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OTEC Przisionsfinish GmbHDieselstrasse 8-1275334 Straubenhardt-Feldrennachwww.otec-online.com
Drag finishing of drills
01. April 2009
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1. What are the advantages of edge rounding for drills?
Increase in the service life by a factor of up to 3.5 times (in the case of steel
alloys)
Increase in the maximum feed rates by a factor of 4.5
(comparing rounded, coated, carbide drills with non-rounded, coated
carbide drills)
Low degree of surface roughness of the boreholes made by edge rounded
drills compared with non-rounded ones.
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Fig. 1: Sharp tool with coating after the first borehole (Source: Kai Risse)
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Fig. 2: Rounded tool with coating after the first borehole
Cutting conditionsMaterial: C45E+N Cutting speed: 35 m/minCutting material: HC-K20 Feed rate 133.7 mm/minTool diameter d: 1 mm Dry
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Fig. 3: Sharp tool with coating after 150 boreholes
Cutting conditionsMaterial: C45E+N Cutting speed: 35 m/minCutting material: HC-K20 Feed rate 133.7 mm/minTool diameter d: 1 mm Dry
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Fig. 4: Rounded tool with coating after 150 boreholes
Cutting conditionsMaterial: C45E+N Cutting speed: 35 m/minCutting material: HC-K20 Feed rate 133.7 mm/minTool diameter d: 1 mm Dry
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Fig. 5: Sharp tool with coating after a borehole with higher feed rate
Cutting conditionsMaterial: C45E+N Cutting speed: 35 m/minCutting material: HC-K20 Feed rate 601.7 mm/minTool diameter d: 1 mm Dry
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Fig. 6: Rounded tool with coating after a borehole with higher feed rate
Cutting conditionsMaterial: C45E+N Cutting speed: 35 m/minCutting material: HC-K20 Feed rate 601.7 mm/minTool diameter d: 1 mm Dry
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Fig. 7: Rounded tool with coating after 300 boreholes with a higher feed rate
Cutting conditionsMaterial: C45E+N Cutting speed: 35 m/minCutting material: HC-K20 Feed rate 601.7 mm/minTool diameter d: 1 mm Dry
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1.1 How much edge rounding is required for TC drills?
For steel alloys, the rule of thumb is:
4 m x diameter of the drill
For a carbide drill with a diameter of 10 mm, this means an edge rounding of
approx. 40 m (according to Kai Risse)
For steel casting alloys:
5 m x diameter of the drill
For aluminium alloys, the following value can be assumed:
2 m x diameter
For the edge rounding of carbide drills, it is important to ensure that the
cutting edge corner is not rounded significantly more than the cutting edge.
In order to prevent tapered drill holes, both cutting edges must be rounded
equally.
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2. Procedure for rounding TC drills by drag finishing in OTEC machines
Drag finishing is a reliable and reproducible method of rounding the edges withan accuracy of +/-1 m.
As a rule, TC drills are finished using the QZ 1-3 abrasive medium.
In order to protect the cutting edges (Fig. 8), it is advisable to operate the
machine in an anticlockwise direction only when rounding up to approx. 50m.
As a rule, the secondary cutting edge becomes somewhat more rounded
than the main cutting edge (see Fig. 9). It this is to be avoided, the drill must
be covered so that only the main cutting edges are exposed to the finishingprocess.
The drill should rotate on its own axis only slowly (slow driven holder Type
SL). This ensures that the main cutting edge is evenly rounded.
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Fig. 8: Rounding of main cutting edge and corners at the
nose
Fig 9: Rounding of main cutting edge and secondary
cutting edge
Rounding of edges and corners
DF Tools without extra drive, QZ 1-3, ID=150mm, n=45, anticlockwise,slow holder
0
10
20
30
40
50
60
0 5 10 15 20
Processing time [min]
Averageradius[m]
Main cutting edge
Nose
Rounding of edges and corners,
DF Tools without extra drive, QZ 1-3, ID=150mm, n=45, anticlockwise,slow holder
0
10
20
30
40
50
60
0 5 10 15 20
Processing time [min]
Averageradius[m]
Main cutting edge
Secondary
cutting edge
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3. Parameters for drag finishing
Fig. 10: Holder load
From a diameter of about 12 mm, the workpieces have such an effect on
each other that that there is a considerable difference in processing timebetween fully-loaded and half full holders. For this reason, only every other
position should be filled in the case of a six-way driven holder (see Fig. 10).
Holder load for a tool diameter of 19mm
DF 4Tools without extra drive, drill assemblies (TC, 19mm), ID=150mm,
speed=50 rpm, anticlockwise, slow holder, QZ 1-3
0
5
10
15
20
25
30
Processingtim
e[min]
Full load
One tool
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Fig. 11: Effect of immersion depth
Immersion depth,
n=20min-1, anticlockwise, slow holder, QZ 1-3,
DF 4 Tool without extra drive, end mill (TC, 10)
0
5
10
15
20
25
0 5 10 15 20 40
Processing time [min]
Averageradiu
s[m]
ID=150 mm
ID=200 mm
Polynomic(ID=150 mm)
Logarithmic(ID=200 mm)
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Fig. 12: Effect of the direction of rotation
Processing time at different ratios of direction of rotation,edge rounding approx. 35m, DF 4 Tools without extra drive, drill assemblies(TC, HM, 10), ID=150mm, speed=50 rpm, anticlockwise, slow holder, QZ 1-3
0
2
4
6
8
10
12
Direction ratio
Processingtime
100% anticlockwise
50-50% clockwise-anticlockwise
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Edge rounding with different granulates
TC drill 10.0; T= 20 min; direction of rotation. 50/50; speed = 25 rpm; DF3 Tools
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
0.045
0.050
0.055
0.060
0.065
Time [min]
Edge rounding [mm]
SIX 70/24
QZ 1/3
HSC 1/300
SIX 70/16
0 2 4 6 8 10 12 14 16 18
Fig. 13: Effect of the media
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3. Smoothing the flute and the cutting edge
A major advantage of drag finishing is that the chip flute is smoothed at the
same time as the cutting edge receives a smooth surface.This offers the following benefits:
Faster chip removal higher feed rates and cutting speeds can be attained
Less breakage at the cutting edge (lower jaggedness), since there are
fewer potential fracture points
Improved bond for the coating
In order to obtain a particularly good polish in the flute (see Fig. 14), a very
smooth finish can be obtained by using polishing granulate K3/400
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0
0.02
0.04
0.060.08
0.1
0.12
0.14
0.16
0.18
0.2
RoughnessRa[m]
unprocessed
processed
Fig. 14: Smoothing at the tool
Special tool 32, DF Tool angled, K3/400, 20min, 90%
anticlockwise, 20mm stroke, nrot = 30 rpm nholder = 135 rpm
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Fig.15: Jaggedness
Jaggedness, TC end mill
0
0.2
0.4
0.6
0.8
1
0 5 10 15 20 40
Processing time [min]
Jagge
dness[m]
n=20, anticlockwise
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4. Advantages of drag finishing
Reliable process, reproducible, with an accuracy of +/- 1 m
Simultaneous smoothing of chip flute and cutting edge, giving better
chip removal, better bonding of coating and higher service life
Affordable process, since operating costs and capital investment
are low Can also be used for the removal of droplets after coating
Rounding values of from 4 m to 80 m can be achieved.