NDT Tech Showcase: Surface Analysis Options
Two-dimensional profilometry, or contact profilometry, is a contact technique that measures a subject’s length or depth, usually at the micrometer or nanometer level. Two-dimensional profilometry typically is nondestructive and uses a diamond-tipped stylus that is drawn across the subject, measuring variations in surface topography. It can rapidly perform long linear scans and quantify high step heights. The technique is appropriate for applications such as measuring films and coatings.
Interferometry, or 3-D profilometry, is a noncontact method that uses light-typically laser light-to measure topography, with the ability to provide accuracy of ±3 nanometers in the Z-axis, and XY resolution as fine as 500 nanometers.
Interferometry is versatile and more efficient than point-to-point surface profiling techniques. Quality applications for interferometry include everything from the aerospace and medical device industries to factory floor applications in the automotive industry.
Two notable forms of interferometry used for industrial applications today are confocal microscopy and holographic interferometry. Confocal microscopy is a technique that increases micrograph contrast and also can reconstruct 3-D images. A confocal microscope eliminates out-of-focus information through the use of point illumination and a pinhole in an optically conjugate plane in front of a detector. Only the light within the focal plane can be detected, which results in high image quality.
This technique currently is used in the scientific and industrial communities. Typical applications are found in the semiconductor, optics, electronics, plastics and paper industries.
Holographic interferometry combines traditional holography with interferometry, allowing detection of material defects and inevitable fatigue failure, as well as the measurement of residual stress and vibration mode analysis. Modern holographic metrology equipment is more precise than conventional interferometry techniques because it overcomes the ambiguity interval, a problem inherent to conventional forms of interferometry. With a conventional interferometer, the range of measurement can be only one wavelength of light because it relies on the difference between the phases of the signals to compute distance. Therefore, if two points on a surface differ by exactly one wavelength of light, it cannot be determined whether they are the same height.
Holographic interferometry is used by metrology laboratories to analyze parts for product development, quality control and warranty studies. It also is used to inspect equipment during the launch of new production lines, as well as sample parts near a production line.
The confocal microscope has been designed specifically for use in R&D and production. Because of its confocal measurement principle the microscope delivers results with high resolution - less than 1 nanometer - within seconds. This makes the instrument suited for manually operated surface analyses in such fields as optics, electronics, plastics and paper. The microscope is available with a variety of lenses and comes with a motorized X, Y-stage for easy sample positioning.
The complete system fully supports the new EN 10247 European standard for determining the content of nonmetallic inclusions in steel, as well as previously existing standards, including DIN 50602, ASTM E 45, ISO 4967; JIS G 0555.
The system can be tailored for further image analysis applications such as grain size analysis and particle analysis. All the components of the microscope, ranging from the camera to the motorized stage, are controlled by Zeiss AxioVision software.
With the new NMI system, quality is determined through an automated process performed by repeatable mathematical calculations. The system also allows automatic objective analysis on up to six samples at a time using batch mode, and can output the results of a batch measurement either individually or combined.
The integrated NMI software offers the option of performing measurements on a large MosaiX image, a composite of many individual tile images. This feature addresses the inaccurate classifications that occur when inclusions cut off at the image edge are not recorded in their entirety during independent individual tile analysis.
The company integrates noncontact sensors with mechanical PC-controlled motion systems. They specialize in high-accuracy models with typical resolutions of 0.125 microns in the X and Y directions, with Z resolutions of 0.01 micron. These are fully automated systems that allow end users to create topographical surface maps of virtually any substrate, without expensive substrate preparation or contacting or altering the sample being tested. Typical samples are 8 inches by 8 inches, with over 6.5 million data points being generated in less than 45 minutes. Systems come with PC-controlled motion tables and analysis software for linking surface parameters to customers’ critical quality control measurements and product performance. Laser triangulation, confocal and white light CLA sensors are typically integrated into profiling systems. Stage sizes and configurations include: rotary stages, XY tables with axis lengths from 2 inches to 60 inches per axis, motorized Z stages, and vertical or horizontal stages and fixturing.
The system’s nano-metric roundness accuracy is ensured by a high-precision glass hemisphere that has a roundness deviation less than or equal to 10 nanometers and individual slope values of less than 2 nanometers/7.2 degrees. This calibration artifact is used to monitor and verify that spindle performance is within specification.
The system includes a Talymin 5 gage head, which offers resolution to 1.2 nanometers, making it suited for high-precision components. Interchangeable probe arms are available for all applications, including small inside diameters and stepped surfaces. The mechanical integrity of its crutch and pivot mechanism eliminates drift during the measurement cycle and assures stability of contact between the gage and component.
To isolate measurements from floor-borne vibration and environmental influences, the system includes an integrated enclosure and dynamic anti-vibration mounts located between its support frame and cast iron base. The spindle, vertical column and horizontal arm are all anchored to the one-piece cast iron base. That stability, along with 0.2-micrometer vertical axis straightness and 0.1-micrometer positioning resolution, make the instrument suited for high-accuracy applications.
Available in two platforms, the NewView 7300 and 7200 are based on proprietary scanning technology, delivering high precision, resolution, linearity and speed. Additionally, a range of surfaces can be measured at high speed-including smooth and rough, and steps and films-with sub-nanometer resolution and precision. The versatility of the NewView 7000–Series accommodates a broad range of applications.
The series incorporates a line of automated positioning stages, enabling programmable measurement routines and precise stitching of large areas. The series is suited to measure rough surfaces, high slopes, films and high-aspect ratio features. The platform includes a range of imaging objectives from 1X to 100X. All platforms are powered by the company’s MetroPro software, which provides a suite of data analysis, automation tools and flexible scripting language.
NanoFocus µsurf technology is based on optical filtering carried out by a confocal spatial filter. The µsurf 3-D topometer uses a confocal imaging technique to capture 3-D images of surface topography in a quick measurement operation. Equipped with a computer-controlled objective lens drive, the µsurf generates height sections at different working distances. Only components of reflected light that are in focus are captured by the CCD camera sensor. Out of focus components are blocked by special multi-pinhole filters. The height sections are stored consecutively in an image stack and a special software algorithm calculates the 3-D topography.
The µsurf analysis software is continuously updated to include the latest industry standards and methods. A range of 2-D and 3-D parameters and filtering techniques are available, including 3-D parameters defined in the new ISO 25178 standard, the first international standard on areal surface texture, and advanced filtering techniques defined in the ISO 16610 standard.
Running on the Vision software platform, the system provides access to more than 200 distinct analyses, and more than 1,000 critical parameters for process control and monitoring. It also allows user-written analyses and integration with user-supplied hardware to provide a platform for custom research and emerging technologies.
The detector/drive unit can be detached from the display unit for measurement in any orientation. The large LCD window displays evaluation results. Digimatic and RS-232C interfaces enable measurement data transfer to a computer or other devices, such as the optional compact battery powered SJ-printer.