Measuring the sharp edges of cutting tools is a challenging process, because it involves a small radius, which requires high lateral resolution and high angles. It is also important to be able to measure a diverse range of heights. The study becomes more difficult when the surface has chipping or other types of deformation. Precision cutting tools generally require a sharp tool edge with radii of several tens of nanometers or even smaller.
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There is an endless range of cutting tools and each has a uniquely shaped edge for its cutting purpose. Tools with round cutting edges could be used for machining surface forms and structures while straight cutting edges are typically used for machining grooves.
Importance of surface metrology inspection for quality control
For a particular tool, the edge's precision is expected to meet intended results during use. Because the depth of cut is controlled to the nanometer level, the tool cutting edge profile is an important factor that influences the final quality of a machined surface. Using 3-D profilometer, the edge correctness can be determined to ensure quality control before production and during the life of the tool.
Measurement objective
In this application, the Nanovea ST400 3-D profilometer is used to measure the cutting edge of a cutting tool shown below (figure 1). We also used the ST400 to verify the full diameter of the bit and resulting hole that it would create during utilization.
Measurement, setup, and tips
This particular application uses a 12 mm optical pen to obtain nanometer measurement of the cutting tool. Measurements were taken in 50 micron steps, which is sufficient to give details of the patterns. A more precise 400 µm optical pen with 1 µm step size was used to precisely measure the cutting edge of the tool. The 400 µm optical pen also allows you to measure angles of up to 80° which is required when measuring cutting edges.
Measurement principle
The axial chromatism technique of the Nanovea ST400 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 refocus 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 focalized 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.
Spectral analysis is done using a diffraction grating. This technique deviates each wavelength at a different position, intercepting a line of CCD elements, which in turn indicates the position of the maximum intensity and allows direct correspondence to the Z height position.
By scanning the full length of the cutting tool it is possible to calculate the full diameter of each of cutting diameter ring and compare them with ideal values.
In this case, the radius was measured at three different locations and compared to what it was supposed to be.
Large diameter = 10.951 mm (0.43114 in.) Ideal = 0.5 in.
Small diameter = 3.1412 mm (0.12367 in.) Ideal = 0.125 in.
Middle diameter = 7.0264 mm (0.27663 in.) Ideal = 0.28125 in.
Nanovea engineers found that the variation compared to the ideal diameter was more pronounced for larger diameters.
Using powerful analysis software you can measure the edge diameter of the tool as shown in the following figures.
For the 15/32, the diameter of the cutting edge is 15.771 µm. You can also see that there is some defect close to the edge.
For the 0.5 in., the diameter of the cutting edge is 6.1825 µm. This surface is much better. It is also possible to calculate the angle between the two surfaces to be 60.477°.
Conclusion
This application has shown how the Nanovea ST400 3-D Profilometer with a 12 mm and 400 µm optical pen can precisely characterize the macro surface and shape as well as the nanometer details of a critical cutting edge. Although a cutting tool was used in this application, Nanovea’s 3-D Profilometer would be an ideal measurement tool for both research and quality control environments. Nanovea’s 3-D Profilometer provides the diverse measurements of larger surface and shape measurements to the precise nanometer measurement of critical edge inspection.
For more information, contact Nanovea info@nanovea.com, or (949) 461-9292, or visit at www.nanovea.com .
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