MANUFACTURING TECHNOLOGY
Micro fastener measurement using 3D metrology
Advances in microelectronics, biomedical and many other industries have increased demand for micro manufacturing, or micromachining, of fastener components at smaller, more precise sizing, in many different materials. Traditional gauging methods cannot assure the precision of such components. Nanovea Incexplains why non-contact optical measurement has become a vital tool for quick and reliable quality control measurement for these small parts.
of a micro fastener is vital to its end use, it will be crucial to monitor and control the end result with reliability. Understanding these parameters allows for best selection of processing and control measures. Assuring the quality control of such parameters will heavily rely upon quantifiable, reproducible and reliable inspection. The Nanovea 3D Non-Contact Profilometers utilise chromatic confocal technology with unique capability to measure the steep angles found during fastener measurement. Where other techniques fail to provide reliable data, due to probe contact, surface variation, angle, or reflectivity, Nanovea Profilometers succeed.
3
Measure objectives In this application, the Nanovea ST400 is used to measure a
micro set screw. There is an endless list of surface parameters that can be automatically calculated after the surface scan. Here we will review a 3D profile and select areas of interest to further analyse, including the 3D dimensions of the tip and 2D extractions for depth and dimensional calculations of the fastener threading.
D non-contact measurement of micro parts is not a capability provided by just any optical measurement technique; in fact few can do so properly. And because roughness, shape, forms and dimensional characteristics
Measurement principle The axial chromatism technique uses a white light source,
where light passes through an objective lens with a high degree of chromatic aberration. The refractive index of the objective lens will vary in relation to the wavelength of the light. In effect, each separate wavelength of the incident white light will re-focus at a different distance from the lens (different height). When the measured sample is within the range of possible heights, a single monochromatic point will be focalised to form the image. Due to the confocal configuration of the system, only the focused wavelength will pass through the spatial filter with high efficiency, thus causing all other wavelengths to be out of focus. The spectral analysis is done using a diffraction grating. This technique deviates each wavelength at a different position, intercepting a line of CCD, which in turn indicates the position of the maximum intensity and allows direct correspondence to the Z height position.
Nanovea optical pens have zero influence from sample
Measurement set up and tips Measurements area randomly selected on the sample, drastic changes in surface topography are not an issue for Nanovea Profilometers. Small height variation down to nanometers up to 27mm of height variation can easily be measured.
reflectivity. Variations require no sample preparation and have advanced ability to measure high surface angles. Capable of large Z measurement ranges. Measure any material: transparent/opaque, specular/diffusive, polished/rough. Measurement includes: profile dimension, roughness finish texture, shape form topography, flatness warpage planarity, volume area, step-height depth thickness and many others.
96 Fastener + Fixing Magazine • Issue 72 November 2011
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