FEATURE SPRINGS & SHOCK ABSORBERS


SPRINGS: THERE’S A LO TO ENSURE MAXIMU


William Hughes has been manufacturing custom-made springs and


wire-forms for over 225 years. With its products still in high demand, we find out how the company manufactures its products – from prototype to the finished high performance spring – by tracing the journey of a compression spring commissioned by a major motor manufacturer


ave you ever wondered how many springs there are in the average family car? Hundreds – and many of them are made by the William Hughes Group. In fact William Hughes has been involved in the


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manufacture of custom-made springs and wire forms for over 225 years. Some say the company’s first involvement with modes of transport began with making springs for stagecoaches. Today, William Hughes has factories in Dorset, Bulgaria and Poland to cope with the demand for its high precision products.


CUSTOMER SOLUTIONS Springs of different sizes roll off the production line in both large and small quantities. As a result, compression, tension and torsion springs, all made to order, are solving a variety of particular problem for customers. As an example, let’s trace the journey of a small red 003 CTS compression spring commissioned by a major motor manufacturer. The company needed to improve the yield from its existing springs, which was running at about 80%. Manufactured from spring steel, this particular spring forms part of the accelerator mechanism of a car and is known as a ‘kickdown’ piston spring. So, the William Hughes engineering team


set to work to figure out how the company’s manufacturing processes could be employed to provide the necessary upgrade. Prototype springs were submitted for evaluation before being approved for bulk production.


THE SPRING MANUFACTURING PROCESS The first process in the manufacture of the upgraded spring was coil winding.


Explains William


Hughes’ engineering director, Emma Burgon: “Normally for our customers, the most important thing is load and a specific length. The loads on a spring, that is the force that it gives at a specific length, are directly proportional to the amount of wire in the spring. This ‘load at length’ is what’s important to the customer. We use the latest CNC technology not only to provide very consistent coiling accuracy but also to measure the free length of every single spring as it comes off the machine. The machine then uses the statistical process control to sort every single part, so we know that what is coming off the machine is good at this point to provide the tight tolerances demanded by our customers.” Any under-length springs are scrapped


while the good springs – normally around 98% of the batch – are stress relieved by passing them through an oven at typically 250˚C. Each spring is then ground flat at both ends using the bowl-fed automated Bennet Mahler grinding machine. The springs must achieve one million


A compression spring being tested for load on a PMZ load testing machine


44 DESIGN SOLUTIONS APRIL 2025


cycles from pre-load, so to extend their working life they are next subjected to a


A compression spring coming off a CFX2 coiling machine


An automatic bowl feeder feeding springs into a grinder and scragging machine


glass shot peening process. Burgon continues: “Shot peening is a mechanical process that de-stresses the surface of the spring, reducing the likelihood of fractures due to the formation of cracks. It creates compressive stresses which makes it harder for cracks to propagate. The surface of the spring is smoothed to obviate nicks, etc. “It is important that the shot peening gets


to the inside of the spring. In the shot peening process, glass beads are thrown at the springs with great force which has the effect of welding together imperfections on the surface, significantly increasing fatigue strength and extending the service life of the spring.” Next, the springs are put into a basket and dipped in a tank of a protective finishing agent called DeltaTone. This inorganic finishing treatment provides the springs with a highly flexible corrosion resistant coat which is coloured


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