Burr-and stress-free flat springs for safety critical applications

Precision Micro, Europe’s largest advanced chemical etching company, is reporting a significant upturn in demand for flat springs as a result of the increasing popularity of specialist Martensitic stainless chrome steels, such as Sandvik 7c27mo2, for this application.

As the fatigue properties of flapper valve steels continue to improve, focus is turning to the method of spring manufacture. Flatness, recoil and fatigue strength are enormously important in this stringent application; material properties that must not be compromised during spring production.

Conventionally, flat springs have been stamped or laser cut but both methods have limitations. Blanking creates deformation, stressing the material and compromising flatness. Laser cutting is a thermal process that causes heat stress and leaves rough edges that could be initiation points for fatigue fracture if not removed completely. Both of these manufacturing techniques generate burrs that need to be removed by tumbling… a process that can in itself mar the material surface finish and add additional process cost.

Despite these steels having excellent corrosion resistance, Precision Micro claims it overcomes all these potential problems with its standard chemical machining process. The process produces perfectly flat springs and imposes no stress on the material. The burr-free parts have an exceptional edge finish with no lips, pits or surface imperfections that could become initiation points for fatigue fracture.

In addition, the company is also able to offer 100% automated optical inspection (AOI) that ensures components are within agreed dimensional limits and identifies any surface imperfections in the material. This investment has been made as a result of long established customer ‘partnerships’ with leading automotive manufacturers, where flat springs are prevalent in safety critical applications, such ABS braking systems, suspensions systems and fuel injection.

Flat springs are expected to flex millions of times over many years and with market-led process innovations, Precision Micro is helping spring manufacturers achieve that objective.

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