Profilometers for roughness measuring data capture are prescribed in the current standards DIN EN ISO 4287 /88 and DIN EN ISO 13565. During measurement, a stylus scans the surface in the direction vertical to machining and images the primary surface that is then evaluated according to the standards. This measuring procedure is established and simple physically. The optical measuring techniques involve interactions of the light waves with the surface, which makes these techniques infinitely more complex.
Extended 3D surface analysis by means of confocal microscopy and focus variation
The principle of confocal measurement is particularly suitable for capturing roughness because, in addition to high vertical resolution, it provides focus variation, white light interferometry and the confocal procedure together, ensures high lateral resolution and causes the least disruptive effects along edges. Of the confocal procedures, the Confovis-patented special procedure of “structured illumination microscopy“ is physically the simplest and most robust procedure. Laser scanning microscopes are clearly at a disadvantage because of the coherence of the laser light source. This enables Confovis also to measure the challenging roughness standards such as Halle KNT 4070/03 and KNT 4058/01, including the Rk parameters acc. to DIN EN ISO 13565, as well as the Jenoptik Hommel standard RNDH2 according to DIN EN ISO 4287/4288 traceable to the standards of the PTB, also with application of VDA 2006 (without lamda s filter). In addition, Confovis is master in applying the proven focus variation measuring technique, which is advantageous to use for Micro-geometries with steep flank angles.
The robust confocal measuring procedure of “structured illumination microscopy“ (SIM) is not a competitor of the focus variation. In fact, both procedures complement each other when data is brought together in a 3D point cloud.
Two measurement procedures in one measurement system
The functionality and lifetime of indexable inserts is essentially determined by the geometrical dimensions, especially the chipping of the cutting edge, and the roughness of the chipping surface. In order to measure these, reliable measurement data is captured with the optical 3D measuring technology by Confovis even for reflective and coated surfaces.
Sample: indexable insert
Determination of cutting edge parameters
- R = 5.4 µm Radius of the cutting edge
- ß = 67.9° Wedge angle
- K factor = 1.08 This shows that the cutting edge has been protracted to the clearance surface.
- Δr = 3.9 µm Distance from the point of the upper edge to the straight cutting point
- Sα = 7.2 µm Distance from the relief point of the clearance surface to the straight cutting point
- Sˠ = = 7.8 µm Distance from the relief point of the rake surface to the straight cutting point
Both products, Duo Vario BASE and TOOLinspect combine two ideally complementary measuring procedures in just one device. Resolution in the single-digit nanometer range — also for reflecting surfaces — is provided by the confocal measuring procedure. Therefore, it is used for roughness measurements and the determination of cutting edge chipping (see below). The outline of a tool’s cutting edge is analyzed by the focus variation technique. With the ring light, that technique, in particular, measures areas with inclinations of up to 85° without problem and thus can be used for analyzing cutting edge parameters. (see top)
Confovis cooperates in the VDI/VDE-GMA Expert Committee 3.64 “Characterization and Measurement of Cutting Edges“ and will implement the standard in the cutting edge evaluation software as soon as the greenprint is available.
The chipping of the edge using high-resolution confocal measurement technology
Measurement areas and data densities as needed
A further example demonstrates which added value the customer gets when using the high-precision confocal measurement method in combination with the focus variation predestined for steep edges.
The area of a surface where chipping and roughness are important is captured by confocal measurement. The high lateral resolution of the confocal measurement shows a breakaway and chipping of the cutting edge. Data of this quality is available also with difficult-to-measure surfaces such as monocrystalline diamond (MC) or polycrystalline diamond (PCD) as well as with different coatings.
For measuring and evaluating the steep flanks, the cutting edge was measured with focus variation with ring light (10x/0.30 NA objective lens). The measurement is optimum for acquiring geometry data. The cutting-edge radius also lends itself well for evaluation. However, a defect in the cutting edge is hardly visible due to the low data density.
Before evaluation, measuring data can be brought together.