve, partly to act as a damping facility to prevent it resonating like a guitar string, and partly to help prevent potential wear induced by rubbing against nearby parts of the metal structure.

Concurrent engineering ensured that the special tooling required for the prototype spring production was developed over a period of just three days, with the first springs being supplied for endurance testing within two weeks. Production capacity will need to be ramped up to some 1,400 units per day to meet demand, and this volume poses no problem for the Stalbridge plant. Mr Korzilius again:

“The project is a good example of what William Hughes is all about. We only make proprietary springs, we have no catalogue and we do not make for stock. We have built a reputation as a problem solving expert that works to customer requirements.”

In another automotive project, William Hughes was called upon to design a customised spring forming part of a spare seat latch mechanism for MPV-type vehicles. Strict regulations govern the securing of these seats into the body of the vehicle and they must not come loose when subjected to shock impacts. As Mr Korzilius explains, “There is a lot of spring technology involved in creating solutions of this ilk.”

Such has been the success of this bespoke spring design that it has now become a generic component. Indeed, it will be fitted to a growing number of new European-built MPVs introduced over the course of the next two years, and production volume levels are expected to reach millions per annum. This production will initially be supported in the UK but will eventually transfer to William Hughes’ production facility in Bulgaria. There is total compatibility between all of the automated CNC spring-making machinery both in the UK and in Bulgaria, ensuring that products and processes are fully transferable between sites.

Spring’s in the air
Springs manufactured by William Hughes are used in a growing number of vital systems used by the aerospace sector, including oxygen units, access hatches and the solenoid valves used to control hydraulic and cabin pressure systems. To meet the industry’s requirement for high temperature performance, many springs destined for these applications are manufactured from exotic materials such as Nimonic, Inconel and Ni-span.

When a tier one aerospace supplier wanted special springs for use in ventilation equipment supplying air to the cockpit of a European-built jet fighter aircraft, William Hughes stepped into the breach. A very tight four-day turnaround was imposed, and engineers at William Hughes worked over one weekend to design and manufacture the bespoke product, an effort that subsequently earned the firm a ringing client endorsement.

Back on the ground again, the company has also supplied bespoke springs to a manufacturer of seats for indoor and outdoor events. The customer approached William Hughes with a problem that a number of other spring manufacturers had been unable to solve. It wanted to extend its folding seat product range into a new market but this required a performance upgrade. To meet the standards for the new application, the pair of springs used to return the seat to the upright position needed to complete twice as many cycles, an increase from 50,000 to 100,000 operations.

The solution proposed by William Hughes was neat, simple and effective. One of the company’s specialities is the manufacture of springs using square section wire, a strategy that allows the section of the wire to be increased without increasing the overall dimensions of the spring.

To address the issue of the extended operational life, the springs were treated with a shot-peening process that enhances fatigue life. The result is a spring that is no bigger than the original round wire spring, but has double the operational life. But shot-peening is just one of several special manufacturing capabilities that William Hughes has to offer.

Others include the application of corrosion-resistant inorganic coatings, heat treatment, precipitation hardening, component assembly, ultrasonic cleaning and full quality control and inspection of finished parts, including the high-precision measurement of length, outside diameter, end coil profile, parallelism and squareness.

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