“A coil spring is simple, yet deceptively complex,” said Greg Hazard, Senior Manager of Product Development for Hyperco. “Look at a spring, and then look at a transmission, a shock absorber, or a brake system. Clearly, the spring is a simple component. It’s only one piece. But, to make a high-performance spring that does the things we ask of it is difficult and complex.”
To dive deeper into what makes a spring perform as intended, we asked Hyperco to share with our readers the process that goes into manufacturing these coiled wonders.
To make a high-performance spring that does the things we ask of it is difficult and complex. – Greg Hazard
A spring begins its life as a design birthed by an engineer. In addition to the 1,200-plus off-the-shelf offerings from Hyperco, the company also creates custom springs. Whether it’s a custom spring or a new one intended for the masses, engineers need to balance several factors to determine how a spring will perform. Sometimes, those attributes conflict with one another.
Attributes, such as free length, solid load, rate, total deflection, inside diameter (ID), and outside diameter (OD) are all important. Still, it is not always possible for the customer to specify a discrete value for each one, especially with tight tolerances on the most important specs. For example, if a customer wants a specific load at a particular spring height, then they can specify either the free length or the rate, but not both. Since manipulating one affects the other, it is a balance between matching the critical specs and allowing the less-than-critical specs to end up where they need to be.
As with many other manufacturers, Hyperco primarily uses high-tensile, chrome-silicon steel wire for its suspension springs in motorsports, from IndyCar to dirt racing to off-road to street performance. The material’s high-tensile strength — the ability to resist being pulled apart — makes it well suited for suspension springs.
The opposite of tensile strength is compressive strength. You may think that compression is more important than the tensile strength with a spring — after all, you typically compress, not pull apart, a spring. However, in essence, a coil spring is a torsion bar wound into a cylinder. Just like a torsion bar, as you compress a coil spring’s length its material twists, which tries to pull it apart.
Coiling Option 1
Hyperco uses one of two methods to form a spring: lathe coiling or CNC coiling.
The traditional method of lathe coiling uses a series of feed rollers to pull the wire into the machine, which then gets drawn around a spinning mandrel. As the wire gets pulled along, guiding arms set the pitch and the final form.
“It lends itself to small volume runs,” said Hazard. “It’s not ideal for high production, because it’s a slower process. It also doesn’t allow flexibility for design.”
Coiling Option 2
For 98-percent of Hyperco’s springs, the company uses CNC coiling.
“CNC coiling gives us a lot of flexibility in varying the coil diameter, pitch angle, and end factors of a spring,” said Hazard.
The CNC coiler uses tooling built in-house, digital commands in the form of a step-by-step program created by the machine’s operator, and decades of experience to turn the wire into the final form of a spring.
It can take several hours to set up a machine for a run. Rarely, does Hyperco make a run of two similar types of springs consecutively. While experience certainly makes the setup process quicker when manufacturing a particular coil spring again, even the slightest tolerance variations in materials require the operator to adjust the program to ensure the springs meet Hyperco’s standard of a 2-percent tolerance in rate linearity.
First Stress Relief & Press
Right after coiling, the spring goes through a stress relief operation. The process heats up the spring taking the stress imparted on it during the forming process and distributes it throughout the diameter of the material. This makes the spring’s performance more predictable as it goes through its travel.
After that, they compress the spring to the point it is solid to lock-in the result of the stress-relief process.
The spring’s ends are then ground flat. This is especially critical for coilover springs, which require a level surface for that spring to sit on. If the ends were uneven, it would cause unnecessary sideload (friction in the shock on a coilover application) and result in a spring that may not deflect evenly.
Next, they shot-peen the springs. Essentially, this involves throwing tiny ball bearings at the surface of the spring.
“It compacts the surface, barely a couple of thousandths-of-an-inch thick,” said Hazard. “The reason why it works so well is the highest stress points of compressing a spring through its travel are on the outside of the material.”
Imparting compressive stress — the opposite of tensile stress — increases the longevity of the spring. This gives the spring more ability to endure tensile stress, increasing the spring’s longevity to meet Hyperco’s lifetime guarantee of rate and height.
Stress Relief and Press Again
Since the two previous steps imparted additional stress, the springs once again goes through stress relief.
“It’s just a light stress relief,” Hazard said. “This stress relief is very touchy because you don’t want to negate the compressive stress that you put into it. Its goal is to remove any stress concentrations.”
Then, just as with the first stress relief, they compress it to solid to lock-in all the changes.
When a batch of springs goes through the process, Hyperco inspects several pieces from the run to ensure they hit all the specs. These tests include rate (or loaded height, if that is the critical spec), free length, perpendicularity of the ground ends to the centerline of the spring, degrees of grind, and other attributes vital to the intended application. This list can change depending on whether the spring is intended for the Hyperco catalog or a specific customer or implementation.
Hyperco powdercoats its springs in-house, typically in the distinctive Hyperco Blue, and then they get laser-etched with the logo, part number, and date code.
From there, it gets packaged to ship to retailers or directly to the customer for custom orders. When racers go to install the springs, most don’t realize how much work went into creating the relatively simple component. However, many do understand its worth.
One of the least expensive components on a race car, yet has one of the most important jobs. – Justin Cockerham
“Kelly Falls [Hyperco Vice President of Motorsports & Performance Aftermarket] often talks about how disproportionate the cost of a spring is, relative to what it does on a race car,” said Hyperco Motorsports Manager, Justin Cockerham. “For something that costs $100, it’s arguably one of the least expensive components on a race car, yet has one of the most important jobs for the vehicle’s performance and handling.”