Presentation Bohrer - Englisch

7/27/2019 Presentation Bohrer - Englisch

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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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01. April 2009 2

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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01. April 2009 3

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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01. April 2009 5

Fig. 3: Sharp tool with coating after 150 boreholes



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01. April 2009 6

Fig. 4: Rounded tool with coating after 150 boreholes



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Fig. 5: Sharp tool with coating after a borehole with higher feed rate



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Fig. 6: Rounded tool with coating after a borehole with higher feed rate



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Fig. 7: Rounded tool with coating after 300 boreholes with a higher feed rate



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01. April 2009 10

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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01. April 2009 11

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


Averageradius[m]

Main cutting edge

Secondary

cutting edge


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01. April 2009 13

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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01. April 2009 14

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


Averageradiu

s[m]

ID=150 mm

ID=200 mm

Polynomic(ID=150 mm)

Logarithmic(ID=200 mm)


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01. April 2009 15

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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01. April 2009 16

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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01. April 2009 18

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


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.

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Presentation Bohrer - Englisch