Surface Flatness Measurement in Precision Manufacturing

The precision manufacturing of parts used in many types of machinery and vehicles increasingly requires that the surface flatness of mating parts be assured. Surface flatness is essential for achieving higher fuel efficiency, lower emissions, and higher-horsepower-to-weight ratios in all types of manufactured vehicles. Surface flatness of a few tens of microns is required to minimize the potential leakage of combustion gases, coolant and lubricants in advanced engines. Efficient transmissions that are a key component of advanced vehicle powertrains must also have micron-level surface flatness to ensure proper operation that optimizes fuel efficiency.

The importance and benefits of achieving improved mating surface flatness cut across all classes of vehicle powertrains: passenger cars, light and heavy trucks, busses, construction vehicles, farm equipment, recreational vehicles and others.




Surface flatness measurement has been performed for decades using incomplete, even sparse, and slow measurements to estimate the dimensional characteristics of mating surfaces. But accurate surface flatness measurement requires dense high-definition sampling of the surface, just as accurate measurement of any widespread phenomenon requires an adequately thorough examination of all of the individual instances that comprise the population.

Modern proven surface flatness measurement technology now permits large surfaces of vehicle and machinery powertrain parts to be entirely examined with sampling densities of dozens of samples per square millimeter, so that a comprehensive “surface map” can be developed for powertrain mating part surfaces. Surface flatness measurement to an accuracy of 1 micron or better can be accomplished for a complete cylinder head, complete transmission valve body or casing, or a complete engine deck face in only 25 to 40 seconds to confirm that the machining process for the powertrain part is performing properly.



Millions of surface sample measurements are captured and combined during that one minute period to produce the surface flatness measurement. That surface flatness measurement effectively defines how closely the mating surface of the powertrain part conforms to a perfect planar surface. Even more significantly, the surface flatness measurement and the associated surface map provide information that identifies where any departures from surface flatness are actually occurring. Older legacy techniques, such as mechanical probes, can neither produce an accurate and reliable flatness measurement, nor produce any meaningful flatness measurement in a timely manner, nor provide any significant insight into where or why departures from required surface flatness are occurring.

The technology that can achieve these breakthrough levels of surface flatness measurement is implemented in the ShaPix® multi-wavelength digital holographic interferometry system. This system was developed and is delivered to precision manufacturers internationally by Coherix®, Inc. from its Ann Arbor, Michigan headquarters. This technology is used in manufacturing plants in multiple roles:

1. For precision-product engineering and prototyping to ensure rapid, correct and efficient product development.
2. For accelerating the launch of manufacturing processes for new precision parts, reducing the time required to “dial in” computer numerical control (CNC) machines and achieve correct processing of parts from the traditional many-week cycle to days. This use can typically save 1 million dollars per day of reduced launch time.
3. For near-the-line high-frequency surface flatness measurement (auditing) of manufactured parts, so as to achieve a tighter process control loop than any legacy mechanical gages are capable of enabling. Thereby process drifts or defect-producing failures are detected within minutes instead of hours or longer.
4. For in-line process control that needs both surface flatness measurement together with the surface defect detection, surface feature verification, surface waviness measurement, and surface leakage susceptibility prediction that the same holographic surface measurement technology can provide.

The corporate-level benefits of applying this high-definition surface flatness measurement and surface defect detection technology in precision manufacturing include shorter product time to market, lower manufacturing costs, reduced manufacturing waste and scrap, less waste in the costly down-stream assembly of defective parts, lower warranty service costs, and higher end-user (customer) satisfaction

Taken altogether, the surface flatness measurement and other surface inspection functions of the multiwavelength digital holographic technology provide a 100% payback of the investment made in the measurement system within weeks when applied in the roles listed above. The figure below shows a view of the Coherix ShaPix Surface Detective™ system in one of its several available configurations.



Unlike other non-contact surface measurement systems, the ShaPix Surface Detective rapidly performs surface flatness measurement and surface defect detection for surfaces as large as a square meter and measurements on parts whose multiple nominally-parallel surfaces which may be separated from being co-planar by more than one centimeter. Measurements for new part types can be specified and set-up in just minutes with no programming being required whatsoever. High-definition color graphic surface maps, as well as accurate quantitative numeric reports, are produced of surface flatness measurements, waviness measurements and detected defects, enabling instant understanding by product and manufacturing engineers and machine operators of the root cause of surface and other part dimensional deviations from specifications.