F1: the Sempre-smooth finish

Surface characteristics can determine a wide range of outcomes in different situations. The Sempre Group brings us the example of how the finish on the body of a Formula 1 car can influence the racer’s finish time, as well as how an engineered part’s surface will help influence its performance. Matt Parry, applications engineer at The Sempre Group, speaks to Natalia Bermejo, product specialist at Sensofar, about how manufacturers can benefit from optical profiling in research and development applications.

Key highlights

• Aerodynamics & part behaviour are affected by surface finish
• Surface finish determines a part’s interaction with its environment
• Interferometry as precise surface measurement
• Optical inspection mitigates the risk of part damage

Much like how aircraft are designed to reduce drag and have the most efficient shape for moving through the air, F1 racing cars follow similar principles to achieve the best aerodynamics in order to improve track performance. The overall shape and design of the car has the biggest impact on aerodynamics, but it goes down to a near-molecular level: paint with the wrong texture, or incorrectly applied layers that result in an uneven surface can negatively impact the aerodynamics of the car. Whereas for a people-carrier it may not be critical, for the high speeds and narrow margins that F1 cars operate in, the smallest difference can have a significant impact on the outcome of a race.

In a similar way, the surface finish of an engineered component directly determines how the part interacts with its environment — the component behaviour is influenced on both a micro- and nanoscale. Adhesivity, contact resistance, biological compatibility, friction, and mechanical wear are all characteristics that are influenced by the surface finish. Therefore, studying the surface can allow for predictions on component behaviour.

Surface measurement

Surface finish measurement is a vital step in assessing whether parts meet their intended purposes. It also enables manufacturers to adapt their manufacturing techniques before mass production.

“Choosing the right measurement tools is vital at this stage — using probes that touch the object could compromise the surface. Optical profiling is therefore the most common choice when checking surface finish. Unlike other methods of measurement, where manufacturers might use a sample for surface measurement, manufacturers can use optical tools on the component itself because it is not invasive.”

Interferometry

Measuring down to the nanometre is important, as even minor irregularities in the surface finish may impact the performance of a component. Areal surface characterisation is possible using interferometry (measurement using the interference of light, radio or sound waves), or optical inspection with devices such as the Sensofar 3D optical surface profiler.  By using a combination of Shifting interferometry (PSI), Extended Phase Shifting Interferometry (ePSI) and Coherence Scanning Interferometry (CSI) techniques, manufacturers can use the profiler to measure a range of surface characteristics.

“PSI is best for ultra-smooth and very flat, continuous surfaces, such as those on optical components. CSI is the most versatile mode, measuring smooth and rough surfaces with 1 nm resolution, and can also measure transparent layers with thicknesses from 1.5 to 100 microns. Meanwhile, ePSI which can be understood as a combination of PSI and CSI, is used for measuring smooth surfaces with structures, making it perfect for measuring features on wafers.

Interferometry has a high level of repeatability and accuracy and is faster than some confocal technologies, like laser confocals. By using this technique, engineers can produce topographies with a high number of measured data points, clearly showing the surface of intricate components.”

Measuring down to the nanometre greatly improves the surface characteristics of parts, whether this is the paint on an F1 car, or a component of a machine. Using optical profiling techniques means that the risk of damaging the part is mitigated. Although it won’t make you a better driver, and it’s far from the determining factor for how a racer will do, the surface finish on the paint is a definite contribution to the performance of an F1 car, as well as critical components.