Extensive analysis of cutting edge

Solid carbide cutting tap

Edge rounding is measured on the first tooth of a solid carbide (SC) thread tap. The surface structure inside the groove is scanned, then the roughness parameters are determined according to DIN EN ISO 4287/88 and DIN EN ISO 13565, and the height parameters according to DIN ISO 25178.

Measuring equipment and methods

The measurements are done on the compact standard measuring system ConfoSurf CLV150. Equipped with the Confocam C1+ 2-in-1 scanning module, the measuring system offers two scanning methods in one system: edge rounding is scanned in "focus variation" scan mode due to the high flank angle.
The roughness measurements are done confocally in "structured lighting" scan mode. Analysis is done in the analysis software MountainsMap®.

Measuring the cutting edge (1st tooth)

Left image:
Extract of the screw tap

Right image:
2D image of the real surface with extract (white stripes) used for the determination of the profile series

Profile series (grey) determined of 500 single profiles and average profile (green) for the determination of the edge parameters.

Determination of cutting edge parameters

cutting edge parameters determined at the average profile

R = 8,01 µm  Radius of cutting edge

β = 95,0° Wedge angle

K-factor = 0,6 
The cutting edge is titled towards the rake face.

Δr = 5,01 µm  Elevation difference (distance from edge crest to line intersection)

sγ= 13,3 µm   Distance from relief point of rake face to line intersection

sα = 22,2 µm  Distance from relief point of flank to line intersection

Analysis according to DIN EN ISO 4287 and DIN EN ISO 13565

Because the surface develops a preferred direction during grinding, measurements are made at 90° to the machining direction. Amplitude parameters obtained from a profile section according to ISO 4287/88 and DIN EN ISO 13565 only allow for limited surface analysis, since they are only scanned along one line. Structural components lying outside this line are therefore disregarded. This can lead to incorrect analyses. Accordingly, a series of profiles are taken over the entire scanned surface segment using the analytical software MountainsMap®. (Image above: intensity view of the surface structure in the groove. The nominal form of was removed and a S-Filter of 2.5 µm was used.)

Primary profile series, produced by a series of 1000 horizontal profile sections. (green: Cross-sectional profile; grey: Envelope profile of all measured profiles)

Minimum, maximum and mean values and standard deviation are calculated from this profile series. From this, it can be determined how greatly the determined values vary over the entire surface.

Area-based analysis (Sa parameters) according to DIN EN ISO 25178

Height parameters according to DIN EN ISO 25178 are calculated from the entire measured data from the optically scanned texture area, and thus allow an area-wide assessment of the microtopography in the measured area.

3D image of the scanned surface

For determining roughness according to DIN EN ISO 25178, an S filter of 2.5 µm is applied to filter out the measurement noise. Then the shape of the surface is removed. To separate roughness and waviness, a Gaussian filter with a nesting index of 0.25 is selected.

The parameter Sa corresponds to the 2D parameter Ra and the 3D parameter Sq corresponds to the 2D parameter Rq. The parameter Sz describes the distance from the highest point to the lowest point (peak to valley) of the entire measured area. The maximum height Sz cannot be compared with the maximum height of the roughness profile Rz, but rather with the parameter Rt.

Areal-based analysis (Sk parameters) according to DIN EN ISO 25178

For characterising various structures of the surface with regard to their functional properties, the areal material ratio curve (Abbott curve) is used. This describes the areal material ratio as a function of the depth of a section plane through the surface. Parameters can be derived from the Abbott curve that characterise the functional behaviour of the scanned surface.